Conce!t Chec" $= Q&estion' For a ternary system# three components are present= temperature is also a ariable. What is the maximum number of phases that may be present for a ternary system# assuming that pressure is held constant? Ans-er' 1or a ternar. s.ste +( B 8, at constant !ress&re + N B %,0 i22s !hase r&le0 E&ation $%<0 2ecoes
> @ F B ( @ N B 8 @ % B 9
Or0
> B 9 F
Th&s0 -hen F B )0 > -ill ha6e its a7i& 6al&e o/ 90 -hich eans that the a7i& n&2er o/ !hases !resent /or this sit&ation is 9$
Conce!t Chec" $
Q&estion' $riefly explain why a proeutectoid phase %ferrite or cementite& forms along austenite grain boundaries.
Chapter 10
Phase Trans/orations in Metals
Conce!t Chec" %)$% Q&estion' Which is more stable# the pearlitic or the spheroiditic microstructure? Why? Ans-er' S!heroiditic icrostr&ct&res are ore sta2le than !earlitic ones$ Since !earlite trans/ors to s!heroidite0 the latter is ore sta2le$
Conce!t Chec" %)$5
Q&estion' (ite two ma@or differences between martensitic and pearlitic transformations. Ans-er' T-o aJor di//erences are' %, atoic di//&sion is necessar. /or the !earlitic trans/oration0 -hereas the artensitic trans/oration is di//&sionless4 and 5, relati6e to trans/oration rate0 the artensitic trans/oration is 6irt&all. instantaneo&s0 -hile the !earlitic trans/oration is tie3de!endent$
Conce!t Chec" %)$8
Q&estion' )a"e a copy of the isothermal transformation diagram for an iron*carbon alloy of eutectoid composition %Figure ,7.& and then s"etch and label on this diagram a time* temperature path that will produce ,778 fine pearlite. Ans-er' elo- is sho-n an isotheral trans/oration diagra /or a e&tectoid iron3 car2on allo. on -hich is incl&ded a tie3te!erat&re !ath that -ill !rod&ce %))F /ine !earlite$
Conce!t Chec" %)$9 Q&estion' $riefly describe the simplest continuous cooling heat treatment procedure that would be used to conert a 37 steel from %martensite + bainite& into %ferrite + pearlite&. Sol&tion' In order to con6ert /ro +artensite @ 2ainite, into +/errite @ !earlite, it is necessar. to heat a2o6e a2o&t #5) C0 allo- co!lete a&steniti;ation0 then cool to roo te!erat&re at a rate e&al to or less than )$))<C>s +1ig&re %)$5=,$
Conce!t Chec" %)$:
Q&estion' !an" the following iron*carbon alloys and associated microstructures from the highest to the lowest tensile strength: 7. wt8( with spheroidite 7. wt8( with coarse pearlite 7.0 wt8( with fine pearlite 7.0 wt8( with coarse pearlite. Bustify this ran"ing. Ans-er' This ran"ing called /or is as /ollo-s' +%, )$< -tFC -ith /ine !earlite +5, )$< -tFC -ith coarse !earlite +8, )$5: -tFC -ith coarse !earlite +9, )$5: -tFC -ith s!heroidite
The )$5: -tF C0 coarse !earlite is stronger than the )$5: -tF C0 s!heroidite 2eca&se coarse !earlite is stronger than s!heroidite4 the co!osition o/ the allo.s is the sae$ The )$< -t F C0 coarse !earlite is stronger than the )$5: -tF C0 coarse !earlite0 2eca&se increasing the car2on content increases the strength +-hile aintained the sae coarse !earlite icrostr&ct&re,$ 1inall.0 the )$< -tF C0 /ine !earlite is stronger than the )$< -tF C0 coarse !earlite inas&ch as the strength o/ /ine !earlite is greater than coarse !earlite 2eca&se o/ the an. ore /errite3 ceentite !hase 2o&ndaries in /ine !earlite$
Conce!t Chec" %)$< Q&estion' For a eutectoid steel# describe an isothermal heat treatment that would be reuired to produce a specimen haing a hardness of ;3
Conce!t Chec" %)$#
Q&estion' A steel alloy is uenched from a temperature within the austenite phase region into water at room temperature so as to form martensite= the alloy is subseuently tempered at an eleated temperature which is held constant. %a& )a"e a schematic plot showing how room*temperature ductility aries with the logarithm of tempering time at the eleated temperature. %$e sure to label your axes.& %b& 2uperimpose and label on this same plot the room*temperature behaior resulting from tempering at a higher tempering temperature and briefly explain the difference in behaior between these two temperatures. Ans-er' +a, Sho-n 2elo- is the !lot that -as re&ested$
+2, The line /or the higher te!erat&re +la2eled 5 , -ill lie a2o6e the one at the lo-er < te!erat&re +la2eled 5 , 2eca&se the 1e8C !articles in te!ered artensite -ill gro- /aster at the higher te!erat&re4 th&s0 at soe gi6en te!ering tie the. -ill 2e larger at the higher te!erat&re$ The allo. te!ered at the higher te!erat&re -ill 2e ore d&ctile 2eca&se there -ill 2e /e-er 31e8C !hase 2o&ndaries +d&e to the larger 1e 8C !articles, that a. i!ede dislocation otion$
Chapter 11
A!!lications and Processing o/ Metal Allo.s
Conce!t Chec" %%$% Q&estion'
$riefly explain why ferritic and austenitic stainless steels are not heat
treatable.
1erritic and a&stenitic stainless steels are not heat treata2le since heat
treata2le is ta"en to ean that artensite a. 2e ade to /or -ith relati6e ease &!on &enching a&stenite /ro an ele6ated te!erat&re$ 1or /erritic stainless steels0 a&stenite does not /or &!on heating0 and0 there/ore0 the a&stenite3to3artensite trans/oration is not !ossi2le$ 1or a&stenitic stainless steels0 the a&stenite !hase /ield e7tends to s&ch lo- te!erat&res that the artensitic trans/oration does not occ&r$
Conce!t Chec" %%$5
Q&estion' 9t is possible to produce cast irons that consist of a martensite matrix in which graphite is embedded in either fla"e# nodule# or rosette form. $riefly describe the treatment necessary to produce each of these three microstructures. Ans-er' 1or gra!hite /la"es0 gra. cast iron is /ored +as descri2ed in Section %%$5,0 -hich is then heated to a te!erat&re at -hich the /errite trans/ors to a&stenite4 the a&stenite is then ra!idl. &enched0 -hich trans/ors to artensite$ 1or gra!hite nod&les and rosettes0 nod&lar and allea2le cast irons are /irst /ored +again as descri2ed in Section %%$5,0 -hich are then a&steniti;ed and ra!idl. &enched$
Conce!t Chec" %%$8
Q&estion' What is the main difference between brass and bron'e? Ans-er' oth 2rasses and 2ron;es are co!!er32ased allo.s$ 1or 2rasses0 the !rinci!al allo.ing eleent is ;inc0 -hereas the 2ron;es are allo.ed -ith other eleents s&ch as tin0 al&in&0 silicon0 or nic"el$
Conce!t Chec" %%$9
Q&estion' Explain why# under some circumstances# it is not adisable to weld a structure that is fabricated with a 3773 aluminum alloy.
