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Direct coagulation casting of alumina via controlled release of high valence counter ions using ammonium polyphosphate (APP) chelate complex as the coagulating agent was proposed. APP chelate complex suspension was prepared from APP and calcium chloride. Calcium used as high valence counter ions was chelated by APP. The average particle size of the chelate complex is 0.13 μm with a narrow particle size distribution which is close to the size of alumina particles. Glycerol diacetate was used to tailor the pH value of the suspension by hydrolysis which produces acetic acid. The lowering of the pH value helps to decompose the chelate complex, and enhance to release the calcium chelated. It is indicated that the viscosity of the suspensions with the addition of APP chelate complex suspension and glycerol diacetate increases to approximately 20 Pa s after heating at 40–70 °C for 1.5–5 h, which is high enough to coagulate the suspension. 55 vol% alumina suspension with a addition of 3 vol% APP chelate complex suspension and 5 vol% glycerol diacetate treated at 60 °C could coagulate completely within 2 h with a compressive strength of 2.1 MPa. Dense alumina with a relative density of above 97% and a flexural strength of 388 ± 23 MPa can be prepared by this method from 55 vol% alumina suspensions without a burnout process. [ABSTRACT FROM PUBLISHER]

Direct coagulation casting of alumina suspension via high valence counter ions (DCC-HVCI) using magnesium citrate as coagulating agent with glycerol diacetate as pH regulator was investigated. Influence of concentrations of glycerol diacetate and magnesium citrate on pH and rheological properties of alumina suspension was investigated. High viscosity enough to coagulate the suspension is achieved by adding magnesium citrate and glycerol diacetate. Hydrolysis of glycerol diacetate shifts the suspension to lower pH which promotes the decomposition of magnesium citrate and contributes enough magnesium ions to coagulate the suspension. Coagulated samples with different shapes can be demolded without deformation by treating 55 vol% alumina suspension with 2 vol% glycerol diacetate and 0.5-1.2 wt% magnesium citrate at room temperature for 2.5-6 h. Dense alumina ceramics with relative density above 99.5 % can be prepared by DCC-HVCI using magnesium citrate as coagulating agent with glycerol diacetate as pH regulator sintered at 1550 °C for 2 h. [ABSTRACT FROM AUTHOR]

Direct coagulation casting of alumina suspension via controlled release of high valence counter ions ( DCC- HVCI) using calcium citrate as coagulating agent was reported. Hydrolysis of glycerol diacetate shifts the pH of suspension to weakly acidic region which helps to decompose calcium citrate and release calcium ions. The effect of concentration of glycerol diacetate and calcium citrate on the pH and viscosity of alumina suspension was investigated at 25°C and 60°C, respectively. The pH of suspensions with glycerol diacetate and calcium citrate decreases to 8.6 and 7.5 treated at 25°C and 60°C, respectively. It is indicated that high viscosity is achieved by adding 2 vol% glycerol diacetate and 0.5 wt% calcium citrate which is enough to coagulate the suspension. Green body with compressive strength of 1.0 MPa is obtained by treating the alumina suspension with 2 vol% glycerol diacetate and 0.5 wt% calcium citrate at 60°C for 1 h. The alumina ceramics sintered at 1550°C have homogeneous microstructure with relative density above 99.0%. [ABSTRACT FROM AUTHOR]

Alumina green bodies were prepared by direct coagulation casting via increasing high valence counter ions ( DCC- HVCI) method. Influence of calcium iodate concentration, coagulation temperature, and the solid loading on the compressive strength of coagulated bodies was investigated. The results show that the wet-coagulated bodies display higher compressive strength than dried ones. The wet strength is above 2.0 MPa which is about one order higher than that prepared by DCC method, whereas the dried strength is in the range of 1.0 MPa. The wet-coagulated body shows elastic deformation, whereas the dried body exhibits typical brittle failure behavior. The mechanism of high wet strength obtained by DCC- HVCI is also proposed. The coagulated bodies prepared from slurries of alumina loading in the range of 50 vol% showed linear shrinkage of 2.6% after drying at 80°C for 24 h. The sample with the powder content of 50 vol% displays a narrow average pore channel size, showing a mean pore diameter of 40 nm. A homogeneous green body and high wet strength can be obtained via the DCC- HVCI method. [ABSTRACT FROM AUTHOR]

