Lindemann tube

The preceding setup allows both X-ray diffraction (32) and absorption experiments (33, 34). The capillary geometry was used until about 30 years ago for ex situ XRD studies in connection with the placement of Lindemann tubes in powder Debye-Scherrer cameras. At that time, films were used to detect the diffracted X-rays. Today, this cumbersome technique has been almost completely replaced as modern detectors are used. 

X-ray diffraction experiments were performed on a STOE STADI-P diffractometer (CuKai radiation X = 1.5406 A) equipped with a linear position-sensitive detector. The solutions and the solids were introduced in a 0.3mm capillary Lindemann tube (Debye-Sherrer geometry). 

Sample cells include Lindemann/capillary tubes (normally < 1 mm in diameter) and aluminium holders. In the latter, thin aluminium windows sandwich the sample in a cylindrical aluminium sample holder. The diffraction from the aluminium is observed in this case, and may be used as a calibration standard. For low-temperature materials, the aluminium window can be replaced by the polymer Kapton. Beryllium may also be used [14]. Sample volumes of between 50 and 100 pL are typically required. 

For the X-ray scattering observations the samples were powdered and placed in Lindemann glass capillary tubes. The capillaries were held for 8 weeks at 293 K in closed containers in contact either with hexane vapour or with aqueous salt solutions of different relative humidity. At the end of the preparation, the capillary tubes were flame-sealed. X-ray measurements were made at the BM2 bending magnet beam line at the ESRF, Grenoble, France. With incident energy 18 keV, the wave vector range explored was 6x 10 [Pg.44]

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.

The cylindrical sample is kept as small as possible to minimize the absorption of diffracted radiation. The optimum thickness is jpmP, where p is the sample density. Cylinders are generally kept at 0.5rmm or less diameter. When dilution is necessary, an amorphous substance such as flour is used as the diluent. It is best that the cylindrical sample not be in a container, but in many cases this is not possible. Satisfactory container materials include lithium borate ( Lindemann glass) or various plastics because of their low mass-absorption coefficients the container is a tube with a wall-thickness of about 0.01-mm. 

To achieve this goal the authors described the circuit shown in Figure 6. The method of measurement was based on Morton s design, in which an unknown e.m.f. is measured by compensation with a calibrated potentiometer in the grid circuit (ZS.). In a later publication (22) Elder described in greater detail the pH measurement with the glass electrode and compared the results of the new vacuum tube instrument to the Lindemann cjuadrant electrometer. 

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