Silicon Oxide
Identifiers
Functions
Where is silicon oxide used, and what role does it play in each application?
Silicon oxide functions across a broad range of applications, primarily as a structural or functional additive. In food, pharmaceuticals, and cosmetics, it acts as an anti-caking, absorbent, abrasive, bulking, opacifying, and viscosity-controlling agent. In industrial products, it serves as a filler in rubber, paints, and plastics, and as a raw material for glass, ceramics, and refractories. In advanced applications, it is used as a barrier coating in packaging, a coating for pigments and phosphors, a filler in electronic materials, and a component in battery anodes and polishing compositions. Its role is defined by its form—amorphous or crystalline—and particle characteristics.
Which product or formulation problem does silicon oxide address?
Silicon oxide addresses formulation problems related to powder flow, moisture control, and mechanical or barrier performance. As an anti-caking agent, it absorbs water and prevents clumping in powdered foods, pharmaceuticals, and cosmetics. As a filler, it improves the mechanical properties of rubber and plastics, and as a barrier layer, it blocks oxygen and moisture in packaging. In sunscreens, it coats zinc oxide to modify surface chemistry, and in phosphors, it enhances reliability. It also serves as an abrasive in polishing and as a carrier in pesticides, solving issues of texture, stability, and delivery.
What supports the main commercial or clinical uses of silicon oxide?
Evidence for silicon oxide's main uses comes from regulatory approvals, industry classifications, and patent filings. It is an approved food additive and is listed as a safe component in food packaging and animal feed. Cosmetic ingredient databases list its functions as abrasive, absorbent, anticaking, bulking, opacifying, and viscosity controlling. Patents demonstrate its use in barrier films, battery anodes, and electronic fillers, indicating claimed technical benefits. However, patent applications are not proof of commercial adoption, and the evidence for clinical uses, such as in bone regeneration, is experimental.
Which formulation trade-offs should researchers consider for silicon oxide?
Researchers must balance silicon oxide's benefits against potential safety and performance trade-offs. Crystalline forms pose respiratory hazards, so amorphous forms are preferred for consumer products. In cosmetics, it must be formulated to be non-irritating. As a filler, its particle size and surface area affect viscosity and flow, requiring optimization. In barrier coatings, it may need co-deposition with other oxides to achieve flexibility and adhesion. Surface modification can alter hydrophobicity, impacting compatibility with different matrices. Concentration limits, such as up to 2% in food, constrain its use.
What are the physicochemical properties of Silicon oxide?
| Property | Value | Category |
|---|---|---|
| Physical Description | Transparent to gray, odorless powder. Irritating to the skin and eyes on contact. Inhalation will cause irritation in the respiratory tract. [Note: Amorphous silica is the non-crystalline form of SiO2.], Dry Powder; Other Solid; Large Crystals; CBI, Dry Powder; Wet Solid; Other Solid; Large Crystals; CBI; Liquid, Dry Powder; Large Crystals; Dry Powder; Large Crystals; Wet Solid; Dry Powder; Liquid; Liquid; Large Crystals; Liquid; Liquid; Other Solid; Dry Powder; Other Solid; Dry Powder; Large Crystals; Liquid; Other Solid; Dry Powder; Large Crystals; Liquid; Wet Solid; Other Solid; Other Solid; Wet Solid; Large Crystals; Dry Powder; Wet Solid; Other Solid; Dry Powder; Wet Solid; Large Crystals; Other Solid; CBI, Liquid; Other Solid; Dry Powder, White, fluffy powder or granules. Hygroscopic, Transparent to gray, odorless powder. [Note: Amorphous silica is the non-crystalline form of SiO2.]; [NIOSH], Solid, COLOURLESS OR WHITE CRYSTALS, Transparent to gray, odorless powder. [Note: Amorphous silica is the non-crystalline form of SiO2.] | Appearance |
| Color/Form | Amorphous powder, Transparent to gray powder (Note: Amorphous silica is the non-crystalline form of O2Si). ... solid, Silica gel is a coherent, rigid, continuous three-dimensional network of spherical particles of colloidal microporous silica, Transparent crystals | Appearance |
| Odor | Odorless | Appearance |
| Taste | Tasteless | Appearance |
| Solubility | Insoluble (NIOSH, 2024), The solubility of the various phases of silicas is very complex and depends upon several factors. Solubility increases with temperature and pH and is affected by the presence of trace metals. Particle size influences the rate of solubility. /Silica/, Insoluble, Silica is rather poorly soluble in water although solubility is higher for the amorphous than for the crystalline morphologies. ... The external amorphous layer in quartz is more soluble than the crystalline underlying core, AMORPHOUS IS SOL IN ALKALIES, ESP WHEN FINELY DIVIDED, Practically insoluble in water or acids. Dissolves readily in HF, forming silicon tetrafluoride, Very slightly sol in alkali, Soluble in hot potassium hydroxide and hot sodium hydroxide solutions. Insoluble in ethanol, Silica is rather poorly soluble in water and solubility is lower for the crystalline than for the amorphous morphologies. ...Solubility increases with temperature and pH and is affected by the presence of trace metals. Particle size influences the rate of solubility, The external amorphous layer in quartz (the Beilby layer) is more soluble than the crystalline underlying core, Solubility in water: none | Formulation Relevant Properties |
| Boiling Point | 4046 °F at 760 mmHg (NIOSH, 2024), 4046 °F, 2230 °C, 2950 °C @760 [mm Hg] | Handling Relevant Properties |
| Melting Point | 3110 °F (NIOSH, 2024), 3110 °F, 1710 °C, 1716 - 1736 °C, 1713 °C, 1722 °C | Handling Relevant Properties |
| Density | 2.2 (NIOSH, 2024) - Denser than water; will sink, 2.2 @ 25 °C, 2.6, Colorless crystals or white powder; odorless and tasteless; density: 2.2-2.6; soluble in molten alkai when finely divided and amorphous /Silicon dioxide/, Density = 2.20 g/cm; Refractive index = 1.459; Surface tension = 5.200 @ 298 K (calc); Thermal conductivity = 1.37 W/m-deg K at 298 deg K ; Heat of Formation = -903.2 kJ/mol at 298 deg K; Heat Capacity = 37.94 J/mol-deg K at 298 deg K; Dielectric Constant = 3.8 /Corning 7940 fused silica/, Density = 2.648 /alpha-Quartz/ /from table/, Density = 2.269 /alpha-Tridymite/ /from table/, Density = 2.318 /alpha-Cristobalite/ /from table/, Density = 2.909 /Coesite/ /from table/, Density = 4.287 /Stishovite/ /from table/, 2.3 g/cm³, 2.334 @25 °C, 2.2 @25 °C, 2.20 | Handling Relevant Properties |
| Vapor Pressure | 0 mmHg (approx) (NIOSH, 2024), approx 0 mm Hg, 10 mm Hg @ 1732 °C, 0 mmHg (approx) | Handling Relevant Properties |
| Corrosivity | Non-corrosive | Handling Relevant Properties |
Which formulation benchmark best contextualizes silicon oxide, and what differs?
A relevant benchmark for silicon oxide is its use as a barrier coating in flexible packaging, where it is often compared to aluminum oxide. Patents show both are used as inorganic barrier layers, but silicon oxide offers transparency and recyclability advantages, while aluminum oxide may provide different barrier properties. The choice depends on the required oxygen and moisture transmission rates, flexibility, and cost. This benchmark highlights silicon oxide's role as a high-performance alternative in sustainable packaging solutions.