Gypsum is the chemical compound calcium sulfate dihydrate. It occurs naturally in crystalline form in marine salt deposits where its geological name is anhydrite. It mixes readily with water to form a plaster-like material that sets rapidly in any desired form. Gypsum has been a decorative and building material since ancient times. Any material’s principle electrical properties are its conductivity and resistivity. Conductivity is a measure of the material’s ability to permit the movement of an electric current and resistivity is a measure of the material’s opposition to electric current flow. Gypsum’s electrical properties are important in their application to a variety of tasks.
Gypsum separates into calcium and sulfate ions in solution in water. The negatively-charged sulfate ions have an electrically corrosive effect on concrete and other hydraulic structures used for irrigation facilities or dams. The management of this electrical property of gypsum is crucial for agriculture and water supplies in many regions where gypsum is present in local rock formations.
Moisture Content Measurement
Solid gypsum is porous to water. Water can pass through pores in a gypsum block inserted in soil that becomes wet from rainfall or irrigation. Two electrodes in the gypsum block measure the electrical resistance of water and some calcium sulfate solution passing between them. The moisture content of the soil can be calculated from the resistance measurement. Such gypsum blocks facilitate the maintenance of necessary moisture conditions for any agricultural crop or water course.
The ability of a building to shield electromagnetic radiation is of increasing importance given the sensitivity of modern electronics. Gypsum provides insulation against this effect. The addition of carbon fibers to a gypsum matrix produces a composite material as strong as cement mortar. When spread over the surface of an internal or external wall, this gypsum composite provides a shield against external electromagnetic radiation, or electromagnetic interference (EMI).
Gypsum compounds can improve the electrical conductivity of materials. Sensors inserted in the ground can measure local geoelectric potential – the electric field within the Earth – associated with earthquake activity In Sumatra. A gypsum coating over the surface of these sensors improves the electric contact between the ground and the sensor.
- University of Arizona: Gypsum (PDF)
- International Institute for Land Reclamation and Improvement; Gypsiferous Soils; J.G. van Alphen and F. de los Rios Romero; 1971 (PDF)
- University of Buffalo; Electronic Properties of Carbon Fiber reinforced Gypsum Plaster; D.D.L Zhung and Q.J. Zheng; 1989 (PDF)
- Government of South Australia: Mallee Wells Irrigation Fact Sheet: Gypsum Blocks (PDF)
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