Calcium sulphate
Calcium sulphate hemihydrate
General
Other names	Plaster of Paris
Molecular formula	CaSO4
Molar mass	136.142 g/mol (anhydrous)
Appearance	white solid
CAS number	[7778-18-9] (anhydrous)
Properties
Density and phase	2.96 g/cm3, solid
Solubility in water	0.24 g/100 ml (20 °C)
Melting point	1460°C (anhydrous)
Refractive Index	1.57
Mohs hardness	3.5 (anhydrite), 2.0 (gypsum)
Structure
Coordination geometry	?
Crystal structure	orthorhombic
Thermodynamic data
Standard enthalpy of formation ΔfH°solid	-1434.5 kJ/mol
Standard molar entropy S°solid	? J.K–1.mol–1
Heat of fusion	205.668
Specific Heat Capacity	0.732324 J/g-°C (anhydrous)
Safety data
PEL-TWA (OSHA)	15 mg/m3
RTECS number	WS6920000
NFPA 704	0 0 0
Supplementary data page
Structure & properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other cations	Magnesium sulfate Strontium sulfate
Related desiccants	Calcium chloride Magnesium sulfate
Related compounds	Plaster of Paris Gypsum
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

Calcium sulphate is a common laboratory and industrial chemical. In the form of γ-anhydrite (a nearly anhydrous form), it is sold as a laboratory desiccant. The hemihydrate (CaSO₄.~0.5H₂O) is better known as plaster of Paris, while the dihydrate (CaSO₄.2H₂O) occurs naturally as gypsum. The anhydrous form occurs naturally as β-anhydrite. Depending on the method of calcination of calcium sulfate dihydrate specific hemihydrates are sometimes distinguished: alpha-hemihydrate and beta-hemihydrate^[1]. They appear to differ only in crystal size. Alpha-hemihydrate crystals are more prismatic than beta-hemihydrate crystals and when mixed with water form a much stronger and harder superstructure^{[citation needed]}. Image File history File links Calcium_sulfate_hemihydrate. ... Image File history File links Calcium_sulfate_hemihydrate. ... This article is about the building material. ... This article or section does not cite any references or sources. ... This article does not cite any references or sources. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... For other uses, see Density (disambiguation). ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... It has been suggested that this article or section be merged with Solution. ... H2O and HOH redirect here. ... The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... The coordination geometry of an atom is the geometrical pattern formed by its neighbors in a molecule or a crystal. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, the orthorhombic crystal system is one of the 7 lattice point groups. ... The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 atmosphere... In chemistry, the standard molar entropy is the entropy content of one mole of substance, under conditions of standard temperature and pressure. ... Heat of fusion is the amount of heat energy which must be absorbed or lost for 1 gram of a substance to change states from a solid to a liquid or vice versa. ... Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the temperature of a unit quantity of a substance by a certain temperature interval. ... The Permissible Exposure Limit (PEL or OSHA PEL) is a legal limit in the United States for personal exposure to a substance, usually expressed in parts per million (ppm). ... If you are searching for the organization, click OSHA. Osha (Ligusticum porteri) is a perennial herb used for its medicinal properties. ... RTECS, also known as Registry of Toxic Effects of Chemical Substances, is a database of toxicity information compiled from the open scientific literature that is available for charge. ... NFPA 704 is a standard maintained by the U.S. National Fire Protection Association. ... Image File history File links NFPA_704. ... This page provides supplementary chemical data on calcium sulfate. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... The relative dielectric constant of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux. ... This page provides supplementary chemical data on calcium sulfate. ... This page provides supplementary chemical data on calcium sulfate. ... Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ... Infrared spectroscopy (IR Spectroscopy) is the subset of spectroscopy that deals with the IR region of the EM spectrum. ... Nuclear magnetic resonance spectroscopy most commonly known as NMR spectroscopy is the name given to the technique which exploits the magnetic properties of certain nuclei. ... Mass spectrometry (also known as mass spectroscopy (deprecated)[1] or informally, mass-spec and MS) is an analytical technique used to measure the mass-to-charge ratio of ions. ... This article is about the electrically charged particle. ... Magnesium sulfate (or sulphate) is a chemical compound containing magnesium and sulfate, with the formula MgSO4. ... Celestite (SrSO4) is a mineral consisting of strontium sulfate. ... A dessicant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately-well sealed container. ... Calcium chloride is an ionic compound of calcium and chlorine. ... Magnesium sulfate (or sulphate) is a chemical compound containing magnesium and sulfate, with the formula MgSO4. ... This article is about the building material. ... It has been suggested that Selenite be merged into this article or section. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... A dessicant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately-well sealed container. ... Hydrate is a term which means different things in inorganic chemistry and organic chemistry. ... This article is about the building material. ... Hydrate is a term which means different things in inorganic chemistry and organic chemistry. ... It has been suggested that Selenite be merged into this article or section. ... Anhydrite is a mineral - anhydrous calcium sulfate, CaSO4. ...

