16 ноября, 2015 
Pokraskin The furnace is allowed to cool to 500 °C when air is admitted in controlled amounts. The oxygen reacts with excess sulfur to form sulfur dioxide, which exothermically oxidizes the di — and triatomic polysulfide ions to S2- and S3- free radicals, leaving sodium sulfoxides and sulfur as by-products. When oxidation is complete, the furnace cools and is unloaded, a full kiln cycle takes between 3 and 4 weeks. The “raw” ultramarine product typically contains 75 wt.% blue ultramarine, 23 wt.% sodium sulfoxides, and 2 wt.% free (uncombined) sulfur with some iron sulfide.
3.5.3.4
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