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Preparation process of metal powder

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-10-29 16:57:00
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Huge potential market to promote technology progress, as application of powder metallurgy products more and more widely, shape and performance requirements of size of metal powder particles is higher and higher, and properties of metal powder size and shape to a large extent depends on powder production method and its preparing process, so powder preparation technology is also in constant development and innovation.

At present, preparation of metal powder has developed many methods, according to production principle can be divided into mechanical method and physical and chemical method. Among mechanical methods, the most important ones are mechanical pulverization and atomization. The main methods of physical chemistry are reduction, electrolysis, hydroxyl and chemical substitution.

Mechanical method is a kind of processing method to break metal into powder with required particle size by means of external mechanical force. Commonly used methods are atomization and mechanical pulverization. It has advantages of simple process and large yield, and can prepare some ultrafine powders of high melting point metals and alloys which are difficult to obtain by conventional methods.

1. Mechanical pulverization

Mechanical pulverization is an independent method of pulverization, which is mainly used for crushing brittle and easy to work hardening metal and alloy, such as tin, manganese, chromium, high carbon iron, iron alloy, etc. This method has low efficiency and high energy consumption. It is often used as a supplement to other powder making methods or for mixing different powders. Solid metal can be broken into powder by crushing, crushing and grinding. Crushing equipment can be divided into two types:

The main role of crushing coarse crushing equipment: crusher, rolling mill, jaw crusher and other coarse crushing equipment;

The main impact and grinding role of fine crushing equipment: hammer crusher, rod mill, ball mill, vibration ball mill, agitating ball mill.

2. Atomization method

The method of directly breaking liquid metal or alloy to make powder is called atomization method, which is most widely used method of making metal powder after reduction method in production scale. Atomized powder with high sphericity, powder particle size controllable, low oxygen content, low production cost, and to adapt to a variety of metal powder production advantages, has become a high performance and special alloy powder preparation technology of  main development direction, but production efficiency is low, rate of ultrafine powder is not high, a relatively large energy consumption of defects such as limiting application of spray method.

Physicochemical method refers to production method of obtaining superfine powder by changing  chemical composition or agglomeration state of raw material in process of powder preparation. According to different chemical principles, it can be divided into reduction, electrolysis, carbonyl and chemical substitution.

1. Reduction method

Reduction of metal oxides and salts is one of most widely used methods for producing metal powders. In particular, when ore and metallurgical industrial wastes such as rolled steel scale are directly used as raw materials, reduction method is most economical. Advantages of reduction method are simple operation, easy control of process parameters, high production efficiency, low cost, suitable for industrial production. The disadvantage is that it is only applicable to metal materials which are easy to react with hydrogen and become brittle and easily broken after hydrogen absorption.

2. Electrolysis

Electrolysis is process of deposition and precipitation of metal powder at cathode by electrolysis of molten salt or aqueous solution of salt. It plays an important role in powder production, and its production scale is second only to reduction method in physico-chemical method, and it can control powder size, and powder purity is high, up to 99.7%.However, electrolysis method consumes more electricity and has a higher cost than reducing powder and atomizing powder. Therefore, in total powder production, proportion of electrolytic powder is relatively small.

3. Hydroxyl method

Since hydroxyl metal is easy to decompose into metal and CO gas at low temperature, hydroxyl metal powder can be prepared by reverse reaction of synthesis of hydroxyl metal. Hydroxyl method can be used to prepare powder of micron level and nanometer level. It can not only make single pure metal and alloy powder, but also make coating powder. The hydroxyl powder itself has a highly developed surface which is incomparable to powder prepared by other methods. It is best material for chemical power plate and catalyst.

4. Chemical substitution

According to strength of activity of metal, with a strong activity of metal will be less active metal from metal salt solution replacement, replacement of metal (metal particles) by other methods to further refine into metal powder called chemical replacement method. This method is mainly applied to preparation of Cu, Ag, Au and other inactive metal powders.

With progress of technology, metal powder has shown a good application prospect in metallurgy, chemical industry, electronics, magnetic materials, fine ceramics and sensors. However, the limitation of traditional preparation technology restricts application of metal powder. Although many new production processes and methods have been applied, the problems of smaller scale and higher cost cannot be solved well. In order to promote the development of metal powder materials, it is necessary to increase innovation, learn from each other and develop a production process with larger output and lower cost.

Keywords in the article: metal powder
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