I'm trying to do the electrolysis of molten hematite and/or eventually magnetite if the temperature goes too high. So the temperature is around 1600°C and I have simply air atmosphere.
I'm looking for the right electrode material(s) which at this temperature 1) doesn't melt 2) doesn't oxidize 3) doesn't dissolve in the electrolyte.
The only option seems to be platinum but it's quite expensive. Any alternatives?
Dear Daniel Csati ,
an alternative, proposal electrode, material for your R&D (case of the air atmosphere) electrolysis of molten hematite might be one of the commercially available electrodes' type and size of Tungsten[1-3] (selection guides[4-7]), commonly used in another high temperature field, as GTAW (Gas Tungsten Arc Welding[1,2]) electrodes.
1. GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum, magnesium, and copper alloys. https://en.wikipedia.org/wiki/Gas_tungsten_arc_welding
2. Tungsten is a rare metallic element used for manufacturing gas tungsten arc welding (GTAW) electrodes. The GTAW process relies on tungsten's hardness and high-temperature resistance to carry the welding current to the arc. Tungsten has the highest melting point of any metal, 3,410 degrees Celsius[3].
3. Guidelines for tungsten electrodes https://www.thefabricator.com/thefabricator/article/arcwelding/guidelines-for-tungsten-electrodes
4. GTAW electrodes' materials (commercial types for GTAW): a)Pure Tungsten (Color Code: Green), b)Thoriated (Color Code: Red), c)Ceriated (Color Code: Orange), d)Lanthanated (Color Code: Gold), e)Zirconiated (Color Code: Brown), f)Rare Earth (Color Code: Gray) https://www.weldingandndt.com/tig-welding-gtaw-electrodes/
5. What type and size of electrode should you use for GTAW and why? https://technoweld.com.au/2019/09/18/what-type-and-size-of-electrode-should-you-use-for-gtaw-and-why/
6. What Tungsten to Use for TIG Welding https://weldingheadquarters.com/what-tungsten-to-use-for-tig-welding/
7. The Arc-Zone Tungsten Selection Guide https://www.rukidding.info/images/TungstenSelectionGuide.pdf
Dear Ioannis Samaras
Thank you for your answer.
Apparently there is always some shielding gas used at GTAW to prevent the tungsten electrode from oxidizing. According to Wikipedia, in any oxygen containing shielding gas, the electrode would easily get consumed.
I expect to develop oxygen on the anode so it would surely oxidize the tungsten electrode. I can achieve at least 2200°C with my setup and the tungsten oxide decomposes at 1700°C already. The decomposing tungsten oxide would then generate again oxygen but it will also contaminate the electrolyte with tungsten.
I found recently a few alloys which would work: platinum-iridium, platinum-rhodium, tungsten-rhenium. They are still expensive, but available in a form of a thin wire. The volume of my molten electrolyte is small anyway, about 3 x 3 x 3 mm (it's generated by a laser spot), so a thin wire would probably do the job.
Inert gases such as argon or helium are used to protect, mainly, the welded area[1]. So, it might work for 1600°C[2], without (oxidizing/)consuming the bulk of the proposal electrodes.
1. What is GTAW (Gas Tungsten Arc Welding)? https://www.tws.edu/blog/welding/what-is-gtaw-gas-tungsten-arc-welding/
2. Your initial question "Which electrode material for high temperature (ca 1600°C) electrolysis?"
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