Qualitative and quantitative morphological study on α and β phases of ammonium pentaborate tetrahydrate

Abstract

A qualitative and quantitative morphological study on the α and β phases of ammonium pentaborate tetrahydrate has been carried out. Crystals of the two phases were obtained by slow evaporation from aqueous solutions. Usually the α phase was obtained with {101}; {\bar 101}; {011} and {110} as crystal forms, a high percentage of the crystals (99%) were twins, with a twofold axis parallel to c as the twin law. When MgCl2.6H2O was added to the solution, the β phase was obtained as prismatic crystals elongated along [\bar 110] with {111}, {\bar 111 } and {001} as crystal forms. Generally, these crystals were also twins, with a twofold axis parallel to [110] as twin law. A qualitative and quantitative morphological study showed the α-phase crystals to have the theoretical growth forms, while the crystal forms of the β phase were explained by the presence in the solution of (H2O)6Mg2+ and Cl− ions.