Mechanisms and kinetics during reactive infiltration of molten silicon in porous graphite

J Roger,G Chollon

doi:10.1016/j.ceramint.2019.01.191

Abstract

Liquid silicon Infiltration (LSI) is a fast and economical process to manufacture SiC-based ceramics. For a better understanding of reactive melt infiltration of liquid silicon, the wetting and infiltration of porous graphite by molten silicon were investigated at 1450, 1500 and 1550 °C for duration comprised between 10 s and 1 h. Infiltrations tests were performed in an argon atmosphere with an inductively heated furnace operating with heating and cooling rates of 300 °C.min−1. The formation and growth of SiC grains were investigated at the outer surface and within graphitic carbon substrates with 11% porosity and a narrow pore size distribution centered at 2 μm. The length of the infiltrated zone and the SiC crystals growth were determined from scanning electron microscopy. Rapid spreading and infiltration of molten silicon are observed from the first 60 s. The growth rate of the interfacial SiC layer obeys a fourth-power law with an activation energy of 260 ± 30 kJ mol−1. Pore filling by SiC is limited by volume diffusion with an activation energy equal to 320 ± 40 kJ mol−1.

Highlights

Silicon Carbide (SiC) is one of the most important advanced ceramic, due to its unique set of properties: wide band gap, good oxidation resistance, high thermal stability and conductivity, low density and high toughness [1,2,3,4]
BSE images were analyzed to examine the behavior of molten silicon at the surface and within the carbon substrate and to quantify the kinetics of the SiC formation at the surface and within the pores
The limiting factor is not the viscous flow of silicon but rather the chemical reaction between carbon and liquid silicon at the reaction front located at the surface and in the pores of the carbon substrate

Summary

Introduction

Silicon Carbide (SiC) is one of the most important advanced ceramic, due to its unique set of properties: wide band gap, good oxidation resistance, high thermal stability and conductivity, low density and high toughness [1,2,3,4]. A wide range of processes was developed for the synthesis of SiC-based materials [5,6]. The main barrier nowadays in the fabrication of silicon carbide-based ceramics is related to complex shape fabricability, processing time, temperatures, pressure, and control of the final product quality. Owing to the above considerations, there is a strong need to develop alternative processing approaches for silicon carbide-based advanced ceramics. The process of silicon infiltration and reaction with carbon is not satisfyingly understood [11,12,13,14,15,16,17,18]. The reaction between molten silicon and carbon complicates the infiltration and conversion process mainly because of its exothermicity and the permeability reduction implied by SiC formation. Liquid silicon-carbon interaction was examined by several authors which concluded that: 1) liquid silicon readily wets carbon and the wetting is enhanced by the SiC formation [22-

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