How to make aluminum powder without a ball mill?

Metal aluminum powder is a silver-white metal powder. 

Physical and chemical properties of aluminum powder

The relative density of aluminum is 2.55, the melting point of aluminum with a purity of 99.5% is 685 degrees, the boiling point is 2065 degrees, and the melting heat is 323kJ/g. During rapid oxidation, the heat release per gram is 15.5kJg. 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. 

Metallic aluminum powder is a large category of metallic pigments due to its wide application, large demand, and many varieties. The aluminum powder particles used in pigments are scaly, and it is precisely because of this scaly particle state that aluminum powder has metallic luster and shielding functions.

Production and process of metal aluminum powder 

1. Aluminum powder produced by ball milling process 

Put steel balls, aluminum shavings and lubricant into the ball mill, crush the aluminum shavings with the rolling steel balls to make it into scaly aluminum powder, fill the ball mill and the pipe with inert gas, this method has high production efficiency and the product The quality is good and safe, laying the foundation for the modern aluminum powder process. This method is still used and is called "dry production". In the ball mill, petroleum solvent is added instead of inert gas, and the produced aluminum powder and solvent are mixed into a slurry to become a slurry aluminum powder pigment. This method has simple equipment, safe process, and the product is very convenient to use. The vast majority of modern aluminum pigments use this method, which is also known as the "wet" process.

2. Atomization process

The process of producing aluminum powder by atomization method can be divided into three types: air atomization method, inert gas atomization method and pressurized water atomization method. The air atomization method is to spray the molten aluminum into a mist with compressed air through a nozzle, and the mist aluminum is condensed into powder, and then the aluminum powder is screened and classified to form an atomized aluminum powder product. The air atomization method is a developed process method, and it is still the most used method to produce aluminum powder by atomization method. It is characterized by large production capacity, low cost, and simple equipment, but the production safety of this method is poor. During the production process, the aluminum powder is suspended in the air flow, and the movement forms a dust mist accompanied by static electricity. When the aluminum dust mist reaches a certain concentration, it encounters sparks. May cause deflagration.

3. Inert gas atomization process 

The inert gas atomization method is a newly developed aluminum powder atomization production method. It is different from the air atomization method in that its production equipment is completely sealed and filled with inert gas, such as argon, nitrogen, etc. The pressurized inert gas sprays the molten aluminum into mist through the atomizer. The inert gas quickly absorbs the heat in the aluminum, and the liquid aluminum in the form of mist beads condenses and shrinks rapidly into a spherical shape. The solidified aluminum powder is separated into various particle size grades in the classifier. The inert gas is reused after dust removal and purification. Since this process adopts sealed equipment and inert gas, the aluminum powder does not have the conditions of oxidative deflagration, so it is very safe. And because the product is extremely fine spherical and has high activity, it has high application value. It is used for high-energy fuels and also for aluminum powder pigments—the raw material for aluminum powder paste for cars. 

4. Pressed water atomization process 

The pressurized water atomization method uses high-pressure water to pulverize the molten aluminum into fine powder in the atomizer, and the aluminum powder in the water is divided into grades of various particle sizes through a cyclone, and then the moisture is removed to become dry aluminum powder.

Aluminum powder for pigments refers to the aluminum powder whose particles are in the shape of scales, 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 consumption are larger. Compared with other pigments, aluminum powder for pigments has more characteristics in the following aspects:

1. Characteristics of scaly covering

The aluminum powder particles are in the form of scales, and the ratio of its sheet diameter to 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. Many 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 film. This is the unique hiding power of aluminum powder. The hiding power of aluminum powder depends on the size of the surface area, that is, the ratio of diameter to thickness. Aluminum is stretched during the grinding process, increasing the diameter-thickness ratio and increasing the hiding power.

2. Shielding properties of aluminum powder

The aluminum powder dispersed in the carrier undergoes floating movement, 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 arranged in parallel in multiple layers in the carrier film . 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 reach the substrate through the capillary pores. This feature is the good physical shielding property 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. If the object is coated with paint containing aluminum powder, its surface is silvery white and bright. This is the characteristic of aluminum powder reflecting light.

4. The "two-color effect" characteristic of aluminum powder

Due to the characteristics of aluminum powder having metallic luster and being parallel to the object to be coated, in the carrier containing transparent pigments, the gloss and color depth of aluminum powder will change with the incident angle and viewing angle of the incident light. The characteristic is called "dual color 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 due to the different weakening of the coating film passing through different thicknesses. When the light enters the film layer containing transparent pigment and aluminum powder, the incident light passes through the pigment particles and becomes colored light, and then reflected by different layers of aluminum powder, the change of color tone and metallic light will occur, depending on the incident light and viewing angle. The angular position gradually shifts from the vertical, and the light passes through pigments with different particle numbers and aluminum powder with different particle sizes, and the hue and metallic light of the reflected light also undergo infinite changes. This characteristic of aluminum powder has been widely used in paint as hammer paint or metallic paint. 

5. Floating characteristics of aluminum powder

A large category of aluminum powder and aluminum paste for pigments is the floating type, which is characterized by floating on the surface of the coating film in a scaly shape.