X-ray Line-broadening Analysis Research Articles

The effect of annealing temperature on hydrothermally grown sisal-like ZnO microstructures

This study has extensively described the fabrication and characterization of sisal-like ZnO microstructures. HMT aqueous solution containing zinc nitrate tetrahydrate as crystalline zinc source has been utilized to synthesize sisal-like ZnO samples via a controlled hydrothermal route. A variety of characterization techniques including FESEM, XRD, FT-IR, and Raman spectroscopy have been employed to investigate the effects related to varying annealing temperatures on morphological and structural properties. The FESEM observations have revealed a transition from hexagonal microrods to modified microrods and then to pointed microrods for sisal-like ZnO architectures as the annealing temperature increases. XRD results have indicated a considerably high purity for as-synthesized ZnO microstructures. The crystalline quantities of ZnO samples have been estimated using various X-ray line-broadening analysis methods including Debye-Scherrer and Williamson-Hall techniques. UV-Vis DRS measurements have been carried out to study optical properties. Results have shown improved light harvesting related to both enhanced absorption intensities and decreased band-gap energies with the increase of annealing temperatures.

Studies on Ni–M (M = Cu, Ag, Au) bimetallic catalysts for selective hydrogenation of cinnamaldehyde

Bimetallic catalysts of the type Ni–M with M=Cu, Ag and Au, and supported on TiO2-P-25 have been prepared by chemical reduction using glucose as the reducing agent. Hydrogenation of cinnamaldehyde (CAL) to yield hydrocinnamaldehyde (HCAL), cinnamyl alcohol (COL) and hydrocinnamyl alcohol (HCOL) has been studied on the catalysts in the temperature range 60–140°C and at 20kg/cm2 pressure, with methanol as solvent. Ni crystallite sizes, measured by X-ray line broadening analysis (XLBA), H2 pulse chemisorption and Transmission Electron Microscope (TEM) techniques, are in the range 8–12nm. Temperature Programmed Reduction (TPR) and Diffuse Reflectance Spectroscopic (DRS) studies indicate the formation of Ni–Cu alloys, while Ni–Ag and Ni–Au exist as bimetallic nanoparticles. High-resolution HRTEM studies show that the bimetallic nanoparticles are in close contact, forming hetero junctions. Changes in the XPS binding energy values for Ni 2p1/2 and Ni 2p3/2 levels reveal that Cu/Ag/Au, tend to increase electron density around Ni, which retards the adsorption of CAL via olefinic bond and weakens NiH bond strength. H2 TPD measurements also indicated weakening of NiH bond. Bimetallic catalysts display higher CAL conversion and selectivity to COL vis-à-vis the corresponding monometallic catalysts at lower reaction temperatures, 60–80°C. But, selectivity to COL decreases at higher temperatures, 100–120°C. Mode of adsorption of CAL and nature of adsorbed hydrogen on bimetallic catalysts influence their activity and selectivity.

Preparation and characterization of Ce-doped and Zr-doped sol–gel inks of titanium alkoxide

Inks of titanium diisopropoxide bisacetylacetonate ([(CH3)2CHO]2Ti(C5H7O2)2) are suitable for the fabrication of photonic bandgap materials by direct ink writing (DIW). Using this method we are able to obtain micro-periodic titania (TiO2) structures with high refractive index by calcining the structures built with those inks. Calcining at high temperatures causes titania grain growth and surface roughness of the structure, which has an influence over its optical properties. In order to inhibit the grain growth of titania nanocrystals when the structures are calcined, we have synthesized using the sol–gel technique titanium diisopropoxide bisacetylacetonate inks doped with Cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) and Zirconyl nitrate hydrate (ZrO(NO3)2·xH2O). The grain growth process of titania powders derived from the calcined doped sol–gel inks during various heat-treatment programs has been investigated by the X-ray line-broadening analysis. It was demonstrated how the dopants reduce the grain growth of the rutile phase after heat treatment. The influence of the dopants on the rheological behaviour of doped inks were studied and compared with the undoped. The flow and oscillation curves as a function of time demonstrate that doped inks have the same rheological behaviour than undoped inks. Thermogravimetric analysis also proves that doped inks keep the same mass loss after calcination than undoped inks. These results show how doped inks can be applied for DIW in the same conditions than undoped inks with a significant reduction of titania grain growth.

X-ray line-broadening analysis of dislocations in a single crystal of Zr

X-ray line-broadening analysis of dislocations in a single crystal of Zr

A study of the mechanochemical synthesis of NaNbO 3

We have studied the mechanochemical synthesis of NaNbO 3, prepared from a powder mixture of Na 2CO 3 and Nb 2O 5. The formation of NaNbO 3 during milling was followed using thermal analysis and X-ray diffraction. According to the thermogravimetric analysis, after 20 and 40 h of milling there was still some residual carbonate, while the X-ray diffraction shows NaNbO 3 as the major crystalline phase present in the mixture. Based on the quantitative XRD phase analysis, the residual reactants were amorphous and as such undetectable with the X-ray diffraction. Furthermore, an X-ray line-broadening analysis was used to determine the NaNbO 3 crystallite size and the microstrain. A decrease in the NaNbO 3 crystallite size coupled with an increase in the amount of microstrains was found from 10 to 40 h of mechanochemical treatment. Finally, the TEM analysis confirmed the NaNbO 3 crystallite size determined by the X-ray line-broadening analysis.

