Sodium silicate (Na2SiO3) structure, properties, uses, risks

The sodium silicate is an inorganic compound formed by two sodium Na ions⁺ and a silicate anion SiO₃^two-. It is also said to be made up of a molecule of silica SiO_two and a sodium oxide Na_twoO. Its chemical formula can be expressed as Na_twoYes₃ or also Na_twoOR.Yes_two.

However, the composition of the sodium silicate can vary depending on the SiO ratio_two/ Na_twoEither by weight or in moles. It is also called soluble silicate or water glass. It can be obtained in the form of powder, large crystal-like pieces or in the form of solutions.

Sodium silicate is widely used in detergents and soaps as it softens the water making cleaning more effective. It is also part of products such as shaving cream.

It is the raw material to prepare SiO silica catalysts_two. Its solutions are used as glue in many applications, ranging from adhesive paper and cardboard, to glass, porcelain, refractory molds, cement and abrasive discs..

Because it is a completely non-combustible material, it is used to make fireproof fabrics, as it is a fire retardant, and as a coating for protective equipment..

Article index

• 1 Structure
• 2 Nomenclature
• 3 Properties
  • 3.1 Physical state
  • 3.2 Molecular weight
  • 3.3 Melting point
  • 3.4 Density
  • 3.5 Solubility
  • 3.6 pH
  • 3.7 Chemical properties
  • 3.8 Other properties
• 4 Obtaining
• 5 Uses
  • 5.1 In soaps and detergents
  • 5.2 In catalysts and silica gels
  • 5.3 As an adhesive or glue
  • 5.4 In oil well drilling fluids
  • 5.5 In various applications
• 6 Risks
• 7 References

Structure

The general formula for sodium silicates is xSiO_two/ Na_twoOr where x is the molar or weight ratio.

Molar ratio means number of moles of SiO_two divided by the number of moles of Na_twoO. Weight ratio means weight of SiO_two divided by weight of Na_twoOR.

Adding more alkali (Na_twoO) the molar or weight ratio is changed.

A sodium silicate solution with a low molar ratio, for example 1/1 (1 mole of SiO_two and 1 mole of Na_twoO) contains mainly SiO monomers₄^4- and S dimers_twoOR₅^two- in addition to the Na ions⁺.

A solution with a high molar ratio such as 3.3 / 1 (3.3 moles of SiO_two for each mole of Na_twoO) has a high proportion of polymeric species or polymers of silicon and oxygen.

Nomenclature

-Sodium silicate

-Sodium Metasilicate

-Soluble glass

-Glass of water (from the English water glass)

-Soluble silicate

Properties

Physical state

-Solid in large pieces that resemble bluish-green crystals

-Colorless to white powdery solid

-Colorless aqueous solutions.

Molecular weight

From the formula Na_twoYes₃: 122.063 g / mol.

Melting point

Na_twoYes₃: 1089 ° C

Density

It depends on the SiO ratio_two/ Na_twoOR.

Solubility

When in the form of large pieces of greenish crystal it is soluble in water if heated and under high pressure. The powder is slightly more soluble, but in both cases its solubility depends on the amount of sodium or Na_twoOr that it owns.

The higher the sodium content (in the form of Na_twoO) faster dissolves.

pH

Its aqueous solutions are strongly alkaline.

Chemical properties

Commercially prepared in SiO relationships_two/ Na_twoOr by weight ranging from 1.5 to 3.3. As SiO increases_two in the relationship decreases the solubility in water and alkalinity.

Dissolving solid silicate in water can form gelatinous or highly viscous mixtures.

Sodium silicate powder can be deliquescent, that is, if it has a high amount of Na_twoOr, it tends to easily absorb water from the environment.

If the pH of its solutions is lowered by adding acid, a gel forms.

Other properties

It is not flammable.

Obtaining

Silica sand SiO is melted to obtain sodium silicates_two with sodium carbonate Na_twoCO₃ anhydrous in an open oven. The mole ratio of sand to sodium carbonate can vary commercially from 0.5 to 3.75.

Applications

In soaps and detergents

Sodium silicates are among the first compounds that were used in detergent formulations.

