Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 Course 1: 1. Intro Introduc ductio tion n to Ceram Ceramics ics 2. !lemen !lementar tary y Cryst Crystall allogr ogra"# a"#y y 3. Ceramic Microstructures '. $raditional (s. ad(anced Ceramics 5. Gener eneral al C#ar #aract acteris eristi tics cs o Ceram eramic ics s ,. Silicate Silicate CeramicsCeramics-a: a: Clays Clays and and aolini aolinite te . Silicate Silicate CeramicsCeramics-: : elds" elds"ars ars and Silica 4. roducts Classi+cation% $erra cotta . !art#en)ares (s. Stone)ares 10. orcelains% 8itreous c#ina 11. 9lumina Ceramics 12. Mullite% Magnesia% and S"inel 13. 13.
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Material Part 1: The Crystalline State 1 Introduction to Ceramics 2 !lementary Crystallogra"#y-1 3 !lementary Crystallogra"#y-2 ' Ceramic Microstructures 5 $raditional (s. ad(anced Ceramics , General C#aracteristics o Ceramics 9""lications Part 2: Silicates, Alumina and Zirconia 4 aolinite and Clays elds"ars and Silica 10 roducts Classi+cation% $erra cotta 11 !art#en)ares 12 Stone)ares 13 orcelains% 8itreous c#ina 1' 9lumina Ceramics 15 Mullite% Magnesia% and S"inel 1, irconia% ;t#er o&ides Part 3: Sintering and Microstructure 1 Sinte interring ing and Micr Micro ostr structu ucturre o Ceramics 14 $#ermodynamics o sintering 1 Matter trans"ort 20 !&"erimental as"ects o sintering 21 Solid "#ase sintering 22 Sintering )it# li*uid "#ase 23 Sintering ad additi(es% r ressure sintering and /ot Isostatic ressing /I 0
Dr. Saad B. H.
Course 2: 1. Sintering Sintering and Microstr Microstructur ucture e o Ceramics 2. $#ermody $#ermodynamic namics s o sintering% sintering% Matter Matter trans"ort 3. !&"erimental as"ects o sintering '. Solid "#ase sintering 5. Sin Sinter tering ing )it# it# li* li*uid uid "#ase #ase:: (itr (itri+ i+ca cattion ion ,. Sintering Sintering additi( additi(es% es% ressur ressure e sintering sintering and /I . Glass e+nition e+nition and and $rans $ransition ition tem"erature 4. Common ty"es o glass . 6a) Materials and 7atc# Calculations 10. 8iscosity o Glass orming Melts 11. $#ermal !&"ansion o Glass 12. 8itreous Coating 13. 13. 7io 7io Cer Ceram amic ics% s% Glas Glasse ses% s% and and Glas GlasssCeramics 6e. no.
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Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 Part 4: Glass and Glass ceramics 2' Glas lass e+ni e+nittion ion and and $rans ansitio ition n tem"erature 25 Common ty"es o glass 2, 6a) Ma Materials an and 7 7a atc# Calculations 2 8iscosity o Glass orming Melts 24 $#ermal !&"ansion o Glass 2 8itreous Coating 30 7io Ceram eramic ics% s% Gla Glass sses es%% and Glas lassCeramics
Dr. Saad B. H.
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Course 1 1 !ntroduction to Ceramics In metals% t#e onding is "redominantly metallic% )#ere delocali?ed electrons "ro(ide t#e @glue@ t#at #olds t#e "ositi(e ion cores toget#er. toget#er. $#is delocali?ation o t#e onding electrons is res"onsile or "ro"erties most associated )it# metals: ductility% t#ermal and electrical conducti(ity% reAecti(ity% and ot#er distincti(e "ro"erties. olymers consist o (ery long% C-ased c#ains to )#ic# ot#er organic atoms Bor e&am"le> C% /% % Cl% D and molecules are attac#ed. $#e onding )it#in t#e c#ains is strong% strong% directional% and co(alent% )#ile t#e onding et)een c#ains is relati(ely )ea=. $#us% t#e "ro"erties "ro"erties o "olymers "olymers as a class are are dictated y t#e )ea=er )ea=er onds% and conse*uently t#ey "ossess lo)er melting "oints% #ig#er t#ermal e&"ansion coeEcients% and lo)er stiFnesses t#an most metals or ceramics. Ceramic materials are inorganic% nonmetallic com"ounds% usually o&ides li=e Si; 2% 9l2;3 and non-o&ides suc# as carides% nitrides% and orides. 7ot# ionic and co(alent onds% or comination o t#em% can e ound in ceramic materials. $#e dominant c#aracteristics o ceramics are summari?ed y t#e ollo)ing: i. They They are are stabl stablee and and resist resistant ant to chem chemical ical attack. attack. ii. ii. They They are are bri britt ttle le,, #ard% and wear resistant. iii. They have high high temperatu temperature re strength. strength. i(. i(. They are good electrical insulators at room tem"erature. v. Their Their therma thermall conduc conductiv tivitie itiess lie betwee between n those o "olymers and o metals .
Ceramic materials may occur in t#e orm o single crystal and in t#e orm o "olycrystalline material B"olycrystalsD. $#ese "olycrystals are oriented )it# res"ect to eac# ot#er in more or less com"letely random )ay. )ay. $#ey are also called grainsH. <#en t#e grains #a(e a diFerent com"osition% t#e ceramic material is o multi"#ase. $#e grains in t#e monolit#ic material are o single "#ase. igure 1 shows a typical cross-section of ceramic material. It composed of an assembly of irregularly shaped grains and pores. The solid-solid interfaces are called @grain boundaries @ and the solid-gas interfaces are called @free surfaces@. Grain boundaries and free surfaces constitute the microstructure o t#e ceramic material.
$o $o otain "olycrystalline ceramic ceramic material% a com"ressed com"ressed +ne-grained "o)der is suected to a #ig# tem"erature tem"erature around B,5-5DJ o its melting "oint. $#e "rocess is called @sintering@> in )#ic# t#e "o)der com"act s#rin=s during #eating% and its ul= density increases to orm t#e ceramic ody. $#e densi+cation o t#e "o)der com"act is accom"anied y coarsening 1
Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 o "rimary grains @grain gro)t#@ and elimination or decrease in (olume o intergranular (oids @"ore s#rin=age@. $#e e(olution and rate o t#ese microstructure c#anges are reerred as @microstructure de(elo"ment@ o t#e sintered ceramic ody.
Dr. Saad B. H.
The mechanical and physical properties of ceramics are depending on their microstructure. The mechanical properties are correlated to the grain size (the diameter of the sphere of the same grain volume while the thermal, magnetic and electrical properties are influenced by the e!istence of the interfaces (grain boundaries and free surfaces. The correlation between the properties of ceramics and their microstructure reflects the importance of sintering studies. "ormally, these studies attempts to attain high density and controlled grain size of the product. $igure 2: The )nit Cel Semiconductors are sugrou" sugrou" o ceramics> t#ey are co(alently onded solids t#at% in addition to )ell =no)n Si and Ge% include Ga9s% Cd$e% and In Ketc. ;t#er semiconductors outside t#e electronic materials are SiC% $i; 2% n;% and ot#ers.
$#e arrangement arrangement o atoms in solids% in general% general% and ceramics% in "articular% "articular% )ill e&#iit long-range order % only short-range order % or a comination o ot#. Solids t#at e&#iit long-range order are reerred to as crystalline solids% )#ile t#ose in )#ic# t#at "eriodicity is lac=ing are =no)n as amorphous% amorphous% glassy % or noncrystalline solids. noncrystalline solids. 2 "lementary Crystallogra#hy 9 long-range order re*uires t#at atoms e arrayed in a t#ree dimensional "attern t#at re"eats. $#e sim"lest )ay to descrie a "attern is to descrie a unit cell )it#in t#at "attern. 9 unit cell is is de+ned as t#e smallest region in s"ace t#at% )#en re"eated% com"letely descries t#e t#ree-dimensional t#ree-dimensional "attern o t#e atoms o a crystal. Geometrically% it can e s#o)n t#at t#ere are only se(en unit cell s#a"es% or crystal systems% systems% t#at can e stac=ed stac=ed toget#er to +ll t#ree-dimensional s"ace. $#e se(en systems% s#o)n in igure igure 3% are cuic% tetragonal% ort#or#omic% ort#or#omic% r#omo#edral% #e&agonal% monoclinic% and triclinic. $#e (arious systems are distinguis#ed rom one anot#er y t#e lengt#s o t#e unit cell edges and t#e angles et)een t#e edges% =no)n as t#e lattice "arameters or lattice constants Ba% % c% a% % β and in $igure 1: Cross section o% ceramic igure 2D. 2D . $#e unit cell #as a numer o "ermutations% "ermutations% "rimiti(e% ase centered% ody centered% and ace centered. /o)e(er% symmetry considerations limit t#e total numer o "ossile "ermutations to 1' 7ra(ais lattices. See igure igure 3.
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Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015
Dr. Saad B. H.
$igure 3: Se+en Crystal Systems and 14
3 Ceramic Microstructures Crystalline solids e&ist as eit#er single crystals or "olycrystalline solids. 9 single crystal is a solid in )#ic# t#e "eriodic and re"eated arrangement o atoms is "erect and e&tends t#roug#out t#roug#out t#e entire s"ecimen )it#out interru"tion. 9 "olycrystalline solid is grains% se"arated rom one com"rised o a collection o many single crystals% termed grains% boundaries . anot#er y areas o disorder =no)n as grain boundaries. $y"ically% in ceramics t#e grains grains are in t#e range o 1 to to 50 Nm and are (isile only under a microsco"e. $#e s#a"e and si?e o t#e grains% toget#er )it# t#e " resence o "orosity% "orosity% second "#ases% etc.% and t#eir distriution descrie )#at is termed t#e microstructure. microstructure. Many o t#e "ro"erties o ceramics are microstructure-de"endent. microstructure-de"endent. 4 Traditional *ersus Ad+anced Ceramics $raditional $raditional ceramics% "ottery% "ottery% scul"ture% scul"ture% sanitary )are% )are% tiles% etc.% are c#aracteri?ed c#aracteri?ed y mostly silicate-ased "orous microstructures microstructures t#at are *uite coarse% non-uniorm% and multi"#ase. $#ey are ty"ically ormed y mi&ing clays and elds"ars% ollo)ed y orming eit#er y sli" casting or on a "otterOs )#eel% +ring in a Aame =iln to sinter t#em% and +nally gla?ing. In a muc# later stage o de(elo"ment% ot#er ceramics t#at )ere not clay or silicateased de"ended on muc# more so"#isticated ra) materials% suc# as inary o&ides% carides% "ero(s=ites% and ot#er com"letely synt#etic materials or )#ic# t#ere are no natural e*ui(alents. $#e microstructures microstructures o t#ese modern or tec#nical ceramics )ere at least an order o magnitude +ner% more #omogeneous% and muc# less "orous t#an t#e traditional. General Characteristics o% Ceramics Ceramic materials are generally: 1. /ard 2.
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!lectrically insulati(e $#ermally insulati(e 6eractory 8ulnerale ulnerale Bsusc Bsusce"ti e"tileD leD to t#ermal t#ermal s#oc= 10. 10. ;&id ;&idat atio ionn-rresis esista tant nt%% C#em C#emic ical ally ly stale
/o)e(er% t#ere )ill e e&ce"tions> some ceramics are electrically and t#ermally *uite conducti(e% )#ile ot#ers are e(en su"erconducting. 9n entire industry is ased on t#e act t#at some ceramics are magnetic. <#y ceramics e&#iit t#ese "ro"ertiesP $#e ans)er o t#is *uestion is one o t#e goals goals o t#e study o t#e structure structure and microstructure microstructure o ceramics. Applications modern a""lications are: Ceramic materials #a(e a )ide range o a""lications. Some modern a""lications
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 1. Ceramic engines engines or trans"ortation trans"ortation and turines or energy energy "roduction "roduction due to t#e reractoriness reractoriness o ceramics and t#eir aility to sustain #ig# loads at #ig# tem"eratures% tem"eratures% toget#er )it# t#eir lo) densities 2. ;"tical communications communications suc# as +er o"tics due to o"tical "ro"erties o a glass glass 3. !lectroo"tic a""lications li=e li=e dis"lays and trans"arent trans"arent dis"lays Bsemiconducti(e Bsemiconducti(e o"tical ceramicsD '. Laser Laser material materials s Bt#e Bt#e acti(e acti(e materi materialsD alsD 5. Sustrates in electronic electronic circuits> due to insulati(e "ro"erties% "ro"erties% lo)-loss lo)-loss actors% actors% and e&cellent t#ermal and en(ironmental staility ,. Ceramic ca"acitors ca"acitors due to e&ceedingly e&ceedingly large large dielectric constants constants o t#e "ero(s=ite "ero(s=ite amily . Magnetic Magnetic ceramics ceramics ased ased on on t#e s"inel s"inel errites errites 4. ie?oelec ie?oelectric tric ceramic ceramics s or sensors sensors and and actuators actuators . $#e nonlinear nonlinear I-8 I-8 c#aracterist c#aracteristics ics or circuit circuit "rotectio "rotection n 10. 10. Ioni Ionica call lly y con condu duct ctin ing g cer ceram amic ics s or or use use as as sol solid id elec electr trol olyt ytes es in #ig# #ig#-tem"erature tem"erature uel cells and a nd as c#emical sensors 11. 11. !lec !lectr trod odes es in "#ot "#otoe oele lect ctrroc#e oc#emi mica call de( de(ic ices es or cell cells s !C% !C% )#ic )#ic# # are are sola solarr cell cells s t#at "roduce electrical energy or #ydrogen in a "rocess similar to t#e electrolysis o )ater 12. 12. 9 ne) ne) re( re(ol olut utio ion n in sili silica cate te cer ceram amic ics s BBSt Ston one e 9ge 9ge mat mater eria ials lsDD is is ta=i ta=ing ng "la "lace ce to to ma=e t#em materials or t#e uture. 9l=ali-acti(ated cements and mortars Balso called geo"olymersD are an e&am"le. In "rinci"le% t#e ad(antages o an all-ceramic engine are se(eral and include lo)er )eig#t% a #ig#er o"erating tem"erature tem"erature t#at translates to #ig#er eEciencies% and less "ollution. It is also "redicted t#at suc# engines )ould not re*uire cooling and maye not e(en any lurication% )#ic# once more )ould sim"liy t#e design o t#e engine% reducing t#e numer o mo(ing "arts% and lo)ering t#e o(erall )eig#t o t#e (e#icle.
