- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Density
- Solubility
- pH
- Chemical properties
- Other properties
- Obtaining
- Applications
- In soaps and detergents
- In catalysts and silica gels
- As an adhesive or glue
- In oil well drilling fluids
- In various applications
- Risks
- References
The sodium silicate is an inorganic compound consisting of two sodium ions Na + and a silicate anion SiO 3 2 -. It is also said molecule consists of a silica SiO 2 and sodium oxide Na 2 O. Its chemical formula can be expressed as Na 2 SiO 3 or Na also 2 O . SiO 2.
However, the composition of the sodium silicate can vary depending on the SiO 2 / Na 2 O ratio by weight or in moles. It is also called soluble silicate or water glass. It can be obtained in the form of a powder, large crystal-like pieces, or in the form of solutions.
Solid sodium silicate Na 2 SiO 3. Ondřej Mangl. Source: Wikimedia Commons.
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 for preparing SiO 2 silica catalysts. 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 fire retardant, and as a coating for protective equipment.
Structure
Simplified structure of polymers in sodium silicate solutions. Benjah-bmm27. Source: Wikimedia Commons.
The general formula for sodium silicates is xSiO 2 / Na 2 O where x is the molar or weight ratio.
Molar ratio means number of moles of SiO 2 divided by number of moles of Na 2 O. Weight ratio means weight of SiO 2 divided by weight of Na 2 O.
Adding more alkali (Na 2 O) changes the molar or weight ratio.
A sodium silicate solution with a low molar ratio, for example 1/1 (1 mole of SiO 2 and 1 mole of Na 2 O) contains mainly SiO 4 4 monomers - and S 2 O 5 2 dimers - in addition to the ions Na +.
A solution with a high molar ratio such as 3.3 / 1 (3.3 moles of SiO 2 for each mole of Na 2 O) has a high proportion of polymeric species or polymers of silicon and oxygen.
Nomenclature
-Sodium silicate
-Sodium meta-silicate
-Soluble glass
-Glass of water (from English water glass)
-Soluble silicate
Properties
Physical state
-Solid in large pieces similar to blue-green crystals
-Colorless to white powder solid
-Colorless aqueous solutions.
Molecular weight
From the formula Na 2 SiO 3: 122.063 g / mol.
Melting point
Na 2 SiO 3: 1089 ° C
Density
It depends on the SiO 2 / Na 2 O ratio.
Solubility
When it is in the form of large pieces of greenish glass 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 2 O it contains.
The higher the sodium content (in the form of Na 2 O) the faster it dissolves.
pH
Its aqueous solutions are strongly alkaline.
Chemical properties
It is commercially prepared in SiO 2 / Na 2 O ratios by weight ranging from 1.5 to 3.3. As SiO 2 increases in the ratio, water solubility and alkalinity decrease.
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 2 O, it tends to easily absorb water from the environment.
If the pH of their solutions is lowered by adding acid, a gel forms.
Other properties
It is not flammable.
Obtaining
To obtain sodium silicates, silica sand SiO 2 is melted with anhydrous sodium carbonate Na 2 CO 3 in an open furnace. The molar ratio of sand to sodium carbonate can vary commercially from 0.5 to 3.75.
Silica sand deposits in an area of India. ರವಿಮುಂ. Source: Wikimedia Commons.
Applications
In soaps and detergents
Sodium silicates are among the first compounds to be used in detergent formulations.
Detergents generally contain sodium silicate in their composition. Author: Karunasanghvi. Source: Pixabay.
Sodium silicate sequesters calcium Ca 2+ and magnesium Mg 2+ ions, eliminating what is called water hardness, 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 gel. Sodium silicate is required to prepare it. Desiccants. Source: Wikimedia Commons.
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 2.
As an adhesive or glue
Concentrated aqueous solutions of sodium silicate 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.
Corrugated or corrugated board is manufactured using sodium silicate glue. Author: Stux. Source: Pixabay.
It is used to glue glass, porcelain, ceramics, textiles, leather, etc. For bonding fiberglass, optical glass, and impact-proof glass containers.
It allows the preparation of 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 grout during the drilling of certain types of formations with very high permeability, such as those consisting of 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.
Oil well drilling. Oil_Rig_NT8.jpg: * derivative work: Mudgineer (talk) Oil_Rig_NT.PNG: Tosakaderivative work: Malyszkz. Source: Wikimedia Commons.
In various applications
Sodium silicate also has a variety of uses. Some are mentioned below.
-In daily care products, for example it is a component of shaving creams.
-In water treatment.
-In the whitening 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 in which the infested grains float to the surface quickly.
-In the electrodeposition of zinc.
-To clean metals.
-In the flotation of minerals it is used as a dispersant for sludge and silt and as a conditioner for the mineral surface.
-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
- Ebnesajjad, S. (2015). Characteristics of Adhesive Materials. Soluble Silicates (Potassium and Sodium Silicate). In Handbook of Adhesives and Surface Preparation. Recovered from sciencedirect.com.
- Fink, JK (2012). Fluid loss additives. Sodium metasilicate. In Petroleum Engineer's Guide to Oil Field Chemicals and Fluids (Second Edition). Recovered from sciencedirect.com.
- US National Library of Medicine. (2019). Sodium silicate. National Center for Biotechnology Information. Recovered from pubchem.ncbi.nlm.nih.gov.
- Kirk-Othmer. (1984). Encyclopedia of Chemical Technology, 3rd ed., John Wiley and Sons.
- Maeda, K. et al. (2007). Zeolites from MOF to Porous Materials - The 40 th Anniversary of International Zeolite Conference. In Studies in Surface Science and Catalysis. Recovered from sciencedirect.com.
- Chopade, SP and Nagarajan, K. (2000). Detergent formulations: ion exchange. In Encyclopedia of Separation Science. Recovered from sciencedirect.com.
- Garcia-Lodeiro, I. et al. (2015). Crucial insights on the mix design of alkali-activated cement-based binders. Effect of silicates: degree of soluble silicate polymerization. In Handbook of Alkali-Activated Cements, Mortars and Concretes. Recovered from sciencedirect.com.