Sodium silicate sequesters calcium Ca ions^two+ and magnesium Mg^two+, eliminating what is called hardness of the water, that is, softening it. By doing this, insoluble precipitates are formed, so it is used in small amounts.

The action of the sodium silicate allows the detergent to function without the mentioned ions affecting the cleaning process.

In catalysts and silica gels

Silica gels are commonly prepared by acidifying a sodium silicate solution to a pH of less than 10 or 11. The time required to gel varies..

Silica can be prepared by mixing sodium silicate with a strong mineral acid. Sodium silicate is used in the manufacture of bases for catalysts, since it is the source of silica SiO_two.

As an adhesive or glue

Concentrated aqueous sodium silicate solutions are used as adhesives and sealants. They can withstand temperatures of up to 1100 ° C.

The main applications of sodium silicate glues are in adhesive paper, corrugated or corrugated cardboard, boxes and cartons. Also for gluing or agglomerating wood or for adhering metal to various types of materials.

It is used to glue glass, porcelain, ceramics, textiles, leather, etc. For bonding fiberglass, optical glass, and impact-proof glass containers.

It allows to prepare refractory cements to build tanks, kettles, furnaces and molds for metal casting, as well as to make waterproof or acid proof mortars or cements.

Sodium silicates can react with silicon fluorides to produce acid-resistant cements, with a low tendency to shrink and a thermal expansion similar to that of steel..

They are also used to make cements for abrasive discs used for polishing..

In oil well drilling fluids

Sodium silicate has been used for many years as a chemical slurry during the drilling of certain types of formations with very high permeability, such as those that are constituted by sand..

High permeability means it lets liquids through easily.

It is added together with a compound that activates the silicate to form a polymer. This polymer provides strength, rigidity and reduces permeability in granular soils..

As the soil is less permeable, the liquid does not pass through it freely and in this way the loss of fluid is avoided during the drilling phase of the well..

In various applications

Sodium silicate also has a variety of uses. Here are some.

-In daily care products, for example it is a component of shaving creams.

-In water treatment.

-In the bleaching of textiles such as wool.

-In the bleaching of paper pulp. For example, to bleach ground wood a mixture containing hydrogen peroxide and sodium silicate among other ingredients is used. Sodium silicate is used to sequester metal ions, which tend to accelerate the decomposition of peroxide..

-For the manufacture of fireproof fabrics. As a fire retardant and as a coating for protective equipment.

-In silica pigments.

-To detect corn kernels infested by insects. A mixture of sodium silicate and water is used where the infested grains float to the surface quickly.

-In zinc plating.

-To clean metals.

-In mineral flotation, it is used as a dispersant for sludge and silt and as a conditioner for the surface of minerals..

-To impregnate wood.

Risks

Sodium silicate, due to its high alkali content, is a strong irritant to the skin, eyes and mucous membranes. If swallowed it can be toxic and irritate mucous membranes in a similar way to caustic soda solutions..

It must be stored separately from strong acids, metals and halogens such as fluorine, with which it reacts violently.

References

1. Ebnesajjad, S. (2015). Characteristics of Adhesive Materials. Soluble Silicates (Potassium and Sodium Silicate). In Handbook of Adhesives and Surface Preparation. Recovered from sciencedirect.com.
2. Fink, J.K. (2012). Fluid loss additives. Sodium metasilicate. In Petroleum Engineer's Guide to Oil Field Chemicals and Fluids (Second Edition). Recovered from sciencedirect.com.
3. U.S. National Library of Medicine. (2019). Sodium silicate. National Center for Biotechnology Information. Recovered from pubchem.ncbi.nlm.nih.gov.
4. Kirk-Othmer. (1984). Encyclopedia of Chemical Technology, 3rd ed., John Wiley and Sons.
5. Maeda, K. et al. (2007). From Zeolites to Porous MOF Materials - The 40^th Anniversary of International Zeolite Conference. In Studies in Surface Science and Catalysis. Recovered from sciencedirect.com.
6. Chopade, S.P. and Nagarajan, K. (2000). Detergent formulations: ion exchange. In Encyclopedia of Separation Science. Recovered from sciencedirect.com.
7. .