What Is Pure Copper?
Pure copper is copper with minimal alloying elements, typically 99.3% copper or higher, and is usually identified by a UNS number such as C11000. In technical standards and everyday industrial use it is simply called copper, which distinguishes it from its alloys: bronze is a copper-tin alloy and brass is a copper-zinc alloy, so neither is pure copper even though the terms are sometimes used loosely. The many alternative names for pure copper describe the refining route, the oxygen content, or the color of the metal, and each name corresponds to a specific grade with its own properties.
Common Alternative Names for Pure Copper
Electrolytic Tough Pitch (ETP) copper, UNS C11000, is the most widely used grade. "Electrolytic" refers to the electrolytic refining that achieves at least 99.9% copper, and "tough pitch" describes the controlled oxygen content of about 0.02–0.05% that is present at casting. ETP copper is the standard material for electrical conductors, cables, busbars, and general-purpose sheet and pipe. Oxygen-free copper (OFC) covers grades such as C10200 (oxygen 0.001% max) and C10100 (oxygen 0.0005% max); C10100 is often called OFHC (oxygen-free high conductivity) copper. Because they contain almost no oxygen, these grades resist hydrogen embrittlement in high-temperature hydrogen atmospheres and are used in vacuum systems, semiconductors, and precision electrical components. Phosphorus-deoxidized copper, UNS C12200, contains 0.015–0.040% phosphorus, which removes oxygen and makes the metal highly suitable for welding and brazing operations. In informal and construction contexts, pure copper is also called red copper because of its bright reddish-orange color.
Copper Content of Major Pure Copper Grades
| Grade (UNS) | Min Copper (wt%) | Key Impurity Limits | Typical Use |
| C11000 (ETP) | 99.90 | Oxygen 0.02–0.05%, Fe 0.005%, Pb 0.005% | Electrical wire, busbars, sheet, pipe |
| C10200 (OFC) | 99.95 | Oxygen 0.001% max | Vacuum and high-purity systems |
| C10100 (OFHC) | 99.99 | Oxygen 0.0005% max, total impurities 0.01% max | Semiconductors, cryogenic and precision parts |
| C12200 (DHP) | 99.90 | Phosphorus 0.015–0.040%, oxygen 0.001% max | Heat exchangers, refrigeration tubing, welded joints |
Copper content requirements are defined by specifications such as ASTM B152 for sheet, strip, and plate, ASTM B187 for bar, and the corresponding ISO and EN standards for wrought copper; always verify against the governing standard edition.
Hardness and Temper of Pure Copper
Pure copper is naturally soft and ductile in the annealed condition, with a Brinell hardness of roughly 35–45 HB and a tensile strength of about 220 MPa. Cold working such as rolling or drawing introduces work hardening: quarter-hard, half-hard, full-hard, and extra-hard tempers reach progressively higher hardness, with full-hard copper reaching roughly 350 MPa tensile strength. When maximum formability is needed, annealing restores the soft condition. Because hardness is measured on clean, oxide-free surfaces, testing should follow ASTM E10 (Brinell) for bulk material and ASTM E18 (Rockwell) for thin sections, and the temper designation should always be stated on the order.
How to Choose the Right Pure Copper Grade
Select the grade by the dominant requirement of the application. For maximum electrical conductivity at the best cost, use ETP copper C11000. For brazing or welding in hydrogen-bearing atmospheres where hydrogen embrittlement is a risk, choose oxygen-free C10200 or C10100. For welded tube and heat-exchanger service, phosphorus-deoxidized C12200 prevents weld porosity and gives reliable joints. For semiconductor, vacuum, and cryogenic hardware, OFHC C10100 provides the highest purity and consistency. When appearance matters, such as plumbing and decorative work, the informal term red copper usually points to a standard ETP or deoxidized grade with a bright copper color.
FAQ
What is the difference between ETP and OFHC copper?
ETP copper (C11000) contains about 0.02–0.05% oxygen and is the most common electrical grade. OFHC copper (C10100) is oxygen-free with 99.99% minimum purity and resists hydrogen embrittlement, making it the choice for vacuum, semiconductor, and cryogenic applications.
Is brass the same as pure copper?
No. Brass is a copper-zinc alloy, and bronze is a copper-tin alloy. Both contain substantial amounts of other elements and are not classified as pure copper, although they are sometimes loosely called copper in everyday speech.
What is red copper?
Red copper is an informal name for pure copper based on its bright reddish-orange color when polished. It usually refers to standard grades such as C11000 or C12200 used in plumbing, roofing, and decorative work.
What is the minimum copper content of pure copper?
By general definition, pure copper contains at least about 99.3% copper. Commercial grades are stricter: ETP and deoxidized grades require 99.90% minimum, C10200 requires 99.95%, and OFHC C10100 requires 99.99%.
Which copper grade is best for welding?
Phosphorus-deoxidized copper C12200 is preferred for welding and brazing because the phosphorus removes oxygen that would otherwise cause porosity and cracking in the weld zone.
Does pure copper work harden?
Yes. Cold working raises the hardness and strength of pure copper, with full-hard tempers reaching roughly double the annealed tensile strength. Annealing restores softness and ductility when further forming is required.
