208.    BERNIER, R.  [Thermomagnetic Study of Iron and Nickel Carbides.  I. Nickel Carbides.  II. Nickel Nitrides.  III. Cementite.  IV. Iron-Nickel Carbides.]  Ann. Chim., vol. 6, No. 12, 1951, pp. 104-161.

                  I.  Dispersion of Ni in ThO2 makes carburization easier.  In 2:1=H2:CO, carburization took place at 150°-200°.  NO hexagonal carbide was obtained for unsupported Ni.  Only with 10-30% ThO2 was the cubic phase eliminated by carburization.  In pure CO the carburization conditions differ from those for synthesis gas.  Chemical analyses were inconclusive but reported in detail.  X-ray diffraction pattern for hexagonal Ni3C is given; a=2.646 Å, c=4.320 Å, c/a=1.633 Å.  Thermomagnetic study showed decomposition starting at 210°, and Curie point of product at 314°.  Product is face-centered cubic with a=3.529 Å (Ni, a=3.516 Å).  On further and higher-temperature heating, the Curie point gradually goes up to normal, and a goes down to normal, showing that a face-centered cubic carbide had been transformed homogeneously to Ni+C.  H2 starts attack at 206° and leads to Ni with Curie opint=359° and normal a.  The face-centered cubic carbide is believed to be Ni4C and is assumed to be intermediate in the Ni3C formation.  No real proof is given for the formula Ni3C.  In N2, decomposition of Ni3C starts at 276°; in H2 at 171°; and in CO at 440°.  In all cases the product went through a lower face-centered cubic carbide stage.  19 refs.

                  II.  NH3 passed over reduced Ni supported on ThO2 at 170° leads to hexagonal close-packed Ni3N, which is always contaminated by face-centered cubic Ni4N.  Thermomagnetic analysis seems to indicate that the hexagonal close-packed product is paramagnetic.  It starts to decompose near 190° C into the face-centered cubic ferromagnetic nitride with Curie point=342°.  X-ray diffraction data fit hexagonal close-packed phase with a=2,668 Å, c=5.294 Å, c/a=1.609 Å.  For the face-centered cubic phase, a=3.521 Å.  It is concluded that nitriding goes by way of face-centered nitride to hexagonal close-packed nitride.  The latter reacts with H2 at 155°, decomposes in N2 near 450°.  8 refs.

                  III.  Gives discussion and bibliography on the thermal stability of Fe3C.  Fe2O3 and reduced Fe powder were treated with 2 H2+CO at 560°-1,000°.  Heating at 800° for 24 hr. of mixtures of carbonyl Fe with acetylenic C or C from CO produced Fe3C.  Fe3C made with 2 H2+O2 at 560° had a Curie point of 210° and at 1,000°, a Curie point of 216°.  This spread is believed to be due to slight differences in composition, the former being richer in C than the latter.  Stepwise destruction of the former gave higher Curie points with each step and partial reduction with H2 at 500°.  At 900°, 28.3% was destroyed after 4 hr., 29.9% after 19 hr.; at 1,050°, 48% was destroyed after 2 hr., 71% after 17 hr., and 79% after 37 hr.  Partial destruction at these 2 temperatures and subsequent heating at 800° showed reformation and new formation of Fe3C in the former case but no change in the latter.  The difference is attributed to differences in crystallinity of the C.  Fe3C reacts with H2 at 590° and with N2 at 690°.  23 refs.

                  IV.  Fe-Ni-C alloys were prepared from Fe and Ni salts (with about 20% ThO2 added for >30% Ni) in solution, precipitated with boiling K2CO3 solution, washed, dried, granulated, and reduced at 450°-600°, depending on the Fe content.  Ferronickels were studied.  Temperature of carburization varied between 170° and 560°.  From 0-40% Ni, substituted cementite was formed (I); from 40-70% Ni, a mixture of (I) and substituted hexagonal close-packed Ni3C (II) was formed; from 70-100%, Ni only (II) was formed.  The Curie point of (I) varies with composition from 210° (0% Ni) to 572° (30% Ni).  (II) decomposes on heating to form ferromagnetic face-centered cubic carbide, starting at about 210°.  In a mixture of (I) and (II) a Curie point of 150° was found for (I), showing that the Curie point drops sharply when >30% Ni is added.  A graph of Curie point of (I) versus % Ni is given.  (I) was stable up to 600° (II) was stable up to 480° in vacuum.  (I) is less stable than pure Fe3C.  150° is the Curie point limit of (I) for about 40% Ni.  16 refs.

                  ----------------.  See abs. 2271, 2276.