Room,low, and high temperature dehydration and phase transitions of kernite in vacuum and in air

Kernite Na₂B₄O₆(OH)₂·3H₂O dehydration in air at high temperature and in vacuum at room temperature has been studied. It was found that kernite easily dehydrates forming a new phase‐I both on heating and in vacuum. The chemical formula Na₂B₄O₆(OH)₂·1.5H₂O of the new phase‐I has been estimated on the basis of thermogravity analysis. It is triclinic with the unit cell parameters a = 7.047(8), b = 8.76(1), c = 13.08(2) Å, α = 93.40(9), β = 95.32(9), γ = 90.28(9)° changing slightly on pressure reduction. Due to the relatively low temperature (353 K) and reversibility of the kernite ⟷ phase‐I transition an anion of the new phase‐I likely consists of the same chains B₄O₆(OH)₂]^2– like in kernite structure. The high anisotropy of kernite thermal expansion was explained by approaching of NaO chains due to the initial removing of water molecules from kernite crystal structure. The behaviour of the new phase‐I at low temperatures in vacuum was also investigated. A formation of an additional new phase II has been detected at the temperature of 93 K. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)