Lattice-parameter measurements with diffractometer

The relative crystallinity and framework compositions were estimated from XRD measurements. Powder X-ray diffraction patterns were obtained with a PW-1130 Philips diffractometer with Ni-filtered CuKa source and a graphite monochromator. The relative crystallinity of the preheated samples, y / is reported as the ratio between the peak heights measured for the sample heated to a predetermined temperature for 2 h and for the sample activated at 400°C. In these calculations (530) and (150) reflections were chosen for faujasites and mordenites, respectively. The number of framework A1 atoms in the unit cell (Nai) was calculated from the lattice parameters according to the equations described in [1,2]. Lattice parameters were determined in the presence of a 10% Y2O3 internal standard for faujasites and a 10% Si internal standard for mordenites. 

Some of these requirements may be contradictory. For example, in measuring the lattice parameter of a thin surface layer with a diffractometer, we must compromise between the low value of 0 required for shallow penetration and the high value of 0 required for precise parameter measurements. 

X-ray diffractometry, T =300K. The lattice parameters and some bond lengths of the three different kinds of samples discussed in sect. 3.1.2 have been measured with X-ray diffraction using either a Guinier camera with internal standard (Rusiecki et al. 1990, Rusiecki and Kaldis 1991, Conder et al. 1994a) or a STOE powder diffractometer... 

Fig. 2. Powder profile of solid C q at atmospheric pressure, measured on a diffractometer equipped with a position-sensitive detector (8) and a 1.5-kW sealed Cu source monochromatized by the (002) reflection of graphite (k = 1.54 A). The powder sample was containol in a Lindemann capillary tube (0.7 mm in diameter). Dots are the measured points (2 hours accumulation), and the solid curve is a least-squares fit to an fee lattice of uniform spherical shells. The best-fit parameters are a = 14.11 A and shell radius Rq = 3.5 A. This sample exhibits much less intensity in the low-angle shoulder of the (111) reflection.

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