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Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 Some o t#e common a""lications common a""lications are listed in ne&t tale: Pro#erty 1& Ther Therma mall Insulation 6eractoriness $#ermal conducti(ity conducti(ity 2& "lectrical "lectrical and dielectric dielectric Conducti(ity erroelectricity Lo)-(oltage insulators Insulators in electronic a""lications Insulators in #ostile en(ironments Ion-conducting Semiconducting onl onlin inea earr II-8 c c#a #arracte acteri rist stic ics s Gas-sensiti(e conduct 3& Magn Magnet etic ic and and su#erconducti+e /ard magnets Sot magnets Su"erconducti(ity 4& # #ttical ical $rans"ar $rans"arency ency $ranslucency $ranslucency and c#emical inertness onlinearity I6 trans"arency & Chem Chemic ical al Catalysis 9nticorrosion 7iocom"atiility & -iomed -iomedica icall and -iomaterials & Mech Mechan anic ical al /ardness /ig#-tem"erature strengt# and retention B)it#standingD 5
Dr. Saad B. H.
A##lications /e0am#les /ig#-tem"erature urnace linings or insulation Bo&ide +ers suc# as Si; 2% 912;3% and r; 2D /ig#-tem"erature urnace linings or insulation and containment o molten metals and slags /eat sin=s or electronic electronic "ac=ages B91D B91D /eating elements or urnaces BSiC% r;2% MoSi2D Ca"acitors B7a-titanate-ased materialsD Ceramic insulation B"orcelain% steatite% orsteriteD Sustrates or electronic "ac=aging and electrical insulators in general B9l 2;3% 91D S"ar= "lugs B9l 2;3D Sensor and uel cells Br;2% 912;3% etcD $#ermistors and #eating elements Bo&ides o e% Co% MnD Cur Current ent sur surge ge "rot "rotec ecto tors rs B7 B7ii-do do"e "ed d n; n;%% SiC SiCDD Gas sensors BSn; 2% n;D
errite magnets QB7a% SrD; ,e2;3R $ransormer cores QBn% MDe 2;3% )it# M Mn% Co% MgR> magnetic ta"es Brare-eart# garnetsD "uri+cation o e&#aust gases /eat e&c#angers BSiCD% c#emical e*ui"ment in corrosi(e en(ironments 9rti+cial oint "rost#eses B9l2;3D
Cutting tools BSiC )#is=er-reinorced 91 2;3% Si3'D Stators and turine lades% ceramic engines BSi3'D
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 usion reactor lining BC% SiC% Si3'D Silicate Ceramicsa: 7aolinite and Clays Kaolinite 1- Structure of Kaolinite aolinite% Si29l2;5B;/D ' or 9l2;3%2Si;2%2/2;% is t#e most common among t#e argillaceous minerals $igure 4: used in ceramics. 9 "roection o its crystalline Pro;ected re#resentation o% the structure is re"resented in igure '. It consists o an alternate stac=ing o QSi 2;5R2- and Q9l2B;/D'R2W layers% )#ic# res"onsile or t#e lamellate c#aracter t#at lead to t#e de(elo"ment o "lates. $#e degree o o crystallinity o t#e =aolinite =aolinite "resent in clays is #ig#ly (ariale. It de"ends largely on t#e conditions o ormation and t#e content o im"urities introduced into t#e crystalline lattice.
2- Evolution of the nature of phases during heat treatment
$igure : 8i9erential thermal analysis /8TA and thermogra+imetric analysis /TGA o% to 'aolinites ith di9erent degrees o% crystallinity
uring t#e #eat treatment% =aolinite =aolinite undergoes a series o transormations transormations as indicated in igure 5. $#e de"arture o )ater% )#ic# occurs rom '50XC on)ards% is a (ery endot#ermic "#enomenon. $#e amor"#ous meta=aolin% 9l 2;3.2Si;2 is t#en ormed. $#e e&ot#ermic e&ot#ermic transormation transormation oser(ed oser(ed et)een ,0 and 0XC 0XC is a structural structural reorgani?ation reorgani?ation o t#e amor"#ous meta=aolin. #ase transormations occur and end into ,
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 mullite stoic#iometry ranging et)een 39l2;3.2Si;2 and 29l2;3.Si;2. uring t#is reaction% amor"#ous silica is released. $#e e&tra amor"#ous silica starts to crystalli?e in t#e orm o cristoalite rom 1%200XC on)ards. It s#ould e noted t#at t#e im"urities "resent% t#e degree o crystallinity Bsee igure 5D% and t#e #eating rate inAuence t#ese transormations. Clays (the Clays (the kaolinite can be one type or component of clays) 1- Common characteristics i. Clays Clays are #ydrate #ydrated d aluminosili aluminosilicate cate minerals minerals )#ose )#ose struct structure ure is made made u" o a stac=ing stac=ing o t)o ty"es o layers containing% res"ecti(ely% aluminum in an octa#edral en(ironment and silicon in tetra#edral coordination. ii. $#e larg large e surace surace area area o clays clays B10–100 B10–100 m2g-1D% t#eir "late-li=e structure% and t#e "#ysicoc#emical nature o t#eir surace enale clays to orm% )it# )ater% colloidal sus"ensions and "lastic "astes. $#is c#aracteristic is largely largely used during t#e manuacture manuacture o silicate ceramics ceramics ecause it ma=es it "ossile to "re"are "re"are #omogenous and stale sus"ensions% suitale or casting% "astes easy to mani"ulate% and green "arts )it# good mec#anical strengt#. strengt#. 7y e&tension% t#e term clay is oten used to denote all ra) materials )it# "ro(en "lastic "ro"erties containing at least one argillaceous mineral. $#e im"urities "resent in t#ese natural "roducts contriute to a large e&tent to t#e coloring o t#e "roduct. 2- Classication $#e clays are are not all t#e same to)ards to)ards easy mani"ulation and e#a(ior e#a(ior during +ring. +ring. Ceramists distinguis# (itriying "lastic clays% reractory "lastic clays% reractory clays% and red clays. Vitrifying plastic clays $#ey are generally generally colored% are are used or t#e remar=ale remar=ale "lasticity o t#eir t#eir "aste. $#ey are made u" o (ery +ne clay "articles% organic matter% iron and titanium o&ides% illite Bormula Si'&9l&DB9l%eD2;10B;/D2 &B/2;DnD and micaceous Brom micaD andYor elds"at#ic im"urities. $#ese clays are are also c#aracteri?ed y #ig# ree silica content. content. Sand can re"resent re"resent u" to 35J o t#e dry matter )eig#t. $#e "roduct called @all clay@ is )idely used or its "lasticity and its "articularly lo) mica content. 9lt#oug# it contains t#e same argillaceous mineral as =aolin% t#is clay #as muc# #ig#er "lasticity ecause o t#e muc# smaller si?e o t#e =aolinite "articles. efractory plastic clays $#ey are ric# in montmorillonite Bormula Bormula BSi'-&9l&DB9l&-(6&D;10B;/D2M2(B/2;Dn )it# 6 Mg% e2W and M % aD% =aolinite or #alloysite BSi 29l2;5B;/D 'B/2;D2D. efractory clays $#ey are used used in #ig# tem"erature tem"erature "rocesses.
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 $#eir com"osition is ric# ric# in alumina. aolins are are t#e most reractory reractory among t#ese t#ese clays. 9l)ays "uri+ed% t#ey contain little *uart?% generally less t#an 2J al=aline o&ides in comined orm% and a small *uantity o mica. $#eir "lasticity is due to t#e t#e =aolinite and% i necessary% necessary% a little smectite or #alloysite. #alloysite. 8ery lo) in coloring element% t#ey are "articularly suited or t#e "re"aration o "roducts in )#ite color. ed clays $#ey are used used or t#e manuacture manuacture o terra cotta cotta "roducts. $#ey #a(e com"le& com"le& com"osition o actually natural natural mi&tures. $#ey generally contain =aolinite% =aolinite% illite andYor ot#er clays ric# in al=aline% sand% mica Bormula Si39l3;10B;/D2D% goet#ite Be;B;/DD andYor #ematite Be 2;3D% organic matter and% (ery oten% calcium com"ounds. $#e latter% ust li=e t#e micas and t#e ot#er al=aline-ric# com"ounds t#at #el" lo)er t#e +ring tem"erature o t#e "roduct.
Silicate Ceramics<: $elds#ars and Silica !he ole of "#ides in $iring of !raditional Ceramics Acidic "#ides% $#ey "#ides% $#ey are ac=one o t#e ceramic and mainly im"ro(e t#e mec#anical "ro"erties. ormula: M;2% e.g. Si;2% Ge;2% $i;2% r;2% Cr;2 K etc &asic "#ides% $#ey "#ides% $#ey are lu&es% i.e. reducing +ring tem"erature. ormula: M; and M2;% e.g. Ca;% Mg;% a2;% 2;% Li2; K etc Amphoteric "#ides% $#ey "#ides% $#ey orm ridges et)een acidic and asic o&ides and "artially sustitute t#em. ormula: M2;3 and M2;5% e.g. 9l2;3% 72;3% 2;5 K etc $eldspars our elds"at#ic minerals are li=ely to enter t#e com"osition o silicate ceramic "astes. $#ey are: Z ort#oclase% a mineral ric# in "otassium )it# t#e com"osition 2;.9l2;3.,Si;2 Z alite% a mineral ric# in sodium )it# t#e com"osition a 2;.9l2;3.,Si;2 Z anort#ite% a mineral ric# in calcium )it# t#e com"osition Ca;.9l2;3.2Si;2 Z "etalite% a mineral ric# in lit#ium )it# t#e com"osition Li 2;.9l2;3.4Si;2 Z soda a2;% sodas# Z "otas# Z lucite ;rt#oclase and alite% )#ic# orm eutectics )it# silica at 0 and 1%050XC res"ecti(ely% are )idely used as Au&. 9nort#ite is rat#er regarded as a sustitute to c#al= 4
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 BCaC;3D. $#ere is a limited use o "etalite. It is used mainly to im"ro(e rig#tness and its negati(e C$!. otassic otassic elds"ar is "articularly a""reciated y ceramists ecause its reaction )it# silica leads to t#e ormation o a li*uid )#ose relati(ely #ig# (iscosity decreases slig#tly )#en t#e tem"erature increases. $#is e#a(ior is considered as a guarantee against t#e e&cessi(e e&cessi(e deormation o t#e "ieces during t#e #eat treatment. In manuacturing o "orcelain% t#e elds"ars can e re"laced y ne"#eline syenite )it# a(erage com"osition Ba%D 2;%9l2;3%2Si;2. $#is roc=% made u" o ne"#elite Bcom"osition: 2;.3a2;.'9l2;3.Si;2D and a mi&ture o "otassium and sodium elds"ars. It is a "o)erul Au&% )#ic# ma=es it "ossile to decrease t#e sintering tem"erature o ceramics and increase t#e al=aline content o t#e (itreous "#ases. /o)e(er% s"ecial care s#ould e ta=en or #omogeneity. Silica Silica% Si;2% is a "olymor"#ic ra) material ound in nature in an amor"#ous Bo"al% "elesD or crystalli?ed orm B*uart?% cristoalite and tridymiteD. Sand contains et)een 5 and 100J o *uart? mass. It is t#e most re*uently used in t#e ceramic industry to contriute to t#e mec#anical strengt# o t#e "arts. In t#e manuacturing "rocesses "rocesses o stone)ares and "orcelains% it is usual to use relati(ely ine sand grains B20 to ,0 NmD. <#en a ceramic is +red% t#e sand can react% "articularly )it# t#e Au&es. $#is reaction is not oten com"lete. $#e transormation transormation o residual *uart? into cristoalite can t#en start rom 1200XC on)ards. $#is transormation transormation is en#anced y t#e rise in tem"erature% t#e use o +ne-grained sand% t#e "resence o certain im"urities% and t#e use o reducing atmos"#ere. $#e orm o silica silica determines t#e t#ermal t#ermal "ro"erties o silicate ceramics. or or e&am"le% *uart? and cristoalite do not #a(e t#e same inAuence on t#e e&"ansion o t#e "roduct. Tuart? can also cause a deterioration o t#e mec#anical "ro"erties o t#e inis#ed "roduct o)ing to t#e aru"t (ariation in dimensions B[LYL \ #$.%&' associated, at &%)*, with the reversible transformation ] *uart? ^ *uart?. 9s t#e crystal o cristoalite ormed rom t#e lu& are usually small% t#e transition ] cristoalite ^ cristoalite% )#ic# occurs at aout 220XC oten causes less damage to t#e +nis#ed "roduct. is outside t#e sco"e o t#is course ut )orry aout it. Enamel and decorations decorations is '- (roducts Classication $#e materials treated treated at #ig#er tem"eratures tem"eratures or in t#e "resence o a large *uantity o Au& are generally t#e least "orous. $#e "orous ceramics Beart#en)ares% Beart#en)ares% +red at 00-1200XCD can e used ust as t#ey are are Bric=s and tilesD or e co(ered )it# enamel. $#e dense "roducts are stone)ares +red at aout 1350XC. 8itreous c#ina orms an 6eed (ring intermediate grou" grou" et)een t#ese t)o amilies.
Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 !erra cotta products
Dr. Saad B. H.
$erra $erra cotta is reerring to "otteries or construction construction "roducts "roducts suc# as roo roo tiles% ric=s% Aues% drainage "i"es% or some Aoor tiles. $erra cotta "roducts )ere otained a long time ago y modeling% drying and +ring common clays. o)adays% t#e com"ositions are more com"le&> t#ey comine clays% additi(es% and coloring agents% )#ic# ma=e it "ossile to im"ro(e t#e manuacturing e#a(ior or t#e +nal c#aracteristics. $#e ra) materials are are added to )ater to orm orm a "lastic "aste )#ose )#ose r#eology must must e ada"ted to t#e s#a"ing "rocess Be&trusion Be&trusion "ossily com"leted y "ressingD. $#e ra) "arts are dried in a (entilated cell or a tunnel dryer. dryer. $#e tem"erature at t#e end o +ring usually ranges et)een 00 and 11,0XC. $erra $erra cotta "roducts "roducts are "orous "orous and mec#anically mec#anically resistant. resistant. $#ey are mar=eted mar=eted ra)% enameled or co(ered )it# a gla?e reali?ed at lo) tem"erature% et)een ,00 and 00XC% called (arnis#. $#ey are a""reciated or t#eir est#etic *uality% t#eir staility t#roug# time and t#eir #ygrot#ermic and acoustic "ro"erties. $#ey re"resent a #ig#ly automated industrial sector% )#ic# is o continual tec#nological de(elo"ments. )-a Earthen*ares products
$igure : Traditional ceramic %amilies % amilies
$#e eart#en)are eart#en)are are made u" o o a "orous "roducts "roducts co(ered co(ered )it# a gla?e. $#e gla?ing ma=es it "ossile to c#ange t#e a""earance o t#e "roduct and to o(ercome t#e #ig# "ermeaility due to t#e e&istence o an o"en "orosity B5 – 20JD. eart#en)ares are used as croc=ery% croc=ery% "ottery% )all tiles ti les Ketc. $#ese "roducts "roducts are "re"ared "re"ared rom rom one or more more clays to )#ic# *uart?% c#al= c#al= BCalcite% CaC;3D% elds"ar% or ground glass is added. !art#en)ares are are "rimarily s#a"ed y sli" casting% iggering o "lastic "aste and "o)der "ressing. 9ter drying% t#e ra) "roduct is suected to a #eat treatment called iscuiting% carried out at a tem"erature ranging et)een a""ro&imately a""ro&imately 00 and 1%230XC. $#e deormation and t#e s#rin=age o t#e "roduct during t#is stage are limited ecause o t#e reractory nature o t#e ra) materials used. $#e "orous "orous iscuit otained is t#en gla?ed gla?ed during gla?ing +ring carried carried out at a tem"erature tem"erature lo)er t#an or sometimes e*ual to t#at o iscuiting. $#e t#ird +ring B(ery rareD% at a lo)er tem"erature% is necessary to +& some decorations de"osited on t#e gla?e% in "articular t#ose containing gold or "latinum and t#ose =no)n as lo) +reH decorations. )-b Stone*ares products Stone)ares #a(e a (itri+ed% o"a*ue% colored% and "ractically im"ermeale "roduct "roduct B0 to 3J o"en "orosityD. "orosityD. $#ey are otained rom a mi&ture o (itriying "lastic clays and Au&% sometimes su""lemented y sand or grog. $#ey are ormed y e&trusion B"i"es% ric=s% etc.D or y granulated "o)der "ressing Btiles% slas% etc.D. $#e +ring tem"erature generally ranges et)een 1%120 and 1%300XC and it orms a critical "arameter. "arameter. In act% sintering at an insuEcient tem"erature tem"erature Bnon-+ringD results in t#e "ersistence o a signi+cant o"en "orosity and a treatment at too #ig# a tem"erature leads to t#e 10
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 deormation deormation o t#e "ieces ecause o t#e e&cessi(ely large *uantity and t#e lo) (iscosity o li*uid ormed. I usage re*uires it% stone)ares stone)ares can e enameled. 9 salt gla?e during +ring can also e carried out Btraditional salt-gla?ed stone)aresD. Stone)ares are =no)n or t#eir un-c#angeaility% e&cellent mec#anical "erormances% and resistance to erosion and c#emical agents. 1+-a (orcelains $#e "orcelain "roducts "roducts are )#ite )#ite and translucent or "ure ra) materials materials and lo) t#ic=ness. orcelains orcelains do not #a(e o"en "orosity B_ 0.5JD% ut are li=ely to e&#iit some large closed "ores Bair #olesD. $#eir ractures are rilliant and #a(e a (itreous a""earance. 9ter 9ter enameling% t#e surace o t#e "ieces is remar=aly smoot# and rilliant. <#en "orcelain is +red% a li*uid "#ase surrounds surrounds t#e solid grains and dissol(es t#e inest o t#em B_ 15 NmD. uring t#is stage% =no)n as "asty usionH% t#e (iscosity is suEciently #ig# or t#e deormation o t#e "ieces to remain )it#in acce"tale limits. $#e solidi+cation o t#e li*uid on cooling leads to t#e ormation o a large *uantity o (itreous "#ase. $#e manuacturing "rocesses "rocesses are c#anging constantly% $#us% $#us% )#en t#e geometry o o t#e "arts allo)s it% "ressure "ressure casting and s#a"ing y isostatic "ressing gradually re"lace iggering and casting in "laster "laster molds. ast ast +ring tec#ni*ues tec#ni*ues are increasingly increasingly used or enamel and decorations. orcelains im"ro(e im"ro(e t#e *uality o t#e "arts y limiting t#e ris=s o deormations. 9 usual trend is to decrease t#e sintering tem"erature. 1+-b Vitreous china $#e term (itreous (itreous c#inaH denotes denotes dense "roducts "roducts otained rom rom "astes close to t#ose used to manuacture elds"at#ic eart#en)ares. $#e elds"ar content o t#ese "astes is increased in order to "roduce% during t#e +ring% a suEcient *uantity o li*uid to eliminate o"en "orosity B_ 0.5JD. 8itreous c#ina are mainly used to manuacture sanitary articles and toug# croc=ery B)as#asin% croc=ery croc=ery or communitiesD% (itreous materials are in t#e middle et)een )#ite "aste stone)ares and "orcelains. $#ese "roducts "roducts are ormed ormed y iggering% casting% or isostatic isostatic "ressing. "ressing. 9 good ra) materials and s#a"ing "rocess is t#at ma=es ma=es it "ossile to otain ra) "ieces )it# a mec#anical strengt# suEcient to )it#stand t#e a""lication o an enamel "aste. Sanitary "roducts are are generally (itri+ed and enameled in a single treatment% carried out in o&idi?ing atmos"#ere atmos"#ere at a tem"erature tem"erature et)een 1.200 and 1.240XC. 9 t)ice-+ring treatment is usually used or croc=ery. $#e +rst +ring is t#us carried out et)een 00 and 50XC. $#e elimination o o"en "orosity and t#e ormation o t#e enamel occur during t#e second +ring at a tem"erature ranging et)een 1.200 and 1.250XC. $#e enamel t#us otained% generally o"aci+ed% can allo) a large (ariety o decorations. 11- Alumina Ceramics
11
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 9lumina is "roduced "rimarily rom au&ite roc=s treated t#roug# t#e 7ayer "rocess. 7au&ite roc=s contain '0-,0J o e*ui(alent alumina% 10-20J iron o&ide% and a""ro&imately a""ro&imately 5J *uart? sand and (arious im"urities. $#e 7ayer "rocess "rocess consists o o attac=ing t#e roc= roc= crus#ed y a #ot caustic caustic detergent Ba;/ solution at a tem"erature o 150–1,0XC% under a "ressure o 0.5 MaD in order to dissol(e alumina in t#e orm o aluminate and to "reci"itate t#e im"urities Be2;3% Si;2% $i;2D. $#ese red de"osit are eliminated y +ltration and% ater cooling% t#e #ydrated sodium aluminate solution a9lB;/D ' is seeded )it# -9lB;/D 3 germs )#ic# leads to a massi(e "reci"itation o t#is latter "#ase. /eat treatments o 7ayer -9lB;/D 3 initially cause de#ydration% t#en a recrystalli?ation recrystalli?ation to many ty"es o transition aluminas t#at can e classi+ed under t#e name o gamma aluminas. a- Structural a""lications o alumina 9lumina ceramics o)e to t#e staility o t#is o&ide and its strong atomic onds. $#eir mec#anical and t#ermal "erormances% #ig# #ardness% #ig# moduli o elasticity% satisactory mec#anical strengt#% )ear resistance% good triological "ro"erties% "ro"erties% and reractoriness. Gi(ing accurate (alues )ould e useless ecause mec#anical "ro"erties are sensiti(e "ro"erties% "ro"erties% )#ic# (ary )it# t#e microstructure% and t#e #ot "ro"erties de"end #ig#ly on t#e tem"erature and c#emical reactions )#en t#e en(ironment is aggressi(e. $o illustrate t#is "oint% a dense +ne-grained alumina ceramic #as a Voung`s modulus o '00 Ga Bt)ice t#e modulus o steelD% a oisson`s ratio o 0.25% a 8ic=ers #ardness o 20 Ga and a mec#anical ending strengt# σ o 300-500 Ma. $oug#ness $oug#ness at 20XC is e*ual to 3.5 Ma Ma m1Y2% )#ic# is a res"ectale res"ectale amount or a ceramic% ut t#is less t#an t#at o metals. uctility is modest. $#e coeEcient o t#ermal e&"ansion is 4.5 10-, -1 B20-1%000XC% 20-1%000D. $#is relati(ely #ig# t#ermal e&"ansion or a ceramic comines )it# a #ig# Voung`s modulus ma=es alumina ceramics are not (ery resistant resistant to t#ermal s#oc=s. 9lumina #as "oor cree" resistance under sustantial load. 9lumina ceramics are est suited or mec#anical uses Be&cluding s#oc=sD or reractory uses. - unctional a""lications o alumina 9lumina ceramics are )idely used y t#e electric and electronic industries. S"ar= "lugs or automoiles illustrate t#e oldest a""lication using 'J 9l 2;3. 9dditionally% alumina is ound in a numer o insulation "roducts% including t#ose re*uiring re*uiring tig#t ceramic-metal sealings. or electronics% t#e main "roduct is t#e insulating sustrate% on )#ic# conducting or resisti(e% e(en ca"aciti(e% or inducti(e% circuits ci rcuits are de"osited. $#e ad(antage o alumina is its (ery #ig# resisti(ity Bit may e recalled t#at or t#is it must e (ery "ure% or at least ree rom im"urities li=e sodium or transition metalsD. 12
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 $#e t#ree limitations limitations o alumina or t#e manuacture manuacture o dielectric sustrates sustrates are: are: i. a modest modest t#ermal t#ermal conduct conducti(ity i(ity B 30 30 < m-1 -1D% -1D% )#ic# )#ic# does does not acilitat acilitate e t#e dissi"ation o t#e #eat "roduced y t#e boule eFect> ii. a coeEcient coeEcient o e&"ansion e&"ansion doule doule t#at o o silicon% )#ic# )#ic# generates generates stresse stresses s at t#e sustrate Bc#i"H interacesD> iii. a mar=ed "ermitti(ity "ermitti(ity B 10D% 10D% )#ic# induces ca"aciti(e ca"aciti(e cou"lings and decreases t#e transit times. 9luminum nitride 9l is one o t#e com"etitors or t#e manuacture o #ig# tec#nology sustrates% )#ere it rings im"ro(ements )it# res"ect to t#e t#ree dra)ac=s mentioned ao(e% ut its manuacture manuacture is e&"ensi(e and delicate. Sa""#ire and "ossily ruy mono-crystals is used due to t#e remar=ale remar=ale comination o o"tical and mec#anical "erormances. be)elry Be)els% scratc#-"roo glass or )atc#esD% laser matrices% sustrates or certain electronic circuits and )a(eguides are t#e "rimary a""lications o sa""#ire mono-crystals% as )ell as arasion-resistant o"tical )indo)s: or military use% ut also arcode readers in su"ermar=ets. 12- ,ullite ,agnesia and Spinel Mullite 39l2;3.Si;2 is t#e only stale crystalli?ed com"ound in t#e inary "#ase diagram o t#e 9l 2;3-Si;2. /o)e(er% mullite is (ery rare in t#e state o natural ore% e&ce"t in some "laces suc# as t#e Scottis# island o Mull% )#ic# e&"lains its name. Its mec#anical strengt# dro"s muc# less *uic=ly )#en t#e tem"erature tem"erature increases t#an in t#e case o alumina: at 1%300XC% most mullite ceramics #a(e a mec#anical strengt# close to t#e one at room tem"erature% tem"erature% and some mullites )it# (itreous segregations segregations e(en #a(e a "ea= mec#anical strengt# at aout 1%300XC. $#ese c#aracteristics c#aracteristics ma=e mullite mullite a material o c#oice or or reractory a""lications $#e maority o magnesia magnesia "roduced is used or reractories in t#e iron and steel industry% )#ere t#e asic o&ide "ro"erties o t#e material are necessary. Magnesia )it#stands t#e (ery #ig# tem"eratures o con(erters B1%00XCD% )#ere it can dissol(e se(eral times its )eig#t o iron o&ide
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Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 )it#out melting and it eFecti(ely resists sealing and t#e attac= o slag.
