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  1. Plaster - Wikipedia › wiki › Plaster

    Plaster of Paris is stored in moisture-proof containers, because the presence of moisture can cause slow setting of plaster of Paris by bringing about its hydration, which will make it useless after some time. When the dry plaster powder is mixed with water, it rehydrates over time into gypsum.

    • Types

      Clay plaster is a mixture of clay, sand and water with the...

    • Applications

      Early 19th Century plasterer at work - painting by John...

    • Safety issues

      The chemical reaction that occurs when plaster is mixed with...

  2. Gypsum - Wikipedia › wiki › Gypsum

    The word gypsum is derived from the Greek word γύψος (gypsos), "plaster". Because the quarries of the Montmartre district of Paris have long furnished burnt gypsum (calcined gypsum) used for various purposes, this dehydrated gypsum became known as plaster of Paris.

    • Massive, flat. Elongated and generally prismatic crystals
    • Prismatic (2/m), H-M symbol: (2/m)
    • 1.5–2 (defining mineral for 2)
    • Monoclinic
  3. Calcium sulfate - Wikipedia › wiki › Calcium_sulfate
    • Overview
    • Hydration states and crystallographic structures
    • Uses
    • Production and occurrence
    • Retrograde solubility
    • On planet Mars

    Calcium sulfate is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite, it is used as a desiccant. One particular hydrate is better known as plaster of Paris, and another occurs naturally as the mineral gypsum. It has many uses in industry. All forms are white solids that are poorly soluble in water. Calcium sulfate causes permanent hardness in water.

    The compound exists in three levels of hydration corresponding to different crystallographic structures and to different minerals in nature: 1. CaSO4: anhydrous state. 2. CaSO4 · 2 H2O: dihydrate. 3. CaSO4 · 1⁄2 H2O: hemihydrate, also known as plaster of Paris. Specific hemihydrates are sometimes distinguished: α-hemihydrate and β-hemihydrate.

    The main use of calcium sulfate is to produce plaster of Paris and stucco. These applications exploit the fact that calcium sulfate which has been powdered and calcined forms a moldable paste upon hydration and hardens as crystalline calcium sulfate dihydrate. It is also convenient that calcium sulfate is poorly soluble in water and does not readily dissolve in contact with water after its solidification.

    The main sources of calcium sulfate are naturally occurring gypsum and anhydrite, which occur at many locations worldwide as evaporites. These may be extracted by open-cast quarrying or by deep mining. World production of natural gypsum is around 127 million tonnes per annum. In addition to natural sources, calcium sulfate is produced as a by-product in a number of processes: 1. In flue-gas desulfurization, exhaust gases from fossil-fuel power stations and other processes are scrubbed to reduce

    The dissolution of the different crystalline phases of calcium sulfate in water is exothermic and releases heat. As an immediate consequence, to proceed, the dissolution reaction needs to evacuate this heat that can be considered as a product of reaction. If the system is cooled, the dissolution equilibrium will evolve towards the right according to the Le Chatelier principle and calcium sulfate will dissolve more easily. Thus the solubility of calcium sulfate increases as the temperature decrea

    2011 findings by the Opportunity rover on the planet Mars show a form of calcium sulfate in a vein on the surface. Images suggest the mineral is gypsum.

    • 7778-18-9, (hemihydrate): 10034-76-1, (dihydrate): 10101-41-4
    • 1,460 °C (2,660 °F; 1,730 K) (anhydrous)
    • CaSO₄
    • 0.26 g/100ml at 25 °C (dihydrate)
  4. plaster of Paris - Wiktionary › wiki › plaster_of_Paris

    Feb 27, 2020 · Noun plaster of Paris (uncountable) A hemihydrate of calcium sulfate, made by calcining gypsum, that hardens when moistened and allowed to dry; used to make casts, molds and sculpture.

  5. Plaster mold casting - Wikipedia › wiki › Plaster_mold_casting
    • Overview
    • Details
    • Advantages and disadvantages

    Plaster mold casting is a metalworking casting process similar to sand casting except the molding material is plaster of Paris instead of sand. Like sand casting, plaster mold casting is an expendable mold process, however it can only be used with non-ferrous materials. It is used for castings as small as 30 g to as large as 7–10 kg. Generally, the form takes less than a week to prepare. Production rates of 1–10 units/hr can be achieved with plaster molds. Parts that are typically made...

    The plaster is not pure plaster of Paris, but rather has additives to improve green strength, dry strength, permeability, and castability. For instance, talc or magnesium oxide are added to prevent cracking and reduce setting time; lime and cement limit expansion during baking; glass fibers increase strength; sand can be used as a filler. The ratio of ingredients is 70–80% gypsum and 20–30% additives. The pattern is usually made from metal, however rubber molds may be used for complex ...

    Plaster mold casting is used when an excellent surface finish and good dimensional accuracy is required. Because the plaster has a low thermal conductivity and heat capacity, the metal cools more slowly than in a sand mold, which allows the metal to fill thin cross-sections; the minimum possible cross-section is 0.6 mm. This results in a near net shape casting, which can be a cost advantage on complex parts. It also produces minimal scrap material. The major disadvantage of the process is that i

  6. plaster of paris | Definition, Uses, & History | Britannica › technology › plaster-of-paris

    Plaster of paris, quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry. Known since ancient times, plaster of paris is so called because of its preparation from the abundant gypsum found near Paris.

  7. Plaster of Paris - Uses, Formula, Preparation › jee › plaster-of-paris

    Plaster of Paris is manufactured by heating gypsum at 423K or 150o C/300o F. CaSO4·2H2O + heat → CaSO4·0.5H2O + 1.5H2O (discharged as steam) On heating gypsum at 423 K, it loses water molecules and becomes calcium sulfate hemihydrate. This product is known as the plaster of Paris.

  8. How to Make Plaster of Paris: 9 Steps (with Pictures) - wikiHow › Make-Plaster-of-Paris

    Jun 25, 2021 · Plaster of Paris is a simple craft material that can be easily made at home. All you need is flour and water, or glue and water if you'd rather not handle flour. Once you've made it, you can use it to make plaster casts, molds, or even chalk! Method 1

    • 2 min
    • 174.6K
    • wikiHow Staff
  9. Plaster of Paris History | Our Pastimes › plaster-of-paris-history

    Mar 02, 2019 · Plaster of Paris was used as far back as the Ancient World where it was popular in Egyptian tombs as well as Roman and Greek architecture and art. It’s been used for decorative flourishes on pillars and columns and along ceilings and railings, from Antiquity through today.

  10. Plaster of Paris (POP)| Uses, Advantages & Disadvantages › blog › plaster-of-paris-pop-uses

    Aug 10, 2019 · Plaster of Paris is a building material which is used for plastering the internal walls as well as making the false ceilings of the house. It is also used to cast decorative elements like mouldings, Cornish, etc. Plaster of Paris is prepared by heating gypsum crystals.

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