| Background and objective: when tensile stresses acting at the crack tip induces pHase transformation of 3mol% yttria stabilized tetragonal zirconia polycrystals(3 Y-TZP),which is known as martensite pHase transformation toughening. So its mechanical properties,such as fracture toughness(about 8-10MPa·m(1/2))?elasticity modulus(about 200MPa)?flexural strength(about 900-1100MPa) are superior to other conventional dental ceramics. Measnwhile Y-TZP is an ideal dental ceramic with excellent biocompatibility?corrosion resistance and abrasive resistance. However the surface of Y-TZP will spontaneously occur t?m transformation initiated and accelerated by water penetration in the temperature range of 20-300? called low temperature degradation (LTD), which will influence its long-term service life life. In addition, Y-TZP is difficult to be processed lead to high production costs, and the bond strength between Y-TZP and veneering ceramics is poor. Synthesis composite ceramic is an ideal way to improve the anti-LTD and machinable property, the addition of Al2O3and BN can improve the fracture toughness ?anti-LTD and machinable property. The present research will study the preparation processes of nano-sized Al2O3-BN coating Y-TZP composite powder, including the best pH value for preparing the 3Y-TZP/3 wt%Al2O3, and the optimum calcination temperature of Al2O3 precursor and amorpHous BN for Al2O3-BN coating 3 Y-TZP powders.Methods: Prepared the 3Y-TZP/3 wt%Al2O3 composite powders by heterogeneous precipitation method, under the different pH values(6.5, 7.5, 8.5, 9.5), analysed through transmission electron microscopy(TEM) to choose the best coating morpHology. Al2O3 precursor prepared under the best pH value was calcined at diferent temperatures(800?,1000?, 1200?, 1400?), then amorpHous boron nitride (BBN) coating 3Y-TZP/3 wt%Al2O3 powder was prepared via in situ reaction with boric acid and urea(calcined with N2 at 850? 5h, 3h and 800? 5h, 3h). TEM and X-ray diffraction (XRD) were used to characterize.Results: ?The peripHery of Y-TZP particles were uniformly coated with Al2O3 precursor when pH was 8.5; at pH was 6.5 and 7.5, only a part of Y-TZP particles were coated with Al2O3 precursor; when pH was 9.5, Al2O3 precursor was homogeneous nucleation and did not coate around Y-TZP particles.?When Al2O3 precursor was calcined at 800?, the coating was amorpHous substance. When Al2O3 precursor was calcined at 1000? and 1200? the coating was spHerical particles concluded were Al2O3 by EDS.And there was no costing around Y-TZP particles, and the ZrO2 particles were agglomeration When Al2O3 precursor was calcined at 140°C. XRD shown that principal crystalline pHase were m-ZrO2 and t-ZrO2 after calcined at 800?, but principal crystalline pHase was t-ZrO2 after calcined at 101000? ?1200??1400?.?The peripHery of Y-TZP particles were coated with Al2O3 and amorpHous BN, and only a little AI-B-O was found when 3Y-TZP/3 wt%Al2O3/10 wt%BN (precursor calcined at 1200?) calcined at 800?for 5h with N2. XRD shown that the proportion of t-ZrO2 was maximum.Conclusions: pH 8.5 was best for preparing the 3 Y-TZP/3 wt%Al2O3 composite. For the preparation of Al2O3-BN coating 3Y-TZP powders, the the optimum calcination temperature of the Al2O3 precursor and amorpHous BN was 1200? and 800? 5h,respectively. |
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