Inorganic powders have become an increasingly important means for modifying polymer composite materials. Filling polymers with inorganic powders not only reduces material costs but also enhances various properties of the polymers, such as strength, rigidity, heat deflection temperature, thermal conductivity, corrosion resistance, flame retardancy, and insulating properties. Among them, silicon micropowders, as a key inorganic filler, are widely used in rubber, plastics, adhesives, and coatings due to their superior stability, reinforcing, thickening, thixotropy, thermal conductivity, heat resistance, high insulation, and low expansion.
Silicon dioxide powder is a particulate material with a certain particle size distribution, primarily composed of SiO2. It is produced through a series of processes including crushing, ball milling (or vibration, air jet milling), flotation, acid washing purification, and high-purity water treatment, starting from natural quartz (SiO2) or fused quartz. Depending on the manufacturing process, it is categorized into crystalline silicon dioxide powder and molten silicon dioxide powder, with the latter available in angular and spherical shapes.
In various forms of silicon dioxide nanoparticles, crystalline silicon dioxide is not the most ideal for polymer systems, as it lacks the dispersion and sediment resistance of molten spherical silicon dioxide, and its thermal shock resistance and coefficient of thermal expansion are inferior to those of molten angular silicon dioxide. Its overall performance is also less than that of the recently developed nano-silicon dioxide. However, when considering cost and economic benefits, crystalline silicon dioxide is more affordable and has a higher thermal conductivity than molten silicon dioxide, making it more preferred for practical applications.
Ultra-fineness is a development trend in the processing and utilization of non-metallic minerals. Ultra-fine silicon dioxide powders offer advantages such as a large specific surface area, high surface activity, and good dispersibility. Compared to ordinary silicon dioxide powders, ultra-fine silicon dioxide has more surface defects and uncoordinated atoms, increasing the likelihood of physical or chemical bonding with polymers. This enhances the interface bonding between particles and the polymer matrix, leading to widespread applications in coatings, paints, engineering plastics, adhesives, and silicon rubber.
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