Le Bail Research Articles

A proposal for bauxite quality control using the combined Rietveld - Le Bail - Internal Standard PXRD method – Part 2: Application to a gibbsitic bauxite from the Paragominas region, northern Brazil

In the bauxite industry – exploration, beneficiation and refining – two main chemical parameters are used for quality control: available alumina (AvAl2O3) and reactive silica (RxSiO2) content. Both are determined using a wet chemistry procedure that simulates the Bayer process at laboratory scale. For gibbsitic bauxites, the subject of this study, the available alumina is associated with the ore mineral gibbsite, and the reactive silica is associated with the deleterious mineral kaolinite. A significant innovation for this industry would be to characterize bauxite ores using mineralogical parameters, i.e., the wt% of gibbsite and wt% of kaolinite via Powder X-ray Diffraction Analysis (PXRD), which has been employed elsewhere but has been time-consuming and imprecise. A recent proposal for quantification of the main mineral components of bauxite ores for quality control in bauxite mining was developed by Paz et al. (2018) using the combined Rietveld - Le Bail - Internal Standard PXRD method. In this work, the method is tested using a Brazilian bauxite ore from the Paragominas region (Pará state, northern Brazil), and the results are evaluated against those from traditional wet chemistry (AvAl2O3 and RxSiO2). The study concluded that the PXRD method was able to produce results that were directly comparable with those from tradition chemical methods, and with the advantage of requiring only a single analytical instrument.

Synthesis, theoretical and experimental characterisation of thin film Cu2Sn1-xGexS3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto-electronic properties. Seven single phase Cu2Sn1-xGexS3 films are prepared from x = 0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density-functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2SnS3 and Cu2GeS3. For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x = 0 to x = 1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 eV with increasing Ge. The net acceptor density of all films is around 1018 cm−3. These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structure.

X-RAY Diffraction and Fourier Transform Infrared Study of Ca-Mg-Al Hydrotalcite from Artificial Brine Water with Synthesis Hydrothermal Treatments

Synthesis of various hydrothermal treatments for synthesis Ca-Mg-Al hydrotalcite from artificial brine water had been performed. The hydrothermal treatment has four variations with a temperature at 180 °C into Teflon lined stainless steel for 18 hours. The XRD result of the synthesis materials after various hydrothermal treatments has hydrotalcite phase and CaCO3. Therefore a preparation method might not discover a mixture of Ca and Al cations uniformly, and then a number of Ca cation agglomerated and enabled evidence that the radius of Ca2+ was larger than Mg2+. Le Bail refinement of the value of reliability index parameter especially X2 values has concern limitation value of reliability index. Lattice parameter a and c have a value of around 22 and 3 Å, respectively. Ca-Mg-Al hydrotalcite possesses crystallite size lower than Mg-Al hydrotalcite commercial. Infrared spectra has found hydroxyl band at region 3474.91 and 3072.74 cm-1, carbonate band at region 1365.66; 1491.04; 857.40; and 685.72 cm-1, and metal band at region 447.50; 553.59; 772.52 cm-1; and 975.06 cm−1.

TOPAS and TOPAS-Academic: an optimization program integrating computer algebra and crystallographic objects written in C++

TOPAS and its academic variant TOPAS-Academic are nonlinear least-squares optimization programs written in the C++ programming language. This paper describes their functionality and architecture. The latter is of benefit to developers seeking to reduce development time. TOPAS allows linear and nonlinear constraints through the use of computer algebra, with parameter dependencies, required for parameter derivatives, automatically determined. In addition, the objective function can include restraints and penalties, which again are defined using computer algebra. Of importance is a conjugate gradient solution routine with bounding constraints which guide refinements to convergence. Much of the functionality of TOPAS is achieved through the use of generic functionality; for example, flexible peak-shape generation allows neutron time-of-flight (TOF) peak shapes to be described using generic functions. The kernel of TOPAS can be run from the command line for batch mode operation or from a closely integrated graphical user interface. The functionality of TOPAS includes peak fitting, Pawley and Le Bail refinement, Rietveld refinement, single-crystal refinement, pair distribution function refinement, magnetic structures, constant wavelength neutron refinement, TOF refinement, stacking-fault analysis, Laue refinement, indexing, charge flipping, and structure solution through simulated annealing.

