ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The conversion of TiO2 (both anatase and rutile) to TiN by carbothermal reduction in nitrogen was found to proceed by progressive reduction through a homologous series of Magneli phase oxides Ti n O2n−1, where n has values of 4–10. The next phase to be observed by X-ray diffraction is Ti3O5, whose formation from the most stable Magneli phase (Ti4O7) is not predicted by the phase diagram, nor by simple thermodynamic calculations. The conversion of triclinic Ti4O7 to monoclinic Ti3O5 appears to be the slow step in the reaction sequence. Formation of TiN then proceeds directly, apparently without the intervention of Ti2O3 or TiO, as usually assumed. A possible cubic oxynitride intermediate was shown by surface analysis to contain no more than 5% oxygen. A small but significant amount of CO is evolved during the formation of Ti4O7, with a larger CO evolution occurring during the nitridation of Ti3O5. Although no direct mass spectroscopic evidence was found for the formation of C3O2, as suggested by previous workers, the present observed weight losses appear to be consistent with this concept. Both the observed reaction sequence and the pattern of CO evolution is consistent with thermodynamic calculations made using a computer program which takes into account the initial nitrogen concentration, and iterates over small temperature intervals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00541555
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