Magnetite diffraction

Figure 2.14. Guinier transmission diffraction patterns using Co K a-radiation. The samples were analyzed after the specific surface area determination. A special embedding technique protected the material from exposure to air, the efficiency of which is demonstrated in the scan of the sample activated at 423 °C. It can be seen that as a consequence of the fracture of the initial magnetite crystallites during reduction, the texture effect in the magnetite diffraction pattern is lost (see scan at 385 °C).

A number of ferrites have been subjected to shock modification and studied with x-ray diffraction as well as static magnetization and Mossbauer spectroscopy [87V01], Studies were carried out on cobalt, nickel, and copper ferrites as well as magnetite (iron ferrite). 

An increasing intensity of the diffraction peaks of hematite is observed when comparing the dried and calcined catalyst as shown in Fig. 2(a), indicating that hematite forms at M er temperatures. No obvious diffraction peaks to lithium such as lithium iron oxide (LiFcsOg) could probably be ascribed to the small fraction of lithium or overlapped peaks betwem hematite and lithium iron oxide. The diffraction peak intensity of magnetite in tested catalysts increases significantly. 

From the X-ray diffraction, XRD pattern in Fig. 19.2, the pre-rasted sample was found to consist of mainly lepidocrocite and magnetite and traces of geothite. The XRD pattern indicated the reduction of several lepidocrocite peaks in favom of ferric-tannate formation after the addition of mangrove tannins. 

The structures of iron oxides have been determined principally by single crystal X-ray diffraction or neutron diffraction with supplementary information coming from infrared spectroscopy, electron diffraction and high resolution electron microscopy. A few years after the first successful application of X-ray diffraction to crystal structure determination, this technique was used to establish the major features of the structures of magnetite (Bragg, 1915 Nishikawa, 1915) and hematite (Bragg Bragg, 1918). 

Figure 28.7 Low-magnification TEM image of sample after activation at 543 K. The carbide nodules growing out of the magnetite crystals are clearly visible. The diffraction pattern in the inset shows spots corresponding to magnetite and the location of the carbide ring.

Figure 28.11 TEM image of a sample after activation at 523 K followed by reaction at 523 K for 45 h. A greater extent of carbidization and resultant breakdown of the original crystals is seen to occur. The inset diffraction pattern shows a more prominent carbide ring while the magnetite spots arc diminished in intensity.

X-ray powder diffraction patterns of the sample after activation at 523 K and 543 K, and after 10 and 45 h of FT synthesis are shown in Figure 28.2 and Figure 28.3, respectively. The pattern in Figure 28.2 has been plotted over 20 values from 25° to 50° since the most intense peaks of the magnetite and the carbide phases fall in this range. While the patterns in... 

Figure 28.6 TEM image of sample after activation at 523 K. Insets show lattice fringes corresponding to the (311) plane of Fe304 (magnetite) and the corresponding diffraction...

Phases listed in order of decreasing intensity of diffraction pattern, e = c-phase (nitride or car bonitride). f f-phase (carbonitride), x M Hftgg carbide, a — a-iron, and M magnetite. 

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