International Gold Number
The International Gold Number (IGN) is a measure of the protective action of clays and other minerals on the colloidal stability of gold sols. It is defined as the number of milligrams of the substance required to prevent the coagulation of 10 ml of a standard gold sol.
The IGN is an important property of clays and other minerals used in the ceramics, paper, and paint industries. In ceramics, clays with high IGNs are used to improve the strength and durability of ceramic products. In paper, clays with high IGNs are used to improve the brightness and opacity of paper. In paint, clays with high IGNs are used to improve the adhesion and durability of paint films.
The IGN is determined by adding increasing amounts of the substance to a standard gold sol and observing the color changes that occur. As the concentration of the substance increases, the gold sol will gradually change from a reddish color to a bluish color. The endpoint of the titration is reached when the gold sol turns a deep blue color.
The IGN is a relative measure of the protective action of clays and other minerals. It is not an absolute measure of the protective action, as it can be affected by factors such as the pH of the solution and the presence of other ions.
Factors Affecting the IGN
The IGN is affected by a number of factors, including:
* The type of clay or mineral. Clays and minerals with high surface areas and high cation exchange capacities tend to have high IGNs.
* The pH of the solution. The IGN is highest at the pH of the point of zero charge (PZC) of the clay or mineral.
* The presence of other ions. The presence of other ions, such as calcium and magnesium, can decrease the IGN.
Applications of the IGN
The IGN is used in a variety of applications, including:
* Ceramics. Clays with high IGNs are used to improve the strength and durability of ceramic products.
* Paper. Clays with high IGNs are used to improve the brightness and opacity of paper.
* Paint. Clays with high IGNs are used to improve the adhesion and durability of paint films.
* Water treatment. Clays with high IGNs are used to remove impurities from water.
* Food processing. Clays with high IGNs are used to stabilize food emulsions.
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