The role of hydrogen and iron in silicon nitridation by ball milling

Abstract

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Structural evolution of titanium powder during ball milling in different atmospheres

“…Chen and Williams reported the competitive gas solid reactions during BM by monitoring pressure change [7]. Si 3 N 4 was synthesized by milling Si powder in NH 3 [8]. Solid-gas reactions of Nb and Ta with nitrogen driven by BM were also investigated [9].…”

Mechanochemical reaction and formation of an amorphous nitride phase during ball milling of Si in NH3

“…8 We found that high N content in the as-milled powder is always accompanied by significant Fe contamination in the powder. When steps were taken to select milling conditions which substantially reduced Fe, the adsorbed N content was low.…”

“…We have previously shown that H is lost during early stages of annealing at Ͻ300°C. 8 Note that differences in Fe content between as-milled and annealed samples are a result of changes in the content of other constituents: the apparent lack of change in the small Cr content is simply a result of round-off errors. Figure 1 shows x-ray diffraction ͑XRD͒ spectra of the above samples.…”

“…1 However, other nitrides such as Si 3 N 4 are much more difficult to form, requiring tight control over ball milling conditions and subsequent thermal annealing to reveal the crystalline nitride phase. 8,9 In the case of Si 3 N 4 formation by ball milling, there have been very few published reports 8-10 and the mechanism for nitride formation remains unclear. For example, what processes take place during milling and what phases are formed both during milling and subsequent annealing?…”

“…15,16 In the case of milling Si in NH 3 , many of the above processes are relevant but it is important to note that Si is extremely brittle and will not plastically deform to the same extent as metals or alloys. Indeed, when Si is milled in vacuum or N 2 it is extremely difficult to amorphize, 8,17 requiring oxygen contamination to stabilize the amorphous phase. In line with our previous suggestion, we propose that the fresh Si surfaces generated by continual fracturing and particle-size reduction should readily adsorb NH 3 gas.…”