Search Results

You are looking at 1 - 10 of 134 items

  • Author: Thomas Armbruster x
Clear All Modify Search
Die Suche, Bergung und Restitution von Kulturgütern durch die westlichen Alliierten nach dem Zweiten Weltkrieg

Abstract

The 29Si MAS NMR spectrum of armenite from Wasenalp (Valais, Switzerland) indicates complete Si, Al ordering. The same chemical shifts (- 82.3, - 95.0, and - 101.8 ppm) were also measured for armenite from Rémigny (Quebec, Canada), however, the intensity ratios of the NMR bands for the latter sample differed. A full sphere of X-ray single-crystal data on an optically homogeneous domain of armenite from Rémigny was collected on a threecircle diffractometer equipped with a CCD area-detector. The crystal structure was refined in the acentric space group Pnc2 [a = 18.660(2), b = 10.697(1) c = 13.874(2) Å ] to R1 5 3.6% based on 4275 reflections. These results confirm complete Si, Al ordering. Mean Si-O distances range between 1.615 and 1.629 Å ; mean Al-O distances between 1.734 and 1.742 Å . Calcium is sevenfold coordinated by six framework O atoms and one H2O molecule. Barium is 12-fold coordinated by framework O atoms. Polarized IR spectra in the region of OH absorptions (between 5700 and 1300 cm-1) were recorded on polished slabs of Wasenalp armenite and structurally related milarite from Val Giuf. In general, milarite and armenite show similar anisotropy of H2O related absorptions.