Microwave use of gypsum dehydration feasibility study

In this paper, we present the base techniques of a new fabrication procedure to obtain β-semy-hidrated calcium sulphate, β-plaster. The plaster is an aerial binder obtained through the dehydration of gypsum (CaSO 4 ×2H 2 O) and forming semy-hidrated calcium sulphate (CaSO 4 ×0,5H 2 O) at temperatures ranging between 110–160 °C. All plaster fabrication procedures used to this day are uneconomic. To obtain a larger deviated power, the application of a more intense electrical field is necessary. The dissipated power can also be increased by increasing the frequency; this can be done easily by using microwaves. They are applied more and more in industrial heating techniques, using high-frequency generators of a high powers and high-power magnetrons. The advantage of the microwave generators which use high-power magnetrons is that they are simple and cheap. The proposed fabrication procedure employs microwave energy and is based on the dielectric propriety of gypsum. As such, it is possible that the gypsum is dehydrated through dialectical heating into a resonant cavity with the microwave power. Water could absorb microwaves and increase the temperature rapidly within a short time. The results show that it is possible to use gypsum as a natural dielectric material in creating plaster through heating in a microwave field. Semi-hydrate produced under these conditions has the following characteristics: the beginning of binding 18–25 min., the end 28–37 min., compression strength after 2 h 2–5 MPa, compression strength of dried products 6–11 MPa. DOI: http://dx.doi.org/10.5755/j01.ct.63.1.4518