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Hydrochemical factors influencing the crystallinity and composition of kaolins and other silicates, revisited
Abstract Increasing pH of aluminum-bearing aqueous solutions causes most of the aluminum to pass from octahedral to tetrahedral coordination over a narrow pH interval: 5.5 to 6.5 at 25°C and 4 to 5 at 100°C. Thus silicates that grow from Al-bearing solutions having pH>6.5 at 25°C (or >5 at 100°C) should incorporate significant Al(tet) substituting for Si (especially if the solution provides monovalent cations to compensate for the charge defect), but should not do so if pH<5.5. This applies to a number of phyllosilicates, quartz, opal-CT, and opal-A in scales formed in tubes of geothermal power plants. In turn the predicted Al(tet)-for-Si substitution can explain the aggregate deformation of certain crystal structures induced by the larger size of the AlO4 tetrahedra, including the curling of the 1:1 layers of halloysite and the observed twisting of the tiny fibers of chalcedonic quartz making up agate layers.
Hydrochemical factors influencing the crystallinity and composition of kaolins and other silicates, revisited
Abstract Increasing pH of aluminum-bearing aqueous solutions causes most of the aluminum to pass from octahedral to tetrahedral coordination over a narrow pH interval: 5.5 to 6.5 at 25°C and 4 to 5 at 100°C. Thus silicates that grow from Al-bearing solutions having pH>6.5 at 25°C (or >5 at 100°C) should incorporate significant Al(tet) substituting for Si (especially if the solution provides monovalent cations to compensate for the charge defect), but should not do so if pH<5.5. This applies to a number of phyllosilicates, quartz, opal-CT, and opal-A in scales formed in tubes of geothermal power plants. In turn the predicted Al(tet)-for-Si substitution can explain the aggregate deformation of certain crystal structures induced by the larger size of the AlO4 tetrahedra, including the curling of the 1:1 layers of halloysite and the observed twisting of the tiny fibers of chalcedonic quartz making up agate layers.
Hydrochemical factors influencing the crystallinity and composition of kaolins and other silicates, revisited
Harvey, Colin C. (author) / Merino, Enrique (author)
Applied Clay Science ; 131 ; 71-73
2016-01-20
3 pages
Article (Journal)
Electronic Resource
English
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