X-ray Powder Diffractograms Research Articles

Preparation and characterization of bulk and nano particles of La 2Zr 2O 7 and Nd 2Zr 2O 7 by sol–gel method

Rare earth zirconium oxides of compositions La 2Zr 2O 7 and Nd 2Zr 2O 7 were prepared by sol–gel method. They were characterized by IR spectra and powder X-ray diffractograms. Nano-sized and bulk particles of La 2Zr 2O 7 and Nd 2Zr 2O 7 were obtained at 500 and above 800 °C, respectively. The particle size was found to increase with increase in the sintering temperature.

Study of hydrogenabsorption by ZrMnFe1-xCox (x = 0.2, 0.4, 0.5 and0.6) alloys

Hydrogen absorption isotherms have been obtained for the C14-type hexagonal-structured alloys ZrMnFe1-xCox (x = 0.2, 0.4, 0.5 and 0.6) in the temperature and pressure ranges30⩽T/ °C⩽100 and 0.1⩽P/bar⩽40 using a high-pressure unit based on the pressurereduction method. The powder x-ray diffractograms show that the lattice constants and the unit-cell volume for ZrMnFe1-xCox (x = 0.2, 0.4, 0.5 and 0.6) alloys decrease withincrease of xCo. The hydrogen absorption isothermsshow the presence of a single plateau region (α + β)in the temperature and pressure ranges studied and it is foundthat the plateau pressure and plateau slope at any given temperature increase with increase of the xCo-content,except in the case of ZrMnFe0.5Co0.5 wherein thehydrogen absorption plateau slope is found to be smaller due tothe ordering of the alloy. The dependence of the thermodynamics of the dissolved hydrogen in ZrMnFe1-xCox-H (x = 0.2, 0.4, 0.5 and 0.6) systems in thetemperature range 30-50 °C on the hydrogenconcentration shows the different phase regions (α,α + β, β) seen in the hydrogen absorptionisotherms. The powder x-ray diffractograms of the hydrides of ZrMnFe0.8Co0.2 show that the formation of different phasesis manifested in the isotherms without there being any structural change and theinclusion of hydrogen in the interstitial sites expands theunit-cell volume by about 21.Comparison of the hydrogenabsorption kinetics of ZrMnFe1-xCox with that of the corresponding Ni alloys in similar experimental conditions showsthat the kinetics is slow in the ZrMnFe1-xCoxalloys.

Quantitative phase analysis of PBSCCO 2223 precursor powders—an XRD/Rietveld refinement study

We analysed x-ray powder diffraction data of spray pyrolytic precursor powders for the oxide-powder-in-tube (OPIT) technology by means of the Rietveld method. For calcinations in air we find a typical phase composition of 2212, 14-24, 11, CP and 3321 at 800 °C (13 h). At 820 °C 2212 is in equilibrium with 14-24 and CP after 48 h calcination. In 8% O2 at 800 °C 2212 exists together with 14-24, 21, CP and CuO, in 99.999% N2 at 760 °C the stable phase assemblage consists of 2212, 21 and CuO. The highest amount of 2212 can be found in the powder calcined at 8% O2 (72.4 wt%) compared with 68.9 wt% for the powder calcined in 21% O2 and 69.3 wt% for the powder calcined in flowing N2. A first trace of 2223 can be observed in powders calcined in air at temperatures of 838 °C and 842 °C. The crystallographic features of the 2212 phase correlate with the calcination atmosphere: under reducing atmospheres the satellite reflections of the x-ray powder diffractogram disappear and the orthorhombic lattice distortion z increases due to Pb2+-incorporation into 2212. With increasing O-content the c lattice parameter becomes significantly shorter in samples calcined in oxidizing atmospheres. It is possible to infer a cationic ratio of Sr:(Sr + Ca) ≈ 0.12 for the 11 phase and Ca:(Ca + Sr + Bi) ≈ 0.57 for 14-24 in precursors from lattice parameter data.

