Silicon nitride ceramic is a non-toxic, tasteless white powder or granule, with a milky white appearance, a wax-like hand, and a low water absorption rate of less than 0.01%. The polyethylene film is transparent and decreases with the increase of crystallinity. Polyethylene film has low water permeability but high air Laser Scribe Film Heating Fixing Ceramic Substrate permeability, which is not suitable for fresh-keeping packaging but suitable for moisture-proof packaging. It is flammable and has an oxygen index of 17.4. It has low smoke during combustion, with a small amount of molten droplets, yellow on the flame and blue underneath, with a paraffin odor. Polyethylene has better water resistance. The surface of the product is non-polar, which is difficult to bond and print, and it is improved by surface treatment. Many branches have poor resistance to light degradation and oxidation.
Its molecular weight is in the range of 10,000 to 100,000. Those with a molecular weight of more than 100,000 are ultra-high molecular weight polyethylene. The Laser Scribe Film Heating Fixing Ceramic Substrate higher the molecular weight, the better the physical and mechanical properties and the closer to the required level of engineering materials. But the higher the molecular weight, the more difficult its processing. The melting point of polyethylene is 100~130℃, and it has excellent low temperature resistance. It can still maintain good mechanical properties at -60℃, but the use temperature is 80~110℃.
It is insoluble in any known solvents at room temperature, and can be dissolved in toluene, amyl acetate, trichloroethylene and other solvents in a small amount above 70°C.
Chemical properties
Polyethylene has good chemical stability and can Laser Scribe Film Heating Fixing Ceramic Substrate withstand dilute nitric acid, dilute sulfuric acid and any concentration of hydrochloric acid, hydrofluoric acid, phosphoric acid, formic acid, acetic acid, ammonia, amines, hydrogen peroxide, sodium hydroxide, potassium hydroxide, etc. at room temperature Solution. But it is not resistant to strong oxidation corrosion, such as fuming sulfuric acid, concentrated nitric acid, chromic acid and sulfuric acid mixture. The above-mentioned solvents will slowly corrode polyethylene at room temperature, while at 90-100°C, concentrated sulfuric acid and concentrated nitric acid will quickly corrode polyethylene, causing it to be destroyed or decomposed. Polyethylene is prone to photo-oxidation, thermal oxidation, and ozone decomposition, and is prone to degradation under the action of ultraviolet rays. Carbon black has an excellent light shielding effect on polyethylene. After being irradiated, cross-linking, chain scission, and formation of unsaturated groups can occur.
Mechanical properties
The mechanical properties of polyethylene are Laser Scribe Film Heating Fixing Ceramic Substrate general, the tensile strength is low, the creep resistance is not good, and the impact resistance is good. Impact strength LDPE>LLDPE>HDPE, other mechanical properties LDPE<LLDPE<HDPE. It is mainly affected by density, crystallinity and relative molecular weight. With the improvement of these indexes, its mechanical properties increase. Environmental stress cracking resistance is not good, but when the relative molecular weight increases, it improves. Good puncture resistance, of which LLDPE is the best.
Thermal characteristics
The heat resistance of polyethylene is not high, and it improves with the increase of relative molecular weight and crystallinity. The low temperature resistance is good, and the brittleness temperature can generally reach below -50℃; and with the increase of relative molecular weight, the lowest can reach -140℃. The linear expansion coefficient of polyethylene is large, up to (20~24)×10-5/K. The thermal conductivity is high.
Electrical characteristics
Because polyethylene has no polarity, it has excellent electrical properties such as low dielectric loss and high dielectric strength. It can be used as frequency modulation insulating material, corona resistant plastic, and high voltage insulating material.
What are the characteristics of silicon nitride ceramics?
2020 11/17