Hydration of dibarium silicate I. Stoicheiometry of hydration

Dibarium silicate, Ba 2 SiO 4 , was hydrated in two ways: in paste form at 25° using a water/solid weight ratio of 0.7:1, and in a polyethylene bottle rotated on a wheel at 5°, 25° and 50°, using a water/solid weight ratio of 9.0:1. When Ba 2 SiO 4 is hydrated in paste form, the stoicheiometry of the reaction at 25° is the same as in bottle‐hydration at 50°: 2BaO.SiO 2 +2.2H 2 O = 1.2BaO.SiO 2 .1.4H 2 O+0.8Ba(OH) 2 . The stoicheiometry of bottle‐hydration at 5° and 25° is represented by the equation: 2BaO.SiO 2 +2.2H 2 O = BaO.SiO.1.2H 2 O+Ba(OH) 2 . Barium silicate hydrate, 1.2BaO.SiO 2 .1.4H 2 O, is well crystallised and has a specific surface area of ˜ 3m 2 /g. The crystals are plate‐like and have a tendency to form clusters. The low‐baria hydrate, BaO.SiO 2 .1.2H 2 O, is poorly crystallised and consists of thin platelets. It has a specific surface area of ˜ 35m 2 /g. The thermal dehydration of fully hydrated barium silicate and of the barium silicate hydrates was investigated by thermogravimetric and differential thermal analysis techniques. The similarities and differences between the barium silicate hydrates obtained in the hydration of barium silicate and the calcium silicate hydrates obtained in the hydration of β‐dicalcium silicate and Ca 3 SiO 5 are discussed. A mechanism of hydration of barium silicate is proposed which involves solution, precipitation and crystallisation steps.