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result(s) for
"Rietveld"
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Effects of ball milling on the structure of cotton cellulose
Cellulose is often described as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.
Journal Article
The possibility of vanadium substitution on Co lattice sites in CoFe2O4 synthesized by sol–gel autocombustion method
In this study, the effect of vanadium addition on the structural and magnetic properties of cobalt ferrite (Co
1−
x
V
x
Fe
2
O
4
; where
x
= 0, 0.05, 0.10, 0.15, 0.20, and 0.25) prepared by a novel sol–gel autocombustion method was investigated. The formation of cubic spinel structure (space group
Fd3m
) was confirmed by X-ray diffraction in combination of Rietveld structure refinement analysis and transform infrared spectroscopic spectrum (FT-IR) analyses. Also, phase and elemental analyses confirmed that an inevitable secondary phase of hematite along with the spinel phase appears by addition of vanadium; therefore, a nanocomposite was formed in the sample containing vanadium. However, the SEM observations in combination of the results obtained by Rietveld structure refinement analysis showed that the presence of vanadium can affect the size of synthesized cobalt ferrite. VSM measurements showed that saturation magnetization and coercivity values are strongly dependent on the vanadium content and particle size, so that the maximum value of coercivity was obtained equal to ~916 Oe for Co
0.85
V
0.15
Fe
2
O
4
.
Highlights
Effect of vanadium ions addition on the magnetic properties of cobalt ferrite.
Effect of adding these ions on morphology and agglomeration of the nanoparticles.
The evolution of structural properties by using the Rietveld method.
Journal Article
X-ray diffraction Rietveld structural analysis of Au–TiO2 powders synthesized by sol–gel route coupled to microwave and sonochemistry
TiO
2
is one of the most studied photocatalyst, however, in order to enhance the photocatalytic activity, several strategies for chemical or physical modifications have been reported. Among these strategies, microwave and sonochemistry assisted synthesis methods have been attracting attention due to the unique characteristics that can be achieved through it. Au–TiO
2
nano powders were synthesized via microwave assisted sol–gel method (SG method) and sonochemistry assisted sol–gel method (SC method) with varying gold load, (containing 0.05, 0.1, 0.3, 0.7, 1.0, 3.0 and 5.0 wt% for SG method and 0.05, 0.1, 0.3, 0.7, 1.0 wt% for SC method). Subsequently, a calcination process was carried out at 450 °C for 3 h. Materials obtained were physicochemical analyzed by SEM, XPS, and XRD analysis. According to XRD analysis, the main crystalline phase of the materials was anatase. Average crystallite size and microstrain present in the powders were studied using the Williamson–Hall method and Debye–Scherrer equation. The crystal structure of all samples was refined by the Rietveld method, and a compression on the unit cell parameters was determined. These analyses revealed an increment in the unit cell strain when Au concentration was increased, and a decrease of the crystallinity in the powders when SG method was used. In the case of SC method samples, crystallinity and strain was found to remain constant.
Highlights
Au–TiO
2
doped powders were synthesized by microwave and sonochemistry assisted process.
Partially oxidized Au was found by XPS with a BE displacement to lower BE.
Rietveld refinement show an increase on lattice parameters with Au added.
Crystallite size varies in accordance to Au content with microwave synthesis.
Journal Article
Physical and nanomechanical properties of the synthetic anhydrous crystalline CaCO3 polymorphs: vaterite, aragonite and calcite
The synthetic anhydrous crystalline CaCO
3
polymorphs—vaterite, aragonite and calcite—were tested using dilatometry and nanoindentation. Microstructural changes in the samples before and after measurements were observed under scanning electron microscope and their phase composition quantified with X-ray powder diffraction with the Rietveld method. The thermal expansion coefficients of vaterite and the hardness and elastic modulus of synthetic aragonite are reported for the first time. The physical and nanomechanical properties were measured under similar conditions for each CaCO
3
polymorph. Aragonite, calcite and vaterite showed volumetric thermal expansion coefficient at 303 K of 49.2(8), 48.6(2) and 44.1(3) 10
−6
K
−1
, respectively. The elastic modulus increased from 5(4), 16(7) to 31(8) GPa for aragonite, calcite and vaterite, respectively. Average hardness was found lower than values from the literature, ranging from 0.3 to 1.3 GPa. The results are considered of interest for the design of CaCO
3
-based materials for applications.
Journal Article
The HighScore suite
HighScore with the Plus option (HighScore Plus) is the commercial powder diffraction analysis software from PANalytical. It has been in constant development over the last 13 years and has evolved into a very complete and mature product. In this paper, we present a brief overview of the suite focusing on the latest additions and its user-friendliness. The introduction briefly touches some basic ideas behind HighScore and the Plus option.
