Red copper is named for its purplish-red color. Generally, we refer to red copper as pure copper, which is actually inaccurate because, strictly speaking, pure copper should theoretically have a copper content close to 100%. Red copper is relatively pure copper but cannot be entirely equated with pure copper.
Red copper contains oxygen and is also known as oxygenated 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 through heat and cold pressure. It is widely used in the manufacture of products that require good electrical conductivity, such as wires, cables, brushes, and copper for electric spark erosion.
The main grades of red copper are: T1, T2, T3.
T1: Copper content is more than 99.95%, and total impurities do not exceed 0.05%.
T2: Copper content is more than 99.90%, and total impurities do not exceed 0.1%.
T3: Copper content is more than 99.7%, and total impurities do not exceed 0.3%.
Additionally, international standards include grades like C11000. The copper content of C11000 is also high, generally requiring copper + silver content to be ≥99.90%.
It is generally believed that oxygen-free copper does not contain oxygen or any deoxidizers or residues; however, it does contain very minute amounts of oxygen and impurities. According to standard regulations, the oxygen content should not exceed 0.003%, total impurities should not exceed 0.05%, and the copper purity should be greater than 99.95%.
Therefore, oxygen-free copper, due to its extremely low oxygen content, has higher electrical and thermal conductivity, better corrosion resistance, and processing properties. It is mainly used for electrical vacuum instruments and parts, such as busbars, conductive strips, waveguides, coaxial cables, vacuum seals, vacuum tubes, and components of transistors. Oxygen-free copper has excellent processing properties suitable for fine processing. Oxygen-free copper can be considered a special type of red copper.
The main grades of oxygen-free copper are: TU1, TU2, C10100, C10200.
TU1: Purity reaches 99.97%, oxygen content does not exceed 0.003%, and total impurities do not exceed 0.03%. This oxygen-free copper has very high purity, excellent electrical, thermal, corrosion resistance, and processing properties, and no hydrogen embrittlement, making it a high-quality copper material commonly used in circumstances demanding high material purity and performance, such as electronics and electrical fields.
TU2: Copper content is greater than 99.95%, oxygen content not higher than 0.003%, and total impurities do not exceed 0.05%. TU2 oxygen-free copper also has good electrical conductivity, hot and cold processing performance, and excellent forgeability, commonly applied to the production and processing of components and equipment requiring conductivity and ductility, such as conductive strips, waveguides, and electrode materials.
C10100: Usually contains more than 99.99% copper, with an oxygen content below 0.001%. This is a high-purity oxygen-free copper material with excellent electrical and thermal conductivity, corrosion resistance, low porosity, and excellent forming and processing properties, widely used in electronics, electrical, aerospace, automobile manufacturing, and transmission machinery industries.
C10200: Copper content ≥99.95%, total impurities ≤0.05%. It can be used for electrical vacuum devices and instruments.
In terms of color
Red copper: Usually appears purplish-red, which is the reason for its name. The color is relatively bright with a certain degree of gloss. Because it easily oxidizes in the air, its surface may gradually form a dark red or dark black oxide film, but the purplish-red color can still be seen.
Oxygen-free copper: Generally appears as a relatively pure copper color, close to silver-white or pale yellow. Due to its extremely low oxygen content, it is relatively stable in the air, oxidizes much slower than red copper, so the surface color change is minimal, and it can maintain a brighter metallic luster for a longer time.
Surface smoothness
Red copper: Because it is relatively soft, it is prone to scratches and abrasions during processing and use, which may affect its surface smoothness. Oxidized red copper's surface may appear relatively rough, losing some metallic sheen.
Oxygen-free copper: Usually has a higher surface smoothness, looking smoother and finer. Because of its high purity and relatively uniform material, it is easier to obtain better surface quality during processing.
Note: Distinguishing oxygen-free copper and red copper by appearance is not an entirely accurate method, as the appearance of copper materials can be influenced by various factors such as processing techniques, surface treatment, and degree of oxidation. In practical applications, accurate differentiation can also be achieved by combining other methods, such as chemical analysis and physical property testing.
Red copper: Relatively low strength and hardness, with a soft texture. This makes red copper prone to deformation during processing and use. For example, when making some thin-walled parts, the strength and hardness of red copper need to be considered to avoid deformation or damage during use.
Oxygen-free copper: After special treatment, it has relatively higher strength and hardness compared to red copper. This makes oxygen-free copper more advantageous in situations requiring certain pressure and wear resistance. For example, in the aerospace field, the high strength and hardness of oxygen-free copper can meet the strict material requirements of aircraft.
In terms of corrosion resistance, oxygen-free copper is better than red copper.
Red copper: The resistivity is about 0.01851Ω·mm²/m (or 1.851×10⁻⁸Ω·m) at 20°C.
Red copper has good electrical conductivity, second only to silver among all metals, making it an important conductive material. However, its electrical conductivity is slightly lower than that of oxygen-free copper. For example, in the electrical field, red copper wires can transmit current well, but in situations requiring extremely high electrical conductivity, they may fall short of requirements.
Oxygen-free copper: The resistivity is about 0.0171μΩ·m (or 0.0171×10⁻⁶Ω·m) at 20°C.
Oxygen-free copper has higher electrical conductivity, generally reaching above 100% IACS (International Annealed Copper Standard), far superior to red copper. This gives oxygen-free copper unique advantages in the electronics and electrical fields. For example, in high-fidelity audio cables, oxygen-free copper can ensure high-quality audio signal transmission and reduce signal loss.
Red copper: Good thermal conductivity, often used to make heat exchangers, radiators, and other thermal equipment. For example, in some industrial equipment, the thermal conductivity of red copper can effectively transfer heat and improve the equipment's efficiency.
Oxygen-free copper: Has slightly higher thermal conductivity than red copper, performing better in situations with extremely high thermal requirements. For example, in high-end electronic devices, the high thermal conductivity of oxygen-free copper can help in heat dissipation, ensuring stable operation of the equipment.
Red copper is widely used in general electrical, electronic, and industrial fields.
Oxygen-free copper excels in high-frequency signal transmission, and it can be used to make high-end wires and cables, high-end electronic products, vacuum tubes, and other products with high electrical conductivity and signal transmission requirements, as well as in fields with stringent material performance requirements like telecommunications and aerospace.
While oxygen-free copper certainly outperforms ordinary red copper in some aspects, one cannot generalize that oxygen-free copper is more high-end. The choice depends on the application scenario and requirements; in different applications, each has its own advantages.
Broadly speaking, oxygen-free copper can be categorized as a type of red copper with specific performance and uses. Therefore, in terms of production costs, the manufacturing process of oxygen-free copper is more complex, usually making its cost higher than that of red copper. Generally, oxygen-free copper can be several thousand yuan more expensive per ton than red copper.
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