What Oxygen-Free Copper C10200 Is
UNS C10200 is a refined, oxygen-free grade of copper. It is produced by melting and casting under conditions that remove oxygen without leaving a harmful residual deoxidant, so the cast structure contains no dispersed cuprous oxide and the finished product has essentially no oxide inclusions at the grain boundaries. The distinguishing specification for the grade is a copper content of 99.95 % minimum, silver counted with the copper, together with an oxygen limit of 0.001 % or 10 parts per million, whichever figure the applicable standard uses.
That single metallurgical difference separates C10200 from electrolytic tough pitch copper such as C11000. In tough pitch copper the oxygen is present as cuprous oxide particles; in C10200 it is not. The consequence is a material that keeps its ductility after high-temperature processing in reducing atmospheres and that conducts current with the highest efficiency available in commercial wrought copper.
Composition and Purity Requirements
Oxygen-free copper is covered by different product standards depending on the mill form: plate, sheet, strip and rolled bar to ASTM B152/B152M, seamless tube to ASTM B75/B75M and ASTM B68/B68M, rod for electrical purposes to ASTM B49, and bus bar to ASTM B187/B187M. The purity requirements are consistent across them, with the balance of the specification devoted to limiting elements that raise electrical resistivity.
| Parameter | Requirement | Reason for the limit |
|---|---|---|
| Copper, including silver | 99.95 % minimum | Sets the conductivity and the achievable surface finish |
| Oxygen | 0.001 % maximum, that is 10 ppm | Prevents cuprous oxide inclusions and hydrogen embrittlement |
| Phosphorus | Not an intentional addition; held as a low residual | Phosphorus in solution sharply reduces conductivity |
| Sulphur, iron, lead, zinc, bismuth and other residuals | Limited by the applicable standard | Each element increases resistivity and can affect hot workability |
Because the deoxidation is achieved by process control rather than by adding a deoxidant such as phosphorus, C10200 keeps a conductivity far above that of the phosphorus-deoxidised grades. Where the end use requires an even lower residual level, the electronic grade C10100 is specified; where a controlled low phosphorus content is acceptable, the low-phosphorus oxygen-free grades are used instead.
Electrical and Thermal Properties
The annealed temper of C10200 is normally specified with a minimum electrical conductivity of about 101 % IACS, the international annealed copper standard, and a correspondingly low volume resistivity. Cold-worked tempers carry a slightly lower conductivity figure because cold work distorts the lattice, and any residual impurity in solution reduces the value further. Thermal conductivity is high and, for the annealed temper, corresponds closely to the electrical figure through the Wiedemann-Franz relationship.
| Property | Typical value | Note |
|---|---|---|
| Electrical conductivity, annealed | about 101 % IACS | Highest value among commercial wrought coppers |
| Volume resistivity at 20 degrees Celsius | about 0.0172 ohm square millimetre per metre | Corresponds to the annealed reference standard |
| Thermal conductivity at 20 degrees Celsius | about 385 - 390 W per metre kelvin | Tracks the electrical value |
| Density | about 8.94 g per cubic centimetre | Used for mass calculations in bus bar design |
| Melting range | about 1080 degrees Celsius | Pure copper melting point, essentially unchanged by the residual elements |
In practice the conductivity figure is the reason the grade is chosen, and it is worth stating how it is measured: conductivity is verified on an annealed specimen cut from the lot, so a certificate that quotes a conductivity value without stating the temper should be read with that in mind. Resistivity testing is normally carried out together with the tensile test on the same sample to avoid a mismatch between the mechanical and electrical results.
Mechanical Properties and Tempers
Oxygen-free copper is a soft, highly ductile material in the annealed condition, and its strength is raised by cold reduction. Tempers are designated in accordance with the standard temper nomenclature used for wrought copper, from annealed through quarter-hard, half-hard and hard. The ranges below are typical for strip and sheet and are given as an indication of normal supply rather than as specification limits.
| Temper | Typical tensile strength | Typical elongation | Typical hardness |
|---|---|---|---|
| Annealed | about 200 - 250 MPa | 45 % and above | about 45 - 60 HV |
| Quarter-hard | about 250 - 300 MPa | 25 - 35 % | about 75 - 90 HV |
| Half-hard | about 300 - 350 MPa | 12 - 20 % | about 90 - 105 HV |
| Hard | about 350 - 400 MPa | 6 - 12 % | about 100 - 120 HV |
The high elongation of the annealed temper is what allows deep drawing, spinning and tight-radius bending without intermediate annealing, and it is the reason C10200 is used for formed components that must also conduct well. Where strength is the governing requirement, the harder tempers are selected and the forming sequence is planned so that the final cold reduction produces the required temper without exceeding the ductility available at each pass.
