Phase equilibrium study in the CaO-K2O-B2O3-H2O system at 25°C

The CaO-K2O-B2O3-H2O system has been investigated at 25 degreesC by extending experimentally data in the literature. By analogy with the corresponding known Na-borates, seven supersaturated mixtures of similar alkali/boron molar ratios were prepared but with potassium substituting for sodium. The mixtures were shaken regularly and attainment of the equilibrium state was monitored by flame emission spectroscopy for potassium. Equilibria were established typically after 1-3 months. The solids in the mixtures were identified by X-ray diffraction technique, and the solutions were analysed using ICP-spectroscopy. Solubility data of KB5O8. 4H(2)O, KB3O3(OH)(4). 2H(2)O, K2B4O5(OH)(4). 2H(2)O, KBO2.1.25H(2)O, and K2CaB8O14. 12H(2)O were determined and used to extend the database of the thermodynamic modelling computer code PHREEQC. Phase diagrams of the CaO-K2O-B2O3-H2O system and its subsystems were constructed for 25 degreesC. (C) 2001 Elsevier Science Ltd. All rights reserved.