Dr. Saad B. H.
S"inel Mg9l2;' #as gi(en its name to a crystalline structure ado"ted y se(eral mineral "#ases. 7ased on t#e notation Mg2W9l23W;'% Mg2W% Mg2W can e re"laced y ot#er di(alent cations li=e e 2W% Mn2W or n2W% and 9l3W can e re"laced y ot#er tri(alent cations li=e e 3W or Cr3W. $#e s"inel structure structure is denoted y 972' Bs"ace grou" d3mD. ense sintered s"inel is trans"arent in a road domain o )a(elengt#s% )#ic# e&"lains its use in t#e manuacture o o"tical )indo)s Bmilitary a""lications in "articularD 1.- /irconia "ther o#ides irconia is an o&ide )it# (ery #ig# melting tem"erature B$ 2%440XCD% )#ic# solidi+es in cuic "#ase Br; 2-c% grou" s"ace m
3 ´
mD% t#en transorms B$ _ 2%30XCD
to tetragonal "#ase B r; 2-t% '2YnmcD and +nally% elo) 1%10XC% ecomes monoclinical Br;2-m% 21YcD. $#is last transition t^m is accom"anied y considerale dimensional (ariations Bs#ear strains o 0.1, and increase in (olume o 'JD% )#ic# largely e&ceed t#e ma&imum stress limit% resulting in a ragmentation o t#e material. 9 sintered ?irconia ?irconia "art% say to 1500XC% rea=s u"% and destroyed during cooling. $#is too= "lace during t#e t^m transition. $#is means t#at "ureH ?irconia can e used only in "o)der orm Bor e&am"le% as starting "roduct or t#e manuacture o ceramic enamelsD% and t#ereore t#ereore or uses t#at do not re*uire re*uire consolidation into a massi(e "art. $o $o "roduce ?irconia ?irconia sintered "ieces% "ieces% r;2 must e comined )it# ot#er o&ides =no)n as staili?ersH BM&;y "rimarily Ca;% Mg;% or V 2;3D: t#e r; 2-M&;y "#ase diagram is t#en modi+ed a(oraly% )#ic# #el"s "reser(e Bat t#e stale state or metastale stateD a staili?ed ?irconiaH% ree rom transitions in t#e entire useul tem"erature range – in "ractice rom t#e sintering tem"erature to room tem"erature. In t#e r; 2-Ca; diagram% or e&am"le% it is oser(ed t#at or 20 molJ Ca;% t#e material remains in cuic "#ase rom room tem"erature tem"erature to "ractically t#e melting tem"erature. tem"erature. 9mong t#e uses o staili?ed ?irconia% denoted SH% )e can mention our main +elds: 1. 2.
t#e "roduct "roduction ion o mono-cr mono-crysta ystals ls or e)elry e)elry%% ecause ecause t#e o"tica o"ticall "ro"erti "ro"erties es o ?irconia ?irconia are not (ery diFerent rom t#ose o a diamond% at an incom"araly lo)er cost> t#e manuac manuactur ture e o cruciles cruciles and and ot#er ot#er reract reractory ory "arts% "arts% ecause ecause o o t#e #ig# #ig# melting melting tem"erature tem"erature and good resistance to corrosi(e corrosi(e mediums% including molten glass Breractories Breractories o 9--S system: 9l 2;3-r;2-Si;2D>
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 3. t#e manuac manuactur ture e o t#ermal t#ermal arrier arriers% s% or e&am"l e&am"le e de"osited de"osited y y "lasma "lasma s"raying s"raying using using "lasma torc#es or t#e internal "rotection o t#e comustion c#amer o et engines% ecause t#e t#ermal conducti(ity o ?irconia is one o lo)est e(er =no)n among nonmetallic inorganic solids B= 1 <.m-1. -1% i.e. 30 times lo)er t#an aluminaD> '. $#e manuact manuacture ure o ionic condu conductors ctors>> $#e intro introductio duction n o i(alent i(alent BCa; BCa; and and Mg;D or or tri(alent BV2;3D metal o&ides t#at are used as staili?ers re*uires% allo)s a considerale moility o residual o&ygen ions% t#e staili?ed ?irconia oFers "ro"erties o ionic conduction t#at allo) its a""lication as solid electrolyte% "articularly in o&ygen sensors and in solid o&ide uel cells. Ceramic steel S #as rat#er modest mec#anical "ro"erties% signi+cantly less remar=ale remar=ale com"ared to alumina )#ic#% associated )it# #ig#er density% #ig#er t#ermal e&"ansion Bconse*uently greater sensiti(ity to t#ermal s#oc=sD and mar=edly increased costs e&"lain )#y t#ese staili?ed ?irconia a priori do priori do not #a(e a mec#anical a""lication. irconia can e&#iit t#e #ig# mec#anical "erormances associated )it# steel% ut also t#at toug#ening mec#anisms recall t#ose used y steel manuacturers. $#e t^m transormation transormation o ?irconia is a martensitic transormation% in analogy )it# t#e transormation transormation used to otain martensite in tem"ered steels% and t#e role o microstructural microstructural "arameters in r;2 is similar to )#at is oser(ed in metals. In transormation toug#ening B$$D% toug#ening indicates t#e increase in toug#ness as )ell as in mec#anical strengt#.
Course 2 1- Sintering and microstructure of ceramics Sintering is at t#e #eart o ceramic "rocesses. "rocesses. /o)e(er% sintering ta=es "lace only in t#e last o t#e t#ree main stages o t#e "rocess B"o)ders ^ orming ^ #eat treatmentsD. treatmentsD. Sintering in(ol(es scienti+c considerations more directly% )#ereas t#e ot#er t)o stages oten stress more tec#nical oser(ations and in(ol(e manuacturing secrets. /o)e(er% 15
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 sintering may e ollo)ed y (arious +nis#ing treatments Brecti+cation% decoration% de"osit o suracing coatings% etc.D. Sintering oten re(eals deects caused during t#e "receding stages% )#ic# are generally o"timi?ed )it# res"ect to sintering% or e&am"le% t#e granularity o t#e "o)ders directly inAuences t#e densi+cation and grain gro)t#. g ro)t#. Generally% t#e success o t#e "o)der treatment is (alidated y t#e "erormances o t#e sintered "art. uring sintering% t#e non-co#esi(e granular medium ecomes a co#esi(e material> t#e consolidation ta=es "lace% and organi?ing t#e microstructure Bsi?e and s#a"e o t#e grains% amount and nature o t#e "orosity% etc.D. /o)e(er% t#e microstructure microstructure determines% to a large e&tent% t#e "erormances o t#e material. $#is is t#e reason )#y sintering meets a com"re#ensi(e com"re#ensi(e attention. Sintering and microstructure are t#us connected. Sintering is t#e asic tec#ni*ue or t#e "rocessing o ceramics% ut ot#er materials can also use it: metals% carides ound y a metallic "#ase and ot#er cermets K etc. 2-a !hermodynamics of sintering i. 9 "o)dery "o)dery agglome agglomerate rate is ote oten n called called com"act% com"act% e(en e(en t#oug# t#oug# its "oros "orosity ity is ty"ica ty"ically lly '0J and t#ereore its com"actness is only ,0J. ii. Sintering Sintering is t#e consolida consolidation tion%% under t#e eFect eFect o tem"eratur tem"erature% e% o a com"act o a nonco#esi(e granular material. $#e "articles o t#e starting "o)der @)elding@ )it# one anot#er to create a mec#anically co#esi(e solid% generally a "olycrystal. iii. $#e surace o a solid #as #as a sur"lus Be&cessD Be&cessD energy Benergy "er unit unit area: S8% )#ere S is or @solid@ and 8 is or @(a"or@D due to t#e act t#at t#e atoms #ere do not #a(e t#e normal en(ironment o t#e solid )#ic# )ould minimi?e t#e ree ent#al"y. i(. i(. In a "olycrystal% t#e grains grains are se"arated se"arated y grain oundaries oundaries )#ose sur"lus energy Bdenoted SS% or G7% )#ere SS is or @solid-solid@ and G7 or @grain oundary@D is due to t#e structural disorder o t#e oundary. (. In gene genera ral% l% SS _ S8% so a "o)der lo)ers its energy )#en it is sintered to yield a "olycrystal: t#e t#ermodynamic engine o sintering is t#e reduction o system`s interacial energies. $#e interacial energy #as t#e orm G 9% )#ere is t#e s"eciic interace energy and 9 its surace area. $#e lo)ering o energy can t#ereore e ac#ie(ed in t#ree )ays: iD y reducing t#e (alue o % iiD y reducing t#e interace area 9% and iiiD y comining t#ese eFects. $#e re"lacement o t#e solid-(a"or solid-(a"or suraces y grain oundaries decreases decreases % )#en SS is lo)er t#an S8. $#e reduction o 9 is ac#ie(ed y grain gro)t#: or e&am"le% t#e coalescence o n small s"#eres )it# surace s and (olume ( results in a large s"#ere )it# (olume 8 n( ut )it# surace S _ ns. In act% t#e term sintering includes our "#enomena% )#ic# ta=e "lace simultaneously and oten com"ete )it# eac# ot#er: – consolidation: de(elo"ment o nec=s t#at )eldH t#e "articles to one anot#er> – densi+cation: reduction o t#e "orosity% t#ereore o(erall contraction o t#e "art Bsintering s#rin=ageD> 1,
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 – grain coarsening: coarsening o t#e "articles and t#e grains> – "#ysicoc#emical reactions: in t#e "o)der% t#en in t#e material under consolidation.
