Powder diffractometer

Powder diffraction studies with neutrons are perfonned both at nuclear reactors and at spallation sources. In both cases a cylindrical sample is observed by multiple detectors or, in some cases, by a curved, position-sensitive detector. In a powder diffractometer at a reactor, collimators and detectors at many different 20 angles are scaimed over small angular ranges to fill in the pattern. At a spallation source, pulses of neutrons of different wavelengdis strike the sample at different times and detectors at different angles see the entire powder pattern, also at different times. These slightly displaced patterns are then time focused , either by electronic hardware or by software in the subsequent data analysis. 

Bragg-Brentano Powder Diffractometer. A powder diffraction experiment differs in several ways from a single-crystal diffraction experiment. The sample, instead of being a single crystal, usually consists of many small single crystals that have many different orientations. It may consist of one or more crystalline phases (components). The size of the crystaUites is usually about 1—50 p.m in diameter. The sample is usually prepared to have a fiat surface. If possible, the experimenter tries to produce a sample that has a random distribution of crystaUite orientations. 

Position Sensitive Detectors. By replacing the scintillation detector in a conventional powder diffractometer with a Position Sensitive Detector (PSD), it is possible to speed data collection. For each x-ray photon received a PSD records the angle at which it was detected. Typically, a conventional scintillation detector records x-ray photons in a range of a few hundredths of a degree at a time. A PSD can measure many degrees (in 20) of a powder pattern simultaneously. Thus, for small samples, data collection, which could require hours with a conventional detector, could take minutes or even seconds with a PSD. 

Area Detectors. A two-dimensional or area detector attached to a powder diffractometer can gready decrease data collection time. Many diffraction appHcations require so much time with a conventional detector that they are only feasible if an area detector is attached to the iastmment. The Siemens General Area Detector Diffraction System (GADDS) uses a multiwire area detector (Fig. 17). This detector measures an x- and ajy-position for each x-ray photon detected. The appHcations foUow. 

Texture Analysis with GADDS. With a conventional detector, a data collection for a pole figure analysis with a powder diffractometer with a texture attachment could take 12 h or more. With an area detector, it is possible to collect enough data for several pole figures (required for an ODF analysis) ia a few minutes. 

The crystallinity of zeolites was determined by X-ray powder diffraction with a Broker D8 Advance X-ray powder diffractometer. Diffractograms of both zeolites exhibited good crystallinity and characteristic diffraction lines with no additional crystalline phases. This was further supported by SEM images. 

Chemical composition was determined by elemental analysis, by means of a Varian Liberty 200 ICP spectrometer. X-ray powder diffraction (XRD) patterns were collected on a Philips PW 1820 powder diffractometer, using the Ni-filtered C Ka radiation (A, = 1.5406 A). BET surface area and pore size distribution were determined from N2 adsorption isotherms at 77 K (Thermofinnigan Sorptomatic 1990 apparatus, sample out gassing at 573 K for 24 h). Surface acidity was analysed by microcalorimetry at 353 K, using NH3 as probe molecule. Calorimetric runs were performed in a Tian-Calvet heat flow calorimeter (Setaram). Main physico-chemical properties and the total acidity of the catalysts are reported in Table 1. 

X-ray powder patterns can be obtained using either a camera or a powder diffractometer. Currently, diffractometers find widespread use in the analysis of pharmaceutical solids. The technique is usually nondestructive in nature. The theory and operation of powder diffractometers is outside the purview of this chapter, but these topics have received excellent coverage elsewhere [1,2]. Instead, the discussion will be restricted to the applications of x-ray powder diffractometry (XPD) in the analysis of pharmaceutical solids. The U.S. Pharmacopeia (USP) provides a brief but comprehensive introduction to x-ray diffractometry [3],... 

Powder diffraction patterns, 19 377, 378 Powder diffractometers, applications for, 26 427-430... 

Nanocrystalline iron-doped Ti02 samples (as-prepared S2 and annealed at 500°C S4 [7]) and undoped samples (Si and S3 [8]) were S5mthesised by a modified sol-gel method. The details of preparation were reported earlier [7, 8]. The X-ray diffiaction of the samples was carried out at room temperature using a Philips powder diffractometer (PW 1820) with monochromatized CuXa radiation. Transmission electron microscopy (TEM) and SAED investigations were carried out by using a JEOL JEM 2010 200 kV microscope, Cs=0.5 mm, point resolution 0.19 nm. 

