Measurements X-ray diffraction

As can be seen in Fig. 5.25 the layer spacing increases with an increasing amount of formamide. This is plausible considering the structure of the lamellar L phase cf. Sect 3.2.2). In this phase the repeat distance measured by X-ray ddfraction is composed of two parts. The first part is a partial or full bilayer of surfactant molecules in which the hydrophilic head groups are surrounded by solvent molecules causing a slight swelling of the surfactant layer. If the solvent concentration exceeds the amount of solvent molecules which can be incorporated into the surfactant layer, the solvent molecules start to build up a separate solvent layer which corresponds to the second part of the overall layer thickness. The easiest way to describe the layer thickness d(T, w) is thus to separate it into the thickness of the solvent layer d iw), which in a first approximation solely depends on the mass fraction w of formamide, and into the thickness of the diol bUayer dbi(T), which maiidy depends on the temperature T  

According to this equation the measured layer spacing is plotted versus the weight fraction w of formamide for different temperatures T — Tc relative to the lamellar L to lyotropic SmC analog phase transition and fitted with a uniform slope. In Fig. 5.26 the data sets for six exemplary relative temperatures and the 

By plotting the intercepts d, l(J) versus the relative temperature T — Tq, the temperature dependence of a hypothetical bilayer thickness for 0 wt% of formamide is obtained (Fig. 5.27b). It exhibits the typical temperature dependence expected for a thermotropic SmA to SmC phase transition. The two kinks in the extrapolated data at r - Tc = -6 and —10 arc caused by the reduction of analyzable data points due to the crystallization of the samples with high solvent concentration. At the lamellar L to lyo-SmC phase transition the calculated layer spacing is at its 

The solvent layer thickness d iw) for different mass fractions of formamide is calculated from the slope m (Fig. 5.27c). It varies between 1.1 and 2.3 nm in the investigated concentration regime. 

---

Leadbetter A J and Norris E K 1979 Distribution functions in hree liquid crystals from x-ray diffraction measurements Moiec. Phys. 38 669-86... 

Amorphous silica, ie, silicon dioxide [7631-86-9] Si02, does not have a crystalline stmcture as defined by x-ray diffraction measurements. Amorphous silica, which can be naturally occurring or synthetic, can be either surface-hydrated or anhydrous. Synthetic amorphous silica can be broadly divided into two categories of stable materials (1) vitreous silica or glass (qv), which is made by fusing quart2 at temperatures greater than approximately 1700°C (see Silica, vitreous silica), and microamorphous silica, which is discussed herein. 

It is difficult to attribute the capacity reduction which occurs above 700°C to structural effects because the structure of the samples is not changed significantly, as indicated by our X-ray diffraction measurements on the CRO samples. On the other hand, the hydrogen content of the samples is dramatically reduced over this temperature range. To investigate the importance of the hydrogen content, we made a series of cells from the other samples. 

Powder X-ray diffraction and SAXS were employed here to explore the microstructure of hard carbon samples with high capacities. Powder X-ray diffraction measurements were made on all the samples listed in Table 4. We concentrate here on sample BrlOOO, shown in Fig. 27. A weak and broad (002) Bragg peak (near 22°) is observed. Well formed (100) (at about 43.3°) and (110) (near 80°) peaks are also seen. The sample is predominantly made up of graphene sheets with a lateral extension of about 20-30A (referring to Table 2, applying the Scherrer equation to the (100) peaks). These layers are not stacked in a parallel fashion, and therefore, there must be small pores or voids between them. We used SAXS to probe these pores. 

As in other shock-modified powders, the x-ray diffraction measurements showed large values of residual strain resulting from extensive plastic defor-... 

The hydrogen treatment procedures, tensile, compression and torsion tests at fixed temperatures, transmission electron or optical microscopy at room temperature as well as X-ray diffraction measurements were detailed elsewhere All experiments were performed so as to compare properties of the same alloy, but modified using different treatment procedures. 

This mechanism is also confirmed by X-ray diffraction measurements [94, 100]. It is also mentioned that the absence of reflexes belonging to Li3NbC>4, in X-ray diffraction patterns obtained for mixtures treated at relatively low temperatures, could be explained by the formation of an amorphous material at the very beginning of the process [103]. 

