COLLOIDAL SILICA

Colloidal Silica is a dispersion of very small amorphous silicon dioxide particles, commercially supplied most often as a stabilized aqueous sol.
Colloidal Silica has a reactive, hydroxyl-bearing particle surface that supports inorganic binding, polishing, surface modification, and controlled gel formation.
Colloidal Silica covered in this profile refers to aqueous commercial dispersions whose concentration, particle size, stabilizers, and pH vary by grade. 

CAS Number: 7631-86-9, identifying the silicon dioxide component
EC Number: 231-545-4, identifying the silicon dioxide component
Molecular Formula: Variable for the commercial dispersion; SiO₂ for the silica phase
Molecular Weight: Not applicable to the dispersion; 60.08 g/mol per SiO₂ formula unit, not per colloidal particle 

Synonyms: Silica sol, aqueous silica sol, silica hydrosol, colloidal silicon dioxide, colloidal SiO₂, colloidal silicon dioxide dispersion, colloidal silicon dioxide suspension, colloidal amorphous silica, amorphous silica sol, synthetic amorphous silica sol, aqueous colloidal silica, colloidal silica dispersion, colloidal silica suspension, silicon dioxide sol, silicon dioxide hydrosol, aqueous silicon dioxide dispersion, amorphous silicon dioxide dispersion, silica nanoparticle dispersion, colloidal nanosilica, nanosilica sol, aqueous nanosilica, silica nanodispersion, dispersed amorphous silicon dioxide, colloidal inorganic silica binder, silica sol binder, silicon dioxide, silicon(IV) oxide, SiO₂, CAS 7631-86-9, EC 231-545-4

APPLICATIONS

Colloidal Silica serves as an inorganic binder in precision investment casting.
Colloidal Silica binds refractory particles within ceramic shell systems used to reproduce intricate component geometry.
Additionally, Colloidal Silica contributes heat resistance and dimensional stability during the casting process.
Colloidal Silica requires selection according to particle size, concentration, slurry compatibility, and the required shell characteristics. 

Colloidal Silica provides binding and stiffening functions in refractory insulation materials.
Colloidal Silica helps consolidate refractory fibers into boards, blocks, papers, felts, and shaped insulation components.
Moreover, Colloidal Silica supplies an inorganic bonding phase suitable for selected high-temperature applications.
Colloidal Silica must be matched to the fiber chemistry and service conditions because finished refractory performance depends on the complete composition. 

Colloidal Silica functions as a fine abrasive in precision polishing and chemical mechanical polishing formulations.
Colloidal Silica supports the shaping and smoothing of silicon, glass, sapphire, and other precision substrates.
In addition, Colloidal Silica offers particle-size control that is important when uniform surfaces and low defect levels are required.
Colloidal Silica intended for electronics applications requires appropriate control of impurities, oversized particles, aggregation, and slurry chemistry. 

Colloidal Silica contributes inorganic reinforcement and surface modification to waterborne coatings.
Colloidal Silica can improve hardness, blocking resistance, and other film properties when compatible grades are incorporated.
Additionally, Colloidal Silica supplied with suitable surface modification can improve compatibility with organic resin systems.
Colloidal Silica requires formulation-specific evaluation because improvements in hardness or blocking resistance do not guarantee improved abrasion resistance in every coating.

Colloidal Silica supports selected cement and concrete applications, including finishing aids and surface densification treatments.
Colloidal Silica contributes reactive silica to systems designed to improve the condition and durability of cementitious surfaces.
Moreover, Colloidal Silica can be applied to both fresh and existing concrete through appropriately formulated treatments.
Colloidal Silica requires assessment against the concrete composition, surface condition, and intended performance requirements. 

Colloidal Silica enables controlled gel formation in geotechnical grouting and ground-consolidation systems.
Colloidal Silica offers low-viscosity dispersions that can penetrate suitable porous formations before gelation.
In addition, Colloidal Silica forms a gel network that restricts water movement within the treated volume.
Colloidal Silica requires application-specific control of gel time, concentration, groundwater chemistry, and geological conditions. 

Colloidal Silica supplies binding and structural functions in catalyst manufacture.
Colloidal Silica helps bind catalyst components, improve adhesion to substrates, and develop useful physical strength.
Additionally, Colloidal Silica provides a controlled silica source for selected zeolite and molecular-sieve manufacturing processes.
Colloidal Silica grades for these applications are selected according to purity, sodium content, particle characteristics, and compatibility with the catalyst system. 

