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COLLOIDAL SILICA

CAS NUMBER: 7631-86-9

EC NUJMBER: 231-545-4

MOLECULAR FORMULA: SiO2

MOLECULAR WEIGHT: 60.08

 

Colloidal silicas are suspensions of fine amorphous, nonporous, and typically spherical silica particles in a liquid phase.
Colloidal silica varies from other types of silica in several significant ways. 

The most noticeable difference is that it's in liquid form, as opposed to powder. 
In addition, it has the widest ranging surface area, and its aggregate size can be as small as the actual size of the primary particle.

Colloidal silica dispersions are fluid, low viscosity dispersions. There are many grades of colloidal silica, but all of them are composed of silica particles ranging in size from about 2 nm up to about 150 nm
Colloidal silicas may be spherical or slightly irregular in shape, and may be present as discrete particles or slightly structured aggregates. 

Colloidal silicas may also be present in a narrow or wide particle size range, depending on the process in which they were created.
The maximum weight fraction of Colloidal silica in the dispersion is limited based on the average particle size.

Dispersions with a smaller average diameters have larger overall specific surface areas and are limited to low concentration dispersions. 
Conversely, dispersions with larger average diameters have lower overall specific surface areas and are available in more concentrated dispersions.

The appearance of colloidal silica dispersion depends greatly on the particle size. 
Dispersions with small silica particles (< 10 nm) are normally quite clear. 

Midsize dispersions (10-20 nm) start to take on an opalescent appearance as more light is scattered. 
Dispersions containing large colloidal silica particles (> 50 nm) are normally white.

Standard colloidal silica dispersions are stable against gelling and settling in pH range of 8 - 10.5.
These colloidal silicas are charge stabilized with an alkali (normally alkalis of sodium, potassium, or lithium) or stabilized with ammonia.  

Under these conditions, the particles are negatively charged.
The dispersion can be destabilized through the addition of excessive electrolytic species (sodium, calcium, chloride, lithium, potassium).

These colloidal silica particles can achieve additional anionic charge stability when as aluminosilicate sites are formed by incorporation of aluminum into the surface layer of the silica particles.
Low pH versions of colloidal silica are also available by the adsorption of cationic aluminum oxide onto the surface of the particles.  

This results in a cationic particle that is stabilized with anionic species - commonly this is chloride. 
These dispersions are stable below a pH of 4. 

Low pH grades can also be obtained by completely deionizing the dispersion.
These grades do not require the presence of stabilizing ions and are also stable below a pH of 3.

Colloidal silicas can be modified to several configurations including but not limited to: adjustments to pH, stabilization ions, surface charge and surface modification. 
Colloidal silica consists of silica molecules suspended in liquid, thereby forming a liquid sol.

The process of creating colloidal silica is closely monitored to ensure that the silica molecules remain stable and separate within the liquid medium without collapsing into smaller component molecules or collecting into unstable silica gels. The liquid dispersion medium exhibits greater density than water and must be electrostatically treated for enhanced ionic stabilization.
Colloidal silica is highly fluid with low viscosity. Uses for colloidal silica vary depending on the size of the silica particles in the solution and the modifiable pH, ionization, and surface charge.

Colloidal silica is extensively used as a rheological additive in personal care products to control flowability.
In the most general terms colloidal silica is a dispersion of amorphous silicon dioxide (silica) particles in water.  

These amorphous silica particles are produced by polymerizing silica nuclei from silicate solutions under alkaline conditions to form nanometer sized silica sols with high surface area.  
A charge is then induced on the silica nanoparticle surface that allows the silica particles to repel one another and form a stable dispersion, or colloid.

Colloidal silica is a stable suspension of spherical silicon dioxide (SiO2) nanoparticles in a liquid, that are hydroxylated on the surface. 
Colloidal silica is found in almost all industrial sectors. 

The applications range from surface treatment in the paper industry, to use as a polishing agent in the electronics industry and use as an additive for varnishes, coatings and paints to improve weather and abrasion resistance. 
Colloidal silica is also a common additive in cosmetics and in the food industry. 

The mean particle size and distribution width define the field of application of the SiO2 particles. 
Typical sizes range from 1 nm to 100 nm.

Colloidal silicas are typically aqueous suspensions in the range of 30 – 500 nm in diameter.  
Colloidal silicas are usually stabilized electrostatically and have densities in the range of 2.1 to 2.3 g/cm3. 

Applications for colloidal silicas include fillers, binders, abrasives, catalysts, and absorbants.
Most size measurements of colloidal silica are performed using dynamic light scattering (DLS) instruments such as the SZ-100 Nanoparticle Analyzer. 

Colloidal silica is used in many applications including catalysis, pharmaceuticals, and coatings. 
Although naturally formed silica materials are widely available, they are often in forms that are difficult to process or are even harmful to health. 

