The latent heat of evaporation of water is very large, reaching 2457.7kj/kg. the evaporation of water-based paint needs to absorb a large amount of heat. The evaporation of water is influenced by the atmospheric temperature, humidity and wind speed. The volatilization rate increases with the increase of temperature, decreases with the increase of air humidity, and increases with the increase of wind speed.
This is because the temperature increases, the thermal movement of molecules more intense, liquid water molecules are more likely to get rid of the attraction of other water molecules and become water vapor molecules. However, with the increase in air humidity, the proportion of water vapor in the air increases, the partial pressure of water vapor increases, and more water vapor molecules become liquid water molecules per unit time. Therefore, the evaporation rate of water decreases with the increase of air humidity. The higher the wind speed, the more water molecules taken away from the volatile surface per unit of time, the faster the evaporation rate.
Copper powder has good electrical conductivity, and its volume resistivity (1.172×10-n·cm) is similar to silver (1.159×10-*g·cm), and the price is cheaper than silver, only 1/20 of silver, as conductive Fillers are getting more and more attention. But the biggest disadvantage of copper powder is that it is easy to oxidize in the air. A non-conductive thin film of Cu gO and CuO is formed on the surface, which makes the conductivity of copper drop rapidly, or even non-conductive, especially copper powder with a large specific surface area oxidizes faster.
In order to prevent the oxidation of copper powder and maintain stable conductivity, copper powder is often surface treated: reducing agents, such as hydroquinone derivatives are added to improve the moisture resistance of copper conductive agents; amine compounds are used as complexing agents For surface protection; use silver-copper gradient powder. Many domestic researchers have done a lot of work in suppressing copper oxidation. According to reports, through the selection, preparation and treatment of copper powder, the prepared coating has stable electrical conductivity and anti-static properties. It is also reported that in copper-based ptfe powder sds electromagnetic shielding coatings, the use of copper can be improved by adding additives such as coupling agents and organic bentonite. The coupling agent molecules respectively adhere to the polymer matrix and the copper powder, and appropriately coat the surface of the copper powder particles, thereby increasing the oxidation resistance of the copper powder. The purpose of adding organic bentonite to coatings is to improve the oxidation resistance, dispersion and sedimentation properties of copper powder on the basis of not reducing the electromagnetic shielding performance of the coating as much as possible.
Nickel powder has good electrical conductivity, its stability is between silver powder and copper powder, is not easy to rust in the atmosphere, and can resist caustic alkali corrosion. Nickel has a specific permeability of about 50 and has a high shielding effect. It is often used in magnetic shield coatings. Nickel is often combined with silver to make composite conductive agents, and alloy powders with aluminum and boron are also used as conductive fillers, so that antistatic coatings have the advantages of aging resistance and humidity resistance.
Aluminum has been widely used as a filler for metal coatings and anti-rust coatings. At the same time, it can also be used as an additive for conductive coatings, often used in spot welding primers.
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