The thermal behaviour of copper diphosphates made by wet process

Abstract

Copper diphosphates (Cu₂P₂O₇ · 5H₂O, Cu_1.6K_0.8P₂O₇ · 1.7H₂O, and Cu_1.5K_1.0P₂O₇ · 2.8H₂O) were made by mixing aqueous solutions of tetrapotassium diphosphate and copper dichloride. When the diphosphates were heated, the decomposition of the diphosphates to orthophosphate was observed at a temperature lower than 150° C. The orthophosphate was polymerized by condensation to polyphosphates in the temperature range of about 150 to 450° C. The polyphosphates reorganized to diphosphate at 450 to 550° C according to the following reaction:

$${\text{MO}} - \mathop {\text{P}}\limits_{\mathop {\text{|}}\limits_{\mathop {\text{O}}\limits_{\text{M}} } }^{\mathop {{\text{||}}}\limits^{\text{O}} } - {\text{O}} - (\mathop {\text{P}}\limits_{\mathop {\text{|}}\limits_{\mathop {\text{O}}\limits_{\text{M}} } }^{\mathop {{\text{||}}}\limits^{\text{O}} } - {\text{O}}) - \mathop {\text{P}}\limits_{\mathop {\text{|}}\limits_{\mathop {\text{O}}\limits_{\text{M}} } }^{\mathop {{\text{||}}}\limits^{\text{O}} } - {\text{OM + }}n{\text{MO}} - \mathop {\text{P}}\limits_{\mathop {\text{|}}\limits_{\mathop {\text{O}}\limits_{\text{M}} } }^{\mathop {{\text{||}}}\limits^{\text{O}} } - {\text{OM}} \to {\text{(}}n + 1){\text{ MO}} - \mathop {\text{P}}\limits_{\mathop {\text{|}}\limits_{\mathop {\text{O}}\limits_{\text{M}} } }^{\mathop {{\text{||}}}\limits^{\text{O}} } - {\text{O}} - \mathop {\text{P}}\limits_{\mathop {\text{|}}\limits_{\mathop {\text{O}}\limits_{\text{M}} } }^{\mathop {{\text{||}}}\limits^{\text{O}} } - {\text{OM}}$$

where M stands for 1/2 copper and/or potassium.