$igure0 Sintering $igure0 Sintering o our "o)der "articles. In general% )e )ant sintering to e @densiying@% in )#ic# case t#e reduction o "orosity im"lies a s#rin=age: L+nal L0 – [L. Some mec#anisms are nondensiying and allo) only grain gro)t#. $#is diagram s#o)s s#o)s a t)o-dimensional system ut t#e "o)der is a t#reedimensional system. 2-b ,atter transport Sintering is "ossile only i t#e atoms can diFuse to orm t#e nec=s t#at )eld t#e "articles )it# one anot#er. anot#er. $#e trans"ort o matter can occur in (a"or "#ase% in a li*uid% y diFusion in a crystal% or t#roug# t#e (iscous Ao) o a glass. Most mec#anisms are acti(ated t#ermally ecause t#e action o tem"erature tem"erature is necessary to o(ercome t#e "otential arrier et)een t#e initial state o #ig#er energy Bcom"acted "o)derD and t#e +nal state o lo)er energy Bconsolidated materialD. 9tomic diFusion in ceramics is suEciently ra"id only at tem"eratures #ig#er t#an 0.,-0.4 $ % )#ere $ is t#e melting "oint Bin D. or alumina% or e&am"le% )#ic# melts at around 2%320 % t#e sintering tem"erature tem"erature c#osen is generally around 1%00 . .- E#perimental aspects of sintering $#e "arameters a(ailale a(ailale to us to regulate regulate sintering and control control t#e de(elo"ment o t#e microstructure microstructure are "rimarily t#e com"osition o t#e starting system and t#e sintering conditions: – com"osition o t#e system: iD c#emical com"osition o t#e starting "o)ders% iiD si?e and s#a"e o t#e "articles% and iiiD com"actness rate o t#e "ressed "o)der> – sintering conditions: iD treatment tem"erature% tem"erature% iiD treatment duration% iiiD treatment atmos"#ere and% i(D "ressure during t#e #eat treatment Bor "ressure sinteringD. (ressureless sintering and pressure sintering In general% sintering is ac#ie(ed solely y #eat treatment at #ig# tem"erature% ut in diEcult cases it can e assisted y t#e a""lication o an e&ternal "ressure: "ressure: – "ressureless sintering: no e&ternal "ressure during t#e #eat treatment> 1
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 – "ressure "ressure sintering Bunder unia&ial load or isostatic "ressureD: a""lication o an e&ternal "ressure during t#e #eat treatment. ressure ressure sintering re*uires a "ressure de(ice t#at )it#stands t#e #ig# sintering tem"eratures% tem"eratures% )#ic# is in act a com"le& and e&"ensi(e tec#ni*ue and t#ereore reser(ed or s"eci+c cases. Sintering *ith or *ithout liuid phase Sintering e&cludes a com"lete melting o t#e material and can t#ereore t#ereore occur )it#out any li*uid "#ase. /o)e(er% it can e acilitated y t#e "resence o a li*uid "#ase% in a more or less aundant *uantity. t#e latter case can e eit#er li*uid "#ase sintering or (itri+cation% de"ending on t#e *uantity o li*uid. – or solid "#ase sintering% t#e *uantity o li*uid l i*uid is ?ero or is too lo) to e detected. Consolidation and elimination o t#e "orosity re*uire re*uire a disru"tion BdisturanceD o t#e granular arc#itecture: arc#itecture: ater t#e sintering% t#e grains o t#e "olycrystal are generally muc# larger t#an t#e "articles o t#e starting "o)der and t#eir mor"#ologies are also diFerent. Solid "#ase sintering re*uires (ery +ne "articles BmicrometricD and #ig# treatment tem"eratures> tem"eratures> it is reser(ed or demanding uses% or e&am"le% trans"arent alumina or "ulic lam"s> – or li*uid "#ase sintering% t#e *uantity o li*uid ormed is too lo) Ba e) (ol.JD to +ll t#e inter-"article inter-"article "orosities. /o)e(er% t#e li*uid contriutes to t#e mo(ements o matter% mainly due to t#e "#enomena o dissolution ollo)ed y re"reci"itation. re"reci"itation. $#e "artial dissolution o t#e "articles modi+es t#eir mor"#ology and can lead to t#e de(elo"ment o ne) "#ases. 9 numer o tec#nical ceramics Breractory materials% alumina or insulators% 7a$i; 3-ased dielectricsD are sintered in li*uid "#ase> – lastly% or (itri+cation% t#ere is an aundant li*uid "#ase Bor e&am"le% 20 (ol.JD% resulting rom t#e melting o some o t#e starting com"onents or rom "roducts o t#e reaction et)een t#ese com"onents. $#is li*uid +lls t#e s"aces et)een t#e non-molten "articles and consolidation occurs "rimarily y t#e "enetration o t#e li*uid into t#e interstices due to ca"illary orces% t#en solidi+cation during cooling% to gi(e crystalli?ed "#ases or amor"#ous glass. $#is ty"e o sintering is t#e rule or silicate ceramics% or e&am"le% "orcelains. /o)e(er% t#e *uantity o li*uid must not e e&cessi(e% and its (iscosity must not e too lo)% ot#er)ise t#e oect )ould colla"se under its o)n )eig#t and )ould lose t#e s#a"e gi(en to it. Sintering *ith and *ithout reaction
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 to allo) t#eir reaction to)ards t#e desired com"ound% ollo)ed y t#e crus#ing o t#is com"ound to otain t#e "o)ders t#at )ill e sintered: – non-reacti(e sintering: an e&am"le is t#at o alumina% ecause t#e "o)ders o t#is com"ound are a(ailale on t#e mar=et> mar=et> – calcination and t#en sintering: an e&am"le is arium titanate B7a$i; 3D. 7a$i;3 "o)ders are e&"ensi(e and some industrialists "reer to start )it# a less e&"ensi(e mi&ture o arium caronate 7aC; 3 and titanium o&ide $i;2 Bor $i/2-&D% t#e mi&ture eing initially calcined y a #ig# tem"erature treatment to orm 7a$i;3% )#ic# is t#en crus#ed to gi(e t#e "o)der t#at )ill e used or sintering> – reacti(e sintering: an e&am"le is t#at o silicon nitride BSi 3'D% or )#ic# one o t#e "re"aration "re"aration met#ods consists o treating silicon "o)ders in an atmos"#ere atmos"#ere o nitrogen and #ydrogen% so t#at t#e reaction t#at orms t#e nitride B3Si W 2 2 ^ Si3'D is concomitant BassociatedD )it# its sintering. $#is tec#ni*ue B67S reaction onded silicon nitrideD ma=es it "ossile to a(oid t#e diEculties o t#e direct sintering o Si 3' and oFers t#e ad(antage o minimi?ing dimensional (ariations% ut t#e disad(antage o yielding a "orous material B 10JD. Mullite and ?irconia mullite can also e "re"ared y reacti(e sintering. ensication% sintering shrin3age $#e starting com"act #as a "orous "orous (olume BD o aout '0J '0J o t#e total (olume. /o)e(er% or most a""lications% )e )ant relati(ely non-"orous% non-"orous% e(en dense% ceramics B 0JD. In t#e asence o reactions leading to an increase in t#e s"eci+c (olume% densi+cation must e accom"anied y an o(erall contraction o t#e "art. ensi+cation can e c#aracteri?ed y linear s#rin=age BdlYl 0D% t#is contraction usually e&ceeds 10J. $#e control o o t#e s#rin=age is o (ital im"ortance or t#e industrialist: industrialist: on t#e one #and% t#e s#rin=age s#ould not result in distortions o t#e s#a"e and on t#e ot#er #and% it must yield +nal dimensions as close as "ossile to t#e desired dimensions Bnear net s#a"eD. In act% an e&cessi(e s#rin=age s#rin=age )ould ma=e t#e "art too small% )#ic# cannot e corrected. 9s )ell% an insuEcient s#rin=age )ould ma=e t#e "art too large> in t#is case mac#ining or ac#ie(ing t#e desired dimension must e done y recti+cation Bre+nement% Bre+nement% minor adustmentD. $#is is oten done y means o diamond grinding )#eel. $#e +nis#ing treatment treatment ecomes more more e&"ensi(e as t#e (olume (olume o matter to e araded araded BgrindedD is larger. inally% it is diEcult to control s#rin=age )it# a relati(e accuracy #ig#er t#an 0.5J. 7ecause o t#e "#enomenon o s#rin=age% dilatometry tests are )idely used or t#e @in situ@ ollo)-u" o sintering: starting )it# t#e @green@ com"act to arri(e at t#e +red "roduct% a #eating at constant s"eed ty"ically com"rises t#ree stages: iD t#ermal e&"ansion% accom"anied y a (a"ori?ation o t#e starting )ater and a "yrolysis o t#e organic inders introduced to su""ort t#e "ressing o t#e "o)der> 1
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 iiD a mar=ed contraction% due to "article rearrangement% rearrangement% t#e de(elo"ment o sintering nec=s and granular c#anges> iiiD a resum"tion o t#e t#ermal e&"ansion o t#e sintered "roduct. orosity orosity is o"en as long as it is inter-connected. inter-connected. $#e material is t#en "ermeale to Auids. orosity orosity is closed )#en it is not inter-connected: inter-connected: e(en i it is not yet dense% t#e material can t#en e im"ermeale. $#e "orosity le(el corres"onding corres"onding to t#e transormation transormation o o"en "ores to closed "ores is aout 10J. 4- Solid phase sintering !he three stages of sintering Solid "#ase sintering reers to t#e case )#ere no li*uid "#ase #as een identi+ed But oser(ations t#roug# electronic microsco"y in transmission sometimes s#o) t#e "resence o a (ery small *uantity o li*uid "#ase% or e&am"le due to a segregation o t#e im"urities along t#e grain oundariesD. Solid "#ase sintering ta=es "lace in t#ree successi(e stages: – initial stage: t#e "article system is similar to a set o s"#eres in contact% et)een )#ic# t#e sintering nec=s de(elo". I is t#e radius o t#e nec= and 6 t#e radius o t#e "articles% t#e gro)t# o t#e ratio Y6 in time t% or an isot#ermal sintering% ta=es ta=es t#e orm: BY6Dn 7tYm. 7 is a c#aracteristic "arameter o t#e material and t#e e&"onents n and m (ary according to t#e sintering "rocess t#at ta=es "lace. or e&am"le% e&am"le% n 2 and m 1 or (iscous Ao)> n 5 and m 3 or (olume diFusion> n , and m ' or grain oundary diFusion> – intermediate stage: t#e system is sc#emati?ed y a stac=ing o "oly#edric Brom "oly#edronD "oly#edronD grains intert)ined at t#eir common aces% )it# "ores t#at orm a canal system along t#e edges common to t#ree grains% connected at t#e *uadru"le "oints Bsee igureD. igureD. $#e "orosity "orosity is o"en. $#is diagram is (alid as long as t#e densi+cation does not e&ceed 0-2J% a t#res#old t#res#old eyond )#ic# t#e interconnection o t#e "orosity disa""ears> – +nal stage: t#e "orosity is closed> only isolated "ores remain% remain% oten located at t#e *uadru"le "oints et)een t#e grains B@tri"le "oints@ on a t)odimensional sectionD ut )#ic# can e tra""ed in intragranular "osition.
iagram o t#e "orosity in t#e orm o interconnected canals along t#e edges o a "oly#edron )it# 1' aces% ty"ical o t#e intermediate stage o sintering
5rain gro*th 9s t#e energy o t#e interaces #as t#e orm 9% )#ere is t#e s"eciic energy o t#e interace and 9 is t#e surace area o t#e interace% t#e system`s energy can e reduced using t)o orderline cases:
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 – "ure densi+cation: t#e "articles "reser(e t#eir original si?e% ut t#e solid-gas interaces BSGD are re"laced y grain oundaries B SSD% )it# a c#ange in t#e s#a"e o t#e "articles> – coalescence and "ure grain gro)t#: t#e "articles "reser(e t#eir original orm% ut t#ey c#ange in si?e y coalescence% t#us reducing t#e surace areas. ure densi+cation #as ne(er een oser(ed: t#ere is al)ays some degree o grain gro)t#. In normal grain gro)t#% t#e a(erage grain si?e increases regularly% )it#out mar=ed modi+cation o t#e relati(e distriution o t#e si?e> t#e microstructure microstructure e&"ands #omot#etically. $#is ty"e o grain gro)t# is t#e one oser(ed in a successul sintering. $#e small grains disa""ear in a(or o t#e coarser grains% )#ic# gro) Bsee igureD. Secondary recrystalli?ation Bor anormal gro)t#% or discontinuous grain gro)t#D ma=es a e) grains gro) ra"idly% at t#e e&"ense o t#e more moderately si?ed grains. $#e +nal microstructure microstructure is (ery #eterogenous% #eterogenous% )it# coe&istence o (ery coarse grains and (ery small grains. $#is ty"e o microstructure microstructure rarely leads to a(orale "ro"erties> t#ereore% t#ereore% it is generally a(oided.
