Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Powder Diffraction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,423 records · Page 79Linked to original sources
PubMed2006

An analytical approach to determine the pore shape and size of MCM-41 materials from X-ray diffraction data.

The pore shape and size of MCM-41 were studied analytically by comparing the observed powder X-ray diffraction intensities with that derived from the MCM-41 crystal structure models, with two different pore shapes, a hexagon and a circle. The powder diffraction patterns from the as-synthesized and the calcined MCM-41 were measured by a synchrotron radiation at SPring-8, Japan. The MCM-41 structure with circular and hexagonal pore shapes explains well for the as-synthesized and the calcined MCM-41 crystals, respectively. The pore size and boundary obtained by this approach agree with those obtained from an N2 gas adsorption measurement combined with the Fourier synthesized density map.

Journal Article↗
PubMed2002

Synthesis of nanoparticles of barium lanthanum hafnium oxide by a modified combustion process.

Barium lanthanum hafnium oxide, a complex perovskite ceramic, has been synthesized as nanoparticles by a modified combustion process for the first time. The Ba, La, and Hf ions required for the formation of Ba2LaHfO5.5 were obtained in solution by dissolving in boiling nitric acid a stoichiometric mixture of BaCO3, La2O3, and HfO2 that had been heated at 1200 degrees C for 4 h. By complexing the ions with citric acid and using ammonia as fuel, it was possible to get Ba2LaHfO5.5 as nanoparticles in a single-step combustion process. The powder obtained by the present combustion process was characterized by X-ray diffraction, BET surface area analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and scanning and high-resolution transmission electron microscopy. According to the results of X-ray and electron diffraction, the powder synthesized through the combustion process showed single-phase barium lanthanum hafnium oxide. The transmission electron microscopic investigations showed a grain size of 42 nm, with a standard deviation of 8 nm. The nanoparticles of Ba2LaHfO5.5 synthesized by the present combustion technique could be sintered to > 97% of the theoretical density at a relatively low temperature of 1425 degrees C. Scanning electron microscopic studies on the sintered Ba2LaHfO5.5 samples showed that the final grain size of the sintered specimen was < 500 nm.

Calcium Compounds↗
PubMed2026

Toward Class Imbalance and Uncertainty in Powder XRD Analysis: A Dual-Channel Fusion Network for Space Group Classification.

Accurate identification of space groups from powder X-ray diffraction (pXRD) is essential for understanding crystal structures and accelerating materials discovery. However, this task remains highly challenging due to inherent peak overlap, experimental noise, and the complexity of the 230-class classification problem. To address the critical issues of class imbalance and data scarcity, we first design a general physics-informed data augmentation pipeline. We then propose a dual-channel fusion uncertainty-aware network (DFUN) for automated space group classification. The DFUN architecture integrates two complementary feature representations: convolutional features extracted directly from raw diffraction profiles and domain-specific peak descriptors. These distinct representations are adaptively fused through a gating mechanism. Furthermore, to mitigate the inherent long-tailed distribution of crystallographic data, we employ a hybrid loss function that combines Focal Loss with Label Smoothing. Finally, we incorporate Monte Carlo Dropout to provide predictive uncertainty estimation, thereby enabling not only accurate classification but also a crucial assessment of the model's reliability. Evaluated on large-scale simulated data and two public data sets (opXRD and RRUFF), DFUN outperforms the evaluated baseline methods across the reported metrics. The framework also provides uncertainty-aware predictions, establishing DFUN as a robust and interpretable solution for high-throughput automated crystallographic analysis from powder diffraction.

Uncertainty↗
PubMed2006

Investigation of excipient and processing on solid phase transformation and dissolution of ciprofloxacin.

