What Purity Means for C110 Copper
Purity in copper is a specification figure, not a marketing phrase. For C11000 the purchase standard fixes a minimum copper content and a maximum oxygen content, and the mill certificate reports both along with the residual impurity level. That is why published numbers for the same material can differ: a value of 99.90% is the guaranteed minimum, while 99.95% or even 99.99% are typical assays that an individual heat may reach but that the specification is not obliged to guarantee.
C110 is the common trade name for copper 110, also written UNS C11000 and formerly CDA 110. It is electrolytic tough pitch copper, meaning it is refined electrolytically and then melted and cast in air, so a controlled amount of oxygen remains in the metal as fine cuprous oxide particles. Those particles are not a defect; they are what makes the grade free machining and gives it the characteristic behaviour that fabricators rely on.
Typical Composition and Oxygen Control
The composition of C11000 is deliberately simple, and almost all of the engineering interest lies in the two numbers that follow copper: oxygen and residual impurities.
| Element | Content |
|---|---|
| Cu | 99.90% minimum, including silver |
| Oxygen | Controlled residual, commonly quoted between 0.02% and 0.04% |
| Metallic impurities | Below roughly 50 ppm in normal commercial ETP copper |
| Conductivity | Approximately 100% IACS in the annealed condition |
Oxygen content is the number that decides whether a coil of C11000 can be welded. Cuprous oxide particles react with hydrogen at elevated temperature, generating steam inside the metal and cracking it, so tube that will be brazed or welded in a reducing atmosphere, or used in a hydrogen bearing process stream, must be ordered as an oxygen free grade instead. For drawn tube, bending, flaring and general fabrication at ambient temperature, the tough pitch structure causes no difficulty.
How C110 Compares with C10100 and C10200
The three grades are often quoted against each other, and the differences are small in percentage terms but decisive in application.
| Grade | Copper content | Oxygen | Typical use |
|---|---|---|---|
| C11000 electrolytic tough pitch | 99.90% minimum | Controlled residual, about 0.02% to 0.04% | Busbar, strip, tube, general electrical and thermal conduction |
| C10200 oxygen free | 99.95% minimum | 0.001% maximum | Welded assemblies, brazed tube, reducing atmospheres |
| C10100 oxygen free electronic | 99.99% minimum | 0.0005% maximum | Vacuum devices, high reliability electronics, waveguides |
The practical rule is that C11000 gives the best combination of conductivity, machinability and cost for parts that are formed and joined without a reducing atmosphere, while the oxygen free grades are chosen when the joining process or the service environment demands it. Paying for C10100 where C11000 would do adds cost without adding performance.
Physical, Electrical and Thermal Behaviour
Density: about 8.94 g/cm³, close to the theoretical value for pure copper.
Electrical conductivity: annealed C11000 is the practical reference for the international annealed copper standard, so it is rated at approximately 100% IACS, and cold work reduces it only slightly.
Thermal conductivity: roughly 390 W/(m·K) at 20 °C, which is why the grade is used for heat exchanger tube, busbar and thermal spreaders.
Melting range: approximately 1083 °C for the copper matrix, with the dispersed oxide particles remaining solid within it.
Elastic modulus: in the region of 117 GPa, giving useful stiffness even in thin drawn tube walls.
Impurity control is what protects those figures. Small amounts of phosphorus, iron or arsenic depress conductivity noticeably, so a specification that guarantees 99.90% minimum copper is also, in effect, a guarantee that the conductivity will stay near the reference value.
Temper, Hardness and Fabrication
Purity and temper are separate variables. C11000 is supplied in a range of tempers, and hardness moves with the amount of cold work rather than with composition: annealed material sits at the bottom of the range, in the region of 45 HV, while heavily cold worked strip reaches the top of the range at around 150 HV and above. Tube for plumbing, refrigeration and heat exchange is usually supplied in the annealed or light drawn condition so that it can be bent and expanded.
Fabrication is where the grade earns its reputation. C11000 is readily hot worked and cold worked, drawn, bent, flared, soldered and brazed, and it machines with a clean chip because of the dispersed oxide particles. Three practices belong in any work instruction. Anneal after heavy cold reduction if further forming is required. Keep sulphur bearing lubricants and ammoniacal compounds away from the surface, because they attack copper. And use a dry nitrogen purge during brazing or welding of any assembly, so that the bore stays bright and free from oxide scale.
Frequently Asked Questions
Q: Is C110 copper 99.9% or 99.99% pure?
The specification minimum for C11000 is 99.90% copper including silver. Higher figures such as 99.95% or 99.99% describe typical assays of individual heats and are not guaranteed by the standard.
Q: Why does C11000 contain oxygen?
ETP copper is melted and cast in air, so a controlled amount of oxygen remains as fine cuprous oxide particles. They improve machinability and have little effect on conductivity, but they prevent the grade from being welded in a reducing atmosphere.
Q: When should C10200 or C10100 be used instead?
Choose an oxygen free grade whenever the part will be welded or brazed in a hydrogen bearing atmosphere, or used in a reducing process stream. C10200 suits most welded assemblies and C10100 is reserved for the highest conductivity and vacuum service.
Q: What is the conductivity of C11000?
Annealed C11000 is rated at approximately 100% IACS, which corresponds to about 58 MS/m, and its thermal conductivity is around 390 W/(m·K). Cold working lowers the electrical figure only slightly.
Q: How hard is C11000 copper?
Hardness depends on temper rather than on purity. Annealed material is in the region of 45 HV and heavily cold worked strip reaches about 150 HV and above, with drawn tube usually supplied in the softer conditions.
Q: Can ordinary commercial copper be substituted for C11000?
Not safely. Substitution without a certificate risks lower copper content or higher oxygen, which can reduce conductivity or cause cracking during welding, so the grade, temper and oxygen limit should always be specified and certified.
