Thermally conductive filler main force - aluminum oxide

Thermally Conductive Filler Aluminum Oxide

Alumina has the advantages of thermal conductivity and insulation, and can be used as a thermally conductive filler in the preparation of thermally conductive insulating adhesives, potting adhesives and other polymer materials. Compared with other fillers, although the thermal conductivity of alumina is not high, it can basically meet the application of "thermally conductive interface materials, thermally conductive engineering plastics, and fillers in the field of aluminum-based copper-clad laminates". Moreover, alumina is an economical filler for high thermal conductivity insulating polymers due to its low price and wide range of sources.

Thermal conductivity of alumina is generated under high temperature conditions of white powder crystals, its crystalline powder, used for thermal conductivity of alumina have spherical alumina, spherical alumina, composite alumina and so on. Thermally conductive alumina must have a narrow particle size distribution, good particle size stability, high thermal conductivity K value, coupling modification of the filler part of high characteristics. Generally speaking, if the average particle size of thermally conductive alumina can be controlled within a reasonable range, the thermal conductivity can reach between 3-10W/(m*K) according to different filler amounts.

Various applications of thermally conductive alumina fillers

Alumina surface modification

Due to the strong surface polarity of alumina, it is difficult to disperse uniformly in the polymer; coupled with its own thermal conductivity is not high, it requires a high filler amount to obtain better thermal conductivity, which will lead to an increase in the viscosity of the composite material is difficult to meet the requirements of the construction of the mobility, but also significantly reduces the mechanical properties of the material, so that the scope of its application is limited. Alumina particles and organic resin matrix interface compatibility is poor, alumina particles are very easy to agglomerate, it is difficult to uniformly dispersed into the polymer matrix. And the difference in surface tension between alumina particles and organic resin is different, which makes it difficult for the polymer matrix to wet the surface of the particles, which leads to the existence of voids at the interface between the two, increasing the interfacial thermal resistance of the composite material.

How to reduce the agglomeration between alumina particles, improve the interfacial compatibility between alumina powder and polymer matrix, and improve their dispersion in polymer matrix, so as to obtain composites with excellent performance, becomes a key issue for the application of alumina in the field of filler materials.

The use of organic surface modifier molecular functional groups in the particle surface adsorption or chemical reaction on the surface of the particles to modify the surface, purposefully change the physical and chemical properties of the powder surface, such as surface energy, surface polarity, etc., is the solution to the poor dispersion of alumina powder is the killer application of the difficult problem.

At present, the surface modifier of common alumina is mainly the traditional silane coupling agent. However, when short-chain silane coupling agents are used as surface modifiers, the effect of thermal conductivity improvement is limited. Therefore, in order to overcome the defects of short-chain silane coupling agent as surface modifier, cetyltrimethoxysilane can be used for surface modification of alumina.

After modified by this silane coupling agent, the alumina powder disperses uniformly, the particles do not have obvious agglomeration phenomenon exists, and the powder angularity is reduced; while the unmodified alumina particles are more agglomerated, and the powder morphology is also rougher. According to the analysis, the modified alumina dispersion may be improved because the alumina surface coating a layer of silane coupling agent, the surface polarity is reduced; modified alumina surface morphology changes may be due to the role of mechanical force when modified, resulting in the reduction of alumina surface corners, become rounded and smooth, to reduce the polarity of the surface of the alumina, to improve the compatibility of its and the silicone rubber purpose.