$#e "ressure on t#e cur(ed interaces is suc# t#at t#e oundaries mo(e to)ards t#eir center o cur(ature: t#e small con(e& grains Bless t#an , sidesD disa""ear )#ile t#e coarse conca(e grains Bmore t#an , sidesD gro) at t#e e&"ense o t#e neig#oring grains
$#e maority o ceramics are multi"#ased materials materials t#at com"rise com"rise ot# crystalli?ed and (itreous "#ases. orcelain orcelain t#us consists o silicate glass @reinorced@ y acicular crystals o crystalli?ed mullite% ut )e can also oser(e millimetric crystal agglomerates )it# a (ery "orous microstructure microstructure Biron Biron and steel reractory reractory materialsD% or +ne grained "olycrystals B_ 10 NmD )it#out (itreous "#ases and )it# (ery lo) "orosity B#i" "rost#esis "rost#esis in alumina or ?irconiaD. It s#ould e em"#asi?ed t#at% in addition to t#e c#emical nature o t#e com"oundBsD in *uestion% it is t#e microstructure microstructure o t#e material Bsi?e and s#a"e o t#e grains% (olume and ty"e o "orosity% distriution o t#e "#asesD t#at controls t#e "ro"erties. 6- Sintering *ith liuid phase% vitrication (arameters of the liuid l iuid phase In general% t#e "resence o a li*uid "#ase acilitates sintering. 8itri+cation is t#e rule or silicate ceramics )#ere t#e reactions et)een t#e starting com"onents orm com"ounds melting at a rat#er lo) tem"erature% )it# t#e de(elo"ment o an aundant *uantity o (iscous li*uid. 8arious tec#nical ceramics% most metals and cermets are all sintered in t#e "resence o a li*uid "#ase. It is rare t#at sintering )it# li*uid "#ase does not im"ly any c#emical reactions% ut in t#e sim"le case )#ere t#ese reactions do not #a(e a mar=ed inAuence% surace eFects are "redominant. $#e main "arameters are t#ereore: 21
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 iD *uantity o li*uid "#ase% iiD its (iscosity% iiiD its )ettaility )it# res"ect to t#e solid% and i(D t#e res"ecti(e soluilities o t#e solid in t#e li*uid and t#e li*uid in t#e solid: !he stages in liuid phase sintering si ntering $#e s#rin=age s#rin=age cur(e recorded recorded during an isot#ermal isot#ermal treatment o o li*uid "#ase sintering s#o)s t#ree stages: – (iscous Ao) and grain rearrangement: rearrangement: )#en t#e li*uid is ormed% t#e limiting "rocess consists consists o a (iscous Ao)% )#ic# allo)s t#e rearrangement o t#e grains. $#e li*uid dissol(es t#e surace surace as"erities and dissol(es dissol(es t#e small "articles. $#e granular rearrangement rearrangement is limited to t#e li*uid "#ase sintering itsel% ut it can e enoug# to allo) com"lete densi+cation i t#e li*uid "#ase is in suEcient *uantity% as is t#e case in t#e (itri+cation o silicate ceramics> – solution-re"reci"itation: solution-re"reci"itation: t#e soluility o t#e solid in t#e li*uid increases at t#e interinter"article "oints o contact. $#e transer o matter ollo)ed y re"reci"itation in t#e lo) energy areas results in densi+cation> – de(elo"ment o t#e solid s=eleton: t#e li*uid "#ase is eliminated gradually y t#e ormation o ne) crystals or solid solutions> )e tend to a""roac# t#e case o solid "#ase sintering and t#e last stage o t#e elimination o "orosity is similar to t#is case. 7- Sintering additives (ressure sintering and hot isostatic pressing 89( 7-a Sintering additives $#e im"ressi(e im"ressi(e eFect o t#e addition o a e) #undred #undred ""m o magnesia on t#e sintering o alumina is t#e est e&am"le o t#e role o sintering additi(es. $#ese additi(es #el" to control t#e microstructure microstructure o t#e sintered materials> t#ey can e classi+ed under t)o categories: – additi(es t#at react )it# t#e asic com"ound to gi(e a li*uid "#ase% or e&am"le y eutectic at a melting "oint less t#an t#e sintering tem"erature. t#e a""earance o an eutectic at – additi(es t#at do not lead to t#e ormation o a li*uid "#ase. $#ese additi(es enale t#e sintering to ta=e "lace in solid "#ase. It alters t#e (alues o t#e diFusion coeEcients and t#e moility o t#e grain oundaries. $#is is t#e case o t#e do"ing o 9l 2;3 )it# a e) #undred ""m o Mg;% ecause t#e lo)est tem"erature at )#ic# a li*uid can a""ear in t#e 9l2;3-Mg; system e&ceeds t#e sintering tem"erature B)#ic#% or alumina% does not go eyond 1%00XCD. 7-b Applying a pressure during sintering :overvie*; 22
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 In most cases% ceramics are sintered y "ressureless "ressureless sintering and it is only or (ery s"ecial a""lications t#at )e use @"ressure @"ressure sintering@ or @#ot "ressing@% )#ic# consists o a""lying a "ressure during t#e #eat treatment itsel. $#e c#aracteristic o "ressure sintering is t#at t#e "ressures "ressures roug#t into "lay – )#ic# are usually aout 10 to 0 Ma% ut can e&ceed 100 Ma – #a(e considerale eFects and oFering our 9d(antages: iD t#ic=ening o materials )#ose interacial energy alances are una(orale> iiD ra"id densi+cation at a""recialy lo)er tem"eratures tem"eratures Bse(eral #undred degrees sometimesD t#an t#ose demanded y "ressureless sintering> iiiD "ossiility o reac#ing t#e t#eoretical density B?ero "orosityD> i(D "ossiility o limiting t#e grain gro)t#> (D "ossiility to otain t#e sintered "art )it# its e&act dimensions Bnet s#a"eD% )it#out t#e need or a mac#ine +nis#ing in a""lications t#at re*uire re*uire #ig# dimensional accuracy. isad(antages o t#e "ressure "ressure sintering ;n t#e ot#er #and% B1D t#e tec#nical com"le&ity o t#e "rocess and B2D t#e #ig# costs ac*uired% as )ell as B3D t#e limitations on t#e geometry o t#e "arts% )#ic# can only #a(e sim"le orms and a rat#er reduced si?e. B'D
23
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 $#e "o)ders to e sintered are generally (ery (ery ine B_ 1 NmD and it is not al)ays al)ays necessary or t#em to contain additi(es re*uired y "ressureless "ressureless sintering Bor e&am"le% Mg; or t#e sintering o 9l 2;3D. $#e usti+ale a""lications o "ressure sintering are% or e&am"le% cutting tools Bceramics or cermetsD or o"tical "arts% )it# t#e essential oecti(es o ac#ie(ing a 100J densi+cation andYor (ery +ne grains. /o)e(er% t#e microstructure microstructure and t#e crystallogra"#ic te&ture te&ture can "resent anisotro"y anisotro"y eFects ecause o t#e unia&ial "ressing. 9lumina or cutting tools% carides B7 'CD or cermets are e&am"les o materials t#at can ene+t rom "ressure sintering and /I. $#e same is true or metallic @su"eralloys@ used in t#e #ot "arts o turoets. /ig# tem"erature com"osite materials are anot#er e&am"le )#ere t#e a""lication o a "ressure "ressure during #eat treatments treatments can e necessary to allo) t#e im"regnation o t#e +rous )ic=s and a(or t#e densi+cation. unctional ceramics B7a$i;3 or% es"ecially% magnetic erritesD can gain rom (ery +ne grains and t#e asence o residual "orosity "orosity made "ossile y "ressure "ressure sintering. 9s o"tical trans"arency trans"arency is no dout t#e "ro"erty t#at is most *uic=ly degraded y t#e "resence o "ores% e(en in i n e&tremely small numers% "erectly trans"arent trans"arent "olycrystalline ceramics BMg9l 2;'% 9l2;3% V2;3% etc.D are e&am"les o materials t#at ene+t rom t#e use o "ressure sintering. 9s regards t#e mec#anisms% "ressure sintering im"lies: iD rearrangement rearrangement o t#e "articles% iiD lattice diFusion% iiiD grain oundary diFusion% i(D "lastic deormation and a (iscous Ao). ressureless ressureless sintering in(ol(es muc# less t#e eFects i and i(. i(. $#e dominant eFects are ii and iii due to t#e #ig# le(el o t#e mec#anical stresses. 7-d 8ot isostatic pressing 89( :e#perimental vie*; $#e "ressuri?ation "ressuri?ation Auid is a li*uid or cold isostatic "ressing "ressing CI. CI. In /I% t#e Auid is a gas Bin general% argon% ut reacti(e atmos"#eres are also used% or e&am"le o&ygenD t#at "ro(ides t#e "ressuri?ation. "ressuri?ation.
2'
Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015
Dr. Saad B. H.
irect /I Bon t#e letD and "ost-sintering /I Bon t#e rig#tD
Consolidation by 89( <#en /I is used directly to consolidate a "o)der% t#e @com"act@ must e enca"sulated in an en(elo"e in a orm #omot#etic to t#at o t#e "art to e otained% )it# (acuum e(acuation o gases% ollo)ed y sealing o t#e en(elo"e. Sot or stainless steels can e used as en(elo"e materials or relati(ely lo) tem"erature treatments treatments B1%100–1%200XCD% )#ereas it is necessary to use reractory metals B$a% MoD or #ig#er tem"eratures tem"eratures treatments. 9s t#e ris=s o distortion ecome #ig#er )#en t#e o(erall "ressing increases% increases% )e gain rom a "o)der "ressed at a #ig# rate and #omogenously By CI "rimarilyD. 9n alternati(e is to carry out a @"re-sintering@ "ro(iding "ro(iding suEcient co#esion to t#e "art to ma=e its #andling "ossile% and t#en to coat it "o)dered glass% )#ic#% at suEcient tem"erature% )ill ecome (iscous enoug# to coat t#e "iece )it# an im"ermeale layer. layer. $#is )ill ma=e it "ossile or /I to ta=e "lace )it#out t#e "ressuri?ed gas eing ale to "enetrate t#e o"en "orosity. 89( as post-sintering operation $#is in(ol(es sintering t#e "art until t#e inter-connected inter-connected o"en "orosity "orosity is eliminated B)#ic# re*uires re*uires a densi+cation o aout 5JD and t#en suecting t#is "art to a secondary /I treatment. $#e greatest ad(antage is a(oiding t#e need or an en(elo"e Bcost% com"le&ity% restrictions restrictions on t#e "ossile orms% necessity to clean t#e end "roduct to eliminate t#e en(elo"eD. It is urt#ermore urt#ermore "ossile% or manuacturers manuacturers )#o do not #a(e an /I e*ui"ment% to su-contract t#is stage to a s"eciali?ed "artner. "artner. $#ere are /I c#amers )#ose si?e is more t#an one meter% )#ic# ma=es it "ossile to treat large "arts or a great numer o small "arts. YY Glass and Glass ceramics
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 <- 5lass enition and !ransition temperature Glass is Glass is an amor"#ous Bnon-crystallineD solid material% )#ic# is oten trans"arent trans"arent and #as )ides"read "ractical% tec#nological% and decorati(e usage in t#ings li=e )indo)"anes% tale)are% tale)are% and o"toelectronics. o"toelectronics. $#e most amiliar% and #istorically t#e oldest% ty"es o glass are ased on t#e c#emical com"ound silica Bsilicon dio&ideD% t#e "rimary constituent o sand. $#e term te rm lass% lass% in "o"ular usage% is oten used to reer only to t#is ty"e o material% )#ic# is amiliar rom use as )indo) glass and in glass ottles. ; t#e many silica-ased glasses t#at e&ist% ordinary gla?ing and container glass is ormed rom a s"eci+c ty"e called soda-lime glass% com"osed o a""ro&imately 5J silicon dio&ide BSi;2D% sodium o&ide Ba 2;D rom sodium caronate Ba 2C;3D% calcium o&ide% also called lime BCa;D% and se(eral minor additi(es. 9 (ery clear and durale *uart? glass can e made rom "ure silica> t#e ot#er com"ounds ao(e are used to im"ro(e t#e tem"erature )or=aility o t#e "roduct. $#e glass–li*uid transition transition Bglass transitionD is t#e re(ersile transition transition in amor"#ous amor"#ous materials rom a #ard and relati(ely rittle state into a molten or ruer-li=e ruer-li=e state. 9n amor"#ous solid t#at e&#iits a glass transition is called a glass. Su"er-cooling Su"er-cooling a (iscous li*uid into t#e glass state is called (itri+cation. es"ite t#e massi(e c#ange in t#e "#ysical "ro"erties o a material t#roug# its glass transition% t#e transition is not itsel a "#ase transition o any =ind> rat#er it is a laoratory "#enomenon e&tending o(er a range o tem"erature tem"erature and de+ned y one o se(eral con(entions. enition of glass% $#e glass is an amor"#ous amor"#ous solid com"letely lac=ing in long range% "eriodic atomic structure% structure% and e&#iiting a region o glass transormation BtransitionD e#a(ior. e#a(ior. 9ny material% inorganic% organic% or metallic% ormed y any tec#ni*ue% )#ic# e&#iits glass transormation transormation BtransitionD e#a(ior% is a glass. !ransition temperature !g $#e most re*uently re*uently used de+nition o o ! g uses t#e energy release on #eating in diFerential scanning calorimetry BSC% see +gureD. $y"ically% $y"ically% t#e sam"le is +rst cooled )it# 10 Ymin and t#en #eated )it# t#e same s"eed. In t#is conte&t% ! g is t#e tem"erature tem"erature corres"onding to "oint 9 on t#e cur(e. $#e linear l inear sections are elo) and ao(e ! g. ! g is t#e tem"erature at t#e intersection o t#e regression lines. ;ne de+nition reers to t#e (iscosity% +&ing ! g at a (alue o 10 13 "oise Bor 1012 asD.
2,
Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015
Dr. Saad B. H.
'- Common types of glass $#e ollo)ing is a list o t#e more common ty"es ty"es o silicate glasses% and and t#eir ingredients% "ro"erties% and a""lications: 1.
$used uart=% uart=% also called fused silica glass vitreous silica glass% glass % is silica BSi;2D in (itreous or glass orm Bi.e.% its molecules are disordered disordered and random% )it#out crystalline structureD. It #as (ery lo) t#ermal e&"ansion% is (ery #ard% and resists #ig# tem"eratures tem"eratures B1000–1500XCD. It is also t#e most resistant against )eat#ering Bcaused in ot#er glasses y al=ali ions leac#ing out o t#e glass% )#ile staining itD. used *uart? is used or #ig# tem"erature a""lications suc# as urnace tues% lig#ting tues% melting cruciles% etc.
2.
Soda-lime-silica glass *indo* glass: glass : silica BSi;2D 2J W sodium o&ide Ba 2;D 1'.2J W lime BCa;D 10.0J W magnesia BMg;D 2.5J W alumina B9l 2;3D 0.,J. It is trans"arent% trans"arent% easily ormed% and most suitale or )indo) glass BAat glassD. It #as a #ig# t#ermal e&"ansion and "oor resistance to #eat B500–,00XCD. It is used or )indo)s% some lo) tem"erature incandescent lig#t uls% and tale)are. Container of Tg byt#at is a slig#t (ariation on Aat glass% )#ic# uses more glassRight: is a Determination soda-lime glass → dilatometry alumina and calcium% and less sodium and magnesium )#ic# are more )ater-solule. )ater-solule. $#is ma=es it less susce"tile to )ater )ater erosion. Left: Measurement of Tg by
differenti al scanning calorimetry ↓ glass (yre# : silica BSi;2D 41J W oric o&ide B7 2;3D 12J W 3. differential Sodium borosilicate soda Ba2;D '.5J W alumina B9l2;3D 2.0J. Stands #eat e&"ansion muc# etter t#an )indo) glass. Used or c#emical glass)are% coo=ing glass% car #eadlam"s% etc. &orosilicate glasses Be.g. glasses Be.g. yre&D #a(e as main constituents: silica and oron o&ide. $#ey #a(e airly lo) coeEcients o o t#ermal e&"ansion e&"ansion B'0 yre& yre& C$! is 3.25h10 3.25h10 –,YXC as com"ared to aout h10 Z,YXC or a ty"ical soda-lime glass% ma=ing t#em more dimensionally stale. $#e lo)er C$! also ma=es t#em less suect to stress caused y t#ermal e&"ansion% t#us less (ulnerale to crac=ing rom t#ermal s#oc=. $#ey are commonly used or reagent ottles% o"tical com"onents% and #ouse#old coo=)are.
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 '. >ead-o#ide glass crystal glass: glass : silica 5J W lead o&ide B;D 25J W "otassium o&ide B 2;D 12J W soda Ba 2;D 2.0J W ?inc o&ide Bn;D 1.5J W alumina 0.'J. 7ecause o its #ig# density Bresulting in a #ig# electron densityD it #as a #ig# reracti(e inde&% ma=ing t#e loo= o glass)are more more rilliant Bcalled @crystal@% t#oug# o course it is a glass and not a crystalD. It also #as a #ig# elasticity% ma=ing glass)are $ale: ale: Some 6a) 6a ) Materials or (ery )ell. OringO. It is also more )or=ale in t#e actory% $ ut cannot stand #eating 5.
