this process. We analyzed the kinetics of thermal transformation of Al-maghemites into Al-hematites and some of its mineralogical aspects. Synthetic substituted maghemites with different degrees of Al-substitution (0.0, 1.0, 2.0, 2.9, 3.8, 5.6, 6.7, 10.0, 12.0, and 17.1 mol% Al) were subjected to a temperature of 500±10 °C for 0, 5, 10, 16, 64, 128, 192, 360, 720, 2160, 3600, 5040, and 6480 min. After thermal treatment, samples were characterized by Xraydiffraction (XRD), differential thermal analysis (DTA), specific surface area (SSA) measurement, and total chemical analysis. XRD patterns were analyzed by Rietveld refinement, and maghemite and hematite contents were calculated using Rietveld refinement and the method proposed by Sidhu. Isomorphic substitution of Fe by Al increased the critical temperature of transformation and the time necessary for maghemite to hematite transformation. Rietveld refinement data showed a better fit than the data adjusted by the Sidhu method. Increasing isomorphic substitution also decreased lattice parameters and mean crystallite dimension (MCD) values in maghemite; but only c-dimension and MCD decreased with increasing Al-substitution in hematite. For maghemite, the SSA increased with isomorphic substitution, rising up to 5.9 mol% Al; for hematite, SSA increased linearly. SSA decreased with heating time, regardless of isomorphic substitution.
4 Figure 2 left presents a characteristic optical micrograph of the cross-section of the nitrided specimens. DIN 32 Cr Mo V 13 nitrided steel presents a white layer with a thickness of 18 μm, and a diffusion zone with about 380 μm depth. The microstructure of the treated surface, obtained by scanning electronic microscope (SEM), is shown in Figure 2 right. The DIN 40 Cr Mn Mo 7 nitrided steel presents a microstructure similar to that shown in figure 2. In this case, however, the thickness of its white layer is lower and equal to 15 μm, while the thickness of its diffusion zone is lower and equal to 150 μm, respectively, when compared to the DIN 32 Cr Mo V 13 nitrided steel layers. In both cases, according to the X-raydiffraction results, the white layer presents, mainly, γ’ (Fe 4 N ) and only traces of nitrides ε (Fe 2-3 N) and the
After cereals, tubers and roots are the major source of starch for food and industrial uses. Arrowroot refers to any plant of the genus Marantha, but the term is most commonly used to describe the easily digested starch ob- tained from the rhizomes of Marantha arundinacae. The rhizomes of this herbaceous plant contain about 20% of starch. As few studies exist on arrowroot starch, the objective of this preliminary work was to study the X-raydiffraction (XRD) patterns of arrowroot starch when treated by γ-radiation with doses up to 15 kGy in a 60 Co
SYNTHESIS OF HYDROXYAPATITE AND STRUCTURAL REFINEMENT BY X-RAYDIFFRACTION. A sample of hydroxyapatite was synthesized and its crystalline structure was analyzed by X-raydiffraction by means of the Rietveld method. Two functions were used to fit the peak profiles, modified Voigt (TCHZ) and Pearson VII. The occupational factors and lattice parameters obtained by both models show that the sample does not contain relevant cationic substitutions. The interatomic distances from Ca1 to oxygens O1, O2 and O3 were adequate for a pure hydroxyapatite without defect at site Ca1. Besides, the use of multiple lines in planes (300) and (002) associated with the model Pearson VII resulted in good agreement with the TCHZ model with respect to the size-strain effects with an ellipsoidal shape of crystallites. In conclusion, the procedures adopted in the synthesis of hydroxyapatite produced a pure and crystalline material. The experimental results of transmission electron microscopy confirmed the predicted shape of crystals.
A primeira caracterização de eletrodos de óxidos de irídio e rutênio utilizando as técnicas de difração de raios X (DRX), microscopia eletrônica de varredura e transmissão (MEV e MET), espectroscopia fotoeletrônica de raios X (XPS) e espec- troscopia no infravermelho (IRS) mostrou que esses materiais são o produto da desidratação incompleta de óxidos de Ru e Ir parcialmente hidratados 1-3 . Foi observado que esses eletrodos
DC conductivity of PVA-CuO nano-composite films have been studied in the present work. The composites were prepared by solution-casting technique. The prepared PVA-CuO composites have been characterized by X- raydiffraction (XRD) analysis, Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDXS); which confirmed the presence of CuO in polyvinyl alcohol and the formation of the composite. DC conductivity studies show thermally activated behavior of all the composites. The conductivity was found to increase with the increase in temperature indicating the semiconducting behavior of all the compositions. The activation energy increases as the content of CuO nanoparticles increases from 1 to 4 in wt% in the PVA- CuO nano-composites. Maximum conductivity was observed in 4 wt% of CuO in polyvinyl alcohol.
