Ultrafine Grinding And Dispersion Behaviors Of Submicron-sized Particles Of Praseodymium-doped Zirconium Silicate In Aqueous Suspension

Ceramic ink-jet printing has attracted much attention due to its advantages compared to the conventional ceramic decoration methods. The preparation of aqueous ceramic inks suitable for ink-jet printing is one of the development aspects in this field. The objective of this dissertation is to prepare an aqueous suspension with submicron-sized particles of praseodymium-doped zirconium silicate as a ceramic ink in ink-jet printing by wet ultrafine grinding in a high-energy density stirred bead mill and investigate the breakage mechanism of the particles in wet ultrafine grinding and the dispersion stability of the suspension.In Chapter 2, aqueous suspension containing submicron-sized praseodymium-doped zirconium silicate as a ceramic yellow ink was prepared by wet ultrafine grinding in a stirred bead mill. The results of X-ray diffraction and color analysis reveal that the non-crystallization of the pigment particle increases after grinding, which consequently affects the color strength of the ink pigment. In addition, the effects of the suspension property(i.e., solid content, dosage of dispersant) and grinding parameters(i.e., stirrer tip velocity, bead size and bead loading) on the particle size were investigated. Furthermore, the effects of parameters(i.e. solid content, stirrer tip velocity, bead loading and grinding time) on the size and the size distribution of the particles in the suspension were investigated through an orthogonal experiment in order to optimize the parameters. The results indicate that the submicron-sized particles with narrower particle size distribution(median particle size 50d=331 nm, RRB uniformity coefficient n=2.8272) in the suspension can be obtained under the optimum conditions(i.e., solid content of 30 wt.%, bead loading of 80 vol.%, stirrer tip velocity of 6.89.., grinding time of 1.5 h).In Chapter 3, the breakage behavior of the praseodymium-doped zirconium silicate particles in aqueous suspension during ultrafine grinding process under optimum grinding conditions was analyzed by population balance model. It is indicated that the abrasive and compressive forces to fracture the particles in the suspension by the stirred bead mill could coexist. In the initial grinding(i.e., before 0.5 h) the coarser particles can be mainly fractured by compressive forces besides abrasive forces, and the finer particles can be further ground by abrasive forces in the prolonged grinding process, leading to the submicron-sized particles.In Chapter 4, the dispersion stability of the submicron-sized particles in aqueous suspension obtained by stirred bead milling under the optimum conditions was investigated by adding various chemical agents(i.e., KCl, SDBS, SDS, TW-20 and TW-80). The results show that a small amount of KCl(1-5 m M) cannot stabilize the suspension. The polymer dispersants SDBS and SDS can modify the electrical property of the particle surface, thus improving the dispersion stability of the suspension. However, the dispersion of suspension undergoes a transition from stable to unstable when the amount of dispersant SDBS or SDS increases. Dispersants TW-20 and TW-80 cannot stabilize the suspensions, resulting in the aggregation of the particles due to the bridging of the polymer chains adsorbed on the particle surface.In Chapter 5, the aggregation behavior of submicron-sized particles of praseodymium-doped zirconium silicate in aqueous suspension with KCl and SDBS was analyzed by a modified population balance model. The model is capable to predict the dispersion/aggregation behavior of particles in the suspension over a long time based on the calculation of stability with the volume mean size of the suspension and parameter c. It is indicated that two mechanisms of particle aggregation could coexist at different dosages of SDBS. The particles in the suspension are properly dispersed at 0.5 wt.% SDBS, but the particles cannot be dispersed at 3.0 wt.% SDBS due to the bridging of excessive polymer chains adsorbed on the particle surface. The collision frequencies are selected under different dispersion/aggregation conditions, allowing the model to predict the particle size distributions at different dosages of SDBS. The particles aggregate due to the low electrical kinetic potentials on the particle surface in the presence of KCl. The model is employed to simulate the aggregation rate and particle volume mean sizes in the suspensions of various solid contents based on the fitted Zeta potentials and the Debye parameters.Finally, the dissertation gives the conclusions and some prospects for future work based on the experimental results and the predication analysis by modified population balance modeling.