Ralph H. Petrucci,' Alexandra Melnyk, and Olaf Muller Western Reserve University Cleveland, Ohio
I I
"Non-Contact" Eutedc Fusion in Binary Systems
In recent years several articles have appeared in THIS JOURNAL relating to the mechanism of eutectic fusion (1-5). One of us (3) has previously described a vapor phase mechanism in which the vapor phase above a pair of organic solids is condensed to the eutectic liquid a t the eutectic temperature. This process can occur even if the solids are maintained out of physical contact, and in such cases the term "non-contact" eutectic fusion has been applied (4). The vapor phase mechanism of eutectic fusion is perhaps best understood in terms of the complete three-dimensional phase diagram for a binary eutectic system ( 5 ) . Although many observations have been made in the past of "non-contact" eutectic fusion in organic systems (4, 6), to our knowledge inorganic systems have not been similarly studied. We wish to report some of our observations of %on-contact" fusion in certain binary inorganic systems. The studies were performed in a Kofler microscope hot stage. The maximum temperature attainable in such a stage is 360°C and as a result the studies were limited to only moderately high temperatures. The solid components of each bimary system were kept out of contact with one another on a cover glass supported in a sublimation block within the hot stage. The liquid condensate was observed in the open regions of the cover glass. Twelve different binary systems were studied and liquid condensates were observed in about one-half of them. It is possible that condensates might have been observed in more of the systems if the experiments had been continued longer, hut if a condensate did not form in a period of a few weeks the particular experiment was discontinued. Even though it was often possible to observe liquid condensates a t temperatures very near the eutectic, to obtain significant amounts of liquid in a reasonable length of time somewhat higher temperatures were used. Liquid condensates were collected for periods of time ranging from a few days to a few months. The liquid samples were frozen by reducing the temperature of the stage to below the eutectic value. Some indication of the composition of the solid mixtures which resulted was gained by observing their melting points. In every case the melting began close to the eutectic temperature, proving that the solid was indeed a mixture of the two components. The end melting points were generally close to the temperatures a t which the liquid condensates were collected. The occasional
1 Present address to which inquiries should be directed: Cslifornia State College, San Bernardino, California.
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variations observed in the end n~ellingpoints would suggest that there was some variability in the composition of the liquid condensates. The results for three of the syst,euls which were studied extensively are presented in the table. These observations were repeated several times by two different investigators (0.11. and A. 31.) working several years apart. Figure 1 is a photomicrograph of the liquid condensate obtained in the system lithium nitrate-sodium nitrate a t 220°C in a period of two months. (The single crystal is lithium nitrate; the crystal cluster, sodium nitrate). Figure 2 shows the crystallizatio~l of the liquid condemate below the eutectic temperature.
Summory of Observations of Non-Contact Eutectic Fusion in lnoraanic Svstems Eutectic temperature'
Temper* Melting point t u x at range of solid mixture derived which irom liquid liquid was condensate collected
NaCNS (mp 311°C) NaC&O* (331")
244°C
269T 269"
246262'C 246261"
KNO1 (335") NaNOo (308")
222O
234" 23X9 265'
222-234" 222-238" 225-235'
-
The temperatures listed in the table far the melting points of the pure components and their binary euteetics are taken from Timmermans (7).
Figure 1 . Liquid condenrote rervlting from "non-contoct" fusion of NoNOa and LiNOJ.
We do not contemplate further studies in the vapor phase mechanism of eutectic fusion in the immediate future, but even at this point it seems reasonable to expect that non-contact fusion can he ohsewed in a wide variety of inorganic systems. Literature Cited (1) (2) (3) (4)
SMITH, N. O., J. CHEM.EDUC.,35, 125 (1958). COPELY, G. N., J. CHEM.EDUC.,36, 596 (1959). PETRUCCI, R. H., J. CIIEM.EDUC.,36,603 (1959). SORUM, C . H., AND DURAND, E. A., J . Am. Chem. Sac., 74,
1071 (1952). (5) P ~ ~ n u c cR. r , H., J. CHEM.EDUC.,42. 323 (1965). (6) PETRUCCI, R. H., m o SORUM, C. H., Can. J . Chem., 34, 649 (1956). J. J., "Physico-chemical Constants of Binary (7) TIMMERMNS, Figure 2. Sclid mixture resulting from c r y ~ t a i l i z a t i o nof liquid condensole of NaNOl ond UNOF
Systems in Concentrated Solutions" (Interscience) John Wiley & Sons, New York, 1959-60, Val. 111.
Volume 42, Number 7, July 1965
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