Therefore, uniform colloidal silicas are generally manufactured using synthetic chemical processes. 
While established high temperature gaseous synthesis methods fall out of favor in our energy conscious society, liquid synthesis methods are current industrial leaders. 

The precipitated Colloidal silica method provides the majority share of commercially produced specialty silicas with its economic advantages predicted to continue to grow in the future. 
Colloidal silica products are stable dispersions of non-agglomerated, amorphous, nanometer-size, and spherical particles of silica. 

The good stability, adjustable particle size distribution and mechanical properties have made colloidal silica a preferred abrasive for many CMP applications. 
Recently, research and analytical efforts have focused on the development of colloidal products with tunable physical and chemical properties to open up new opportunities in the CMP industry segment.

Colloidal Silica is a slurry that is used for final polishing in a number of industries. 
Unlike standard abrasive slurries, colloidal silica falls into a category called C.M.P, or Chemical Mechanical Polishing. 

Colloidal silica’s common in sapphire and silicon wafer manufacture, metallurgical sample preparation, and medical implant polishing.
A C.M.P process uses a combination of fine Colloidal silica particles and a chemical reaction based on the PH and oxidation ability of the colloidal base to produce surface finishes that are generally unobtainable using fine abrasive slurries. 

Typically less than 2nm. 
Unlike conventional abrasive processes where the abrasive is cutting or plucking material from a substrate, a CMP process will oxidize a micro layer of a substrate and then this layer is brushed off using the fine, but highly concentrated, silica particles.

In a normal abrasive slurry you can expect 15-20wt% concentration of abrasive particles, but in a colloidal slurry as much as 50wt% of silica particles can be present. 
This greatly increases the amount of silica (SiO2) particles that work on a substrate making the polishing very uniform and efficient. 

Also, the SiO2 particles are incredibly uniformly spherical, which again, is difficult to match with standard abrasive particles where the shape is far less uniform.
Colloidal silica is a widely used material in industry. 

Colloidal Silica is an epoxy thickening additive used to control the viscosity of the epoxy. 
Colloidal silica prevents epoxy runoff in vertical and overhead joints. This is a very strong filler. 

Colloidal silica creates a smooth mixture, ideal for general epoxy bonding and filleting. 
Colloidal silica is also our most versatile epoxy filler.

Often used in combination with other fillers, 406 can be used to improve strength, abrasion resistance, and consistency of epoxy fairing compounds. 
The result is a tougher, smoother surface.

Colloidal Silica is the most popular binder used in the precision investment casting industry today. 
Colloidal silica offers the investment caster a safe, economical, easy to use slurry component that performs well as either primary or backup slurry.

Colloidal Silica systems are very stable; able to form a long life ceramic slurry with a large range of refractory materials due to the binder’s chemical inertness. 
This versatility allows Colloidal Silica to form the basis of ceramic shells used for the casting of a large range of metal alloys.

Ceramic shells formed with colloidal silica binder’s offer several advantages for the investment process. 
The exceptionally strong bonds formed by the colloid enables ceramic shells to have a superior green and fired strength. 

 

 


USES OF COLLOIDAL SILICA:


Applications that use colloidal silica vary widely. 
Colloidal silica can be used to enhance or direct the movement of substances within various processes. 

For example, Colloidal silica is used in the paper manufacturing process to draw liquid from the finished paper quickly, thereby allowing the paper to dry faster while retaining its strengthening starch. 
Similarly, colloidal silica can be used to absorb moisture in industrial settings where moisture levels are high. 

Depending on the size of its constituent particles, colloidal silica may be used to enhance the movement of materials or to increase surface friction.
Colloidal silica can also be used as a reference material for both particle size and zeta potential. 

Colloidal silica silica is a well known and characterized colloidal material that has been studied using various particle size analysis techniques including acoustic spectroscopy, laser diffraction and dynamic light scattering.
Colloidal silica is usually used in combination with a polyurethane polishing pad which has voids within the structure of the pad to hold the colloidal silica. 

Colloidal silica is applied using a peristaltic pump and a constant drip feed similar to a conventional abrasive lapping process. 
Colloidal silica’s important to maintain the wetness of the process so there is no drag out of material.

Colloidal silica dioxide is widely used in pharmaceuticals, cosmetics, and food products. 
Colloidal silicas small particle size and large specific surface area give it desirable flow characteristics that are exploited to improve the flow properties of dry powders in a number of processes such as tableting and capsule filling.

Colloidal silica dioxide is also used to stabilize emulsions and as a thixotropic thickening and suspending agent in gels and semisolid preparations. 
With other ingredients of similar refractive index, transparent gels may be formed. 

