Belay Zeleke Dilnesa - Eawag-Empa Library

CHAPTER 2 MATERIALS AND METHODS
2.2.2. Synchrotron powder diffraction
Synchrotron powder diffraction data were collected at the Swiss-Norwegian Beam Line
(SNBL) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. The
powder material was introduced into glass capillaries (0.5 mm diameter). Data collection
was performed at 295 K at a wavelength of = 0.72085 Å using a MAR345 image plate
detector with the highest resolution (3450 x 3450 pixels with a pixel size of 100 m). The
calculated absorption coefficient mR (m = powder packing factor, = linear absorption
coefficient, R = radius of the capillary) was estimated at 0.65. Three sample-to-detector
distances were used (150, 250 and 350 mm) in order to combine the advantages of high
resolution and extended 2 range. The detector parameters and the wavelength were
calibrated with NIST LaB6. The exposure time was 60s with a rotation of the capillary by
60°. The two-dimensional data were integrated with the Fit2D program which produced
the correct intensity in relative scale [36]. This 2D detector was used in order to perfectly
define the background, to observe very weak diffraction peaks, and to improve the
accuracy of the integrated intensities by achieving a better powder average. Uncertainties
of the integrated intensities were calculated at each 2-point applying Poisson statistics to
the intensity data, considering the geometry of the detector. The instrument resolution
function was determined from the LaB6 data.
2.2.3. Thermogravimetric analysis
Thermogravimetric analysis (TGA) was carried out to determine the weight loss and
characterize the thermal behavior of the solids. The analysis was carried out in a N2
atmosphere on about 8-12 mg of crushed material at a heating rate of 20°C/min over the
temperature range from 30-980°C using a Metter Toledo TGA instrument.
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