Preparation Of Spherical Magnesium Oxide And Its Application In Thermal Conductive Materials

Magnesium oxide is a kind of chemical raw material which was widely applied in many fields, magnesium oxide with a special morphology has a good prospect in some areas. Magnesium oxide with a special morphology can not be directly prepared, generally precursor of basic magnesium carbonate or Mg (OH) 2 with a special morphology was firstly prepared and then magnesium oxide with the special morphology was obtained via calcining the precursors. Based on the former research results, the research interest in this paper was mainly focused on the preparation of spherical magnesium oxide. In this paper, magnesium chloride hexahydrate and anhydrous sodium carbonate were used as the raw materials, sodium dodecyl benzene sulfonate (SDBS) as additive (surface modification), the appropriate synthetic methods and better experimental conditions of spherical magnesium carbonate were investigated; then spherical magnesium oxide was obtained via calcining spherical magnesium carbonate; finally, the obtained spherical magnesium oxide was filled into PVC polymer materials with a high mass fraction, testing the heat conduction performance of PVC composite in order to investigate the effect of magnesium oxide on the thermal conductivity. The specific research contents as follows:Using hexahydrate magnesium chloride, anhydrous sodium carbonate as raw materials and sodium dodecyl benzene sulfonate (SDBS) as additive, spherical basic magnesium carbonate was prepared by an indirect synthesis method. In order to explore the optimum conditions of the indirect synthesis method, auxiliary additives, reactant concentration, concentration ratio of reactants, reaction temperature, pyrolysis temperature and stirring time were selected as affecting factors, the products obtained at these different reaction conditions were characterized and analyzed by XRD and SEM, respectively. The characterized results indicate that under the conditions of MgCl2 solution and Na2CO3 solution concentration ratio of 2:1, concentrations of 1.2mol/L and 0.6 mol/L, reaction temperature 70 ?, pyrolysis temperature 120? stirring time 60s and SDBS as an additive, the obtained production is spherical basic magnesium carbonate 4MgCO3·Mg(OH)2·4H2O particles which exhibit tight and uniform balls with a particle size distribution between 25-40 ?m.Spherical basic magnesium carbonate 4MgCO3·Mg (OH)2·4H2O obtained under the above optimum conditions and rod carbonate magnesium MgCO3·3H2O were characterized by thermal gravimetric analysis, the thermal gravimetric characteristic results of them indicate that the calcining processes have two stages. The first stage is the water loss process of these products, the second stage begin after a period of platform,which is the thermal decomposition of MgCO3 to produce MgO. The calcining time and temperature were obtained by the thermal gravimetric analysis, respectively. Basic magnesium carbonate 4MgCO3·Mg (OH) 2·4H2O and magnesium carbonate MgCO3· 3H2O were calcinated from room temperature to 800? at the heating rate of 10?/min, the results indicate that these two magnesium carbonates were changed to magnesium oxide MgO at 490? and calcining time was 2700s. The morphology of the obtained MgO is similar to the precursors before calcination.The above obtained magnesium oxide was filled into PVC polymer materials with a high mass fraction, and the obtained composites were characterized by SEM and thermal conductivity determination. The results show that the composite with spherical magnesium oxide formed a good heat conduction network and the thermal conductivity of it was increased 8.5 times. The result shows that spherical magnesium oxide is a good thermal conductivity material filler.