A direct coagulation casting method for silicon nitride suspension via dispersant reaction was reported. Tetramethylammonium hydroxide (TMAOH) was used as dispersant to prepare silicon nitride suspension with high solid loading and low viscosity. Influences of TMAOH and pH value on the dispersion of silicon nitride powder were investigated. Glycerol diacetate (GDA) was used to coagulate the silicon nitride suspension. Influences of the concentration of glycerol diacetate on the viscosity and pH value of the suspension were investigated. It was indicated that high viscosity sufficient to coagulate the suspension was achieved by adding 1.0–2.0 vol% glycerol diacetate at 40–70 °C. The coagulation mechanism was proposed that the silicon nitride suspension was destabilized by dispersant reacting with acetic acid which was hydrolyzed from glycerol diacetate at elevated temperature. Coagulated samples could be demolded without deformation by treating 50 vol% silicon nitride suspensions with 0.2 wt% tetramethylammonium hydroxide and 1.0–2.0 vol% glycerol diacetate at different temperatures. Dense silicon nitride ceramics with relative density above 98.8% had been prepared by this method using glycerol diacetate as coagulating agent sintered by different methods. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) ceramics were prepared by direct coagulation casting via high valence counterions (DCC–HVCI) using magnesium citrate as a coagulating agent assisted by the hydrolysis of glycerol diacetate. The colloidal behavior of PZT suspensions was evaluated by measuring the zeta potential and the viscosity. The dispersant content and solid loading were optimized to prepare concentrated PZT suspension. The results indicated that PZT suspension with solid loading up to 56 vol% can be prepared by the addition of 0.5 wt% ammonium polyacrylate at pH=10.6. The critical coagulation concentrations of magnesium and lead in 56 vol% PZT suspensions are 15 and 35 mM, respectively. The viscosity of 56 vol% PZT suspensions with 0.5–1.0 wt% magnesium citrate and 2 vol% glycerol diacetate is higher than 30 Pa s at 60 °C for 30 min which is sufficient to coagulate the suspensions. The coagulating time is 60–90 min at 50–70 °C. The compressive strength of the coagulated wet samples decreases with the increase of coagulating temperature, but increases with the increase of magnesium citrate content. The strength is in the range 1.5–2.8 MPa which is sufficiently high for demolding and handling without deformation. Dense PZT ceramics sintered at 1250–1280 °C show homogeneous microstructures with relative densities of 99.2–99.7% and good piezoelectric properties compared with a traditional die pressing method. [ABSTRACT FROM AUTHOR]

Direct coagulation casting via controlled release of high valance counter ions (DCC-HVCI) has been reported in recent years. In this paper, concentrated yttria-stabilized zirconia (YSZ) suspensions were coagulated using DCC-HVCI method with magnesium citrate as coagulating agent assisted by pH shift in the presence of glycerol diacetate. The effect of ammonium polyacrylate (PAA-NH 4 ) on the dispersibility of YSZ powder was investigated. The influence of concentrations of glycerol diacetate and magnesium citrate on pH and viscosities of YSZ suspensions was studied. The results indicate that concentrated YSZ suspensions can be coagulated by adding 2 vol% glycerol diacetate and magnesium citrate above 0.5 wt% at room temperature for 2–5 h. The compressive strength of coagulated wet samples is above 2.0 MPa. YSZ ceramics sintered at 1450 °C show homogeneous microstructures with relative densities of 98.9–99.2%. Flexural strength of YSZ ceramics is 869±84 MPa. [ABSTRACT FROM AUTHOR]