| Magnesium hydroxide [Mg(OH)2] is an important inorganic functional material with good properties. Due to its special properties, for example excellent activity, adsorption, buffered performance, high decomposition temperature, non-toxic, no-corrosion, et al, Mg(OH)2 is widely used in the field of flame-retardation, adsorption, catalysis, and so on. In the recent years, Mg(OH)2 is a product that has the most species, the highest output, and the widest useage in the international non-refractory material field. And it is also one of the products that is praised highly by the developed country in the process of enviromental protection and beneficial ecological development. But the Mg(OH)2, prepared at room temperature, can’t play a good role in the field of flame-retardation, adsorption, catalysis, and so on because of its small particle size, non-uniform morphology, strong surface polarity, and agglomeration. To solve this problem, crystal morphology and particle size must be changed.Hydrothermal technology is the traditional method of changing the morphology and particle size of Mg(OH)2, which use water as the solvent. But this method needs high reaction temperature, long reaction time, and the growth of crystal is hard to control. While, at present, it has never been reported that unique non-water solvent is used in hydrothermal modification of Mg(OH)2. n-Butanol is used as the hydrothermal solvent in the paper. And the growth habit of Mg(OH)2 crystal was investigated. The morphology, crystal structure and specific surface area of the products were characterized by scanning electron microscope, X-ray diffractometer, and nitrogen adsorption BET analyzer. The mineralizers of KOH and NaOH were added respectively in this experiment, the obviously different results were found when the reaction condition (the concentration of mineralizer, temperature, time, et al) changed. At the condition of temperature 150℃, mineralizer KOH with the concentration of 6.67 mol·L-1and reaction time 5 hours, the specific surface area of the product decreased from 38.58 m2·g-1 to 18.45 m2·g-1, and the morphology was hexaganol shape. While, at the same condition, the morphology of the product was thin hexaganol plates uniformly arrayed like a honeycomb, and the specific surface area increased from 38.58 m2·g-1 to 155.28 m2·g-1 with mineralizer NaOH. The same results can also be obtained by n-propanol or i-propanol solvent, with the surface area 140.65 m2·g and 139.04 m2·g-1 respectively. This may be caused by the interaction between NaOH and n-butanol (or n-propanol or i-propanol), and then they may take part in the process of solution-recrystallization of Mg(OH)2.The influence of mineralizer on the particle size of Mg(OH)2 hydrothermal product was researched at the temperature of 150℃and water solvent in the paper. The result shows that the morphology and particle size of Mg(OH)2 are effected obviously by compound mineralizers NaOH+NaCl, NaOH+EDTA, or NaOH+SDBS.Furthermore, the polit-scale experiments of the preparation and hydrothermal modification of Mg(OH)2 were carried out at the basis of lab experiments. The results show that there isn’t magnified effect of the preparation of Mg(OH)2. But, hydrothermal modification of Mg(OH)2 is marked difference. The optimum process condition of pilot-scale hydrothermal modification experiment is obtained, and the specific surface area of product decreases from 34.85 m2·g-1 to 12.3 m2·g-1.At last, the preparation of magnesium hydroxy carbonate [Mg5(CO3)4(OH)2·4H2O] by carbonization at elevated pressure was carried out by using Mg(OH)2 and CO2. The influence of reaction temperature, time and partial pressure of CO2 on the purity of product were investigated. |
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