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Gypsum

Notes

*5/2/2012

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Notes

“Gypsum-based building products are commonly used in construction. Wallboard made of gypsum is fire retardant and can be used in the construction of walls of almost any shape. It is used primarily as an interior wall and ceiling product. Gypsum has sound-deadening properties. It is relatively easily patched or replaced if it becomes damaged. There are a variety of decorative finishes that can be applied to the wallboard, including paint and wallpaper. Even with all of these advantages, it is still a relatively inexpensive building material.

Gypsum is also known as calcium sulfate dihydrate, terra alba or landplaster. Plaster of Paris is also known as calcined gypsum, stucco, calcium sulfate semihydrate, calcium sulfate half-hydrate or calcium sulfate hemihydrate. Synthetic gypsum, which is a byproduct of flue gas desulfurization processes from power plants, may also be used. When it is mined, raw gypsum is generally found in the dihydrate form. In this form, there are approximately two water molecules of water associated with each molecule of calcium sulfate.

In order to produce the hemihydrate form, the gypsum can be calcined to drive off some of the water of hydration by the following equation: CaSO.sub.4.2H.sub.2O.fwdarw.CaSO.sub.4.1/2H.sub.2O+3/2H.sub.2O

A number of useful gypsum products can be made by mixing the stucco with water and permitting it to set by allowing the calcium sulfate hemihydrate to react with water to convert the hemihydrate into a matrix of interlocking calcium sulfate dihydrate crystals. As the matrix forms, the product slurry becomes firm and holds a desired shape. Excess water must then be removed from the product by drying.

In the absence of additives to prevent it, set gypsum absorbs up to 50% of its weight when immersed in water. Boards or panels that absorb water swell, become deformed and lose strength. This property is undesirable in products that are likely to be exposed to water. In areas such as bathrooms or kitchens, high temperature and humidity are common, and walls are likely to be splashed. In such areas, it is preferable to use a gypsum board that exhibits water resistancy, thus maintaining strength and dimensional stability.”

[Wang et al, US Patent 8,133,600 (3/13/2012)]

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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 5/2/2012.

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