Ciprofloxacin, a very slightly soluble antibiotics, is known to exist as both anhydrous and hydrous forms. This study was carried out to investigate the solid phase transformation of ciprofloxacin during conventional formulation processing that impacts the performance of solid dosage forms. In addition, alternative processing and formulation options were also evaluated to circumvent phase transformation. Anhydrate and hydrate of ciprofloxacin were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) and powder dissolution. As expected, the anhydrate exhibited significantly higher dissolution rate than the hydrate. However, it rapidly converted to the hydrate upon exposure to aqueous medium. Interestingly, premixing the anhydrate with HPMC in the presence of water or ethanol was found to inhibit the processing-induced phase transition. Further studies demonstrated that wet granulation could be an option for preparing tablets with high loading of ciprofloxacin anhydrate through proper selection of excipients and control of processing conditions. Dissolution study of ciprofloxacin in HPMC based extended release matrix tablets indicated different dissolution rates between tablets containing the anhydrate and hydrate, suggesting transformation to the hydrate was significantly inhibited by HPMC in the gel layer of the hydrated tablets.

Anti-Infective Agents↗
PubMed2001

Use of solid corrugated particles to enhance powder aerosol performance.

PURPOSE: To study the dispersion performance of non-porous corrugated particles, with a focus on the effect of particle surface morphology on aerosolization of bovine serum albumin (BSA) powders. METHODS: The solid-state characteristics of the spray-dried BSA powders, one consisting of smooth spherical particles and another corrugated particles, were characterized by laser diffraction, X-ray powder diffraction, scanning electron microscopy, confocal microscopy, thermogravimetric analysis, surface area analyzer, and buoyancy method. The powders were dispersed using the Rotahaler and the Dinkihaler coupled to a four-stage liquid impinger operating at 30 to 120 L/min. Fine particle fraction (FPF) was expressed as the wt. % of BSA particles of size < or =5 microm collected from the liquid impinger. RESULTS: Apart from the morphology and morphology-related properties (specific surface area, envelope density), the corrugated particles and spherical particles of BSA had very similar solid-state characteristics (particle size distribution, water content, true density, amorphous nature). Using the Dinkihaler, the FPFs of the corrugated particles were 10-20 wt. % higher than those of the smooth particles. Similar FPF differences were found for the powders dispersed by the Rotahaler, but the relative changes were larger. In addition, the differences were inversely proportional to the air flows (17.3% at 30 L/min, 25.2% at 60 L/min, 13.8% at 90, 8.5% at 120 L/min). Depending on the inhaler, capsule and device retention and impaction loss at the impinger throat were lower for the corrugated particles. CONCLUSIONS: Enhanced aerosol performance of powders can be obtained by surface modification of the particles. The surface asperities of the corrugated particles could lower the true area of contact between the particles, and thus reduce the powder cohesiveness. A distinct advantage of using corrugated particles is that the inhaler choice and air flow become less critical for these particles.

Administration, Inhalation↗
PubMedDate not supplied

Crystallographic characteristics of plasma-sprayed calcium phosphate coatings on Ti-6Al-4V.

The purpose of this study was to investigate the crystallographic characteristics of 3 sets of plasma-sprayed hydroxyapatite (HA) coatings prepared with different degrees of crystallinity on Ti-6Al-4V substrates. X-ray diffraction analyses were performed on the coatings to determine mean percent crystallinity, calcium phosphate phases present, average crystallite size, and residual strain. The mean percent crystallinity for the 3 sets of coatings ranged from 49 to 60%. The coatings that achieved the highest crystallinity consisted almost entirely of HA. As the coating crystallinity decreased, increasing amounts of alpha- and beta-tricalcium phosphate and tetracalcium phosphate were detected. The mean HA crystallite size for the 3 sets of coatings ranged from 0.02 to 0.05 micron. Differences in mean interplanar spacing for selected crystallographic planes of HA, compared with the pure ICDD (International Center for Diffraction Data) powder standards, implied that the coatings were in an uneven state of tensile strain.

