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.