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Colloidal Silica
01 Particle & Surface
- SS-SOL is colloidal silica consisting of spherical particles of silicon dioxide (SiO2)
dispersed in water
- Silica surface is charged by hydroxyl ions formed by loss of protons from water molecules in the spaces between the oxygen atoms of the structures.
- According to this electric charge of particles, it has formed gelation, aggregation and colloid. If the particles are smaller than 7nm in diameter the sol is almost as clear as water.
- From 10nm to 30nm there is a characteristic opalescence or transparency when seen it. And above about 50nm the appearance is white and milky.
- Silica surface is charged by hydroxyl ions formed by loss of protons from water molecules in the spaces between the oxygen atoms of the structures.
- According to this electric charge of particles, it has formed gelation, aggregation and colloid. If the particles are smaller than 7nm in diameter the sol is almost as clear as water.
- From 10nm to 30nm there is a characteristic opalescence or transparency when seen it. And above about 50nm the appearance is white and milky.
02 Effect of pH
The colloidal silica has very different stabilizing by pH degree. In general, the higher concentration
or the smaller particle size, the greater effect of pH. The colloidal silica are extraordinarily stable at
pH 2 where the zeta potential is zero and become increasingly sensitive electrolytes at higher pH.
The particles in colloidal silica are stable above the pH 8 that is to be seen right fig. Most of SS-SOL
are stands between 9 and 10.5. It means all of SS-SOL are stable in constructional.
The SS-SOL30A is stable as pH 2. It is the one and only as acidity production. This is produced in
special process own know how and it has a modified particles with another ions. So it could be mixed
with another sol like alumina sol and organic solvents and it is stable against change of pH and
SS-SOL30A is also comparatively stable at neutral pH range. At the result of our ability to control the characteristics of colloidal SS-SOL could apply for all of today’s industrial applications.
03Use of SS-SOL
New type of commenrcial colloidal silica become availavle and others disappear from the market.
Therefore lt is not possible to predict which kinds will remain available in the future, but past and current types are listed in our catalogue.
The following types of applications are listed according to the purpose the colloidal silica
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Increasing the coefficient of friction
Increasing the friction of solid surfaces. For example, railway tracks, waxed floors, and textile fibers. -
Adhesion, Film
Forming strong and rigid solid surface. -
Stiffening
Because it can be produced rigid gel by sintering, it is used for stiffening powder. -
Increasing cohesion by Gelation
It can increase cohesion, formed uniform gel by gelation. And it can be dispersed. Therefore it can be stabilized supporter -
Increasing hydrophilicity & prevention electrification
Hydrophilicity can be increased by Si-OH, and electrification can be prevented. -
Increasing activity
Because of lower ion concentration and higher silica concentration, when liquid is mixed reaction is uniform. And activity rate is faster. -
Lager surface
After dried colloidal silica, it can be got silica gel large that has surface area and uniform pore. -
Impregnant & Filler
It is used for filler of porous substance. And it is environmental harmony because of lower Na+ concentration.
04 Making Catalysts, Gels, Asdorbents
The obvious advantage of stating with colloidal silica instead of sodium silicate are the ease of
incorporation with other catalyst components, the minimum washing required to remove unwanted salts,
and the wider, more than uniform pore structure obtained by forming the gel from relatively large, uniform
colloidal particles.
The advantage of a catalyst base of colloidal silica spheres in a densely packed arrangement is that at elevated temperature, the mass cannot readily contract further and collapse or sinter, and the uniform pores between the uniformly packed uniform particles provide a constant surface area and high degree of catalytic activity.
The silica sol containing metal salts can be spay-dried or freeze-dried to give small spherical gel particles which can be further compacted as desired. Sol can be converted to a fine powder by dispersing the sol in a partly water-miscible organic solvent, gelation the silica, and distilling off the liquids.
The advantage of a catalyst base of colloidal silica spheres in a densely packed arrangement is that at elevated temperature, the mass cannot readily contract further and collapse or sinter, and the uniform pores between the uniformly packed uniform particles provide a constant surface area and high degree of catalytic activity.
The silica sol containing metal salts can be spay-dried or freeze-dried to give small spherical gel particles which can be further compacted as desired. Sol can be converted to a fine powder by dispersing the sol in a partly water-miscible organic solvent, gelation the silica, and distilling off the liquids.
