Sodium silicate is the most important of the soluble silicates. Sodium silicate available in Solid Lumps (crystalline solid), liquid solutions and powder form, this material is often called “water glass” or “Liquid Glass” and is ordinarily supplied as a colorless, viscous water solution displaying little tack. They are readily soluble in water, producing neutral solutions and alkaline solutions, Positive pressure and temperature must be used to hold the substrates together. This material will withstand temperatures of up to 1100 °C and 10kg/cm2 pressure. The chemical formula of Sodium silicate is (Na2O)x·(SiO2)y. such as sodium metasilicate Na2SiO3, sodium orthosilicate Na4SiO4, and sodium pyrosilicate Na6Si2O7. Mainly three types of Sodium silicate available in Market (1) Neutral sodium silicate, (2) Alkaline sodium silicate, (3) customized sodium silicate, all three types silicate available in solid and water liquid form.
The main applications of sodium silicate listed.
Silicate adhesives are in bonding paper and making corrugated boxboard, boxes, and cartons. They are also used in wood bonding and in bonding metal sheets to various substrates; in bonding glass to glass, porcelain, leather, textiles, stoneware, and so on; bonding glass-fiber assemblies; optical glass applications; manufacture of shatter-proof glass; bonding insulation materials; refractory cements for tanks, boilers, ovens, furnaces; acid-proof cements; fabrication of foundry molds, briquettes, and abrasive polishing wheel cements. Soluble silicates may also be reacted with silicon fluorides or silica to produce acid-resistant cements with low shrinkage and a thermal expansion.
Sodium silicate is frequently used in drilling fluids to stabilize borehole walls and to avoid the collapse of bore walls. It is particularly useful when drill holes pass through argillaceous formations containing swelling clay minerals such as smectite or montmorillonite
Concrete and general masonry treatment
concrete treated with a sodium silicate solution helps to reduce porosity in most masonry product such as concrete, stucco, plasters, This effect aids in reducing water penetration, but has no known effect on reducing water vapor transmission and emission, A chemical reaction occurs with the excess Ca(OH)2 , present in the concrete that permanently binds the silicates with the surface, making them far more durable and water repellent. This treatment generally is applied only after the initial cure has taken place (7 days or so depending on conditions). These coating are known as silicate mineral paints, An example of the reaction of sodium silicate with the calcium hydroxide found in concrete to form calcium silicate hydrate (or C-S-H) gel, the main product in hydrated Portland cement.
Soap bar and Detergent auxiliaries
It is used in detergent auxiliaries such as complex sodium silicate and modified sodium silicate. The detergent granules gain their ruggedness from a coating of silicates. It is very largely use in soap bar making industries and commercial detergent making industries. Because of its oil and grease removal and cleaning power. Sodium silicate is to prevent mineral deposits on surfaces after washing by removing water hardness. It is also main component in manufacturing of ZEOLITE powder, which use as water softener, detergent coating agent, P.V.C product as fire retardant, rubber product as softener, catalytic agent.
Sodium silicate is used as an alum coagulant and an iron flocculent in west water treatment plants. Sodium silicate binds to colloidal molecules, creating larger aggregates that sink to the bottom of the water column. The microscopic negatively charged particles suspended in water interact with sodium silicate. Their electrical double layer collapses due to the increase of ionic strength caused by the addition of sodium silicate (doubly negatively charged anion accompanied by two sodium cations) and they subsequently aggregate. This process is called coagulation.
Water glass is a useful binder of solids, such as vermiculite and perlite. When blended with the aforementioned lightweight aggregates, water glass can be used to make hard, high-temperature insulation boards used for refractory, passive fire protection and high temperature insulations, such as moulded pipe insulation applications. When mixed with finely divided mineral powders, such as vermiculite dust (which is common scrap from the exfoliation process), one can produce high temperature adhesives. The intumescence disappears in the presence of finely divided mineral dust, whereby the water glass becomes a mere matrix. Water glass is inexpensive and abundantly available, which makes its use popular in many refractory applications.
It is used as a binder of the sand when doing sand casting of C.I, C.S, C.A. It allows the rapid production of a strong mold, by passing Co2 through the mixture of sand and sodium silicate in the mold box, which hardness it almost instantly.
