Fabrication of porous SiC sheets with controlled porosity from waste clutch boards
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1220-BB02-06
Fabrication of porous SiC sheets with controlled porosity from waste clutch boards. Yuya Domi and Shiro Shimada Graduate School of Engineering, Hokkaido University, Sapporo, 060-8628, Japan
ABSTRACT When clutch boards are fabricated as friction sheets in automatic transmission of motorcars, their useless fragments are disposed of in quantities of several tens of tons a month. Clutch boards are composed of diatomaceous earth, carbon powder/fiber and phenol resin. When clutch boards were fired in Ar, clutch boards were carbonized with excess carbon. In order to produce porous SiC sheets, excess carbon was reacted with SiO formed from Si and SiO2 at 1500 °C in Ar. High temperature treatment of the SiC sheets at 1700-1900 °C in vacuum could control the pore size of SiC sheets, having a main pore diameter range of 10 to 20 μm. The porosity of the SiC sheets was reduced from 79% to < 60% by heating in SiO gas the carbonized sheets impregnated with phenol resin at 1500 °C. The tensile strength of the SiC sheets obtained by the repeated cycle of impregnation and decomposition of the resin was increased with decreasing the porosity. The strength of 19 MPa was achieved at a porosity of 39% in the sheets obtained at 1700 °C. When aluminum-tri-sec-butoxide (ASB) solution was impregnated into the SiC sheets oxidized at 1000-1200 °C in air and then heated at 14001500 °C in Ar, SiC-mullite composite sheets were produced, with the strength increased by oxidation-bonding.
INTRODUCTION Silicon carbide (SiC) has excellent properties, such as high hardness, good thermal shock resistance, low thermal expansion coefficient, and high-oxidation resistance. Because of these properties, porous SiC ceramics have been used as diesel particulate filters for the removal of fine carbon particles from the exhausts of diesel engines [1, 2]. The Dynax Corporation (Chitose-city, Hokkaido, Japan) produces friction sheets in automatic transmission of motorcars. After ring-shaped clutch linings have been cut out from the original sheet, the resulting disc sheets are useless and disposed of in quantities of several tens of tons a month. These sheets are composed of diatomaceous earth, carbon powder/fiber and phenol resin. They are either buried in landfills or reused as cements or as fuel for boilers. In this respect, it is worth to investigate the effective reuse of these clutch sheets. Shimada et al. fabricated porous SiC sheets from clutch boards [3], but no attempt was made to obtain the SiC sheets with the controlled pore size and distribution. This paper reports the fabrication of porous SiC sheets with the porosity and pore diameter distribution controlled by heat-treatment at high temperature (1500-1900 °C) of carbonized clutch sheets impregnated with phenol resin. The tensile strength of the porous SiC sheets was measured to find out the optimum strength.
EXPERIMENTAL Carbonization of the Waste Clutch Sheets The clutch boards are composed of 23 wt% of diatomaceous earth, 10 wt% of carbon (activated carbon) and phenol resin with
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