Moist heat treatment on physicochemical change of chitosan salt films

Chitosan salt films were prepared by casting method using acetic, citric, formic, glycolic, lactic, malic and propionic acids as solubilizers. The films were then exposed to moist heat at 60 °C and 75% relative humidity for several time intervals. The influence of moist heat treatment on their physicochemical characteristics was investigated. All freshly prepared films were soluble in deionized water and HCl buffer solution. Chitosan citrate film also dissolved in phosphate buffer solution. After treatment, the percentage of water sorption and dissolution of chitosan films in three media were gradually decreased. Longer alkyl group and less carboxyl and hydroxyl groups in the molecule of organic acid resulted in lower percentage of water sorption and dissolution of treated films. The FT-IR spectra revealed that there was amide formation between chitosan and organic acids after treatment especially in chitosan acetate and propionate films. However, the absorption peaks of ammonium ['NH 3 +] and free carboxylate groups were still remained in treated chitosan citrate and malate films. Change in the degree of crystallinity from powder X-ray diffractogram and thermal characteristic from DSC thermogram were also related to the water sorption and dissolution of films.

Hydrogen storage properties of ZrMnFe1−xNix (x=0.2, 0.4, 0.5 and 0.6) alloys

Hydrogen absorption pressure–composition isotherms have been investigated for the ZrMnFe1−xNix (x=0.2, 0.4, 0.5 and 0.6) alloys having the C14 type hexagonal structure in the temperature and pressure ranges 30≤T≤100°C and 0.1≤P≤40 bar using a pressure reduction method. Powder X-ray diffractograms show that the lattice constants and the unit cell volume of ZrMnFe1−xNix (x=0.2, 0.4, 0.5 and 0.6) alloys decrease with increasing Ni content. The P–C isotherms show the presence of a single plateau region (α+β) in the temperature and pressure ranges studied and it was found that the plateau pressure and plateau slope at any given temperature increase with increasing Ni content except for ZrMnFe0.5Ni0.5, where the plateau slope is found to be small due to the atomic ordering in the alloy due to presence of Fe and Ni in a 1:1 molar ratio. The desorption isotherms of ZrMnFe0.5Ni0.5 at 30 and 50°C show that the hysteresis is very small. The dependence of the thermodynamics of dissolved hydrogen in ZrMnFe1−xNix–H (x=0.2, 0.4, 0.5 and 0.6) systems in the temperature range 30–50°C on the hydrogen concentration have shown the existence of α, α+β and β phase regions as seen in the isotherms. The powder X-ray diffractograms of the alloy hydrides show that these alloys do not undergo a structural transformation upon hydrogenation. In ZrMnFe0.5Ni0.5, the kinetics of hydrogen absorption during activation and after several cycles at 30°C have been studied and compared.

XRD Rietveld-analysis of PBSCCO-2223 precursor powders used in OPIT processing: Pb/sup 2+/ solubility in 2212

The phase assemblage in PBSCCO precursor powders for 2223-OPIT production has been investigated in a quantitative way with Rietveld analysis of x-ray powder diffractograms. The investigated precursors were made by spray pyrolysis of solutions of the appropriate bulk chemical composition of Pb/sub 0.33/Bi/sub 1.80/Sr/sub 1.87/Ca/sub 2.00/Cu/sub 3.00/O/sub 10 /+/sub /spl delta//, and subsequent calcination to remove volatile elements and to form a suitable precursor phase assemblage at temperatures between 800/spl deg/C and 820/spl deg/C, in air or under reducing conditions. The influence of temperature and atmosphere on the powder quality was investigated with regard to different minor phases, and the Pb-content of the 2212-phase.