Aluminosilicate glass: glass: silica 5J W alumina 1,J W lime 10J W magnesia .0J W arium o&ide B7a;D ,.0J W oric o&ide B7 2;3D '.0J. !&tensi(ely used or +erglass% used or ma=ing glass-reinorced "lastics Boats% +s#ing rods% etc.D and or #alogen ul glass.
,.
"#ide glass: glass: alumina 0J W germanium o&ide BGe;2D 10J. !&tremely clear glass% used or +er-o"tic +er-o"tic )a(eguides in communication net)or=s. Lig#t loses only 5J o its intensity t#roug# 1 =m o glass +er. /o)e(er% most o"tical +er is ased on silica% as are all t#e glasses ao(e.
?otes% i. 9not#er 9not#er common common glass ingre ingredient dient is crus#e crus#ed d al=ali al=ali glass or @cullet @cullet@@ ready ready or recycle recycled d glass. $#e recycled glass sa(es on ra) materials and energy. energy. Im"urities in t#e cullet can lead to "roduct and e*ui"ment ailure. ii.
ining agents suc# as sodium sulate% sodium c#loride% or antimony o&ide may e added to reduce t#e numer o air ules in t#e glass mi&ture.
iii. Glass atc# calculation is t#e t#e met#od y )#ic# t#e correct correct ra) ra) material mi&ture mi&ture is determined to ac#ie(e t#e desired glass com"osition. )- a* ,aterials and &atch Calculations a* ,aterials In general% glasses are "roduced eit#er rom #ig# *uality% c#emically "ure com"onents% or rom a mi&ture o ar less "ure minerals. 6esearc# 6esearc# s"ecimens% o"tical glasses% and many glasses used or lo) (olume% #ig# tec#nology a""lications are "roduced using t#ose c#emicals )e mig#t routinely encounter in any c#emical laoratory. 7ul= commercial "roducts% on t#e ot#er #and% are "roduced rom minerals% )#ic# ty"ically #a(e names and com"ositions% )#ic# are not amiliar. $#e names o many o t#ese minerals and t#eir com"ositions are listed in t#e adacent tale. Gra(imetric actors% )#ic# allo) calculation o t#e yield o t#e desired glass com"onent or eac# )eig#t unit o 24
Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 ra) material% are also listed in t#is tale. E#ercise% use E#ercise% use a tale o atomic )eig#ts and calculate t#e listed Gra(imetric actors in t#e adacent tale. /int: List t#e )eig#ts o t#e ;&ides or yoursel to sim"liy calculations. ;&ide 7a; Ca; ; Li2; Mg; 2; a2; n; e2;3 Mn; $i;2 2;5 Sr; r;2 /2; 72;3 9l2;3 Si;2
Dr. Saad B. H.
M< 153.' 0 5,.10 223.2 0 2.40 '0.30 '.20 ,2.00 41.'0 1,0.0 0 1.00 .0 1'2.0 0 103., 0 123.2 0 14.00 1.00 ,.,0 102.0 0 ,0.10
&atch Calculations 7atc#es containing only o&ides in t#eir e&act state as e&"ressed y t#e glass ormula% or e&am"le% in(ol(e (ery sim"le calculations% )#ile atc#es using a numer o diFerent minerals% )#ere a glass com"onent may e "resent in t)o or more ra) materials% re*uire muc# more com"licated calculations. 9ll atc# calculations ollo) t#e same "rocedure. "rocedure. irst% determine t#e )eig#t raction o eac# com"onent re*uired to "roduce t#e desired molar com"osition. 7egin y multi"lying t#e mole raction o eac# com"onent y t#e molecular )eig#t o t#at com"onent. e&t% total t#ese contriutions to determine t#e molecular )eig#t o t#e glass% and t#en di(ide eac# indi(idual contriution y t#e molecular )eig#t o t#e glass 2
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 to determine t#e )eig#t raction o eac# com"onent. inally% multi"ly t#e )eig#t raction o eac# com"onent y t#e amount o glass to e "roduced B!&am"le 3.1D. $#e atc# )eig#t o any com"onent% )#ic# decom"oses during melting% is adusted y multi"lying t#e )eig#t raction o t#at com"onent y t#e a""ro"riate gra(imetric actor or t#e ra) material actually used in t#e atc# B!&am"le 3.2D. Use o ra) materials% )#ic# su""ly more t#an one atc# com"onent% re*uires additional calculations% as illustrated in !&am"le 3.3.
I )e use alite elds"ar as t#e source o alumina% )e also otain some o t#e soda and silica needed or t#e atc#. Using t#e gra(imetric actors or alite in t#e tale% )e +nd t#at )e t#at '1.4 g o alite )ill yield t#e re*uired 4.15 g o alumina. $#is amount o alite also yields '.5 g o soda and 24.4 g o silica Bdi(ide t#e )eig#t o alite y t#e gra(imetric actor to +nd t#e yield or a gi(en amount o aliteD. 9ter sutracting t#ese *uantities rom t#e re*uired re*uired amounts o soda and sand% )e +nd t#at )e must add 1'.45 g o soda and '3.11 g o sand. I )e use a 2C;3 as t#e source o t#e additional
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 soda% )e )ill re*uire 1'.45 & 1.1 25.3 g o a 2C;3. inal 7atc#: a2C;3 25.3 g% 9lite '1.4 g% Sand '3.11 g 1+- Viscosity of 5lass $orming $orming ,elts Viscosity enitions and !erminology 8iscosity is a measure o t#e resistance o a li*uid to s#ear deormation% i.e.% a measure o t#e ratio et)een t#e a""lied s#earing orce and t#e rate o Ao) o t#e li*uid. I a tangential orce diFerence% % is a""lied to t)o "arallel "lanes o area% 9% )#ic# are se"arated y a distance% d% t#e (iscosity% η% is gi(en y t#e e&"ression: e&"ression:
ηdY9(% dY9(% )#ere ( is t#e relati(e (elocity o t#e t)o "lanes. η Qa.sR% 1 a.s10 "oise I t#e (elocity (aries directly )it# t#e a""lied s#ear orce% t#e (iscosity is inde"endent o orce and t#e li*uid is said to e#a(e as a ?e*tonian liuid . 9t #ig# s#ear stresses% many glass orming melts e&#iit an a""arent decrease in (iscosity )it# increasing s#ear stress. stress. $#is orm o non-e)tonian e#a(ior is =no)n as pseudo"rocesses. plastic Ao)% plastic Ao)% or shear-thinning% shear-thinning% and is im"ortant in #ig# s#ear rate orming "rocesses. is t#e reci"rocal o t#e (iscosity% oten used )it# ordinary li*uids. $luidity is 9 numer o s"eci+c (iscosities #a(e een designated as reerence "oints on t#e (iscosity-tem"erature (iscosity-tem"erature cur(e or melts. $#ese "articular (iscosities (iscosities #a(e een c#osen ecause o t#eir im"ortance in (arious as"ects o commercial or laoratory "rocessing o glass orming melts. $#ese reerence "oints are summari?ed in t#e adacent tale% and are s#o)n on a ty"ical cur(e o (iscosity (ersus tem"erature or a soda-lime-silica melt in ne&t +gure. Common Viscosity ,easurement !echniues Viscometers : $#ey are 1. otation Viscometers: commonly used at room tem"erature tem"erature to measure t#e (iscosity o a )ide (ariety o li*uids in t#e range o 1 to l0 ' a.s. Use o t#ese (iscometers at tem"eratures u" to 1,00XC re*uires t#at t#e "arts e&"osed to t#e melt e constructed o "latinum or "latinum alloys. $#ese (iscometers consist o a small cylinder% or s"indle% )#ic# is rotated inside a large cylindrical crucile containing t#e melt. 31
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 9lternati(e designs o t#ese (iscometers enale t#em to measure (iscosities u" to 10 .s. 2. $alling Sphere Viscometers: directly t#roug# t#e Viscometers : 8iscosities can e measured directly determination o t#e resistance o a li*uid to t#e motion o a s"#ere alling t#roug# t#e li*uid under t#e inAuence o gra(ity. gra(ity. $#is met#od yields data in t#e range 1 to l0 , as. Viscometers : $#e most )idely used (iscometers are ased on 3. $iber Elongation Viscometers: measurements measurements o t#e rate o elongation o a +er o =no)n dimensions under a =no)n load. $#is met#od can e used or (iscosities ranging rom l05 to 10l2 a.s. '. &eam-&ending Viscometers: Viscometers : $ransormation range (iscosities o l0 4 to 1013 a.s are oten measured measured y t#e eam-ending met#od% in )#ic# a small eam o =no)n crosssectional area% 9% is "laced in a 3-"oint ending con+guration )it# a load% M% a""lied at t#e center o t#e eam. !emperature ependence of Viscosity $#e (iscosity can oten oten e +tted% at least o(er o(er limited tem"erature tem"erature ranges% y an 9rr#enian e&"ression o t#e adacent orm: $#e ηo is a constant> ∆/η is t#e acti(ation energy or (iscous Ao)% 6 is t#e gas constant% and $ is t#e tem"erature in . In general% 9rr#enian e#a(ior is oser(ed )it#in t#e glass transormation range B10 13 to l0 a.sD and at #ig# tem"eratures )#ere melts are (ery Auid. /o)e(er% t#e acti(ation energy or (iscous Ao) is muc# lo)er or t#e Auid melt t#an or t#e #ig# (iscosity o t#e transormation region. $#us% $#e 8ogel-$ulcher 8ogel- $ulcher -$amman -$amman 8$ e*uation adds a t#ird +tting (ariale% $o% to t#e 9rr#enian e&"ression e&"ression to account or t#e (ariaility o t#e acti(ation energy or (iscous Ao). Ao). In addition% ∆/η is re"laced )it# a ne) (ariale% 7% as indicated y t#e adacent e&"ression: 9ctually% researc#ers researc#ers ound t#at 7 is com"osition de"endent and utili?e it to model com"osition-(iscosity com"osition-(iscosity relation at diFerent tem"eratures. tem"eratures. Dr. Dr. Saad B. H. Farid "ulis#ed Farid "ulis#ed a com"lete model or t#e ioacti(e glass. 11- !hermal E#pansion of 5lass $#e coeicient o linear t#ermal t#ermal e&"ansion
$y"ical $y"ical cur(e or (iscosity as a unction o BIS$ ∆L tem"erature is deinedor asasoda-lime-silica Q∆LYL R.∆ $%melt )#ere 0
is
t#e c#ange o lengt# o a material o initial lengt# L0 #eated to a tem"erature diFerence
∆ $. $#e units o are reci"rocal reci"rocal degrees. $#e coeEcient usually de"ends de"ends u"on tem"erature% tem"erature% as s#o)n in t#e +gure. $#us% it is necessary to s"eciy t#e tem"erature range o(er )#ic# ∆L is measured. $#e usual range is rom 0 to 300XC% or rom room tem"erature to a tem"erature ust elo) t#e glass transition 32
Ceramics and Glasses 3rd year – Lecture notes Farid 2014-2015 2014-2015 range% )#ere (olume c#anges ecome greater.
Dr. Saad B. H.
9 (olume e&"ansion coeEcient can e de+ned as Q∆8Y80R.∆ $ or a (olume c#ange ∆8 and initial (olume 80. I ∆8 is small% as is usually t#e case% t#e (olume coeEcient e*uals 3. $#e density ρ and s"eci+c (olume 8 o t#e glass at tem"eratures u" to t#e strain tem"erature tem"erature can e calculated rom t#e density ρ0 at 25XC and t#e coeEcient o t#ermal e&"ansion: 8 Q1 Y ρ0R Q1 W 3 B $ - 25 DR % ρ ρ0 Y Q1 W 3 B $ – 25 DR% )#ere $ is t#e tem"erature in XC. $#ermal s#oc= s#oc= resistance and and t#e racture racture o seals et)een diFerent diFerent materials de"end on t#ermal e&"ansion. $#us% t#e e&"ansion o glass as t#e tem"erature is increased is an im"ortant measure o its resistance resistance to t#ermal s#oc=. $#e #ig#er t#e e&"ansion coeEcient% t#e more li=ely is racture during ra"id #eating and cooling. onuniorm (olume c#anges% resulting rom tem"erature gradients during #eating or cooling% cause stresses t#at are larger t#e greater t#e (olume c#anges. 9 (itreous silica ea=er #eated to 1000XC can e das#ed into )ater )it#out rea=ing it% ecause it #as t#e lo) e&"ansion coeEcient o aout 0.5 × 10-, XC-1. ;n t#e ot#er #and% a "late o sodalime glass 0., cm t#ic=% )it# a coeEcient o aout × 10-, XC-1% can e crac=ed )it# a tem"erature tem"erature diFerence et)een aces o aout 50XC. Matc#ing o e&"ansion coeEcients o t)o materials eing sealed toget#er is essential to "re(ent racture racture in t#e seal during #eating or cooling. 9 diFerence in coeEcients o less t#an aout 0.2 × 10-, XC-1 is o"timum or glass sealing% alt#oug# acce"tale seals can oten e made )it# diFerences u" to aout 0.5 × 10-, XC-1. $#e greater t#e diFerence% t#e more li=ely is ailure o t#e seal. ;t#er actors t#at inAuence t#e strengt# ractional c#ange in lengt# "lotted against o a seal are its geometry% t#e com"leteness o remo(al o residual stressesglass y tem"erature or an annealed annealing% and diFerences in strain tem"eratures in sealing t)o glasses. S"ecial seal designs allo) materials )it# large diFerences in coeEcients o t#ermal e&"ansion to e sealed toget#er. $#e c#ange in lengt# o a glass glass rod can e measured measured )it# a dilatometer% in )#ic# t#e increase in lengt# o a glass rod is com"ared to t#at o a (itreous silica rod. 7ot# rods are #eld in t#e same urnace and #eated toget#er at a constant rate% and t#e diFerence in t#eir lengt#s is measured )it# a diFerential sensor. $#e coeEcient o t#ermal t#ermal e&"ansion also is a unction o com"osition. com"osition. $#is is e&tremely e&tremely im"ortant to learn or t#e designers o gla?es% enamels% dental "orcelains Bs"ecial ty"es o enamels and gla?es or synt#etic dentsD% metal sealsK etc. Usually% eac# com"osition material #as linear contriution to t#e t#ermal e&"ansion o glass% ut 33
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 anomalies are re*uently ound es"ecially )it# t#e contriution o al=alis. 9gain% a )or= "ulis#ed by Dr. Saad B. H. Farid e&"lains Farid e&"lains t#is anomaly or t#e Bsodium-"otassiumorateD solder glass. $#e ne&t tale is a sim"le e&am"le o t#e com"osition com"osition de"endence o ot# ot# $g and t#e coeEcient o t#ermal e&"ansion. $#e (alues o t#e coeEcient o t#ermal e&"ansion dis"layed in t#e tales are multi"les o 10 - XC as usually ound in glass industry documentations.
