Reaction-bonded mullite

A similar reaction route has been developed for reaction bonded mullite (RBM, aluminum silicate). In this case the powder formulation also includes a source of silicon (silicon metal, silicon carbide, or silica), in addition to aluminum metal and alumina, and the final product contains mullite as the major phase. The RBM process is frequently modified by additions of zircon (ZrSi04), which provide an additional source of silicon and result in a dispersion of fine zirconia particles in the product which restricts grain growth to ensure a fine uniform microstructure. It is again possible to reduce residual porosity while retaining the near-net-shape characteristics, but at the time of writing this process is still under development and some way from commercial exploitation. 

The present study aims at investigating the Reaction Bonded Silicon Carbide (RBSC) process to produce porous mullite-bonded SiC ceramics. Wu and Claussen (1991) reported a technique to produce mullite ceramics starting from Al, SiC and AI2O3 powder mixtures. However for the purpose of this study it was decided to use only SiC and Al 03 as the precursor powders with SiC as the major component so that after completion of the reaction the microstructure would be SiC bonded with mullite phase, with no residual alumina. This material was then tested for its mechanical properties like Young s modulus. Modulus of Rupture. Properties of Silicate-based SiC refractories have been reported to a certain extent by Reddy and others. Its potential use as a refractory material has been evaluated by measuring its thermal shock resistance. A sample refractory that has been designed in the... 

Ding S., Zhuc S., Zenga Y Jiang D., Fabrication of mullite-bonded porous silicon carbide ceramics by in situ reaction bonding, J. Eur. Ceram. Soc., 2007,27,2095-2102. 

She, H. Schneider, T. Inoue, M. Suzuki, S. Sodeoka, K. Ueno, Fabrication of low-shrinkage reaction-bonded alumina-mullite composites . Materials Chemistry and Physics 68 (2001) pp 105-109. 

The authors described the reaction mechanism as occurring by impregnation of the sample, bond reaction, and bond depletion. Immediately the alkali consumes the cristobalite and attacks the glass of the matrix bond. Next the fine crystalline mullite bridges associated with the bonding matrix react with the soda. The mullite x-ray peak intensity is quickly reduced. The extent of attack on the coarser crystalline mullite is intensified at higher temperatures or as the reaction proceeds. When equilibrium... 

Abstract Clays are ubiquitous constituents of the Earth s crust that serve as raw materials for traditional ceramics. Mineralogically, clays are phyllosilicates or layered aluminosilicates. Bonding is strong within layers, but weak between layers, allowing clays to break into micrometer-sized particles. When mixed with water, clays develop plasticity and can be shaped easily and reproducibly. When heated, clays undergo a series of reactions that ultimately produce crystalline mullite and a silica-rich amorphous phase. Beyond the structure and properties of clays, the science that developed to understand traditional ceramics continues to serve as the framework for the study of advanced ceramics. 

IN-SITU REACTION SINTERING OF POROUS MULLITE-BONDED SILICON CARBIDE, ITS MECHANICAL BEHAVIOR AND HIGH TEMPERATURE APPLICATIONS... 

In-Situ Reaction Sintering of Porous Mullite-Bonded Silicon Carbide... 

In-Situ Reaction Sintering of Porous Mullite-Bonded Silicon Carbide, 127 Its Mechanical Behavior and High Temperature Applications Neelkanth Bardhan and Parag Bhargava... 

A very high level of potassium vapor in a waste to energy plant caused the brick lining to expand and fracture due to the formation of kaliophilite from the reaction of the glassy matrix with the vapor. The kaliophilite/matrix reaction resulted in a large volumetric expansion and distortion of the brick. The problem was solved when the mullite-bonded brick was replaced with a phosphate-bonded brick. 

Some of the more subjective features are pore distribution, bond stmcture, degree of reaction, or dissolution and microcracking. In order to evaluate these parameters, it may be necessary to etch a sample to enhance grain boundaries or increase the contrast between components such as mullite and glass in refractory grog grain or corundum in calcined bauxite. 

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