Conce!t Chec" %%$:
Q&estion' 4n the basis of melting temperature# oxidation resistance# yield strength# and degree of brittleness# discuss whether it would be adisable to hot wor" or to cold wor" %a& aluminum alloys# and %b& magnesium alloys.
Conce!t Chec" %%$< Q&estion' %a& (ite two adantages of powder metallurgy oer casting. %b& (ite two disadantages. Ans-er' +a, Ad6antages o/ !o-der etall&rg. o6er casting are as /ollo-s' %, It is &sed /or allo.s ha6ing high elting te!erat&res$ 5, etter diensional tolerances res<$ 8, Porosit. a. 2e introd&ced0 the degree o/ -hich a. 2e controlled +-hich is desira2le in soe a!!lications s&ch as sel/3l&2ricating 2earings,$ +2, The disad6antages o/ !o-der etall&rg. o6er casting are as /ollo-s' %, Prod&ction o/ the !o-der is e7!ensi6e$ 5, Heat treatent a/ter co!action is necessar.$
Conce!t Chec" %%$#
Q&estion' What are the principal differences between welding# bra'ing# and soldering? Cou may need to consult other references. Ans-er' 1or -elding0 there is elting o/ the !ieces to 2e Joined in the 6icinit. o/ the 2ond4 a /iller aterial a. or a. not 2e &sed$ 1or 2ra;ing0 a /iller aterial is &sed -hich has a elting te!erat&re in e7cess o/ a2o&t 95:C +=))1,4 the /iller aterial is elted0 -hereas the !ieces to 2e Joined are not elted$ 1or soldering0 a /iller aterial is &sed -hich has a elting te!erat&re less than a2o&t 95:C +=))1,4 the /iller aterial is elted0 -hereas the !ieces to 2e Joined are not$
Conce!t Chec" %%$=
Q&estion' Name the three factors that influence the degree to which martensite is formed throughout the cross section of a steel specimen. For each# tell how the extent of martensite formation may be increased. Ans-er' The three /actors that in/l&ence the degree to -hich artensite is /ored are as /ollo-s' %, Allo.ing eleents4 adding allo.ing eleents increases the e7tent to -hich artensite /ors$ 5, S!ecien si;e and sha!e4 the e7tent o/ artensite /oration increases as the s!ecien cross3section decreases and as the degree o/ sha!e irreg&larit. increases$ 8, Q&enching edi&4 the ore se6ere the &ench0 the ore artensite is /ored$ Water !ro6ides a ore se6ere &ench than does oil0 -hich is /ollo-ed 2. air$ Agitating the edi& also enhances the se6erit. o/ &ench$
Chapter 12
Str&ct&res and Pro!erties o/ Ceraics
Conce!t Chec" %5$% Q&estion' 5able ,.3 gies the ionic radii for D + and 4* as 7.,3/ and 7.,7 nm# respectiely. %a& What would be the coordination number for each 4* ion? %b& $riefly describe the resulting crystal structure for D 4. %c& Explain why this is called the antifluorite structure. Ans-er' +a, 1irst0 let &s /ind the coordination n&2er o/ each O 53 ion /or K 5O$ Ta"ing the cation3anion radii ratio
r + K
r 2O
=
0.138 nm 0.140 nm
= 0.986
1ro Ta2le %5$50 the coordination n&2er /or o7.gen is eight$ +2, According to Ta2le %5$90 /or a coordination n&2er o/ eight /or 2oth cations and anions0 the cr.stal str&ct&re sho&ld 2e cesi& chloride$ Ho-e6er0 there are t-ice as an. K @ as O53 ions$ There/ore0 the centers o/ the K@ ions are !ositioned at the corners o/ c&2ic &nit cells0 -hile hal/ o/ the c&2e centers are occ&!ied 2. O 53 ions$ +c, This str&ct&re is called the anti/l&orite cr.stal str&ct&re 2eca&se anions and cations are interchanged -ith one another /ro the /l&orite str&ct&re +1ig&re %5$:,$
Conce!t Chec" %5$5
Q&estion' (an 2chott"y defects exist in D 4? 9f so# briefly describe this type of defect. 9f they cannot exist# then explain why. Ans-er' This &estion can 2e ans-ered in t-o -a.s0 as /ollo-s' +%, es0 Schott". de/ects can e7ist in K5O4 each de/ect -ill consist o/ one O 53 6acanc. and t-o K@ 6acancies$ +5, No0 in the strict sense0 Schott". cannot e7ist in K 5O i/ -e consider this t.!e o/ de/ect to consist o/ a cation3anion !air4 /or e6er. O 53 6acanc. created there &st e7ist t-o K @ 6acancies$
Conce!t Chec" %5$8
Q&estion' What point defects are possible for )g4 as an impurity in Al 4 3?
Conce!t Chec" %5$9
Q&estion' %a& For the 2i4*Al4 3 system# what is the maximum temperature that is possible without the formation of a liuid phase? %b& At what composition or oer what range of compositions will this maximum temperature be achieed? Ans-er' +a, According to 1ig&re %5$5: this a7i& te!erat&re is %=) L %)C0 +2, -hich is !ossi2le /or co!ositions 2et-een a2o&t ## -tF Al 5O8 and 6irt&all. %)) -tF Al5O8$
Chapter 13
A!!lications and Processing o/ Ceraics
Conce!t Chec" %8$% Q&estion' $riefly explain why glass*ceramics are generally not transparent.
