Diffractometer specimen preparation

The powder pattern of the unknown is obtained with a Debye-Scherrer camera or a diffractometer, the object being to cover as wide an angular range of 20 as possible. A camera such as the Seemann-Bohlin, which records diffraction lines over only a limited angular range, is of very little use in structure analysis. The specimen preparation must ensure random orientation of the individual particles of powder, if the observed relative intensities of the diffraction lines are to have any meaning in terms of crystal structure. After the pattern is obtained, the value of sin 9 is calculated for each diffraction line this set of sin 9 values is the raw material for the determination of cell size and shape. Or one can calculate the d value of each line and work from this set of numbers. 

Interplanar Spacings. Diffractometer alignment procedures require the use of a well-prepared polycrystalline specimen. Two standard samples found to be suitable are silicon and a-quartz (including Novaculite). The 26 values of several of the most intense reflections for these materials are listed in Table 7.6 (Tables of Interplanar Spacings d vs. Diffraction Angle 26 for Selected Targets, Picker Nuclear, White Plains, N.Y., 1966). To convert to d for Ka or to d for Ka2, multiply the tabulated d value (Table 7.6) for Ka by the factor given below ... 

In preparation for XRD, 0.50 g samples were placed in platinum pans and heated at 10°C/min in a furnace where the control thermocouple was in contact with the specimen container. Specimens were quenched by immediate exposure to room temperature then ground with a mortar and pestle to pass through a 325 mesh screen. X-ray diffraction was performed using a Philips9 x-ray diffractometer. Diffraction patterns were obtained with 29 values ranging from 20° to 60° 29. The diffracted x-rays were counted over 0.02° intervals for 2... 

Viscosities of the polymeric materials were obtained in tetrahydrofuran with an Ubbelohde-type viscometer at 30.00 0.02 C. The infrared absorption spectra in the region of 400-4000/cm were measured for the sample by Hitachi Model EPI-G3 infrared spectrophotometer. The samples were prepared by the KBr pellet technique. The thermal behavior of the specimens was observed with a Rigakudenki DSC-TGA apparatus. The X-ray diffraction pattern of the powdered polymer was taken in the region of 3-37 by a Rigakudenki Model 3D-F X-ray diffractometer with the use of Ni-filtered copper K radiation. 

The shape of the average specimen is such that only rarely can it be directly placed into the diffractometer for analysis, so that special care has to be taken to achieve the random distribution of the crystallites to have meaningful peak intensities. The problems arising in sample preparation are (1) Particle size. The powdered sample must consist of particles smaller than 5 pm. Collection and separation of particles of these dimensions can be effected by sieving, sedimentation, or elutriation. (2) Surface flatness. Special precautions are needed to make the surface smooth and flat, with its plane including the diffractometer axis. If required, common binders, for instance, collodion, paraffin wax, or silicone grease, are applicable. (3) Preferred orientation. When it is necessary to ensure that the particles do not show preferred orientation, mix crushed glass or other amorphous medium with the powder or coat the plane surface of the sample carrier with a film of adhesive that dries at a moderate rate and then dust a layer of powder on the adhesive, polyfvinyl chloride), after it has become tacky. 

Wide-angle X-ray scattering experiments were performed in transmission mode with an HZG diffractometer. For these purposes, specimens with dimension of 100x20x2 mm were prepared from extmdates. Radial scans of intensity vs. diffraction angle 20 were recorded in the range of 10-30 ° by steps of 0.05 ° and step scan interval of 5 s at ambient temperature. The degree of orientation of PP phase (O) was evaluated as a ratio between the intensities of (110) reflection (/no) and (040) reflection (/040), O =/ o/(/no + /o4o). 

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