“Spontaneous” growth of fibrous products on the surface of silicic acid gels

Abstract

We have observed occurrence of fibrous products on gel surface in four-component system of KK (silicic acid sol)–H2O–HCl–NH3, KK–H2O–HCl–NaOH and KK–H2O–HCl–TEA (triethanolamine). Bundles of fibres occur in the system with NH3, sticks and needles in system with NaOH, and finally in the system with TEA we can mostly observe the occurrence of crystalline products. Dependency of product morphology on initial sol composition is occurring in observed systems. In the case of system with NH3, mostly the length of nascent fibres is influenced by the composition, and in the systems with NaOH and TEA it is also final shape of nascent products. Morphology of nascent products in systems with NH3 and NaOH is controlled by quantity of added HCl, but in the system with TEA it is quantity of added TEA. It is characteristic for all observed systems that “spontaneously” occurring products consist of crystalline phase, that is chloride of respective alkali, and amorphous phase, that is SiO2. Beginning of respective chloride crystallization in observed systems probably initializes occurrence of products on gel surface. Further growth of crystals is influenced by present colloid of SiO2 that interacts with surface of growing crystal leading to anisotropy of its growth and therefore to “spontaneous” occurrence of fibrous products.