Journal Article
Study on quantitative Rietveld analysis of XRD patterns of different sizes of bismuth ferrite
Bismuth ferrite (BiFeO
3
or BFO), is an extremely promising multiferroic material having broad range of applications. In the present study, we investigated the optimization of annealing temperature for the preparation of pure phase bismuth ferrite using quantitative Rietveld analysis of XRD patterns. The rhombohedral structure was confirmed by X-ray diffraction with
R3c
space group as a primary phase (pure BFO) along with a cubic secondary phase (Bi
25
FeO
40
) having space group
I23
. The quantitative analysis of refine data shows the decrease in the values of fitting parameters in case of double refinement and hence convergence towards the best fitting. Also, with the increase in annealing temperature, very nominal decrease in phase percentage of secondary phase was observed. At annealing temperature of 780 °C, the intensity of (110) planes suddenly becomes more in comparison to (104) planes. The average crystallite size of samples was calculated using Scherrer formula, W–H plot method, and Rietveld method, and lattice strain was derived from the W–H plot method. Overall, the crystallite size increases with the increase in annealing temperature. It has been also observed that the strain, lattice parameters, unit cell volume, and effective bond lengths decrease with the increase in annealing temperature, but no significant change was observed in bond angles with the variation in annealing temperature.
Journal Article
Crystal structure and magnetic properties study on barium hexaferrite of different average crystallite size
Barium hexaferrite (BHF) is a promising material for technological applications. Hence, the large production of BHF for industrial application needs attention. Therefore, the effect of annealing temperature on the crystal structure, morphology, and magnetic properties of barium hexaferrite has been explored in this article. The BaFe
12
O
19
(BHF) was prepared by the sol–gel method and annealed at different temperatures (800 °C, 900 °C, 1000 °C, and 1100 °C). The crystal structure of BHF is investigated by the Rietveld refinement of XRD patterns using Fullprof suit software. Bond lengths and bond angles have been calculated using the Rietveld refined crystal structure parameters. The FESEM micrograph reveals the cylindrical shape of BHF particles for the samples annealed above 900 °C. Large average grain size has been observed for 1100 °C annealed BHF sample. The average crystallite size (obtained from XRD analysis) and particle size (obtained from FESEM) increase with an increase in annealing temperature of BHF. It is observed that the magnetic properties of BHF depend on bond angles and bond lengths between Fe and O atoms at different crystallographic sites. The saturation magnetization and coercivity are found to increase with the increase in average crystallite or particle size, but the variation is very small.
Journal Article
Low-Cost Hydroxyapatite Powders from Tilapia Fish
Synthetic hydroxyapatite {HAp, Ca
10
(PO
4
)
6
(OH)
2
} is a bioactive and biocompatible material widely used in healthcare for bone implants and grafts, due to its chemical and structural similarity with biological hydroxyapatite present in bone tissues. In this work, HAp was processed by calcination of tilapia fish bones from fish reared in net tanks and slaughtered at the age of 360 days. The bones were cleaned and dried, calcined at 900°C for 8 h and submitted to high energy milling for 8 h, to produce HAp powder. The thermogravimetric analysis and differential thermal analysis (TGA-DTA), dynamic light scattering (DLS), x-ray diffraction (XRD), Rietveld refinement, Fourier-transform infrared spectroscopy (FTIR) with attenuated total reflection (ATR), Raman spectroscopy and scanning electron microscopy (SEM), were techniques used to characterize the material produced. The results indicate that the methodology employed is effective for the production of nanostructured HAp powder, with particle size ranging from 600 nm to 1200 nm and grain size between 0.25 and 1.1 µm (evaluated by SEM in one piece of calcined bone). TGA-DTA analysis indicates complete removal of organic components at temperatures above 600°C. XRD analysis and refinement by the Rietveld method indicated the presence of a single crystalline phase, HAp, with a Ca/P ratio of 1.66. The results obtained by Raman spectroscopy and FTIR-ATR show the presence of characteristic vibrational bands of HAp. In conclusion, the results of this work showed that the methodology used allowed the production of a natural and crystalline hydroxyapatite, with a Ca/P molar ratio of 1.66, with potential for use in bone reconstruction.
Journal Article
Dependence of structural/morphological and magnetic properties of LaCoO3 nanoparticles prepared by citrate nitrate auto combustion
Perovskite LaCoO
3
nanopowders were synthesized via solution auto-combustion chemical route, using lanthanum and cobalt nitrates as oxidants and citric acid as fuel. Qualitative and Quantitative phase analysis performed by Rietveld refinements indicated the presence of pure single LaCoO
3
phase. From fit parameters, goodness of fit “S” parameter (close to 1) and the difference between the experimental and theoretical XRD patterns. FTIR spectra showed two characteristics bands at 408 and 589 cm
−1
characteristics of metal oxygen bands vibration, thus confirming the formation of LaCoO
3
phase, whereas the strong absorption band at 589 cm
−1
was assigned to Co–O stretching vibration and O–Co–O deformation modes of LaCoO
3
compound. SEM micrographs clearly revealed quite spherical particles with a mean size in the range 139–178 nm and high tendency to clustering, meanwhile EDAX analysis confirmed the corresponding chemical composition with homogeneous distribution of the constituent elements. A weak paramagnetic order is observed irrespective of
F
/
O
ratio, with slight increase of the effective magnetic moment with
F
/
O
ratio; 2.72–2.93
μ
B
, due to the presence of more high spin states.
Journal Article