Gypsum is a mineral from the sulfate group: hydrated calcium sulfate. Also eponymous rock, consisting predominantly of this mineral. The name of the mineral has Greek roots and was used to refer to fired gypsum products. Chemical formula: CaSO 4 2H 2 O.
The luster is glassy, pearlescent, silky or matte. Hardness 1.5-2. Specific gravity 2.2-2.4 g/cm3. Colorless, white, grayish, yellowish, pink, red, blue. The line is white. The cleavage of leafy varieties is very perfect. Solid granular, dense, earthy, leafy, fibrous, also individual crystals, dovetail-like doubles, druses (reminiscent of appearance surface of the brain or rose). Monoclinic system. The crystals are ingrown. The leaves are flexible, but not elastic.
Features . It has a non-metallic luster, slight hardness (gypsum is soft), a white line, low density, and not greasy to the touch. May be confused with anhydrite. Differs in hardness. Anhydrite has medium hardness.
Chemical properties . When heated to 107⁰C, it turns into CaSO 4 1/2 H 2 O, which, when wetted with water, hardens (“sets”). Dissolves in hydrochloric acid.
Varieties:
- WITHElenite– parallel-needle-shaped. The shine is silky.
- Maryino glass– thick-sheet transparent plaster.
- Alabaster– fine-grained, variously colored gypsum.
Gypsum desert rose Selenite Maryino glass Alabaster
Origin
Gypsum is formed on the surface of the Earth (representing lagoonal and lacustrine chemical sediment) or by hydration of anhydrite of sedimentary origin under the influence of cold groundwater (vadose water).
Satellites. IN sedimentary rocks ah: rock salt, anhydrite, sulfur, calcite.
Application of gypsum
Gypsum is used in architecture and sculpture, in the paper industry, in medicine, as a fertilizer in agriculture, in the production of sulfuric acid, cement, enamels, glazes and paints. Maryino glass is used in the optical industry. Due to its excellent sound insulation and ability to quickly set, alabaster is often used in construction during finishing works.
Selenite is an ornamental stone. Selenite and gypsum are used to make decorative tabletop sculptures of small forms (figurines, boxes, vases, etc.). Construction parts are made from gypsum: cornices, slabs, blocks, bas-reliefs.
Sulfur is obtained from gypsum and anhydrite: when heated, CaSO 4 transforms into calcium sulfide CaS, which upon contact with water forms hydrogen sulfide. When H 2 S is burned with a small amount of oxygen, sulfur and water are formed.
Place of Birth
Gypsum deposits are located on the western slope of the Urals, in the Volga region, Donbass (Artemovskoye), Prikamye, Fergana (Shorsu), near Murom on the river. Oka, in Tula, Ryazan, Kaluga, Arkhangelsk, Nizhny Novgorod regions, in Crimea, Karelia and Tatarstan. Selenite deposits are located near the Kungur Ice Cave. Widely distributed in other countries: USA, Iran, Canada, Spain.
Gypsum- mineral, hydrous calcium sulfate. The fibrous variety of gypsum is called selenite, and the granular variety is called alabaster. One of the most common minerals; the term is also used to designate the rocks it consists of. Gypsum is also commonly called a building material obtained by partial dehydration and grinding of the mineral. The name comes from the Greek. gypsos, which in ancient times meant both plaster itself and chalk. A dense snow-white, cream or pink fine-grained variety of gypsum known as alabaster
See also:
STRUCTURE
Chemical composition - Ca × 2H 2 O. Monoclinic system. The crystal structure is layered; two sheets of anionic 2- groups, closely associated with Ca 2+ ions, form double layers oriented along the (010) plane. H 2 O molecules occupy spaces between these double layers. This easily explains the very perfect cleavage characteristic of gypsum. Each calcium ion is surrounded by six oxygen ions belonging to SO 4 groups and two water molecules. Each water molecule binds a Ca ion to one oxygen ion in the same bilayer and to another oxygen ion in the adjacent layer. PROPERTIES
The color varies, but usually white, gray, yellow, pink, etc. Pure transparent crystals are colorless. Impurities can be colored in various colors. The color of the dash is white. The luster of the crystals is glassy, sometimes with a pearlescent tint due to microcracks of perfect cleavage; in selenite it is silky. Hardness 2 (Mohs scale standard). The cleavage is very perfect in one direction. Thin crystals and fusion plates are flexible. Density 2.31 - 2.33 g/cm3.
