Preparation Of Y₂O₃ Uniformly Coated AlON Powder For Ceramics

In this thesis,single-phase AlON powders were successfully synthesized by aluminothermic reduction nitridation method,and then the as-synthesized powders were milled using planetary ball-milling,followed by the treatment of hydrolysis resistance.Thereafter,the sintering aids were introduced through the chemical precipitation method to coat the powder surface uniformly.Finally,AlON ceramics were prepared by pressureless sintering.The effects of particle size of alumina,raw material ratio,mixing mode and reaction temperature on the morphology and phase of AlON powders were studied.In addition the influences of milling parameters on the phase and morphology of powder after ball-milling was investigated.In this work,we also to explore the effects of phosphoric acid treatment on the phase,morphology and hydrolysis resistance of powder.Dependence of density,phase and morphology of AlON on ceramics sintering temperature and introduction method of sintering aids.The raw material alumina with particle size of 500nm and Al powder with particle size of 1-3 μm was mixed through the roller method to obtain the mixture of AlN content of 27mol%.Pure-phase AlON powders with maximum particle size of about 5μm were synthesized at 1800℃ for 3h.After ball-milling with the speed of 250r/min for 30h,the AlON powder with uniform particle size distribution and a maximum size of 500nm can be obtained.The AlON powder exhibited obvious hydrolysis resistance after phosphoric acid treatment.Using 0.5wt%Darvan C-N as a dispersant,a well-dispersed AlON aqueous suspending solution containing Y(NO3)3 were obtained.Then add ammonia water with a concentration of 0.01mol/L to pH=9.1.Thereby,uniform coating of Y2O3 sintering aid was formed.Finally,the AlON ceramics with relative density of 98.61%were successfully prepared by pressureless sintering at 1920℃.It was found that pores only remained at the grain boundaries.Compared with those prepared by the conventional addition method of sintering aids,the AlON ceramics prepared by chemical precipitation method with sintering aids had higher density,fewer porosity andsmaller pores.Figure[60]table[10]reference[102]...