Preparative Technique And Properties Characterization Of Fused Silica Ceramics

The crucible is used as a vessel for loading polycrystalline silicon ingot. It has a harsh use conditions, which has to work continuous above 40 hours under the high temperature 1500℃one time.The quartz ceramics have outstanding performance, such as, low thermal expansion coefficient, good thermostability, resistance-to-bake, low thermal conductivity etc, so they are fit for loading polycrystalline silicon. At present, there are two preparation methods to make Fused Silica Ceramic Crucibles, one is Slip Casting, and the other is Gel-Casting. The paper preparated Fused Silica Ceramic Crucibles by Gel-Casting and improved their volume density and so on by adding Si₃N₄, which Caused their physical properties to close or better than the Ceramic Crucibles made by Slip Casting for making up for defects of Gel-Casting.Fused Silica ceramics were fabricated by the gel-casting method. Acrylamide (AM) was used as a catalyst, N,N,-methylenenebisacrylamide (MBAM) was used as a cross linker and ammonium persulfate (APS) was used as an initiator. The influences on the properties to quzrtz-ceramics were studied by XRD, SEM and so on. The results indicate that there is no appearance of the cristobalite phase in the samples. The quartz grain composition is reasonable, and the samples structure is even texture. The cold bending strength is 23 MPa, the cold crushing strength is 90 MPa, the volume density is 1.7 g/cm³, and the apparent porosity is 16% under the condition-the solid content is 50%, which physical properties are lower than the samples made by the Slip Casting. Some reaction factors (such as volume content, pH value) were studied, which influence on the slurries properties of Fused Silica ceramics; Some other reaction factors (such as curing temperature, AM, APS) were studied too, which influence on the slurries curing time of Fused Silica ceramics. The results indicate that the high quality slurries are obtained under these conditions-the solid content is 80%, the pH value is 3-5. And curing time of slurries are relatively stable, which meet the slurres molding, that under these conditions-the curing temperature is 60℃, AM is 6 g/kg, APS is 0.5-2.1 g/kg. The paper also preliminary studied the Acrylamide (AM) curing mechanism of gel-casting method.The influence on the properties to quzrtz-ceramics for adding Si₃N₄ was studied by XRD, SEM and so on via the Fused Silica ceramics were fabricated by the gel-casting method. The results indicate that the addition of Si₃N₄ enhances the quzrtz-ceramics'sintering and restrains the appearance of the cristobalite phase. The cold bending strength and volume density increase with Si₃N₄ content, while the apparent porosity decreases with Si₃N₄ content. When the Si₃N₄ content is 2%, the cold bending strength is 37.13 MPa, the volume density is 1.96 g/cm3, and the apparent porosity is 11%.While adding Si₃N₄ caused conglobation of slurres, the paper used three ways to remove the conglobation of slurres caused by adding Si₃N₄, The results indicate that adding PEG and ultrasonic dispersion can't remove slurres conglobation, but, slurry dispersion with ball-milling for 6h can remove the slurres conglobation.The influence on the properties to quzrtz-ceramics for sintering temperature was studied. The results indicate that the cold bending strength and volume density increase with sintering temperature enhances, while the apparent porosity decreases with sintering temperature decreases under the sintering temperature 1150℃-1190℃. When the sintering temperature is 1210℃, there are appearances of the cristobalite phase in the samples. So the sintering temperature must below 1210℃.Lastly, the paper did some research on Fused Silica Ceramics Crucibles for their properties characterization, and found an appropriate characterization method form different ways, and formulated measurement standard.