Alloys↗
PubMed2005

Effect of pulverization of the bulk powder on the hydration of creatine anhydrate tablets and their pharmaceutical properties.

The hydration behavior and expansion properties of untreated and pulverized creatine anhydrate (CRA) tablets were studied under 60 and 75%RH at 25 degrees C by using differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD). The tablet hardness of untreated and pulverized CRA tablets was significantly decreased after hydration. There was a linear relationship between the degree of hydration and the tablet hardness of untreated CRA tablets compressed at 1000 kg/cm2. In contrast, the relationship between the degree of hydration and the tablet hardness of pulverized CRA tablets was nonlinear. These results suggest that the reduction in hardness of pulverized CRA tablets does not depend solely on the hydration level of crystal water. PXRD analysis indicated that the diffraction pattern of the pulverized CRA powder was similar to that of the untreated CRA powder. However, the diffraction intensity of the pulverized CRA powder was slightly lower than that of the untreated CRA powder at high angle. The micropore radius of both untreated and pulverized CRA tablets was significantly increased after hydration, but analysis of the relationship between micropore radius and fractional hydration of crystal water showed that untreated CRA tablets were more affected than pulverized CRA tablets. Therefore, the reduction in tablet hardness depends not only on the hydration behavior but also on the crystal orientation of the CRA powder.

Calorimetry, Differential Scanning↗
PubMed1996

Kinetic study of the setting reaction of a calcium phosphate bone cement.

The setting reaction of a calcium phosphate bone cement consisting of a mixture of 63.2 wt % alpha-tertiary calcium phosphate (TCP)[alpha-Ca3(PO4)2], 27.7 wt % dicalcium phosphate (DCP) (CaHPO4), and 9.1 wt % of precipitated hydroxyapatite [(PHA) used as seed material] was investigated. The cement samples were prepared at a liquid-to-powder ratio of: L/P = 0.30 ml/g. Bi-distilled water was used as liquid solution. After mixing the powder and liquid, some samples were molded and aged in Ringer's solution at 37 degrees C. At fixed time intervals they were unmolded and then immediately frozen in liquid nitrogen at a temperature of TN = -196 degrees C, lyofilized, and examined by X-ray diffraction as powder samples. The compressive strength versus time was also measured in setting samples of this calcium phosphate bone cement. The crystal entanglement morphology was examined by scanning electron microscopy. The results showed that: 1) alpha-TCP reacted to a calcium-deficient hydroxyapatite (CDHA), Ca9(HPO4)(PO4)5O H, whereas DCP did not react significantly; 2) the reaction was nearly finished within 32 h, during which both the reaction percentage and the compressive strength increased versus time, with a strong correlation between them; and 3) the calcium phosphate bone cement showed in general a structure of groups of interconnected large plates distributed among agglomerations of small crystal plates arranged in very dense packings.

Bone Cements↗
PubMed1999

A study of Li2TiOSiO4 and Li2TiOGeO4 by X-ray powder and electron single-crystal diffraction, 17O MAS NMR andO K-edge and Ti L2,3-edge EELS.

X-ray powder and electron single-crystal diffraction of crystals of Li(2)TiOSiO(4) and Li(2)TiOGeO(4) showed them to be tetragonal, space group P4/nmm unit-cell parameters a = 6.4379(2), c = 4.40032(2) Å for Li(2)TiOSiO(4) and a = 6.6110(8), c = 4.4372(6) Å for Li(2)TiGeO(4). The compounds are isostructural with their sodium analogues but are considerably compressed along the c axis owing to the smaller size of lithium compared with sodium atoms. Square-pyramidal TiO(5) groups are joined in these compounds by tetrahedral SiO(4) and GeO(4) groups, respectively. (17)O nuclear magnetic resonance spectra of the two compounds, isotopically enriched with (17)O, showed peaks due to the apical titanyl, Ti-O, and basal, bridging, Ti-O-Si or Ti-O-Ge, oxygen atoms of the title compounds. By comparison with reference spectra, oxygen K edges and titanium L(2,3) edges of electron energy-loss spectra were tentatively assigned.