Self-assembly of [Cu(CN) 4] 3− ions with cationic {Me 3Sn} + or {Me 2Sn(CH 2) 3SnMe 2} 2+ fragments in the presence of a nBu 4N + template

As described earlier, solutions of n Bu 4NCl and K 3[Cu(CN) 4] react with Et 3SnCl to zeolite-like [(Bu 4N)(Et 3Sn) 2Cu(CN) 4] ( 1), but with Me 3SnCl exclusively to [(Bu 4N)(Me 3Sn)Cu 2(CN) 4] ( 2), the crystal structure of which is reported here for the first time. The n Bu 4N + guest ions of 2 are accommodated between planar, negatively charged layers, wherein three-coordinated Cu(I) ions are interlinked by CN and CN·SnMe 3·NC bridges (2:1). The slightly modified new homologue of 2: [( n Bu 4N){Me 2Sn(CH 2) 3SnMe 2} 0.5Cu 2(CN) 4] ( 3), displays an almost identical powder X-ray diffractogram as 2 and, moreover, surprisingly similar solid-state NMR spectra for the nuclei 13C, 15N and 119Sn. A three-dimensional host framework is postulated to encapsulate the n Bu 4N + guest of 3, the Sn atoms of adjacent layers being therein tied pair-wise together by trimethylene tethers, (CH 2) 3. For further comparison, the solid-state NMR data of the new coordination polymer [{Me 2Sn(CH 2) 3SnMe 2} 0.5Au(CN) 2] ( 5) are also presented.

About Binary and Ternary Alkaline Earth Metal Nitrides

Binary and ternary alkaline earth metal nitrides compounds have been synthesized and characterized by the means of X-ray structure analysis. By the reaction of the alkaline earth metals Be, Mg, and Ca with dry nitrogen, we obtained crystalline material of Be3N2 (1), Mg3N2 (2), and Ca3N2 (3), respectively. For these three compounds we could confirm the cubic anti bixbyite structure (Ia3 (#206); 1: a = 814.92(1) pm; 2: 997.26(6) pm and 3: a = 1147.86(2) pm). By reacting 1 : 2 : 1 mixtures of Ae (Ae = Ca, Sr) : Mg : NaN3 we synthesized the ternary nitrides CaMg2N2 (4) and SrMg2N2 (5). We confirmed the structural data obtained by Rietveld-analysis of X-ray powder diffraction data for 4 and found 5 to be isotypic (anti-C–M2O3 structure, trigonal, P 3ml (#164); 4: a = 354.77(5) pm, c = 609.60(12) pm; 4: a = 362.20(5), c = 635.90(13) pm). The indexing of the powder diffractogram of “Ca3Mg3N4” and refining the lattice parameters (hexagonal, a = 352.9(2) and c = 607.5(5) pm) suggest its identity with 4. The black “low-temperature phase of Ca3N2” has been synthesized and and the X-ray powder diffractogram has been recorded. The reactions of this phase are also described. The yellow “high-temperature phase of Ca3N2” was found to be Ca4N2(CN2).

Hydroformylation of propene and 1-hexene catalysed by a α-zirconium phosphate supported rhodium-phosphine complex

The reaction of the amphiphilic ligand {4-[bis(diethylaminoethyl)aminomethyl]diphenyl}phosphine with α-zirconium phosphate, of intermediate surface area (24 m 2 g −1), provided a phosphine functionalised support in which electrostatic interaction between ammonium groups on the ligand and de-protonated surface hydroxyl groups on the support provided the binding force. The X-ray powder diffractogram of the material showed that the binding lowers the crystallinity of the carrier and that the ligand is not intercalated but bound at the outer surface and at the entrances to the interlamellar space. Reaction of the phosphine functionalised support with Rh(CO) 2(acac) led to CO-phosphine exchange and formation of an immobilised complex of the composition LRh(CO)(acac) (L=surface bound phosphine). When applied as catalyst in continuous gas-phase hydroformylation of propene and in liquid phase hydroformylation of 1-hexene the immobilised complex showed intermediate activity and regioselectivity.

Thermal decomposition and stability in a series of heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X=Cl, Br, I)

Heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X= Cl, Br, I), which have metal-metal bonds, have been prepared in order to study their thermal stabilities as a function of the halogen coordinated to mercury atoms. The characterization of the above complexes was carried out by elemental analysis, IR and NMR spectroscopies. Their thermal behaviour has been investigated and the final product was identified by IR spectroscopy and by X-ray powder diffractogram.