Direct kinetic measurements from the changes in diffracted beam intensities with time during heating of the reactant are illustrated in the work of Haber et al. [255]. Gam [126] has reviewed the apparatus used to obtain X-ray diffraction measurements in thermal analysis. Wiedemann [256] has designed equipment capable of giving simultaneous thermo-gravimetric and X-ray data under high vacuum. X-Ray diffraction studies enable the presence, or absence, of topotactic relationships between reactant and product to be detected [92,102,257—260], Results are sometimes considered with reference to the pseudomorphic shape of residual crystallites. 

Baranowski [680] concluded that the decomposition of nickel hydride was rate-limited by a volume diffusion process the first-order equation [eqn. (15)] was obeyed and E = 56 kJ mole-1. Later, Pielaszek [681], using volumetric and X-ray diffraction measurements, concluded from observations of the effect of copper deposited at dislocations that transportation was not restricted to imperfect zones of the crystal but also occurred by diffusion from non-defective regions. The role of nickel hydride in catalytic processes has been reviewed [663]. 

No matter how thorough, a kinetic study does not really determine a mechanism in the same sense that single-crystal X-ray diffraction measurements determine a structure. The reaction mechanism is but a scientific postulate that is open to revision when new data, new insights, or new theories of reactivity emerge. 

Another seven-membered ring that shows some aromatic character is tropone (44). This molecule would have an aromatic sextet if the two C=0 electrons stayed away from the ring and resided near the electronegative oxygen atom. In fact, tropones are stable compounds, and tropolones (45) are found in nature. However, analyses of dipole moments, NMR spectra, and X-ray diffraction measurements show that tropones and tropolones display appreciable bond alternations. ... 

Structure of Complexes in Solution Derived from X-Ray Diffraction Measurements Georg Johansson... 

The TEM images of 12 wt.% Co/MgO calcined at 873 K (Catalyst I) before and after reduction are shown in Fig. 1 (a) and (b), respectively. Although Co metal phase was detected in reduced Co/MgO by X-ray diffraction measurements (XRD) [7, 8], no Co metal particle was observed on both catalysts. EDS elemental analysis showed that primary particles contain both Mg and Co elements, whose concentrations were about the same as loaded amounts. Figure 2 shows TEM image of 12 wt.% Co/MgO calcined at 1173 K (Catalyst II). 

Figure 8.8 Space-filling model based on small-angle X-ray diffraction measures, showing how two hemidiscotic molecules of 8 can give rise to a disk-like shape. (Adapted from Ref [11].)...

FIGURE 27.9 (a) Voltammetry curve for the UPD of TI on Au(l 11) in 0.1 M HCIO4 containing ImMTlBr. Sweep rate 20mV/s. The in-plane and surface normal structural models are deduced from the surface X-ray diffraction measurements and X-ray reflectance. The empty circles are Br and the filled circles are Tl. (b) Potential-dependent diffraction intensities at the indicated positions for the three coadsorbed phases. (From Wang et al., 1998, with permission from Elsevier.)... 

Kaltseis et al. [234] have investigated the recoil-free fraction of the 46.5 keV transition of W in anhydrous lithium tungstate. Their results can be expressed by an effective Debye temperature of 172 9 K which is in good agreement with a value of 205 40 K derived from X-ray diffraction measurements of Li2W04 powder. 

Alloys of CoSnP [17] and CoZnP [16] have been prepared by electroless deposition. Both Zn and Sn increase the Hc, and Sn also improves the corrosion resistance and the appearance. For Sn alloys, X-ray diffraction measurements suggest that the Sn addition orients the c axis parallel to the plane of the film and decreases the grain size. 

Since the tack and green strength of these rubbers may depend on their ability to undergo strain induced crystallization, this behavior was studied and compared with that shown by NR. Information on the strain induced crystallization behavior of these experimental rubbers was obtained from x-ray diffraction measurements and from rheo-optical studies. 

Figure 2.67 Typical cell configurations employed in obtaining in situ electrochemical X-ray diffraction measurements (a) transmission (Laue configuration), (b) reflection (Bragg configuration).

---