Natural, unrefined calcium sulphate is a translucent, crystalline white rock.

Commercial production and recovery

The main sources of calcium sulphate are the naturally-occurring gypsum and anhydrite which occur at many locations world-wide as evaporites. These may be extracted by open-cast quarrying or by deep mining. World production of natural gypsum is around 100 million tonnes per annum. A sample of evaporite material Evaporites (IPA: ) are water-soluble, mineral sediments that result from the evaporation of bodies of surficial water. ...

In addition to natural sources, calcium sulphate is produced as a by-product in a number of processes:

• In flue gas desulfurization, exhaust gases from fossil-fuel-burning power stations and other processes (e.g. cement manufacture) are scrubbed to reduce their sulfur oxide content, by injecting finely ground limestone or lime. This produces an impure calcium sulfite, which oxidizes on storage to calcium sulfate.
• In the production of phosphoric acid from phosphate rock, calcium phosphate is treated with sulfuric acid. Calcium sulfate precipitates out.
• In the production of hydrogen fluoride, calcium fluoride is treated with sulfuric acid, precipitating calcium sulfate.
• In the refining of zinc, solutions of zinc sulfate are treated with lime to co-precipitate heavy metals such as barium.

The precipitation processes tend to concentrate radioactive elements in the calcium sulfate product. This is particularly the case with the phosphate by-product, since phosphate rocks naturally contain actinides. Over 200 million tonnes per annum^[2] of calcium sulphate waste is produced by the phosphate industry worldwide. Flue gas desulfurization is technology that employs a sorbent, usually lime or limestone, to remove sulfur dioxide(SO2) from the gases produced by burning fossil fuels. ... Fossil fuels are hydrocarbons, primarily coal and petroleum (fuel oil or natural gas), formed from the fossilized remains of dead plants and animals[1] by exposure to heat and pressure in the Earths crust over hundreds of millions of years[2]. The theory that hydrocarbons were formed from these... A power station (also power plant) is a facility for the generation of electric power. ... For other uses, see Limestone (disambiguation). ... It has been suggested that Portlandite be merged into this article or section. ... This article is about orthophosphoric acid. ... Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal. ... Hydrogen fluoride is a chemical compound with the formula HF. Together with hydrofluoric acid, it is the principal industrial source of fluorine and hence the precursor to many important compounds including pharmaceuticals and polymers (e. ... Calcium fluoride (CaF2) is an insoluble ionic compound of calcium and fluorine. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... Zinc sulfate (ZnSO4) is a colorless crystalline, water-soluble chemical compound. ... It has been suggested that Portlandite be merged into this article or section. ... For other uses, see Barium (disambiguation). ... The actinide series encompasses the 15 chemical elements that lie between actinium and lawrencium on the periodic table, with atomic numbers 89 - 103[1]. The actinide series is named after actinium. ...

