瞬間気流焼成によって得られたII型無水石こうの性質

抄録

This paper is concerned with a process of manufacturing II-CaSO₄ from powdered gypsum (CaSO₄·2H₂O) and the properties of the products obtained from the process.
Apart from fluorogypsum (II-CaSO₄) formed as by-product in the industrial manufacture of hydrofluoric acid, II-CaSO₄ is usually produced by calcining (at 600-800°C) in a rotary kiln or shaft kiln, which consumes a larger amount of heat energy.
In order to manufacture II-CaSO₄ at lower cost, the authors have developed a new technique of manufacturing II-CaSO₄ which calcines powdered gypsum (CaSO₄·2H₂O) instantly by dispersing it into an atmosphere of high temperature gas including flames.
The main characteristics of this technique are as follows:
(1) Time for calcining is a few seconds.
(2) Heat for calcining is below half of those of the old techniques.
(3) II-CaSO₄ can be produced even at 250°C which is below the conversion temperature, from III-β-CaSO₄ to II-CaSO₄, obtained by DTA.
The properties of the products calcined at 250, 600 and 800°C, such as pore size distribution, heat of hydration and micro-structures of hydrated bodies were investigated.
On the basis of these results, it has been proven that the hydration reaction of each product proceeds under the same mechanism. The rate of heat evolution depends upon their micropore distribution and size of crystallite which are characterized by the calcining temperatures.
Using this new calcining technique, consequently, various types of II-CaSO₄ can be obtained only by changing the calcining temperature.