A proposal for bauxite quality control using the combined Rietveld – Le Bail – Internal Standard PXRD Method – Part 1: hkl model developed for kaolinite

In the bauxite industry – exploration, beneficiation and refinery – two main chemical parameters are used for the quality control: available alumina (AvAl2O3) and reactive silica (RxSiO2). Both are determined using a procedure that simulates the Bayer process at the laboratory scale. For gibbsitic bauxites, the subject of this study, the available alumina is associated with gibbsite, and the reactive silica is associated with kaolinite. Significant quantities of kaolinite increase the operational costs because under the conventional conditions of the Bayer process, kaolinite reacts with NaOH (leaching agent) to form a sodalite-type desilication product, which results in irreversible NaOH losses. In Northern Brazil (Pará State), where the world's largest metallurgical alumina refinery (Hydro Alunorte) is located, the loss of caustic soda due to sodalite formation has been reported to be much higher than the estimated value based on the amount of reactive silica that has been measured by quality control. However, the estimated experimental errors are usually within the deviations expected by the certified values, and thus has prevented obtaining a clear answer to this problem. A great innovation for this industry would be to make this control by mineralogical parameters, i.e., the wt% of gibbsite and wt% of kaolinite via Powder X-ray Diffraction Analysis (PXRD). Even with the fast increase in the last years of studies related to mineralogical phase quantification using PXRD analysis, there are still some challenges related to bauxite quantification. For instance, the lack of crystal structure information related to kaolinite, which has been underestimated when trying to apply the Rietveld method with available Crystallographic Information File (CIF). In this work, a combination of the Rietveld, Le Bail and Internal standard methods was tested, and the results were very promising for a Brazilian gibbsitic bauxite. This combination not only improved the quality of gibbsite and kaolinite quantification, but also decreased computer processing time, making it a more convenient and fast procedure, both requirements for an industrial control method.

SYNTHESIS AND CHARACTERIZATION OF CERAMIC METAL Ni-YSZ PREPARED FROM LOCAL ZIRCON SAND AT VARIOUS Ni:YSZ COMPOSITION

<p>This research synthesized a cermet Ni-YSZ, in which the YSZ (yttria stabilized-zirconia) was synthesized from the local zircon sand, ZrSiO<sub>4</sub>, as a side product of tin mining plant in Bangka island, Indonesia. The synthesized YSZ in this research is zirconia, ZrO<sub>2</sub> doped by 8 % mol of yttrium dioxide. The synthesis used solid state reaction method and the result was characterized its crystal structure and its cell parameters by XRD analysis equipped with Le Bail refinement, surface morphology analysis, and an impedance analysis to understand its ionic conductivity. The cermet Ni-YSZ was synthesized at a various composition of Ni:YSZ i.e., 20:80, 30:70, and 40:60 (b/b). The analysis shows that Ni-YSZ is in two phases of Ni and YSZ without any presence of a third phase. It indicates that there was no solid state reaction between Ni and YSZ during synthesis. In this Ni-YSZ cermet, the Ni phase in a cubic structure, and the YSZ is also in a cubic structure. Morphological study shows that the addition of Ni to YSZ allows the morphology to become more roughness with larger grain size. This research found that the Ni-YSZ 20:80 has highest ionic conductivity.</p>

