New nano-sized Al2O3-BN coating 3Y-TZP ceramic composites for CAD/CAM-produced all-ceramic dental restorations. Part I. Fabrication of powders

Partially sintered 3 mol % yttria-stabilized tetragonal zirconium dioxide (ZrO2, zirconia) polycrystal (3Y-TZP) ceramics are used in dental posterior restorations with computer-aided design-computer-aided manufacturing (CAD/CAM) techniques. High strength is acquired after sintering, but shape distortion of preshaped compacts during their sintering is inevitable. The aim of this study is to fabricate new machinable ceramic composites with strong mechanical properties that are fit for all-ceramic dental restorations. Aluminum oxide (Al2O3)-coated 3Y-TZP powders were first prepared by the heterogeneous precipitation method starting with 3Y-TZP, Al(NO3)(3) center dot 9H(2)O, and ammonia, then amorphous boron nitride (BN) was produced and the as-received composite powders were coated via in situ reaction with boric acid and urea. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to analyze the status of Al2O3-BN on the surface of the 3Y-TZP particles. TEM micrographs show an abundance of Al2O3 particles and amorphous BN appearing uniformly on the surface of the 3Y-TZP particles after the coating process. The size of the Al2O3 particles is about 20 nm. The XRD pattern shows clearly the peak of amorphous BN among the peaks of ZrO2. (C) 2009 Elsevier Inc. All rights reserved.