| The advantages of green compacts formed by cold isostatic pressing (CIP) are high strength, high density, homogeneous density and so on. Especially, the CIP could achieve near net-shape or net-shape forming, and avoid external volume change during nitridation, which made it possible for the ceramic products with reduced manufacture cost and even without additional processing.The effects of water introduction, binder amount, filling process and pressing technique on the molding of silicon powder were studied in this paper. The moulds design was studied based on thermocouple-protection tube, nozzle, crucible and squeeze head. Additionally, the sintering process of reaction-bonded silicon nitride was investigated. The main conclusions are shown as follows:(1) The relationship of the fluidity, packed density, compression ratio of the silicon powder, the shape, strength of the green compacts and the mount of the polyvinyl alcohol (PVA) and water was discussed. The controlled proper amount of water and PVA are 0.5~1wt% and 15wt% respectively.(2) The vibration frequency is a key factor on the filling and molding of the silicon powder. While the vibration frequency is equal to or less than 29Hz, the velocity of densification accelerates with the elevated frequency, the powder packed is homogeneous, and the green compacts are well-molded. While the vibration frequency is changed from 30 to 50Hz, the powder come into being sympathetic vibration, which make the powder difficult to be densification and inhomogeneous, and the green compacts will be lamination crack. The vibration frequency is finally determined to be 26~29Hz, and the vibration time to be 110-130s.(3) The molding pressure is an important factor on the performance of compacts. The densification molding pressure of hard brittle material is higher than that of plastic material because of the higher compression strength of hard brittle material. For the hard brittle silicon powder, the density and the strength of the green compacts increase with increasing the forming pressure. When the pressure reaches up to 275MPa, the density and strength gradually approaches constant (the density is about 1.61 g.cm-3, and the strength is about 2.0MPa.). Dwell time and forming pressure are determined to be 20s and 200MPa, respectively. The axial density deviation of compacts pressed with determined process is within ±1.8%, and the radial densitydeviation is within ±0.9%.(4) The moulds design was studied for the four type components. The powder can be regularly filled when applying the supporting steel pipe. Using the flexible stress transfer system, the rigidity match between the closing plug and the rubber canning is fulfilled, some key technical matters on the terminal effect, the lose angle and side phenomena is solved, the quality and the yield is improved, and the accurate compacts shaped is to be true. For the flexible stress transfer system, we present an application for patent which is a CIP device for molding a ceramic tube with blind hole. Moreover, thermocouple-protection tube is manufactured successfully, and the length is 700mm, outer diameter is 28mm and inner diameter is 16mm. The thin crucible (the wall thinckness is 2mm) is also pressed successfully. The radial tolerance of the products is confined within ±0.2mm, and the terminal shape is regular.(5) According to the principle that the mount of residual silicon is less and the silicon flowing phenomena is avoided after sintering, the best nitride process of the step sintering is determined, in which the rate of lifting temperature is 5℃/min and hold time is 1h at 1300℃, 2h at 1350℃, 8h at 1380℃, and 4h at 1395℃. The residual silicon mass percent is about10~15%, the material density is 2.43~2.52g.cm-3, the bending strength is 190.7-211.6MPa, and the open porosity is 14.21-15.24%.
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