T H E PHASE DIAGRAM FOR T H E SYSTEM SULFCR-NAPHTHALENE AND I T S RELATION TO INTROFACTION* BY HAMNETT P. MUNGER WITH MARC DARRIN AND GEBHARD STEGEMAX
I. Introduction This investigation was undertaken to determine whether the phase diagram for naphthalene and sulfur might offer some explanation for the change in the rate of impregnation of sulfur into specific materials on the addition of substances called introfiers. An introfier is a substance which 'facilitates impregnation. A. Previous Work. It has been shown by Darrin' that several groups of organic substances act as introfiers in the impregnation of fibrous material by sulfur. The molecular structure required by sulfur introfiers is a plurality of cyclic nuclei.* The binary systems, consisting of sulfur and a sulfur introfier, which have been investigated are triphenyl-methane-sulfur,3 quinoline-sulfur,? p-dichlorbenzene-s~lfur.~ The data for these substances were not sufficiently complete to give an explanation for their introfying property. Xaphthalene is one of the most practical sulfur introfiers and was used during this investigation. II. Experimental A. Materials. Pure, resublimed naphthalene (m. pt. 80.1OC.)and rolled sulfur (99.9y0) were used in this investigation. Appropriate quantities of the materials were sealed in Pyrex tubes, I S mm X IOO mm. The tubes were kept in an oven a t IZ~OC. B. Apparatus. The freezing point measurements were made in a p a r a f h bath. The mechanism used to keep the sample uniformly mixed consisted of a rocking frame kept in motion by an eccentric. The temperature of the bath was measured by a thermometer graduated in I/IoOC.The thermometer was calibrated by comparing it with a Bureau of Standards thermometer. C. Procedure. I n order to obtain the freezing point of a mixture of naphthalene and sulfur, the tube containing the mixture was placed in the bath and cooled until crystals appeared. By heating the bath gradually and * Presented to the Chemistry Department of the University of Pittsburgh by Hamnett
P. Munger in partial fulfillment of the requirements of the degree of Doctor of Philosophy.
Contribution So. 181 from the Department of Chemistry of the University of Pittsburgh. Darrin: Ind. Eng. Chem., 20, 801 (1928). * Darrin: U. S.Patent 1,644,711(Oct 11,1927). a Smith, Holmes, and Elliott: J. Am. Chem. Soc., 27,797 (1905). Hamnick and Holt: J. Chem. SOC.,130, 1995 (1926). Bruni and Pellimola: Atti. Bccad. Lincei, 3011, 158;Chem. Abs., 17,2814 (1923).
594
HAMXETT P. M U S G E R W I T H MARC D A R R I S A S D GEBHARD STEGEMAN
allowing time for equilibrium to be established between the solid and liquid, a temperature was found a t which the solid phase was in equilibrium with the liquid phase, and which was o.i°C.below the temperature a t which only the liquid phase was present. This temperature was the freezing point of the mixture. The composition of the solid phases was determined by analyzing large crystals which were obtained by carefully cooling the mixtures in the tubes. The desired crystal type was obtained by regulating the rate of cooling and the temperature a t which the solid phase separated. The different crystals were easily identified by their form. 111. Results A. The Phase Diagram. The freezing point curves for the various solid phases are shown in Fig. I . From the graph, it will be seen that there a r 5 three stable solid phases in contact with the liquid phase, namely, monoclinic sulfur (A-B), solid solution of naphthalene in sulfur (liquidus C-D, solidus G-H), naphthalene (E-F). A metastable phase, a second solid solution of naphthalene in sulfur (liquidus K-L, solidus >'I-N) is shown. B. Relation to Introfactzon. Two very important factors, in the penetration of solids by liquids, are viscosity and surface tension. It has been found that the decrease in the freezing point of a mixture is usually accompanied by a corresponding decrease in viscosity. It has been pointed out by Darrin' that solubility is often an indication of introfying properties but not a measure of this property. A decrease in the freezing point of a mixture indicates an increase in mutual solubility of the two components. An interesting comparison can be drawn from the data on impregnation shown in Table I and the freezing-point data obtained in this investigation. From a comparison of the ratios of the increase in impreg-
TABLE I Impregnation of Fiberboard with Sulfur using Kaphthalene as the Introfier after Different. Immersion Periods* Mixture
o hlin.
I
hlin. c7 /O
Pure Sulfur jyoNaphthalene Difference 107, Naphthalene Difference Ratio of Diff. 5% : 10%
0.635***
5 Min.
7c
Freezing Point**
c-7
ic
35 I48 =I3 Ii3 138
117. j°C
83
31 IO8 77 130 99
0.675
0.78
0.82
0.620
28 84 56 I11
* Impregnation data secured from Darrin' ** Freezing-point data from present investigation. * * * ExtraDolated. LOC.cit
1 5 Min.
108.8
8.7 104.6 12.9
PHASE DIAGRAM FOR SULFUR NAPHTHALENE
595
nation by using 5 and I O per cent of naphthalene in sulfur with the ratio of the decrease in freezing point of these same mixtures, the close agreement between the ratios for one minute impregnation and the freezing point lowering is suggestive, If these results are extrapolated in order to obtain the ratio of the initial introfying power, the result is even more remarkable. It is to be remembered that after impregnation has begun, other factors, such as the degree of saturation of the fibrous material, etc., enter in to decrease the effectiveness of the introfier.
%NAPHTHALENE
FIG.I
Although the depression of the freezing point of sulfur is apparently a measure of the initial introfying power of the introfier, this freezing point lowering can not be taken as a criterion of substances having introfying properties. An introfier must first have the ability to change the specific wetting properties of sulfur before its relative effectiveness can be predicted from freezing point data. Pittsburgh, Pennsylvania.