Journal Article↗
PubMed2005

Effect of tablet geometrical structure on the dehydration of creatine monohydrate tablets, and their pharmaceutical properties.

The effects of compression and pulverization on the dehydration kinetics and hardness of creatine monohydrate tablets were studied using a variety of kinetic equations and physical models. The dehydration behavior of unpulverized and pulverized tablets was investigated by using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). The hardness of both unpulverized and pulverized monohydrate tablets was significantly decreased after dehydration. The relationship between the degree of dehydration and the tablet hardness of both unpulverized and pulverized monohydrate tablets formed a straight line. The results suggest that the reduction in tablet hardness is dependent on the dehydration of crystal water, and the values of the slopes indicate that the bonding energy of the unpulverized sample was stronger than that of the pulverized sample. The dehydration kinetics of the unpulverized and pulverized monohydrate tablets were evaluated by analyzing the fit of the isothermal DSC data using a variety of solid-state kinetic models. The dehydration of the unpulverized tablets at various levels of compression pressure followed the 3-dimensional growth of nuclei mechanism. In contrast, although the dehydration kinetics of pulverized monohydrate tablets compressed at 500 and 750 kg/cm2 followed the 3-dimensional diffusion mechanism, those compressed at 1000 kg/cm2 followed the 3-dimensional growth of nuclei mechanism. The PXRD analysis indicated that the diffraction intensity of the pulverized monohydrate powder was significantly lower than that of the unpulverized powder. The diffraction peaks of the (h00) planes and the micropore structure of the unpulverized monohydrate tablets were affected by pulverization and compression force, respectively.

Compressive Strength↗
PubMed2001

Neutron diffraction study of phi-Bi(8)Pb(5)O(17): structure refinement and analysis of cationic ordering.

The triclinic crystal structure of the varphi phase in the structure of the Bi(2)O(3)-PbO phase diagram has been recently solved by the synergetic use of electron and X-ray diffraction on a polycrystalline Bi(8)Pb(5)O(17) sample. In the present work the problem is re-examined on the basis of powder neutron diffraction data: the structure has been confirmed and refined by the Rietveld method. The increased accuracy of the O-atom positions allowed the study of the cationic ordering in this structure by means of bond-valence calculations and charge distribution analysis. The results, confirmed by the refinement of the site occupancies, indicate that the structure is ordered to a large extent, with Bi and Pb atoms occupying preferentially different lattice sites. In this frame, the varphi phase being the most ordered one in the considered region of the Bi(2)O(3)-PbO phase diagram, it should represent the thermodynamically stable low-temperature polymorph.

Journal Article↗
PubMed2002

Structure and dynamics of ND3BF3 in the solid and gas phases: a combined NMR, neutron diffraction, and Ab initio study.

