Preparation Of Magnesium Oxide Powder And Its Properties In Thermally Conductive And Electrically Insulating Composites

In recent years,thermally conductive and electrically insulating polymer composite materials have been used to gradually replace the traditional thermally conductive materials or component parts in the fields of electrical and electronic engineering due to the excellent electrical insulation,resistance to chemical corrosion,ease of processing,light weight and good thermal conductivity of fillers.Filling suitable thermally conductive fillers is an effective way to prepare polymer-based thermally conductive and electrically insulating materials,which shows a great application value.In this paper,whisker-like magnesium oxide（W-Mg O）,flake-like magnesium oxide（F-Mg O）and cubic magnesium oxide（C-Mg O）and their corresponding precursors were firstly prepared by using magnesium chloride（Mg Cl₂·6H₂O）and sodium carbonate（NH₄HCO₃）as raw materials under hydrothermal condition.Also,the morphology and crystal evolution of Mg O precursors with different morphologies were exployed.The three different morphologies of Mg O particles and the modified three different morphologies of Mg O particles by TMC-105 titanate coupling agent were filled into polypropylene（PP）matrix with different filler content to prepare Mg O/PP composite system（W-Mg O/PP、F-Mg O/PP、C-Mg O/PP）and the modified Mg O/PP composite system,namely T-Mg O/PP composite system（T-W-Mg O/PP、T-F-Mg O/PP、T-C-Mg O/PP）,respectively.The effects of the composition ofMg O/PP composite system and T-Mg O/PP composite system on their morphology,thermal conductivity,electrical insulation and mechanical property were investigated,respectively.The mainly conclusions were as follows:（1）W-Mg O,F-Mg O and C-Mg O precursors with controllable morphology could be prepared by changing the reaction temperature and reaction time in the experiment.The calcined Mg O particles could maintain the morphology of the corresponding precursors.The diameter of W-Mg O is about 1μm,and the length range is 27-35μm.F-Mg O is an irregular particle size,and the flakes are in a scattered.The C-Mg O particle size is 7-9μm.（2）The morphology of Mg O,its loading and its distribution in the PP matrix have important influence on the performance of Mg O/PP composite system.The thermal conductivity of the T-Mg O/PP composite system increases with the increase of the T-Mg O filler content,and the volume resistivity of Mg O/PP composite system shows a decreasing trend,while the tensile property of Mg O/PP composite system shows a trend of increasing first and then decreasing.When the Mg O filler content is 20 vol%,the thermal conductivity of C-Mg O/PP composite reaches the highest value of 0.603 W/（m·K）,and the volume resistivity of C-Mg O/PP composite is 5.6×10¹¹Ω·cm,its tensile strength and elongation at break are 14.13 MPa and 6.75%,respectively.（3）The TMC-105 titanate coupling agent was used to modify the Mg O particles with different morphology.It was found that the interface between the modified Mg O particles and the PP matrix was tight bonded.Moreover,a good filler-matrix interface effect was formed in the composites,which improved the compatibility of the interface between the filler and the PP matrix.（4）The thermal conductivity of the T-Mg O/PP composite system increases with the increase of the T-Mg O filler content,the volume resistivity shows a decreasing trend,and the tensile property shows a trend of increasing first and then decreasing.Compared to the Mg O/PP composite system,the thermal conductivity of the T-Mg O/PP composite system is greatly improved,the electrical insulation performance is not greatly affected,and the tensile property is significantly improved.It is proved that the surface modification of the filler can improve the interfacial bonding between the filler and the matrix,and reduce the interface thermal resistance between the filler and the matrix.When the filler content of T-Mg O filler is 20 vol%,the thermal conductivity of T-C-Mg O/PP composite reaches 0.72 W/（m·K）,and the volume resistivity of C-Mg O/PP composite is 3.89×10¹¹Ω·cm,its tensile strength and elongation at break are25 MPa and 9.89%,respectively.