Chemical Vapor Infiltration with Microwave Heating

Microwave Heated Chemical Vapor Infiltration: Densification Mechanism of SiCf/SiC Composites

“…49,50 As shown in Fig. 31 This results in a local decrease in temperature within the infiltrated region, 28 or a need to increase the microwave power to maintain the same temperature. Examination of the separate real and imaginary parts of the data, not presented here to save space, actually shows that this is because the material becomes more reflective of microwaves.…”

“…Crusting reduces the ingress of the gas and results in the need to stop the process repeatedly to reopen the channels by machining if high residual porosity is to be avoided. [27][28][29] Volumetric heating of the dielectric coupled with surface heat losses results in the center of the component being hotter than the surface, potentially by up to several hundred degrees centigrade. 4,15,20 In an attempt to overcome this problem, an approach based on the forced flow of gases, combined with the deliberate creation of a temperature gradient across the preform (FCVI), has been developed.…”

“…21,22 However, although uniformity and efficiency are enhanced compared with ICVI, 23 disadvantages include the need for complex temperature and gas flow control, something that is magnified when processing multiple parts and geometries. 28,31,33 The work presented here investigates the densification mechanisms for SiC fiber-reinforced SiC matrix composites (SiC f /SiC) processed by MCVI using principally scanning electron microscopy (SEM) and X-ray absorptiometry (XRA). 26 However, PCVI displays low efficiency in terms of conversion of gas to solid phase and the capital equipment costs are very high, making scaleup difficult.…”

Microwave Combustion and Sintering Without Isostatic Pressure

“…Infiltration of Si3N4 in NicalonTM cloth (Devlin et al 1993), SiC and Zr02 into reticulated SiC foam, NicalonTM cloth and Zr02 based porous fiber boards (Yin et al 1997) were also experimentally demonstrated. Experiments conducted in these reports required the application of microwave radiation at a fixed frequency.…”

Carbide, Nitride and Boride Materials Synthesis and Processing

“…These generally operate at reduced pressure 0-10 kPa; 7.5-75 torr) for deposition rate control. In a new development for this technique, there have been some exploratory efforts in using microwave heating to produce the thermal gradient (Devlin et al, 1992(Devlin et al, , 1993Morell, Economou and Amundson, 1992a;Spotz et al, 1993;Day et al, 1994). Density gradients are minimized by a low reaction temperature, although in order to get economical densification rates, deposition is often sufficiently rapid to overcoat the outer surface before infiltration is complete.…”