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GypSum

Gypsum (Calcium Sulfate Dihydrate)

Results: Between 100 and 300°C, the double-step dehydration of the calcium sulfate-dihydrate occurred. In the first step, 1.5 out of 2 water molecules were released from the system and half-hydrate was formed. In the second, the half-hydrate dehydrates further on and forms anhydrate. Starting at 348°C, the anhydrate converts to β-calcium sulfate (exothermal effect). At 1219°C the β-calcium sulfate converts to α-calcium sulfate, clearly visible as a sharp exothermal effect in the DSC curve. At temper- atures above 1250°C, a further mass loss can be seen. This mass loss refers to the sulfate decomposition. Calcium sulfate converts into calcium oxide. The enodthermal peak at 1380°C is due to melting of an eutectic mixture of calcium sulfate and calcium oxide. AS-009-2006 llab@ngb.netzsch.com STA 409 PC Luxx® http://www.netzsch-thermal-analysis.com/en/literatur/download/42/

Digital Fire: http://digitalfire.com/4sight/mineral/ceramic_mineral_gypsum_calcium_sulphate_83.html

http://www.walkerceramics.com.au/faults_remedies.htm Pin holed Glaze Pinholes in glaze after firing. Caused by gas evolution from body and/or glaze during firing. (3) Soluble salts (sulphates) in body. (a) Add 0.01 - 0.25% Barium Carbonate to the body.

Materials such as manganese dioxide in clay can give off oxygen in glost and decorating fires if they are not decomposed during bisk firing. REFERENCES ceramicdefects.com/wwdftbl.pdf