The degree of viscosity increase depends on the polarity of the liquid (polar liquids generally require a greater concentration of Colloidal silica dioxide than nonpolar liquids). 
Viscosity is largely independent of temperature. 

However, changes to the pH of a system may affect the viscosity1.
In aerosols, other than those for inhalation, Colloidal silica dioxide is used to promote particulate suspension, eliminate hard settling, and minimize the clogging of spray nozzles. 

Colloidal silica dioxide is also used as a tablet disintegrant and as an adsorbent dispersing agent for liquids in powders. 
Colloidal silica dioxide is frequently added to suppository formulations containing lipophilic excipients to increase viscosity, prevent sedimentation during molding, and decrease the release rate. 
Colloidal silica dioxide is also used as an adsorbent during the preparation of wax microspheres; as a thickening agent for topical preparations; and has been used to aid the freeze-drying of nanocapsules and nanosphere suspensions.

 

-In papermaking colloidal silica is used as a drainage aid. 

-Colloidal silica increases the amount of cationic starch that can be retained in the paper. 

-Cationic stach is added as sizing agent to increase the dry strength of the paper.

-Investment casting - used in moulds

-An abrasive - for polishing silicon wafers

-Carbonless paper

-Catalysts

-Moisture Absorbent

-Colloidal silica increase the bulk & taped density of powder & granules also

-Colloidal silica is also be used in Lubrication of Tablet

-Stabilizing and rigidizing refractory ceramic fiber blankets

-Abrasion resistant coatings

-Increasing friction - used to coat waxed floors, textile fibers and railway tracks to promote traction

-Antisoiling – fills micropores to prevent take up of dirt and other particles into textiles

-Surfactant – used for flocculating, coagulating, dispersing, stabilising[disambiguation needed] etc.

-Liquid silicon dioxide (colloidal silica) is used as a wine and juice fining agent.

-Absorbent

-Colloidal silica is used in concrete densifiers and polished concrete.

-In manufacturing Quantum dots, small semi-conductors used in various scientific research settings.

 

 


APPLICATION OF COLLOIDAL SILICA:


Collodial silica can be used in numerous applications and it enhances functionality in an ever-growing number of products. 
To give a couple of examples our products enhances the performance of waterborne coatings by delivering anti-soling properties as well as provides increased durability and strength in cementing operations. 

Choosing the right colloidal silica can be a challenge. 
Subtle differences in particle morphology, particle size, and ionic species can make all the difference.

Colloidal silica hasn't always been the versatile problem solver that it is today.  
In fact, early colloidal silicas were not commercially useful because they were too unstable and contained only low levels of silica.  

Colloidal silica wasn't until the production of Colloidal silica in the late 1940's that the applications for colloidal silica began to expand.  
One of the earliest applications for colloidal silica was in anti-slip coatings for floors.  

Colloidal silica is a very common final polishing stage for metallographic sample analysis. 
This is because Colloidal silica is generally guaranteed to give a damage free specimen. 

These types of samples are viewed under high magnification, so it is important when looking at the structures of a material that damage caused by the preparation processes is not confused with the material make up itself. 
For modern material analysis software, a scratch free finish is critical. 

Scratches or any other damage on a specimen can confuse the software giving incorrect readings. 
This is particularly important with hardness testing software.

For some metallographic samples, the chemical make-up of colloidal silica can be used to etch the surface revealing grain boundaries and other structures.
Colloidal Silica is also used as a final polishing process after sub-micron alumina pre polishing for the preparation of mineral samples ready for Electron Back Scatter Diffraction (EBSD). 

The reason for its use is the same as any other application in that it gives a perfect damage free sample surface. 
The EBSD analysis reveals more than standard X-ray diffraction and is now a standard tool for fine –scale structure of intact coralline skeleton analysis.

 

-Densification of concrete, cement, and other materials

-Fine retention in paper manufacturing

-Enhanced bonding of waterborne adhesives

-Improved surface friction and anti-slip properties

-Wastewater filtration flocculant

-Investment casting binding

-Anti-soilant textile coatings

-Anti-blocking aid for films

-Scratch resistant surface coatings

-Ceramic fiber binder and rigidizing agent

-Catalyst attrition resistance

-Abrasive polishing agent

-Strength-enhancing additive to plastics, mortar, and concrete

-Binders in ceramic compounds for high temperature applications

-Clarification of wine, beer and fruit juice concentrate

-Polishing agents in wafer and memory-chip production

-A component of silicate-based paints and plasters

-Retention aids in papermaking

 

 

PROPERTIES OF COLLOIDAL SILICA:


Usually they are suspended in an aqueous phase that is stabilized electrostatically. 
Colloidal silicas exhibit particle densities in the range of 2.1 to 2.3 g/cm3.

Most colloidal silicas are prepared as monodisperse suspensions with particle sizes ranging from approximately 30 to 100 nm in diameter. 
Polydisperse suspensions can also be synthesized and have roughly the same limits in particle size. 