Conce!t Chec" %8$5 Q&estion' -pon consideration of the 2i4 *Al4 3 phase diagram %Figure ,.& for the following pair of compositions# which would you @udge to be the more desirable refractory? Bustify your choice. 7 wt8 Al4 3*/7 wt8 2i4 wt8 Al4 3*1 wt8 2i4 Ans-er' The 5: -tF Al5O83#: -tF SiO5 -ill 2e ore desira2le 2eca&se the li&id&s te!erat&re -ill 2e greater /or this co!osition +%#9)C 6ers&s %#%)C,4 there/ore0 at an. te!erat&re -ithin the &llite @ li&id region on the !hase diagra0 there -ill 2e a lo-er /raction o/ the li&id !hase !resent than /or the 5) -tF Al 5O83=) -tF SiO5 co!osition0 and0 th&s0 the echanical integrit. -ill 2e greater$
Conce!t Chec" %8$8
Q&estion' Explain why it is important important to grind grind cement into a fine powder powder.. Ans-er' Ans-er' It is i!ortant i!ortant to grind ceent ceent into a /ine !o-der !o-der in order to increase increase the s&r/ace area o/ the !articles o/ ceent$ The h.dration reactions 2et-een -ater -ater and the ceent occ&r at the s&r/ace s&r/ace o/ the ceent !articles$ !articles$ There/ore There/ore00 increasin increasing g the a6aila2le a6aila2le s&r/ace s&r/ace area allo-s /or ore e7tensi6e 2onding$
Conce!t Chec" %8$9
Q&estion'
Conce!t Chec" %8$:
Q&estion' 5hic" ceramic wares are more li"ely to crac" upon drying than thin wares. Why is this so? Ans-er' Ans-er' Thic" Thic" ceraic -ares are ore li"el. to crac" &!on &!on dr.ing than thin thin -ares 2eca&se o/ the di//erential in shrin"age /ro the s&r/ace to the interior o/ a cross3section -ill 2e greater /or a thic" -are$ The reason /or this is that the the -ater 2eing eliinated d&ring d&ring dr.ing has a longer distance to tra6el /ro the interior to the s&r/ace /or the thic"er -are$
Conce!t Chec" %8$< Q&estion' Explain why a clay# once it has been fired at an eleated temperature# loses its hydroplasticity. Ans-er' The !henoenon o/ h.dro!lasticit. res<s -hen -ater olec&les /or a thin /il aro&nd the sall cla. !articles$
D&ring /iring0 these indi6id&al !articles 2ecoe /&sed
together 2. the 6isco&s li&id that /ills in the !ore 6ol&e 2et-een the !articles?the !ore 6ol&e that -as occ&!ied 2. -ater in the h.dro!lastic state$ This 6isco&s li&id /ors a glass atri7 on s&2se&ent cooling$
Chapter 14
Pol.er Str&ct&res
Conce!t Chec" %9$% Q&estion' ifferentiate between polymorphism %see (hapter 3& and isomerism. Ans-er' >olymorphism is -hen t-o or ore cr.stal str&ct&res are !ossi2le /or a aterial o/ gi6en co!osition$ 9somerism is -hen t-o or ore !ol.er olec&les or re!eat &nits ha6e the sae co!osition0 2&t di//erent atoic arrangeents$
Conce!t Chec" %9$5
Q&estion' 4n the basis of the structures presented in the preious section# s"etch the repeat unit structure for poly%inyl fluoride&. Ans-er' Inas&ch as !ol.+6in.l chloride, has the re!eat &nit str&ct&re sho-n in 1ig&re %9$5+2,0 re!lacing the side32onded chlorine ato -ith a /l&orine ato -ill .ield a !ol.+6in.l fluoride, re!eat &nit0 as sho-n 2elo-$
Conce!t Chec" %9$8
Q&estion' What is the difference between con/ig&ration and con/oration in relation to polymer chains? Ans-er'
Relati6e to !ol.er chains0 the di//erence 2et-een configuration and
conformation is that con/oration is &sed in re/erence to the o&tline or sha!e o/ the chain olec&le0 -hereas0 con/ig&ration re/ers to the arrangeent o/ ato !ositions along the chain that are not altera2le e7ce!t 2. the 2rea"ing and re/oring o/ !riar. 2onds$
Conce!t Chec" %9$9
Q&estion'
2ome polymers %such as the polyesters& may be either thermoplastic or
thermosetting. 2uggest one reason for this. Ans-er' Therosetting !ol.esters -ill 2e crosslin"ed0 -hile thero!lastic ones -ill ha6e linear str&ct&res -itho&t an. a!!recia2le crosslin"ing$
Conce!t Chec" %9$:
Q&estion' %a& (ompare the crystalline state in metals and polymers. %b& (ompare the noncrystalline state as it applies to polymers and ceramic glasses. Ans-ers' +a, 1or cr.stalline etals0 the indi6id&al atos are !ositioned in a !eriodic or ordered arrangeent o6er relati6el. large atoic distances$ The long3range order in !ol.er cr.stals res<s /ro the !ac"ing o/ adJacent !ol.er chains$ +2, 1or noncr.stalline ceraic glasses0 the atoic randoness e7ists o&tside the &nit$ The disorder in !ol.ers res<s /ro chain isalignent$
iO
4 4
−
Chapter 15
Characteristics0 A!!lications0 and Processing o/ Pol.ers
Conce!t Chec" %:$% Q&estion' When citing the ductility as percent elongation for semicrystalline polymers# it is not necessary to specify the specimen gauge length# as is the case with metals. Why is this so? Ans-er' The reason that it is not necessar. to s!eci/. s!ecien ga&ge length -hen citing !ercent elongation /or seicr.stalline !ol.ers is 2eca&se0 /or seicr.stalline !ol.ers that e7!erience nec"ing0 the nec" norall. !ro!agates along the entire ga&ge length !rior to /ract&re4 th&s0 there is no locali;ed nec"ing as -ith etals and the agnit&de o/ the !ercent elongation is inde!endent o/ ga&ge length$
Conce!t Chec" %:$5
Q&estion' An amorphous polystyrene that is deformed at ,7 ( will exhibit which of the behaiors shown in Figure ,.? Ans-er' Aor!ho&s !ol.st.rene at %5) C 2eha6es as a r&22er. aterial +1ig&re %:$=0 c&r6e ( ,4 there/ore0 the strain3tie 2eha6ior -o&ld 2e as 1ig&re %:$:c$
Conce!t Chec" %:$8
Q&estion' For the following pair of polymers# do the following: %,& state whether it is possible to decide if one polymer has a higher tensile modulus than the other= %& if this is possible# note which has the higher tensile modulus and then cite the reason%s& for your choice= and %3& if it is not possible to decide# then state why not. 2yndiotactic polystyrene haing a number*aerage molecular weight of 77#777 g6mol 9sotactic polystyrene haing a number*aerage molecular weight of 07#777 g6mol. Ans-er'
No0 it is not possible$
oth s.ndiotactic and isotactic !ol.st.rene ha6e a
tendenc. to cr.stalli;e0 and0 there/ore0 -e ass&e that the. ha6e a!!ro7iatel. the sae cr.stallinit.$ 1&rtherore0 since tensile od&l&s is 6irt&all. inde!endent o/ olec&lar -eight0 -e -o&ld e7!ect 2oth aterials to ha6e a!!ro7iatel. the sae od&l&s$
Conce!t Chec" %:$9 Q&estion' For the following pair of polymers# do the following: %,& state whether it is possible to decide if one polymer has a higher tensile strength than the other= %& if this is possible# note which has the higher tensile strength and then cite the reason%s& for your choice= and %3& if it is not possible to decide# then state why not. 2yndiotactic polystyrene haing a number*aerage molecular weight of 077#777 g6mol 9sotactic polystyrene haing a number*aerage molecular weight of 77#777 g6mol. Ans-er' es0 it is possible$ The s.ndiotactic !ol.st.rene has the higher tensile strength$ oth s.ndiotactic and isotactic !ol.ers tend to cr.stalli;e0 and0 there/ore0 -e ass&e that 2oth aterials ha6e a!!ro7iatel. the sae cr.stallinit.$ Ho-e6er0 tensile od&l&s increases -ith increasing olec&lar -eight0 and the s.ndiotactic PS has the higher olec&lar -eight +<))0))) g>ol 6ers&s :))0))) g>ol /or the isotactic aterial,$
Conce!t Chec" %:$:
Q&estion' For the following pair of polymers# plot and label schematic stress*strain cures on the same graph. >oly%styrene*butadiene& random copolymer haing a number*aerage molecular weight of ,77#777 g6mol and ,78 of the aailable sites crosslin"ed and tested at 7 (. >oly%styrene*butadiene& random copolymer haing a number*aerage molecular weight of ,7#777 g6mol and ,8 of the aailable sites crosslin"ed and tested at / (.
