Debye-Scherrer powder camera

The X-ray powder diffraction pattern of sodium valproate was determined by visual observation of a film obtained with a 143 2 mm Debye-Scherrer Powder Camera (Table IV). An Enraf-Nonius Difractis 601 Generator 38 KV and 18 MA with nikel filtered copper radiation A = 1.5418, was employed (4). 

Figure 5.8 A Debye-Scherrer powder camera for X-ray diffraction. The camera (a) consists of a long strip of photographic film fitted inside a disk. The sample (usually contained within a quartz capillary tube) is mounted vertically at the center of the camera and rotated slowly around its vertical axis. X-rays enter from the left, are scattered by the sample, and the undeflected part of the beam exits at the right. After about 24 hours the film is removed (b), and, following development, shows the diffraction pattern as a series of pairs of dark lines, symmetric about the exit slit. The diffraction angle (20) is measured from the film, and used to calculate the d spacings of the crystal from Bragg s law.

The film is in contact with the cylindrical brass frame of the camera and is held in position by springs 8. Sharp edges E terminate the exposed part of the film abruptly. Light is excluded by a brass cover which fits over the whole camera the X-rav beam is admitted through a hole covered with black paper. Further details of the construction and use of Debye- Scherrer powder cameras can be found in a paper by... 

FIGURE 12-17 Schematic of (a) a Debye-Scherrer powder camera (b) the film strip after development. D, D, and T indicate positions of the film in the camera. 

Outline how you would interpret X-Ray diffraction data, if any, obtained for the following CPs and using the following X-Ray methods P(ANi)Cl P(Di-Ac)s Debye-Scherrer powder camera Weissenberg camera Precession camera Wide Angle X-Ray Diffraction Automated Diffractometer. 

Considering the fact that the X-ray diffraction pattern of a crystal depends on its lattice structure, pigment powders can be analyzed with a Debye-Scherrer diffraction camera to establish a correlation between X-ray diffraction and crystal modification. It is synthetically not possible to produce a defined crystal modification of a new pigment. Attempts to modify the preparative procedure or to apply different aftertreatment may result in a pigment of two or more crystalline forms, different not only in lattice structure, but also in color and performance. 

Fig. 3-13 Debye-Scherrer powder patterns of copper (FCC), tungsten (BCC), and zinc (HCP). Filtered copper radiation, camera diameter = 5.73 cm.

X-ray powder diffraction studies are perfonned both with films and with counter diffractometers. The powder photograph was developed by P Debye and P Scherrer and, independently, by A W Hull. The Debye-Scherrer camera has a cylindrical specimen surrounded by a cylindrical film. In another commonly used powder... 

X-Ray Powder Patterns. Samples for x-ray pattern determinations were sealed in 0.2-mm. glass capillary tubes under an atmosphere of argon. The samples were then exposed to nickel-filtered, CuKa radiation in an 11.459-cm. Debye-Scherrer camera for 18 to 20 hours. 

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. 

Powder photographs were taken with a 57.3-mm radius Debye-Scherrer camera and nickel-filtered Cu Ka radiation (Xmean = 1.5418 A). For intensity work, the multiple-film technique was used. The lattice constant, derived from 23 reflections from 42.56° to 73.47° 20 and corrected for film shrinkage with a parallel film of a reference substance, was Oo = 15.02 A with an estimated standard deviation of 0.01 A. 

The X-ray powder data were measured by the large Debye-Scherrer camera at SPring-8 BL02B2 using solvent-free (Sc2C2) C84 powder sample. The exposure time on the IP was 80 min. The wavelength of incident X-rays was 0.75 A. The... 

The compound layer formed in the transition zone between nickel and bismuth was investigated metallographically, by X-rays and electron probe microanalysis (EPMA). X-ray patterns were taken both from the cross-sections in the planes parallel to the initial Ni-Bi interface (after successive removal of the specimen material and polishing its surface) and the powdered phases using Cu Ka radiation. Two methods of obtaining X-ray patterns were employed. Firstly, X-ray photographs were obtained in a 57.3 mm inner diameter Debye-Scherrer camera. Secondly, use was made of a DRON-3 diffractometer to record X-ray diffractograms. 

X-ray Powder Diffraction. Photographs were taken on products in quartz capillaries using Debye-Scherrer cameras. 

The x-ray diffraction patterns were obtained by mounting the sample particles on a glass filament in a 114.59-mm diameter powder camera (Debye-Scherrer) and irradiating with Cu-Ka x-rays at 30 kV and 15 mA for periods of time ranging from 8 to 24 h. 

