Alumina ceramics temperature is 80~105℃, amorphous density is 1.04~1.06 g/cm3, crystal density is 1.11~1.12 g/cm3, melting temperature is 240℃, resistivity is 1020~1022 ohm·cm. The thermal conductivity is 0.116W/(m·Kelvin) at 30℃. Normal polystyrene is an amorphous random polymer with excellent thermal insulation, insulation and transparency. The long-term use temperature is 0-70°C, but it is brittle and easy to crack at low temperature. In addition there are isotactic and syndiotactic and atactic polystyrene. Identical polymers have high crystallinity, and syndiotactic polymers have partial crystallinity. Polystyrene (PS) includes ordinary polystyrene, expanded polystyrene (EPS), high impact polystyrene (HIPS) and syndiotactic polystyrene (SPS). Ordinary polystyrene resin is non-toxic, odorless, colorless transparent particles, glass-like brittle material, its products have extremely high transparency, light transmittance can reach more than 90%, good electrical insulation performance, easy to color, and process Good fluidity, good rigidity and good chemical resistance. The shortcomings of ordinary polystyrene are brittleness, low impact strength, stress cracking, poor heat resistance and resistance to boiling water. Ordinary polystyrene resin is an amorphous polymer. The side group of polystyrene macromolecular chain is benzene ring, and the random arrangement of bulky side group is benzene ring determines the physical and chemical properties of polystyrene, such as high transparency . Rigidity. High glass transition temperature, brittle and so on. Expandable polystyrene is made by impregnating ordinary polystyrene with a low-boiling physical foaming agent. It is heated and foamed during the processing and is specially used to make foam plastic products. High impact polystyrene is a copolymer of styrene and butadiene, and butadiene is the dispersed phase, which improves the impact strength of the material, but the product is opaque. Syndiotactic polystyrene has a syndiotactic structure and is produced using metallocene catalysts. The developed new polystyrene varieties have good performance and belong to engineering plastics. Alumina ceramics generally have a head-to-tail structure, the main chain is a saturated carbon chain, and the side group is a conjugated benzene ring, which makes the molecular structure irregular, increases the molecular rigidity, and makes PS a non-crystalline linear polymer. Due to the presence of benzene ring, PS has a high Tg (80~105℃), so it is transparent and hard at room temperature. Due to the rigidity of the molecular chain, it is easy to cause stress cracking.
Alumina ceramics are colorless and transparent, can be freely colored, and their relative density is second only to PP and PE. It has excellent electrical properties, especially good high-frequency characteristics, second to F-4 and PPO. In addition, it is second only to methacrylic resin in terms of light stability, but its radiation resistance is the strongest among all plastics. The most important feature of polystyrene is that it has very good thermal stability and fluidity during melting, so it is easy to mold and process, especially injection molding, and is suitable for mass production. The molding shrinkage rate is small, and the dimensional stability of the molded product is also good.
What are the properties of alumina ceramics?
2020 12/07