A Note on the Solubility of Water in a Molten Sodium Silicate

JSGT 1956 V40 T025-T031

Sodium silicate, approximately Na₂O.2SiO₂, has been saturated with water vapour at 1, 0·238, 0·117, and 0·064 atm partial pressure in nitrogen at 900, 1000, and 1100°. Samples were analysed by pumping off the water vapour in vacuum at 1200° for 3–10 h and measuring monometrically. The solubility is of the order of 3 N.cc/g at 1100° and 1 atm. From 900 to 1100° the solubility decreases by only 10%. Solubility as measured is not strictly proportional to (p_H2O)^1/2 as suggested by the relation H₂O + ≡Si–O–Si≡ ® ≡SiOH + HOSi≡ but falls below the expected figure at low partial pressures. This is thought to be due to the production of metallic sodium vapour by dissociation of the silicate melt in vacuum, which condenses in the cool parts of the apparatus and removes water vapour.

J. W. Tomlinson