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DOE OSTI2020

Materials Data on NiMoO4 by Materials Project

NiMoO4 is zeta iron carbide-derived structured and crystallizes in the monoclinic P2/c space group. The structure is three-dimensional. Mo6+ is bonded to six O2- atoms to form distorted MoO6 octahedra that share corners with eight equivalent NiO6 octahedra and edges with two equivalent MoO6 octahedra. The corner-sharing octahedra tilt angles range from 47–56°. There are a spread of Mo–O bond distances ranging from 1.82–2.16 Å. Ni2+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with eight equivalent MoO6 octahedra and edges with two equivalent NiO6 octahedra. The corner-sharing octahedra tilt angles range from 47–56°. There are four shorter (2.07 Å) and two longer (2.12 Å) Ni–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Mo6+ and one Ni2+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Mo6+ and two equivalent Ni2+ atoms.

36 MATERIALS SCIENCE↗

NASA NTRS1983

The oxidation behavior of a model molybdenum/tungsten-containing alloy in air alone and in air with trace levels of NaCl(g)

Thermogravimetric, metallographic, and X-ray studies of a model alloy, Ni-(17 a/o)Al-(10 a/o)Mo+W, oxidized in dry air at 600-1200 C and in air with 10 ppm NaCl gas at 900 C, are reported. The alloy was melted under Ar and pretreated in flowing H2 for 24 h at 1300 C. Polished 1.3 x 1.3 x 0.2-cm specimens were washed and degreased prior to oxidation in a quartz tube within a furnace for up to 120 hr. The oxidation activation energy of the alloy is determined to be about 30 kcal/mole. The specimens oxidized at 900 C and hotter exhibited oxidized and nitrided phases covered by complex NiMoO4, NiWO4, and NiAl2O4 scales and a porous, nonprotective outer layer of NiO. The oxidation behavior is found to be determined by the formation and growth of the scale, especially the (Mo,W)O2 component. Al2O3 scale layers were not formed, and further runs with pure O2 or Ar-(20 percent)O2 ruled out an explanation of this phenomenon based on aluminum nitride formation. The oxidation was accelerated by the addition of NaCl gas, a finding attributed to the reaction of NaCl with external locally protective Al2O3 scales and with the internal(Mo, W)O2 layers.

Smeggil, J. G.↗