The decrease in D-->A bond lengths, previously reported for some Lewis acid/base complexes, in going from the gas to the solid phases is investigated by obtaining an accurate crystal structure of solid ND(3)BF(3) by powder neutron diffraction. The B-N internuclear distance is 1.554(3) A, 0.118 A shorter than the most recent gas-phase microwave value and 0.121 A shorter than the single molecule geometry optimized (1.672 A, CISD/6-311++G(d,p)) bond length. The crystal structure also shows N-D.F-B hydrogen bonds. The effects of this change in structure and of intermolecular hydrogen-bonding on nuclear magnetic shielding (i.e., chemical shifts) and the nuclear quadrupolar coupling constants (QCC) are investigated by ab initio molecular orbital and density functional theory calculations. These calculations show that the nitrogen ((15)N and (14)N) and boron ((11)B and (10)B) chemical shifts should be rather insensitive to changes in r(BN) and that the concomitant changes in molecular structure. Calculations on hydrogen-bonded clusters, based on the crystal structure, indicate that H-bonding should also have very little effect on the chemical shifts. On the other hand, the (11)B and (14)N QCCs show large changes because of both effects. An analysis of the (10)B[(19)F] line shape in solid ND(3)(10)BF(3) yields a (11)B QCC of +/-0.130 MHz. This is reasonably close an earlier value of +/-0.080 MHz and the value of +/-0.050 MHz calculated for a [NH(3)BF(3)](4) cluster. The gas-phase value is 1.20 MHz. Temperature-dependent deuterium T(1) measurements yield an activation energy for rotation of the ND(3) group in solid ND(3)BF(3) of 9.5 +/- 0.1 kJ/mol. Simulations of the temperature-dependent T(1) anisotropy gave an E(a) of 9.5 +/- 0.2 kJ/mol and a preexponential factor, A, of 3.0 +/- 0.1 x 10(12) s(-)(1). Our calculated value for a [NH(3)BF(3)](4) cluster is 16.4 kJ/mol. Both are much higher than the previous value of 3.9 kJ/mol, from solid-state proton T(1) measurements.

Journal Article↗
PubMed2004

Single molecule diffraction.

For solving the atomic structure of organic molecules such as small proteins which are difficult to crystallize, the use of a jet of doped liquid helium droplets traversing a continuous high energy electron beam is proposed as a means of obtaining electron diffraction patterns (serial crystallography). Organic molecules (such as small proteins) within the droplet (and within a vitreous ice jacket) may be aligned by use of a polarized laser beam. Iterative methods for solving the phase problem are indicated. Comparisons with a related plan for pulsed x-ray diffraction from single proteins in a molecular beam are provided.

Electrons↗
PubMed2006

An accurate quantitative analysis of polymorphs based on artificial neural networks.

Measurement precision based on homogeneous and accurate standard samples has been reported to result in significant improvement in the sensitivity and accuracy of the quantitative analysis of polymorphic mixtures. The purpose of this study was to further improve the accuracy of the quantitation based on data processing by artificial neural networks (ANNs), using such high quality standard samples. Homogeneous powder mixtures of alpha- and gamma-forms of indomethacin (IMC) at various ratios (0-50% alpha-form content) were subjected to X-ray powder diffractometry. The two diffraction peaks selected as the best combination in multiple linear regression (MLR) were used in the ANN with an extended Kalman filter as a training algorithm. The results obtained by ANN had better predictive accuracy at lower contents (0-5%) compared to those of MLR. ANNs for the diffraction data based on high quality standard samples provide an extremely precise and accurate quantification for polymorphic mixtures.

Algorithms↗
PubMed2000

Spin frustration in MII[C(CN)3]2 (M = V, Cr). A magnetism and neutron diffraction study.

Three-dimensional coordination network solids of MII[C(CN)3]2 (M = V, Cr) composition possess interpenetrating rutile-like network structures. Each [C(CN)3]- bonds to three different metal ions in a triangular array, affording a geometrical topology akin to a Kagomé lattice leading to competing spin exchange interactions and spin frustration. The crystal and magnetic structure of CrII[C(CN)3] was determined by Rietveld refinement of the powder neutron diffraction data at 2 and 15 K and belongs to the orthorhombic space group Pmna [a = 7.313(1) A, b = 5.453(1) A, c = 10.640(1) A, Z = 2, T = 15 K]. Each CrII has a tetragonally elongated octahedral structure with four Cr-N(1) distances of 2.077(2) A and two significantly longer axial Cr-N(2) distances of 2.452(2) A. Magnetic susceptibility measurements between 1.7 and 300 K reveal strong antiferromagnetic interactions for both V- and Cr[C(CN)3]2 with theta = -67 and -46 K, respectively, from a fit to the Curie-Weiss law. Long-range magnetic ordering does not occur for M = V above 1.7 K, in contrast to M = Cr, which antiferromagnetically orders at low temperature. This is attributed to Jahn-Teller distorted CrII site relieving frustration in one dimension, leading to 2-D Ising antiferromagnetism, as observed by both magnetic susceptibility and specific heat studies. Neutron diffraction experiments at 2 K for Cr[C(CN)3]2 yielded additional Bragg reflections as a result of antiferromagnetic ordering with the moments on the CrII atoms aligned parallel to c and 4.7(1) microB. Fitting of the magnetic order parameter to a power law yielded TN = 6.12(4) K and beta = 0.18(1) consistent with 2-D Ising behavior. A TN of 6.13 K is also observed from the specific heat data.

