Journal of the American Ceramic Society, Vol.101, No.7, 2809-2818, 2018
Process modeling of the low-temperature evolution and yield of polycarbosilanes for ceramic matrix composites
The volatilization of polycarbosilanes is important to the processing and performance of polymer infiltration and pyrolysis-based ceramic matrix composites. Low molecular weight (MW) polycarbosilane is often present in preceramic polymers and enhances viscosity for the purpose of composite infiltration. Due to the volatility of low MW chains, a model was developed to semi-empirically determine the MW distribution and then predict the mass yield and evolution of the MW distribution as a function of temperature and time for StarPCS SMP-10. The enthalpy of vaporization, the temperature dependence of the enthalpy of vaporization, the temperature dependence of the normal boiling point and a representation of the molecular weight distribution were fit using a series of thermogravimetric measurements, involving isothermal holds on a particular batch of SMP-10. Once calibrated for SMP-10 in this fashion, the molecular weight distribution of different batches of SMP-10 could be fit using a thermogravimetric measurement involving a reduced temperature-time series. The model was then predictive of mass loss over time for temperatures below the onset of curing (>90 degrees C). Understanding this volatilization enables improved SiC yield, reduced processing time and minimizing void/bubble formation.