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The size of SiO2 particles in silica sol also affects the strength of shell(white fused alumina powder). The stability of silica sol with average particle size of 20 nm and concentration of 20% SiO2 is approximately the same as that of silica sol with average particle size of 10 nm and concentration of 10% SiO2, and it will not be dissolved in water(wholesale brown fused alumina). Therefore, the stability of silica sol is the result of the balance between the attractive cohesive force and repulsive force.

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The SiO2 particles contained in silica sol are very small, which have a large specific surface area(240 grit aluminum oxide powder), so they have large surface energy and have the tendency of spontaneous condensation. In addition, the possibility of agglomeration is also increased due to the collision caused by the irregular Brownian motion of particles(black silicon carbide manufacturers). The viscosity of silicon soluble amine is an important technological property of binder for investment casting.(cheap refractory grade alumina suppliers hungary)

Considering the quality of mold shell and shell making process(aluminium oxide powder price), it is required that the silica sol should have enough SiO2 concentration and suitable low viscosity, so as to improve the powder liquid ratio of the coating and improve the surface quality and strength of the shell. If a small amount of hydrochloric acid is added into the silica sol and the pH value is about 2 ~ 3(brown fused alumina suppliers). The particles are connected by s-0-si silyl ether bond, and water is precipitated.

(cheap refractory grade alumina suppliers hungary)However, if the viscosity of silica sol binder is too low, the fluidity of silica sol coating will be increased when the viscosity of silica sol binder is too low(aluminum oxide polishing grit), which will reduce the uniform covering performance of the surface coating layer, and make the surface layer easy to produce uneven flow lines, which will affect the surface quality(brown fused alumina factory). Only when all the moisture was removed did it form xerogels with high structural strength and hardness.

The higher the SiO2 concentration (weight ratio) in silica sol is, the higher the viscosity of silica sol is(black corundum price). The gelation of silica sol is essentially the result of the aggregation and condensation of SiO2 particles in the sol during the drying process of silica sol. Generally, the kinematic viscosity of silica sol with 30% SiO2 should be controlled in the range of 4 ~ 10 mm / s(white fused aluminum oxide), which can be used in investment casting production as a suitable high-quality binder for coating preparation.(cheap refractory grade alumina suppliers hungary)

When the water content in the silica sol decreases gradually and the concentration increases(alumina company), the probability of collision between the colloidal particles increases due to the Brownian motion of the particles, and the particles adhere to each other. The reaction formula is as follows: with the increase of silica ether bond between particles When the particles agglomerate with each other(black silicon carbide suppliers), the sol changes into gel, the acidic silica sol is obtained.

(cheap refractory grade alumina suppliers hungary)The process of silica sol continuous dehydration and concentration and gelation is irreversible, that is, the silica gel formed after gelation is completed(pink fused aluminum oxide). If the silica sol is not well dried and there is a small amount of gel in the silica gel, the shell will be swollen or deformed when it meets water, which will affect the strength of the shell and the quality of the casting(high purity fused aluminum oxide). The polycondensation reaction of silanol group takes place on the contact surface.