(1) Characteristics of aluminum powder
Aluminum is a silver-gray metal with a relative weight of 26.98, a relative density of 2.55 and a purity of 99.5%. The melting point of aluminum is 685 degrees, the boiling point is 2065 degrees, and the latent heat of fusion is 323kj/g. Aluminum has reducibility and is easily oxidized. , exothermic during the oxidation process. When rapidly oxidized, the heat release per gram is 15.5 kj/g. Aluminum is a ductile metal and is easy to process. The oxide film on the metal aluminum surface is transparent and has good chemical stability.
The aluminum powder for pigment refers to the aluminum powder whose particles are scaly, the surface is coated with a treatment agent, and is suitable for use as a 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, its output and dosage are larger.
(2) Compared with other pigments, aluminum powder for pigments has more characteristics, which are reflected in the following aspects:
1. The characteristics of scaly covering The aluminum powder particles are scaly, and the ratio of the diameter to the thickness is about (40:1)-(100:1). After the aluminum powder is dispersed into the carrier, it has the characteristics 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 ratio of diameter to thickness. Aluminum is stretched during the grinding process, the diameter-thickness ratio is continuously increased, and the covering power is also increased.
2. The shielding properties 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 in the Multiple layers in the carrier film are arranged in parallel. The pores between each layer of aluminum powder are staggered from each other, cutting off the capillary pores of the carrier film, and the external moisture and gas cannot pass through the capillary pores to reach the substrate. This feature is the good physical shielding of 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. It is painted with paint containing aluminum powder. The surface of the object is silvery white and bright, which is the characteristic of aluminum powder reflecting light.
4. "Dual-color effect" characteristics of aluminum powder Due to its metallic luster and the characteristics of being parallel to the coated object, the gloss and color depth of aluminum powder in a carrier containing transparent pigments vary with the incident angle and viewing angle of the incident light. The change occurs with changes in light and color, a property known as the "dichroic effect". The aluminum powder is arranged in different layers in the coating film. When the incident light hits each layer of aluminum flakes, the reflected light is obviously different in brightness because it passes through the coating film with different thicknesses and is weakened differently. 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, the color tone and metallic light will change, and the incident light and viewing angle will change. The angular position shifts gradually from the vertical, and the light passes through pigments with different particle numbers and aluminum powders with different particle sizes, and the color and metallic light of the reflected light also change infinitely. 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 powder paste for pigments is floating type, which is characterized by flakes floating on the surface of the coating film.