Monochromator Guinier

X-ray Diffraction Studies. They are performed under vacuum with a Guinier type focussing camera equipped with a bent quartz monochromator giving a linear collimation of the CuK (X = 1.54 A) radiation (8). 

On the debit side, the Seemann-Bohlin camera has the disadvantage that the lines registered on the film cover only a limited range of 26 values, particularly on the low-angle side. The Seemann-Bohlin camera, in itself, is now virtually obsolete (the diffractometer has greater resolution), except in combination with a monochromator. The combination is then called a Guinier camera (Sec. 6-14). 

The combination of a focusing monochromator and a focusing camera is known as a Guinier camera, pioneered by Guinier in the late 1930s. Later investigators produced... 

Fig. 6-16 Cameras used with focusing monochromators. Only one diffracted beam is shown in each case. After Guinier [G.IO].

G.IO Andre Guinier. X-Ray Crystallographic Technology (Lx>ndon Hiiger and Watts, 1952). Excellent treatment of the theory and practice of x-ray diffraction. The title is not fair to the book, which includes a considerable body of theory and detailed experimental technique. The theory and applications of the reciprocal lattice are very well described. Includes treatments of focusing monochromators, small-angle scattering, and diffraction by amorphous substances. 

Figure 2.14. Diagram showing haw a Guinier crystal monochromator works...

Figure 5.6 The single perfect crystal as monochromator for use with SR (a) flat crystal (b) curved crystal for minimum reflected dXIX (Guinier setting) (c) curved crystal at overbend (d) finite source size contribution to 6X/X in the reflected beam (monochromator at Guinier setting). From Helliwell (1984) and reproduced with permission of the Institute of Physics.

Figure 5.7 Reflection from an asymmetrically cut crystal monochromator. The width of the reflected beam is compressed relative to that of the incident beam. The asymmetrically cut single crystal when bent to the Guinier setting (figure 5.6(b)) provides a minimum 6XIX and a foreshortened focussing distance (equation (5.7)).

In the context of oscillation camera data processing for the monochromator at 1.5 A with a demagnification of 10-30 the system would be far from the Guinier setting the exact (dX/X) (equation 5.9)) would depend on the length of the crystal monochromator illuminated (see section 6.1). 

X-ray diffraction experiments were performed in a Guinier camera with a Johansson monochromator using Cu K, radiation (2. = 1.5406). 

Figure 16. Principle of the Guinier method a) Seemann - Bohlin circle b) Monochromator c) Reflection d) Specimen...

Figure 17. Guinier method, showing the four possible relative positions of specimen and monochromator A) Symmetrical transmission B) Asymmetrical transmission C) Symmetrical reflection D) Asymmetrical reflection...

Figure 30. Beam path of the Guinier diffractometer a) Line focus of X-ray tube b) Monochromator c) Specimen d) Detector slit...

In the following discussion the X-ray diffraction (XRD) patterns of a series of six industrial catalysts are compared. High-resolution scans were obtained with monochromated Co radiation on a transmission Guinier diffractometer. Phase analyses were carried out on an automated Phillips APD 10 powder diffractometer using postmonochromated Cu radiation. In Fig. 2.2, relevant sections of the diffraction patterns of catalysts from three industrial sources are displayed. The observed reflections can be assigned to magnetite and wustite as the main components of the catalysts. The catalysts differ markedly in their content of crystalline wustite. It should be stressed here that XRD is not a suitable method for quantitative determination of the wustite content, since it depends on the crystallinity of the phase analyzed. The nonstoichiometric nature of wustite and its close structural... 

Figure 2.2. Guinier transmission diffraction patterns of industrial catalyst precursors using monochromated Co K a-radiation.

Figure 2.3. High-resolution scans over characteristic spinel reflections of some catalyst precursors using the Guinier transmission geometry and monochromated Co radiation. The graph indicates the dependence of the spinel lattice parameter determined from the dependence of the spinel lattice parameter determined from the (440) reflection on the aluminum content built into the lattice. Note that all catalyst samples contain nominally the same amount of aluminum. Lattice parameters above the line indicate the presence of an excess of calcium besides aluminum. The data Ml-3 are pure alumina spinel samples.

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