3377.     TESTUT, R.  [Chromium Carbides.]  Compt. rend., vol. 203, 1936, pp. 1007-1009; Chem. Abs., vol. 31, 1937, p. 332.

        Powdered Cr and excess C heated in an electric furnace above 1,700 form Cr3C2, which is not attacked by O2 below 1,000, and so is separated from excess by heating in O2 at 900.  It is insoluble in hot concentrated HCl, and is slowly volatile above 1,900.  Between 1,500 and 1,700 Cr5C2 is formed with some Cr3C2; this is less as temperature is nearer 1,500.  Cr5C2 is soluble in concentrated HCl but not in the 10% acid; it also is not attacked by O2 below 1,000.  Below 1,400, some Cr2O3 is formed.  Cr5C2 also is formed by heating Cr in C2H2.  CO passed over Cr at a temperature above 1,350 reacts according to 19 Cr+6 CO→3 Cr5C2+2 Cr2O3, the rate rapidly increasing with temperature.  Below 1,350 some C also is formed.