Effect of nanocrystalline alumina on ionic conductivity and phase transition in CsCl

Conductivity, structure and thermodynamic parameters of CsCl in (1− x)CsCl– xAl 2O 3 composites are investigated. As the heterogeneous dopant, highly-dispersed alumina with specific surface area 210 m 2/g is used. Maximum conductivity 9×10 −4 S/cm at 400°C occurs at x=0.6. As x rises, conductivities of bcc and fcc phases tend to level off and at x>0.6 no conductivity drop due to the phase transition occurs. The phase transition enthalpy decreases with x and at x>0.6 no bcc–fcc phase transition is detected by DSC technique. New peaks attributed to fcc-phase with the lattice parameter a=0.694 nm are observed on X-ray powder diffractograms. At high x conductivity enhancement is likely to be due to the presence of the high-temperature fcc phase of CsCl stabilized on CsCl–Al 2O 3 interfaces.

Nanocrystalline and metastable phase formation in vacuum thermal decomposition of calcium carbonate

Well characterised, polycrystalline powders of commercially procured CaCO 3 were thermally decomposed in the vacuum as well as in the flowing gas atmosphere for the purpose of studying solid state transformations. The characterisation of the end product CaO, obtained from the thermal decomposition, revealed contrasting features in the powder X-ray diffractograms. While the flowing gas method, conducted inside a thermogravimetric analyser (TGA), indicated formation of stable microcrystalline calcia, the decomposition under dynamic vacuum revealed formation of metastable-nanocrystalline calcia. The latter study was carried out in an evolved gas analysis-mass spectrometry (EGA-MS) facility. Experiments were also conducted inside the high temperature XRD (HTXRD) machine. The paper attempts to bring out possible mechanisms responsible for formation of these end products with such glaring structural contrast. Non-equilibrium conditions prevalent under dynamic vacuum condition as well as misfit strain energy available from CaCO 3/CaO interface are presumed to be the reason behind such metastable transformations. Kinetic analysis of the transformation revealed prevalence of nucleation and growth phenomena. Corresponding Arrhenius factors were also calculated.

Morfologia e cristalinidade de hidroxicarbonato de zinco obtido via precipitação homogênea: influência dos ânions cloreto e nitrato

The effects of chloride and nitrate anions and their respective concentrations, as well as urea presence, on solid phase morphologies were investigated. Zinc hydroxide carbonate was prepared by aging diluted zinc salt solution in presence of urea at 90oC. Samples were identified by X-ray powder diffractograms showing the characteristic patterns of hydrozincite. The crystallinity was correlated with the concentrations of reagents. Spherulitic-type aggregates and single acicular particles were obtained from diluted chloride and nitrate solutions while porous aggregates of uniform size were formed from solutions with high chloride and urea concentrations.

Phase Assemblage in PBSSCO OPIT High-Temperature Superconductor Precursor Powders - Rietveld Analysis of X-ray Diffractograms

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Deep-freezing of potato starch

Samples of oven-dried, air-dried, and moisturised potato starch (5, 13, and 24% w/ w moisture content, respectively) were frozen in liquid nitrogen. Samples after thawing were studied by means of cross-polarised light beam microscope (CLBM), Fourier Transformation Infrared Spectroscope (FT-IR), powder X-ray diffractometer, and non-contact Atomic Force Microscope (nc-AFM). Rapid deep-freezing followed by thawing produced changes on the granule surface. They were accompanied by internal alteration manifested by FT-IR spectra and powder X-ray diffractograms. The results depended on the water content in the sample. Deep-freezing of moistened starch resulted in increased crystallinity of granules. It had minor effect on the granule aqueous solubility and characteristics of gelation.