Figure 3.3. Two Debye-Scherrer cameras with covers, which have been loaded with x-ray film and installed on the x-ray generator, ready for collecting powder diffraction data.

Cylindrical samples, which are common in the Debye-Scherrer cameras Figure 3.2), are also used in powder diffractometry. Similar to flat transmission samples, small amounts of powder are required in the cylindrical specimen geometry. This form of the sample is least susceptible to the non-random distribution of particle orientations, i.e. to preferred orientation effects. 

The specimen in the Debye-Scherrer method has the form of a very thin cylinder of powder placed on the camera axis, and Fig. 4-18(a) shows the cross section of such a specimen. For the low-an le reflection shown, absorption of a particular ray in the incident beam occurs along a path such as AB at 5 a small fraction of the incident energy is diffracted by a powder particle, and absorption of this diffracted beam occurs along the path BC. Similarly, for a high-angle reflection, absorption of both the incident and diffracted beams occurs along a path such as DE -I- EF). The net result is that the diffracted beam is of lower intensity than one would expect for a specimen of no absorption. 

A powder pattern of zinc is made in a Debye-Scherrer camera 5.73 cm in diameter with Cu Ka radiation. 

Basically, a diffractometer is designed somewhat like a Debye-Scherrer camera, except that a movable counter replaces the strip of film. In both instruments, essentially monochromatic radiation is used and the x-ray detector (film or counter) is placed on the circumference of a circle centered on the powder specimen. The essential features of a diffractometer are shown in Fig. 7-1. A powder specimen C, in the form of a flat plate, is supported on a table H, which can be rotated about an axis O perpendicular to the plane of the drawing. The x-ray source is S, the line focal spot on the target T of the x-ray tube S is also normal to the plane of the drawing and therefore parallel to the diffractometer axis O. X-rays diverge from this source and are diffracted by the specimen to form a convergent diffracted beam which comes to a focus at the slit F and then enters the counter G. A and... 

This is a very recent development. It involves a side-window position-sensitive proportional counter (Sec. 7-5), a multichannel analyzer, and the rpeasurement of the angular positions of many diffraction lines simultaneously. The anode wire of the counter, which is long and curved, coincides with a segment of the diffractometer circle and is connected, through appropriate circuits, to an MCA. The powder specimen is in the form of a thin rod centered on the diffractometer axis. The geometry of the apparatus therefore resembles that of a Debye-Scherrer camera (Fig. 6-2), except that the curved film strip is replaced by a curved counter. 

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. 

As a simple example, we will consider an intermediate phase which occurs in the cadmium-tellurium system. Chemical analysis of the specimen, which appeared essentially one phase under the microscope, showed it to contain 46.6 weight percent Cd and 53.4 weight percent Te. This is equivalent to 49.8 atomic percent Cd and can be represented by the formula CdTe. The specimen was reduced to powder and a diffraction pattern obtained with a Debye-Scherrer camera and CuKa. radiation. 

Schematic diagram of a sealed laboratory X ray tube with key components indicated (left), and a photograph of a tube (right). In modern tubes the clear glass vacuum housing has been substituted by ceramic. Manufactur ers provide various dimensions for the W filament, leading to broad , normal , fine and long fine focus tubes. The X rays emerge from the four circular Be windows in the base, two of which are parallel to the filament, providing a line source of X rays, and two of which are perpendicular, providing a point source . A line source from a fine or long fine focus tube is preferred for a modern powder diffractometer. Historically, point sources were used for Debye Scherrer cameras.

XRD patterns were recorded on a Philips X-ray generator with a Debye-Scherrer camera. CuKa X-rays (X, = 1.5418 A) were used as the X-ray source. XRD measiuements were performed on powdered washcoat scraped fi om the comer region of exposed channels on the outer surface of the cores. The XRD apparatus used to analyze the samples have been described in detail previously [8]. Particle sizes were estimated using the Scherrer equation with correction for instrumental line broadening. 

A Debye-Scherrer camera consists of a metal cylinder provided with a photographic film. The primary beam is perpendicular to its axis. The distance between two symmetrical lines, produced by the intersection of a cone with the cylinder, is 46R, 6 being the Bragg angle (in radians) and R the radius of the camera. The interval is derived from Bragg s law. The powder method gives us only the norms of the reciprocal vectors. The set of norms corresponds to the projection of the reciprocal lattice onto a straight line. 

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