Mecanismos de ativação mecânica de misturas de Níobio e Alumínio para a síntese por reação do NbAl3 / Mechanical activation mechanisms of niobium and aluminium mixtures for the reaction synthesis of NbAl3

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

28/03/2008

RESUMO

In this work, mechanical activation of mixtures of niobium and aluminum powders (75 at.% of Al) was carried out by high energy ball milling, in order to produce NbAl3 by combustion synthesis. The purpose was to investigate activation mechanisms present and the eventual preponderancy of one of them. Beside mixtures, aluminum and niobium powders were separately activated by milling (pre-activation). Reaction synthesis, by simultaneous combustion mode, was conducted on compacted pellets made of activated and non-activated powder mixtures. The thermal behavior of the compacted pellets upon heating was recorded and main thermal characteristics of the combustion reaction were evaluated. Lattice parameter, crystallite size and microstrain for niobium and aluminum were measured by X-ray diffraction analysis, using the Rietveld method. Scanning electron microscopy was used for microstructural characterization of milled powders and reacted pellets. The growth of interface area in the aggregates of aluminum and niobium, formed during milling, was shown to be the main activation mechanism. Both pre-activated niobium and increased quantities of stearic acid (milling process control agent) hinder the interface formation. The main effect of mechanical activation in the reaction synthesis was to reduce the ignition temperature with the increase of the milling time. High density of crystal defects attained during milling (pre-activation of single powders or activation of the mixtures) produced no measurable effects to the thermal behavior of pellets.

ASSUNTO(S)

ativação mecânica combustion synthesis mechanical activation nbal3 nbal3 síntese por combustão

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