Silica sol is the dispersion of nano-sized silica particles in water or solvent.Since SiO2 in silica sol contains a large amount of water and hydroxyl groups, it can also be expressed as msio2.nh2o.There are different ways to prepare silica sol.The most commonly used methods include ion exchange, one-step hydrolysis of silica powder, and silane hydrolysis.
Silica sol is a colloidal solution, odorless, non - toxic.Silica sol is the dispersion of nano-sized silica particles in water or solvent.Since SiO2 in silica sol contains a large amount of water and hydroxyl groups, it can also be expressed as sio2.nh2o.
The ion exchange process of silica sol was developed in the 1940s by the American company NALCO. After that, it was perfected by the American company dupont in the 1950s and 1960s. At present, it is the most mature and widely used process.This process has certain requirements for materials such as water glass, ion exchange resin and operation technology, which are the weakness of domestic products.Relatively speaking, the process of one-step hydrolysis of silica powder is relatively simple and is widely used in China.However, silica sol prepared by this method usually has a particle size of about 10-20 nanometers, and the interface between particles is not clear, the morphology is non-spherical and cannot be controlled, and the interface between particles is not clear, so it is usually used in casting and other industries in large quantities, but not in many fields with higher requirements such as precision polishing and catalyst.Compared with the internationally renowned silica sol brand, the main disadvantages of domestic silica sol at present are high impurity content, no strict control of particle size, no strict detection of particles than the surface, low concentration of silica, poor stability under acidic or neutral conditions, short service cycle, more or less with a little color, less variety and so on.At present the internationally renowned silica sol brand has dupont to pass reiss LUDOX series.
The development of
Silica sol inorganic polymer coatings have been developed in recent years.The key technology to prepare the coating is
Water-soluble sodium ions in water glass are removed by special methods.In general, it can be achieved by ion exchange, acid neutralization, water decomposition, electrodialysis and other methods to generate an extremely fine colloidal aqueous solution of silica ultrafine particles with particle size of 580nm (general emulsion particles are 800-1000nm), in which the content of Si2O is 20%-30%, the content of Na2O is 0.3%, and the ratio of silicon oxide to sodium oxide is more than 40%.Silica sol inorganic polymer coating is prepared by using silica solution/gel as base material, pigment and various additives.When the silicon solution loses water, monomer silicic acid gradually polymerizes into high poly silica gel. With the evaporation of water, colloidal molecules increase, and finally form -sio-o-sio-coating film: io-si-oh + ho-si-oh has the property of certain amount of film-forming dissolution due to the low content of NA2O in silica sol, and its water resistance and heat resistance are obviously better than that of organic coating.The coating film is dense and hard, does not produce static electricity, the dust in the air is difficult to adhere to.In the present architectural coating, its anti - pollution ability is stronger.
Fine particles, have a strong penetration to the base, can penetrate through the capillary to the base inside, and with the concrete base in the reaction of calcium hydroxide calcium silicate, so that the coating has a strong adhesive force.
But the volume shrinkage of silica sol is large in the process of film formation, and the coating film is easy to crack.Silica sol can be dissolved with acrylate, vinyl acetate and other emulsions.The properties of the two are complementary to each other, and the organic and inorganic composite coatings with excellent properties can be prepared.