The amount of Fe203 supported on zeolite and the Si02/Al203 molar ratio (S/A ratio) of the prepared catalysts were obtained by X-ray fluorescence spectrometry (Rigaku Denki, 3080E). Specific surface areas were measured by BET method (Yuasa, QUANTACHROME). Unit cell dimension (U.D.) was determined from the diffraction angles of (642) with an X-ray powder diffractometer (Rigaku Denki, RU-200). Silicon was used as the reference. 

Sayetat F, Prat A (2001) A new X-ray powder diffractometer working in the 87 1000 K range for phase-transition analyses. J Appl Crystallogr 34 311-317... 

Fig. 3. X-ray diffractogram of Class-F bituminous coal fly ash. Analytical conditions diffraction data were collected using a Philips X-ray powder diffractometer (45 kV/30-40 mA CuKa theta-compensating variable divergence slit diffracted-beam graphite monochromator scintillation detector) automated with an MDI/Radix Databox. The scan parameters were typically 0.02° step size for 1 s count times over a range of 5-60° 2-theta. All data were analysed and displayed using a data reduction and display code (JADE) from Materials Data Inc., livermore, CA.

X-ray powder diffraction was recorded using a conventional x-ray powder diffractometer with Cu-Ka radiation. Polyimide film on which sample particles are deposited is glued on a glass sample holder with vacuum grease. Figure 1.6.9 shows the recorded diffraction pattern. An analysis of the pattern is made by comparing the lattice parameters and diffraction intensities of the particles and those of known iron compounds, and shows that the particles are Fe304. 

Powder X-ray diffraction patterns of PSM and AMM samples were recorded using a SHIMADZU XRD-6000 powder diffractometer, where Cu target Ka-ray was used as the X-ray source. 

The phase composition of catalysts was studied by X-ray diffraction [XRO) technique. XRD spectra were recorded by using a Phillips 17D0 powder diffractometer equipped with a graphite crystal monochromator and CuK radiation. 

The mineralogical composition of all the samples included in the study was determined by XRD, using the same powdered sample prepared for XRF analysis. Measurements were performed using a PANalytical X Pert PRO alphal powder diffractometer (radius = 240 mm) using the Cu Ka radiation (A. = 1.5418 A), with a working power of 45 kV - 40 mA. The incident beam was passed through a 0.04 radians Soller slit, and the diffracted beam passed through a second slit. Moreover, the diffracted beam was Ni filtered. An X Celerator... 

The Collection is a source of reference patterns for pure crystalline phases. The data may be helpful in identifying known zeolitic materials and indexing their diffraction patterns. Because so many factors related to both the zeolite crystal and the diffraction instrument affect powder diffraction data, phase identification is not always straightforward and frequently requires additional data. Considerable care should be exercised in comparing calculated diffraction patterns to experimental patterns. For example, the use of fixed versus variable incident slits on a powder diffractometer can drastically change the relative intensities of a diffraction pattern, and it should be emphasized that calculated patterns are only as accurate as the structure refinements on which they are based. 

Cavatur and Suryanarayanan [1.164] have developed a low-temperature X-ray powder diffractometer (XRD) technique to study the solid states of solutes in frozen aqueous solutions. In frozen naftillin sodium solution (22% w/w), no eutectic crystallization was observed. Annealing at -4°C caused solute crystallization, which increased with annealing time. Two other products studied showed that XRD provides information about the degree of crystallinity without the interference of other events. 

Crystal structure and phase distribution of the powders at room temperature were studied with an x-ray powder diffractometer (Bruker AXS-D8, Karlsruhe, Germany). The measurements were performed in the 20 range of 10-90°C at 40 kV and 40 mA, using Cu-Ka radiation. In all measurements, the step size was 0.03°C, and data collection period was 2 sec. in each step. Ka2 peaks are suppressed in the x-ray diffraction measurements. 

---