| The size, size distribution and morphology are key to the properties and added-value of ultra-fine NiO particles, and should be controlled strictly in the process of preparation. Because of the complexity of the process, it was still difficult to control and predict the particle size and morphology precisely. Based on the review of the recent advance of research on this issue, the essence of the complexity and unstability of the preparation process was analyzed and the controlled-release precipitation was put forward to solve this problem. Three solution systems of Ni(II)-CO(NH2)2-H2O, Ni(II)-NH3-CO32--H2O, Ni(II)-NH3-C2O42--H2O were designed and applied to prepare ultra-fine NiO precursor particles with different morphologies. Study on drying and calcination of the precipitated particles was also done, and the appropriate techniques of preserving the size and morphology of the precipitated particles during drying and calcination were developed.In the solution system of Ni(II)-CO(NH2)2-H2O, mono-dispersed spherical NiO precursor particles were prepared by homogeneous precipitation. Based on the chemical pattern recognition technique, the semi-experienced mathematic model was deduced by analyzing the experimental data, which could be well used to predict the size & dispersity of the precipitated particles obtained under different conditionsand calculate the effect degree of the process parameters on the characteristics of the produced particles quantitatively. By this technique, the useful information contained in the experimental data can be visualized in the figures, in which the different classes of samples were divided distinctly into separate areas. The obtained model was proved to be useful for the optimum design of precipitation process effectively. From the point of view of total interface energy of the precipitation system, an improved La Mer model was proposed, which describes the process mechanism as "nucleation-aggregation-growth by molecular diffusion". The electro-kinetic behavior of the particles and its effect on the aggregation process were also studied to verify the suitability of the above-proposed model. In this chapter, by the aid of chemical pattern recognition, uniform spherical precursor particles ranged from several sub-micrometers to micrometers in average size can be prepared by homogeneous precipitation process.In chapter 3, based on the principles of simultaneous equilibrium and mass equilibrium, a series of thermodynamic equilibrium equations of the complex system of Ni(II)-NH3-CO32--H2O(T=298K) were deduced, and the equilibrium curves of lg[Ni]T~ pH were drawn, which indicated the equilibrium area and composites of the solutions at different ammonia compositions and pH. Under the guidance of these equilibrium diagrams, the appropriate precipitation process and experimental schemes weredesigned, and loose flocculation particles or dense particles and mono-dispersed flake particles were produced. It was found that ammonia concentration and pH were essentially important to formation of different kinds of particles. When pH was relatively low, i.e., <7.0, free Ni2+ and the 1 ,2-coordinated complexes of ammonia with nickel dominated in the solution, and in this case, when mixed with precipitant, the burst nucleation started and rapid coagulation was the dominant growth pattern for nano-sized particles, which led to the formation of loose flocculation particles, and thereby self-preservation phenomenon occurred, which was beneficial to keep the size distribution of the precipitated particles relatively stable. When pH was relatively high, i.e., >7.0, the 3~6-coordinated complexes of ammonia with nickel dominated in the solution and consequently these coordinated complexes should firstly decompose to slowly release the nickel ion as the ions source for precipitation. On this occasion, slow crystallization was the dominant growth pattern of the nuclei, which easily led to the formation of spherical or flake particles.In chapter 4, based on the similar calculation principles as...
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