Polypyrrole@α-Al2O3 and polypyrrole@CeO2 core-shell hybrid nanocomposites

PPy@ α-Al2O3 and PPy@CeO2 nanocomposites were synthesized free of acids by in situ polymerization and characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and DC electrical conductivity measurements. X-ray diffraction pattern of Polypyrrole revealed a semi crystalline structure. The Le Bail method was performed using the X-ray diffraction pattern of polypyrrole and allowed the proposition of the unit cell parameters (P21/c, a = 9.0173 Å, b = 7.1641 Å, c = 6.4184 Å, α = 90°, β = 117.7°, γ = 90°), which is composed by a dimeric molecule disposed along the [001] direction. A cauliflower-like morphology was observed in polypyrrole, which consists of incomplete spheres forming nanoparticle clusters. Core-shell morphology was verified in the nanocomposites consisting of a thin layer of polymer reinforcement disposed over the metal oxides matrices. Differential scanning calorimetry measurements allowed verifying the hydrophobic behavior of the inorganic phase, promoting the repulsion of the internal water molecules out from the polymer phase. Then the initial decomposition temperature of the nanocomposites has become smaller. The polypyrrole electrical conductivity is lower than the nanocomposites and may be related with the absence of hydration water in nanocomposites and also to the surface conductivity due to the thin polymer layer. PPy@ α-Al2O3 and PPy@CeO2 nanocomposites presented DC electrical conductivity 80% higher when compared to the as-synthesized polypyrrole. Thus, the aim of this paper was to characterize structural and morphologically the pure polypyrrole as well as the PPy@α-Al2O3 and PPy@CeO2 nanocomposites and correlate these results with the DC electrical conductivity measurements.

Ca6.5Pb1.5ZnBi(VO4)7, a novel whitlockite-type vanadate: crystal structure refinement and properties characterization

Novel compounds Ca8−xPbxZnBi(VO4)7(0 ≤x≤ 1.5) solid solution with the whitlockite-type structure were synthesized by a standard solid-state method. The unit-cell parameters were determined by X-ray powder diffraction and using Le Bail decomposition. The crystal structural of Ca6.5Pb1.5ZnBi(VO4)7was refined by Rietveld method. It is found that Pb2+cations occupy a half of theM3 site, whereas theM1 andM2 sites are predominantly occupied by calcium with admixture of Bi3+cations. TheM5 site is fully occupied by Zn2+cations. TheM4 site in the structure of studied sample remains vacant and does not participate in the cations arrangement. Optical second harmonic generation demonstrates high non-linear optical activity. Dielectric investigations confirm polar space groupR3c. Changes in the non-linear optical and ferroelectric parameters are matched with lead and zinc cation distribution over the sites of the whitlockite-type structure.

Synthesis, characterization of new Bi3+ containing apatites: Formation of red emitting phosphors by Eu3+ incorporation

Single phase phosphosilicates, Ca7Bi3(PO4)5(SiO4)O2, Ca6Bi4(PO4)3(SiO4)3OF and Ca8Bi2(PO4)4(SiO4)2F2 have been synthesized and characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The charge balanced stoichiometries in the present investigation derived out of cationic and anionic variations lead to the formation of apatites with high Bi3+ content. PXRD Le Bail refinements were carried out in space group P63 (No. 173) instead of P63/m. Eu3+ substitution has been carried out to append luminescence property to the lattice. Investigation of Eu3+ luminescence revealed emission features consistent with its presence in the lower symmetry (6c) and the higher symmetry (2b) sites. The CIE coordinates of the Eu3+ doped (5mol%) apatite samples resulted in red emission.

