Solid-Liquid Phase Diagram of Naphthalene-Diphenylamine Two-Component System Michael Go, Nate Manaloto, Ronald Reyes* *Faculty, Ateneo de Manila University; email:
[email protected]
Abstract . The The expe experi rime ment nt aims aims to be able able to cons constr truc uctt a phas phasee diag diagra ram m of
Naphthalene Naphthalene-Diphen -Diphenylam ylamine ine two-componen two-componentt system system at constant constant atmospheri atmosphericc pressure for thermal analysis. From the phase diagram, the eutectic composition (XE) and eutectic temperature (TE) are determined and are compared with the literature value. Commercial Naphthalene is used to undergo this test, and see if it is of the same caliber as the standard Naphthalene. Naphthalene-Biphenylamine. Eutectic point. Newton’s Law of Cooling. Thermal Arrest. Thermal Break. Keywords. Naphthalene-Biphenylamine.
Introduction. In invest investiga igatin ting g the hetero heterogene geneous ous
Figure 1. A Phase Diagram for a two component system in
equilibrium between solid and liquid phases of a two-
which which the solids solids are partia partially lly misci miscible ble and the liquid liquidss are
component system, a phase diagram is constructed. In
complete miscible.
constructi constructing ng phase diagrams, cooling curves forms
The binary solid-liquid diagram in Figure 1 shows the
the the basi basiss for for “ther “therma mall anal analys ysis is”. ”. From From the the phas phasee
stabi tabillity ity of dif differ ferent ent phas phases es as a funct unctiion of
diagram, diagram, the eutectic eutectic compositio composition n (XE) and eutectic
temperatur temperaturee and compositio composition. n. This example (Figure (Figure
temperature (TE) are determined.
1) shows shows a case case wher wheree the the soli solid d comp compon onen ents ts are are partiall partially y miscible, miscible, α+β. α(s) represents represents a solid solid state mixtu mixture re predom predomina inantl ntly y compos composed ed of substa substance nce A, with B present as an impurity, and β(s) represents the oppo opposi site te cas case wher wheree A is an impur mpuriity. ty. When When a substance is dissolved in a liquid and the freezing point of the liquid is lowered, this is called freezing pint depression, a colligative property that depends on the number of solute particles present in the solvent. The shape of the phase boundaries between the (α + liqui liquid d regi region on)) + (β + liqu liquid id regi region) on),, the the liqu liquid idus us curves curves,, descri describes bes the freezi freezing ng point point depres depressio sion n for this mixture. The equation of the liquidus curves can be derive derived d from from the Clausi Clausiusus-Cla Claper peryon yon equati equation on
unde underr the the assu assump mpti tion on that that the the solu soluti tion on beha behaves ves
Napht Naphthal halene ene follow followed ed by succes successiv sivee additio additions ns of
ideally:
Diphenylamine
to
the
previous
run;
and
a
Diphenylamine-rich series similarly prepared with the
T(XA) = Tf.A. + ln(XA)RTFA2/dHA = TA-((1-XA) + (1-X A)2/2 + …) RT f.A2/dHA
Naphthalene-rich series*. Heat the mixture in water Tf.A is the freezing point of compound A, and is also shown in Figure 2. dHA is the heat of fusion for compou pound A and XA is the the mole mole frac fracti tion on of compound A. An analogous equation can be written for compound B. The two liquidus curves intersect at the eutectic point, C.
bath until completely melted, and then, remove the water bath and measure the temperature periodically (e.g (e.g.. ever every y 15 secon seconds ds for for the the firs firstt 5 minu minute tes, s, 30 seconds for the next five minutes, and every minute for the latter parts until the eutectic temperature is reached) until the system is essentially solid.
In the absence of a phase change, the rate of change in temperature follows Newton’s Law of cooling. The Newton’s Law of cooling predicts that there is an
Table 1. Approximate range of composition for the two-component Naphthalene-Diphenylamine mixture Approximate Range of Composition
exponential approach to the ambient temperature. A
Pure A -
Pure B -
solid is formed because the rate of cooling is changed
Naphthalene: 10 g.
