High-energy Powder X-ray Diffraction Research Articles

Unravelling dynamic recrystallisation in a microalloyed steel during rapid high temperature deformation using synchrotron X-rays

Microstructure evolution during high-strain rate and high-temperature thermo-mechanical processing of a 44MnSiV6 microalloyed steel is investigated using in situ synchrotron high-energy powder X-ray diffraction. The conditions selected replicate a newly developed near solidus high-strain rate process designed for reducing raw material use during the hot processing of steels. High temperatures (exceeding 1300 °C) and high strain rate ε˙ = 9 s-1 processing regimes are explored. The lattice strains and dislocation activity estimated from diffraction observations reveal that the microstructure evolution is primarily driven by dynamic recrystallisation. A steady-state stress regime is observed during deformation, which develops due to intermittent and competing work hardening and recovery processes. The texture evolution during the heating, tension, shear deformation and cooling stages is systematically investigated. The direct observation of phase evolution at high-temperature and high-strain rate deformation enables a comprehensive understanding of new manufacturing processes and provides deep insights for the development of constitutive models for face-centred cubic alloys.

Sr(II) and Ba(II) Alkaline Earth Metal-Organic Frameworks (AE-MOFs) for Selective Gas Adsorption, Energy Storage, and Environmental Application.

Two new alkaline earth metal-organic frameworks (AE-MOFs) containing Sr(II) (UPJS-15) or Ba(II) (UPJS-16) cations and extended tetrahedral linker (MTA) were synthesized and characterized in detail (UPJS stands for University of Pavol Jozef Safarik). Single-crystal X-ray analysis (SC-XRD) revealed that the materials are isostructural and, in their frameworks, one-dimensional channels are present with the size of ~11 × 10 Å2. The activation process of the compounds was studied by the combination of in situ heating infrared spectroscopy (IR), thermal analysis (TA) and in situ high-energy powder X-ray diffraction (HE-PXRD), which confirmed the stability of compounds after desolvation. The prepared compounds were investigated as adsorbents of different gases (Ar, N2, CO2, and H2). Nitrogen and argon adsorption measurements showed that UPJS-15 has SBET area of 1321 m2 g-1 (Ar) / 1250 m2 g-1 (N2), and UPJS-16 does not adsorb mentioned gases. From the environmental application, the materials were studied as CO2 adsorbents, and both compounds adsorb CO2 with a maximum capacity of 22.4 wt.% @ 0 °C; 14.7 wt.% @ 20 °C and 101 kPa for UPJS-15 and 11.5 wt.% @ 0°C; 8.4 wt.% @ 20 °C and 101 kPa for UPJS-16. According to IAST calculations, UPJS-16 shows high selectivity (50 for CO2/N2 10:90 mixture and 455 for CO2/N2 50:50 mixture) and can be applied as CO2 adsorbent from the atmosphere even at low pressures. The increased affinity of materials for CO2 was also studied by DFT modelling, which revealed that the primary adsorption sites are coordinatively unsaturated sites on metal ions, azo bonds, and phenyl rings within the MTA linker. Regarding energy storage, the materials were studied as hydrogen adsorbents, but the materials showed low H2 adsorption properties: 0.19 wt.% for UPJS-15 and 0.04 wt.% for UPJS-16 @ -196 °C and 101 kPa. The enhanced CO2/H2 selectivity could be used to scavenge carbon dioxide from hydrogen in WGS and DSR reactions. The second method of applying samples in the area of energy storage was the use of UPJS-15 as an additive in a lithium-sulfur battery. Cyclic performance at a cycling rate of 0.2 C showed an initial discharge capacity of 337 mAh g-1, which decreased smoothly to 235 mAh g-1 after 100 charge/discharge cycles.

Multi-analyser detector (MAD) for high-resolution and high-energy powder X-ray diffraction.

