Reflection in XRD

After calcinations at 450-500 °C, the materials basically consist of small crystalline particles. These sometimes show very broad reflections in XRD due to the small particle size which is below 5 nm at low temperatures. However, XRD patterns show increasing particle size with increasii temperatures. This is consistent with decreasii values in sorption measurements due to sintering processes. The synthesis of pure spinel or perovskite phases (Table 4) could be performed by mixing the desired molar ratios of the materials and applying temperatures above 700 °C. 

Powder X-ray diffraction is one of the convenient methods for ordered mesoporous materials with guest nanoparticles [78]. The presence of guest species within the mesoporous structure can be detected by a reduction of the intensities typical for mesoporous silica Bragg reflections in XRD [25,80]. This method al-... 

Figure 4.3 Thermal stability of organically modified MMT as reflected in XRD patterns (top) before and (bottom) after heat treatment at 290 °C for 8 h in vacuo. From top to bottom, three organo-MMT systems are shown MMT modified by octadecylammonium (top two patterns), hexadecylimida-zolium (middle two patterns), and dihexylimidazBlium (bottom two patterns). Figure reproduced...

In catalyst characterization, diffraction patterns are mainly used to identify the crystallographic phases that are present in the catalyst. Figure 4.5 gives an example where XRD readily reveals the Pd reflections in two Pd/Si02 catalysts. 

In situ XRD spectra were collected on beam line X18A at the National Synchrotron Light Source (NSLS) located at Brookhaven National Laboratory (BNL). The X-ray wavelength (X) was 1.195 A. The step size of the 29 scan was 0.02° in the regions with Bragg reflections and 0.05° in the regions without reflections. The XRD spectra were collected in the transmission mode (Liu et al., 2004). 

Lead nitrate complexed with EDTA and lead perchlorate and sodium sulphide have been used for PbS ECALE-deposition.158159 The films were cubic and highly (200) oriented, and AFM images showed the same cubic structure.158159 PbSe films were also cubic, and the band gap of a film after 50 deposition cycles was 8000cm-1.160 PbSe/PbTe superlattices, with 4.2-nm and 7.0-nm periods, have been grown by ECALE.161 The (111) reflection in the XRD pattern showed a first-order satellite peak and one second-order peak, indicating the formation of the superlattice. AFM images of the superlattice structure showed a small amount of three-dimensional growth.161... 

A strong texture can be deduced from the XRD spectrum. The intensity of the [020] reflection as compared with those of the [120] and [031] reflections in boehmite is 10 times larger than can be expected for a random distribution of crystal directions and is in accordance with the model shown in Figure 2.7. 

The reflections in the XRD pattern of an LDH fall into three groups ... 

A mixture of intercalating clays is generally found in the subsurface. Interstratification of kaolinite and smectite has been reported in some cases (e.g., Schultz et al. 1971 Lee et al. 1975a, 1975b Yerima et al. 1985). This fact is reflected in an XRD... 

The preparation of precious metal supported catalysts by the HTAD process is illustrated by the synthesis of a wide range of silver on alumina materials, and Pt-, Pt-Ir, Ir-alumina catalysts. It is interesting to note that the aerosol synthesis of alumina without any metal loading results in a material showing only broad reflections by XRD. When the alumina sample was calcined to 900°C, only reflections for a-alumina were evident. The low temperature required for calcination to the alpha-phase along with TEM results suggest that this material was formed as nano-phase, a-alumina. Furthermore, the use of this material for hexane conversions at 450°C indicated that it has an exceptionally low surface acidity as evidenced by the lack of any detectable cracking or isomerization. 

The metal ion-implanted titanium oxide catalysts were calcined in O2 at around 725-823 K for 5 hr. Prior to various spectroscopic measurements such as UV-vis diffuse reflectance, SIMS, XRD, EXAFS, ESR, and ESCA, as well as investigations on the photocatalytic reactions, both the metal ion-implanted and unimplanted original pure titanium oxide photocatalysts were heated in O2 at 750 K and then degassed in cells at 725 K for 2 h, heated in O2 at the same temperature for 2 h, and, finally, outgassed at 473 K to 10 lorr [12-15]. 

Low-angle powder X-ray diffractometry. In Figure 1 XRD reflection patterns of a non silylated calcined Si-MCM-41 (a), an one which is pre-silylated (b) and an one silylated with APTES (c) are compared. The calcined and the outer surface silylated MCM-41 show the characteristic reflexions. The intensities of the reflections in the functionalized sample are reduced as expected from an increased scattering for filled pores.9 The unessentially changed d spacings confirm the preserved structure.10... 

The P-XRD patterns of the host structure in compounds A and B show a reduction of the reflections in comparison to the pristine MCM-48 silica material (figure 1). 

Unlike covellite, the silver sulfide reaction with Hg(0) vapor is not exclusively a redox process. XRD analysis showed that no silver sulfide remained in samples having consumed 42 wt% Hg(0) and that cinnabar formation was minimal. The products formed are mercurial amalgam, HgAg, and Ag,HgS as reflected in Reaction (2). Reaction (2) does not account for two third of the initial sulfur present, however, no residual crystalline sulfur was observed in the diffraction data. None the less, this reaction reflects partial reduction of the silver(I) and oxidation of Hg(0). 

The gold sulfides appear to react with Hg(0) in a similar manner as the covellite redox process. It was expected that there would be significant formation of amalgams, as in Reaction (2), but XRD analysis revealed the formation of cinnabar and metallic gold as reflected in Reaction (3) and (4). 

By spin coating the mixture containing the prehydrolyzed TMOS and a 0.2 M aqueous solution of C18TAC (pH=2, at the molar ratio of TMOS C18TAC=9.2.T), a transparent thin film formed on the substrate. The X-ray diffraction pattern of the film (Figure 1a) showed a sharp diffraction peak with the d value of 4.6 nm, which accompanied the 2nd order reflection. In order to remove the surfactants from the substrate to obtain porous silica films, the as coated film of the silica-surfactant mesostructured material was calcined in air at 450 °C. Sharp diffraction peak was observed in the XRD pattern of the calcined film... 

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