Synergistic Sintering Of Solid-liquid Phases And Densification Control Of B₄C & PZT Ceramics

The advanced ceramic have been widely used in the fields of high technology such as aerospace,new energy,nuclear industry and military industries and they also show huge potential in many other fields due to their excellent mechanical properties and many unique acoustical,optical,electrical and magnetic physical properties.Many developed countries,like United States,Japan,European countries and Russia have invested deeply in developing advanced ceramic and improved the research level significantlyl.The sintering density is a key factor that the mechanical properties and other unique functions could be achieved,which has been the main evaluation indicator of optimal design of sintering processing technology parameters.In this research work,based on the view point of adjusting and controlling main factors influencing sintering density of ceramics,an effective method which controlling sintering density to achieve densification sintering during synthesizing ceramics has been explored,which could meet the request of application properties of ceramic materials and products,achieve decreasing manufacture cost and reducing energy loss,provide more complete theoretical support for forming mechanism and improve application of advanced ceramic in high technology fields and industrial manufacture.The key points of research focus on fabrication of boron carbide?B₄C?structure ceramic and lead zirconate titanate?PZT95/5?piezoelectric functional ceramic with high sintering density at low sintering temperature.The sintering test of synergistic sintering effect of solid-phase and liquid-phase sintering aids of different composition,sintering temperature,sintering time were carried out,the characterization of microstructures and mechanical properties were investigated.Based on the comparison and analysis of microstructure and properties of different kinds sintering aid,based on sintering kinetics and Arrhenius equation;the compensation analysis of the effects of sintering temperature on the apparent activation energy and fitting parameter of kinetics equation were investigated.The comprehensive evaluation factor?which shows the inherent relationship between the green density,theorical density and sintering density has been adopted to study the sintering processing.Considering of temperature compensation,apparent activation energy and parameters of equations mentioned above,the densification model of synergistic sintering with both solid-phase and liquid-phase sintering aids is a function of sintering temperature,sintering holding time,composite and initial green packed density.And the accuracy of this model was assessed by the mean absolute error and correlation coefficient?R?.The synergistic sintering effect of solid-phase and liquid-phase sintering aids are proposed to form solid solutions and in-situ reacting liquid phases,by using pressureless sintering method,the influence of carbon on B₄C sintering performance was studied.The inorganic carbon?carbon black?and organic carbon source?phenolic resin?were chosen to be different varieties of carbon sources,this study was focused on that the influence of relative sintering density,microstructure and mechanical properties of B₄C ceramic with addition of carbon black alone or phenolic resin alone or mixture of carbon black and phenolic resin,the contribution of carbon to the toughness of the ceramic were discussed.The B₄C ceramics with mixture of carbon black and phenolic resin?carbon black to phenolic resin are 11:3?has the optimized properties,that relative sintering density,bending strength and fracture toughness achieve 94.8%,322 MPa and 3.17Mpa�m^1/2,respectively;the microstructures of B₄C samples show that the very fine grains and pores;and the grain and pores evenly distribute across the samples.Carbon have contributed the toughness of the ceramic;the toughening mechanism is due to the crack deflection and the microcrack toughening.Based on synergistic sintering effect of solid-phase and liquid-phase sintering aids,the influence of oxide on B₄C sintering performance was studied as well.The added silicon carbide was fixed with the content of 0.2wt%and fixed carbon content with the radio of 3.5:1?black carbon and phenolic resin ratio?was selected,the B₄C ceramic were fabricated by adding alumina oxide?Al₂O₃?and yttrium oxide?Y₂O₃?as liquid phase sintering aids.The influence of sintering temperature and composition on microstructure and mechanical properties of B₄C ceramic were investigated respectively.The results show that in Al₂O₃-Y₂O₃-C-SiC-B₄C system which could reduce the sintering temperature to 2200?,and adding mixture of Al₂O₃ plus Y₂O₃,the optimized properties including relative sintering density,bending strength,hardness and fracture toughness achieve 95.2%,358MPa,26.44Gpa and3.31MPa?m^1/2,respectively.The microstructures and densification mechanism of B₄C samples which were produced by synergistic sintering effect of solid-phase and liquid-phase sintering aids were studied by means of analysis methods of Scanning Electron Microscopy?SEM?and Energy Dispersive Spectrometer?EDS?.The results show that the in-situ synthesized liquid phase Y₃Al₅O₁₂?YAG?promote and improve the densification sintering of Al₂O₃-Y₂O₃-C-SiC-B₄C sintering systems;But the excess liquid phase could lead to abnormal grain growth and coarsening,which damages the densification of B₄C ceramics.Experiment of the direct adding Y₃Al₅O₁₂?YAG?powder into B₄C sintering system also gave indirect evidence to this conclusion.The results of anti-penetration performance of ceramic composite armor show B₄C ceramic have potential applications as superior protection materials in military personnel and vehicle equipment.Based on the study of synthesize of B₄C ceramics,the study of densification synthesize PZT95/5 piezoelectric ceramic by synergistic sintering with both solid-phase and liquid-phase sintering aids at low sintering temperature was carried out,firstly the effect of phase structure,sintering properties and piezoelectric properties of PZT95/5 doped with cadmium oxide?CdO?were systematically studied.The research shows that the sintering temperature could be reduced from 1350?to1100?and a pure perovskite-phase was obtained and no secondary phase was observed,by doping 0.5mol%or 1.0mol%CdO alone,the sintering properties and the piezoelectric properties were very similar to the PZT95/5 sintered at 1350?.By fixing CdO content,CuO and Lithium carbonate?Li₂CO₃?were used as main liquid phase sintering aids,the effect of phase structure,sintering properties and piezoelectric properties of PZT95/5 doped with different content of CuO and Li₂CO₃were investigated.The research shows that the sintering temperature could be further reduced to 1100?and a pure perovskite-phase was obtained and no secondary phase was observed.The experimental results show that PZT95/5 ceramic using liquid sintering aid of Li₂CO₃ have better sintering properties and excellent piezoelectric properties under 1050?.On the basis of the powders sintering synthesis theoretical and sintering kinetics equations,considering of temperature compensation,apparent activation energy and parameters of equations mentioned above,the densification model of synergistic sintering with both solid-phase and liquid-phase sintering aids is a function of sintering temperature,sintering holding time,composite and initial green packed density.The guideline to evaluate the accuracy assessment of model are mean absolute error and correlation coefficient?R?.The correlation coefficient of predicted value and measured value of B₄C structure ceramic and PZT95/5piezoelectric ceramic prepared at different sintering conditions are compared.The results show that there is a strong correlation between the calculated membrane and predicted value,and mean absolute error is less than 20%.