For high-resolution powder diffraction in material science, high photon energies are necessary, especially for in situ and in operando experiments. For this purpose, a multi-analyser detector (MAD) was developed for the high-energy beamline P02.1 at PETRA III of the Deutsches Elektronen-Synchrotron (DESY). In order to be able to adjust the detector for the high photon energies of 60 keV, an individually adjustable analyser-crystal setup was designed. The adjustment is performed via piezo stepper motors for each of the ten channels. The detector shows a low and flat background as well as a high signal-to-noise ratio. A range of standard materials were measured for characterizing the performance. Two exemplary experiments were performed to demonstrate the potential for sophisticated structural analysis with the MAD: (i) the structure of a complex material based on strontium niobate titanate and strontium niobate zirconate was determined and (ii) an in situ stroboscopy experiment with an applied electric field on a highly absorbing piezoceramic was performed. These experiments demonstrate the capabilities of the new MAD, which advances the frontiers of the structural characterization of materials.

Probing the Dynamics of Platinum Surface Oxides in Fuel Cell Catalyst Layers Using in Situ X-ray Diffraction

The processes leading to degradation of Pt nanoparticles inside commercial hydrogen fuel cell catalyst layers are studied in situ, using time-resolved high-energy powder X-ray diffraction. Advances...

Local structure and phase transitions of KNbO3

Bond length distributions of nearest- and higher-neighbor distances in KNbO3, which is the parent compound of lead-free piezoelectric materials, have been obtained by X-ray pair-distribution function (PDF) analysis. The Rietveld analysis of high-energy powder X-ray diffraction data as a function of temperature from 15 to 1073 K over four phases shows the variation in structure from rhombohedral to cubic structures. The refinements on the local structure by the PDF method indicate that only the rhombohedral structure can describe the observed bond distributions within the unit cell. The rhombohedral distortion is maintained locally in all four phases.

Metal-organic framework MIL-101(Fe)-NH2 functionalized with different long-chain polyamines as drug delivery system

Mesoporous metal-organic framework MIL-101(Fe)-NH2 was prepared and post-synthetically modified with amines of different chain lengths: ethylenediamine (en) and 1,2-bis(3-aminopropylamino)ethane (bap). Three prepared samples (MIL-101(Fe)-NH2, MIL-101(Fe)-NH2-en, MIL-101(Fe)-NH2-bap) were studied as carriers for drug delivery of non-steroidal antiinflamatory drug naproxen. The modification of MIL-101(Fe)-NH2, encapsulation of the drug and stability of the carriers were monitored by the combination of different analytical techniques such as elemental analysis (EA), infrared spectroscopy (IR), thermogravimetry (TG), measurements of zeta potential (ζ), high-energy powder X-ray diffraction (HE-PXRD), 1H NMR spectroscopy and N2 adsorption measurements. The naproxen release studies were performed into two simulated body fluids with different pH: the simulated gastric fluid (pH = 2) and the simulated intravenous solution (pH = 7.4). Results of naproxen release clearly showed the impact of pH and amine functional groups on the naproxen release. The number of amine groups in en and bap influenced the release process more significantly in solution with pH = 7.4 than pH = 2.

New members of MOF-76 family containing Ho(III) and Tm(III) ions: Characterization, stability and gas adsorption properties

Two novel three-dimensional microporous coordination polymers with composition {[Ln(μ6-BTC)(H2O)]·DMF}n (Ln = Ho(III) (1) and Tm(III) (2); BTC-benzene-1,3,5-tricarboxylate) have been solvothermally synthesized and their preparation conditions were optimized. Single crystal X-ray diffraction experiments showed, that both compounds display similar structures with (6, 6)-connected nets and 1D sinusoidally shaped channels with sizes about 6.7 × 6.7 Å2. Activation process and stability of the frameworks were studied by infrared spectroscopy measured at different temperatures, thermogravimetry coupled with evolved gas analysis and by high energy powder X-ray diffraction experiments measured during in-situ heating. The compounds exhibited high thermal stability, up to 600 °C. Nitrogen and carbon dioxide measurements at low pressures showed BET surface area of 600 m2 g−1 for the sample 1 and 590 m2 g−1 for the sample 2. The carbon dioxide uptake at 0 °C and 1 atm was ∼12 wt.% for both compounds. The adsorption behaviour of 2 has been also investigated by high pressure adsorption measurements of pure methane, carbon dioxide, and nitrogen at 30 °C and pressures up to 26 bar. The measured maximal adsorption capacities were 5.03 wt.% of CH4 at 20 bar, 6.10 wt.% of N2 and 21.95 wt.% of CO2 at 26 bar and 30 °C.

