Thermal decomposition of some hexaborates

Thermal decomposition of iron(II) and cobalt(II) hexaborates has been investigated. The methods applied to investigate the process were differential thermal analysis, derivatography, crystallooptics and x-ray study. The following iron(II) hexaborate hydrates, FeO · 3B₂O₃ · 7.5H₂O, FeO · 3B₂O₃ · 5H₂O, FeO · 3B₂O₃ · 0.5H₂O; iron(III) borates, Fe₂O₃ · 6B₂O₃ and 2Fe₂O₃ · B₂O₃; cobalt(II)hexaborate hydrates CoO · 3B₂O₃ · 7.5H₂O, CoO · 3B₂O₃ · 5H₂O, CoO · 3B₂O₃ · 0.5H₂O, CoO · 3B₂O₃ and the decomposition product 2CoO · 3B₂O₃ have been isolated. Hepta- and semihydrates of cobalt(II) and iron(II) hexaborates have been proved to be isomorphous. It has been established that in the case of cobalt and iron hexaborates the exothermic maximum refers to a decomposition reaction and to the formation of a borate containing a smaller proportion of boron and boric anhydride.