Study On Surface Treatment Of Silicon Carbide Powder And Rheological Behavior Of Slurries

Colloidal forming process is an effective technology aimed to produce the highly reliable and complicated structured SiC ceramic component. It has been known as a key problem and technical challenge to produce the uniform and stable ceramic slurry with high-solid-content and low-viscosity. Starting from the micro-structure and surface property of SiC, this project is devoted to acquiring the feasible chemical structures and oxidations procedures as well as exploring the powder surface treatments and new modified methods. Adopting such methods as acid pickling, high-temperature oxidizing calcinations, hydrothermal treatment and dispersant modifications, this project has discussed the change of the surface property in the SiC powder and also other factors, such as, formations mechanism and rheological property for the stable formations of SiC slurry.Moreover, this paper will be devoted into the micro-difference between powder and slurry.The quantitative analysis on the influence of impurity ions and surface oxide layer on the rheological property of slurry will be also mentioned. In additions, this project has made a study about the surface treatment and modifications technologies, which are more practicable for the industrial productions. The main research results are presented as follows:1. The analysis of differences in microstructure between SiC powder and slurry: Two types of SiC powder, which one produced at home and the other made at abroad, have been selected. With the aid of XRD, SEM and Zetasizer Nano, etc. a systematic study of the crystal form, grain size and surface properties has been carried out. It is found that there is no obvious difference between the two types of SiC powder in terms of crystal form and external appearance. However, there is a remarkable distinctions between them in terms of surface property, slurry rheological property and stability. For the slurry being made at abroad, it not only has lower viscosity, but also has advantages over the home produced slurry in stability and dispersity.2. The influence of impurity ions on the dispersity of SiC powder and the slurry rheological property: The ICP-AES has been adopted to quantitatively measure the influence of the impurity ions on the surface property of SiC powder and slurry rheological property. After the removal of the impurity ions, the absolute value of Zeta potential of the Si C powder has remarkably increased, accompanied by the distinctly improving stability and rheological property of slurry. The metal impurity ions existing on the surface of SiC powder as well as the impurity ions in the water phase is an important factor affecting the slurry rheological property.3. The influence of SiC surface oxide layer on the slurry rheological property: The results show that the main factor causing the viscosity increased of SiC slurry is the impurity ions that exist either on the powder surface or in the water phase instead of the oxide layer on the powder surface?mainly as SiO₂?. After removal of the impurity ions,high-temperature oxidizing calcination can decrease the quantity of the Si-OH on the surface and produce the relatively higher active SiO₂. The electrostatic repulsive force on the powder surface may be enhanced in a basic solutions and further improve the rheological property of slurry.4. The influence of the hydrothermal treatment on the SiC powder: The hydrothermal treatment changed the quantity of Si-OH on the SiC surface and making the contact angle increased. The hydrophilic property of SiC surface has been weakened. The free water restricted on the powder surface is released and the viscosity of the SiC slurry becomes lower. This technology is worthy of further investigation to modify the SiC powder.5. The applications of dispersant during hydrothermal modifications process of the SiC powder: Butylamine, tetramethylammonium hydroxide?TMAH? and the newly synthesized MA101 are used for modifying the SiC powder surface by hydrothermal treatment. After the modifications, the absolute values of Zeta potential become larger,also the electrostatic repulsive force between grains increasing. The stability and dispersity of the slurry have been also obviously improved. The modifications of MA101 has achieved the best effect. Only a small amount of MA101 can remarkably improve thepowder surface property.