Study Of Preparation Of Whiskers And Exploitation Of Magnesium Resources

Crystal whisker is one of the strongest known forms of solid and has been widely employed as reinforcing additive of composite materials. At present, the preparation and application of whisker are in the frontier of research and development of materials around the world. Two conventional methods were systematically studied in the preparation of MgO whiskers: the method of hydrolysis of MgCl₂ with flux and the method of decomposition of precursor whiskers. A novel method was developed to prepare crystal whiskers and successfully applied in the preparation of MgO whiskers and ZnS whiskers. Besides, the investigation was also made on the preparation of magnesium hydroxychloride whiskers and Mg(OH)₂ whiskers. These methods can also be applied in the preparation of other crystal whiskers, including nanowhiskers.The research project is one of the national eleventh five-year scientifical supporting and planning projects, named as systematical engineering study of ecological exploitation of KCl and MgCl₂·6H₂O minerals and focuses on deep exploitation of magnesium minerals. The crystallization process of MgCl₂·6H₂O was developed based on the fact of the minerals and phase equilibrium data from literature and qualified products of MgCl₂·6H₂O were prepared in laboratory. The effects of the composition of raw materials and the end-point of evaporation were investigated on the quality of product.In the study of the method of hydrolysis with flux, the optimization of reaction conditions was performed and the effects of reactants, temperature and the nature of flux were systematically investigated. The yield and quality of crystal whiskers had been improved greatly after optimization.The reaction equilibrium and process were analyzed according to the thermodynamic data and the properties of molten salt reported in literature. The growth mechanism of MgO whiskers prepared by hydrolysis was brought forward based on experimental investigation and theoretical analysis. The role of flux was explained based on the structure of molten salt.According to the crystal whisker growth mechanism, a novel green method was invented to prepare crystal whiskers and MgO whiskers were prepared successfully. The new process was thermodynamically analyzed and the effects of temperature and flux were investigated on the growth of MgO whiskers in experiments. ZnS whiskers were also prepared with the novel method. The preparation reaction was thermodynamically analyzed and the effects of flux and temperature were investigated on the growth of crystal whiskers. Theoretical prediction of ZnS morphology was performed with molecular simulation software Cerious2 and the special morphology of ZnS whiskers was analyzed based on crystal growth theories.The method of decomposition of precursors has been researched, in which magnesium hydroxychloride whiskers and magnesium hydroxide whiskers were used as the precursors to prepare MgO whiskers. Learning from the formation mechanism of magnesium hydroxychloride in magnesium cement, a detailed analysis was made on the growth mechanism of magnesium hydroxychloride whiskers. Magnesium hydroxychloride whiskers were prepared successfully with Mg(OH)₂, Ca(OH)₂ and magnesium chloride solution and the process of the preparation and transformation of magnesium hydroxychloride whiskers is optimized. XRD, SEM and TEM studies were performed on the morphology and crystal structure of crystal whiskers before and after transformed to MgO whiskers.The growth and transformation kinetics of magnesium hydroxychloride whiskers were investigated with chemical titration and XRD for the first time and the transformation was analyzed based on crystal structures of crystal whiskers.All the contents above have never been reported at present.