Editing Sodium silicate (section)

=== Foundries, refractories and pottery ===
{{Main|Sand casting#Sodium silicate}}
{{See also|Calcium silicate}}

It is used as a binder of the sand when doing [[sand casting]] of all common metals. It allows for the rapid production of a strong mold or core by three main methods.{{Citation needed|date=September 2023}}

* Method 1 requires passing carbon dioxide gas through the mixture of sand and sodium silicate in the sand molding box or core box. The carbon dioxide reacts with the sodium silicate to form solid silica gel and sodium carbonate.{{citation needed|date=March 2024}} This provides adequate strength to remove the now hardened sand shape from the forming tool. Additional strength occurs as any unreacted sodium silicate in the sand shape dehydrates.
* Method 2 requires adding an [[ester]] (reaction product of an acid and an alcohol) to the mixture of sand and sodium silicate before it is placed into the molding box or core box. As the ester hydrolyzes from the water in the liquid sodium silicate, an acid is released which causes the liquid sodium silicate to gel. Once the gel has formed, it will dehydrate to a glassy phase as a result of [[Syneresis (chemistry)|syneresis]]. Commonly used esters include acetate esters of glycerol and ethylene glycol as well as carbonate esters of propylene and ethylene glycol. The higher the water solubility of the ester, the faster the hardening of the sand.{{Citation needed|date=September 2023}}
* Method 3 requires microwave energy to heat and dehydrate the mixture of sand and sodium silicate in the sand molding box or core box. The forming tools must pass through microwaves for this to work well. Because sodium silicate has a high dielectric constant, it absorbs microwave energy very rapidly. Fully dehydrated sand shapes can be produced within a minute of microwave exposure. This method produces the highest strength of sand shapes bonded with sodium silicate.{{Citation needed|date=August 2024}}

Since the sodium silicate does not burn during casting (it can actually melt at pouring temperatures above 1800&nbsp;°F), it is common to add organic materials to provide for enhanced sand breakdown after casting. The additives include sugar, starch, carbons, wood flour and phenolic resins.

Water glass is a useful binder for solids, such as [[vermiculite]] and [[perlite]]. When blended with the latter lightweight fraction, water glass can be used to make hard, high-temperature insulation boards used for refractories, [[passive fire protection]], and high-temperature insulations, such as in 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{{clarification needed|reason=what intumescence? This has not previously been referred to|date=March 2024}} disappears in the presence of finely divided mineral dust, whereby the waterglass becomes a mere matrix. Waterglass is inexpensive and abundantly available, which makes its use popular in many refractory applications.

Sodium silicate is used as a [[deflocculant]] in casting slips helping reduce [[viscosity]] and the need for large amounts of water to liquidize the clay body. It is also used to create a crackle effect in pottery, usually wheel-thrown. A vase or bottle is thrown on the wheel, fairly narrow and with thick walls. Sodium silicate is brushed on a section of the piece. After five minutes, the wall of the piece is stretched outward with a rib or hand. The result is a wrinkled or cracked look.

It is also the main agent in "magic water", which is used when joining clay pieces, especially if the moisture level of the two differs.<ref>{{cite web | url=http://lakesidepottery.com/HTML%20Text/Tips/pottery-magic-mud-magic-water-paper-clay.htm | title=Ceramic, Pottery, Sculpture and Kintsugi Repair &#124; China repair and restoration }}</ref>