Gypsum and Gypsum products are available in different forms. Gypsum is chemically known as Calcium sulfate dihydrate. It is a white powdery mineral widely found in nature. It is mainly used for making dental casts.
Gypsum
Gypsum is chemically known as calcium sulfate dihydrate and it contains calcium and sulfur, which is bound to oxygen and water. Gypsum is an abundant mineral and takes various forms including alabaster, which is a material, used in decoration and construction. The White Sands National Monument in New Mexico is the world’s largest gypsum dune field.
This is a non-toxic mineral and it can be helpful to humans, animals, plant life, and the environment. The majority of gypsum is produced in North America and is used to manufacture gypsum board or building plasters and it is used in many other ways.
Types of Gypsum
Natural gypsum occurs in sedimentary of rock formations and it is found in over 85 countries. United States, Canada and Mexico have some of the largest reserves of high-quality gypsum. It is mined in 17 states. Lowa, Texas, Utah, and New Mexico are important producers.
Process
Gypsum rock is mined or quarried, crushed and ground into a fine powder. In a process called calcining, the powder is heated at 350 degrees F, driving off three fourths of the chemically combined water. The calcined gypsum, or hemihydrate, becomes the base for gypsum plaster, gypsum board and other gypsum products. . Natural gypsum and FGD gypsum have the same chemical composition, they are calcium sulfate dihydrate
FGD gypsum production and sales encourages power producers to capture waste for reuse, rather than storing. The production of this extremely pure type of gypsum reduces environmental pollution.
The increased use of FGD gypsum has also encouraged new plants to be sited much closer to major population centers. This close proximity between manufacturing facilities and distribution centers saves energy and decreases pollution. A significant percentage of gypsum products distributed are manufactured near installation sites.
Synthetic gypsum that is suitable for use in wallboard includes flue-gas desulfurization (FGD) gypsum, fluorogypsum, citrogypsum, and titanogypsum. Titanogypsum is a by-product from manufacturing titanium dioxide.
Both the natural and the synthetic gypsum used in gypsum board are considered non-toxic and safe. Some types of FGD gypsum are generally considered unsuitable for use in gypsum board due to potential environmental hazards. Certain impurities occasionally occur with natural as well as synthetic gypsum. The impurities are generally inert and harmless and typically consist of clay, anhydrite, or limestone in natural gypsum and fly ash in synthetic gypsum. Each individual source must be analyzed separately to assess its particular suitability, which may vary depending on purity levels of the specific materials.
FORMS
The different forms are the ROCK in dull colour. The ALABLASTER, which is a fine-grained variety, and the GYPCRETE (gypcrust) which in turn is the hard layer formed on soil. The SELENITE SATIN SPUR is the fibrous with silky luster.
USES
The Gypsum and the Gypsum products are used for construction purposes. It is also used in industry for making pottery, moulds etc. It is used by orthopedics to make plaster casts and helps the dentist for the cast preparation, models and dies, impression material, investment material, mounting of Casts, as a mold material for processing of complete dentures etc.
DESIRABLE PROPERTIES
The most desirable properties of Gypsum and the Gypsum products includes the Accuracy, dimensional stability, ability to reproduce, strength, resistance to abrasion, compatibility with the impression materials, colour, biological safety, cost , and its ease of use.
CHEMICAL & PHYSICAL NATURE OF GYPSUM PRODUCTS
As gypsum is dihydrate form of calcium sulphate, on heating, it loses some of its water and is converted to calcium sulphate hemihydrate . When calcium sulphate hemihydrate is mixed with water, the reverse reaction takes place and calcium sulphate hemihydrate is converted back to calcium sulphate dihydrate. This reaction is exothermic.
Types of Gypsum products
The major types of Gypsum products that are available are, Type I — Impression Plaster. Type II — Dental Plaster. Type III — Dental Stone Type IV — Improved Dental Stone or Die stone or High Strength Stone. Type V — Dental Stone, High Strength, High Expansion.
