metal powder preparation technology
With the application of powder metallurgy products more and more widely, the requirements for the size, shape and performance of metal powder particles are higher and higher, and the performance and size shape of metal powder largely depend on the production method and production process of powder, so the preparation technology of powder is also developing and innovating constantly.
At present, many methods have been developed for the preparation of metal powder, which are mainly divided into physical-chemical method and mechanical method according to the production principle. In the mechanical method, atomization method and mechanical crushing method are the most important. The most important physical and chemical methods are reduction method, electrolysis method and hydroxyl method.
Mechanical method is a kind of processing method to crush metal into powder with required particle size by means of mechanical external force. The chemical composition of the material is basically unchanged during the preparation process. At present, atomization method and mechanical crushing method are widely used. It has the advantages of simple process and large output. It can be used to prepare ultrafine powders of high melting point metals and alloys which are difficult to obtain by conventional methods.
Mechanical comminution is not only an independent milling method, but also an indispensable supplementary process for other milling methods. The solid metal is broken into powder by crushing, crushing and grinding. Crushing equipment is divided into two categories:
The main crushing equipment: crusher, roll mill, jaw crusher, etc;
The main crushing and grinding equipment: hammer crusher, rod mill, ball mill, vibration ball mill, stirring ball mill, etc.
Preparation of metal powder by high energy ball milling
Mechanical comminution is mainly used to crush brittle and work hardening metals and alloys, such as tin, manganese, chromium, high carbon iron, ferroalloy, etc. Because of its low efficiency and high energy consumption, it is often used as a supplement to other pulverizing methods or for mixing powders with different properties.
The method of directly crushing liquid metal or alloy to obtain powder is called atomization method, which is second only to reduction method in production scale and widely used. Atomized powder has the advantages of high sphericity, controllable powder size, low oxygen content, low production cost and adaptability to the production of various metal powders. It has become the main development direction of high performance and special alloy powder preparation technology. However, the application of atomization method is limited by low production efficiency, low yield of ultra-fine powder and relatively large energy consumption.
Physical chemical method refers to the production method of ultrafine powder by changing the chemical composition or agglomeration state of raw materials in the process of powder preparation. According to the different chemical principles, it can be divided into reduction method, electrolysis method, carbonyl method and chemical replacement method.
Reduction of metal oxides and salts to produce metal powder is one of the most widely used milling methods. Especially when ore and metallurgical industrial wastes such as rolled steel scales are directly used as raw materials, the reduction method is the most economical. The advantages of reduction method are simple operation, easy control of process parameters, high production efficiency and low cost, which is suitable for industrial production. The disadvantage is that it is only suitable for metal materials which are easy to react with hydrogen and become brittle and easy to break after hydrogen absorption.
Electrolysis is a method of electrodeposition of metal powder on the cathode by electrolysis of molten salt or salt aqueous solution. It plays an important role in powder production. Its production scale is second only to reduction method in physicochemical process, and its particle size can be controlled. The purity of the powder is high, and the purity of the powder can reach more than 99.7%. However, the electrolysis process consumes more electricity and costs more than reducing powder and atomizing powder. Therefore, in the total powder production, the proportion of electrolytic powder is relatively small.
Because carbonyl metals are easy to decompose into metal and CO gas at low temperature, carbonyl metal powder can be prepared by reverse reaction of carbonyl metal synthesis. Not only micron powder but also nanometer powder can be prepared by carbonylation method; not only single pure metal and alloy powder, but also coated powder can be prepared. Carbonyl powder itself has a highly developed surface which can not be compared with other methods. It is the best material for chemical power plate and catalyst.
Chemical displacement method
According to the activity of metal, the less active metal is replaced from the metal salt solution by the metal with strong activity, and the metal (metal powder) obtained by replacement is further refined into metal powder by other methods, which is called chemical replacement method. This method is mainly applied to the preparation of inactive metal powders such as Cu, Ag, Au, etc.
With the progress of technology, metal powder has shown good application prospects in metallurgy, chemical industry, electronics, magnetic materials, fine ceramics, sensors and so on. However, due to the limitation of traditional preparation technology, the application of metal powder is restricted. Although many new production processes and methods have been applied, the problems of small scale and high cost can not be solved well. In order to promote the development of metal powder materials, it is necessary to strengthen the innovation, learn from each other's strengths, and develop production processes with larger output and lower cost.