stable and irreversibly transforms to an orthorhombic structure above 460 o C. The structure of the latter was determined from studies on monocrystalline samples, whereas for the monoclinic variant there are no single crystals available so far. It was found only one monoclinic variant and the structure associated with this variant is based on studies on polycrystals. We analyzed a monoclinic oxide powder sample by X-raydiffraction and refined its pattern by means of the Rietveld Method. We obtained that the monoclinic variant belongs to space group P 2 1 /c, with lattice parameters a = 5.615(3), b = 4.782(2), c = 5.574(2) ˚ A, β = 120.13(1) o .
The assumptions made to derive the Scherrer equation are very close to the ones made in the kinematical theory of X-raydiffraction, used for crystals with appreciable defects or of small size (Zachariasen, 1945). For large and perfect crystals, the kinematical theory cannot (always) be assumed and the dynamical theory of X-raydiffraction should be applied instead. This theory treats the crystal as a three-dimensional complex dielectric constant and uses Maxwell’s equations to describe the interactions between incident and diffracted beams, and all waves inside the crystal (Zachariasen, 1945; Batterman & Cole, 1964; Authier, 2001). This means that the waves scattered by each atom (or atomic plane) are subse- quently scattered by other atoms (or atomic planes) giving rise to distinct phenomena that do not appear in the kinematic theory, such as the Darwin width (Authier & Malgrange, 1998), primary extinction (Authier & Malgrange, 1998) and the Borrmann effect (Batterman & Cole, 1964). The Darwin width is the smallest possible width of a diffraction peak even in an infinitely large crystal. The primary extinction happens when the diffracted beam is diffracted again in the direction of the primary beam while inside the crystal, therefore decreasing the energy transferred to the diffracted beam. The Borrmann effect is the anomalous transmission of X-rays through a thick crystal, which should be completely absorbed
The polycrystalline sample of Nb was obtained by electron-beam zone melting and was supplied in the form of swaged rod of 3 mm in diameter, by FAENQUIL/Lorena. Samples 50 mm long which had been chemically polished to 1 mm diameter in a mixture of nitric and fluoric acids, were used for the internal friction and xraydiffraction (XRD) measurements.
routes and characterized by scanning electron microscopy, differential thermal analysis, thermogravimetric analysis and X-raydiffraction, whereas the superconducting properties by dc magnetization and electrical resistivity measurements. Also, hardness and elastic modulus were measured by instrumented indentation. It was found that Cu sites are substituted by Ag ions, as well as that metallic Ag also fills the pores in the grain boundaries. The results obtained are in agreement with those reported in the literature and demonstrated that the addition of silver to the Y Ba 2 Cu 3 O 7−δ
diffraction peaks in XRD pattern from the R1 sample (Figure 1b) are sharper than those in XRD pattern from the S1 sample (Figure 1a), suggesting higher crystallinity of the sample obtained by refluxing method. On the other hand, broader peaks in X-raydiffraction patterns of the sample obtained from sonochemical method could be an evidence of smaller particle sizes. The crystallite size can be estimated from XRD data by the Scherrer formula: , where λ is the X-ray wavelength of 1.5418 Å, θ is the Bragg diffraction angle and B is the full width at half maximum (FWHM) of 2θ. 21,22 Crystallite sizes calculated
Spinel-type solid solutions were synthesized by the Pechini method and calcined between 500 and 900 °C for 4 hours and at 900 °C for 8 hours to produce ceramic pigments. The resulting powders were characterized by thermogravimetric analysis, Fourier-transform infrared spectroscopy (FTIR), X-raydiffraction (XRD), scanning electron microscopy (SEM), particle size analysis and BET surface area measurements. The formation of spinel took place upon calcination at 700 °C. IR spectroscopy revealed the presence of N 1 and N 2 bands, typical of
Potassium hydrotris(2-mercaptothiazolyl)borate, KMt, (1) and potassium hydrotris(2- methimazole), KTm, (2), were prepared by reacting the appropriate amine thiol with KBH 4 . They were characterized by spectroscopic methods and elemental analysis. Solid state structures of KMt.4H 2 O and compound 2 were determined by X-raydiffraction analyses. The softer nature of the anion in the former as compared to 2 is indicated by the lack of interaction of the anion with the cation, that has water molecules in its coordination sphere. In KMt.4H 2 O the geometry around the potassium cation is distorted octahedral and in 2, distorted square pyramidal. In 2 the potassium ion is coordinated to two sulfur atoms of one hydrotris(methimazole)borate unit and to other three sulfur atoms belonging to neighboring KTm units. Both compounds have a polymeric structure.
