(1) The 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 latent heat of fusion is 323kj/g. Aluminum has reducing properties and is easily oxidized. hot. 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 aluminum surface 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 being used as a pigment. Aluminum 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.

(2) Compared with other pigments, aluminum powder for pigments has more characteristics, which are shown in the following aspects:

1. The characteristic 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 into the carrier, it has the characteristic of being parallel to the substrate. The aluminum powder is connected to each other, and the large and small 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, that 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. The shielding characteristics of aluminum powder. The aluminum powder dispersed in the carrier floats, and the result of its movement is always to make itself parallel to the substrate coated by the carrier, forming a continuous aluminum powder layer, and this aluminum powder layer is Multiple layers are arranged in parallel in the carrier film. The pores between each layer of aluminum powder are staggered to each other, cutting off the capillary pores of the carrier film, and external moisture and gas cannot pass through the capillary pores to reach the substrate. This feature is the good physical shielding of the aluminum powder.

3. The optical characteristics 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. It is coated with paint containing aluminum powder. The surface of the object is silvery white and bright, which is the characteristic of the light reflected by the aluminum powder.

4. The "dual-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 vary with the incident angle and viewing angle of the incident light. Changes occur in light and color, and this characteristic is called the "dual-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 layer 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, incident light and viewing angle will occur.