Study On Gelcasting Forming Process Of ZrO₂ All-ceramic Crown

As living standards rise, the demand for all-ceramic crown is increasing, then zirconia(ZrO2) ceramics make the best preparation materials for all-ceramic crown as its excellent biocompatibility and anti–corrosion. The traditional method of preparing ZrO2 all-ceramic crown is CAD/CAM technology, the ceramic need to be pre-sintering firstly, its progress is complex and inefficient which seriously limit its development and application. Gel-casting is a newly developed ceramics forming process, and has numerous benefits, so it is very suitable for preparing the complex shape and nontoxic biocompatibility, such as all-ceramic crown. In this paper, gel-casting is used to fabrication the ZrO2 all-ceramic crown using nano-ZrO2 powder as raw material. Meanwhile, we explore and research the entire process.The stability and dispersion of ZrO2 ceramic slurry is studied. The influence of the slurry pH and the amount of dispersant on slurry has been explored to get the optimal content. The results show that the zirconia slurry of 50%( by volume) in solid content with viscosity 300 mPa.s was obtained by adding the dispersant of PAA-NH4 with pH11.Regarded the zirconia slurry of 50%( by volume) in solid content as object,analyzed the influence of initiator, catalyst and temperature on gelation time during the whole process. The results show that: when the added initiator with mass fraction of 0.6wt.%, catalyst’s mass fraction reaches 1.8wt.%,it can quickly gel reaction, and when the slurry is placed in a thermostatic water bath at 60 ℃, the gelation time can be shortened to 6 ~ 10 min.Air drying method has been used to study the drying process of the gel-casting, strictly controlled the drying process temperature and humidity, and study the shrinkage and mechanical properties of green body drying, further proof slurry with a high solid volume fraction and an appropriate organic monomer ratio, can produce the green body with excellent performance. The experimental results show that: under the conditions of the prior as low temperature and high humidity, the later as high temperature and low humidity, can obtained a green body with complete shape and uniform shrinkage.The ZrO2 ceramic is pressureless sintered and sintering properties are researched. The sintering method is decided according to the TGA-DSC data of AM and green body, The microstructure properties and mechanical property of the sintered body have been investigated. We find that the ZrO2 sintered body with stable phase and reasonable component is obtained at 1450℃,and the flexural strength is 763.1MPa;the ZrO2 sintered body with an initial zirconia slurry of 50%( by volume) has a bulk density of 5.45g/cm3 and a relative density of 98.18%,and its flexural strength is 716.2MPa.