Cameras powder

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... 

The Pyrex tube was suspended, with capillary down, in a small-holed rubber stopper which, in turn, was fastened to a goniometer head by a length of stout copper wire. The solid material within the capillary was photographed in a cold room (4°C.) using copper x-radiation, a camera with radius 5 cm., and oscillation range 30°. The effective camera radius was established by superimposing a powder spectrum of NaCl during an exposure of the sample the lattice constant for NaCl at 4°C. was taken to be 5.634 A. 

A series of powder photographs was taken in a Norelco camera 360 mm. in circumference which holds the film in the Straumanis arrangement and permits a maximum Bragg angle of 87-6°. The copper K radiation was filtered through 0-001 in. nickel foil. Eastman No-Screen X-ray film was used throughout. All photographs were taken at room temperature, 26 + 2° C. 

An X-ray powder photograph taken with a focusing camera and X rays monochromatized by crystal reflection would probably show more than 100 powder lines, providing a more rigorous text of the proposed structure. Accurate values of predicted intensities of the lines will become available only after coordinates have been assigned to all of the atoms, a formidable task with such a complicated structure. This task is now being attempted (S. Samson, personal communication). 

High resolution transmission electron microscopy (HRTEM) micrographies were performed with a JEOL JEM-3010 microscope operating at 300 kV (Cs= 0.6 mm, point resolution 1.7 A). Images were recorded with CCD camera (MultiScan model 794, Gatan, 1024 x 1024 pixels, pixel size 24 x 24 pm2). The powder samples were mixed in ethanol and then ultrasonicated for 10 min. A drop of the wet sample was placed on a copper grid and then allowed to dry for 10 min before TEM analysis. 

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],... 

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). 

There s a pressure device on the system because the sample must make contact with the diamond. If you squirt a liquid on the diamond, it makes perfect contact if you sprinkle a powder on the diamond, powders don t make perfect contact. To make perfect contact with a powder, take two to three turns of the pressure device. You just take a little piece off the intended sample. You could actually break a pill, and the dust that falls off is enough for the analysis. You must make contact and the pressure device squashes the sample down to make contact. If you sprinkle a little piece of powder on the diamond, you wouldn t get spectra. Squash that powder, and you can actually see the powder being squashed when you use the little video camera. You can immediately see the spectrum show up. You have all the pressure you need do not get worried about crushing the sample as you are making it touch the diamond. 

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.

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. 

X-ray powder diffraction patterns of samples heated at temperatures between 20 and 500 C were recorded in situ by using a Philips instrument equipped with vacuum camera (5x10 Pa). Heating rates of 5 C min l and CuKot radiation were used. Infrared spectra were obtained using a conventional greaseless IR cell the procedure and sample preparation have been described elsewhere (6). Al MAS-NMR spectra were recorded using a 400 MHz Bruker instrument. 

Khariton Ratner (Ref 1) observed by rapid photography methods (such as described in Vol 2 of Encycl under CAMERAS), that detonation of NG in a tube smaller than 5 mm diameter came to an abrupt halt after propagating thru a length of ca 100 diameters. The same phenomenon of detonation break was observed with NGc. Apin Bobolev (Ref 2) extended the investigation to solid expls, such as PETN, RDX PA (in powdered form) and to the frozen NG (stable form crysts). 

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 cameras. A powder camera consists essentially of an aperture system to define the X-ray beam, a holder for the specimen, and a framework for holding the photographic film. For most identification purposes a camera 9-10 cm in diameter is found satisfactory an X-ray beam about 0 5 mm wide is generally used, the powder specimen being a little narrower than this—of the order of 0 3 mm. 

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... 

Ftg. 61. Essential parts of a powder camera. A, aperture system B, guard tube CD, trap JS9 knife edges P, specimen S, springs XE, path of scattered X-rays. 

---