Nanocrystalline Composite Layer Realized by Simple Sintering Without Surface Treatment, Reducing Hydrophilicity and Increasing Thermal Conductivity

The surface treatment for a polymer‐ceramic composite is additionally performed in advanced material industries. To prepare the composite without a surface treatment, the simplest way to manufacture an advanced ceramic‐particle is devised. The method is the formation of a nanocrystalline composite layer through the simple liquid‐phase sintering. Using magnesia (MgO) which shows hydrophilicity, a nanocrystalline surface layer is realized by liquid‐phase sintering. The amorphous matrix of nanocrystalline composite layer makes MgO hydrophobic and ensures miscibility with polymers, and the nanocrystalline MgO ensures high thermal conductivity. In addition, the liquid phase removes the open pores and makes the surface morphology smooth MgO with smooth surface (MgO‐SM). Thermal interface materials (TIM) prepared with MgO‐SM and epoxy show a high thermal conductivity of ≈7.5 W m−1K−1, which is significantly higher than 4.5 W m−1K−1 of pure MgO TIM. Consequently, the formation process of a nanocrystalline surface layer utilizing simple liquid‐phase sintering is proposed as a fabrication method for a next‐generation ceramic‐filler. In addition, it is fundamentally identified that the thermal conductivity of MgO depends on the Mg deficiency, and therefore a poly‐crystal MgO‐SM (produced at a low temperature) has a higher thermal conductivity than a single‐crystal MgO (produced at a high temperature). Advanced ceramic filler is devised to omit the surface treatment process in the production of polymer‐ceramic filler composites. The simple heat‐treatment process for manufacturing ceramic fillers is used to manufacture the advanced material. It has a surface layer composed of nanocrystalline particles and an amorphous matrix, which reduces the hydrophilicity of ceramic fillers and shows excellent functional properties.