12- Vitreous Coating enition of the Vitreous Coating 8itreous 8itreous Coating includes coating o a ceramic "art Bgla?ingD and coating o metallic "art BenamelD. Coating includes "#ysical and c#emical ad#esion> in addition% matc#ing t#ermal e&"ansion e&"ansion and attaining t#e correct coating tem"erature are o "rime im"ortance. 9ctually% in synt#etic dental coating% it is =no)n t#at t#e diFerence in t#ermal e&"ansion s#ould not e&ceeds W0.3 ×10-,XC-1 and coating tem"erature tem"erature o W50XC o t#e coat com"ared )it# t#e coated surace. 5eneral escription of the Vitreous Coating 1. $#e gla?e layer layer de"osited on t#e "art generally #as a t#ic=ness ranging ranging et)een 0.15 and 0.5 mm. Its "ur"ose is to mas= t#e "orosity andYor t#e color o t#e "art% to ma=e t#e surace o t#e "iece smoot# and rilliant and to im"ro(e t#e c#emical resistance o t#e ceramic. 2. $#is layer% trans"arent trans"arent or o"a*ue% )#ite or colored% colored% is otained otained rom a silica-ric# ceramic com"osition ca"ale o de(elo"ing glass during t#e #eat treatment. treatment. 3. $#e com"osition o t#e gla?e gla?e also contains many ot#er constituents% constituents% in "articular al=aline and al=aline eart# o&ides. $#ey #el" to adust t#e melting "oint% t#e t#ermal 3'
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 e&"ansion coeEcient% t#e surace tension% and t#e (iscosity to t#e gla?ing conditions% and ensure t#e )etting and ad#esion o t#e gla?e on t#e "art. '. $#e enamels enamels used or s#eet s#eet enameling enameling #a(e #a(e many common common "oints "oints )it# t#ose t#ose descried #ere. Composition of the Vitreous Coating 1. $#e "ro"erties "ro"erties o t#e coat coat are oten oten analy?ed y considering t#at t#at it is made u" u" o a comination o acid o&ides res"onsile res"onsile or t#e (itreous structure structure Bmainly Si; 2 and 72;3D% am"#oteric o&ides B9l 2;3D% and asic o&ides B 2;% a2;% Ca;% Mg;% ;D. 2. It s#ould e noted noted t#at t#e role o Au&% traditionally reser(ed reser(ed or asic asic o&ides% o&ides% is no) increasingly "layed y acid or am"#oteric o&ides% suc# as 7 2;3 or 7i2;3. 3. 8itreous coat is otained otained rom a mi&ture o ra) materials materials mineral andYor andYor ground rits. $#e ra) materials used are mainly elds"ars% elds"ars% =aolin% *uart? *uart? and c#al= CaC;3 or dolomite CaMgBC;3D2. '. rits are mi&tures o com"onents "re"ared "re"ared y melting se(eral se(eral com"ounds at #ig# tem"erature tem"erature B$ 1%'00XCD. 9ter *uenc#ing in air or )ater% t#e "roduct% )#ic# is mar=edly (itreous in c#aracter% is ground. 5. In order to im"ro(e rit layer ad#esion ad#esion to t#e surace o t#e "art% )ater-solule )ater-solule salts% =aolin% or (olatile o&ides can e used )it#out #arm in t#e com"osition o t#e coat. ,.
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Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 e used. $#e s"eci+c amounts de"end u"on details o t#e enamelOs total ormulation% "rocessing% and ser(ice re*uirements. re*uirements. 2. orcelain orcelain enamel co(er coats are designed designed to "ro(ide "ro(ide s"eci+c s"eci+c color and a""earance a""earance c#aracteristics comined )it# resistance to atmos"#eric and li*uid corrosion% corrosion% surace #ardness% arasion resistance% and resistance to #eat and t#ermal s#oc=% as re*uired. Co(er coat ormulations are a(ailale to "ro(ide a )ide (ariety o a""earance "ro"erties. $#ey range rom o"a*ue )#ites t#roug# "astels and medium-strengt# medium-strengt# colors to strong% dar= colors. 9 )ide selection o glosses is also a(ailale% ranging rom t#e #ig#-gloss sanitary )are +nis#es to t#e ull-matte arc#itectural enamels. 3. orcelain orcelain enamel co(er coats are are classi+ed as o"a*ue By r;2% antimony o&ides S;j% $i;2% semi-o"a*ue% and clear. ;"a*ue enamels are used or )#ite and "astel Bmuted × (i(idD co(er coats% semi-o"a*ue enamels are used or most o t#e medium strengt# colors% and clear enamels are necessary to "roduce rig#t By al=alis es"ecially Li2;D% strong colors. 1.- &ioactive 5lasses and 5lass-Ceramics 9ntroduction Glass-ceramics are an im"ortant class o materials t#at #a(e een commercially *uite successul. $#ey are "olycrystalline materials "roduced y t#e controlled crystalli?ation o glass. $#ey are com"osed o randomly oriented crystals )it# some residual glass% ty"ically et)een 2 and 5 "ercent% )it# no (oids or "orosity. Glass ceramics ound )ide a""lications as dielectric materials% mac#inale materials% iomaterialsK etc. Ceramics% glasses% and glass-ceramics include a road range o inorganicYnonmetallic com"ositions. In t#e medical industry% t#ese materials #a(e een essential or eyeglasses% diagnostic instruments% c#emical )are% t#ermometers% tissue culture Aas=s% and +er o"tics or endosco"y. Insolule "orous glasses #a(e een used as carriers or en?ymes% antiodies% and antigens% oFering t#e ad(antages o resistance to microial attac=% "/ c#anges% sol(ent conditions% tem"erature% and "ac=ing under #ig# "ressure re*uired or ra"id Ao). Ceramics are also )idely used in dentistry as restorati(e materials suc# as in gold-"orcelain cro)ns% cro)ns% glass-+lled ionomer cements% and dentures. $#is section ocuses on on ceramics% glasses% and glass-ceramics used used as im"lants. 9lt#oug# do?ens o com"ositions #a(e een e&"lored in t#e "ast% relati(ely e) #a(e ac#ie(ed clinical success. $#e science and "ractice o iomaterials e&amines diFerences in "rocessing and structure% descries t#e c#emical and microstructural microstructural asis or t#eir diFerences in "#ysical "ro"erties% and relates "ro"erties and tissue res"onse to "articular clinical a""lications. It is essential to recogni?e t#at no one material is suitale or all iomaterial a""lications. 9s a class o iomaterials% ceramics% glasses% and glass-ceramics are generally used to re"air or re"lace s=eletal s=eletal #ard connecti(e tissues. $#eir success de"ends u"on ac#ie(ing a stale attac#ment to connecti(e tissue.
3,
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 !ypes of &ioceramics @!issue Attachment $#e mec#anism o tissue tissue attac#ment is directly directly related to t#e ty"e ty"e o tissue res"onse res"onse at t#e im"lantktissue interace. o material im"lanted in li(ing tissue is inert ecause all materials otain a res"onse rom rom li(ing tissues. $#ere are our ty"es o im"lant-tissue res"onse: lac3ing : in t#is case% t#e materials cause tissue reactions% )#ic# 1. &iocompatibility is lac3ing: may e systemic or local. Systemic res"onses can e to&ic or allergic and triggered y t#e "roducts o metallic corrosion and "olymer degradation% release o micro "articles rom materials% and t#e "resence o contaminants. 2. &iocompatible &ioinert &iotolerant : I t#e material is nonto&ic and iologically inacti(e Bnearly inertD% t#en% +rous tissue o (ariale t#ic=ness orms. 3. &ioactive: nonto&ic and iologically acti(e% an interacial ond &ioactive: I t#e material is nonto&ic orms. '. &ioresorbable: surrounding tissue &ioresorbable: I t#e material is nonto&ic and dissol(es% t#e surrounding re"laces it. I.e. t#e material is gradually resored eore t#ey +nally disa""ear% and is totally re"laced y ne) tissues in (i(o. $#ere are are our diFerent ty"es o attac#ing "rost#eses "rost#eses Ban arti+cial arti+cial ody "artD to t#e t#e s=eletal system. $y"es o ioceramic-tissue attac#ment and t#eir classi+cation are: $y"e $y"e o attac#ment 1.
!&am"le
ens ense% e% non" non"or orou ous% s% near nearly ly iner inertt cer ceram amic ics s att attac ac# # y one gro)t# into surace irregularities irregularities y cementing t#e de(ice into t#e tissues or y "ress-+tting "ress-+tting into a deect termed @mor"#ological +&ation@D
912;3 Bsingle crystal and "olycrystallineD
or "or "orous ous ine inert rt im im"l "lan ants ts%% on one e ingr ingro) o)t# t# occu occurs rs t#at t#at mec#anically attac#es t#e one to t#e material Btermed @iological +&ation@D. /ydro&ya"atite-coated /ydro&ya"atite-coated "orous metals
912;3 B"olycrystallineD
3.
. ens ense% e% non" non"or orou ous s sur surac acee-rreact eacti( i(e e cera cerami mics cs%% glasses% and glass-ceramics attac# directly y c#emical onding )it# t#e one Btermed @ioacti(e +&ation@D
7ioacti(e glasses 7ioacti(e glass-ceramics /ydro&ya"atite /9
'.
ens ense% e% non" non"or orou ous% s% Bor Bor "or "orou ousD sD resor esora al le e cer ceram amic ics s are designed to e slo)ly re"laced y one.
2.
Calcium sulate B"laster o "arisD $ricalcium $ricalcium "#os"#ate Calcium-"#os"#ate salts
&ioactive 5lasses and 5lass Ceramics Certain com"ositions o glasses% ceramics% glass-ceramics% and com"osites #a(e een s#o)n to ond to one. $#ese materials #a(e ecome =no)n as ioacti(e ceramics. Some e(en more s"ecia1i?ed com"ositions o ioacti(e glasses )ill ond to sot tissues as )ell as one. 9 common c#aracteristic o ioacti(e glasses and ioacti(e ceramics is a time de"endent =inetic modi+cation o t#e surace t#at occurs u"on 3
Ceramics and Glasses 3rd year – Lecture notes Dr. Saad B. H. Farid 2014-2015 2014-2015 im"lantation. $#e surace orms a iologically acti(e caronated /9 layer t#at "ro(ides t#e onding interace )it# tissues. 7ioacti(e materials de(elo" an ad#erent interace )it# tissues t#at resist sustantial mec#anical orces. 7onding to one )as +rst demonstrated or a com"ositional range o ioacti(e glasses t#at contained Si; 2% a2;% Ca;% and 2;5 in s"eci+c "ro"ortions. $#ere $#ere are t#ree =ey com"ositional com"ositional eatures to t#ese ioacti(e glasses% )#ic# distinguis# t#em rom traditional soda-lime-silica glasses: 1. Less Less t#an t#an ,0 molJ molJ Si; Si;2 2. /ig# a2; and Ca; content 3. /ig# ig# Ca; Ca;Y Y2;5 ratio $#ese eatures eatures ma=e t#e surace #ig#ly reacti(e reacti(e )#en it is e&"osed e&"osed to an a*ueous medium. Many ioacti(e silica glasses are ased u"on t#e ormula called '5S5% signiying '5 )tJ Si;2 BS t#e net)or= ormerD and 5:1 ratio o Ca; to 2;5. Glasses )it# lo)er ratios o Ca; to 2;5 do not ond to one. /o)e(er% sustitutions in t#e '5S5 ormula o 5-15 )tJ 72;3 or Si;2 or 12.5 )tJ Ca 2 or Ca; or #eat-treating t#e ioacti(e glass com"ositions to orm glass-ceramics glass-ceramics #a(e no measurale eFect on t#e aility o t#e material to orm a one ond ut only lo)ering t#e melting tem"erature and increase increase t#e microstructure #omogeneity. /o)e(er% adding as little as 3 )tJ 91 2;3 to t#e '5S5 ormula "re(ents onding to one.
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