| Magnesium hydroxide(MH) nanowhiskers is a new kind of environmental protection functional material, which has characteristics of low surface energy, excellent mechanical properties and higher elastic modulus. It can improve the mechanical properties of the polymers when used as a composite additive. Moreover the burning retardancy and smoke depressing of composite are effectively improved. At present, the study of MH nanowhiskers is still at the experimental stage, especially the formation mechanism of which is relatively rare. In this paper, the monodisperse MH nanowhiskers was prepared via hydrothermal synthesis method, and the formation mechanism of which was investigated.In this thesis, MH nanowhiskers were prepared by the magnesium oxysulfate whiskers(MOS), of which raw material being magnesite, and Na OH via the method of hydrothermal conversion. To investigate the property of synthetic product, the factor of MOS property and its concentration, mole ratios of Na OH/MOS, additive and its addition, reaction temperature, reaction time and agitation intensity were studied by the method of single-factor. The SEM, XRD, EDS, FT-IR and TG-DSC were used to analyze the surface morphology, phase composition, elemental composition, functional groups and thermal stability of the synthetic product; According to the statistics method of single whisker’s percentage in a certain amount of total content(≥200), the dispersion of MH nanowhiskers was characterized. The optimal preparation technology of the MH nanowhiskers was gained through continuous adjusting and optimizing the influence factors, and which are as follows: the mole concentration of MOS which has diameter less than 200 nm and L/D more than 100 for 0.03mol/kg, the mole ratio of Na OH to MOS for 4.5:1, the reaction temperature for 180℃, the reaction time for 4 h, the stirring speed for 100r/min, the best additive for sodium stearate, the ratio of sodium stearate to MOS for 2%. The product which is prepared at the optimal conditions has the average morphology for average diameter(D) of 85 nm, average length(L) of 14 μm and average ratio of L/D for 100. And each of them in the range of 80~95nm, 10~15μm and 100~180 are 57%, 66% and 70% of the total content(≥100) respectively. The XRD pattern showed that the synthetic product is pure. The decomposition temperature range of the MH nanowhiskers is 318~490 ℃, the product gets the fastest thermal decomposition rate when the range is 380~420℃.The reaction solution was extracted at different time by sampling at process of hydrothermal reaction under optimum conditions, and the concentration of OH- ion and SO42- ion in which was measured. Based on the principle of crystallization dynamics, experimental data were handled using software MATLAB and numerical solution of Runge-Kutta. The crystallization kinetics equations was obtained :On the basis of OH-:22300.179()()dcc c c c dt￥- = - -On the basis of SO42-:22300.154()()dcc c c c dt￥= - -According to the above mentioned analysis, it confirmed the kinetic model of MH nanowhiskers forming was MA-2 correspondingly. The crystallization process was in the control of multi-core surface reaction. Based on crystallization kinetics model and related theories, and with the result of this experiment. It was found after analysis that the forming process of MH nanowhiskers included template mechanism that take MOS as template and screw dislocation growth pattern under the L-S mechanism in this experimental system. |
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