Study Of Preparation And Properties Of Alumina-based Ceramic Microspheres

In this thesis the ceramic microspheres with high spherical, 100 m average diameter were prepared, with bauxite as the raw material. The properties including morphology, sphericity, internal structure, failure strength and size distribution of the microspheres between pre sintering and post sintering were investigated.The preparation of high dispersion stability and good fluidity bauxite slurry was researched. The results show that both of the ionic dispersants which are sodium polyacrylate (PAAS) and sodium hexametaphosphate (SHMP) have little influence on the dispersion stability of the bauxite slurry in the acid condition, but in the alkaline condition, both of PAAS and SHMP can reduce the Zeta potential and increase the dispersion rate, which lead to the slurry hold on high dispersion and stable state. UN-adjust the pH value of the slurry, when the PAAS addition amount is 0.08 wt% or the SHMP addition amount is 0.15wt%, the slurry can hold on high dispersion and stable state, continuing increase the PAAS and SHMP addition amount, the dispersion and stable state of the slurry can be affected very limited. By the analysis of IR, the results show that the adsorptions of the PAAS and SHMP on the bauxite surface are belonged to physical adsorption, new chemical bonds and hydrogen bonds have not found in the infrared spectrums. When the PAAS and SHMP addition amount are 0.08 wt%, the fluid type of the slurry from"bingham fluid"change into"expansion fluid", as the slurry solid content increased, the"shear thickening"phenomenon of the slurry is more obviously. In this experiment choose UN-adjust pH value, PAAS addition amount is 0.08 wt% as the experimental conditions, can prepare high dispersion stability, good fluidity bauxite slurry, which used to prepare microsphere by centrifugal spray drying.The effects of slurry solid content and operation technology on the sphericity and average diameter of the microspheres were investigated. Results show that as the slurry solid content increased, the diameter of the microspheres will increase, and the particle size distribution will become wider, low sphericity microspheres are easy to form. The results of orthogonal regression experiments indicate that: the dry air temperature Z1 and the rotation rate of spray head Z2 show negative effects on the average diameter of the microspheres, and the feed flow rate Z3 shows a positive effect. The order of these three factors are the feed flow rate Z3 > the rotation rate of spray head Z2 > the dry air temperature Z1 > the interaction of the Z1Z2. The effects of the dry air temperature Z1, the rotation rate of spray head Z2 and the feed flow rate Z3 on the sphericity of the microspheres aren't simple linearity relation, the interaction of these three factors should be considered. The order of the influence degree on sphericity of the factors are the interaction of Z2Z3 > the dry air temperature Z1 > the interaction of Z1Z2 > the feed flow rate Z3 > the interaction of Z2Z3 > the rotation rate of spray head Z2. The slurry solid content is 70 wt%, the dry air temperature is 250℃, the rotation rate of spray head is 6000 rpm and the feed flow rate is 1 L/h these parameters are selected in the experiments, which can prepare high spherical microspheres, the diameter of the microspheres concentrate on 100 m, and the particle size distribution is narrow.The sinter process of microspheres and the properties of the ceramic microspheres were researched. The results indicate that high sphericity and smooth-faced alumina based ceramic microspheres can be obtained by twice sintering process. The phases of the ceramic microspheres which sintered at 1350℃are corundum and mullite, the inner structure of the microspheres are solid liked, and the fracture strength of the microspheres is 7.29 MPa, the diameter of the microspheres concentrate on 70-110 m, shows a normal distribution.