Modelling micro-level volume expansion during reactive melt infiltration using non-isothermal unreacted-shrinking core models

Abstract

Reactive melt infiltration is a process used to manufacture silicon carbide fibre-reinforced silicon carbide (SiC/SiC) composites. The present stage of research on reactive infiltration is primarily experimental, wherein complete infiltration is rarely achieved and unreacted silicon still remains in the composite. This paper deals with the micro-modelling aspect of reactive melt infiltration and estimates volume expansion due to mass transfer and reaction for cylindrical fibres. The thickness of the reaction product layer forming the matrix in the composite is determined by using an unreacted-shrinking core (URSC) model for cylindrical geometry in terms of physical parameters (diffusivity of the reactants and temperature) and non-dimensional physical quantities (such as the Sherwood number, Nusselt number and Thiele modulus). The effectiveness factors for the chemical reaction are determined as a function of time for various sets of physical parameters. The amount of volume expansion is found by determining the growth of the radius of the reaction product layer. It is concluded that lower initial temperatures of the solid reactant and higher ratios of heat capacity of reaction product to heat of reaction are favourable for infiltration. Determining the volume expansion in a single particle will later help in determining the transient permeability in a fibre preform during infiltration and also in optimizing this process.