Masaki Narisawa

Silicone Resin Applications for Ceramic Precursors and Composites

This article reviews the applications of silicone resins as ceramic precursors. The historical background of silicone synthesis chemistry is introduced to explain the production costs and supply availability of various silicones. Thermal degradation processes of silicones are classified in terms of the main chain structure and cyclic oligomer expulsion process, which determine the resulting ceramic yield and the chemical composition. The high temperature decomposition of Si-O-C beyond 1,400 °C in an inert atmosphere and formation of a protective silica layer on material surfaces beyond 1,200 °C in an oxidative atmosphere are discussed from the viewpoints of the wide chemical composition of the Si-O-C materials. Applications of the resins for binding agents, as starting materials for porous ceramics, matrix sources with impregnation, fiber spinning and ceramic adhesions are introduced. The recent development of the process of filler or cross-linking agent additions to resin compounds is also introduced. Such resin compounds are useful for obtaining thick coatings, MEMS parts and bulk ceramics, which are difficult to obtain by pyrolysis of simple organometallic precursors without additives.

Investigation of Curing Process on Melt Spun Polymethylsilsesquioxane Fiber as Precursor for Silicon Oxycarbide Fibers

Polymethylsilsesquioxane (PMSQ) fiber was exposed to metal chloride vapors in a controlled atmosphere or electron beam irradiation in air to promote the curing process. The cured fibers were pyrolyzed at 1273K to compare the efficiency of individual curing method. The cured fibers were investigated by FT-IR, an optical microscope and TG analysis. In the case of successful curing, averaged diameter and tensile strength were analyzed on the obtained Si-O-C fibers.

Synthesis of SiC Based Fibers with Continuous Pore Structure by Melt- Spinning and Controlled Curing Method

Silicon carbide (SiC) based fibers with continuous pore structures were synthesized by the precursor method using a polycarbosilane (PCS) and polymethylhydrosiloxane (PMHS) polymer blends. The pore formation process can be explained by hydrogen gas dissolution in the polymer melt and desaturation process of the dissolved gas during the fiber spinning. We investigated the effect of PMHS additives with different chemical and physical natures on the obtained pore structures, because PMHS decomposition process played a role of hydrogen gas source. The individual polymer melts were characterized by viscosity measurement, gas chromatograph analysis and thermogravimetric (TG) analysis in order to obtain details of pore structure control.

Synthesis of SiOC Base Fibers from Silicone Resin with Low Carbon Content and Control of Surface Functionality by Metal Chloride Treatment in Vapor

Melt spinnable silicone resin with a low carbon content was spun to fiber form with an averaged diameter of 16.8 uf06dm. When the resin fiber was cured by SiCl4 vapor and pyrolyzed at 1273K in inert atmosphere, Si-O-C fiber with smooth surface was obtained. The measured tensile strength was relatively low. The fiber, however, showed oxidation resistance during high temperature exposure under an air flow. When the fiber was cured by TiCl4 with an increased vapor pressure at 313K, 40% mass gain was observed after the curing. SiO2-TiO2 fiber was obtained by pyrolysis in an air flow, while SiOC-TiO2 fiber was obtained by pyrolysis in an inert atmosphere. Structure of TiO2 and the resulting fiber surface morphology strongly depended on the temperature and the atmosphere during the pyrolysis.

Microstructure of SiC-Si-Al2O3 composites derived from silicone resin - metal aluminum filler compounds by low temperature reduction process

Concentrated slurry of a silicone resin with low carbon content, 3 ?m aluminum particles and ethanol were prepared. After casting, addition of cross-linking agent and drying, silicone resin-aluminum composite with thick sheet form was obtained. The prepared sheet was heat-treated at 933 or 1073K with various holding times to characterize formed phases during the heat treatments. XRD patterns and FT-IR spectra revealed free Si formation and existence of Si-O-Si bond at 933K. The Si-O-Si bond, however, disappeared and silicon carbide was formed at 1073K. SEM observation indicated formation of cracks bridged with a number of tiny struts at 933K and conversion to wholly porous structure at 1073K.