It has noticeable solubility in water. A remarkable feature of gypsum is the fact that its solubility with increasing temperature reaches a maximum at 37-38°, and then drops quite quickly. Largest decrease solubility is established at temperatures above 107° due to the formation of “hemihydrate” - CaSO 4 × 1/2H 2 O.
At 107°C, it partially loses water, turning into white alabaster powder (2CaSO 4 × H 2 O), which is noticeably soluble in water. Due to the smaller number of hydration molecules, alabaster does not shrink during polymerization (increases in volume by approximately 1%). Under item tr. loses water, splits and fuses into white enamel. On coal in a reducing flame it produces CaS. It dissolves much better in water acidified with H 2 SO 4 than in pure water. However, at a concentration of H 2 SO 4 above 75 g/l. solubility drops sharply. Very slightly soluble in HCl.
MORPHOLOGY
Crystals, due to the predominant development of faces (010), have a tabular, rarely columnar or prismatic appearance. Of the prisms, the most common are (110) and (111), sometimes (120), etc. The faces (110) and (010) often have vertical hatching. Fusion twins are common and come in two types: 1) Gallic by (100) and 2) Parisian by (101). It is not always easy to distinguish them from each other. Both of them resemble a dovetail. Gallic twins are characterized by the fact that the edges of the prism m (110) are located parallel to the twin plane, and the edges of the prism l (111) form a reentrant angle, while in Parisian twins the edges of the prism Ι (111) are parallel to the twin seam. It occurs in the form of colorless or white crystals and their intergrowths, sometimes colored by inclusions and impurities captured by them during growth in brown, blue, yellow or red tones. Characteristic are intergrowths in the form of a “rose” and twins - the so-called. "swallowtails"). It forms veinlets of a parallel-fibrous structure (selenite) in clayey sedimentary rocks, as well as dense, continuous fine-grained aggregates resembling marble (alabaster). Sometimes in the form of earthy aggregates and cryptocrystalline masses. Also makes up the cement of sandstones.
Pseudomorphoses of calcite, aragonite, malachite, quartz, etc. on gypsum are common, as are pseudomorphs of gypsum on other minerals.
ORIGIN
A widely distributed mineral natural conditions is formed in various ways. The origin is sedimentary (typical marine chemogenic sediment), low-temperature hydrothermal, found in karst caves and solfataras. Precipitated from sulfate-rich aqueous solutions when sea lagoons and salt lakes dry out. Forms layers, layers and lenses among sedimentary rocks, often in association with anhydrite, halite, celestine, native sulfur, sometimes with bitumen and oil. It is deposited in significant quantities by sedimentation in lake and sea salt-bearing dying pools. In this case, gypsum, along with NaCl, can be released only in the initial stages of evaporation, when the concentration of other dissolved salts is not yet high. When a certain concentration of salts is reached, in particular NaCl and especially MgCl 2, anhydrite will crystallize instead of gypsum and then other, more soluble salts, i.e. The gypsum in these basins must belong to earlier chemical sediments. Indeed, in many salt deposits there are layers of gypsum (as well as anhydrite), interbedded with layers rock salt, are located in the lower parts of the deposits and in some cases are underlain only by chemically precipitated limestones.
In Russia, thick gypsum-bearing strata of Permian age are distributed throughout the Western Urals, in Bashkiria and Tatarstan, in Arkhangelsk, Vologda, Gorky and other regions. Numerous deposits of Upper Jurassic age are established in the North. Caucasus, Dagestan. Remarkable collection samples with gypsum crystals are known from the Gaurdak deposit (Turkmenistan) and other deposits in Central Asia (in Tajikistan and Uzbekistan), in the Middle Volga region, in the Jurassic clays of the Kaluga region. In the thermal caves of Naica Mine, (Mexico), druses of uniquely sized gypsum crystals up to 11 m long were found.
