The kinetics of unidirectional capillary infiltration of silicon melt into microporous carbon preforms has been investigated as a function of the pore morphology and melt temperature. The infiltrated specimens showed alternating bands of dark and bright regions, which corresponded to the unreacted free carbon and free silicon regions, respectively. The decrease in the infiltration front velocity for increasing infiltration distances is in qualitative agreement with the closed-form solution of capillaritydriven fluid flow through constant-cross-section cylindrical pores. However, drastic changes in the thermal response and infiltration front morphologies were observed for minute differences in the preform's microstructure. This suggests the need for a dynamic percolation model that would account for the exothermic nature of the silicon-carbon chemical reaction and the associated pore-closing phenomenon.

Exothermic reactions between a porous matrix and an infiltrating melt provide a more economic alternative for synthesizing many ceramics, intermetallics, and composites. It has recently been demonstrated that infiltration of cast microporous carbon preforms by silicon melt can be used to fabricate high-density, nearly net-shaped silicon carbide components at significantly reduced cost. This paper describes the synthesis of reaction-bonded silicon carbide by reactive infiltration of microporous carbon preforms. The kinetics of unidirectional infiltration of silicon melt into microporous carbon preforms as a function of pore morphology and melt temperature is investigated in this paper. Qualitative agreement between experimental data and a mathematical model for capillarity-driven fluid flow through cylindrical pores is demonstrated. Experimental evidence of high parametric sensitivity is also presented. A simplified model relating fluid flow, transport, and reaction phenomena is formulated to interpret experimental evidence of pore closing and free silicon entrapment. A robust numerical formulation is also described.