Key Engineering Materials Vols. 336-338

Abstract: Zirconia Ferrule is a key part for manufacturing fiber connectors. The ceramic injection molding (CIM) process of the optical ferrule was simulated with the commercial CAE software moldflow. In order to obtain the optimum results, the orthogonal method was introduced to discuss the influence of each parameter such as die temperature, melt temperature, ram speed and gate dimension with the two kinds of distribution layout system respectively. The simulation results show that the curved distribution runner system is more suitable than the rectangular distribution one in the optical ferrule molding. Moreover, the effect of gravity on the ceramic injection molding process was discussed for determining a more reasonable balanced runner system of the special designed two-plate mold with six die cavities. It was found that short shot occurred at the top of the die cavity while other five cavities were filled well in the original designed mold. And when the top die cavity’s round runner with section diameter of 4.0mm was increased to 4.17 mm, each cavity was balanced filled without short shot.

Abstract: In previous report, we succeeded in preparing dense nano-sized ceramics with the composition of Y- α-sialon (m=1.35, n=0.675) by high-energy mechanical milling followed by spark plasma sintering. The superplastic deformation of the obtained nano-ceramics was studied in this report. A good ductility of the nano-sized ceramics has been confirmed, which arised from the nano-sized grains and large amount of transient liquid phase. The effects of deformation on the phase and microstructural evolution were also studied. The nano-sized grains promoted the formation of elongated α-sialon grains during post-annealing at 1850oC for 3 h, which would strengthen and toughen the deformed ceramics.

Abstract: Gelcasting was used to form large and thin walled shapes of fused silica. Large square crucibles of 720x720x420 with a thickness of 14mm for polycrystalline silicon melting and fused silica radoms of up to 500mm in diameter and 1000mm in height with a thickness of 10 to 12 mm have been formed and sintered with excellent homogeneity. Process parameters have been discussed such as dispersion of the ceramic particles in the casting slurry and design of the casting moulds. Simultaneous vibration treatment was applied during the casting process for more homogeneous structure of the formed bodies for some of the casting shapes.

Abstract: According to the heat transmission theory, in the aid of computer, the temperature distribution in the cylinder cavity was calculated. The temperature of the mould has much influence on the time for the injection material’s temperature of the cavity center to drop to the injection material softening temperature. The influence of the processing parameters on the density of the injection molding specimens was also investigated. It turns that the injection molding specimens’ density changes little with the increase of injection temperature and pressure, but changes a lot with the increase of holding pressure time.

Abstract: A new dewaxing method for low-pressure injection molded ceramics is presented. Supercritical extraction with carbon dioxide was used to remove paraffin wax from the ceramic green parts. The composition of organic additives for low-pressure injection molding feedstock and the extraction condition for the green parts were investigated. Moreover, the properties of sintered ceramic samples dewaxed by supercritical carbon dioxide were compared with those by thermal dewaxing. The results show that the new binder system containing 50wt% paraffin wax, 35% bee wax and 15% stearic acid fulfills the requirements of both low-pressure injection molding feedstocks and supercritical dewaxing, where the feedstock has high fluidity, low viscosity and quick solidification. The efficient extraction condition for supercritical dewaxing from the green parts is at 30MPa pressure and 45°C. Under this condition, defect free ceramic green parts can be obtained. Dewaxing methods have significant influence on the properties of sintered parts. The mechanical properties of the sintered sample can be improved by supercritical dewaxing. With this method, the bending strength of sintered samples (σ = 331.6 MPa) is higher than that obtained by thermal treatment (σ = 312.3MPa). The sintered samples dewaxed by supercritical CO2 have shown the property of higher density and less distortion compared to the thermal dewaxing method. Moreover, with supercritical extraction the dewaxing time can be reduced to about one tenth of the time required by thermal dewaxing.

Abstract: Water-soluble binder based injection molding of submicrometer-sized and stabilized zirconia was reported in this paper. The binder phase is chosen as the mixtures of polyethylene glycol, high-density polyethylene, polyvinyl butyral and stearic acid. Binder removal is accomplished by a two-steped process. The water-soluble constituent is firstly removed by dissolution in the water and the remaining is removed through the followed thermal treatment. The apparent viscosities of different kinds of feedstock were tested. The influences of water-leaching time and temperature on the efficiency of PEG removal were discussed.

Abstract: Two kinds of commercial alumina compacts made by injection molding with different solid loading are studied. Solid loading is the key factor for the injection molding process and the properties of green body and sintered compacts. The results show that higher solid loading leads to better properties of the compacts such as density and fracture strength, however the viscosity of the feedstock would increase. Smaller sized alumina powder leads to a higher critical solid loading value. Macroscopic defects such as voids and cracks could be introduced into the injection molding samples if the molding variables are not optimized. The properties of sample are improved by adjusting the variables such as injection pressure, holding pressure, holding time and barrel temperature.

Abstract: A heated sprue device for ceramic injection moulding was used to research the defects in injection-moulded technical ceramics. By use of the heated sprue device, the problem of sprue solidification was resolved and the density of the injection moulding specimens was increased while the defects eliminated. The influence of the processing parameters on the defects of the injection molding specimens was investigated in detail by X-ray radiography camera and photograph. It turns that the sprue solidification time has much influence on the defects in injection-moulded technical ceramics. Reasons causing the results above were also analyzed. Based on the research, bars of 20mm in diameter without macroscopic defects and turbine blade of fine property with Si3N4/SiC(w) materials were prepared by injection moulding.

Abstract: In the present work the influence of two different thermal debinding atmosphere, vacuum and air, on the properties of 5wt% Y2O3-doped aluminum nitride (AlN) ceramics was investigated. The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compact was fabricated by employing powder injection molding technique. The polymer-wax binder consists of 60wt% paraffin wax (PW), 35wt% polypropylene (PP) and 5wt% stearic acid (SA). The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. After the removal of binder, specimens were sintered at 1850˚С in nitrogen atmosphere at atmospheric pressure. The result reveals that debinding atmosphere has significant effect on the thermal conductivity and densification of AlN ceramics. The microstructure and secondary phase identification was determined by scanning electron microscopy and X-ray diffraction. The thermal conductivity and density of injection molded AlN ceramics are 177.3W·m-1·K-1 and 3.31g·cm-3 in the air and 200.8W·m-1·K-1 and 3.28g·cm-3 in the vacuum.

Abstract: Single carrageenan and combinations of carrageenan with other polysaccharides, including locust bean gum and konjak gum, are applied to form green bodies of microwave ceramics by gel-casting technique. Similar dielectric properties of the samples are achieved and compared with ceramics formed by dry pressing method.