Properties of Silicates

Because the physical properties of silicates vary so widely, PQ makes available many different types of products. Among them are lump and powdered glass, liquid silicates, hydrous silicates, metasilicates, and potassium silicates. The raw materials needed to produce soluble silicates are silica sand, soda ash (or potash), and water.

PQ Soluble Silicate Products are distinguished by Product Form (solid or liquid), by Ratio, and by Total Solids. 

Liquid silicates include the PQ family of sodium silicates, potassium silicates, and lithium silicates.  Solid silicates include glass products, hydrous (spray-dried) powders, sodium metasilicates, and sodium aluminosilicates (zeolites). 

The ratio of a silicate product refers to the Weight Ratio or Mole Ratio of Silica to Alkali in the silicate product.  So for example, a 3.22 wt ratio silicate and contains 3.22 wt % SiO2 for each 1 wt % Na2O.  Ratio is one of the most important silicate properties as it determines physical properties of the silicate as well as solubility and reactivity.  

A second very important property (particularly with liquid silicates) is the Total Solids, also referred to as Total Dissolved Solids.  Total solids refers to the sum of Silica and Alkali in the silicate product.  PQ supplies a variety of silicates with varying Total Solids at equivalent ratios to meet the diverse needs of our customers.

Many customers utilize silicates for the value of the silica in their application or processing.  The significant soluble Silica concentration in PQ silicates is due to stabilization from the alkali concentration in the silicate.    A Gravimetric or Volumetric silica analysis can be used to determine silica concentrations. Atomic absorption spectroscopy is another method for determining silica concentrations. All three techniques require experienced, highly trained operators. An automated computer program can also be used.  Alkali is determined via a pH titration using commercially available autotitrators. 

Liquid silicates demonstrate a density greater than that of water.  Density is a measure of total dissolved solids in a silicate.  Baume' is a unit of specific gravity specific to the Soluble Silicate industry.  Baume' is measured by a use of a hydrometer or a digital densitometer under strictly controlled temperature conditions.  Density or Baume' is a function of silicate solids and temperature.  Density and Baume' increase as solids increase or as temperature decreases.  

Due to the presence of alkali in a silicate to maintain silica solubility, all silicates show an alkaline pH.  pH is a function of silicate composition and solids concentration. The pH value of silicates does not truly reflect the alkali content of solution, due to the strong buffering capability of silica. This means the pH of a silicate solution is kept constant until almost complete neutralization. The buffering capacity of silicate solutions increases with increasing ratio of silica to alkali.

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