![]() cardboards and railway tracks to promote traction Increasing friction - used to coat waxed floors, textile fibers.Stabilizing and rigidizing refractory ceramic fiber blankets.It is also be used in Lubrication of Tablet.It increase the bulk & taped density of powder & granules also.As binder or silica source in catalysts.An abrasive - for polishing silicon wafers.Investment casting - used as the inorganic binder in moulds.Cationic starch is added as sizing agent to increase the dry strength of the paper. It increases the amount of cationic starch that can be retained in the paper. ![]() In papermaking colloidal silica is used as a drainage aid.For example, 50 nm particles can be concentrated to greater than 50 wt% solids while 10 nm particles can only be concentrated to approximately 30 wt% solids before the suspension becomes too unstable. The maximum concentration obtainable depends on the on particle size. The colloidal suspension is stabilized by pH adjustment and then concentrated, usually by evaporation. Because of the very small size, the surface area of colloidal silica is very high. Substitution of some of the Si atoms by Al is known increase the negative colloidal charge, especially when it is evaluated at pH below the neutral point. Hydrogen ions from the surface of colloidal silica tend to dissociate in aqueous solution, yielding a high negative charge. These products are often called precipitated silica or silica sols. If the pH is kept slightly on the alkaline side of neutral, then the subunits stay separated, and they gradually grow. These products are often called silica gels. If the pH is reduced below 7 or if salt is added, then the units tend to fuse together in chains. Initial acidification of a water-glass ( sodium silicate) solution yields Si(OH) 4. Whether or not these subunits are joined together depends on the conditions of polymerization. The subunits of colloidal silica particles are typically in the range of 1 to 5 nm. Smaller particles are difficult to stabilize while particles much greater than 150 nanometers are subject to sedimentation.Ĭolloidal silicas are most often prepared in a multi-step process where an alkali-silicate solution is partially neutralized, leading to the formation of silica nuclei. Polydisperse suspensions can also be synthesized and have roughly the same limits in particle size. ![]() Most colloidal silicas are prepared as monodisperse suspensions with particle sizes ranging from approximately 30 to 100 nm in diameter. Colloidal silicas exhibit particle densities in the range of 2.1 to 2.3 g/cm 3. Usually they are suspended in an aqueous phase that is stabilized electrostatically. It may be produced by Stöber process from Tetraethyl orthosilicate (TEOS).
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