Complex permittivity, permeability, magnetic and microwave absorbing properties of Bi3+ substituted U-type hexaferrite

Bi3+ substituted polycrystalline samples of Barium U-type hexaferrite, (Ba1-3xBi2x)4Co2Fe36O60 (0.05≤x≤0.15, in steps of 0.05), were prepared through solid state reaction route. The effect of Bi3+ substitution on the structural properties of Barium hexaferrrite samples was investigated through X-ray diffraction (XRD) studies. Le Bail refinement of XRD patterns confirmed the formation of desired U-type hexaferrite phase in all the prepared samples. The room temperature magnetic hysteresis (M-H) loops shows that the saturation magnetization (Ms) initially increases to 63.5emu/g for x=0.10 sample and then reduces to 55.3emu/g for x=0.15 sample. Nicholson-Ross-Weir (NRW) algorithm has been employed to calculate the complex permittivity (ε∗=ε′-iε″) and permeability (μ∗=μ′-iμ″) spectra in 2–18GHz frequency range. The reflection loss (RL) was calculated from the complex permittivity (ε∗) and permeability (μ∗) spectra using transmission line theory. The minimum reflection loss (RLmin) of −35.5dB (MW absorption of 99.97%) was obtained for (Ba0.55Bi0.30)4Co2Fe36O60 sample at 10.6GHzMW frequency. Moreover, the broad frequency bandwidth of 8.4GHz (over X- and Ku-band), for the reflection loss of −10dB (90% MW absorption) or less, was attained in (Ba0.55Bi0.30)4Co2Fe36O60 sample.

A new method for production of glass-Ln2Ti2O7 pyrochlore (Ln = Gd, Tb, Er, Yb)

Glass-Ln2Ti2O7 pyrochlore (Ln=Gd, Tb, Er, Yb) was fabricated by sintering the pelletized mixture of glass precursor and Ln-Ti composite at 1200°C. The phase pure pyrochlore was in-situ crystallized in the amorphous glass matrix. The Ln-Ti composite was prepared by a simple soft chemistry route in an aqueous solution to ensure the homogeneity of the product. Thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy techniques were employed to investigate the glass-Ln2Ti2O7 pyrochlore structure formation. The cell parameters for the pyrochlore structures by Le Bail fitting are in good agreement with the published data. The presence of the melting glass matrix facilitates the pyrochlore formation, with particle sizes in the range of 1–3μm. This new aqueous synthetic method provides a simple pathway to produce glass-Ln2Ti2O7 pyrochlore without using organic solvent and/or milling procedures, making it an attractive potential method for scale-up production.

Fermi-liquid behavior of binary intermetallic compounds Y3M (M = Co, Ni, Rh, Pd, Ir, Pt)

A series of polycrystalline samples of Y3M (M = Co, Ni, Rh, Pd, Ir, Pt), intermetallic binary compounds were synthesized by the arc-melting method. Powder x-ray diffraction (pXRD) confirmed the orthorhombic cementite-type crystal structure and allowed for the estimation of the lattice parameters. Physical properties were investigated by means of electrical resistivity and heat capacity measurements between 1.9 K and 300 K. All tested compounds show metallic-like behaviour with RRR values ranging from 1.3 to 8.3, and power-law temperature dependence of resistivity was observed, with . No superconductivity was detected above 1.9 K. The Debye temperature, estimated from the low temperature heat capacity fit, ranged from 180 K (Y3Pt) to 222 K (Y3Co). The highest value of the Sommerfeld coefficient γ was found for Y3Pd (19.5 mJ mol−1 K−2). The pXRD pattern of Y3Rh indicated the presence of Y5Rh2, a previously unreported Pd5B2-type phase, whose unit cell parameters were refined using the LeBail method. Density functional theory calculations were performed and theoretical results revealed strong enhancement of the measured electronic specific heat, which was 30%–100% larger than computed. Quadratic temperature dependence of resistivity and enhanced electronic specific heat indicated a Fermi-liquid behavior of electrons in these materials.

Crystal structure refinement of new vanadates Ca8−xPbxCdBi(VO4)7

New Ca8−xPbxCdBi(VO4)7with the whitlockite-type structure were prepared by a standard solid-state method in air. Le Bail decomposition was used to determine unit-cell parameters. Structural refining was carried out by Rietveld's method. It is found that Bi3+cations located partially inM1 andM2 sites along with calcium, whileM3 site is settled in half by Pb2+-ions. Second-harmonic generation demonstrate highest non-linear optical activity and along with dielectric investigations indicate polar space groupR3c.

