The transformation of amorphous silica to crystalline silica under hydrothermal conditions

✍ Scribed by Peter Bettermann; Friedrich Liebau

• Publisher: Springer
• Year: 1975
• Tongue: English
• Weight: 689 KB
• Volume: 53
• Category: Article
• ISSN: 0010-7999
• DOI: 10.1007/bf00402452

✦ Synopsis

Hydrothermal syntheses were made mainly in the binary system SiO2-H20 in a temperature range between 300 ~ C and 500 ~ C and pressures from 0.2 kbar up to 4.0 kbar with various starting materials. In this way the transformation behavior of different amorphous silicas via cristobalite and keatite to quartz were observed. This behavior depends mainly on the parameters: pressure, temperature, run duration and state of the starting material. Four reaction paths have been observed: in most experiments the complete reaction sequence "amorphous silica--,cristobalite~keatite~quartz" took place. Less often the reactions : "amorphous silica~cristobalite~quartz" and : "amorphous silica~keatite-+quarts" were observed.

Very few samples were found with a direct transition of amorphous silica into quartz at high pressures. A kinetic model is given in form of a pressuretemperature-time diagram of the system SiO2-H20 under hydrothermal conditions.