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Ancient Uses
The Phoenicians of the ancient Canaan lived in coastal cities around 1200 BC. This ancient society used soluble silicates that dissolved in liquid as binding materials for building structures. At a basic level, a silicate is sodium combined with sand. When dissolved under high pressure, the sand and sodium form a clear liquid. Once dried, the liquid forms a powder to use as a bond.
Silicate's Properties
As a manufactured product, silicate needs a weight ratio of SiO2 to Na2O, which is silicon combined with oxygen to sodium combined with oxygen. Manufacturers maintain a ratio between 1.5 to 3.2 to product different silicate types. The ratio depends on the binding mechanism creating the material, time required to produce the binding material and what material combines with the binding material.
Four Reactions
As a compound, sodium silicate is unlike other chemically combined elements, which only go through one or two reactions. Sodium silicate allows for four reactions. The first is hydration or dehydration, depending on what you require of the silicate. As a liquid silicate holds water, once you remove the fluid, you produce a stickier, thick compound. The second is gelation or polymerization. As the pH or acidity level fluctuates below 10.7, the silicate forms polymers, formed from multiple bonds. While gelation creates a higher water resistance, dehydration produces the better binding material. The third reaction is precipation, when the silicate reacts with metal to form a new metal silicate that's unable to dissolve in liquid. Finally, silicates also form cement activation and acceleration. In this reaction, they awaken a material known as pozzolan in cement applications. Pozzolan forms from volcanic ash, cement kiln dust or metallic slag. These materials combine with silicates to produce an environmentally friendly alternative to other cements.
Contemporary Uses
Silicates create three different materials: film binder, matrix binder and chemical binder. As a film binder, they create a glassy film and have the highest ratio of silicates. Film binders also dry quickly and require heat to create a more water-resistant surface. When used with pozzolan, silicates form a matrix bind that gives sufficient bond strength but without harsh chemicals. Chemical binders are the least friendly to the environment because you need a high ratio of silicates. These reactions work best for metal applications to produce insoluble binds.