The application of aluminum hydroxide in silicone rubber insulators

Silicone rubber is a special synthetic rubber, which is different from the C-C bond main chain of most rubbers, which has a Si-O bond structure. The particularity of the structure of silicone rubber determines its special chemical properties, such as high-temperature resistance, low-temperature resistance, high voltage resistance, arc resistance, electrical insulation, leakage resistance, and chemical inertness to lubricants and other media. Its excellent electrical insulation, leakage resistance, and other properties make silicone rubber very suitable for use as an organic insulating material in the electrical and electrical industry. In recent years, silicone rubber insulators have been widely used in electrical insulation systems, such as power station insulators, switch insulators, insulator bushings, etc. Since the 1980s, the demand for organic silicon composite insulators in high-voltage lines has increased year by year and has been widely used in national power grids. Silicone rubber insulators have their special properties:

1. Hydrophobicity

Silicone rubber insulators have good water repellency. The surface of silicone rubber has an inductive and dispersive force to water so that the water on the surface is scattered without rolling off. This is because the water molecules inside the liquid are much more attractive than the outside air, making most of the fog and water droplets exist in a spherical shape. When the fog and water droplets continue to increase, they will slide down the silicon rubber slope, which makes the silicone rubber exhibit hydrophobicity.

2. Electrical performance

There is no conductive structure in silicone rubber, and there is no conductive ion in the molecule, so silicone rubber is a good insulator with a large volume resistivity; secondly, white carbon black and aluminum hydroxide are added to the silicone rubber, they are low conductivity materials. Due to the hydrophobic mobility of silicone rubber, the particles are basically wrapped in the molecule, it is difficult to contact the outside water and cannot form ions. After years of practical development, silicone rubber has been widely used in high-voltage and ultra-high voltage circuits.

3. Resistance to tracking and corrosion resistance

Leakage tracking is caused by the accumulation and spread of carbides caused by the electric current and spark discharge generated by the dirt. Adding proper aluminum hydroxide filler can effectively improve the tracking resistance and corrosion resistance of silicone rubber. Aluminum hydroxide will decompose at the high temperature generated by the discharge and will also react with free carbon. Aluminum hydroxide decomposes to produce aluminum oxide and water vapor. The heat absorbed by the reaction is 2.09kj/mol, which greatly reduces the temperature of the surface of the material. At the same time, water forms a strong flow of water vapor at high temperatures to brush off the carbon particles deposited on the surface of the sample. Weakening the development of electrical tracking; aluminum hydroxide reacts with free carbon to convert it into volatile carbon (CO or CO2), which can weaken the development of electrical tracking. In addition, aluminum hydroxide and the alumina produced by the reaction have good thermal conductivity, can effectively conduct the energy generated by the discharge, limit the generation of thermal oxidation and thermal degradation, and reduce the decomposition of silicon rubber and the formation of carbon particles.

The smaller the particle size of aluminum hydroxide, the more uniform the distribution inside and on the surface of the material, the faster the thermal decomposition rate, which can effectively inhibit the formation of carbonized channels, and improve the ability of resistance to tracking. Because aluminum hydroxide contains a large number of hydroxyl groups, too much aluminum hydroxide will make the surface of the silicone rubber hydrophilic. Once there is moisture on the surface, a water film will be formed, leading to flashover, and too much aluminum hydroxide will also affect the silicon The mobility of small molecules in rubber.

In the silicone rubber formulation, aluminum hydroxide has a greater impact on the mechanical properties, electrical properties, water repellency, and flame retardancy of the products. Years of studies have shown that adding aluminum hydroxide filler can improve the performance of silicone rubber such as tracking resistance, electrical corrosion resistance, arc resistance, and flashover resistance.

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