THE THERMAL BEHAVIOR OF THE BINARY SYSTEMS OF LITHIUM-POTASSIUM PHOSPHATES

Abstract

The thermal behavior of some phosphates, lithium hydrogen phosphates represented by Li_xH_3-xPO₄ (x=1, 1.5, 2) mixed with potassium dihydrogen phosphate, were investigated using DTA-TG, XRD and HPLC-FIA. These results showed a formation region, and the reason for the formation of cyclic phosphates was discussed.
The formation region in LiH₂PO₄-KH₂PO₄ system, LiH₂PO₄and KH₂PO₄ influenced. The samples of R ( indicated that the molar ratio of LiH₂PO₄ to KH₂PO₄)≅1:1 therefore showed original thermal behaviors in which cyclic phosphates were produced slightly above 450°C. In the Li_1.5H_1.5PO₄-KH₂PO₄ system, the addition of KH₂PO₄ to Li_1.5H_1.5PO₄ greatly influenced the thermal behavior of Li_1.5H_1.5PO₄ and suppressed the change of Li_1.5H_1.5PO₄ to Li₃HP₂O₇, while the addition of Li_1.5H_1.5PO₄ to KH₂PO₄ influenced slightly the thermal behavior of KH₂PO₄. In the Li₂HPO₄-KH₂PO₄ system, the addition of KH₂PO₄ to Li₂HPO₄ influenced slightly the thermal behavior of Li₂HPO₄, while the addition of Li₂HPO₄ to KH₂PO₄ influenced that of KH₂PO₄.
Although the thermal behavior of Li_1.5H_1.5PO₄ due to heating was the disproportionation reaction which was composed of the main-reaction (the formation of linear poly-phosphate) and a side-reaction (that of cyclic-phosphate), the addition of KH₂PO₄ to Li_1.5H_1.5PO₄ restricted the side-reaction to some extent. This seems to be due to the suppression of the formation of Li₃HP₂O₇ producted at first step of the side-reaction.