| [Objective]Research the influence of different heating rate on the cutting nano-oxidation of zirconium ceramics linear shrinkage, compressive strength and other mechanical properties and microstructure, and explore the suitable sintering process, then to provide a theoretical basis for the development of high performance zirconia ceramic.[Methods]1. The specimens production and sintering:Choose the market sales IPS e.max ZirCAD CAD/CAM all-ceramic basal crown materials, produce the required experimental specimen on request, use Programat(?)S1high-temperature crystallization furnace after polishing and drying, heat to1500℃at200℃/h,400℃/h,600℃/h,1000℃/h heating rate,2h heat preservation, then complete the second sintering.2. Physical and chemical properties test of The specimens:Prepare all together20items specimen which meet the requirements, each group of5items.Measure and analyze linear shrinkage, three-point flexural strength, Vickers hardness and fracture toughness of the material at different heating rates. By scanning electron microscopy and X-ray diffraction observe the fracture surface of the specimen and the surface microscopic morphology and fracture surface of the crystalline structure, and then analysis the statistical data.[Results]1. Linear shrinkage rate: Linear shrinkage of zirconia material was in rendering an upward trend with the improvements of the heating rate. Upward trend slowed down in the heating rate to400℃/h. 2. Sintered density and apparent porosity: With the rise of heating rate, the relative density of the zirconia ceramic was in rendering downward trend, the maximum relative density was at200℃/h, the relative density was99.9%; the porosity was in gradually increasing trend.3. Three Point Flexure Stress: With the rise of the heating rate, the three Point Flexure Stress of the zirconia ceramic was in rendering downward trend, the maximum flexural strength was at200℃/h group, its three-point flexural strength was873.22Mp.4. Vickers hardness and the fracture toughness: With the rise of the heating rate, the vickers hardness of the zirconia ceramic was in rendering downward trend, the maximum Vickers hardness values appeared in the200℃C/h group, the Vickers hardness value was11426.67Mpa; with increasing heating rate, the fracture toughness of zirconia ceramics was also in rendering downward trend.5. Scanning electron microscopy (SEM) observation: With the rise of the heating rate, the internal porosity of zirconia ceramics sintered body slightly increased, some grain grew and in uneven size, when heating rate was at200℃/h, the fracture pattern was mainly intergranular fracture, and then gradually transformed into a hybrid fracture with the rise of the heating rate, that the existence of both intergranular fracture and transgranular fracture could be also seen.6. X-ray diffraction (XRD): The main phase of the materials are tetragonal, with the increase of the heating rate, a few of single monoclinic phase crystals began to appear.[Conclusions](1) Under the condition of sintering temperature of900℃/1500℃and defferent heating rates,when the heating rate was200℃/h3Y-TZP has the best mechanical properties, it also can completely meet the requirement of all ceramic materials. (2) By400℃/h,600℃/h,1000℃/h heating rate for3Y-TZP for sintering will reduce zirconia mechanical performance, but the impact of the heating rate rise with slow; At the same time with the higher heating rate of sintering3Y-TZP specimens still have enough mechanical properties, basicly they also can meet the requirements of the all ceramic materials.(3) In the clinical sintering for3Y-TZP, we should choose the low heating rate for sintering first, in order to ensure that the restoration has enough mechanical properties and long-term effect. |
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