Effect of Two Kinds of Rare Earth Oxides on Zirconia Restoration

Objective: To evaluate the colouration of zirconia ceramic by adding two kinds of rare earth oxides. Methods: Added different concentrations of Fe2O3and CeO2in tetragonal zirconia poly crystals stabilized with 3Y-TZP powder compacted at 200MPa using cold isostatic pressure, and fully sinter. The chromaticity of sintered bodies was measured with spectrophotometer. Results: self-colored zirconia by two kinds of rare earth oxides: The lightness of zirconia by adding cerium oxides was about 85 and a* decreased slightly. The color shifted to more yellow-green color. The chroma of the ceramics became more intensity, the lightness decreased with the increasing of the content of ferrum oxides and the color change to red-yellow direction. Conclusion: Zirconia ceramic could be colorized by Fe2O3and CeO2.

Porous Silicon Nitride Prepared by Cold Isostatic Pressure

Porous silicon nitride with pore forming agent of starch were prepared by cold isostatic pressing, forming problem of complex shapes were solved by methods of carbonization of starch and decreasing forming pressure. Products of porous silicon nitride had the performance parameter with density 1.5g/cm3, porosity over 55%, bending strength over 100 MPa.

Sintering of the ultrahigh pressure densified hydroxyapatite monolithic xerogels

Dense and translucent ceramics were prepared by sintering of cylindrical preforms of hydroxyapatite extruded from xerogels. Extruded specimens were dried as monoliths and then consolidated by applying cold isostatic pressure, ranging from 500 to 1500 MPa. Upon heating the samples began to densify at 610 °C, and the densification/sintering was completed at 870 °C as was evidenced by the dilatometry plot indicating no further shrinkage. The sintered specimens thus formed were translucent in appearance. Further heating of the samples up to 1200 °C resulted in their “bloating” or creation of pores in the originally dense matrix. Pore creation within the structure is reproducible, it proceeds from the surface to the interior of the sample, and its spreading can be thermally controlled. Pore evolution within the single phase dense polycrystalline material is not related to the frequently occurring phenomenon of microcracking in ceramics during cooling.