Hydrophobic silica xerogels containing trimethylsilyl (TMS) and dimethylsilyl (DMS) organic hydrophobic functional groups were synthesized using waterglass as the starting material. Five types of hydrophobic silica xerogels with varying surface coverages of the TMS and DMS groups were synthesized by changing the molecular structure of siloxane, which was used to introduce the hydrophobic moieties into the hydrogel and to investigate the resultant surface structures and thermal characteristics. The results revealed that the relative area of silica xerogels was smaller with a higher coverage of DMS groups. In addition, the thermal decomposition temperature of the silyl group shifted to higher temperatures, and the weight reduction during heating was also relatively limited in the above samples.
In order for wide bandgap semiconductor power devices to be practical use in various power electronics applications, a 2in1 600V75A power package with a 200 degree Celsius heat resistance was newly developed on the premise of mass production. This package designed to specify a low inductance of less than 24nH enables SiC and GaN-based devices to be driven with a high slew rate up to 5kA/us under hard-switching condition. Furthermore, this package encapsulated by a epoxy resin of a high heat resistance and equipped with thick Cu heat spreader allow these power devices to be driven up to 200 degree Celsius and dissipate heat in large quantities (thermal resistance Rth,jc: 0.6K/W), which is found to make cooling heat sink simplified. We introduced 50ASiC-MOSFET in this package, and verified the operation on a power conditioner for Solar Photovoltaic cells up to 4kW output. A high power conversion efficiency of 97.7% was measured by our SiC power packages on downsized cooling heat sink in 1/4 volume, which was more efficient than Si-IGBT module by 1.5%.
In this study, we investigated the influence of the addition of carbon materials on the heat resistance and flame retardancy of silica xerogels. A mixed dispersion prepared by adding 0.1 to 2.5 wt% each of the carbon materials, graphene oxide (GO), poly (3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS), and carbon black (CB) to waterglass (SiO 2 6%) was used as the raw material. By adding acid to this dispersion, a sol-gel reaction was carried out and the hydrogel obtained was hydrophobized with hydrochloric acid and a mixed solution of siloxane/isopropylalcohol . Finally, novel carbon-silica xerogel composites (SX-Carbon-X) were prepared via ambient pressure drying. Similarly, glass-fiber-reinforced silica xerogel composite sheets (GFR-SX-Carbon-X) were prepared by impregnating glass fibers with sol. The bulk densities of the samples obtained ranged from 0.204 to 0.217 g/cm 3 , their thermal conductivities ranged from 0.0187 to 0.0203 W/(m • K). As the amount of carbon material added was increased, the thermal decomposition temperature of the SX-Carbon-X shifted to higher temperatures. In the cone calorimeter test of GFR-SX-Carbon-X, moreover, adding at least 0.5% of the carbon material significantly reduced the combustion time and the peak heat release rate (PHRR), and the flame retardancy improved remarkably.
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