Calciumsulfat

BeschreibungCalcium sulfate and its hydrates are important industrial compounds that have been used throughout history. Calcium sulfate is obtained naturally from mined gypsum rock, but it also exists in mineral form. Gypsum forms in beds as sedimentary rock when calcium sulfate, which is a natural component of seawater, is deposited as shallow marine water bodies evaporate. Gypsum is a transparent, soft, white mineral and is the most common sulfate mineral.

HistoryGypsum’s use dates back to prehistoric times. Archeological evidence shows that it was mined from caves and used to paint ancient gravestones. The earliest evidence of its use as a building material dates from 6000 b.c.e. in the southwest Asian areas of ancient Anatolia and Syria. Egyptians used gypsum and plaster in their buildings and monuments, with both found in the Great Pyramids built around 3700 b.c.e. Calcium sulfate has been used for more than 2,000 years in China to produce tofu. The word gypsum comes from the Greek word for chalk, gypsos. The Greek natural philosopher Theophrastus (371–286 b.c.e.) referred to gypsum in his writings. Gypsum was extensively used in Roman times and throughout the Middle Ages. In the 1700s, Paris was a leading plaster center, with most of its buildings made using plaster. After the fire of London in 1666 destroyed 80% of the city, the king of France ordered all wooden houses in France to be covered with plaster as protection against fire. The hemihydrate form got the name plaster of Paris from the extensive gypsum deposits quarried in the Montmartre district of Paris. In 1765 and 1766, Antoine Lavoisier (1743–1794) presented papers to the French Academy of Science on gypsum that explained the setting of plaster. Lavoisier determined that gypsum is a hydrated salt and that set plaster occurs when the hemihydrate form rehydrates back to gypsum.

VerwendenThe largest use of calcium sulfate is in the construction industry, which accounts for more than 90% of its production.Gypsum has hundreds of other applications outside the construction industry. It can be used agriculturally for several purposes: to supply calcium and sulfur to soils, to balance pH, and to condition soil. Food grade calcium sulfate is used as a calcium supplement in enriched foods such as flour, cereals, and baked goods. It is used as a gelling and firming agent with canned vegetables. Calcium sulfate is the most common tofu coagulant. The positively charged calcium ion in calcium sulfate attracts the negatively charged groups in protein molecules, causing thermally denatured proteins to coagulate. Anhydrous calcium sulfate is used as a filler to whiten food and consumer products such as frostings, ice creams, paper, paints, and toothpaste. Powdered gypsum can be used as a chalk for marking athletic fields and other large areas.