Studies on Formation and Recrystallization of Intermediate Reaction Products in the System Magnesia-Silica-Water

Mixtures of magnesia and silicic acid ranging in composition from 0.5 to 2.0 M/S were treated hydrothermally at temperatures of 75° to 350°C. for various periods of time. The reaction solids were examined by differential thermal analysis, X ray, and electron microscopy and analyzed chemically. The intermediate products of reaction ranging in composition between that of talc (0.75 M/S) and chrysotile (1.5 M/S) comprised a continuous series of cryptocrystalline needle-like crystaIs matted tightly together and showing the same X-ray pattern. The initial reaction product of the 0.75 to 1.50 M/S raw mixtures was a cryptocrystalline solid having a 1.5 M/S ratio. This phase subsequently reacted with the residual silica, so long as any was available, to form a solid having the composition of the raw mix, but only at relatively moderate temperatures(100°to175°C.). As the temperature was increased the crystals of the 0.75 and 1.50 M/S compositions increased in size, but all remained submicroscopic. The compositions intermediate between 0.75 and 1.5 M/S crystallized as mixtures of talc and chrysotilelike products. The chrysotilelike product appeared as minute needles which did not possess any apparent flexibility.