15 mL of DME, at -30 ºC and the resulting mixture was stirred for 20 h. The LiBr formed during the reaction was filtered off and the solvent evaporated under vacuum. The residue was purified by column chromatography (kieselgel/hexane) to give two yellow bands. The first was characterised as compound 1 (250 mg, 20%), and the second as compound 2 (200 mg, 16%). Recrystalisation from hexane at room temperature af- forded yellow crystals suitable for X-raydiffraction study for both compounds.
800 °C. Mössbauer, X-raydiffraction (XRD), thermogravimetric analysis (TG/DTA), scanning electron microscope (SEM), elemental analysis CHN, Raman, potentiometric titration, saturation magnetization and Brunauer-Emmett-Teller (BET) analyses showed that the materials prepared at 400 °C are composed mainly of a graphitic and amorphous carbon containing dispersed magnetite (Fe 3 O 4 ). At higher temperatures, metallic iron (Fe
(or atomic plane) are also scattered by the other atoms (or atomic planes) and those waves are also subsequently scat- tered by other atoms and so on. This multiple scattering creates a wavefield inside the crystal and is properly dealt with by the dynamical theory of X-raydiffraction, which considers the dielectric constant of the crystal a three-dimensional and periodic complex quantity and uses Maxwell’s equations to describe the interactions of all beams (waves). This theory explains distinct phenomena that are not predicted by the kinematical theory, such as the Darwin width, primary extinction and the Borrmann effect (Darwin, 1914a,b; Zachariasen, 1945; Batterman & Cole, 1964; Pinsker, 1978; Authier & Malgrange, 1998; Authier, 2001). Muniz et al. (2016) suggested that there is a limit of applicability of the Scherrer equation that is closely related to the limit between the dynamical and kinematical theories. They determined the Scherrer limit for three crystals, LaB 6 , Si and CeO 2 , and found
of SiO 2 , stable and adherent, that promotes the adherence of Al 2 O 3 present on the aluminum surface. Starting from the scanning electronic microscopy characterizations, the chemical analysis for energy dispersive spectroscopy, and phase analysis by X-raydiffraction, the detected phases could be identified and the mechanisms present during the corrosion tests were defined.
Phyllanthus niruri (Pn) is a plant that has been shown to interfere in the growth and aggregation of calcium oxalate (CaOx) crystals. In the present study we evaluated the effect of Pn on the preformed calculus induced by introduction of a CaOx seed into the bladder of male Wistar rats. Pn treatment (5 mg/rat/day) was initiated immediately or 30 days after CaOx seeding and thus in the presence of a preformed calculus. Animals were sacrificed 50 or 70 days after surgery. The resulting calculi were weighed and analyzed by X-raydiffraction, stereomicroscopy and scanning electronic microscopy. Precocious Pn treatment reduced the number (75%, P < 0.05) and the weight (65%, P < 0.05) of calculi that frequently exhibited a matrix-like material on its surface, compared to the untreated CaOx group. In contrast, Pn treatment in the presence of a preformed calculus did not prevent further calculus growth; rather, it caused an impressive modification in its appearance and texture. Calculi from Pn-treated animals had a smoother, homogeneous surface compared to the spicule shape of calculi found in the untreated CaOx group. XRD analysis revealed the precipitation of struvite crystals over the CaOx seed and Pn did not change the crystalline composition of the calculi. This suggests that Pn interfered with the arrangement of the precipitating crystals, probably by modifying the crystal-crystal and/or crystal-matrix interactions. Results suggest that Pn may have a therapeutic potential, since it was able to modify the shape and texture of calculi to a smoother and probably more fragile form, which could contribute to elimination and/or dissolution of calculi.