Calcium sulfate can also be recovered and re-used from scrap drywall at construction sites.

Dehydration reactions

Heating gypsum to between 100°C and 150°C (302°F) partially dehydrates the mineral by driving off approximately 75% of the water contained in its chemical structure. The temperature and time needed depend on ambient partial pressure of H₂O. Temperatures as high as 170°C are used in industrial calcination, but at these temperatures γ-anhydrite begins to form. The reaction for the partial dehydration is: Dehydration is the removal of water (hydor in ancient Greek) from an object. ...

CaSO₄·2H₂O + heat → CaSO₄·½H₂O + 1½H₂O (steam)

The partially dehydrated mineral is called calcium sulfate hemihydrate or calcined gypsum (commonly known as plaster of Paris) (CaSO₄·nH₂O), where n is in the range 0.5 to 0.8.^[3] This article is about the building material. ...

The dehydration (specifically known as calcination) begins at approximately 80°C (176°F), although in dry air, some dehydration will take place already at 50°C. The heat energy delivered to the gypsum at this time (the heat of hydration) tends to go into driving off water (as water vapor) rather than increasing the temperature of the mineral, which rises slowly until the water is gone, then increases more rapidly. Calcination is the process of heating a substance to a high temperature, but below its melting or fusing point, to bring about thermal decomposition or a phase transition in its physical or chemical constitution. ...

The endothermic property of this reaction is exploited by drywall to confer fire resistance on residential and other structures. In a fire the structure behind a sheet of drywall will remain relatively cool as water is lost from the gypsum, thus preventing (or substantially retarding) damage to the framing (through combustion of wood members or loss of strength of steel at high temperatures) and consequent structural collapse. In thermodynamics, the word endothermic describes a process or reaction that absorbs energy in the form of heat. ... For the musical group Drywall, see Drywall (musical project) Example of drywall with joint compound, the common interior building material. ... The term framing can have several possible meanings: framing (telecommunication), where it relates to synchronization framing (economics), where it relates to rational choice theory framing (World Wide Web), where it relates to the use of multiple panes within a web page framing (communication theory), where it relates to the contextual... A combustion reaction taking place in a igniting match Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... For other uses, see Wood (disambiguation). ... For other uses, see Steel (disambiguation). ...

In contrast to most minerals, which when rehydrated simply form liquid or semi-liquid pastes, or remain powdery, calcined gypsum has an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice:

CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O This reaction is exothermic. In thermodynamics, the word exothermic describes a process or reaction that releases energy in the form of heat. ...

This phenomenon is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an alternative to adobe (which loses its strength when wet). The conditions of dehydration can be changed to adjust the porosity of the hemihydrate, resulting in the so-called alpha and beta hemihydrates (which are more or less chemically identical). Cast earth is a building material which was developed relatively recently and is coming into use more frequently as it is studied further. ... Renewal of the surface coating of an adobe wall in Chamisal, New Mexico Adobe is a natural building material composed of sand, sandy clay and straw or other organic materials, which is shaped into bricks using wooden frames and dried in the sun. ...

On heating to 180°C, the nearly water-free form, called γ-anhydrite (CaSO₄.nH₂O where n=0 to 0.05) is produced. γ-Anhydrite reacts slowly with water to return to the dihydrate state, a property exploited in some commercial desiccants. On heating above 250°C, the completely anhydrous form called β-anhydrite or "natural" anhydrite is formed. Natural anhydrite does not react with water, even over geological timescales, unless very finely ground. A dessicant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately-well sealed container. ... Anhydrite is a mineral - anhydrous calcium sulfate, CaSO4. ...

The variable composition of the hemihydrate and γ-anhydrite, and their easy inter-conversion, is due to their possessing nearly-identical crystal structures, containing "channels" that can accommodate variable amounts of water, or other small molecules such as methanol. Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naptha or wood spirits, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). ...

