Jingtao Ma

Effects of dispersants and soluble counter-ions on aqueous dispersibility of nano-sized zirconia powder

Abstract The effect of different dispersants and water leaching on aqueous dispersibility of zirconia powder was studied. Zeta potentials of aqueous solutions containing nano-sized zirconia powder and different dispersants, such as ammonium polyacrylic acid (PAA-NH 4 ) and tetramethyl ammonium hydroxide (TMAH) and water leaching were characterized. Better dispersion of nano-sized zirconia powder in aqueous solutions was achieved with the addition of dispersant and water leaching.

Study on gelcasting and properties of recrystallized silicon carbide

Gelcasting of recrystallized silicon carbide (RSiC) was described in this paper. The Zeta potentials of recrystallized silicon carbide powders dispersing in aqueous solution and the rheological property of the suspension were investigated. A concentrated suspension of solid loading as high as 75 vol.% for gelcasting was prepared successfully. At the same time the complex green bodies with uniformity of density and high flexural strength were fabricated by gelcasting through this kind of suspension. The performance and microstructure of green bodies and sintered samples was measured and observed. Recrystallized silicon carbide parts were prepared by gelcasting.

Gelcasting of alumina ceramics in the mixed acrylamide and polyacrylamide systems

Ceramic gelcasting without inhibition of gelation due to the presence of oxygen must be performed in a nitrogen atmosphere to avoid surface spallation of the green body, which is a complex and expensive process. This study shows that the surface spallation of ceramic green bodies gelcast in air could be suppressed by introducing a proper amount of water-soluble polymer, polyacrylamide (PAM), to the acrylamide monomer solution. The dispersion of Al2O3 powder in a water solution containing PAM was investigated. The rheological behavior and the gelling behavior of the alumina suspension were analyzed. Flexural strength and microstructure of the gelcast green and sintered bodies were studied.

Study on gelcasting of silicon nitride-bonded silicon carbide refractories

Abstract Gelcasting is a very useful technique for producing ceramic green parts with near-net-shapes. Although it has been successfully applied to shape fine ceramic systems where micrometer- and submicrometer-size particles are used as starting powders, there is little report on gelcasting of refractories manufactured by coarse raw materials. In the present paper, dispersion and rheological properties of concentrated suspensions of SiC/Si mixtures with coarse particles (∼350 μm) and their gelcasting processes were discussed. A stable SiC/Si suspension with solids loading up to 70 vol.% was prepared, from which uniform green bodies with complex shapes were successfully gelcast. The performances of green bodies and sintered samples were measured and their microstructures were studied. After nitridation of the gelcast components at 1450 °C for 10 h in 0.1 MPa nitrogen atmosphere, the bulk density of 2.61 g cm −3 and flexural strength of 55.4 MPa were obtained.

Gelcasting of ceramic suspension in acrylamide/polyethylene glycol systems

A new polyethylene glycol/acrylamide-based gelcasting system has been developed. The new system performs at least as well as, and in some cases better than, the original acrylamide-based system. The development of this system is for the sake of eliminating the surface-exfoliation phenomenon of green bodies gelcast in air. This study concentrates attention on dispersion, rheological and gelation behavior in the new system and flexural strength of green body.

Effects of liquid medium and ball-milling on the surface group and aqueous dispersibility of Si3N4 powder

Abstract Influences of liquid medium and ball-milling process on the particle surface group and aqueous dispersibility of silicon nitride powder were investigated in this paper. After ball-milling in different liquids, the particle surface group and aqueous dispersibility of silicon nitride powder have different alternations. For the powders treated with identical ball-milling process in different liquids, the subsequent calcination in static air recoveries the same surface characteristics and hence the same aqueous dispersibility. Ball-milling process has significant effect on the particle surface group and its aqueous dispersibility. Under conditions of high weight ratio of milling-balls to powders and large rotary speed, the reaction of ruptured Si–O–Si surface groups with ethanol is dominant and the large amount of Si–O–C–R structures depresses its aqueous dispersibility remarkably.

Gelcasting of alumina ceramic in mixed PVP–HEMA systems

Abstract Aqueous gelcasting with a low toxicity monomer system has attracted increasing attention. The present study attempts to enhance the flexural strength of green bodies gelcast from a low toxicity hydroxyethyl methacrylate (HEMA) system by introducing an appropriate amount of the water soluble polymer polyvinylpyrrolidone (PVP). The rheological properties and gelling characteristics of PVP–HEMA/Al2O3 suspensions were examined. In addition, the flexural strength and microstructure of the gelcast green and sintered bodies are discussed.

Sol–gel preparation of ZrC–ZrO 2 composite microspheres using fructose as a carbon source

AbstractZrC–ZrO2 composite ceramic microspheres were prepared by internal gelation combined with carbothermic reduction using fructose as a chelating agent and carbon source. Fructose in the precursor solution formed complex with zirconium ions, which was conducive to the refining of the microstructure of the sintered composite. ZrC–ZrO2 composite with ZrC content as high as 60 wt% could be prepared. In this paper, fructose was used as a chelating agent and an organic carbon source to prepare ZrCO microspheres by internal gelation and carbothermic reduction. The fructose in the precursor solution could form complex with zirconium ions, which was conducive to the refining of the microstructure of the sintered composite. ZrC–ZrO2 composite with crystal size of ZrO2 and ZrC in nanometer range and ZrC content as high as 60 wt% could be successfully prepared.