Ferroelectric properties and structural refinement of whitlockite-type phosphate Ca8.5Pb0.5Ho(PO4)7

The system of phosphates Ca9−xPbxHo(PO4)7were obtained by solid-state reaction and were found to be isotypic with whitlockite-typeβ-Ca3(PO4)2(polar space groupR3c). The crystal structure encloses five crystallographic sitesM1–M5 different in size and oxygen coordination. The unit-cell parameters were determinate using Le Bail decomposition. Rietveld method structural refining showed that Ho3+ions are located statistically with calcium inM1 andM2 sites, while Pb2+-ions are located in theM3 site. Examination of optical second-harmonic generation evidences non-linear optical activity and confirms polar space groupR3c. Structural mechanisms and dielectric features of phase transitions are strongly influenced by the exact distributions of atoms over the crystallographic sites.

A novel molten-salt electrochemical cell for investigatingthe reduction of uranium dioxide to uranium metal by lithium using in situ synchrotron radiation.

A novel electrochemical cell has been designed and built to allow for in situ energy-dispersive X-ray diffraction measurements to be made during reduction of UO2 to U metal in LiCl-KCl at 500°C. The electrochemical cell contains a recessed well at the bottom of the cell into which the working electrode sits, reducing the beam path for the X-rays through the molten-salt and maximizing the signal-to-noise ratio from the sample. Lithium metal was electrodeposited onto the UO2 working electrode by exposing the working electrode to more negative potentials than the Li deposition potential of the LiCl-KCl eutectic electrolyte. The Li metal acts as a reducing agent for the chemical reduction of UO2 to U, which appears to proceed to completion. All phases were fitted using Le Bail refinement. The cell is expected to be widely applicable to many studies involving molten-salt systems.

Synthesis of the supported catalysts by co-impregnation and sequential impregnation methods

The non-sulfide catalysts Co-Mo/USY were prepared with three different methods, i.e. co-impregnation and two sequential impregnation procedures. The phases of the synthesized materials and their composition were characterized with X-ray diffraction. Furthermore, the X-ray diffraction patterns were analyzed using Le Bail methods with Rietica software. Finally, an overview of the substitution effect of cobalt and molybdenum on the metal content and acidity of the catalyst were also investigated.

Electrosynthesis of Metal-Organic Frameworks (MOFs)Based on Nickel(II) and Benzene 1,3,5-Tri Carboxylic Acid (H3BTC): An Optimization Reaction Condition

Electrosynthesis of metal-organic frameworks based on nickel(II) and benzen 1,3,5-tricarboxylic acid (H3BTC) to form [Ni3(BTC)2] has been conducted. This study aims to determine the optimum electro-synthetic conditions of [Ni3(BTC)2] by varying the solvents, electrolytes, as well as the voltages. The optimum condition was determined based on the percent yield of the product which upon washing and drying at room temperature showed pale green precipitate. The materialhas high crystallinityaccording to XRD analysis with the main peak observed at 2θ 19° and 28° and appropriate with [Ni3(BTC)2] pattern (CCDC No. 1274034). The refinement results using Le Bail methods revealed the Rp and Rwp values are 3.29% and 3.47%, respectively. The coordination between nickel(II) and carboxylate moeties of the linker has been characterized using FTIR and showed significant shift from 1723 cm-1 to 1608 cm-1. The compound has thermal stability up to 400 °C according to TG/DTA analysis. The SEM analysis confirmed that compound has morphology nanoplates shape with a thickness of 75 ± 0.023 nm. Another interesting feature of the obtained material is the occupancy of the reversible frameworks, which proved after methanol absorption. The optimum condition of the electro-synthesis of [Ni3(BTC)2] achieved in the methanol with TBATFB (0.1 M) as electrolyte, and the voltage of 15 V at room temperature with a yield of 99.99%.

