8. Sodium: accelerator, control agent and chromate former

The patent explicitly names soda, i.e. sodium carbonate (Na₂CO₃), as an influencing factor. Soda accelerates and controls the oxidation to chromate. According to the patent specification, a sufficient addition of soda can substantially accelerate the conversion to chromate at or just below 1,000 °C. With an addition of 5 to 10 per cent by weight of soda, relative to the ferrochromium, Udy describes a conversion of approximately half of the chromium to chromate at 1,000 °C; the remaining portion is present in the chromite/Cr₂O₃ state.

Sodium is thus a constituent that is effective in process-chemical terms and can promote and control chromate formation. The statements on calcium chromate without soda are in section 7; sodium chromate is additionally listed in the patent claims. [1]