Flake alumina has a special two-dimensional flake structure (length to diameter ratio greater than 10:1), the particle size is usually in the range of several microns to tens of meters, the thickness of about hundreds of nanometers, mainly through the molten salt method, sol-gel method, ball milling mixing method and other routes prepared, widely used in thermal conductivity filler, toughening agent, refractory materials and pearlescent pigments. When flake alumina is used as filler, micron alumina with high length-to-diameter ratio is easier to contact with each other in polymer matrix to form an effective thermal conductivity network, which can effectively improve the thermal conductivity of thermal interface materials. Therefore, at the same alumina filling amount, the thermal conductivity of the flake alumina filled thermal silicone gasket is better than that of the spherical alumina filled thermal silicone gasket. In addition, two-dimensional flake aluminum oxide can also be structural design, through vacuum assisted extraction filtration, hot pressing, electrostatic spinning and other technologies to induce two-dimensional flake structure layer by layer orderly assembly, forming an effective heat conduction channel in the plane, so as to design and develop anisotropic heat conduction materials with high in-plane thermal conductivity, which can be applied to large plate heat dissipation and other application scenarios.

    However, because the surface energy of flake alumina particles is larger than that of spherical alumina, the surface fluidity is worse, and the contact and collision between flake alumina particles and particles are more intense than that of spherical alumina, the viscosity of the mixture system composed of flake alumina and polymer will be higher, and eventually the flexibility of the silicone thermal gasket will be greatly reduced. In addition, compared with spherical alumina, the flake alumina is more likely to settle in the composite system during the preparation process, resulting in the upper and lower layers of the silicone thermal gasket, and the uniformity is significantly reduced. Therefore, flake alumina as a thermal conductive filler has higher requirements for the molding process, which is also the main reason why it is relatively rarely used in thermal conductive silicone gaskets.

    The spherical alumina has a regular spherical structure, and the particle size is usually in the range of a few microns to tens of meters. It is mainly prepared by liquid phase precipitation method, high temperature plasma method and spray pyrolysis method. The spheroidization rate and yield of commercially available spherical alumina powder are relatively high, and the particle size can also be customized according to the specific use scenario, and the comprehensive use cost is relatively low. When spherical alumina is used as the filler, the higher the sphericity of the particles, the smaller the surface energy, the better the surface fluidity, and the more evenly mixed with the polymer matrix, the better the fluidity of the mixing system, and the better the uniformity of the composite material prepared after film formation. Therefore, when spherical alumina is used as thermal conductive filler to prepare thermal conductive silicone gaskets, the higher the sphericity of alumina particles, the higher the flexibility and better mechanical properties. Therefore, compared with flake alumina, the thermal interface material prepared by using spherical alumina as thermal conductive filler has better flexibility and mechanical properties.

    In summary, the thermal interface material filled with flake alumina has better thermal conductivity, but it is not easy to form, poor uniformity and flexibility, and the current application scenarios are few. It is urgent to develop new composite strategies and preparation methods to solve the problems of difficult forming and poor flexibility. Although the thermal interface material filled with spherical alumina has slightly poor thermal conductivity, it has better flexibility and mechanical properties, and is more widely used in the market.