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The Sintering Process and Mechanical Properties of Zirconia/Calcium Phosphate Compound Ceramic

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Tutor: WangFuPing
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: dental ceramics,sintering process,mechanical properties,calcium phosp
CLC: R783.1
Type: Master's thesis
Year:  2012
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Abstract:
Now the civil independent dental ceramic materials production is still in itsinfancy,so most of the raw materials are needed to be imported abroad. Themachinable dental ceramics that made by our country have many defects,low flexuralstrength,bad toughness and the hardness is too high.The composite ceramic in this studyis prepared by doping calcium phosphate which has high biocompatibility in zirconiamatrix.After sintering,we will get machinable composite ceramics.The calcium phosphate powders were prepared by the sol-gel technology.,mixphosphate powder with the zirconia powder,then after optimization of the sinteringprocess,the zirconia/calcium composite ceramics are prepared.After studyingmechanical properties of the composite ceramics prepared and analyzing the factorsaffect,we got that the most important sintering process was the sintering temperature.Atdifferent sintering temperatures,there always the monoclinic phase of zirconia andtetragonal zirconia exist in the composite ceramics.And the cubic solid solutionc-Ca0.15Zr0.85O1.85will appear in the sintering at1400¡æ.At the same time,we shouldtest the fracture of the ceramic composite and show the microstructure by scanningelectron microscopy.Then it can be proved that the main fracture mode of ceramiccomposite are transgranular fracture and intergranular fracture,when the sinteringprocess is appropriate,transgranular fracture is the main.Some sintering processes like holding time, heating rate and calcium phosphate contentalso have important effects on the mechanical properties.Holding time and thecomposite ceramic heating rate mainly affect the density of the porosity and grainsize,therefore, the appropriate holding time and heating rate is very important on themechanical properties of composite ceramics.The content of calcium phosphate directlyaffects the mechanical properties of composite ceramics,the mechanical properties ofceramic composite linear increase with the reduction of calcium phosphate.But whenthe content of calcium phosphate is too low,the hardness of the ceramic composite willbe higher than the hardness of dental ceramics,so we need to select the content ofcalcium phosphate comprehensively.After the test it is proved that when the sinteringtemperature is1350¡æ, the holding time is4h,the heating rate of2.5¡ãC/min and theincorporation of calcium phosphate is35%, we will get to the best effect. The sintering of composite ceramic can be calculated by the calculation of the sintering activationenergy of composite ceramic,it is very important for making the sintering curve.Besideswe analyzed the mass transfer mechanism of composite ceramic sintering process basedon it, the macroscopic is mobile mass transfer and diffusion mass transfer,themicroscopic is atomic diffusion and ion diffusion.In the best sintering process,themechanical properties of Composite material is549MPa of the bendingstrength,140GPa of the elasticity modulus,9.1MPa.m1/2of the fracture toughness,and8.5GPa of the hardness,which are in line with the requirements of ceramics on themechanical properties.
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