Preparation Process And Mechanical Properties Of Al₂O₃-Based Composite Ceramics

The Al₂O₃-based ceramics are essential structural materials, which havebeen widely used as electronics, machine, aerospace industry, etc. But lowerfracture toughness, thermal shock resistance and creep resistance limits theirapplications and development. Recently, many researchers have tried to promatethe mechanical performances of alumina ceramics though doping polyphasematerials. The toughening alumina ceramics dispersed with t-ZrO₂ and ductilemetal has been paid more attention in the fields of composite ceramics materialstoday.This paper focuses on fabricating of Ni/ZrO₂/Al₂O₃ composite powders bycoprecipitation-hydrothermal processing, comparing with the Al₂O₃, Ni/Al₂O₃,ZrO₂/Al₂O₃ and tri-phase composite in the applied magnetic field, studying themechanics of powders formation and increasing fracture toughness by FESEM,TEM and XRD. Alumina precursor and zirconia precursor prepared by coprecipitation,nickel precursor by chemical reduction method which were mixed and addedinto an autoclave and the mixture was heated for 12h at 300℃under autogenouspressure of 1,4-butanediol solution. The 12vol.ï¼…Ni/12vol.ï¼…ZrO₂/Al₂O₃composite powders fine dispersed was obtained. The results show that aluminais boehmite, the t-ZrO₂ and Ni inclusions are uniformly distributed in thecomposite ceramic with the diameters of t-ZrO₂ and Ni particles are 5-10nm and80-100nm respectively.Mechanical properties and toughening mechanism of composites in theabove mentioned at normally continuous sintering were investigated. Therelationship between mechanical property, sintering process and.microphotograph were analyzed. The experimental results show that the volumedensity of composite is 4.671g/cm³ and relative density is 97ï¼…. The t-ZrO₂particles and Ni ones of composite ceramics, are smaller than the critical one0.1μm and 0.5-1μm, respectively. The mean microhardness of Ni/ZrO₂/Al₂O₃composite is 11.6GPa. The fracture toughness of tri-phase composite is 9.56MPa·m^0.5. The deformed nickel particles can be observed on the fracture surfaceby FESEM.The second part is non-alumina prepared from the industrial sludge. Theindustrial sludge was investgated by EDS. There are several tens elements, themost was aluminum. The industrial sludge consists of alumina hydrate andamorphous. Preparation of nonalumina by extracting aluminum hydroxide from industrial sludge is feasible method. Two kinds of method has been proposedaccording to the elements, that is carbon dioxide injection method andhydrolysis method.The industrial sludge was dissolved in 2M HCl solution, then slowlytitrated by 2M NaOH. The cleaned sodium aluminate was obtained by strictlycontrolling the Ph value. The aluminum hydroxide powder was prepared withcarbon dioxide injection method and hydrolysis method by washing severaltimes and drying. Nonalumina powder was obtained by calcining at 1100℃for2h. The sludge, Al(OH)₃, andα-Al₂O₃ powder were characterized by FESEM,EDS and XRD. The results indicate that double hydrolysis is simpler, lessimpurity and higher output than other. The fact that the average purity ofaluminum oxide can reach 98ï¼…is demonstrated by EDS analysis. The doublehydrolysis method is fit forα-Al₂O₃ production from industrial sludge.