Commercial plasters

Storage conditions of commercial plasters often result in partial hydration of the hemihydrate material. Dynamic or isothermal thermogravimetry can be used to estimate the primary phases and impurities present in commercial plaster. In dynamic TG experiments at low heating rates, the hemihydrate and dihydrate contents can be estimated from separate mass change steps of the respective dehydration reactions shown in the resulting TG curves. 

A typical TG curve of a commercial plaster (Fig. 29) shows two steps for mass loss. The first step is caused by the dehydration of calcium sulfate dihydrate. The second step is due to the dehydration of calcium sulfate hemihydrate. The second step is attributed to the hemihydrate present in the original sample and also to that formed during the first step of decomposition. 

Thermogravimetry can be used for quality control of commercial plasters either by d5mamic or isothermal methods. The partial hydration of the plasters, which have not been well stored, can be subjected to identification and estimation. 

Dweck, J., Lasota, E. I. P., Quality Control of Commercial Plasters by Thermogravimetry, Thermochimica Acta, 318 137-142 (1998)... 

Although the use of simple diluents and adulterants almost certainly predates recorded history, the use of fillers to modify the properties of a composition can be traced as far back as eady Roman times, when artisans used ground marble in lime plaster, frescoes, and po22olanic mortar. The use of fillers in paper and paper coatings made its appearance in the mid-nineteenth century. Functional fillers, which introduce new properties into a composition rather than modify pre-existing properties, were commercially developed eady in the twentieth century when Goodrich added carbon black to mbber and Baekeland formulated phenol— formaldehyde plastics with wood dour. 

The hermhydrate (stucco) is normally produced by heat conversion of the dihydrate from which 3/2 H2O is removed as vapor. The resulting powder is also known as plaster of Paris [26499-65-0]. Stucco has the greatest commercial significance of these materials. It is the primary constituent used to fabricate products and ia formulated plasters used ia job- or shop-site appHcations. 

Calcined Anhydrite. Soluble anhydrite, or second-settle stucco, has physical properties similar to those of gypsum plaster. It hydrates to the dihydrate rapidly in water. Its outstanding property is its extreme affinity for any moisture, which makes it a very efficient drying agent (see Desiccants). In ambient moisture-laden air, it readily hydrates to hemihydrate. Soluble anhydrite, under the trade name Drierite, is widely used as a desiccant in the laboratory and in iadustry. A small amount is also used as an insecticide carrier. Small amounts of soluble anhydrite are unintentionally produced in most commercial calciners during hemihydrate production. 

Demolition and construction wastes. Wastes from razed building and other structures are classified as demolition wastes. Wastes from the construction, remodeling, and repair of commercial and industrial buildings and other similar structures are classified as construction wastes. These wastes may include dirt, stones, concrete, bricks, plaster, lumber, shingles, and plumbing, heating, and electrical parts. 

NR pressure-sensitive adhesives with a high tackifier content can be used as commercial tapes and surgical plasters. These PSA require the elimination of the gel fraction and a reduction in molecular weight to facilitate solution. 

Gypsum-treated muds have proved useful for drilling anhydride and gypsum, especially where these formations are interbedded with salt and shale. The treatment consists of conditioning the base mud with plaster (commercial calcium sulfate) before the anhydride or gypsum formation is penetrated. By... 

Cellulose and Acetylated Cellulose These adsorbents are commercially available in various forms e.g., particle size, degree of acetylation, with or without binders like starch or Plaster of Paris. 

Calcium carbonate occurs in nature as hmestone in various forms, such as marble, chalk, and coral. It is probably the most widely-used raw material in the chemical industry. It has numerous apphcations, primarily to produce cement, mortars, plasters, refractories, and glass as budding materials. It also is used to produce quicklime, hydrated lime and a number of calcium compounds. It is produced either as powdered or precipitated calcium carbonate. The latter consists of finer particles of greater purity and more uniform size. They also have many important commercial apphcations. Various grades of precipitated calcium carbonate are used in several products, such as textiles, papers, paints, plastics, adhesives, sealants, and cosmetics. 

Adsorbent The adsorbent may consist of finely divided adsorbent materials for chromatography. It can be applied directly to the glass plate, or it can be bonded to the plate by means of plaster of Paris or with starch paste. Pretreated chromatographic plates are available commercially. 

Gypsum is a white substance, which is used commercially for fabrication into wallboard, and conversion into plaster of Paris. When gypsum is heated a little above 100° C it loses three quarters of its water of crystallization, forming the. ppwdered substance CaS04 ... 

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