What is oxygen-free copper? How does it differ from ordinary copper?
Oxygen-free copper is generally considered to be pure copper, free of oxygen and any deoxidizers or residues. However, it actually still contains very trace amounts of oxygen and some impurities-very trace amounts! According to standards, its oxygen content should not exceed 0.003%, its total impurity content should not exceed 0.05%, and its copper purity should be greater than 99.95%.
As a result, oxygen-free copper, due to its extremely low oxygen content, has higher electrical and thermal conductivity, as well as better corrosion resistance and processability. Oxygen-free copper is primarily used in parts for vacuum instruments and meters, such as busbars, conductive strips, waveguides, coaxial cables, vacuum seals, vacuum tubes, and transistor components. Oxygen-free copper has excellent processability and is suitable for fine machining. Oxygen-free copper can be considered a special type of copper. The main grades of oxygen-free copper include: TU1, TU2, C10100, and C10200.
TU1: Purity reaches 99.97%, oxygen content no greater than 0.003%, and total impurity content no greater than 0.03%. This oxygen-free copper boasts exceptional purity, excellent electrical and thermal conductivity, corrosion resistance, and processability, and is free of hydrogen embrittlement. It is a high-quality copper material commonly used in applications requiring high purity and performance, such as electronics and electrical engineering.
TU2: Copper content exceeds 99.95%, oxygen content no greater than 0.003%, and total impurity content no greater than 0.05%. TU2 oxygen-free copper also exhibits excellent electrical conductivity, hot and cold working properties, and weldability, with excellent forgeability. It is often used in the production and processing of environmental components and equipment requiring both electrical conductivity and ductility, such as conductor bars, waveguides, and electrode materials.
C10100: Typically contains over 99.99% copper and has an oxygen content less than 0.001%. This is a high-purity oxygen-free copper material with excellent electrical and thermal conductivity, corrosion resistance, low porosity, and excellent formability. It is widely used in industries such as electronics, aerospace, automotive manufacturing, and transmission machinery.
C10200: Copper content ≥ 99.95%, total impurities ≤ 0.05%. It can be used in vacuum devices, instruments, and meters.
Ordinary copper, also known as red copper, gets its name from its purple-red color. While it is often referred to as pure copper, this is inaccurate. Strictly pure copper theoretically should contain close to 100% copper. While it is a relatively pure copper, it is not completely equivalent to pure copper.
Red copper contains oxygen, also known as oxygen-containing copper. The copper content of red copper ranges from 99.5% to 99.99%. Red copper has good electrical and thermal conductivity, excellent plasticity, and is easy to process by hot pressing and cold pressing. It is widely used in the manufacture of products that require good conductivity, such as wires, cables, brushes, and special electro-spark copper.
The main grades of red copper are: T1, T2, and T3.
T1: Copper content is at least 99.95%, with total impurities not exceeding 0.05%.
T2: Copper content is at least 99.90%, with total impurities not exceeding 0.1%.
T3: Copper content is at least 99.7%, with total impurities not exceeding 0.3%.
In addition, international standards include grades such as C11000. C11000 also has a higher copper content, generally requiring a copper + silver content of ≥ 99.90%.
The differences in appearance between oxygen-free copper and ordinary red copper are as follows:
Color
Red copper typically appears purple-red, which is where its name comes from. The color is bright and has a certain glossiness. Due to its easy oxidation in air, a dark red or dark black copper oxide film may gradually form on the surface, but the overall purple-red color can still be seen.
Oxygen-free copper generally has a purer copper color, approaching silvery white or pale yellow. Due to its extremely low oxygen content, oxygen-free copper is relatively stable in air and oxidizes much more slowly than copper, resulting in minimal surface color change and a longer-lasting, bright metallic luster.
Surface Finish:
Copper: Due to its relatively soft nature, it is susceptible to scratches and abrasions during processing and use, which may affect its surface finish. Oxidized copper may appear rough and lose some of its metallic luster.
Oxygen-free copper: It typically has a smoother, more delicate surface finish. Because oxygen-free copper is highly pure and relatively uniform, it is easier to achieve a good surface quality during processing.
Note: Distinguishing oxygen-free copper from copper by appearance is not an entirely accurate method, as the appearance of copper can be affected by various factors, including processing techniques, surface treatment, and oxidation level. In practical applications, other methods, such as chemical analysis and physical property testing, can be used to accurately distinguish between the two.
Differences in Strength and Hardness:
Copper: Relatively low in strength, softer in hardness, and softer in texture. This makes it susceptible to deformation during processing and use. For example, when manufacturing thin-walled parts, the strength and hardness of copper must be considered to prevent deformation or damage during use.
Oxygen-free copper: After special treatment, it has relatively high strength and greater hardness than red copper. This makes oxygen-free copper advantageous in applications requiring resistance to certain pressures and wear. For example, in the aerospace industry, the high strength and hardness of oxygen-free copper meet the stringent material requirements of aircraft.
In terms of corrosion resistance, oxygen-free copper is more resistant than red copper.
The difference in resistivity between the two:
Red copper: At 20°C, the resistivity is approximately 0.01851 Ω·mm²/m (or 1.851×10⁻⁸Ω·m).
Red copper has excellent electrical conductivity, second only to silver among all metals, making it an important conductive material. However, its conductivity is slightly lower than that of oxygen-free copper. For example, in the electrical field, copper wires can effectively transmit current, but they may not meet the requirements in applications where extremely high conductivity is required. Oxygen-free copper: The resistivity at 20°C is approximately 0.0171 μΩ·m (or 0.0171×10⁻⁶Ω·m).
Oxygen-free copper has a higher conductivity, generally exceeding 100% IACS (International Annealed Copper Standard), significantly higher than red copper. This gives oxygen-free copper unique advantages in electronics and electrical applications. For example, in high-fidelity audio cables, oxygen-free copper ensures high-quality audio signal transmission and reduces signal loss.
The company has a cluster of leading copper processing production lines in China, including:
German imported precision copper tube production line (annual output of 30,000 tons)
Japanese technology copper foil rolling line (thinnest up to 6μm)
Fully automatic copper bar continuous extrusion line
Intelligent copper sheet and strip finishing mill unit
Digitalized control and management of the whole production process is realized through MES system, and the dimensional accuracy of the products can reach ±0.01mm.