Why the Oxygen Limit Matters
When copper that contains cuprous oxide is heated in a hydrogen-bearing atmosphere, the hydrogen diffuses into the metal and reacts with the oxide to form steam. Because steam cannot escape, it generates internal pressure at the grain boundaries, and the result is intergranular cracking and a loss of ductility known as hydrogen embrittlement. The effect appears after bright annealing, after furnace brazing and in any welded joint where the oxide-containing material is heated.
C10200 avoids the problem at source. With the oxygen held at or below 10 ppm there is essentially no oxide to react with hydrogen, so the grade can be bright annealed, brazed and welded without special atmosphere restrictions. This is also why oxygen-free copper is preferred for vacuum components, where both the absence of oxide inclusions and the low outgassing rate of a clean, high-purity surface are important, and for components that must be plated or bonded where internal defects would show up after finishing.
Grain size control is part of the same specification: the annealed product is normally supplied with a fine, uniform grain structure, verified by the grain-size practice of ASTM E112, because a uniform grain structure gives predictable forming behaviour and a consistent surface after polishing or chemical etching.
Processing, Joining and Applications
C10200 is formed by cold rolling, drawing, deep drawing and bending; joined by soft soldering, silver brazing, gas-shielded arc welding and electron beam welding; and finished by machining, polishing, plating or chemical cleaning. Soft soldering demands a properly activated flux because copper oxidises quickly at soldering temperature, while brazing filler metals wet the surface readily and produce joints with good electrical continuity.
Typical applications follow directly from the combination of high conductivity, high ductility and freedom from oxide inclusions:
Bus bar, switchgear connections and transformer windings where conductor efficiency and heat removal both matter.
Waveguide, coaxial components and radio-frequency cavities, where surface conductivity governs loss.
Vacuum chamber parts, seals, electrodes and electron-gun components, where cleanliness and low outgassing are required.
Superconducting magnet stabiliser and cryogenic components, where the copper carries current if the superconductor quenches.
Semiconductor and thin-film equipment parts, sputtering targets and evaporation sources produced from high-purity copper.
Formed parts such as gaskets, shielding cans, heat-pipe envelopes and motor commutators that need both formability and conductivity.
For export orders the grade is normally released with a certificate showing the heat analysis, the oxygen content, the conductivity measured on an annealed specimen and the mechanical properties of the specified temper, so that the buyer can confirm that the material is oxygen-free and not merely a phosphorus-deoxidised substitute.
FAQ
Q: What is the difference between C10200 and C11000 copper?
C11000 is electrolytic tough pitch copper, which contains oxygen as dispersed cuprous oxide and typically 99.90 % copper. C10200 is oxygen-free, with 99.95 % copper minimum and oxygen at or below 10 ppm, which gives it higher conductivity and resistance to hydrogen embrittlement.
Q: How much oxygen does C10200 contain?
The standard limit is 0.001 %, which is 10 parts per million. In good commercial practice the measured value is usually below that figure, and it is reported on the mill certificate for high-purity orders.
Q: Does C10200 contain phosphorus?
No. Phosphorus is not an intentional addition in this grade. Deoxidation is achieved by process control instead, and the residual phosphorus level is kept low because even small amounts in solution reduce electrical conductivity.
Q: Why is the annealed conductivity about 101 % IACS rather than 100 %?
The international annealed copper standard was fixed on an early reference specimen. Modern oxygen-free copper refined to a very low impurity level can exceed that reference value in the annealed condition, which is why values slightly above 100 % IACS are quoted.
Q: Can C10200 be brazed or welded in a hydrogen atmosphere?
Yes. Because there is no oxide at the grain boundaries to react with hydrogen, the grade can be bright annealed, furnace brazed and welded without the intergranular cracking that affects tough pitch copper in the same conditions.
Q: Which product forms are normally available?
Plate, sheet, strip and rolled bar to ASTM B152/B152M, seamless tube to ASTM B75/B75M and B68/B68M, rod for electrical purposes to ASTM B49, and bus bar to ASTM B187/B187M.
