Colloidal silica
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Colloidal silicas are suspensions of fine
Properties
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
Manufacture
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 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
The
Applications
- In papermaking colloidal silica is used as a drainage aid. It increases the amount of cationic starch that can be retained in the paper. Cationic starch is added as sizing agent to increase the dry strength of the paper.
- High temperature binders
- Investment casting - used as the inorganic binder in moulds
- An silicon wafers
- Carbonless paper
- As binder or silica source in catalysts
- Desiccant
- As lubricant in the manufacture of pharmaceutical capsules and tablets.[1]
- Stabilizing and rigidizing refractory ceramic fiber blankets
- Abrasion resistant coatings
- Increasing friction - used to coat waxed floors, textile fibers, cardboards and railway tracks to promote traction
- Antisoiling – fills microporesto prevent take up of dirt and other particles into textiles
- Surfactant – used for coagulating, dispersing, stabilisingetc.
- Liquid silicon dioxide (colloidal silica) is used as a wine and juice fining agent.
- Liquid silicon dioxide (colloidal silica) is used as a wine and juice
- Absorbent
- Colloidal silica is used in concrete densifiers and polished concrete.
- In manufacturing Quantum dots, small semi-conductors used in various scientific research settings.
- Reduced porosity and increased protection from alkali-silica reaction (ASR). [2]
See also
- Silica dioxide
References
- ^ "Lubricant Excipients". American Pharmaceutical Review. Retrieved 2023-10-05.
- ^ "Colloidal Silica | R-E-D Industrial Products". R-E-D Industrial. Retrieved 2024-02-20.