APPLICATION
Today, the mineral "gypsum" is mainly a raw material for the production of α-gypsum and β-gypsum. β-gypsum (CaSO 4 ·0.5H 2 O) is a powdered binder material obtained by heat treatment of natural dihydrate gypsum CaSO 4 ·2H 2 O at a temperature of 150-180 degrees in apparatus communicating with the atmosphere. The product of grinding β-modification gypsum into a fine powder is called building gypsum or alabaster; with finer grinding, molding gypsum is obtained or, when using high-purity raw materials, medical gypsum. During low-temperature (95-100 °C) heat treatment in hermetically sealed apparatus, α-modification gypsum is formed, the grinding product of which is called high-strength gypsum.
When mixed with water, α and β-gypsum hardens, turning back into gypsum dihydrate, with the release of heat and a slight increase in volume (by approximately 1%), however, such secondary gypsum stone already has a uniform fine-crystalline structure, the color of various shades of white (depending on raw materials), opaque and microporous. These properties of gypsum are used in various fields of human activity.
Gypsum (eng. Gypsum) - CaSO 4 * 2H 2 O
CLASSIFICATION
| Strunz (8th edition) | 6/C.22-20 |
| Nickel-Strunz (10th edition) | 7.CD.40 |
| Dana (7th edition) | 29.6.3.1 |
| Dana (8th edition) | 29.6.3.1 |
| Hey's CIM Ref. | 25.4.3 |
PHYSICAL PROPERTIES
| Mineral color | colorless turning to white, often colored by impurity minerals yellow, pink, red, brown, etc.; sometimes sectorial-zonal coloring or distribution of inclusions across growth zones inside crystals is observed; colorless in internal reflexes and at random. |
| Stroke color | white |
| Transparency | transparent, translucent, opaque |
| Shine | glassy, close to glassy, silky, pearlescent, dull |
| Cleavage | very perfect, easily obtained by (010), almost mica-like in some samples; along (100) clear, turning into a conchoidal fracture; according to (011), gives a splintered fracture (001) |
| Hardness (Mohs scale) | 2 |
| Kink | smooth, conchoidal |
| Strength | flexible |
| Density (measured) | 2.312 - 2.322 g/cm 3 |
| Radioactivity (GRapi) | 0 |
In traumatology and orthopedics, hardening bandages are used for immobilization. Used as hardening dressings various means and materials.
Gypsum hardens much faster than other materials, so it is used more often. Much credit for improving the plaster cast and its use for fractures belongs to the remarkable Russian surgeon N.I. Pirogov, who was still in Crimean War 1854-1856 widely used it in wounded people with gunshot fractures.
What is gypsum, the quality of medical gypsum
Gypsum- This is calcium sulfate powder, calcined at a temperature not exceeding 140°. The formula of gypsum after firing due to loss of water is: 2CaSO4-H2O. Gypsum should be stored in a sealed container in a dry place, since damp plaster hardens very slowly.
Medical plaster should be white, powdery, soft to the touch, without lumps, should harden quickly (in 5-10 minutes) and be durable in products.
The quality of gypsum is best determined in the laboratory. If this is not possible, use practical tests.
Sample 1. Clamp the plaster into a fist. A significant part of the plaster easily penetrates through the interdigital gaps, and only part of the plaster remains in the clenched fist. After unclenching the fist, good quality plaster crumbles. If a compressed lump of plaster remains on the palm, it means it is moistened.
Sample 2. A plaster cast of 2-3 layers is applied to the forearm or hand. At good quality gypsum hardening occurs within 5-7 minutes. After removal, the splint does not crumble and retains its given shape.
Sample 3. Mix a slurry of 5 parts gypsum and 3 parts water and leave for 5-10 minutes. During this time, good plaster should harden. If you press on the hardened mass with your finger, the plaster does not disintegrate and moisture does not appear on its surface. Good plaster, after hardening, breaks into several pieces. Poor quality plaster kneads and releases moisture.