The co!ol.er tested at 5)C -ill dis!la. elastoeric 2eha6ior +c&r6e ( o/ 1ig&re %:$%, inas&ch as it is a rando co!ol.er that is lightl. crosslin"ed4 /&rtherore0 the te!erat&re o/ testing is a2o6e its glass transition te!erat&re$ On the other hand0 since −=:C is 2elo- the glass transition te!erat&re o/ the other !ol.+st.rene32&tadiene, co!ol.er0 the stress3strain 2eha6ior &nder these conditions is as c&r6e A o/ 1ig&re %:$%$
Conce!t Chec" %:$< Q&estion' 9n terms of molecular structure# explain why phenol*formaldehyde %$a"elite& will not be an elastomer. %5he molecular structure for phenol*formaldehyde is presented in 5able ,.3.& Ans-er' The olec&les in elastoers &st 2e t-o3diensional chains that are lightl. crosslin"ed and ca!a2le o/ 2eing t-isted and "in"ed in the &nstressed state$
Phenol3
/oraldeh.de has a rigid three3diensional str&ct&re consisting o/ tri/&nctional re!eat &nits0 -hich does not eet these criteria /or chain con/oration and /le7i2ilit.$
Conce!t Chec" %:$#
Q&estion' For each of the following two polymers# plot and label a schematic specific olume*ersus*temperature cure %include both cures on the same graph&: 2pherulitic polypropylene# of 8 crystallinity# and haing a weight*aerage molecular weight of 1#777 g6mol 2pherulitic polystyrene# of 8 crystallinity# and haing a weight*aerage molecular weight of ,77#777 g6mol Ans-er'
Sho-n 2elo- are the s!eci/ic 6ol&e36ers&s3te!erat&re c&r6es /or the
!ol.!ro!.lene and !ol.st.rene aterials$
Since 2oth !ol.ers are 5:F cr.stalline0 the. -ill e7hi2it 2eha6ior siilar to c&r6e $ in 1ig&re %:$%=$ Ho-e6er0 !ol.st.rene -ill ha6e higher elting and glass transition te!erat&res d&e to the 2&l"ier side gro&! in its re!eat &nit str&ct&re0 and since it has a higher -eight3a6erage olec&lar -eight$
Conce!t Chec" %:$= Q&estion' For the following two polymers# %,& state whether is possible to determine whether one polymer has a higher melting temperature than the other= %& if it is possible# note which has the higher melting temperature and then cite reason%s& for your choice= and %3& if it is not possible to decide# then state why not. 9sotactic polystyrene that has a density of ,., g6cm 3 and a weight*aerage molecular weight of ,7#777 g6mol 2yndiotactic polystyrene that has a density of ,.,7 g6cm 3 and a weight*aerage molecular weight of ,#777 g6mol. Ans-er' es0 it is possible to deterine -hich o/ the t-o !ol.st.renes has the higher 5 m$ The isotactic !ol.st.rene -ill ha6e the higher elting te!erat&re 2eca&se it has a higher densit. +i$e$0 less 2ranching, and also the greater -eight3a6erage olec&lar -eight$
Conce!t Chec" %:$
Q&estion' uring the winter months# the temperature in some parts of Alas"a may go as low as ( %0F&. 4f the elastomers natural isoprene# styrene*butadiene# acrylonitrile* butadiene# chloroprene# and polysiloxane# which would be suitable for automobile tires under these conditions? Why? Ans-er'
1ro Ta2le %:$90 onl. nat&ral !ol.iso!rene0 !ol.+st.rene32&tadiene,0 and
!ol.silo7ane ha6e &se/&l te!erat&re ranges that e7tend to 2elo- :: C$ At te!erat&res 2elo- the lo-er &se/&l te!erat&re range liit0 the other elastoers listed in this ta2le 2ecoe 2rittle0 and0 there/ore0 are not s&ita2le /or a&too2ile tires$
Conce!t Chec" %:$%) Q&estion' 2ilicone polymers may be prepared to exist as liuids at room temperature. (ite differences in molecular structure between them and the silicone elastomers.
The li&id silicones -ill ha6e lo- olec&lar -eights and 6er. little
crosslin"ing0 -hereas the olec&lar -eights /or the elastoers -ill 2e &ch higher4 the elastoers -ill also ha6e soe crosslin"ing$
Conce!t Chec" %:$%%
Q&estion'
2tate whether the molecular weight of a polymer that is synthesi'ed by
addition polymeri'ation is relatiely high# medium# or relatiely low for the following situations: %a& !apid initiation# slow propagation# and rapid termination %b& 2low initiation# rapid propagation# and slow termination %c& !apid initiation# rapid propagation# and slow termination %d& 2low initiation# slow propagation# and rapid termination. Ans-er' +a, 1or ra!id initiation0 slo- !ro!agation0 and ra!id terination the olec&lar -eight -ill 2e relati6el. lo-$ +2, 1or slo- initiation0 ra!id !ro!agation0 and slo- terination the olec&lar -eight -ill 2e relati6el. high$ +c, 1or ra!id initiation0 ra!id !ro!agation0 and slo- terination a edi& olec&lar -eight -ill 2e achie6ed$ +d, 1or slo- initiation0 slo- !ro!agation0 and ra!id terination the olec&lar -eight -ill 2e lo- or edi&$
Conce!t Chec" %:$%5
Q&estion' Nylon 0#0 may be formed by means of a condensation polymeri'ation reaction in which hexamethylene diamine GN< H%(< &0 HN< I and adipic acid react with one another with the formation of water as a by*product. Write out this reaction in the manner of Euation ,.;. Note: 5he structure for adipic acid is
Ans-er' The /ollo-ing re!resents the reaction 2et-een he7aeth.lene diaine and adi!ic acid to !rod&ce n.lon <0< -ith -ater as a 2.!rod&ct'
Conce!t Chec" %:$%8 Q&estion' %a& Why must the apor pressure of a plastici'er be relatiely low? %b&
I/ the 6a!or !ress&re o/ a !lastici;er is not relati6el. lo-0 the !lastici;er a.
6a!ori;e0 -hich -ill res< in an e2rittleent o/ the !ol.er$ +2,
The cr.stallinit. o/ a !ol.er to -hich has 2een added a !lastici;er -ill 2e
diinished0 inas&ch as the !lastici;er olec&les /it in 2et-een the !ol.er olec&les0 -hich -ill ca&se ore isalignent o/ the latter$ +c, The tensile strength o/ a !ol.er -ill 2e diinished -hen a !lastici;er is added$ As the !lastici;er olec&les /orce the !ol.er chain olec&les a!art0 the agnit&des o/ the secondar. interchain 2onds are lessened0 -hich -ea"ens the aterial since strength is a /&nction o/ the agnit&de o/ these 2onds$
Conce!t Chec" %:$%9
Q&estion' For a rubber component that is to be ulcani'ed in its final form# should ulcani'ation be carried out before or after the forming operation? Why?
Chapter 16
Co!osites
Conce!t Chec" %<$% Q&estion' (ite the general difference in strengthening mechanism between large*particle and dispersion*strengthened particle*reinforced composites. Ans-er' The aJor di//erence in strengthening echanis 2et-een large3!article and dis!ersion3strengthened !article3rein/orced co!osites is that /or large3!article the !article3 atri7 interactions are not treated on the olec&lar le6el0 -hereas0 /or dis!ersion3strengthening these interactions are treated on the olec&lar le6el$
Conce!t Chec" %<$5
Q&estion' 5he following table lists four hypothetical aligned fiber*reinforced composites %labeled A through &# along with their characteristics. 4n the basis of these data# ran" the four composites from highest to lowest strength in the longitudinal direction# and then @ustify your ran"ing.
