.¦Â-sialon/al <sub> 2 </ Sub> O <sub> 3 </ Sub> Synthesis Of Composite Powders And ¦Â-sialon Combination Of Spinel Composites

The objective of this work was to synthesizeβ-SiAlON/Al₂O₃ powders with different contents ofβ-SiAlON.β-SiAlON/Al₂O₃ powders were prepared wth bauxite and light burned gibbsite as the raw materials and Al/Si and C/Si as combined reduction agents.The heating-up procedure of reduction-nitridation was determined by TG-DSC,phase composition examined by XRD and microstructure observed by SEM and EDS.β-SiAlON/Al₂O₃ powders with differentβ-SiAlON contents were designed with the highestβ-SiAlON content of 97%and the lowest content of 33%. In-situβ-SiAlON bonded spinel composite materials were prepared based on the optimal formulations and procedures for synthesizingβ-SiAlON/Al₂O₃ powders.The influence of the content of in-situβ-SiAlON on the properties of the composite materials at room temperature was investigated for acquiring the optimal formula of the composite materials.The results show that SiO₂ was not present in theβ-SiAlON/Al₂O₃ powder synthesized by ordinary furnace and microwave furnace with reducing agents Al/Si and C/Si,indicating that SiO₂ was transformed intoβ-SiAlON.Bauxite-basedβ-SiAlON/Al₂O₃ powder with Al/Si(FAS) as reducing agents was synthesized at relatively low temperature and the contents ofβ-SiAlON in theβ-SiAlON/Al₂O₃ powders could be controled.In contrast,bauxite-basedβ-SiAlON/Al₂O₃ powder with C/Si(FCS) as reducing agents had to be prepared at higher temperature(1500℃). Alumina-based samples(AAS) with Al/Si as reducing agents were relatively difficult to synthesizeβ-SiAlON/Al₂O₃ powders and the contents ofβ-SiAlON inβ-SiAlON/Al₂O₃ powders were hard to control.Bauxite-based samples with Al/Si(FAS) as reducing agents embedded with the silicon carbide powder was sucessfully transformed intoβ-SiAlON/Al₂O₃ at low temperature(1200℃),which is lower than that embedded with carbon.It is found that the contents ofβ-SiAlON inβ-SiAlON/Al₂O₃ powders fired at 1400℃with SiC embedding were in accordance with theβ-SiAlON contents as designed.The synthesizing temperatures for FAS samples with microwave heating was decreased by about 150-200℃and the holding time shortened by about 2/3 compared with ordinary furnace heating.The contents ofβ-SiAlON in theβ-SiAlON/Al₂O₃ powder could be relatively controlled.β-SiAlON/Al₂O₃ powder was synthesized from AAS samples with microwave furnace at lower temperatures compared with ordinary furnace.Phase distribution was observed by scanning electron microscopy and energy dispersive spectrometer.The results show that residual Al₂O₃ inβ-SiAlON/Al₂O₃ powder was wrapped byβ-SiAlON,which indicates thatβ-SiAlON/Al₂O₃ powder may have the characteristics of pureβ-SiAlON though the powder is not pureβ-SiAlON powder.Bauxite-basedβ-SiAlON/spinel composite materials were prepared at 1400℃. The composite materials with designed 20wt%in-situ℃-SiAlON possessed apparent porosity of 16.2%,MOR of 24MPa and CCS of 130MPa at room temperature.