Resumo

LEAL-CRUZ, A.L; PECH-CANUL, M.I  e  DE LA PENA, J.L. A low-temperature and seedless method for producing hydrogen-free Si₃N₄. Rev. mex. fis. [online]. 2008, vol.54, n.3, pp.200-207. ISSN 0035-001X.

A simple, seedless method for the synthesis of Si₃N₄ from a hydrogen-free precursor system (Na₂SiF_6(s)-N_2(g)) was developed. From thermodynamic calculations and experimental results it is concluded that the gaseous chemical species SiF_x (SiF₄,SiF₃, SiF₂, SiF and Si) formed during the low-temperature dissociation of Na₂SiF₆ in a conventional CVD system react in-situ with nitrogen to produce Si₃N₄. Whiskers, fibers, coatings and powders were obtained via the Na₂SiF₆-N₂ system at pressures slightly above atmospheric pressure. Not only does the feasibility of the reactions for Na₂SiF₆ dissociation and Si₃N₄ formation increase with the temperature but also, once the SiF_x chemical species are formed by the former, the latter reaction is even more viable. Amorphous Si₃N₄ is obtained at temperatures of up to 1173 K while crystalline α- and β-Si₃N₄ are formed in the range 1273-1573 K and with processing times as short as 120 minutes. Optimal conditions for maximizing Si3N4formation were determined.

Palavras-chave : Thermodynamics; CVD; Amorphous Si₃N₄; α- and β-Si₃N₄; gas-solid precursors.

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