Sodium silicate solution is used as a fixative for hand dyeing with reactive dyes that require a high pH to react with the textile fiber. After the dye is applied to a cellulose-based fabric, such as cotton or rayon, or onto silk, it is allowed to dry, after which the sodium silicate is painted on to the dyed fabric, covered with plastic to retain moisture, and left to react for an hour at room temperature
Passive fire protection
Sodium silicates are inherently Intumescent They come in prill (solid beads) form, as well as the liquid, water glass. The solid sheet form must be waterproofed to ensure long-term passive fire protection (PFP). Standard, solid, bead-form sodium silicates have been used as aggregate within silicone rubber to manufacture plastic pipe firestop devices. The silicone rubber was insufficient waterproofing to preserve the intumescing function and the products had to be recalled, which is problematic for firestops concealed behind drywall in buildings. Pastes for caulking purposes are similarly unstable. This, too, has resulted in recalls and even litigation. Only 3M’s “Expantrol” version, which has an external heat treatment that helps to seal the outer surface, as part of its process standard, has achieved sufficient longevity to qualify for DIBt approvals in the US for use in firestopping. Not unlike other intumescents, sodium silicate, both in bead form and in liquid form, are inherently endothermic, due to liquid water in the water glass and hydrates in the prill form. The absence in the US of mandatory aging tests, whereby PFP systems are made to undergo system performance tests after the aging and humidity exposures, are at the root of the continued availability, in North America, of PFP products that can become inoperable within weeks of installation. Indiscriminate use of sodium silicates without proper waterproofing measures is contributors to the problems and risk. When sodium silicates are adequately protected, they function extremely well and reliably for long periods. Evidence of this can be seen in the many DIBt approvals for plastic pipe firestop devices which use waterproofed sodium silicate sheets.
(10) Metal repair
Sodium silicate is used, along with magnesium silicate in muffler repair and fitting paste. When dissolved in water, both sodium silicate and magnesium silicate form a thick paste that is easy to apply. When the exhaust system of an internal combustion engine heats up to its opening temperature, the heat drives out all of the excess water from the paste. The silicate compounds that are left over have glass-like properties, making a temporary, brittle repair.
(11) Automotive repair
Sodium silicate is also used currently as an exhaust system joint and crack sealer for repairing mufflers, resonators, tailpipes, and other exhaust components, with and without fiberglass reinforcing tapes. In this application, the sodium silicate (60–70%) is typically mixed with kaolin (40-30%), an aluminum silicate mineral, to make the sodium silicate “glued” joint opaque. The sodium silicate, however, is the high-temperature adhesive; the kaolin serves simply as a compatible high-temperature coloring agent. Some of these repair compounds also contain glass fibers to enhance their gap-filling abilities and reduce brittleness. Sodium silicate can be used to fill gaps within the head gasket. Commonly used on aluminum alloy cylinder head, which are sensitive to thermally induced surface deflection. This can be caused by many things including head-bolt stretching, deficient coolant delivery, high cylinder head pressure, overheating, etc. “Liquid glass” (sodium silicate) is added to the system through the radiator, and allowed to circulate. Sodium silicate is suspended in the coolant until it reaches the cylinder head. At 100–105 °C (212-221 °F), sodium silicate loses water molecules to form a glass seal with a remelt temperature above 810 °C (1,490 °F). A sodium silicate repair can last two years or longer. The repair occurs rapidly, and symptoms disappear instantly. This repair works only when the sodium silicate reaches its “conversion” temperature at 100–105 °C. Contamination of engine oil is a serious possibility in situations in which a coolant-to-oil leak is present. Sodium silicate (glass particulate) contamination of lubricants is detrimental to their function. Sodium silicate solution is used to inexpensively, quickly, and permanently disable automobile engines. Running an engine with about 2 liters of a sodium silicate solution instead of motor oil causes the solution to precipitate, catastrophically damaging the engine’s bearings and pistons within a few minutes. In the United States, this procedure was used to comply with requirements of the Car Allowance Rebate system program.
(12) Food and medicine
Sodium silicate and customized silicates is the primary components in “instant” wrinkle remover creams, which temporarily tighten the skin to minimize the appearance of wrinkles & under-eye bags. These creams, when applied as a thin film and allowed to dry for a few minutes,
Waterglass has been used as an egg, vegetable preservative with large success, primarily when refrigeration is not available. Fresh-laid eggs, vegetable are immersed in a solution of sodium silicate (waterglass). After being immersed in the solution they were removed and allowed to dry. A permanent air tight coating remains on it.
Sodium silicate gel is also used as a substrate for algal growth in aquaculture hatcheries.