Co!osite
1i2er T.!e
Gol$ 1raction 1i2ers
1i2er Strength +MPa,
A
glass
)$5)
8$: × %)
glass
)$8:
8$: × %)
C
car2on
)$9)
:$: × %)
D
car2on
)$8)
:$: × %)
A6e$ 1i2er ength +,
Critical ength +,
=
)$#)
%5
)$#:
=
)$9)
=
)$:)
8 8 8 8
Ans-er' The ran"ing /ro highest to lo-est strength in the longit&dinal direction is as /ollo-s' C0 D0 0 and A$ Co!osite C is the strongest inas&ch as the car2on /i2ers are contin&o&s and are stronger than glass0 and it has the highest /i2er 6ol&e /raction$ Co!osite D is o/ lo-er strength than C 2eca&se it has a lo-er J f 4 other-ise the car2on /i2ers are also contin&o&s$ Material is ne7t 2eca&se the glass /i2ers are -ea"er than car2on4 these /i2ers are also contin&o&s$ Co!osite A is the -ea"est since it is co!osed o/ the -ea"er glass /i2ers0 the /i2ers are discontin&o&s0 and J f is the lo-est o/ all /o&r aterials$
Conce!t Chec" %<$8
Q&estion' (ite one desirable characteristic and one less desirable characteristic for each of %,& discontinuous* and oriented*fiber*reinforced composites and %& discontinuous* and randomly oriented*fiber*reinforced composites. Ans-er'
1or discontin&o&s3 and oriented3/i2er3rein/orced co!osites one desira2le
characteristic is that the co!osite is relati6el. strong and sti// in one direction4 a less desira2le characteristic is that the echanical !ro!erties are anisotro!ic$ 1or discontin&o&s3 and randol. oriented3/i2er3rein/orced co!osites0 one desira2le characteristic is that the !ro!erties are isotro!ic4 a less desira2le characteristic is there is no single high3strength direction$
Chapter 17
Corrosion and Degradation o/ Materials
Conce!t Chec" %#$% Q&estion' Would you expect iron to corrode in water of high purity? Why or why not? Ans-er' Iron -o&ld not corrode in -ater o/ high !&rit. 2eca&se all o/ the red&ction reactions0 E&ations %#$8 thro&gh %#$#0 de!end on the !resence o/ soe i!&rit. s&2stance s&ch as H@ or Mn@ ions or dissol6ed o7.gen$
Conce!t Chec" %#$5
Q&estion' )odify Euation ,1.,; for the case in which metals ) , and ) are alloys. Ans-er' 1or this case0 it is necessar. to ta"e into acco&nt the co!ositions o/ etals M % and M5$ I/ M% and M5 re!resent concentrations o/ etals M % and M5 in their res!ecti6e allo.s0 the e&ation 2ecoes
(
0
0
∆V = V 2 − V 1
)
−
RT
!" 1n+ #!" 2 #
nF
!" 2n+ #!" 1 #
ln
Conce!t Chec" %#$8 Q&estion'
$riefly explain why concentration polari'ation is not normally rate
controlling for oxidation reactions. Ans-er'
Concentration !olari;ation is not norall. rate controlling /or o7idation
reactions 2eca&se an &nliited s&!!l. o/ etal atos at the corroding electrode inter/ace -ill al-a.s 2e !resent$
Conce!t Chec" %#$9
Q&estion' %a& From the galanic series %5able ,1.&# cite three metals or alloys that may be used to galanically protect nic"el in the actie state. %b& 2ometimes galanic corrosion is preented by ma"ing an electrical contact between both metals in the couple and a third metal that is anodic to these other two. -sing the galanic series# name one metal that could be used to protect a copper*aluminum galanic couple. Sol&tion' +a, The /ollo-ing etals and allo.s a. 2e &sed to gal6anicall. !rotect nic"el in the acti6e state +i$e$0 lie 2elo- Ni in the gal6anic series,' tin0 lead0 8%< and 8)9 stainless steels0 cast iron0 iron0 steel0 al&in& allo.s0 cadi&0 coerciall. !&re al&in&0 ;inc0 agnesi&0 and agnesi& allo.s$ +2, inc0 agnesi&0 and agnesi& allo.s a. 2e &sed to !rotect a co!!er3al&in& gal6anic co&!le$
Conce!t Chec" %#$: Q&estion' (ite two examples of the beneficial use of galanic corrosion.
Conce!t Chec" %#$<
Q&estion' 9s Euation ,1.3 eually alid for uniform corrosion and pitting? Why or why not? Ans-er' E&ation %#$58 is not e&all. 6alid /or &ni/or corrosion and !itting$ The reason /or this is that0 -ith !itting0 the corrosion attac" is 6er. locali;ed0 and a !it a. !enetrate the entire thic"ness o/ a !iece +leading to /ail&re, -ith 6er. little aterial loss and a 6er. sall corrosion !enetration rate$ With &ni/or corrosion0 the corrosion !enetration rate acc&ratel. re!resents the e7tent o/ corrosion daage$
Conce!t Chec" %#$#
Q&estion' 5in cans are made of a steel# the inside of which is coated with a thin layer of tin. 5he tin protects the steel from corrosion by food products in the same manner as 'inc protects steel from atmospheric corrosion. $riefly explain how this cathodic protection of tin cans is possible since tin is electrochemically less actie than steel in the galanic series %5able ,1.&$ Ans-er' Tin o//ers gal6anic !rotection to the steel in tin cans e6en tho&gh it +tin, is electrocheicall. less acti6e than steel /ro the gal6anic series$ The reason /or this is that the gal6anic series re!resents the reacti6ities o/ etals and allo.s in sea-ater4 ho-e6er0 /or the /ood sol&tions that are contained -ithin the cans0 tin is the ore acti6e etal$
Conce!t Chec" %#$=
Q&estion' From a molecular perspectie# explain why increasing crosslin"ing and crystallinity of a polymeric material will enhance its resistance to swelling and dissolution. Would you expect crosslin"ing or crystallinity to hae the greater influence? Bustify your choice. or h.drogen,0 and relati6el. -ea" in co!arison to the strong co6alent 2onds associated -ith the crosslin"s$
Conce!t Chec" %#$
Q&estion' ist three differences between the corrosion of metals and each of the following: %a& the corrosion of ceramics %b& the degradation of polymers Ans-er' +a, Three di//erences 2et-een the corrosion o/ etals and the corrosion o/ ceraics are' %, Ceraic aterials are ore corrosion resistant than etals in ost en6ironents$ 5, Corrosion o/ ceraic aterials is norall. J&st a cheical dissol&tion !rocess0 -hereas /or etals it is &s&all. electrocheical$ 8, Ceraics are ore corrosion resistant at ele6ated te!erat&res$ +2, Three di//erences 2et-een the corrosion o/ etals and the degradation o/ !ol.ers are' %,
Degradation o/ !ol.ers is ordinaril. !h.siocheical0 -hereas /or etals0 corrosion is electrocheical$
5,
Degradation echaniss /or !ol.ers are ore co!le7 than the corrosion echaniss /or etals$
8, More t.!es o/ degradation are !ossi2le /or !ol.ers?e$g$0 dissol&tion0 s-elling0 and 2ond r&!t&re +2. eans o/ r adiation0 heat0 and cheical reactions,$
Chapter 18
Electrical Pro!erties
Conce!t Chec" %=$% Q&estion' 9f a metallic material is cooled through its melting temperature at an extremely rapid rate# it forms a noncrystalline solid %i.e.# a metallic glass&. Will the electrical conductiity of the noncrystalline metal be greater or less than its crystalline counterpart? Why? Ans-er'
The electrical cond&cti6it. /or a etallic glass -ill 2e less than /or its
cr.stalline co&nter!art$ The glass -ill ha6e 6irt&all. no !eriodic atoic str&ct&re0 and0 as a res<0 electrons that are in6ol6ed in the cond&ction !rocess -ill e7!erience /re&ent and re!eated scattering$ +There is no electron scattering in a !er/ect cr.stal lattice o/ atos$,
Conce!t Chec" %=$5
Q&estion' 5he room*temperature electrical resistiities of pure lead and pure tin are .70
× ,7*1 and ,.,, × ,7*1 *m# respectiely. %a&
)a"e a schematic graph of the room*temperature electrical resistiity ersus
composition for all compositions between pure lead and pure tin. %b& 4n this same graph# schematically plot electrical resistiity ersus composition at ,7(. %c& Explain the shapes of these two cures# as well as any differences between them.
