Published online by Cambridge University Press: 09 July 2018
A basic lead carbonate-montmorillonitec omplexw as prepared by treating a natural montmorillonite hydrothermally for 120 h at 250°C with lead powder, dry ice and lead nitrate solution. The product is a non-swelling material showing well-outlined, hexagonal, thin plates <1 µm in size; the symmetry is pseudo-orthorhombic, a = 5·141(7) Å, b = 9·005(5) Å, c = 17·420(4) Å, and Z = 2. The X-ray powder pattern is characterized by a 17·4 Å reflection and an integral series to the 14th order. The TG-DTA curves of this 17 Å-mineral showed one endotherm around 400°C accompanied by weight loss and two exthotherms at about 680 and 780°C By applying hightemperature X-ray diffractometry (XRD) and infrared (IR) spectroscopy, it was found that the endotherm is due to decomposition of carbonate hydroxide in the interlayer, while the two exthotherms are caused by crystallization of a hexagonal phase of PbAl2Si2O8 and by the conversion of this phase into lead feldspar, respectively. The crystal structure of the 17 Å-mineral was determined and refined as a 2:1 dioctahedral smectite interlayered with a hydrocerussite-like layer by a one-dimensional Fourier synthesis method.
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