Smaller particles are difficult to stabilize while particles much greater than 150 nanometers are subject to sedimentation.
Colloidal silicas are produced in a variety of grades that range in a number of factors.  

Particle size typically varies from 5nm to 40nm, and particle size distribution can vary from narrow to wide depending on the manufacturing process. 
Standard colloidal silica is stable at a pH from 8 - 10.5 and carries an anionic surface charge that is stabilized with sodium or ammonium.  

In certain grades, some of the silicon atoms in the silica particle are replaced with aluminate ions to allow for enhanced stability in a wider pH range, usually 3.5 - 10.5.
Colloidal silica can also be produced to carry a positive surface charge that is stable in the acidic pH range.  
This is accomplished by modifying the surface of the particle with aluminum and charge stabilizing the particle with a chloride anion.

 

-Particle sizes from 3 to 100 nm

-Silica concentrations from 7 to 50%

-Specific surface area 40 to 800 m²/g (according to Sears)

-Application-specific modifications (e.g. ammonium-stabilised, aluminate-modified, cationic etc.)

-Definable particle size distributions (narrow, broad, monomodal or bimodal etc.)

 

 

 

MANUFACTURE OF COLLOIDAL SILICA:


Colloidal 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. 
The subunits of colloidal silica particles are typically in the range of 1 to 5 nm. 

Whether or not these subunits are joined together depends on the conditions of polymerization. 
Initial acidification of a water-glass (sodium silicate) solution yields Si(OH)4.

If the pH is reduced below 7 or if salt is added, then the units tend to fuse together in chains. 
These products are often called silica gels. 

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 precipitated silica or silica sols. 

Hydrogen ions from the surface of colloidal silica tend to dissociate in aqueous solution, yielding a high negative charge. 
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. 

Because of the very small size, the surface area of colloidal silica is very high.
The Colloidal silica is stabilized by pH adjustment and then concentrated, usually by evaporation. 

The maximum concentration obtainable depends on the on particle size. 
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.

 

 

PRODUCTION OF COLLOIDAL SILICA:

Colloidal silica dioxide is prepared by the flame hydrolysis of chlorosilanes, such as silicon tetrachloride, at 18008℃ using a hydrogen–oxygen flame. 
Rapid cooling from the molten state during manufacture causes the product to remain amorphous.

 


STORAGE OF COLLOIDAL SILICA:

Colloidal silica is hygroscopic but adsorbs large quantities of water without liquefying. 
When used in aqueous systems at a pH 0–7.5, Colloidal silica is effective in increasing the viscosity of a system. 

However, at a pH greater than 7.5 the viscosityincreasing properties of Colloidal silica dioxide are reduced; and at a pH greater than 10.7 this ability is lost entirely since the silicon dioxide dissolves to form silicates. 
Colloidal silica powder should be stored in a well-closed container.

 

 


SYNONYM:

Quartz
Dioxosilane
Cristobalite
Diatomaceous earth
Silica gel
Tridymite
Sand
112945-52-5
Infusorial earth
Silicic anhydride
KIESELGUHR
14808-60-7
Aerosil
Crystalline silica
Diatomaceous silica
Dicalite
Wessalon
Glass
Ludox
Nyacol
Zorbax sil
112926-00-8
Silica, amorphous
Cab-O-sil
Christensenite
Crystoballite
Silicon(IV) oxide
61790-53-2
Siliceous earth
Synthetic amorphous silica
Amorphous silica
QUARTZ (SIO2)
Silica, colloidal
60676-86-0
Chalcedony
Diatomite
Agate
Cab-o-sil M-5
colloidal silica
Cristobalite (SiO2)
Fused silica
Quartz glass

 

 


IUPAC NAME:

Amorphous Colloidal Silica
AMORPHOUS SILICA
Amorphous Silica
Amorphous silica
amorphous silica
Amorphous silico dioxide
Amorphous silicon dioxide hydrate
Dioxide de silicium
Dioxosilane
dioxosilane
dioxoslian
Fumed Silica
JIOS Aerova aerogel powder
Kieselgel
Kieselsäuren, amorphe
N.A.
oxid křemičitý (amorfní)
Precipitated amorphous silica
Quarz

 

 

TRADE NAME:

ABSIL -100
ABSIL-HC
AC6120 carrier
Acematt [Silica, precipitated]
Admafine Silica
AEROPERL
Aeroperl [Silica, fumed, pyrogenic]
AEROSIL [Silica, fumed, pyrogenic]
Airlica
Alusilica
ApART™ System, ApART™ Catalyst System
ARSIL
ART Hydroprocessing catalysts
BARIACE
BARIFINE
BECOSORB

 

 

 

 

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