Modeling and Development of a Microwave Heated Pilot Plant for the Production of SiC-Based Ceramic Matrix Composites

Abstract

This paper outlines the development of a microwave heated apparatus for the production of silicon carbide (SiC) based ceramic matrix composites via chemical vapor infiltration. An innovative pilot scale reactor was designed and built. A coupled thermal and electromagnetic model was developed in order to predict the temperature profile inside the reactor. The results obtained from the model demonstrated that the electric field inside the sample was constant. This fact is particularly important in order to prevent the thermal instabilities (run-aways) that are typical in the case of microwave heating. Therefore the heating was uniform with the aid of a mode stirrer that achieved a better distribution of the microwave power and then improved the process efficiency. The infiltration cycles were carried out on SiC fiber preforms and resulted in an excellent average weight increase with respect to the initial sample. By using microwave heating, the treatment times were considerably reduced with respect to the conventional process times reported in the literature. The microstructure of the SiC composites were observed by scanning the electron microscopy in order to evaluate the quality and the degree of densification which was achieved within the fiber tows. The SiC deposition inside of the sample was sufficiently homogeneous and compact, even if a certain degree of inter-tow porosity was still evident.

Mathematical Modelling of Microwave Pyrolysis

“…Cioni and Lazzeri [16] applied two commercial packages to predict the temperature profile and electromagnetic field in microwave chemical vapour infiltration process of silicon carbide. The developed model coupled the thermal and electromagnetic analysis in order to simultaneously estimate the electromagnetic field and temperature distribution.…”

“…Solving heat conduction equation in 3D nodal elements coupled with electromagnetic equations and applying properties as a function of temperature provides a clear picture and better understanding of microwave heating. The general flow chart of iteration method can be found in Refs [7,12,16,17]. In the flow chart, firstly the electromagnetic equation is solved at the beginning of the time step, following computation of absorbed power which is the source of the heat in thermal calculation, then, temperature profile was obtained by solving the heat conduction equation.…”

Reactive silicon infiltration of carbon bonded preforms embedded in powder field modifiers heated by microwaves

“…Danko et al [11] compared material's properties of pre-ceramic polymers pyrolysed both by microwave and by conventional systems. SiC fibres preforms were efficiently infiltrated with SiC by MW chemical vapour deposition (CVD) [12] thanks to the inverse temperature profile of the preform. RSI was successfully accomplished by Karandikar et al.…”

Microwave Pyrolysis of Plastic

“…Microwave energy can be delivered directly to the reacting or processing species by using their dielectric properties or by adding absorbers to materials which allows more volumetric heating of materials [20,21]. The high heating rate can be several orders of magnitude greater than with conventional heating [20][21][22]. Microwave generator can respond quickly to changes in process parameters with a feedback loop of an automated process [20].…”

“…The high heating rate can be several orders of magnitude greater than with conventional heating [20][21][22]. Microwave generator can respond quickly to changes in process parameters with a feedback loop of an automated process [20]. Microwave heating results from induced currents so the heating tends to be volumetric however the penetration of microwaves is influenced by the properties of the material.…”