+c, U!on cons<ation o/ the P23Sn !hase diagra +1ig&re $=, -e note &!on e7tra!olation o/ the t-o sol6&s lines to at roo te!erat&re +e$g$0 5) C,0 that the single !hase
!hase solid sol&tion e7ists 2et-een !&re lead and a co!osition o/ a2o&t 5 -tF o/ Sn3= -tF P2$
In addition0 the co!osition range o6er -hich the !hase is sta2le is 2et-een
a!!ro7iatel. -tF Sn3% -tF P2 and !&re tin$ Within 2oth o/ these co!osition regions the resisti6it. increases in accordance -ith E&ation %=$%%4 also0 in the a2o6e !lot0 the resisti6it. o/ !&re P2 is re!resented +scheaticall., as 2eing greater than that /or !&re Sn0 !er the !ro2le stateent$
1&rtherore0 /or co!ositions 2et-een these e7trees0 2oth and !hases coe7ist0 and allo. resisti6it. -ill 2e a /&nction o/ the resisiti6ities the indi6id&al !hases and their 6ol&e /ractions0 as descri2ed 2. E&ation %=$%5$ Also0 ass /ractions o/ the and !hases -ithin the t-o3!hase region o/ 1ig&re $= change linearl. -ith changing co!osition +according to the le6er r&le,$ There is a reasona2le dis!arit. 2et-een the densities o/ P2 and Sn +%%$8: g>c 8 6ers&s #$8 g>c8,$ Th&s0 according to E&ation $< !hase 6ol&e /ractions -ill not e7actl. e&al ass /ractions0 -hich eans that the resisti6it. -ill not e7actl. 6ar. linearl. -ith co!osition$ In the a2o6e !lot0 the c&r6e in this region has 2een de!icted as 2eing linear /or the sa"e o/ con6enience$ At %:)C0 the c&r6e has the sae general sha!e0 and is shi/ted to signi/icantl. higher resisti6ities inas&ch as resisti6it. increases -ith rising te!erat&re +E&ation %=$%) and 1ig&re %=$=,$
In addition0 /ro 1ig&re $=0 at %:)C the sol&2ilit. o/ Sn in P2 increases to
a!!ro7iatel. %) -tF Sn?i$e$0 the !hase /ield is -ider and the increase o/ resisti6it. d&e to the solid sol&tion e//ect e7tends o6er a greater co!osition range0 -hich is also noted in the a2o6e /ig&re$
The resisti6it.3te!erat&re 2eha6ior is siilar on the tin3rich side0 -here0 at
%:)C0 the !hase /ield e7tends to a!!ro7iatel. 5 -tF P2 += -tF Sn,$ And0 as -ith the roo3te!erat&re case0 /or co!ositions -ithin the @ t-o3!hase region0 the !lot is a!!ro7iatel. linear0 e7tending 2et-een resisti6it. 6al&es /o&nd at the a7i& sol&2ilities o/ the t-o !hases$
Conce!t Chec" %=$8
Q&estion' Which of Kn2 and (d2e will hae the larger band gap energy E g? (ite reason%s& for your choice. Ans-er' inc s&l/ide -ill ha6e a larger 2and ga! energ. than cadi& selenide$ oth are II3GI co!o&nds0 and n and S are 2oth higher 6erticall. in the !eriodic ta2le +1ig&re 5$, than Cd and Se$ In o6ing /ro 2otto to to! &! the !eriodic ta2le0 Eg increases$
Conce!t Chec" %=$9
Q&estion'
At relatiely high temperatures# both donor* and acceptor*doped
semiconducting materials will exhibit intrinsic behaior %2ection ,/.,&.
4n the basis of
discussions of 2ection ,/. and the preious section# ma"e a schematic plot of Fermi energy ersus temperature for an n*type semiconductor up to a temperature at which it becomes intrinsic. Also note on this plot energy positions corresponding to the top of the alence band and the bottom of the conduction band. Ans-er' elo- is sho-n the scheatic !lot o/ 1eri te!erat&re 6ers&s te!erat&re$
As noted in the !re6io&s section0 at lo- te!erat&res0 the aterial is e7trinsic and the 1eri energ. is located near the to! o/ the 2and ga!0 in the 6icinit. o/ the donor le6el /or an n3 t.!e seicond&ctor$ With increasing te!erat&re0 the aterial e6ent&all. 2ecoes intrinsic0 and the 1eri energ. resides near the center o/ the 2and ga! +Section %=$:,$
Conce!t Chec" %=$:
Q&estion' Will Kn act as a donor or as an acceptor when added to the compound semiconductor LaAs? Why? %Assume that Kn is a substitutional impurity&. Ans-er' inc -ill act as an acce!tor in aAs$ Since n is /ro gro&! II o/ the !eriodic ta2le0 it -ill s&2stit&te /or a4 /&rtherore0 a n ato has one less 6alence electron than a a ato$
Conce!t Chec" %=$<
Q&estion' 4n the basis of Figure ,/.,1# as dopant leel is increased# would you expect the temperature at which a semiconductor becomes intrinsic to increase# to remain essentially the same# or to decrease? Why? Ans-er' According to 1ig&re %=$%#0 as do!ant le6el is increased0 the !osition o/ the hori;ontal E7trinsic Region line o6es &!-ard$ Th&s0 the !oint at -hich the intrinsic region 2ecoes doinant o6es hori;ontall. to higher te!erat&res$
Conce!t Chec" %=$#
Q&estion' 4n the basis of the electron*concentration*ersus*temperature cure for n* type silicon shown in Figure ,/.,1 and the dependence of logarithm of electron mobility on temperature %Figure ,/.,;a&# ma"e a schematic plot of logarithm electrical conductiity ersus temperature for silicon that has been doped with ,7 , m*3 of a donor impurity. Now briefly explain the shape of this cure.
