Effects of surface area, polymer char, oxidation, and NiO additive on nitridation kinetics of silicon powder compacts

    loading  Checking for direct PDF access through Ovid

Abstract

The oxidative stability of attrition-milled silicon powder under reaction-bonding processing conditions has been determined. The investigation focused on the effects of surface area, polymer char, preoxidation, nitriding environment, and a transitional metal oxide additive (NiO) on the nitridation kinetics of attrition-milled silicon powder compacts tested at 1250 and 1350°C for 4 h. Silicon powder was wet-attrition-milled from 2 to 48 h to achieve surface areas (SAs) ranging from 1.3 to 63 m2/g. A silicon powder of high surface area (63 m2/g) was exposed for up to 1 month to ambient air or for up to 4 days to an aqueous-based solution with the pH maintained at 3,7, or 9. Results indicated that the high-surface-area silicon powder showed no tendency to oxidize further whether in ambient air for up to 1 month or in deionized water for up to 4 days. After a 1-day exposure to an acidic or basic solution the same powder showed evidence of oxidation. As the surface area increased so did the percentage nitridation after 4 h in N2 at 1250 or 1350°C. Adding small amounts of NiO significantly improved the nitridation kinetics of high-surface-area powder compacts but both preoxidation of the powder and residual polymer char delayed it. Conversely, the nitridation environment had no significant influence on the nitridation kinetics of a high-surface-area powder. Impurities present in the starting powder and those accumulated during attrition milling appeared to react with the silica layer on the surface of silicon particles to form a molten silicate layer which provided a path for rapid diffusion of N2 and enhanced the nitridation kinetics.

Related Topics

    loading  Loading Related Articles