Papers by Author: Li Ming Zhang

Abstract: Colloidal injection moulding of ceramics (CIMC), an innovative technique combining the advantages of conventional injection moulding and colloidal forming process, is applied to prepare thin-wall rutile tube for high capacity ozone generator. The forming process is studied detailed and the processing parameter of forming, drying and sintering schedule is determined in this research. The wall thickness of the sintered tube is 1.5~2mm and its inner diameter is about 26 mm, length is about 300 mm. The electric properties of the tube are also measured under different conditions. The above-mentioned tube is applied in ozone generator and the yield of ozone is about 55mg·L-1.

Abstract: The thin-film of silicon deposited by RTCVD on pressureless sintered SiC substrate with the size of 30mm×20mm, which is cleaned by ultrasonic method and chemical treatment. The crystal size of silicon columnar grain can reach 190 µm and its preferred orientation is [111] after ZMR process.

Abstract: The effects of solid volume fraction (SVF) on the gelation of alumina suspensions for gelcasting, debonding and sintering of the green body were studied. It was found that with SVF rising, the gelation of alumina suspension delayed; and the strength of green body decreased. On the other hand, high SVF resulted in that polymerized acrylamide split at a relative low temperature. These phenomena manifest that the fast polymerization of monomers in high SVF alumina suspension was inhibited, and the flexibility of the gelcasting was improved. However, Excessive solid volume fraction was prone to a bad rheological behavior of alumina suspension, and deteriorated the microstructure and properties of sintered body.

Abstract: Zirconia suspensions with coarse particles were prepared and the rheogical behavior and sediment stability of such suspensions with different dispersants were studied. It was found that ZrO2 suspension stabilized with TAC (tri-ammonium citrate) has an obvious shear-thinning behavior and rapid settlement; In contrast, the suspension stabilized with arabic gum shows a shear-thickening behavior and hardly any settlement. Considering both fluidity and settlement stability, APA (ammonium-polyacrylate) was chosen as the dispersant to increase the solid volume fraction of ZrO2 suspension. Utilizing the above suspension, a kind of refractory nozzle for precision casting of a Cu-Cr alloy was prepared by gelcasting. Such nozzle has a very good resistance to thermal shock and flux scouring.

Abstract: Ultrasonic wave were used to accelerate the solidification of Si3N4 suspensions for gelcasting. Different zones of the suspension solidified simultaneously under ultrasonic effect and structure defects in the green body caused by asynchronous solidification of the suspension could be avoided. It was found that the amount of initiator and catalyst for the polymerization of acrylamide monomers in the suspension can be reduced significantly and the flexibility of gelcasting processing could be improved. The mechanisms of the ultrasonic effect can be explained as following: on one hand, ultrasonic can increase the temperature of the suspension homogeneously; on the other hand, ultrasonic activates monomers, initiator and catalyst, and then boosts the reaction that initiator decomposes and generates free radicals and accelerates the polymerization rate of acrylamide monomers greatly.

Abstract: The origin of the inner stress in the ceramics green bodies prepared by colloidal forming was studied. The results show that the inner stress originates from the nonuniform shrinkage during the solidification of the precursor suspension and the drying of the green bodies, and the gradients of temperature, initiator concentration and moisture are the important original factors causing the inner stress. The inner stress could result in cracks in the green bodies during debinding.

Abstract: A process of fast uniform mixing & controllable colloidal forming of ceramics was invented to thoroughly avoid the crucial effect of temperature on colloidal forming of ceramics. The ceramic suspension was divided into two components A and B. The monomer was added into A, and the initiator was added into B. Under this condition, there were no reactions in separate A or B because of segregation of the monomer and the initiator. Both of the suspensions could keep good fluidity until they were mixed quickly and uniformly. The mixture would fast solidify under a determined pressure. The highly automatic equipment also had been developed for this process.