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Binary Solid-Liquid Phase Diagram and Eutectic of Naphthalene and Diphenylamine Mixtures


Definitions:
eutectic "The lowest melting point of an alloy or solution of two or more substances (usually metals) that is obtainable by varying the proportion of the components."
eutectic point "Melting point of eutectic mixture. The lowest temperature at which the eutectic mixture can exist in the liquid phase."
-- Hawley's condensed chemical dictionary, 14th ed., 2002.

This binary system has been a popular experimental topic in physical chemistry lab classes for many years. The experimental procedure for measuring the cooling and freezing of a binary mixture is straightforward and described in many lab texts. (1) Literature values for this system's behavior are a bit obscure, however. This table is adapted from Timmermanns (2) and is in turn based on values reported by Roloff.(3) It shows freezing points in Celsius for various compositions by weight-percent of the N-DPA mixture.

FREEZING POINTS OF NAPHTHALENE (C10H8) + DIPHENYLAMINE (C12H11N)
WT. % DPA WT % Naphth. Freezing Temp. C WT. % DPA WT % Naphth. Freezing Temp. C
0.0 100.0 79.5 58.6 41.4 41.4
11.0 89.0 77.5 60.5 39.5 39.3
24.1 75.9 68.0 61.0 39.0 40.3
25.6 74.4 66.8 63.2 36.8 35.7
34.7 65.3 61.5 63.2 36.8 35.6
41.9 58.1 55.9 63.4 36.6 37.7
44.2 55.8 54.7 65.0 35.0 33.3
50.6 49.4 49.6 65.7 34.3 35.4
50.8 49.2 49.2 67.4 32.6 33.1
51.5 48.5 48.5 41.4 58.6 32.0
53.1 46.9 46.7 69.3 30.7 31.6
55.0 45.0 45.6 69.3 30.7 31.3
56.1 43.9 45.0 71.5 28.5 32.0
57.9 42.1 42.4 73.8 26.2 34.1
57.0 43.0 38.4 75.2 24.8 35.2
60.5 39.5 40.5 75.5 24.5 35.1
62.6 37.4 38.4 76.6 23.4 36.7
64.0 36.0 36.5 77.6 22.4 37.1
65.0 35.0 40.5 78.2 21.8 36.8
66.6 33.4 33.3 79.3 20.7 38.6
67.1 32.9 33.7 79.6 20.4 38.0
68.4 31.6 32.3 82.0 18.0 39.6
68.6 31.4 32.6 84.2 15.8 42.0
70.0 30.0 32.0 86.6 13.4 43.2
70.6 29.4 31.5 88.8 11.2 45.2
71.5 28.5 32.8 93.9 6.1 48.4
72.4 27.6 33.1 95.02 5.0 49.8
73.1 26.9 33.2 100.0 0.0 52.6
73.5 26.5 33.3      

The currently accepted melting points for the pure compounds are: (4)
naphthalene (C10H8, CAS RN 91-20-3): 80.26° C
diphenylamine (C12H11N, CAS RN 122-39-4): 53.2° C

According to this table, the eutectic composition is approximately 31 wt. % naphthalene, with simultaneous crystallization around 31° C, which agrees with the results of Boardman. (5)

References

1. Karunakaran, K. "Theoretical prediction of eutectic temperature and composition." Journal of Solution Chemistry, 10 1981, 431-6.

2. Timmermans, Jean. Physico-chemical constants of binary systems in concentrated solutions. (Interscience, 1959) vol.1, 577.
QD 503 T566 1959 Chemistry Library Reference; Find in another Library

3. Roloff, Max. "Beiträge zur Kenntis der Kryohydrate." Zeitschrift für physikalische Chemie, 17 1895, 325-56.
The naphthalene-diphenylamine tables are found on p.338. (Note: Timmermans erroneously cites an 1893 article by Roloff.)

4. CRC Handbook of Chemistry and Physics, 86th ed., 2004-05.

5. Boardman, Shelby and Youngblood, Libby. "Experimental determination of a binary eutectic phase diagram: a laboratory exercise for introductory mineralogy-petrology." Journal of Geological Education, 23 1975, 52-54.
This article describes one experimental procedure for determining time-temperature curves and contains graphs of crystallization curves for pure naphthalene and 50%, 40% and 30% napthalene mixtures, and a binary phase diagram for the system.

For further information on finding thermodynamic data, see

Finding Data 101
ThermoDex
Finding Thermodynamic Information