05 Inorganic Binder, Stiffener
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Molded Refractory Bodies
A mullite bonded refractory was made by mixing colloidal silica and basic aluminum chloride in proportions to form mullite and using this as a binder for mullite powder to form a mullite refractory body at 1300℃. Refractory bodies of silllimanite have been bonded with a mixture of colloidal silica and basic aluminum chloride acting as a binder for sillimanite powder, fired at 1300~1400℃. Cold-molded metal bodies with thermal conductivity can be made from metal powders using colloidal silica and latex as the binder. -
Binders for Fibers
An inorganic binder for inorganic fibers is made by dispersing clay in colloidal silica, then acidifying to pH 3.5 and adding an aluminum salt such as aluminum formate. Fire-resistant reflective insulating material is made by binding fibrous potassium tianate with a mixture of latex and colloidal silica. Colloidal silica is used as binder in highly refractory aluminosilicate fibers. The stiffness and strength of organic fiber sheets or papers can also be improved with colloidal silica. In paperboard used for corrugating, stiffness is improved by impregnating with colloidal silica. From 1 to 5% colloidal silica in certain paper pulps gives improvement in strength, stiffness, stability, etc.
06 Frictionizing Effets
The high friction observed between surfaces of sandpaper can be duplicated on an invisible scale
on various surface of colloidal silica. One of the early large-scale applications of colloidal silica
was in floor wax to make it less.
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Fibers
Colloidal silica is coated with a cationic quaternary ammonium type of surfactant before application to textiles for good frictionizing. Because of its fractionizing effects, silica is also an aid in processing wool. Slippage of glass fibers is prevented and colors are simultaneously bonded to the surface by the application of colored metal oxides along with colloidal silica and heating to bond the coating. To prevent knots in nylon fishnets from slipping, colloidal silica is mixed with and water applied to the knots. -
Paper & Film
The surface of polyethylene terephthalate drafting film is improve with respect to reception of pencil
and ink by applying colloidal silica along with an acid-soluble film-forming material.
07 Antisoiling Surface
A film of colloidal silica on the surface of fiber, as in carpets, greatly reduces the pickup of
dirt and leaves a cleaner appearance after vacuuming. It has been postulated that the silica form
a smooth adherent film to which soil particles do not cling, especially because it fills crevices in
the fiber surface the would otherwise be filled with dark particles of dirt. Similar effects are reported
on painted surfaces, plastic fiber, window shades, and wallpaper. To reduce soiling of hydrophilic
surface such as upholstery fabric by making it both hydrophobic and soil resistant, a
polydimethylsiloxane oil is incorporated with colloidal silica using a metallic soap emulsifier,
and applied to the cloth an cured.
08 Hydrophilizing Surfaces
A water-wettable surface is important in the lithographic printing art, where printing surfaces
holding the oil-ink must be hydrophobic and ink-wettable, but the nonprinting water-wettable
surface must be very resistant to encroachment by the oil-ink, and permanently hydrophilic.
Transfer of oil-printing is prevented by a spray of colloidal silica. A hydrophilic nature of “planographic” paper printing plates is preserved or renewed by colloidal silica. A hydrophilic film of colloidal silica contains dispersed ink-receptive material, which is released to the surface by pressure or heat to form printing areas. A similar effect is involved in planographic offset masters.
Transfer of oil-printing is prevented by a spray of colloidal silica. A hydrophilic nature of “planographic” paper printing plates is preserved or renewed by colloidal silica. A hydrophilic film of colloidal silica contains dispersed ink-receptive material, which is released to the surface by pressure or heat to form printing areas. A similar effect is involved in planographic offset masters.
09 Modifying Adhesion
Colloidal silica can be applied to surfaces either to increase the adhesion to other materials, in
effect by roughening the surface if the silica is adherent, or to decrease adhesion by holding
otherwise “sticky” surface apart.
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Increasing Adhesion
If silica particles are anchored to or embedded in a surface, the submicroscopic roughness and polarity of the surface are increased and adhesion of a second material is generally improved: on the other hand, if the silica is present as a loose. Friable coating, or is applied as mixture with a silicone or fluorocarbon polymer, adhesion is reduced. Silica particles are embedded into the surface of polyethylene film to improve the adhesion of coatings of thermoplastic polymers. A fluorocarbon polymer surface is made cementable by coating it with the mixture of dispersed polytetrafluoroethylene and colloidal silica, and heating the surface to over 500℃ for a few minutes. A film of polyethylene is strongly adherent if heated against paper coated with colloidal silica. A coating composition of polytetrafluoroethylene contains alkali metal silicate and colloidal silica to improve adhesion and electrical insulating properties on metal surfaces. First treating the fiber with colloidal silica and heating to just below the fusion temperature improve the adhesion of colored coatings on glass fibers.
