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Silicone gel is widely used as an insulation material in electrical engineering. Scientists from WACKER and the University of Kassel now want to incorporate special, electrically active fillers to imbue it with partial conductivity – this would open up entirely new application fields.
Anyone entering the coffee room of the Department of Power Systems and High Voltage Engineering at the University of Kassel must be prepared to encounter a camera-equipped multicopter. Professor Albert Claudi, head of the department, sometimes sends his flying camera on test flights through his office door, into the coffee room, and back again. Claudi’s multicopter has an advantage over the standard mail-order drones that proud amateur gardeners use, for example, to record their horticultural art from up in the air: it takes pin-sharp photos. To make sure that the images aren’t blurred, the electrical engineer has embedded the camera in silicone gel, which absorbs shocks. Prof. Claudi has big plans for silicone gels – together with WACKER, he is working on developing the polymers and their technical properties.
“With a smart silicone gel, defects or irregular surfaces in electrical conductors would cause fewer problems in the future.”Prof. Albert Claudi, University of Kassel
Electrification in Cars on the Rise
Silicone gels are an integral part of everyday life. For example, they can be found in aluminum boxes installed under the front passenger seats of many cars. The boxes contain control units for seat belt pretensioners and airbags. Some ten other such microcomputers, also encased in aluminum, travel the roads in almost every car nowadays – most of them located in the engine compartment.
“Modern vehicles contain less and less mechanics, while electrification has increased greatly,” says Jens Lambrecht, global product development manager at WACKER in Burghausen. POWERSIL® silicone gels keep moisture away from the sensitive electronic parts and reliably protect against corrosion. Their advantage is that they are soft and thus create no mechanical stress for the components. This holds true for temperatures between -50 °C and the maximum conceivable operating temperature in the vehicle. Specialty grades can even withstand a temperature range of -100 to +250 °C. No comparable material can do this. “Hard encapsulants, such as epoxy resin, would contract and expand under these conditions and literally crush the sensitive electronic parts,” explains Lambrecht.
In addition, silicones offer processing advantages. The low-viscosity silicone compound can be poured onto circuit boards. Only then does it take on a gel consistency and stick where it is. Expansion at high temperatures, too, can now be controlled, because Prof. Claudi and Wacker Chemie AG have discovered a way to compress silicone gels.
Smart Silicones Are the Goal
Prof. Albert Claudi in front of the University of Kassel. After working at renowned industrial companies for twelve years, he joined the university’s Department of Power Systems and High Voltage Engineering in 2000.
The scientists now want to transform the highly insulating compound into a smart silicone gel. This entails incorporating millions of minuscule particles of metal-oxide mixtures into the highly pure material. The particles, such as so-called microvaristors, act as nanoresistors within the gel, where their conductivity varies with localized field strength. Enriched in this way, the POWERSIL® gel has special properties in high-voltage applications. At low field strengths, it continues to be highly insulating. At high field strengths, it is conductive. There are numerous possible applications. “With the smart gel, defects or irregular surfaces in electrical conductors would cause fewer problems in the future,” explains Claudi. High field strengths often occur in these areas. They trigger discharges and, at worst, can cause a breakdown – possibly with dramatic consequences.
The gel displaces the electric field at precisely these areas through increased localized conductivity. “This would allow many devices to have more compact designs. Connecting parts, for instance, still need a lot of space to accommodate the insulation material,” says Claudi. There is plenty of scope for further research, too. For example, what is the influence of the particle size? Can silicone gel also be modified with other materials? How reliable are the gels after ten or more years of use?
Ideas at the Ready
The application areas for silicone gels are therefore expansive. Prof. Claudi has had ideas for the next step in their development for some time now – after all, he has more than ten years of experience in insulation and electrics to draw on. His multicopters are no leisure pursuit either, but intended for flying over and monitoring high-voltage cables.