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.