Characteristics of aluminum powder
Aluminum is a silver-gray metal, with a relative mass of 26.98, a relative density of 2.55, and a purity of 99.5%. The melting point of aluminum with a purity of 99.5% is 685 degrees, the boiling point is 2065 degrees, and the melting endothermic is 323kj/g. Aluminum has reducing properties and is easily oxidized. Exothermic. During rapid oxidation, 15.5 kj/g of heat is released per gram. Aluminum is a ductile metal and easy to process. The oxide film on the surface of metal aluminum is transparent and has good chemical stability.
The aluminum powder used for the pigment refers to the aluminum powder whose particles are in the form of scaly, the surface is coated with a treatment agent, and is suitable for pigment. Aluminum powder paste is a mixture of pigment aluminum powder and solvent. Its use and characteristics are roughly the same as aluminum powder. Because it is easy to use, the output and dosage are larger. Compared with other pigments, aluminum powder for pigments has more characteristics in the following aspects:
1. The characteristics of scaly covering
The aluminum powder particles are scaly, and the ratio of the sheet diameter to the thickness is about (40:1)-(100:1). After the aluminum powder is dispersed in the carrier, it has the characteristic of being parallel to the substrate. Numerous aluminum powders are connected to each other. The particles fill each other to form a continuous metal film, which covers the substrate and reflects the light outside the coating film. This is the unique hiding power of aluminum powder. The hiding power of aluminum powder depends on the surface area, which is the diameter-to-thickness ratio. Aluminum is stretched during the grinding process, the diameter-to-thickness ratio continues to increase, and the hiding power also increases.
2. Shielding characteristics of aluminum powder
The aluminum powder dispersed in the carrier floats, and the result of its movement always makes itself parallel to the substrate coated by the carrier, forming a continuous aluminum powder layer, and this aluminum powder layer is arranged in multiple layers in the carrier film in parallel . The pores between each layer of aluminum powder are staggered, cutting off the capillary pores of the carrier film, and external moisture and gas cannot pass through the pores to reach the substrate. This feature is the good physical shielding of the aluminum powder.
3. Optical properties of aluminum powder
Aluminum powder is made of aluminum with light color and high metallic luster. Its surface is smooth and can reflect 60%-90% of visible light, ultraviolet light and infrared light. The object is coated with paint containing aluminum powder, and its surface is silvery white and bright. This is the characteristic of aluminum powder reflecting light.
4. The "two-color effect" characteristics of aluminum powder
Because aluminum powder has the characteristics of metallic luster and parallel to the coated object, in the carrier containing transparent pigments, the gloss and color depth of aluminum powder change with the incident angle and viewing angle of the incident light. The characteristic is called the "two-color effect". The aluminum powder is arranged in different levels in the coating film. When the incident light illuminates each layer of aluminum flakes, the coating film of different thickness is weakened differently, and the reflected light is obviously different in brightness. When light enters the film containing transparent pigments and aluminum powder, the incident light passes through the pigment particles to become colored light, and then is reflected by different levels of aluminum powder, and changes in color tone and metallic light will occur, incident light and viewing angle The angular position shifts gradually from vertical, and the light passes through pigments of different particle numbers and aluminum powders of different particle sizes, and the color tone and metallic light of the reflected light also undergo infinite changes. This characteristic of aluminum powder has been widely used in coatings as hammer paint or metallic paint.
5. Floating characteristics of aluminum powder
A large type of aluminum powder and aluminum paste for pigments is the floating type, which is characterized by scaly floating on the surface of the coating film.
