The Mechanism of Reaction between Calcium Sulfate Hemihydrate, Calcium Hydroxide and Calcium 2-Oxogluconate

Abstract

Calcium 2-oxogluconate is one the widely used reagents for a cement admixture. It is apparent from the results of experiments that the setting time can be remarkably retarded through an addition of calcium 2-oxogluconate to the 8-CaSO₄ 1/2 H₂0 paste under a high alkalinity in the presence of Ca (OH) 2. The present investigation was initiated in order to solve the mechanism of reaction between 8-CaO^2-.1/2 H₂O, Ca (OH) 2 and calcium 2-oxogluconate. The solubility of 8-CaSO₄/2 H₂0 in aqueous solution of calcium 2-oxogluconate is approximately constant independent of concentration. For example, the solubility of total CaO in aqueous solution of calcium 2-oxogluconate involved 8-CaSO₄.1/2 H₂0, and the concentration of calcium 2-oxogluconate are placed in Total [CaO], and C in (mol/l), respectively.
Total [CaO] C 0. O^2-0
On the other hand, in any case of Ca (OH) 2, the solubility of Ca (OH) 2 in aqueous solution of calcium 2-oxogluconate is abnormally high. It is proportional to the concentration of calcium 2-oxogluconate.
Total [Ca (OH)2] t 2 C 0. O^2-1
These reasons are attributed to the soluble complex formation. Therefore, calcium complex has been formed by the combination of one CA²⁺ ion and 1 mol/l 2-oxogluconic acid. Further, the authors confirmed by the electro-conductivity as Well as the solubility. The formation of calcium complex is also supported by IR spectra.