Diphenylamine: 10 g.
as part of the heat exchanged with the surroundings
R un
B (g)
Wt. % A
Run
A (g)
Wt. % B
that that contri contribut butes es to the phase phase transi transitio tion. n. During During the
1A
0.0
100
1B
0.0
100
2A
1.5
87
2B
1.5
87
3A
2.0
74
3B
2.0
74
4A
2.5
63
4B
2.5
63
5A
3.0
51
5B
3.0
51
freez eezing point of a pure subst bstance, when hen the temperatur temperaturee remains remains constant, constant, this is called called thermal thermal arrest. In a two-component system, as the temperature is lowered, one component begins to freeze while the other component component still still remains remains in the liquid state. In this this free freezi zing ng proc proces ess, s, the the liqui liquid’ d’ss conc concent entra rati tion on mixture changes as more and more solid forms, and
Results.
this consequently changes the freezing point. For this reason, the rate of cooling is not constant, but is diff differ erent ent from from the the rate rate of cool coolin ing g of the the orig origin inal al liquid. liquid. This change in the rate of cooling is known as thermal break. When the liquid reaches a certain ratio of the two components, a thermal arrest is observed. This This temp temper erat ature ure and and conce concent ntra rati tion on poin pointt is also also
Figure 2. The constructed phase diagram with the
freezing points plotted, temperature (y-axis) and mole fraction of Naphthalene (x-axis). The best fitted curve is used and the eutectic point and temperature were determined. Eutectic composition (XE) = 0.76381045
known as the eutectic point.
Eutectic temperature (TE) = 21.8121115 Experimental .
The
binary
system
will
be
Discussion: In the constructed phase diagram, a few
naphthalene-diphenylamine. Make two series of runs:
changes were made. The best fitted curve was used in
a Naph Naphth thal alen enee-ri rich ch seri series es begi beginn nnin ing g
order to get the eutectic point. The experimental value
with with pure pure
of
the
eutectic
point is
0.764 764
mole
fraction
We woul would d like like to ackn acknow owle ledg dgee the the Chem Chemis istr try y
compos compositi ition on of Naphth Naphthale alene ne and 21.81 21.81⁰C for for the
Department of the Ateneo de Manila University for
temperature. Comparing it with the values taken by
suppo upport rtiing
other studies, it was found that the eutectic point is
equi equipm pmen ents ts neces necessa sary ry for for the the comp comple leti tion on of the the
around 0.36-0.38 mole fraction of naphthalene, and
project.
the temperature temperature roughly roughly 31⁰C. The high deviation of
our our
proj projec ectt
and and
prov proviiding ding
us
the the
References.
the results from the previous one can be seen in the experimental procedure, and the result itself. As can
University of Colorado. “Binary Solid-Liquid Phase
be seen in the results, the points were not successive
Diagram.”
and not comple complete. te. As such, such, there was a huge huge break break
and and empt empty y spac spacee betw betwee een n the the 0.3 0.3 and and 0.8 mole
BSL.pdf>
fraction of Naphthalene interval. As such, the eutectic point point can only be roughly roughly estimated by extending the best fitted curves. Having more points can lead to a more visualize-able and more accurate results. The recommendation for the experiment is that it can add more solutes for each runs that can extend the points further nearer the eutectic point, or if not change the five runs where the solute are added 1.5 g. each run instead of adding in a 0.5g increment. The The majo majorr sour source ce of erro errorr in the the expe experi rime ment nt is temperature reading. Since the temperature is read not automa automatic ticall ally y by a machin machine, e, but manual manually ly by the experimenter experimenter.. Furthermor Furthermore, e, when the system system is not stirred, the whole solution is not in equilibrium which lead leadss to a devi deviat atio ion n in temp temper erat atur uree read readin ing g that that even eventu tual ally ly lead leadss to super supercoo cooli ling ng of the the syst system em.. Although this will eventually be eliminated, however, this this coul could d have have been been prev prevent ented ed if the the syst system em was stirred consistently. The recommendation is that an automatic stirrer can be used rather than a manual one. Acknowledgement .
Will Willia iams ms Diagram.”
Accessed
Coll Colleg ege. e.
on
“Bin “Binar ary y
Accessed
on
October
6,
Soli Solidd-Li Liqu quid id October
6,
2010.
Phas Phasee 2010.
Figure 1. A Phase Diagram for a two component system in which the solids are partially miscible and the
liquids are complete miscible.
Figure 2. The constructed phase diagram with the freezing points plotted, temperature (y-axis) and mole
fraction of Naphthalene (x-axis). The best fitted curve is used and the eutectic point and temperature were determined.
Diphenylamine with 3 grams of Naphthalene as impurity, the graph illustrate illustratess the thermal Figure 3. A run of Diphenylamine break and the thermal arrest.
