Abstract
Current production and consumption of copper and copper alloy powders in China is reviewed. China is now the largest producer of copper powder globally and many of the technological gaps with other producers have been closed or eliminated. Priorities for further development are proposed.
The consumption of copper and copper alloy powders is second only to iron powders in the PM industry worldwide, the main applications being oil bearings, friction materials, diamond tools, thermal conductivity and contact materials, and chemical catalysts.1–3 In China, production of copper powders for PM amounted to about 16 000 t in 2012, mainly for use in iron-based structural parts, oil bearings and copper-based structural parts.
According to the China Association of Automobile Manufacturers, automotive production was 19·27 million in the 10 months to October 2014. By 2015, assuming 5% growth, annual production will be more than 23 million units, and car ownership in China will reach 150 million. 4 Were the mass of PM products per car to reach European levels, China's annual demand for PM parts for the automotive applications alone would reach 0·45 Mt and copper and copper alloy powder consumption would be more than 32 000 t.
China is also becoming the biggest global producer of of diamond tools, one-third of production being exported; annual consumption of copper and copper alloy powders in this sector is about 9000 t. The annual consumption of copper and copper alloy powders for friction materials is about 5000 t, mostly for use in friction plates for cars, trucks and construction vehicles. In the past few years, copper powder consumption for carbon brushes has also increased rapidly and now represents more than 4000 t of electrolytic copper powder.
Overview of copper and copper alloy powder technology and market
The variety of powders manufactured in China has become increasingly rich, including electrolytic copper powder, atomised copper and copper alloy powders (spherical, near-spherical, flake), partially alloyed and alloyed bronze and brass powders, coated powders (Cu/Fe, Cu/C, Ag/Cu), and ultrafine copper powders. Production routes include electrolysis, water and gas atomisation, diffusion, hydrometallurgy, and physical (air crushing, grinding).3–8
Copper and copper alloy powder consumption in China has grown by more than 25% annually in the past decade. In 2012, total production of copper and copper alloy powder was 45 000 t, including for non-PM applications such as pigments, of which electrolysis and atomisation accounted for about 88%.1–3 At present, there are 10 electrolytic copper powder producers with output over 20 000 t, accounting for about 40% of the world total.1–3 GRIPM, one of the top three global producers, has annual production capacity of 10 000 t.
Atomised powder is becoming more dominant in the market and it is expected that atomised and AOR (atomisation oxidation–reduction) copper and copper alloy powder will make up more than 60% of the global market by 2015. There are more than 50 atomised powder producers currently active in China.1–3 Partially alloyed Cu/Sn diffusion bonded powder, with higher compressibility than atomised pre-alloyed powder and better segregation properties than elemental mixes, is widely produced for use in oil bearings and diamond tools. The content of copper in coated iron powders is generally 10–22%, achieved by chemical displacement. Copper coated iron powders are widely used in oil bearings, diamond products and friction materials,9–11 due to their lower cost, completely or partially replacing copper powder, bronze powder, and iron and copper mixed powder. Current demand for coated powder in China is about 4000 t and there are about 10 manufacturers.2,3
In 2012, global copper and copper alloy powder production was 110 000 t, of which about 60% was in Asia, 20% in North America and 25% in Europe. The largest Chinese producers are GRIPM (electrolytic and atomised) 13 000 t, Chongqing Huahao (electrolytic and atomised) 6000 t, Jinchuan Group (electrolytic) 4000 t and Zhongketongdu (atomised) 4000 t. However, many small scale manufacturers need improved environmental and energy efficiency, automation and manufacturing technology and the ability to move into more profitable markets.
In terms of production efficiency, equipment, product specifications, environmental protection and other aspects, GRIPM, Tianjin RuiErPu and Chongqing Huahao Co. have reached internationally competitive levels. GRIPM has reduced electrolytic power consumption by more than 15% and sulphuric acid consumption by 20%, and achieved zero emissions by optimising the electrolysis process and electrolyte concentration, and by automatic control of rectifier equipment. Implementation of continuous electrolysis increased production by more than 10% and improved product quality and stability; high purity copper powder containing 10 ppm Pb is now produced, matching that of international competitors. In GRIPM, the introduction of counter-current washing reduced water consumption by more than 40% and achieved copper recovery of ≥99·8%. Electrolytic copper powder of low apparent density (0·6–1·0 g cm−3) is now produced at annual capacity of 2000 t. Chongqing Huahao was the first company in China to develop robotic scraping of powder from the electrolytic tank to reduce labour and improve product stability. Tianjin RuiErPu has developed mass production of electrolytic copper powder of low apparent density (0·8–1·0 g cm−3).