Colloidal Silica participates in microparticle retention and drainage systems used in papermaking.
Colloidal Silica works with suitable starch or polymer systems to improve retention of fibers, fines, and other furnish components.
Moreover, Colloidal Silica can support dewatering and paper-machine operation when the wet-end chemistry is properly balanced.
Colloidal Silica performance depends on particle structure, surface area, furnish composition, and the accompanying retention chemicals.

Colloidal Silica supplied in appropriate processing grades serves as a clarification aid for beverages such as beer, wine, and juice.
Colloidal Silica assists the removal of undesirable suspended or colloidal components during clarification.
In addition, Colloidal Silica requires selection according to the beverage composition and the intended separation process.
Colloidal Silica suitability for food processing depends on the exact grade, purity specifications, permitted use, and applicable regulatory requirements. 

Colloidal Silica formulated for battery applications supports electrolyte gel formation in selected lead-acid batteries.
Colloidal Silica can help immobilize sulfuric acid electrolyte in gel-cell designs.
Additionally, Colloidal Silica can contribute to reducing acid stratification in suitable absorbed-glass-mat battery systems.
Colloidal Silica requires battery-specific control of impurities, chloride content, particle structure, and compatibility with the electrolyte. 

DESCRIPTION

Colloidal Silica contains amorphous silicon dioxide particles dispersed in a liquid carrier.
Colloidal Silica has a disordered silica structure rather than the ordered structure associated with crystalline quartz.
Additionally, Colloidal Silica particles contain many connected silicon–oxygen units, so the SiO₂ formula describes composition rather than a discrete nanoparticle molecule.
Colloidal Silica therefore requires distinction between the formula-unit molar mass and the much larger, size-dependent mass of individual particles.

Colloidal Silica ranges in appearance from clear or translucent to opalescent or milky white.
Colloidal Silica becomes more strongly light-scattering as particle characteristics and concentration change.
Moreover, Colloidal Silica is available with narrow or broad particle-size distributions and with discrete or structured particles.
Colloidal Silica commercial grades include particle sizes ranging approximately from 2 to 150 nm, although no single range defines every product. 

Colloidal Silica carries surface silanol groups that influence hydration, surface interactions, and bonding behavior.
Colloidal Silica conventional alkaline grades generally have negatively charged particles stabilized by suitable counterions.
In addition, Colloidal Silica can destabilize when incompatible electrolytes or uncontrolled pH changes alter the stabilizing conditions.
Colloidal Silica may then aggregate or gel, changing viscosity and application performance.

Colloidal Silica is available in sodium-stabilized, ammonia-stabilized, acidic, cationic, and surface-modified commercial forms.
Colloidal Silica properties therefore depend on more than the silicon dioxide concentration alone.
Additionally, Colloidal Silica differs from sodium silicate solutions, silica gel, precipitated silica, and dry fumed silica.
Colloidal Silica should not be treated as interchangeable with a dry product designated “colloidal silicon dioxide” solely because the names are similar. 

Colloidal Silica aqueous sols are normally noncombustible, while their labeling depends on the complete formulation.
Colloidal Silica can cause skin drying or discomfort, and splash exposure requires appropriate eye protection.
Moreover, Colloidal Silica should be handled without generating unnecessary aerosols or airborne dust from dried residues.
Colloidal Silica is sensitive to freezing, which can cause irreversible agglomeration or gelation and loss of useful dispersion properties. 

