In commercial practice, where temperatures are low, a number of commercially available materials are satisfactory as a container for molten aluminum. None of these, however, resists attack by aluminum in the temperature range 1800' to 2000'C. An investigation was conducted to find a material completely inert to aluminum at these high temperatures. Aluminum nitride emerged as the material that was inert to aluminum and showed satisfactory properties as a ceramic material. A method of preparing high-purity AlN by striking a d.-c. arc between two high-purity aluminum electrodes in a nitrogen atmosphere is described. A refractory having excellent strength and low porosity was achieved by hydrostatic pressing and firing at high temperatures. The mechanical, electrical, thermal, and chemical properties of the refractory are discussed.

A phase diagram of the system Al2O3-A14C3 is proposed. Two intermediate oxycarbides, A14O4C and A120C, were established. Eutectic melting between alumina and A1404C occurred at 1840°C. No other low melting was observed. The alumina phase was not corundum but was similar to delta-alumina. Because of the high reactivity of aluminum carbide and all the intermediate compounds with moisture and oxygen, use of refractories based on the system Alz03-A14C3 must be limited to applications where these agents are excluded. The behavior of highalumina refractories in the presence of carbon is explained. I. Literature ReviewGREAT deal of work on the system aluminum oxidecarbon is recorded in the technical and patent litera-A ture. Moissan' prepared aluminum carbide from aluminum and carbon in a high-temperature resistance furnace, and there is other early evidence that A14C3 results spontaneously from its elements and is the preferred product from the reaction of alumina and carbon up to approximately 2000°C. Prescott and Hincke,2 B r~n n e r ,~ and Treadwell and Gyger4 made equilibrium pressure measurements of the system Al2O3-C. The results were very discordant, undoubtedly because of different assumptions about the nature of the re-Presented at the Fall Meeting Equilibrium Between Aluminum Oxide and Carbon," J. A m . Fig. 4. Microstructures of solidified A1203-AI& melts, showing successive stages in the formation of AleOC from the peritectic reaction of Al& with the melt (250 X).

358 pp.; Ceram. Abstr., 9 181 689 (1930). * ( a ) M. H. Jellinek and I. Fankuchen, "X-Ray Diffraction Examination of Gamma Alumina," InJ. Eng. Chem.. 37 [2] 158-63 (1945); Cerum. Abstr., 24 [5] 101 (1945). ( b ) M. H. Jellinek and I. Fankuchen, "X-Ray Examination of Pure Alumina Gel," I d . Eng. Chem., 41 [lo] 2259-65 (1949);Cerum. Abstr., 1950, August, p. 172a.

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A series of amorphous stibonic acids, RSb03H2, one stibinic acid, (p-CH3Ph)2Sb02H, and Ph3SbO have been studied by mSb Móssbauer spectroscopy. The isomer shift, , decreases almost linearly with increasing number of R groups. Both the stibonic and stibinic acids have appreciable values of as well as quadrupole coupling constants on the order of ±10 mm s'1. Using an additive model to obtain orbital populations along the Sb ligand bonds for various assumed geometries, it is concluded that the typical Sb site in the amorphous acids has approximately trigonal-bipyramidal geometry with bridging oxygens in apical positions. The orbital population along the equatorial Sb-OH bond, 0 , is appreciably larger than the apical 0 in Ph4SbOH.

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