Thermal Expansion of Ni–Ti–Sn Heusler and Half-Heusler Materials from First-Principles Calculations and Experiments

We coupled first-principles calculations and the quasiharmonic approximation combined with experiments (X-ray diffraction and dilatometry measurements) to determine the thermal properties of NiTiSn (half-Heusler) and Ni2TiSn (Heusler) compounds. These properties are important especially if they are to be used in thermoelectric applications. First, the calculation of their mode Grüneisen parameter shows that it is positive throughout the first Brillouin zone. This suggests that these compounds undergo a regular thermal expansion. Then, the calculation of the Ni2TiSn thermal expansion shows an excellent agreement, even in the high temperature range, with our high energy powder X-ray diffraction measurements (ESRF) and dilatometry experiments. In the case of NiTiSn, this agreement is less impressive. This could be due to stronger phonon–phonon interactions that are not considered within the quasiharmonic approximation but also to the difficulty of making high-quality NiTiSn samples. Finally, the constant-pressure and constant-volume heat capacities have been calculated for both compounds and compared with the experimental data reported in the literature. In particular, we have decomposed the constant-volume heat capacity of Ni2TiSn into a purely electronic and a phonon-mediated contribution, and we discuss each of them.

Ce(III) and Lu(III) metal–organic frameworks with Lewis acid metal sites: Preparation, sorption properties and catalytic activity in Knoevenagel condensation

Two novel coordination polymers with composition {[Ln(BTC)(H2O)]·DMF}n (where Ln=Ce(III) (1) and Lu(III) (2), BTC=benzene-1,3,5-tricarboxylate, DMF=N,N′-dimethylformamide) have been prepared under solvothermal conditions. Properties of the compounds were investigated by single crystal X-ray diffraction, high-energy powder X-ray diffraction during in-situ heating, thermogravimetry with simultaneous evolved gas analysis, infrared spectroscopy performed at different temperatures, elemental analysis and inductively coupled plasma mass spectrometry. Sorption properties of the synthesized complexes were investigated using nitrogen and carbon dioxide adsorption experiments. Catalytic activity of compound 2 was tested in Knoevenagel condensation reactions in a series of aromatic and non-aromatic aldehydes with different active methylene compounds (malononitrile, methyl cyanoacetate), in which the reactivity of aldehydes in condensation reactions increases in the order: 2-naphthaldehyde<4-tert-butyl benzaldehyde<benzaldehyde<cyclohexane carbaldehyde<n-heptanal.

Investigation of Surface Structures by Powder Diffraction: A Differential Pair Distribution Function Study on Arsenate Sorption on Ferrihydrite

Differential pair distribution function (d-PDF) analysis of high energy powder X-ray diffraction data was carried out on 2-line ferrihydrite nanoparticles with arsenate oxyanions adsorbed on the surface to investigate the binding mechanism. In this analysis, a PDF of ferrihydrite is subtracted from a PDF of ferrihydrite with arsenate sorbed on the surface, leaving only correlations from within the surface layer and between the surface and the particle. As-O and As-Fe correlations were observed at 1.68 and 3.29 A, respectively, in good agreement with previously published EXAFS data, confirming a bidentate binuclear binding mechanism. Further peaks are observed in the d-PDF which are not present in EXAFS, corresponding to correlations between As and O in the particle and As-2nd Fe.