OFHC Copper is a copper alloy used in aerospace applications. Melting point: 1,083 °C. Tensile strength: 220 MPa.
Inside a liquid-rocket engine, a metal wall sits just millimeters from a flame hotter than 3,000 degrees Celsius and somehow does not melt. The secret is an ultra-pure copper called OFHC, which pulls heat away faster than almost any other practical metal.
Quick facts
- Full name: Oxygen-Free High-Conductivity copper — copper refined so almost no oxygen remains inside its crystal lattice (the orderly grid of atoms that makes up the metal).
- Purity: about 99.95–99.99% pure copper, with oxygen content of roughly 0.001% or less and total impurities of about 0.03% at most.
- Common grades: C10100 (Oxygen-Free Electronic, or OFE) at 99.99% purity and ≥101% IACS conductivity; C10200 (Oxygen-Free, or OF) at 99.95% purity and ≥100% IACS. IACS is a standard scale where 100% equals the conductivity of pure annealed copper.
- Thermal conductivity: roughly 390–400 watts per meter-kelvin — among the highest of any engineering metal.
- Other strengths: high ductility (it can bend and stretch without cracking), high impact strength, good creep resistance, easy welding and brazing, and very low outgassing in a vacuum.
What it is and how it works
Ordinary copper traps tiny amounts of oxygen, which forms copper-oxide specks inside the metal. Those specks get in the way of both heat and electrons, so they slightly lower conductivity. OFHC copper is refined to remove that oxygen, which is why it reaches near-maximum electrical and thermal conductivity.
In a rocket, the standout property is heat handling. A liquid-rocket combustion chamber — where fuel and oxidizer burn — runs at around 3,000–3,300 degrees Celsius, hotter than the melting point of any metal a chamber could realistically be built from. The wall survives through regenerative cooling. The inner liner is made of copper with hundreds of tiny channels milled into it, and cold propellant — liquid hydrogen, methane, or kerosene — is pumped through those channels on its way to the engine. Think of it like the radiator and coolant loop in a car, but with the coolant being the rocket’s own fuel.
Copper’s job is to conduct the intense heat on the flame side through the thin wall and into the flowing coolant fast enough that the metal never reaches its own melting point. Removing oxygen also prevents hydrogen embrittlement: when ordinary oxygen-bearing copper meets hot hydrogen, the hydrogen reacts with the internal copper oxide to form steam that cracks the metal from the inside. Oxygen-free copper has no oxide to react with, eliminating that failure mode — essential for hydrogen-fueled engines.
Why it matters
Regeneratively cooled copper liners are what make high-performance, high-pressure, reusable liquid-rocket engines possible. Without a material that moves heat as fast as oxygen-free copper, the thin wall facing the flame would simply melt or burn through.
The trade-off is durability. Pure OFHC copper is fairly soft and loses strength when hot, so flight engines almost always use copper alloys built on the same oxygen-free chemistry. Small additions of silver, zirconium, chromium, or niobium create dispersion-strengthened alloys that hold their strength at red heat while keeping most of copper’s conductivity. Even then, liners suffer thermal-fatigue cracking and “blanching” — surface roughening and burn-through caused by combustion gases that swing between oxidizing and reducing. An RS-25 liner could begin cracking in as few as three flights, which drove decades of NASA materials work toward longer-life alloys.
Where it is used and notable examples
- Space Shuttle Main Engine / RS-25: the main combustion chamber liner is NARloy-Z (copper with 3% silver and 0.5% zirconium), with roughly 390 channels carrying liquid hydrogen, housed inside an Inconel 718 structural shell.
- RL10 upper-stage engine (Centaur, DCSS): newer RL10C/E variants use a 3D-printed copper-alloy thrust chamber, cutting fabrication time from about 20 months to 4–6 months and reducing part count by roughly 98%.
- GRCop-84 and GRCop-42: NASA Glenn copper-chromium-niobium alloys made by powder metallurgy for stronger, longer-life liners, hot-fire tested with liquid-oxygen plus hydrogen, methane, and kerosene.
- Protective coatings: copper-chromium coatings on OFHC copper walls help resist blanching and oxidation damage.
- Spacecraft vacuum and electronics hardware: OFHC copper is used for thermal straps and cryogenic and RF components, where high conductivity and low outgassing matter.
Cu 99.99%, O2 < 0.001%
| DENSITY | 9 kg/m³ |
| TENSILE STRENGTH | 220 MPa |
| YIELD STRENGTH | 69 MPa |
| STRENGTH-TO-WEIGHT | 24608.5 kN·m/kg |
| MELTING POINT | 1,083 °C |
| MAX SERVICE TEMPERATURE | 200 °C |
| THERMAL CONDUCTIVITY | 391 W/m·K |
| THERMAL EXPANSION | 17.0 µm/m·K |
| CATEGORY | Copper Alloy |
| DESIGNATIONS | UNS C10100, ASTM B170, CDA 101 |
| MANUFACTURER | Various (Aurubis, KME, Mitsubishi) |
| DENSITY | 9 kg/m³ |
| TENSILE STRENGTH | 220 MPa |
| YIELD STRENGTH | 69 MPa |
| MELTING POINT | 1,083 °C |
| MAX SERVICE TEMP | 200 °C |
| THERMAL CONDUCTIVITY | 391 W/m·K |
| THERMAL EXPANSION | 17.0 µm/m·K |
| CORROSION RESISTANCE | Fair |
| WELDABILITY | Good |
| MACHINABILITY | Good |
| COST RATING | Moderate |