PROPERTIES

Product Name: Colloidal Silica
Chemical Name: Silicon dioxide, amorphous, colloidally dispersed
Common Name: Silica sol
Chemical Family: Inorganic oxide
Functional Class: Colloidal inorganic binder, polishing abrasive, surface modifier, and gelling component
CAS Number: 7631-86-9 for the silicon dioxide component
EC Number: 231-545-4 for the silicon dioxide component
Molecular Formula: Variable for the dispersion; SiO₂ for the silica phase
Formula-Unit Molar Mass: 60.08 g/mol for SiO₂
Particle Molecular Weight: Not represented by a single molecular-weight value
Physical State: Liquid dispersion with solid silica particles
Appearance: Clear, translucent, opalescent, or milky white; grade dependent
Odor: Often little odor; ammonia-stabilized grades may have an ammonia odor
Silica Concentration: Grade dependent; commercial examples include approximately 15–50% silica by mass
Representative Particle Size: Approximately 2–150 nm across selected commercial product ranges
Particle Shape: Commonly approximately spherical; irregular and structured particles also occur
Surface Functional Groups: Silanol groups and siloxane linkages
Surface Charge: Commonly negative in conventional alkaline sols; cationic and modified grades also available
pH: Grade dependent; acidic, neutral, and alkaline versions are available
Density: Concentration, formulation, and temperature dependent
Viscosity: Grade dependent; many aqueous sols are fluid, relatively low-viscosity dispersions
Water Dispersibility: Supplied as a colloidal aqueous dispersion
Water Solubility: Silica remains predominantly particulate; this is a dispersion rather than a simple molecular solution
Volatility: Silica particles are nonvolatile; the carrier and some stabilizers can evaporate
Boiling Behavior: Primarily governed by the aqueous carrier; concentration changes during evaporation
Freezing Behavior: Freezing can irreversibly destabilize the dispersion
Flash Point: Normally not applicable to ordinary aqueous silica sols
Primary Industrial Functions: Binding, polishing, reinforcement, surface modification, controlled gelation, and retention assistance 
GHS Classification: Formulation dependent; some standard aqueous grades are not classified as hazardous
Signal Word: Grade dependent; may be absent for grades not classified as hazardous
Hazard Statements: Determined by the current regional grade-specific SDS
Transport Information: Standard aqueous grades may be transported as nondangerous goods; verify the actual formulation and regional SDS
Stability-Sensitive Additions: Incompatible electrolytes, multivalent ions, oppositely charged additives, and uncontrolled pH adjustment
Reactive Incompatibilities: Water-reactive chemicals; additional incompatibilities depend on formulation
Storage Conditions: Protect from freezing, prolonged excessive heat, evaporation, and contamination
Representative Storage Range: Approximately 5–35 °C for selected commercial aqueous grades; the individual grade instructions control
Shelf Life: Grade, purity, packaging, storage conditions, and manufacturer dependent

FIRST AID

Inhalation:

Move the affected person to fresh air following aerosol or dust exposure. Obtain medical attention if coughing or respiratory discomfort persists, and seek urgent assistance for breathing difficulty.

Skin Contact:

Remove contaminated clothing and rinse the exposed area thoroughly with water. Wash with mild soap if necessary and obtain medical advice for persistent irritation.

Eye Contact:

Immediately rinse with clean running water for at least 15 minutes, holding the eyelids open. Remove contact lenses if easily possible and continue rinsing. Obtain prompt medical attention for persistent pain, redness, or visual disturbance.

Ingestion:

Rinse the mouth. Do not induce vomiting. Contact a poison center or physician for advice if a significant amount has been swallowed or symptoms develop. Never give anything by mouth to an unconscious person. 

Note to Physicians:

Treat symptomatically. Assess the actual grade’s pH, stabilizers, and other ingredients using the product SDS.

HANDLING AND STORAGE

Handling:

Avoid eye contact, prolonged skin contact, and unnecessary mist generation. Maintain clean transfer equipment and prevent contamination that could destabilize the dispersion.

Engineering Controls:

Provide ventilation appropriate to the operation. Use local exhaust where spraying, aerosol formation, or handling of dried residues creates airborne exposure. Provide accessible eyewash facilities.

Personal Protection:

Wear protective gloves and safety goggles. Use a face shield in addition to goggles where substantial splashing is possible. Select protective clothing according to the exposure conditions.

Respiratory Protection:

Respiratory protection is generally unnecessary for controlled transfer without aerosol formation. Use approved protection where an exposure assessment identifies inadequately controlled mist, dust, or stabilizer-related exposure. 

Storage:

Keep containers closed in a clean, temperature-controlled location. Protect from freezing and prolonged excessive heat. Follow the exact grade’s temperature limits, and do not return contaminated or gelled material to fresh stock.

Material Compatibility:

Use compatible tanks, pumps, seals, and transfer lines. Stainless steel and suitable polymer construction materials are commonly selected, subject to grade-specific confirmation. Prevent contact with water-reactive chemicals and unvalidated additions that alter pH or ionic conditions.

Equipment Care:

Prevent deposits from drying in pumps, valves, and piping. Clean equipment promptly after use through an approved procedure, and contain the resulting wash water.

Spill and Leak Procedures:

Restrict access and control the slip hazard from spilled liquid. Contain and collect with suitable liquid-absorbent material. Avoid procedures that create aerosols or disperse dried silica residues.

Environmental Precautions:

Prevent uncontrolled discharge to drains, soil, groundwater, or surface water. Manage collected liquid and contaminated wash water through an authorized treatment or disposal route.

Fire Response:

Use extinguishing media appropriate to the surrounding fire. Ordinary aqueous silica sols do not provide a combustible fuel, but firefighters should use appropriate protection where heated containers, mist, or other formulation ingredients are involved.

Waste Disposal:

Dispose of unused dispersion, contaminated absorbents, and packaging in accordance with applicable waste regulations. Account for stabilizers, preservatives, and process contaminants when determining the disposal route.