Uses

Expanding on gypsum's role as a building material, at least two teams of researchers are currently designing robots that will build houses out of gypsum and concrete.^[4] A team headed by Dr Behrokh Khoshnevis at the University of Southern California and a team headed by Dr Rupert Soar at Loughborough University’s School of Mechanical and Manufacturing Engineering in England are both working on robots that will spray gypsum or concrete to create the shell of a house. The California team expects that their robot will be able to do so in only 24 hours and plans to build the first prototype shell before April of 2007. The British team's robot, in contrast, is expected to take at least a week to build a house, but possesses more advanced features such as "weaving in ducts for water pipes, electrical wiring and ventilation within the panels of gypsum or concrete." In addition to drastically decreasing the amount of time it takes to build a house, Khoshnevis claims that the automated, two-material construction technology will reduce the cost of building a house to a fifth of today's prices. The Trojan Shrine, better known as Tommy Trojan located in the center of University of Southern California campus. ... Loughborough University is located in the market town of Loughborough, Leicestershire in the East Midlands of England. ... For other uses, see England (disambiguation). ...

Gypsum is also used in the production of the following:

• Blackboard chalk
• Cement
• Drywall
• Plaster, which has many uses including medical, construction, and artistic.
• Paint filler
• Gesso
• Molds for Casting metals
• Agricultural soil amendment
• Solidifying earth (cast earth construction)
• Tofu coagulation
• Improving mineral content of brewing water
• Dietary calcium additives in breads and cereals
• Delayed release fish feeders (base)
• Pharmaceuticals
• Desiccant - anhydrous calcium sulfate (anhydrite) is sold under the brand name Drierite®
• Burtonisation

The Needles, situated on the Isle Of Wight, are part of the extensive Southern England Chalk Formation. ... In the most general sense of the word, cement is a binder, a substance which sets and hardens independently, and can bind other materials together. ... For the musical group Drywall, see Drywall (musical project) Example of drywall with joint compound, the common interior building material. ... This article is about the building material. ... Gesso is the Italian word for chalk (akin to the Greek word gypsum), and is a powdered form of the mineral calcium carbonate used in art. ... This article is about the manufacturing process. ... A soil amendment is any of a class of materials which are used to adjust the soil for increased fertility. ... Cast earth is a building material which was developed relatively recently and is coming into use more frequently as it is studied further. ... For other uses, see Tofu (disambiguation). ... A 16th century brewer A 21st century brewer This article concerns the production of alcoholic beverages. ... For other uses, see Calcium (disambiguation). ... For the 1970s rock and roll band, see Bread (band). ... Cereal crops are mostly grasses cultivated for their edible seeds (actually a fruit called a grain, technically a caryopsis). ... Pharmacology (in Greek: pharmacon is drug, and logos is science) is the study of how chemical substances interfere with living systems. ... A dessicant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately-well sealed container. ... Anhydrite is a mineral - anhydrous calcium sulfate, CaSO4. ... Calcium sulfate is a common laboratory and industrial chemical. ... Burtonisation is the act of adding sulphate, often in the form of gypsum, to the water used for the brewing of beer, in order to bring out the flavour of the hops. ...

See also

• Bathybius haeckeli

Bathybius haeckeli was a substance that British biologist Thomas Henry Huxley discovered and initially believed to be a form of primordial matter, a source of all organic life. ...

References

1. ^ H F W Taylor, Cement Chemistry, Academic Press, 1990, ISBN 0-12-683900-X, pp 186-187
2. ^ USGS data: world "refined" phosphate rock production is 140 m t: nearly all this is converted to phosphoric acid: 1.7 t of gypsum is produced per t of apatite.
3. ^ Taylor ibid, pp 186-187
4. ^ Booth, Robert. "Robo-builder threatens the brickie", The Times, 2007-01-14. Retrieved on 2007-01-27. 

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 14th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 27th day of the year in the Gregorian calendar. ...

External links

• International Chemical Satefy Card 1215
• NIOSH Pocket Guide to Chemical Hazards