KTaO 3 powders and thin films prepared by polymeric precursor method

This work presents perovskite-type KTaO 3 powders and thin films synthesis, using a low-cost route based on Pechini method. Powders and films were studied by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. Pyrochlore-free samples are achieved at moderate temperatures (650 °C). Nevertheless, it was verified that with temperature increasing, a small amount of secondary perovskite phases, presenting lowered lattice parameters, is formed in powders. These phases are attributed to stoichiometric deviation due to K losses during thermal treatment. The EDS results support this hypothesis. The microstructure of a sample annealed at 625 °C was studied by X-ray line-broadening analysis. The sample contains a negligible amount of structural distortions and the crystallites are on average isotropic. Concerning KTaO 3 films, it was observed that substrates play an important role. While the films prepared onto sintered alumina substrates present pyrochlore contamination, films prepared onto (100) SrTiO 3 and (100) LaAlO 3 are single phased (only perovskite phase is present) and highly oriented. KTaO 3 is epitaxial onto (100) SrTiO 3 and textured onto (100) LaAlO 3. Moreover, films are crack-free and homogeneous. Refractive indexes, measured by ellipsometry, are about 1.95 and the film thickness is in the range of 130 nm per layer.

X-ray line-broadening analysis of deformation mechanisms during rolling of commercial-purity titanium

X-ray line-broadening techniques were used to establish deformation mechanisms in textured commercial purity (CP) titanium specimens that were rolled at various temperatures. The results indicated that conventional line-broadening techniques developed specifically for polycrystalline powders could be used on textured materials to deduce the slip-system activity and dislocation density that develop during thermomechanical processing if appropriate averaging procedures are followed. The deduced slip-system activity and densities revealed a transition in deformation behavior from a heavily-twinned to an untwinned mode with an increase in deformation temperature for CP titanium.

Characterization of Dislocation Structures in Hexagonal Close-Packed Metals by X-ray Line-Broadening Analysis

Characterization of Dislocation Structures in Hexagonal Close-Packed Metals by X-ray Line-Broadening Analysis

Formation process of nanocrystalline materials from x-ray diffraction profile analysis: Application to platinum catalysts

It’s well known that x-ray line profile analysis is a powerful and convenient method to probe the microstructural characteristics of nanocrystalline samples. In the literature well-documented techniques are normally used to obtain crystalline size distributions from x-ray line-broadening analysis. However, it is less considered that the shape of such size distributions may be a means to determine by which mechanism the particles have grown. A simple method is presented here to distinguish between two different growth mechanisms: the coalescence and Ostwald ripening process. An application of the method to platinum nanoparticle electrocatalysts with different size distributions, dispersed on high-surface-area carbon blacks, is discussed.

Crystallisation of thin anatase coatings on muscovite

Wet-chemically precipitated anatase coatings on muscovite are investigated by high-temperature as well as high-resolution X-ray diffraction, thermogravimetry and transmission electron microscopy (TEM). X-ray diffraction detects intrinsic macrostrains in the as-prepared samples. Their temperature dependent reduction can be correlated with thermogravimetrically determined mass loss. Application of X-ray line-broadening analysis in combination with TEM leads to a deeper insight in the evolution of microstructure. The combination of these methods and the complementary information they provide proves crucial relations between microstructure, strain and impurities.

A Monte Carlo Estimate of Crystallite-Size and Microstrain Distribution Functions from X-ray Line Broadening

A method of X-ray line-broadening analysis is presented whereby the coherence length and microstrain contributions can be calculated using a Monte Carlo interference-function-fitting algorithm. The method is based on the `column-like' crystal model and can be applied to both single and multiple-order reflections. Examples on simulated diffraction peaks, deformed face-centred-cubic palladium powder and heavily textured deformed body-centred-cubic low-carbon-steel sheets are presented and comparisons are made with currently applied methods.

