Thermal decomposition of agardites (REE) : relationship between dehydroxylation temperature and electronegativity

The thermal decomposition of a suite of synthetic agardites of formula ACu₆(AsO₄)₂(OH)₆·3H₂O where A is given by a rare earth element has been studied using thermogravimetric analysis techniques. Dehydration of the agardites occurs at low temperatures and over an extended temperature range from ambient to around 60 °C. This loss of water is attributed to the loss of zeolitic water. The mass loss of water indicates 3 mol of zeolitic water in the structure. Dehydroxylation occurs in steps over a wide range of temperatures from 235 to 456 °C. The mass loss during dehydroxylation shows the number of moles of hydroxyl units is six. There is a linear relationship between the first dehydroxylation temperature and the electronegativity of the agardites (REE).