Fabrication of Silicon Carbide Whisker/Alumina Composite by Thermal‐Gradient Chemical Vapor Infiltration

Abstract

SiC(w)/Al 2 O 3 composites were made from an AlCl 3 -H 2 -CO 2 mixture by a thermal-gradient chemical vapor infiltration (CVI) method. Al 2 O 3 was deposited from the reaction of AlCl 3 and H 2 O, which was produced from the oxidation of H 2 by CO 2 . The densification rate was measured at various reactant compositions and total pressures. When the reaction rate or total pressure increased, the rate-controling step shifted from H 2 O production to AlCl 3 diffusion, which led to premature pore closing. To obtain dense composites in a short infiltration time, the diffusion rate of AlCl 3 had to be increased by decreasing the total pressure.

Alumina Matrix Composites with Non-Oxide Nanoparticle Addition and Enhanced Functionalities

“…After gelation and drying, the xerogel containing SiC nanoparticles is calcined, crushed, sieved, and finally used for preparation of nanocomposites. Other attempts to prepare the nanocomposite powders use more exotic techniques, such as a Teflon-activated self-propagating aluminothermic reaction (Equation (1)) [ 28 ]: 4Al + SiO 2 + 3C→3SiC + 2Al 2 O 3 or thermal-gradient chemical vapor infiltration of SiC porous preforms with a gaseous mixture of AlCl 3 , H 2 , and CO 2 , resulting in inhomogeneous distribution of constituent phases [ 29 ].…”

Preparation and Microstructure of Nextel 720/Mullite-Corundum Composite

“…When the diffusion rate of chlorides into the voids is rapid compared with the rate of H 2 O production, the oxides deposition rate is proportional to the rate of H 2 O production, which is the rate-controlling step. Because chlorides exist in excess of the H 2 O within the pores, the oxides deposition rate is independent of chlorides concentration [11]. On the other hand, when the diffusion rate of chlorides is not as rapid as the rate of H 2 O production, the oxides deposition rate is not proportional to the rate of H 2 O production, and diffusion of chlorides is the rate-controlling step in CVI.…”

Rate analysis of chemical vapor deposition by use of the thin tubular reactor

“…The reaction rate constants of the decomposition of the reactant are the slopes of the trend lines. The results were successfully applied to the numerical simulation of a thermal-gradient chemical vapor infiltration process for the production of silicon carbide whisker/ alumina composites [5,14,15].…”