Powder-reflection sampling method measurements

Surface area of samples was measured by the standard low-temperature argon desorption method. Diffraction patterns were recorded using a DRON-UMl diffractometer (CoKa radiation). UV-Vis reflectance spectra of powdered samples were recorded with use of Specord M-40 spectrophotometer using MgO as a reference. Concentration of acid centers was determined by desorption of ammonia at different temperatures in vacuum with use of gravimetric installation, as well as by measuring of 4-nitrotoluene adsorption from solution. 

X-ray diffractograms were measured l y reflection method with CuKq. Samples of membrane were measured laying surface of membrane parallel to the reflection plane. Other samples were measured as powders smaller than 60 mesh. 

In addition to the methods described above, the diffuse reflection method (Chapter 12), the attenuated total reflection (ATR) method (Chapter 13), and the infrared microscopy methods (Chapter 16) can be used for measuring infrared spectra from solid samples. The ATR method is particularly suitable for rubbery samples, and it is also useful for powder samples as well as films and liquid- and paste-like samples on substrate plates. The diffuse reflection method may be used to obtain infrared spectra from powder samples appropriately mixed with KCl or KBr powder. The infrared microscope method is useful for examining a sample such as a single fiber or a small crystal. 

If used for continuous monitoring applications and if the sample is a powder then the technique of choice is most likely NIR or Raman. NIR works well with diffuse reflectance, and Raman is comparable in its method of measurement. 

A serious problem, however, for both paramagnetic and coherent magnetic scattering measurments, at least until higher reflectivity polarizers are available or alternative techniques of polarization analysis are developed, is the low intensity obtained after reflection from the sample as well as from two polarizing crystals. Even for location of apparatus at a high flux reactor, with current techniques the measurement of covalent spin reductions in powder samples can be made as efficiently by profile analysis of a conventional powder diffraction pattern as by polarization analysis. Polarized beam methods including polarization analysis will however, be essential for the determination of form factors. 

Solids are usually ground with a material such as potassium bromide and compressed into a pellet. Moisture must be absent, and the transparent disk is placed in the window of the spectrometer. In general, however, measurement of intensity of absorption in the solid phase is unreliable due to scattering and reflection losses, and a uniform distribution of sample in the pellet is difficult to achieve. One method of handling solutions is to allow them to soak into a KBr wedge, evaporate the solvent, and compress the tip into a microdisk or pellet (C26) alternatively the sample (1 /tl) may be either placed directly on the KBr disk (B13) or mixed with a little KBr powder and subsequently incorporated in the disk. These microdisk techniques can be used for the examination of gas chromatograph effluent. For multiple analyses, an enclosed turntable system loaded with the disks can be used. 

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