X-ray Diffraction Analysis on Post Treatment of Ca-Mg-Al-Layered Double Hydroxide Slurry

This research objectives to study post treatment on Ca-Mg-Al-Layered Double Hydroxide (Ca-Mg-Al-LDH) slurry which was prepared from brine water by cooling treatment. The cooling rate was varied from 1 to 3 °C/min by using stirring and without stirring, and the cooling time was done at 0, 30 minutes and 24 hours. The quantitative X-ray diffraction (QXRD) was employed on Ca-Mg-Al-LDH using Le Bail refinement method. The refinement results found another Mg-Al-LDH and Ca-Al-LDH phases, such as Mg(OH)2, Al(OH)3 and CaCO3. The highest phase composition on material Ca-Mg-Al-LDH using Le Bail refinement was showed by Al(OH)3.

Crystal structure of Al5O3N3(15R)

Having synthesised an AlON-bonded ceramic corundum material, Al5O3N3(15R) polytype coexisting withα-Al2O3was identified. The sample was prepared from an alumina-rich mixture of Al2O3and AlN substrates and fired at 1650 °C in a nitrogen atmosphere. Using the X-ray external standard quantitative method, one of the reaction products,α-Al2O3, was quantified. From the remaining substrates the stoichiometric composition of the second phase was calculated. The applied method of crystal structure determination consisted of three stages. In the first stage, the Le Bail method of X-ray pattern decomposition was used for the extraction of Al5O3N3(15R) diffraction lines from a two-phase diffractogram. The space group and unit-cell dimensions from the isostructural SiAl4O2N4SiAlON phase, producing the same X-ray pattern, were used as input data. Next, the direct structure determination in real space was applied for initial structural model derivation, which was followed by Rietveld refinement. The solved crystal structure of Al5O3N3(15R), except the stacking sequence, proved to be closely related to the structure of Al7O3N5(21R) polytype. The Al5O3N3(15R) is trigonal with space groupR-3m, unit-cell dimensionsa0= 3.0128 Å,c0= 41.8544 Å, and volumeV= 329.00 Å3. The model of Al5O3N3(15R) polytype structure has positional disordering in one of three (6c) Al sites, which leads to stacking faults in six tetrahedral layers. Every third tetrahedron from LR3and LR4, LR8and LR9, LR13andLR14layers is rotated by 180°.

A strategy to achieve efficient dual-mode luminescence in lanthanide-based magnetic hybrid nanostructure and its demonstration for the detection of latent fingerprints

We have synthesized a novel inorganic-organic hybrid nanostructure (IOHN) composed of fluoride nanophosphor (NaGd0.78Er0.02Yb0.2F4) and β-diketones complex (Eu(DBM)3Phen). The Le Bail fitting of X-ray diffraction data suggests that the nanophoshor crystallizes in a hexagonal structure (P63/m space group). The TEM studies reveal that the nanophosphor and the IOHN both have average particle size of 6–8nm. The Eu(DBM)3Phen and NaGd0.78Er0.02Yb0.2F4 show characteristic down-shifting (DS) and up-conversion (UC) emission, under UV and NIR excitation, respectively. The IOHN comprises an excellent dual-mode optical features (DS and UC) of both the phases. Energy transfer from Er3+ (doped in inorganic phase) to Eu3+ (coordinated in organic phase) clearly demonstrates for a viable coupling between both the phases. IOHN material was found to be unique for the visualization of latent fingermarks. Because of ultrafine particle size the surface to volume ratio is relatively higher which improves the attachment of particles with the fingermarks. On the other hand, the strong paramagnetic property helps to remove excess material with magnetic wand easily. These properties provide an opportunity to probe even very weak fingermarks. Notwithstanding this, the dual-mode emission is useful for the visualization of latent fingermarks on multi-color surfaces as well.