Structural and hydrogen solubility studies on ZrMnFe 1− xCo x ( x=0.2, 0.3 and 0.5) alloys

The hydrogen solubility properties in ZrMnFe 1− x Co x ( x=0.2, 0.3 and 0.5) alloys have been studied in the ranges 10⩽P(mbar)⩽1000 and 30⩽ T(C)⩽100 using low pressure unit based on the pressure reduction method. The powder X-ray diffractograms show that the lattice constants and the unit cell volume of C 14 based ZrMnFe 1− x Co x ( x=0.2, 0.3 and 0.5) alloys decrease with increase of Co content. Comparing with the hydrogen solubility properties in ZrMnFe, it has been found that the substitution of Co at Fe site in ZrMnFe decreases the hydrogen solubility ( r=n H/ n f.u.), except in ZrMnFe 0.5Co 0.5. This suggests that in ZrMnFe 0.5Co 0.5, the electronic effects are dominant over the size effects in determining the hydrogen solubility properties due to the charge transfer effects between Fe/Co ligand and hydrogen atom.

Crystalline Solids of Alloy Clusters

AuAg alloy clusters protected with octadecanethiol (ODT) monolayers form crystalline solids whose powder X-ray diffractograms can be indexed to single cubic unit cells. These solids can also be regarded as superlattices of alloy clusters. The bulk Au:Ag ratio is significantly different from the metal salt feed ratio used for the synthesis of the alloy clusters. The surface plasmon resonance band of the alloy clusters shift monotonically with change in composition and only one distinct band is seen in the composition range, indicating that the single metal core containing alloy clusters are not forming. The shifts observed can be linearly related to the compositions. Atomic emission spectroscopy gives similar compositions as determined from absorption spectroscopy. The monolayer coverage determined from thermogravimetry increases with an increase in silver concentration. Thermal stability of the monolayers is comparable to pure Au and Ag clusters and no change in desorption temperature is observed with composition. Both monolayer melting and superstructure melting transitions are seen in the differential scanning calorimetry of the solids. Infrared spectroscopy suggests that the monolayers are essentially solidlike and the conformations are similar to the monolayers on pure Ag clusters. Some of the bands exhibit factor group splitting in the Au-rich composition, which is observed in other compositions upon annealing.

Molecular packing in the new unit cell of poly(p-hydroxybenzoic acid) whisker crystal

A preliminary structure model for the new unit cell (orthorhombic, a=1.487nm;b=0.572nm;c(chainaxis)=1.258nm) of poly(p-hydroxybenzoic acid) whisker crystals was proposed on the basis of energy calculations, assuming the space group to be Pbca as the highest one. First, the torsion angle of phenyl ring and mutual shift of molecular stems along the chain direction were varied, and several models were selected according to the packing energy. Then the models were further optimized by varying other parameters. The most probable model was selected by comparing the simulated powder X-ray diffractograms of the optimized models with the experimental one from literature. According to the calculated X-ray and electron diffraction intensity values of the final model, the model was judged to be reasonable. The final model possesses a molecular conformation similar to those for previous unit cell proposed by other researchers.

Structure analysis of phosphated zirconia catalysts using XRD and nitrogen adsorption methods

Phosphated zirconia catalysts were prepared by impregnating two different precursors (zirconium hydroxide and crystalline ZrO 2) with an aqueous solution of diammonium hydrogen phosphate. X-ray powder diffractograms and nitrogen adsorption isotherms at −196°C on pure and phosphated zirconia catalysts were investigated. The pore volume was calculated from the adsorption branch to explore the modification of porosity for pure and phosphated zirconia. Pore structure analysis shows that phosphated zirconia, resulted from calcination of zirconium hydroxide at low temperature, exhibited high surface area and accessible porosity. Whereas for those calcined at higher temperatures, inaccessible porosity is shown to predominate. Phosphation of crystalline zirconia did not modify either surface area or the porosity, as compared to pure zirconia. The influence of phosphation on the structure of zirconium hydroxide and zirconia during the calcination course was studied.

Thermal decomposition and stability in a series of heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X=Cl, Br, I)

Heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X= Cl, Br, I), which have metal-metal bonds, have been prepared in order to study their thermal stabilities as a function of the halogen coordinated to mercury atoms. The characterization of the above complexes was carried out by elemental analysis, IR and NMR spectroscopies. Their thermal behaviour has been investigated and the final product was identified by IR spectroscopy and by X-ray powder diffractogram.