Electrolysis and diffusion are currently the main methods to produce copper and copper alloy powder of low apparent density. Whereas the power consumption to manufacture electrolytic powder is 3800–4200 kWh t−1, that for atomised copper and copper alloy powder is only 2000 kWh t−1. Optimising the atomisation parameters allows powder of apparent density ≤2·4 g cm−3 to be obtained, thus substituting for some electrolytic powders at reduced cost. Atomisation also has lower environmental impact than electrolytic production. In recent years the quality of Chinese atomised powder has improved rapidly, through self-development and the importing of advanced equipment and technology. There remain gaps with the international market in areas such as nozzle design, automation, energy consumption, and product quality. Secondary processing of the powder also requires development, e.g. for copper based catalysts, thermal conductivity material, imitation flake and gold powder.
In China, production of partially alloyed powder by the diffusion method has made significant progress. Product quality and stability can now satisfy the requirements of PM manufacturers, although the global market continues to be dominated by companies such as SCM and AcuPowder.
Production of copper coated iron powder in China has matured. These powders are synthesised by a substitution reaction, with cupric liquor and reduced iron powders as the main raw materials.9,10 However, the waste water contains large amounts of ferric sulphate and must be treated before disposal, and therefore a closed loop process is desirable to reduce production costs. 3
Copper coated graphite powder is widely used in carbon brushes, contactor materials, self-lubricating bearings, and dry-cutting diamond saw blades. In China this sector is under-developed and powder manufacturers and electric carbon product manufacturers are being encouraged to undertake joint development.
Future developments
With respect to powder production, the following aspects have been identified as requiring development effort in China: low energy, low environmental impact (closed loop) electrolytic processes (including water saving); low apparent density electrolytic copper powders; high and low density water atomised powders; high performance copper alloy powders for diamond tools; hydrometallurgical production routes; industrialisation of high grade copper alloy powders such as imitation flake gold powder, MIM powders, fine powders and copper/non-metallic composite powders; improved bonding for iron/copper composite powders.
A number of applications priorities have also been identified:11–14
heat pipe radiators have advantages over air cooled radiators of high thermal efficiency and conductivity, reduced noise and energy savings. In recent years, Taiwan funded enterprises have set up factories in mainland China (Taiwan is the world leader in heat pipe production, at 12 million units per month). In 2012, copper powder consumption for heat pipes in Taiwan and mainland China reached 4500 t. Electronics and automotive engine cooling elements have potential for growth, with copper powder as the raw material for long, thin complex features manufactured in large quantities by MIM
metallic pigmented coatings, conductive rubber and copper slurries consume large amounts of copper and copper alloy powder, as do art jewellery and metal printing. Metal-like light silver remains a fashionable colour for high-end cars, and bronze cars are also becoming more popular. Electromagnetic shielding coatings represent a further growth market
superfine or flake copper alloy powders are used to produce catalysts for methyl chlorosilane, which consist of copper or cuprous oxide containing zinc, tin and other additions; current annual demand in China is >4000 t
other priority areas include PM electrical contact materials, high strength, high conductivity copper alloys (e.g. Al2O3 dispersion strengthened copper alloy powders for welding electrodes), sterilisation products and automotive engine lubricants.
Conclusions
China has become the largest producer and user of copper and copper alloy powder. While great progress has been made, there remain gaps in technology and practice versus the most advanced global producers. Manufacturing processes, energy consumption, environmental impact, and automation of the electrolytic and hydrometallurgy routes must be improved. The generic technologies and equipment relating to water atomisation require development, to replace electrolytic and gas atomisation where feasible. Alternative hydrometallurgy routes for copper coated iron powder require a breakthrough to continue to provide high quality, cheap raw materials for the PM, diamond tool and other downstream industries.
The Chinese automotive industry will continue to grow steadily, leading to increasing demand for copper powders. Applications in cooling, paint, welding and chemical catalyst applications will also drive market development. As a result, copper and copper alloy powders have bright prospects in China.
Footnotes
Acknowledgements
Financial sponsorship by the Technology Innovation Fund of Beijing General Research Institute for Nonferrous Metals under Contract No. 2012110042000022 and the Outstanding Talents Training Project of Huairou District, Beijing is acknowledged. Based on a presentation at Euro PM 2013, organised by EPMA at Gothenburg, Sweden on 13–15 September 2013.