10 Coating Compoitions
Organic coating compositions with improved adhesion, hardness, durability, and electrical properties
are obtained by adding colloidal silica to organic polymer dispersions. Inorganic coatings may employ
silica as the main component or as a binder in the composition. In coatings mainly consisting of silica
the problem is to prevent shrinkage and crazing. The film-forming properties of colloidal silica are
improved by dispersing microfibrous materials in the sol to minimize crazing. Inorganic paint for
asbestos board can be made with silica as a binder. Hard, weather-resistant paint is made with a
combination of colloidal silica, lithium hydroxide and potassium silicate or alkali metal phosphate, clay,
and figment, and backed on in the presence of steam. Colloidal silica stabilized with tetraethanol
ammonium silicate was used as a binder for iron oxide and clay pigments.
11 Reinforcing Organic Polymers
The strengthening or reinforcing effects of colloidal silica in organic
polymers, films, and fibers are so varied that they are not categorized.
Silica has been incorporated into polyolefins, thermoplastic organic
polymers, polyamides, and other types.
Copolymerization of colloidal silica and soluble silicate polyester gives
a strong water-impermeable mass. Aqueous sols are used in the rubber
industry mainly for stiffening open-cell foamed rubber. The silica deposited
on the walls of the pores apparently has frictionizing effects, making the
foam less easily compressed and thus increasing load bearing capacity.
A pickup of only 3% SiO₂ increase compression resistance by 90%
12 Polishing Agent for Silicon Wafers
In the electronics industry wafers cut from single crystals of silicon are polished to extreme smoothness
using colloidal silica as a polishing medium at high pH.
13 Miscellaneous Optical Effects, Color, Photography
Numerous patents have been issued on antireflection coatings in which silica in various forms is
deposited as a thin, adherent layer, generally on the surface of glass or plastic sheets and lenses.
Films of colloidal silica are deposited in various ways. A film of colloidal silica on glass reduces glare
when of the right thickness. A “black mirror” transparent to infrared is made by depositing layers of
nickel (10~15nm) and SiO₂(80~90nm): it is used to absorb solar energy. To produce interference
colors in paints, a mica pigment is coated with TiO₂and SiO₂ of correct thickness. A coating inside
electric light bulbs to diffuse light without adsorption is formed with colloidal silica, which may also be
used to bond a phosphor to the inner surface of a lamp bulb. Photographic and diazo-type papers are
coated with colloidal silica. In Polaroid photographic film colloidal silica plays an essential role in the
receiving layer to which the image is transferred and in which the black silver positive image is developed.
14Use in Biological Research-Density Gradient
Colloidal silica has found use as a high-density medium for separating biological materials by
centrifugation. The use of a mixture of colloidal silica mixed by polyethylene glycol of molecular
weight 3000~3700 in a tries buffer solution at pH 7.5 as a density gradient solution in centrifuging
and purifying a virus. In separating blood cells in colloidal silica medium some structural changes
were observed.
15 Sounrce of Chemistry Reactive silica
Colloidal silica is much more chemically reactive than the most finely pulverized sand, not only
because the specific surface area is several hundred times greater, but also because amorphous
silica is 10 times as soluble in water as crystalline quartz.
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Soluble Silicates
Silica rapidly depolymerizes in the presence of strong alkali. Thus colloidal silica can be converted to a solution of sodium polysilicate containing from 4.2 to 6.0 moles of silica per mole of sodium oxide or lithium polysilicate and lithium silicate is not soluble in hot water. For lower ratio silicates the advantage of starting with colloidal silica is only a matter of convenience because of the rapid reaction rate. -
Glass Compositions
Homogeneous glasses can be made by admixing the other components intimately with colloidal silica. The chemical reactivity of colloidal silica plays a role in colored or conductive coatings on glass or refractory materials in which a vitrified bond is developed without damaging the substrate. -
Forming Solid Silicates-Cements
The oldest known reaction of amorphous silica is that in Raman cement where lime was mixed with sand and colloidally subdivided silica of volcanic origin mined at Pozzuoli, Italy, and Greek island of Santorini. This was the basis of the extremely impervious cement linings used in cisterns throughout the Mediterranean area and in construction throughout the Raman Empire without which some of the vast domes could never have been built. Sand and lime alone do not form such cement.
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