DYNAMIC CONVECTION-DRIVEN THERMAL-GRADIENT CHEMICAL-VAPOR INFILTRATION

The operation of the process of chemical vapor infiltration using a co mbination of pressure pulsing and thermal gradients is theoretically i nvestigated in this study. Past studies had shown that pulsing of the pressure in the gas phase can lead to a dramatic reduction of the dens ity gradients in the densifying structure, in comparison to those seen in isobaric diffusion-driven Pinfiltration, with significant gradient s present only in the vicinity of the external surface of the preforms . Using a detailed model for chemical vapor infiltration under unstead y nonisothermal conditions, we show that temperature gradients, create d in our study through microwave heating, can, in conjunction with pre ssure pulsing, eliminate the density gradients in the final product. M oreover, appropriate tuning of the operational parameters can lead to a situation where densification proceeds from the interior of the pref orm toward the external surface.