Sample 4. Two spoons of gypsum are mixed with the same amount of water; A ball is rolled out of the resulting gypsum slurry. When it hardens, it is thrown onto the floor from a height of 1 m. A ball of benign plaster will not break. A ball of poor quality plaster crumbles.
How ornamental material gypsum has been popular since ancient times different nations. From gypsum stone they cut out openwork vases, figurines, ashtrays, etc. In Russia, the art of making stucco decorations from plaster flourished at its peak during the construction of St. Petersburg. The architectural structures of the northern capital were richly decorated stucco decoration, which the old masters performed with great taste and understanding of the properties of the material.
Gypsum, or hydrous calcium sulfate, refers to minerals. In its pure form it is colorless and transparent, and in the presence of impurities it has gray, yellowish, pink, brown and other colors. Precipitates from aqueous solutions rich in sulfate salts during the drying out of sea lagoons and salt lakes.
Gypsum materials obtained by heat treatment and grinding of natural gypsum stone and some gypsum-containing industrial waste.
According to heat treatment conditions gypsum binders are divided into two groups: low-firing and high-firing.
Low-fired gypsum includes construction, molding, high-strength gypsum and gypsum-cement-pozzolanic binder; to high-fired ones - anhydrite cement and estrichgypsum.
Depending on the setting and hardening time gypsum binders are divided into: A - fast-hardening
(2-15 min), B - normal hardening
(6-30 min), B - slow-hardening
(20 minutes or more).
By grinding degree distinguish between binders coarse (I), medium (II) and fine (III) grinding.
For example, marking gypsum binder G-7-A-II means: G - gypsum binder, 7 - compressive strength (in MPa), A - fast hardening, II - medium grinding.
Gypsum binder powder mixed with water (50-70% by weight of gypsum) forms a plastic dough that quickly sets and hardens. It turns out gypsum stone, the strength of which increases as it dries. It is important to remember that when hardening, gypsum increases in volume by 0.3-1%, and take this into account when making products by casting into molds.
Products made from gypsum have high hygroscopicity, therefore they must be kept relative humidity air no more than 60%.
Unlike other binders, gypsum can be used without fillers, without fear of cracks, since they do not shrink, but, on the contrary, increase in volume. If necessary, the filler can be sawdust, shavings, firewood, slag, expanded clay, slag pumice.
Gypsum solutions and dough must be applied before crystallization begins, because with prolonged mixing and compaction they lose their astringent properties. The setting process can be slowed down or accelerated appropriate additives.
To slow down setting additives are used to increase the plasticity of the mixture: 5-10% solution wood glue, 2-3% borax solution, 5-6% sugar solution, 3-4% glycerin in the form water emulsion, 5% ethyl alcohol solution. A good and cheap substitute is specially prepared hide glue. It is crushed into small pieces and filled with cold water (preferably boiled) in a ratio of 1:5 (by weight). After 12 hours, add 1 part of lime dough to the soaked glue and boil in a water bath, stirring until ready. If you add 1 part of the prepared composition to 100 parts of gypsum, the setting time of the gypsum will last up to 40-60 minutes. It should be remembered that retarders reduce the strength of gypsum products.
To speed up setting binder is added to it with a 3-4% solution table salt(or sodium sulfate, potassium sulfate) or ground hardened gypsum in small quantities.
How to increase the water resistance and strength of gypsum.
1. Mix the plaster with water with the addition of borax and glue (per 1 liter of water - 80 g of borax and 20 - 30 g of glue).
2. When mixing gypsum, for every 100 parts of water, add 2 parts of gelatin and 1 part of alum.
3. When mixing gypsum, add 50% silicic acid. After molding, dry the casting, heat it to 80°C and soak it in barium chloride or calcium chloride (dipping).
4. Dry the plaster product and soak it in a saturated borax solution. Then coat twice with hot barium chloride solution. After drying, rinse the product with hot soap solution to wash away soluble salts.
5. Hold the product at a temperature of 125°C until dehydrated, then immerse it in a solution of caustic barium and treat it with a solution of oxalic acid.
