Research On The Processes And Properties Of Al₂O₃ Ceramic Microspheres Prepared By Micro-droplet Jetting Rapid Forming

Ceramic microsphere has recently attracted much attention owing to its low density,high specific surface area,low thermal conductivity,high stability and attractive optical properties,which contributes to their extensive application in the areas such as catalysis,drug delivery,chromatography separation,chemical reactors and controlled release of various substances.Some physical properties of microspheres are essential for the potential applications in catalysts or adsorbents,such as particle size,pores shape,pore size,and morphology of the particle.Among several ceramics microspheres,alumina is the most common crystalline material used as a support body for catalysts or adsorbents.Preparation of alumina microspheres with excellent mechanical properties and desirable pore structure is very important to the development of novel catalysts and adsorbents for various applications.Therefore,a new method for forming Al₂O₃ ceramic microspheres based on droplet jet technology and slurry solidification is proposed in this paper to achieve precise control of the sphericity,size and morphology of ceramic microspheres,and to study the ceramic microspheres sintering process and performance,to form a highly efficient and controllable process of Al₂O₃ ceramic microspheres,has important theoretical and practical significance.Based on the mechanism of the formation process of the droplet injection,the physical model of the impact needle in the droplet injection was established firstly.The dynamic grid technology was used to simulate the impact process of the striker.The results showed that the stroke of the striker,the feed pressure and the viscosity of the fluid were the key factors affecting the fluid velocity at the nozzle are based on the results of the simulation analysis.The droplet injection rapid prototyping test equipment is designed and constructed.It is mainly composed of a pneumatic extrusion nozzle,an air pressure control system,a motion platform and a control system.The micro-droplet rapid prototyping device was used to conduct the forming test of Al₂O₃ ceramic microspheres.The influence of ceramic slurry properties on the mold ability of ceramic microspheres was studied.The optimum slurry composition parameters were determined,and different researches were analyzed.The effects of nozzle diameter and slurry extrusion pressure on the particle size of Al₂O₃microspheres were studied.The results show that the slurries appear to exhibit shear-thinning flow behavior,and its viscosity decreases with the increase of the shear rate.When the PVA addition amount is 3 wt.%,the solid content is 45 vol.%,the slurry has good rheological properties.At this time,a high solid content and low viscosity ceramic slurry can be obtained.It is suitable for droplet-jetting forming.Glycerol is used as a molding medium,and boric acid is used therein.When the amount of boric acid is 10wt.%,the curing time of the slurry is 4.5 min.The droplets have good formability;the controllability of the particle size distribution can be achieved by adjusting nozzle size and slurry extrusion pressure.The dry sintering experiments of Al₂O₃ ceramic microspheres were performed.The effects of different sintering temperatures on the properties of Al₂O₃ ceramic microspheres were studied.The influence mechanism was analyzed and the optimum sintering process was determined.The results show that the second sintering method of pre-sintering and final sintering can effectively avoid the sticking phenomenon of microspheres in the sintering process.