!ecall that Euation ,/.,0 expresses the dependence of
conductiity on electron concentration and electron mobility $ Ans-er' The scheatic !lot o/ logarith electrical cond&cti6it. 6ers&s te!erat&re is sho-n 2elo-$
According to E&ation %=$%<0 the electrical cond&cti6it. o/ an n3t.!e seicond&ctor is !ro!ortional to the !rod&ct o/ electron concentration + n, and the electron o2ilit. + e,?i$e$0
σ µ n µ e
1ro 1ig&re %=$%a0 there is no c&r6e /or n B %)5% 384 ho-e6er0 i/ one -ere !lotted it -o&ld reside 2et-een and ha6e the sae general sha!e as the %) 5) 38 and %)55 38 c&r6es?that is0 the logarith o/ the electron o2ilit. decreases -ith increasing te!erat&re$ et &s noconsider indi6id&all. the three regions on the log electron concentration 6ers&s te!erat&re !lot
o/ 1ig&re %=$%#$ 1or the /ree;e3o&t region o/ the c&r6e +i$e$0 at lo- te!erat&res,0 the logarith o/ the electron concentration increases signi/icantl. -ith increasing te!erat&re$ The !rod&ct o/ this !ortion o/ the c&r6e and the region o/ the c&r6e in 1ig&re %=$% a o6er the co!ara2le te!erat&re range res<s in a net increase in log cond&cti6it. -ith increasing te!erat&re +!er the a2o6e !lot,?the diinishent o/ log e -ith te!erat&re is ore grad&al than the increase o/ log n$ O6er the e7trinsic region o/ 1ig&re %=$%#0 log n reains constant -ith increasing te!erat&re0 -hereas log e contin&es to decrease +!er 1ig&re %=$%a,$ The net res< o/ ta"ing the !rod&ct o/ these t-o c&r6es is that cond&cti6it. -ill decrease -ith increasing te!erat&re$ It /ollo-s that the log 6ers&s te!erat&re c&r6e -ill necessaril. ha6e to !ass thro&gh a a7i& at soe te!erat&re J&st 2elo- the onset o/ the e7trinsic region$ 1inall.0 /or the intrinsic region o/ 1ig&re %=$%#0 log n increases draaticall. -ith te!erat&re0 and -hile log e contin&es to decrease +al2eit not as draaticall.0 1ig&re %=$% a, the net res< o/ ta"ing the !rod&ct o/ these t-o c&r6es is an increase o/ electrical cond&cti6it. -ith increasing te!erat&re0 !er the a2o6e !lot$ 1&rtherore0 the log 3te!erat&re c&r6e also !asses thro&gh a ini& at soe te!erat&re near the 2eginning o/ the intrinsic region o/ 1ig&re %=$%#$
Conce!t Chec" %=$=
Q&estion' Would you expect increasing temperature to influence the operation of p*n @unction rectifiers and transistors? Explain. Ans-er' I/ the te!erat&re o/ a p*n J&nction recti/ier or a J&nction transistor is raised high eno&gh0 the seicond&cting aterials -ill 2ecoe intrinsic and the de6ice -ill 2ecoe ino!erati6e$ 1&rtherore0 di//&sion o/ do!ant s!ecies /ro a p to an n region and 6ice 6ersa a. occ&r0 -hich -o&ld also lead to !er/orance !ro2les$
Conce!t Chec" %=$
Q&estion' For solid lead titanate %>b5i4 3 & what "ind%s& of polari'ation is %are& possible? Why? Note: ead titanate has the same crystal structure as barium titanate %Figure ,/.3&. Ans-er' Electronic0 ionic0 and orientation !olari;ations -o&ld 2e o2ser6ed in lead titanate$ Electronic !olari;ation occ&rs in all dielectric aterials$ The lead0 titani&0 and o7.gen -o&ld &ndo&2tedl. 2e largel. ionic in character$ 1&rtherore0 orientation !olari;ation is also !ossi2le inas&ch as !eranent di!ole oents a. 2e ind&ced in the sae anner as /or aTiO8 as sho-n in 1ig&re %=$8:$
Chapter 19
Theral Pro!erties
Conce!t Chec" %$% Q&estion' %a& Explain why a brass lid ring on a glass canning @ar will loosen when heated. %b& 2uppose the ring is made of tungsten instead of brass. What will be the effect of heating the lid and @ar? Why? Ans-er' +a, A 2rass lid on a glass canning Jar -ill loosen -hen heated 2eca&se 2rass has the greater coe//icient o/ theral e7!ansion 5) × %)3< +C,3% 6ers&s a!!ro7iatel. × %)3< +C,3% /or glass0 Ta2le %$%$ +2, I/ the ring is ade o/ t&ngsten instead o/ 2rass0 the ring -ill tighten &!on heating inas&ch as the glass -ill e7!and ore than t&ngsten$ The 6al&es o/ l /or glass and t&ngsten are × %)3< +C,3% and 9$: × %)3< +C,3%0 res!ecti6el.$
Conce!t Chec" %$5
Q&estion' 5he thermal conductiity of a plain carbon steel is greater than for a stainless steel. Why is this so?
Conce!t Chec" %$8
Q&estion' 5he thermal conductiity of a single*crystal ceramic specimen is slightly greater than a polycrystalline one of the same material. Why is this so? Ans-er' The theral cond&cti6it. o/ a single cr.stal is greater than a !ol.cr.stalline s!ecien o/ the sae aterial 2eca&se 2oth !honons and /ree electrons are scattered at grain 2o&ndaries0 th&s decreasing the e//icienc. o/ theral trans!ort$
Conce!t Chec" %$9
Q&estion' Which of a linear polyethylene % M n M 7#777 g6mol& and a lightly branched polyethylene % M n M 07#777 g6mol& has the higher thermal conductiity? Why?
Conce!t Chec" %$: Q&estion' Explain why# on a cold day# the metal door handle of an automobile feels colder to the touch than a plastic steering wheel# een though both are at the same temperature. Ans-er' On a cold da.0 the etal door handle /eels colder than the !lastic steering -heel 2eca&se etal has the higher theral cond&cti6it.0 and0 there/ore0 cond&cts heat a-a. /ro ones s"in ore ra!idl.$
Chapter 20
Magnetic Pro!erties
Conce!t Chec" 5)$% Q&estion Q&estion''
(ite the ma@or ma@or similari similarities ties and differ differences ences between ferromag ferromagnetic netic and
ferrimagnetic materials. Ans-er' The siilarities 2et-een /erroagnetic and /erriagnetic aterials ar e as /ollo-s' +%, There is a co&!ling interaction 2et-een 2et-een agnetic oents o/ adJacent atos>cations atos>cations /or 2oth aterial t.!es$ +5, oth /erroagnets and /erriagnets /or doains$ +8, H.steresis $*< 2eha6ior 2eha6ior is dis!la.ed /or 2oth0 and0 th&s0 !eranent agneti;ations are !ossi2le$ The di//erences 2et-een /erroagnetic and /erriagnetic aterials are as /ollo-s' +%, Magnetic oent co&!ling co&!ling is !arallel /or /or /erroagnetic aterials0 aterials0 and anti!arallel /or /erriagnetic$ +5, 1erroagnetics0 2eing etallic aterials0 aterials0 are relati6el. good good electrical cond&ctors4 cond&ctors4 inas&ch as /erriagnetic aterials are ceraics0 the. are electricall. ins&lati6e$ +8, Sat&ration agneti;ations agneti;ations are higher /or /erroagnetic /erroagnetic aterials$
Conce!t Chec" 5)$5
Q&estion Q&estion''
What What is the differ differenc encee betwe between en the spine spinell and iners inersee spinel spinel crysta crystall
structures?
