Preparation of reformed MgO filler with high humidity resistance by a hydrothermal coating technique.

Abstract

MgO is an excellent candidate for thermal conductive fillers due to its high thermal conductivity, low electric conductivity, low cost, and appropriate hardness, though the reaction with water to form Mg(OH)2 causes a decrease in the weatherability of MgO. In order to improve the humidity resistance of MgO, the core (MgO)-shell (MgCO3) structure was designed using hydrothermal reactions under-compressed CO2 gas. The reactions proceeded rapidly to produce Mg(OH)2, 4MgCO3-Mg(OH)2-4H2O, and MgCO3 depending on reaction conditions. It was found that the reactions at high temperature under high CO2 pressure with a high heating rate suppressed the reaction of MgO and increased the amount of MgCO3 in the reaction products. The addition of ethanol enhanced this tendency, which resulted in the successful formation of reformed MgO particles covered by thin MgCO3 layers consisting of fine crystals. Humidity resistance tests of the PPS plates including the reformed MgO fillers confirmed that coating of MgO particles by MgCO3 layers improved weatherability.

Keywords

• magnesium oxide
• thermal conductive filler
• weatherability
• coating by magnesium carbonate
• hydrothermal reactions