6. Add a silicone compound, for example, sodium methyl siliconate (0.5% by weight of gypsum), into dry gypsum.
To obtain colored plasters It is recommended to use mineral alkali-resistant pigments: ocher, mummy, yellow lead, English red lime, slaked with solution copper sulfate, - for yellow and red colors;
chromium oxide and water-insoluble pigment B - for green coloring;
ultramarine and cobalt, giving Blue colour;
umber and lime, slaked with a solution of copper sulfate, to obtain Brown;
manganese peroxide, graphite, burnt bone - for black color.
Pigments (up to 10% by weight) are introduced into dry plaster.
Plaster can be used twice. For this purpose cast, hardened plaster dehydrated at a temperature of 120-160°C and crushed. Such gypsum acquires the ability to set, but at the same time its strength is somewhat reduced.
Gypsum has been known since ancient times, but has not yet lost its popularity, even many modern materials cannot compete with him. It is used in construction, porcelain, ceramic, oil industry and in medicine.
Description of building material
Gypsum is made from gypsum stone. To obtain gypsum powder, the stone is fired in rotary kilns and then ground to form a powder. Gypsum is most common in construction.
Walls, plastered gypsum mortar, capable of absorbing excess moisture and give it away when the air is too dry.
Gypsum formula
The name gypsum comes from Greek word gypsos. This material belongs to the class of sulfates. His chemical formula CaSO4?2H2O.
There are two types of gypsum:
- Fibrous - selenite;
- Grainy - alabaster.
Photos of gypsum varieties
Selenite Alabaster
Technical characteristics and properties
Everyone has gypsum mixtures specifications have great similarities, let’s focus on the properties and features building gypsum.
These include:
- Density. Gypsum has a dense, fine-grained structure. The true density is 2.60-2.76 g/cm?. When loosely poured, it has a density of 850-1150 kg/m2, and when compacted, the density is 1245-1455 kg/m2.
- How long does it take to dry? The advantages of gypsum include rapid setting and hardening. The gypsum sets in the fourth minute after mixing the solution, and after half an hour it completely hardens. Therefore, the finished gypsum solution must be used immediately. To slow down the setting, water-soluble animal glue is added to the plaster.
- Specific gravity. Is the specific gravity of gypsum measured in kg/m? in the MKGSS system. Since the ratio of mass is equal to the volume it occupies, the specific, volumetric and bulk weight of gypsum is approximately the same.
- What temperature can it withstand? t melting). Gypsum can be heated to 600-700°C without destruction. The fire resistance of gypsum products is high. Their destruction occurs only six to eight hours after exposure to high temperature.
- Strength. Construction gypsum has a compressive strength of 4-6 MPa, high-strength - from 15 to 40 MPa or more. Well-dried samples have two to three times higher strength.
- GOST State standard of gypsum 125-79 (ST SEV 826-77).
- Thermal conductivity. Gypsum is a poor conductor of heat. Its thermal conductivity is 0.259 kcal/m deg/hour in the range from 15 to 45°C.
- Solubility in water. R dissolves in small quantities: 2.256 g dissolves in 1 liter of water at 0°, 2.534 g at 15°, 2.684 g at 35°; with further heating, the solubility decreases again.
The video talks about building gypsum and how you can improve its properties by giving additional strength:
Types of gypsum
Gypsum has the greatest variety of uses among other binding materials. It allows you to save on other materials. There are many varieties of gypsum.
Building
It is used for the production of gypsum parts, partition boards for plastering works. Work with gypsum mortar must be carried out very quickly a short time– from 8 to 25 minutes, it depends on the type of plaster. During this time it must be completely used up. When hardening begins, gypsum already gains about 40% of its final strength.
Since cracks do not form on the gypsum during hardening, when mixing the solution with lime mortar, which gives it plasticity, you don’t have to add various fillers. Due to short terms setting retarders are added to gypsum. Construction gypsum reduces labor intensity and construction costs.
In deposits by blasting gypsum-containing rock. The ore is then transported to factories in the form of gypsum stones.
High strength
By chemical composition high-strength gypsum is similar to building gypsum. But building gypsum has smaller crystals, while high-strength gypsum has large crystals, so it has less porosity and very high strength.
High-strength gypsum is produced by heat treatment in a sealed apparatus into which gypsum stone is placed.
