Gips – razlika između verzija

 

 

<!--Heating gypsum to between 100°C and 150°C (302°F) partially [[dehydrate]]s the mineral by driving off exactly 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 the anhydrite begins to be formed.

The reaction for the partial dehydration is:-->

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:-->

 

 

<!--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).-->

Anhydrite reacts slowly with water to return to the dihydrated state, a property exploited in some commercial [[desiccant]]s.-->

 

<!--Gypsum occurs in nature as flattened and often [[crystal twinning|twinned]] [[crystal]]s and transparent cleavable masses called [[selenite]]. It may also occur silky and fibrous, in which case it is commonly called ''satin spar''. Finally it may also be granular or quite compact. In hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly-tinted variety of gypsum is called [[alabaster]], which is prized for ornamental work of various sorts. In arid areas, gypsum can occur in a flower-like form typically opaque with embedded sand grains called [[desert rose (crystal)|desert rose]].-->

<!--

Gypsum is a very common mineral, with thick and extensive [[evaporite]] beds in association with [[sedimentary rock]]s. The largest deposits known occur in [[stratum|strata]] from the [[Permian]] age. Gypsum is deposited in lake and sea water, as well as in [[hot spring]]s, from [[volcano|volcanic]] vapors, and sulfate solutions in veins. [[Hydrothermal]] [[anhydrite]] in veins is commonly hydrated to gypsum by groundwater in near surface exposures. It is often associated with the minerals [[halite]] and [[sulfur]].-->

 

<!--The word gypsum is derived from the [[aorist]] form of the [[Greek language|Greek]] verb ''μαγειρεύω'', "to cook", referring to the burnt or calcined mineral. Because the gypsum from the [[quarry|quarries]] of the [[Montmartre]] district of [[Paris]] has long furnished burnt gypsum used for various purposes, this material has been called plaster of Paris.-->

 

<!--Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, the unique conditions of the [[White Sands National Monument]] in the US state of [[New Mexico]] have created a 710 km² (275 sq mile) expanse of white gypsum sand, enough to supply the construction industry with drywall for 1,000 years.<ref name='The Albuquerque Journal 1999-02-07'>{{cite news | last = Abarr | first = James | title = Sea of Sand | pages = | publisher = The Albuquerque Journal | date = [[1999-02-07]] | url = http://www.abqjournal.com/venue/travel/tourism/heritage_whitesands.htm | accessdate = 27. 01. 2007. }}</ref> Commercial exploitation of the area, strongly opposed by area residents, was permanently prevented in 1933 when president [[Herbert Hoover]] declared the gypsum dunes a protected national monument.-->

 

<!--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.<ref name='Times Online 2007-01-14'>{{cite news | first=Robert | last=Booth | coauthors= | title=Robo-builder threatens the brickie | date=[[2007-01-14]] | publisher=The Times | url =http://www.timesonline.co.uk/article/0,,2087-2546574,00.html | work = | pages = | accessdate = 27. 01. 2007. | language = }}</ref> 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.

 

*[[Burtonisation]]-->

 

* [[Popis minerala|Spisak minerala]]

* [[Lime (mineral)|Lime]]

{{reflist}}

 

{{Commonscat|Gypsum}}

* [http://webmineral.com/data/Gypsum.shtml WebMineral data]

 

== Vidi ==

{{Minerali}}

 

[[Kategorija:Neorganska jedinjenja]]

[[Kategorija:Minerali]]