Hydrated silica

Use in toothpaste

Diatomaceous earth, originally mined as "tooth powder" is a naturally occurring hydrated silica. As a fine gel abrasive, frequently combined with softer calcium carbonate (from chalk) it helps to remove plaque. Milled to a slightly larger size, the grains are more aggressive and are used in tooth bleaching formulations. Hydrated silica is a useful abrasive in toothpastes because it does not chemically interact with other active ingredients, especially sodium fluoride.

Nature

Hydrated silicas can form in nature through biotic processes primarily involving benthic microorganism activity in the oceans. However, there are several abiotic processes that form hydrated silicas, such as precipitating out of solution, forming a diagenetic alteration product, or replacing pre-existing minerals in sedimentary rocks.

In its pure form, as manufactured for toothpaste, it is an odorless, tasteless, white, gelatinous substance, which is chemically inert. One of the primary industrial methods to acquire hydrated silica is through a sol-gel process.

Hydrated silicas can be categorized into three main categories based on differences in crystallinity:

1. Hydrated silicate glass (Lowest crystallinity)
2. Opal
3. Microcrystalline quartz (Highest crystallinity) One of the most common ways to detect and identify hydrated silicas in laboratory is through near infrared and thermal infrared spectroscopy.

Chemical formula

Chemical Formula: : SiO2 · nH2O : 1 SiO2 + 1 H2O → H2SiO3 : 1 SiO2 + 2 H2O → H4SiO4 [also known as Si(OH)4] : 2 SiO2 + 1 H2O → H2Si2O5 : 2 SiO2 + 3 H2O → H6Si2O7 : 3 SiO2 + 2 H2O → H4Si3O8 : 3 SiO2 + 4 H2O → H8Si3O10 : 4 SiO2 + 1 H2O → H2Si4O9 Hydrated silicas exhibit a trend of decreasing bonded water molecules as the crystallinity of the silica molecule increases, with microcrystalline quartz's typically containing the least water content and macrocrystaline quartz having negligible water.

Flame retardant

Hydrated silica compounds, such as hydrated silica aluminate (HSA), can be combined with traditional flame retardants, such as magnesium hydroxide and aluminium hydroxide, to increase their effectivity. A hydrated silica compound's effectiveness as a flame retardant is dependent upon the presence of chemically bonded transition metals, commonly iron and titanium.

Safety

Hydrated silica is listed by the US Food and Drug Administration as "Generally Recognized as Safe."

References

Opal: http://www.galleries.com/minerals/mineralo/opal/opal.htm Paint/Varnish: https://www.whatsinproducts.com/chemicals/view/1/1683 Beer: http://www.freepatentsonline.com/4975405.html

References

1. (November 1997). "Cleaning Power and Abrasivity of European Toothpastes". Advances in Dental Research.
2. "Amethyst Galleries: Opal".
3. {{Greenwood&Earnshaw
4. "Hydrated silica gel for stabilization treatment of beer".
5. (November 2017). "Baking soda as an abrasive in toothpastes". The Journal of the American Dental Association.
6. (2021). "Modern Sample Preparation for Chromatography".
7. (2011). "Comprehensive Biomaterials".
8. (April 2013). "Hydrated silica on Mars: Combined analysis with near-infrared and thermal-infrared spectroscopy". Icarus.
9. (February 2020). "Ingredients -- Hydrated silica".
10. (August 2018). "Improvement of flame retardancy and thermal stability of polypropylene by P-type hydrated silica aluminate containing lanthanum". Polymer Degradation and Stability.
11. (2024). "Fire Retardancy of Polymeric Materials".