anions anions -hich -hich a. 2e occ&!ie occ&!ied d 2. the cations cations$$
The di6alen di6alentt cation cationss +e$g$0 +e$g$0 1e 5@, occ&!. occ&!.
tetrahedral !ositions !ositions /or 2oth str&ct&res$ The di//erence lies in the occ&!anc. occ&!anc. /or the tri6alent cations +e$g$0 1e 8@,$ 1or s!inel0 s!inel0 all tri6alent tri6alent ions reside reside in octahedra octahedrall sites4 -hereas0 -hereas0 /or the in6erse s!inel0 hal/ are !ositioned in tetrahedral sites0 the other hal/ are located in octahedral sites$
Conce!t Chec" 5)$8
Q&estion' Explain why repeatedly repeatedly dropping dropping a permanent magnet magnet on the floor causes it to become demagneti'ed. Ans-er' Ans-er' Re!eatedl. Re!eatedl. dro!!ing dro!!ing a !eranent !eranent agnet on the /loor ca&ses it to 2ecoe deagn deagneti eti;ed ;ed 2eca& 2eca&se se the Jarrin Jarring g ca&ses ca&ses large large n&2er n&2erss o/ agnet agnetic ic di!ole di!oless to 2eco 2ecoee isaligned 2. di!ole rotation$
Conce!t Chec" 5)$9
Q&estion'
2chematically s"etch on a single plot the $*ersus*< behaior for a
ferromagnetic material %a& at 7 D# %b& at a temperature @ust below its (urie temperature# and %c& at a temperature @ust aboe its (urie temperature. $riefly explain why these cures hae different shapes. Ans-er' These $36ers&s3 < 2eha6iors are s"etched scheaticall. 2elo-$
At ) K0 the sat&ration agneti;ation -ill 2e a a7i&0 and the h.steresis loo! -ill ha6e the largest area$
At a higher te!erat&re +.et 2elo- the C&rie te!erat&re, the sat&ration
agneti;ation -ill decrease and the si;e o/ the h.steresis loo! -ill diinish$ 1inall.0 a2o6e the C&rie te!erat&re0 /erroagnetic 2eha6ior ceases0 and the aterial 2ecoes !araagnetic0 -ith linear $36ers&s3 < 2eha6ior4 the slo!e o/ this line segent is 6er. sall$
Conce!t Chec" 5)$:
Q&estion'
2chematically s"etch the hysteresis behaior for a ferromagnet that is
gradually demagneti'ed by cycling in an < field that alternates direction and decreases in magnitude. Ans-er' A scheatic s"etch sho-ing the h.steresis 2eha6ior /or a /erroagnet that is grad&all. deagneti;ed 2. c.cling an < /ield that alternates direction and decreases in agnit&de is sho-n 2elo-$
Conce!t Chec" 5)$< Q&estion' 9t is possible# by arious means %e.g.# alteration of microstructure and impurity additions&# to control the ease with which domain walls moe as the magnetic field is changed for ferromagnetic and ferrimagnetic materials.
2"etch a schematic $*ersus*<
hysteresis loop for a ferromagnetic material# and superimpose on this plot the loop alterations that would occur if domain boundary moement were hindered. Ans-er'
Hindering doain 2o&ndar. o6eent -ill enhance the coerci6it. o/ the
agnetic aterial0 -itho&t !rod&cing a signi/icant alteration o/ the sat&ration /l&7 densit.$ Th&s0 scheatic $*< 2eha6iors -ith and -itho&t doain 2o&ndar. o2str&ction are sho-n 2elo-$
Chapter 21
O!tical Pro!erties
Conce!t Chec" 5%$% Q&estion' $riefly discuss the similarities and differences between photons and phonons.
Phonons are elastic -a6es that e7ist -ithin solid aterials$
Photons are
electroagnetic energ. !ac"ets that a. e7ist in solid aterials0 as -ell as in other edia$ 5, There is a considera2le dis!arit. 2et-een the 6elocities o/ !hotons and !honons$ The 6elocit. o/ a !hoton is the sae as the 6elocit. o/ light in the !artic&lar edi&4 /or a !honon0 its 6elocit. is that o/ so&nd$
Conce!t Chec" 5%$5
Q&estion' Electromagnetic radiation may be treated from the classical or the uantum* mechanical perspecties. $riefly compare these two iewpoints. Ans-er'
1ro the classical !ers!ecti6e0 electroagnetic radiation is -a6e3li"e in
character0 and the !ossi2le energies o/ the radiation are contin&o&s$
1ro the &ant&3
echanical !ers!ecti6e0 electroagnetic radiation is d&al3li"e in character +2eing 2oth -a6e3li"e and !article3li"e,0 and not all energies are !ossi2le +i$e$0 energ. is &anti;ed,$
Conce!t Chec" 5%$8
Q&estion' Why are metals transparent to high*freuency x*ray and *ray radiation? Ans-er' Energies o/ these high3/re&enc. 73ra. and 3ra. radiation are greater than energies /or 6isi2le light$ Metals are trans!arent to these t.!es o/ radiation 2eca&se electron e7citations are not !ossi2le4 that is0 there are no e!t. energ. states a6aila2le /or electron transitions 2. the a2sor!tion o/ !hotons ha6ing these energies$ 1or e7a!le0 electron e7citations /ro the 1eri energ. +1ig&re 5%$9a, -o&ld 2e to -ithin an energ. 2and ga! 2et-een this !artiall.3/illed 2and and an e!t.0 higher3energ. 2and +not sho-n,$
Conce!t Chec" 5%$9
Q&estion' Which of the following oxide materials when added to fused silica %2i4 &# increases its index of refraction: Al 4 3# 5i4# Ni4# )g4? Why? Cou may find 5able ,.3 helpful. Ans-er' In ionic aterials0 the larger the si;e o/ the co!onent ions the greater the degree o/ electronic !olari;ation$ U!on cons<ation o/ Ta2le %5$8 -e /ind that the Al 8@0 Ti9@0 Ni5@0 and Mg5@ ions are all greater in si;e than the Si 9@ ion +)$):80 )$)<%0 )$)<0 and )$)$)#5 n0 res!ecti6el.0 6ers&s )$)9) n,0 and0 there/ore0 all o/ these ions -ill increase the inde7 o/ re/raction -hen added to SiO 5$
Conce!t Chec" 5%$:
Q&estion' Are the elemental semiconductors silicon and germanium transparent to isible light? Why or why not?
Conce!t Chec" 5%$<
Q&estion' (ompare the factors that determine the characteristic colors of metals and transparent nonmetals. Ans-er'
The characteristic color o/ a etal is deterined 2. the distri2&tion o/
-a6elengths o/ the nona2sor2ed light radiation that is re/lected$ The characteristic color o/ a trans!arent nonetal is deterined 2. the distri2&tion o/ -a6elengths o/ the nona2sor2ed light radiation that is transitted thro&gh the aterial$
