X-ray diffraction instruments

It is quite possible that, sometime in your laboratory operations, you will have a need to use or come in close proximity to radioactive materials. These may be radioactive sources that are contained in closed systems, such as analytical instrumentation (X-ray diffraction, analytical detectors, etc.), or that are not contained but rather are open sources of radioactive materials, such as C-labeled compounds or H-labeled compounds. 

Physico-chemical characterizations were performed on the finished ceria-doped silicas. Surface area measurements (BET) and mesopore size distribution (BJH) were carried out by means of Sorptomatic 1900 (Carlo Erba) instrument. X-ray diffraction patterns were recorded with a D 5005 X-Ray Diffractometer (SIEMENS) using Cu Ka radiation coupled with a graphite monochromator. The crystallite sizes of ceria phase were calculated from the line broadening of the most intense reflection using the Scherrer equation [13]. 

In general, however, one would recommend that differential thermal analysis be used along with other more determinative methods such as X-ray diffraction. It can then give valuable information, which cannot be obtained by any other technique. Indeed, for a complete mineralogical analysis of a soil clay, it would be unrealistic to rely on any one determinative method, as none can give complete information. Instrumental (X-ray diffraction, thermal methods, infrared absorption spectroscopy, and electron microscopy and diffraction) and chemical (selective dissolution, cation exchange, and total analysis) methods all contribute some information, and only by application of all available can an accurate assessment be made. 

Present day techniques for structure determination in carbohydrate chemistry are sub stantially the same as those for any other type of compound The full range of modern instrumental methods including mass spectrometry and infrared and nuclear magnetic resonance spectroscopy is brought to bear on the problem If the unknown substance is crystalline X ray diffraction can provide precise structural information that m the best cases IS equivalent to taking a three dimensional photograph of the molecule... 

Instrumental Methods for Bulk Samples. With bulk fiber samples, or samples of materials containing significant amounts of asbestos fibers, a number of other instmmental analytical methods can be used for the identification of asbestos fibers. In principle, any instmmental method that enables the elemental characterization of minerals can be used to identify a particular type of asbestos fiber. Among such methods, x-ray fluorescence (xrf) and x-ray photo-electron spectroscopy (xps) offer convenient identification methods, usually from the ratio of the various metal cations to the siUcon content. The x-ray diffraction technique (xrd) also offers a powerfiil means of identifying the various types of asbestos fibers, as well as the nature of other minerals associated with the fibers (9). 

Surface areas were determined from the adsorption isotherms of nitrogen at 77 K, using a Micromeritics ASAP 200 instrument. Powder X-ray diffraction patterns were obtained with a CGR theta 60 instrument using CuKa monochromated radiation. Reducibility and the amount of Cu species were determined by temperature programmed reduction (TPR) with H2 (H2/Ar 3/97, vol/vol). The experimental set up has been described previously [6]. 

Some properties of the rock used in this study were measured The cation exchange capacity (cec) was determined by the barium sulfate method as described by Mortland and Mellor (33). Surface area was measured by using a Digisorb Meter (Micromeritics Instrument Corporation) through nitrogen adsorption. Estimation of mineral composition and indentification of the rock were performed by X-ray diffraction. 

Nitrogen adsorption was performed at -196 °C in a Micromeritics ASAP 2010 volumetric instrument. The samples were outgassed at 80 °C prior to the adsorption measurement until a 3.10 3 Torr static vacuum was reached. The surface area was calculated by the Brunauer-Emmett-Teller (BET) method. Micropore volume and external surface area were evaluated by the alpha-S method using a standard isotherm measured on Aerosil 200 fumed silica [8]. Powder X-ray diffraction (XRD) patterns of samples dried at 80 °C were collected at room temperature on a Broker AXS D-8 diffractometer with Cu Ka radiation. Thermogravimetric analysis was carried out in air flow with heating rate 10 °C min"1 up to 900 °C in a Netzsch TG 209 C thermal balance. SEM micrographs were recorded on a Hitachi S4500 microscope. 

X-ray diffraction studies are usually carried out at room temperature under ambient conditions. It is possible, however, to perform variable-temperature XPD, wherein powder patterns are obtained while the sample is heated or cooled. Such studies are invaluable for identifying thermally induced or subambient phase transitions. Variable-temperature XPD was used to study the solid state properties of lactose [20], Fawcett et al. have developed an instrument that permits simultaneous XPD and differential scanning calorimetry on the same sample [21], The instrument was used to characterize a compound that was capable of existing in two polymorphic forms, whose melting points were 146°C (form II) and 150°C (form I). Form II was heated, and x-ray powder patterns were obtained at room temperature, at 145°C (form II had just started to melt), and at 148°C (Fig. 2 one characteristic peak each of form I and form II are identified). The x-ray pattern obtained at 148°C revealed melting of form II but partial recrystallization of form I. When the sample was cooled to 110°C and reheated to 146°C, only crystalline form I was observed. Through these experiments, the authors established that melting of form II was accompanied by recrystallization of form I. 

Introduce instrumental techniques used in analysis of the bioinorganic systems I will lecture on (Chapter 3 Instrumental and Computer-Based Methods). Typically, these would be electron paramagnetic resonance (EPR) and Mossbauer spectroscopies not often covered in undergraduate instrumental analysis courses plus X-ray diffraction and NMR techniques used for structural analyses of metalloproteins and their small molecule model compounds. 

Figure 8. Powder X-Ray Diffraction Pattern of Aspirin (u.S.P. Reference Standard). Instrument Norelco... 

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