- Author
- Clifton, J. R.
- Title
- Some Aspects of the Setting and Hardening of Gypsum Plaster. Technical Note.
- Coporate
- National Bureau of Standards, Washington, DC
- Report
- NBS TN 755, January 1973,
- Distribution
- Available from National Technical Information Service
- Keywords
- plaster, hardening (materials); gypsum cements, hardening (materials); coagulation; crystallization; hydration; temperature; impurities; retardants; electron microscopy | thermal analysis
- Abstract
- The mechanisms by which gypsum plaster sets and hardens have been investigated and the results generally are consistent with the crystallization theory. No evidence for the presence of colloidal intermediates has been found. The crystallization theory is modified to include, as an intermediate species, solvated calcium sulfate hemihydrate molecules. Evidence is presented that supports the belief that more than one reaction is responsible for the setting and hardening of gypsum plaster. The roles of accelerators and retarders have been studied by calorimetric, differential thermal analysis, and scanning electron microscopic techniques. The cation is more effective than the anion in accelerating the setting and hardening of gypsum plasters; the catalytic order follows the sequence M(+) M(2+) M(3+). Small amounts of retarders can severely retard the setting and hardening processes. Influences of temperature, impurities, and production conditions on the setting rates of gypsum plasters are discussed. (Author)