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Oxidation of Polycrystalline Niobium Nitride
Author(s) -
Gallagher P. K.,
Sinclair W. R.
Publication year - 1982
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198200044
Subject(s) - chemistry , arrhenius equation , activation energy , isothermal process , exothermic reaction , nitride , niobium , monoclinic crystal system , mole fraction , atmospheric temperature range , niobium nitride , crystallite , analytical chemistry (journal) , order of reaction , thermodynamics , crystallography , kinetics , reaction rate constant , crystal structure , organic chemistry , physics , layer (electronics) , quantum mechanics
Isothermal and dynamic TG were used to follow the oxidation of a sieved fraction, 177–250 μm, of niobium nitride powder in a flow of dry 0.1% O 2 in Ar. The material underwent enormous expansion during the oxidation. The isothermal weight gain was measured in the temperature range from 817 to 897 K. It followed a pseudo‐first order reaction rate law best with an Arrhenius activation energy of 50 kcal mole −1 . Dynamic studies at 1 K min −1 the pseudo‐first order rate law yielded similar values of 48 kcal mole −1 in 0.1% O 2 in Ar and 55 kcal mole −1 in air. Because of its highly exothermic nature, the reaction will lead to a thermal runaway situation at heating rates approaching a temperature of 600 K at 20 K min −1 , in air or at even lower rates of heating in pure O 2 , for material in this particle size range. Examination of the weight gain and X‐ray diffraction patterns of partially oxidized samples did not give any indication of intermediate species, such as oxynitrides or oxides of niobium, other than Nb 2 O 5 . The final product was a low temperature, pseudohexagonal polymorph of Nb 2 O 5 but monoclinic γ'‐Nb 2 O 5 appeared as an intermediate.