Physicochemical studies using amylose as an in vitro model for resistant starch

The effects of hydrolysing amylose gels and films with porcine pancreatic alpha-amylase were studied in order to construct an in vitro model of resistant starch. Both gels and films proved to be partially resistant to hydrolysis, their susceptibility decreasing with increasing substrate concentration. Storage of gels for 1 day resulted in levels of crystallinity from 6 to 12%. Hydrolysis of these gels produced significant increases (from 272 to 557%) in crystallinity in all cases. The amount of resistant material remaining after hydrolysis increased (from 33% to 50%) with increasing gel concentration. Storage of amylose gels for 7 days resulted in levels of crystallinity of 28 to 35%. Hydrolysis of these gels led to increases in crystallinity, but to a lesser extent (from 148 to 175%) than before. The amount of resistant material remaining after hydrolysis increased (from 41 to 50%) with increasing gel concentration. Size-exclusion chromatography of resistant material from hydrolysed films indicated the presence of a high molecular weight component corresponding to undigested amylose, in addition to a low molecular weight component corresponding to partially digested amylose. Chromatograms of resistant material from both gels stored for 1 day and those stored for 7 days were almost identical and contained only a low molecular weight component with no sign of undigested amylose. X-ray line-broadening analysis showed the average sizes of the crystallites in the resistant material produced by hydrolysis of gels stored for both 1 day and 7 days to be approximately equal. The ability of the enzyme to diffuse into its substrate played a major part in the resistance to hydrolysis of amylose films, but had a much less important role in the resistance of gels. Not only crystalline, but also amorphous portions of amylose gels, were found to be resistant to enzymic hydrolysis. The resistant portion of amylose gels was modelled in vitro with a view to explaining the structure of resistant starch in vivo.

X-ray diffraction analysis of substructures in plastically deformed BCC materials

A procedure for line-shape analysis of broadened X-ray (or neutron) diffraction peaks is presented and specified for b.c.c. materials, which takes into account the effect of interfaces, internal stress of the 2nd kind and a dislocation distribution with weak defect correlation. Application of the technique is demonstrated by the estimation of dislocation densities in plastically deformed α-iron and steel. The results confirn that X-ray line-broadening analysis is suitable for integrated substructure characterization, but it becomes also evident that local structural inhomogeneity end the texture of the sample material must carefully included into the interpretation of experimental data

Profile-fitting procedures in the X-ray line-broadening analysis of polycrystalline materials

Profile-fitting procedures in the X-ray line-broadening analysis of polycrystalline materials

Shock compaction of cubic boron nitride powders

C-BN powders with different grain sizes were dynamically compacted by explosive shock loading using approximate peak pressures from 33 to 77G Pa. The density and the microhardness of the resulting c-BN compacts were strongly dependent upon the grain size of the c-BN powders used as the starting materials. The best c-BN compacts, with 98% of the theoretical density and microhardness of 51.3G Pa, were obtained from the coarse c-BN powder (40 to 60μm). In the compacted fine c-BN powder (2 to 4μm) conversion of the c-BN to low density forms of BN at a residual temperature degraded the interparticle bonding significantly. X-ray line-broadening analysis of the compacted c-BN powders indicated that the residual lattice strain increased with the increase in grain size of the starting powder, while the crystallite size was independent of the grain size.

The role of the surface layer on the power law breakdown in high temperature creep

The dislocation density as computed from X-ray line-broadening analysis was measured in the surface layer, i.e. π s, and in the interior, i.e. π i, of aluminum alloy 1100 specimens crept at high temperatures. The power law breakdown occurred when π s > π i. In the power law breakdown region, π s increased rapidly with strain and stress while π i increased incrementally to higher plateau levels as the stress was increased. The decrease in dislocation density on annealing after creep consisted of two stages: a rapid stage with an activation energy of 14.3 kJ mol −1 and a slower stage with an activation energy of 127.9 kJ mol −1. The recovery process was the same for specimens crept within and above the power law region.

A precise determination of the shape, size and distribution of size of crystallites in zinc oxide by X-ray line-broadening analysis

The Fourier and variance methods are used to analyse the breadths of X-ray diffraction peaks from ZnO powder obtained from the thermal decomposition of Zn3(OH)4(NO3)2. The shape, size, distribution of size and orientation of the crystallites are determined. It is found that the form is markedly anisotropic and that on average the crystallites may be regarded as cylinders with a diameter of about 110 Å and height about 240 Å, but that they are in fact right prisms whose cross section is an irregular hexagon. There is excellent agreement between the experimental results and the predictions of line-broadening theory, with quantitative confirmation from electron micrographs of the sample.

The non-additivity and curvature corrections in the variance method of X-ray line-broadening analysis

A previous paper by Edwards & Toman on the subject of the variance non-additivity and curvature corrections is revised and extended. The formula for the curvature correction is given in a form which facilitates evaluation for cases of crystallite size broadening by crystallites of known shape; the formula involves the shape parameter M which is evaluated for the shapes of a sphere, a rectangular parallelepiped, a tetrahedron and an octahedron.

Meteorites: An X-ray analysis of deformed kamacite

An X-ray line-broadening analysis was carried out to study the degree and nature of lattice damage that is present in the kamacite phase of iron meteorites. Single plates of kamacite were removed from three octahedrites, and diffraction-line profiles were measured on a spectrometer for several orders of (110) and (200) reflections. With identical X-ray geometry, corresponding line-profile measurements were made of the (110) and (200) reflections from an annealed single crystal in order to correct for inherent geometrical breadths. The contributions of the two principal factors affecting kamacite line breadth, i.e., particle size and elastic strain, have been evaluated. The results are examined in the light of the probable state of the kamacite as inferred from metallographic observations.