Influence of rice husk on the properties of fiber-reinforced silicon sol shells used in investment casting process

Abstract

Herein, short carbon fibers were incorporated in silica sol slurry to enhance the strength of silica sol shell for investment casting. The content of carbon fibers, with a length of 3.0 mm and diameter of 7.32 µm, was varied from 0 to 1 wt. % of the refractory powder mass. The influence of fiber content on rheological properties was systematically investigated. The results showed that the apparent viscosities of slurry with different amounts of fibers decreased with increasing shear rate. The apparent viscosity of as-prepared slurry increased with increasing fiber content and a maximum value of 149.25 × 10−3 Pa·s was attained at the fiber content of 0.4 wt. %, which corresponded to an increase of 22.6%. The high shear viscosity of the slurry initially increased with the increase in carbon fiber content, followed by a gradual decrease. Similarly, thixotropic loop area of the as-prepared slurry, with 0.4 wt. % carbon fibers, exhibited maximum value of 239.41 Pa·s −1, corresponding to an increase of 265%. Moreover, when the fiber content exceeded 0.6%, the gas permeability was significantly increased, which can be attributed to the high fiber content, the occurrence of agglomeration and clustering. To improve the permeability and reduce the residual strength of the shell, rice husk was added in the back slurry. The rice husk modified fiber-reinforced shell exhibited higher green strength and lower residual strength. When the content of rice husk was 1.0%, the residual strength decreased by 29.10%. The porosity and permeability of shell after roasting has improved.