Journal Article↗
PubMed2003

Hydroxylapatite and titanium: interfacial reactions.

The chemical reactions between hydroxylapatite (HA) and titanium were studied in three different kinds of experiments to increase understanding of how to bond HA to titanium for implant materials. HA powder was bonded to a titanium rod with hot isostatic pressing. Interdiffusion of the HA elements and titanium was found in concentration profiles measured in the electron microprobe. Titanium was vapor-deposited on sintered HA discs and heated in air; perovskite (CaTiO(3)) was found on the HA surface with Rutherford backscattering and X-ray diffraction measurements. Powder composites of HA and titanium and TiO(2) were sintered at 1100 degrees C; again, perovskite was a reaction product, as well as beta-Ca(3)(PO(4))(2), from decomposition of the HA. These results demonstrate chemical reactions and interdiffusion between HA and TiO(2) during sintering, resulting in chemical bonding between HA and titanium. Thus, cracks and weakness at HA-titanium interfaces probably result from mismatch between the coefficients of thermal expansion of these materials. HA composites with other ceramics and different alloys should lead to better thermal matching and better bonding at the interface.

Biocompatible Materials↗
PubMed2002

Interactions of oxyphenbutazone with different cyclodextrins in aqueous medium and in the solid state.

The interactions between a nonsteroidal anti-inflammatory drugs, oxyphenbutazone (OPB), with two cyclodextrins, beta-cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD), have been studied in an aqueous medium and in the solid state. Differential scanning calorimetry, hot stage microscopy, thermogravimetric analysis and X-ray diffraction (XRD) powder have been the techniques used to characterize the interactions in the solid state. Although OPB forms inclusion compounds with beta- and gamma-CD in the aqueous medium, only the OPB/gamma-CD inclusion compound was obtained in the solid state by the kneading method. The XRD powder used at different temperatures has proven be a useful tool in characterizing the behaviour of these binary systems.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

The effect of crystal morphology and mill type on milling induced crystal disorder.

Milling is a key process in the preparation of many solid dosage forms. One possible milling induced change is the production of small levels of disorder or amorphous material found predominantly at the surface of a powder, which could lead to significant chemical and physical instability. The influence of crystal habit on this change was investigated using beta-succinic acid, in plate like and needle like morphologies. beta-Succinic acid crystals with these habits were processed in a ball mill and a jet mill. SEM images indicated jet milled material was finer than the ball milled product. Powder X-ray diffraction of the milled powders revealed an amorphous halo at lower angles and peak broadening suggesting disorder though this could not be quantified accurately. In addition, a partial conversion during milling to the alpha form was noted. Quantitation of the alpha form in the milled powders indicated it was present at <2% (w/w). Plate and needle shaped particles had similar heats of solution pre-milling, however, all milled powders had lower heats of solution compared to the unmilled powers. The contribution of the alpha polymorph to the lower heats of solution was calculated to be insignificant. Therefore, the reduced heat of solution is attributed to a loss in crystallinity. The largest decreases were seen in the plate like morphology. These findings suggest that beta-succinic acid crystals with plate like morphology are more prone to crystallinity loss on milling compared to the needle like morphology. The mill type has also been shown to influence the final crystallinity.

Calorimetry, Differential Scanning↗