The scope of application of high-strength gypsum is extensive. Various are prepared from it building mixtures, build fireproof partitions. It is also made from various shapes for the production of porcelain and earthenware sanitary products. High-strength gypsum is used in traumatology and dentistry.
Polymeric
Orthopedic traumatologists are more familiar with synthetic polymer plaster; plaster bandages are produced on its basis for applying bandages for fractures.
Advantages of polymer plaster casts:
- three times lighter than conventional plaster;
- easy to apply;
- allow the skin to breathe, as they have good permeability;
- resistant to moisture;
- allow you to control bone fusion, as they are permeable to x-rays.
Cellacast
Bandages are also made from this plaster; their structure allows the bandage to be stretched in all directions, so very complex bandages can be made from it. Cellacast has all the properties of a polymer bandage.
Sculpted or molded
This is the most highly durable gypsum, it does not contain any impurities, it has high natural whiteness. It is used for making molds for sculptures, plaster figurines, sculpting souvenirs, in the porcelain and earthenware, aviation and automotive industries.
This is the main component of dry putty mixtures. Molding gypsum is obtained from building gypsum; for this, it is additionally sifted and ground.
Known for several centuries, it still remains relevant in our time. The most common rosettes are gypsum, they are easy to make with your own hands.
Acrylic
Acrylic plaster is made from water-soluble acrylic resin. After hardening, it looks similar to regular plaster, but is much lighter. Ceiling stucco and other decorative details are made from it.
Acrylic gypsum is frost-resistant and has little moisture absorption, so it can be used to decorate building facades, creating interesting design solutions.
Working with acrylic plaster is very simple. If you add a little marble chips or aluminum powder or other inert fillers to the solution, acrylic plaster products will closely resemble marble or metal ones.
This is what acrylic plaster looks like
Polyurethane
Gypsum stucco can also be made from polyurethane or polystyrene gypsum. It costs much less than ordinary gypsum, and its qualities are almost no different from it.
White
By using white plaster seal seams, cracks, make stucco molding and carry out other types of construction and repair work. It is compatible with various types building materials. White gypsum hardening time 10 minutes.
Fine grain
Fine-grained gypsum is also called translucent. It is used to fill seams, joints in slabs, etc.
Liquid
Liquid gypsum is prepared from gypsum powder.
It is prepared using the following technology:
- Pour water in the required quantity.
- Pour in gypsum and mix immediately.
- The density of the solution can be varied. A liquid solution is made to fill the molds
Waterproof (moisture resistant)
Waterproof gypsum is obtained by processing raw materials according to special technology. To improve the properties of gypsum, stillage, a waste product from the production of ethyl alcohol, is added to it.
Refractory
Gypsum is a non-flammable material, non-flammable, but plasterboard sheets, made from it are quite flammable. To give them fire resistance, tongue-and-groove gypsum is used. It is used wherever it is required to increase fire resistance.
Architectural
Architectural gypsum does not contain toxic components, it is very plastic. Its acidity is similar to that of human skin. Classic modeling from architectural plaster is very popular among designers; there is a very high demand for it.
It requires certain knowledge, so you should first carefully study the features of such work, and only then proceed to practice.
Stamps
Plaster marking is carried out after testing standard samples of sticks for bending and compression two hours after they are molded. According to GOST 129-79, twelve grades of gypsum are established, with strength indicators from G2 to G25.
Plaster substitute
An analogue of gypsum is a finely dispersed grayish-white powder - alabaster. It is also popular in construction. Alabaster is obtained from natural gypsum dihydrate by heat treatment at temperatures from 150 to 180? C. Externally, alabaster and gypsum are no different from each other.
Alabaster is used to plaster walls and ceilings at low indoor humidity. Gypsum panels are produced from it.
What is the difference between plaster and alabaster?
Gypsum and alabaster have the following differences:
- Alabaster is more limited in application, as it is used only in the construction industry. Gypsum is also used in medicine.
- Alabaster dries instantly, so it is not suitable without the addition of special substances.
- Gypsum is safer for environment and human health.
- Alabaster has greater hardness than gypsum.