Abstract
The temperature influence factor on the kinetics of hydration of hemi hydrated calcium sulphate β has been studied in this work under microwave irradiation between 10℃ and 50℃ by isothermal calorimetry. Results show that the temperature corresponding to a maximum of the maximum rate of hydration or a minimum of tm, the existence of which could be shown theoretically and experimentally during the conventional hydration does not exist under microwave irradiation. This maximum rate or minimum of tm, is replaced by a limit (above 40℃) which has been determined and interpreted.
Highlights
Our work on the hydration study of calcium hemi-hydrate under microwave irradiation [1,2], shows that the time tm, corresponding to the maximum of the thermal flow in the hydration reaction changes with the hydration test temperature
A limit of tm beyond the temperature of 40 ̊C appears that differs from the results obtained by conventional heating [3,4]
The hydration phenomenon of calcium sulphate hemi hydrate to gypsum is based on two simultaneous processes [5]: Dissolution: hemi-hydrate + water → solution
Summary
Our work on the hydration study of calcium hemi-hydrate under microwave irradiation [1,2], shows that the time tm, corresponding to the maximum of the thermal flow in the hydration reaction changes with the hydration test temperature (between 10 ̊C and 40 ̊C). The hydration phenomenon of calcium sulphate hemi hydrate to gypsum is based on two simultaneous processes [5]: Dissolution: hemi-hydrate + water → solution. N FD moles of dehydrate, being the number of calcium sulphate moles in the balanced solution with the formed gypsum at the end of reaction at that temperature. ΑG: global rate of the hemi hydrate conversion into gypsum. NG: represents the number of the formed gypsum moles at time t. We can define the dissolution rate SH of hemi hydrate by taking for reference at the origin of time, the solution saturated by. NSH: represents the number of moles of hemi hydrate not yet dissolved at time t. Conservation of the number of calcium sulphate moles under all their forms can be written: ND. ND: represents the numbers of calcium sulphate moles in the solution at time t. The conservation relation will be the following: dNG dt dN SH dt dN D dt where:
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