Carbon electrodes for aluminum electrolysis are blocks of ground charcoal or coke bound with 15-20% pitch, pressed and baked at 1,000-1,200 °C, and the anode is consumed as it works: the carrier gives about 0.4 kg of carbon per kilogram of aluminum, so a cell making 1 kg an hour burns 288 kg of anode in 30 days. It is real engineering and genuinely out of reach for most villages, because it needs a pitch supply, a press, a sealed baking kiln and clean carbon.
Part of Aluminum Smelting
Why a smelting cell needs baked carbon electrodes, how much it consumes, and the workshop that makes them.
The Anode Is A Reactant, Not A Fitting
The blocks are made of ground filler with 15-20% pitch and baked at 1,000-1,200 °C (Anode Fabrication). The anode takes part in the reaction: 2Al₂O₃ + 3C → 4Al + 3CO₂ (carrier). Carbon is therefore a raw material consumed in proportion to the metal, and the electrode shop must keep up. The cathode, in contrast, is a permanent lining (Cathode Lining). Baked carbon is also the electrode for arc furnaces in this tree (EAF Operation for Stainless).
Worked Example: Carbon Demand
At the carrier’s 0.4 kg carbon per kg of metal and a cell making 1 kg per hour:
- Per hour: 0.4 kg.
- Per day: 0.4 × 24 = 9.6 kg.
- Per 30 days: 9.6 × 30 = 288 kg of baked carbon.
The stoichiometric floor is 0.334 kg C per kg Al (3 × 12.01 / (4 × 26.98), atomic masses recalled), so the carrier’s 0.4 includes extra burn. Each kilogram of aluminum releases 1.22 kg of CO₂ (3 × 44.01 / 107.9).
What You Need
- Filler carbon: petroleum coke or high-quality hardwood charcoal (carrier). Petroleum coke will not exist; charcoal comes from Charcoal Production. Charcoal ash and impurities enter the bath and the metal, as I recall; use dense, low-ash charcoal, and beech is listed as low-ash there.
- Pitch binder from coal tar (Coal Tar Distillation).
- A press, a mixing vessel, and a sealed baking kiln (Anode Fabrication).
Common Mistakes
- Sizing the electrode shop from the cell, not the consumption. The anode must be replaced continuously.
- Using resin or wood pitch as if it were coal-tar pitch. The carrier specifies coal tar pitch; wood pitch behaves differently and I cannot source its use here.
- Skipping the bake. Unbaked blocks do not conduct or hold together.
Safety
Hot pitch, fume and kiln fire
Pitch is mixed at 150 °C; hot pitch burns skin and its fume is harmful, which I recall includes carcinogens, though the corpus gives no limit. Baking releases flammable gas from the pitch. Work outdoors, away from fuel, and keep a dry-sand pile for fires; never fight pitch fires with water.
What’s Next
- Learn next: Anode Fabrication - mixing, pressing and baking
- Combine with: Cathode Lining - the permanent carbon in the cell