Investigations of catalyst and energy storage materials using 57Fe Mössbauer spectroscopy

To improve the understanding of how functional materials operate is key to developing the next generation of materials in their respective fields. In complex, mixed-phase systems this can often be problematic due to the presence and interference from non-active phases such as support systems or matrices that complicate the data from spectroscopic techniques. The use of techniques that can observe single elements can be a powerful method by which to observe the phase of interest. Mössbauer spectroscopy is a powerful, isotope specific spectroscopic technique that uses gamma rays to probe the hyperfine structure of the nucleus. In this work 57Fe Mössbauer spectroscopy was employed in a collaborative effort with industrial scientists from Johnson Matthey to help develop shared understanding of a selection of industrially important materials. Lanthanum ferrites are used as heterogeneous three-way catalyst materials for petrol car emission control; iron carbides play important roles in Fischer-Tropsch synthesis; iron molybdates are catalysts for the oxidation of methanol to formaldehyde; and lithium iron phosphate is an energy storage material. These were all chosen to be a part of the studies contained in this thesis. The motivations behind the catalytic studies were of a similar theme – improve the understanding of how these materials operate, how they age, and how changes to the synthesis process and resulting material properties can influence the performance of the materials. The materials chosen, the methods of their synthesis and the differences between them, with performance data for their respective application, chosen for their industrial relevance, were related to their hyperfine structure through 57Fe Mössbauer spectroscopy. Debye temperatures of iron carbides and rare-earth orthoferrite perovskites were approximated through variable temperature Mössbauer spectroscopic studies and other techniques. The studies of lithium iron phosphate, initially of powdered samples, some of which were extracted from electrodes, culminated in in-operando Mössbauer measurements of full cells at the ESRF synchrotron facility. Commercial materials were studied along with the effect of fabricating electrodes, and the charge state of electrodes, yielding useful information on their hyperfine structure. The studies herein, driven by industrial questions, have shown the strengths of Mössbauer spectroscopy for these various research fields

Variable temperature 57Fe-Mössbauer spectroscopy study of nanoparticle iron carbides

Near-phase-pure nanoparticle iron carbides (Fe3C and Fe5C2) were synthesised. Debye model calculations were used with hyperfine parameters gathered by 57Fe Mössbauer spectroscopy within a temperature range of 10 K to 293 K, with analysis providing Debye temperatures of 422 K and 364 K for two Fe sites in Fe5C2 and 355 K for ferromagnetic Fe3C. The intrinsic isomer shifts were calculated as 0.45 mm s−1 and 0.43 mm s−1 for iron sites 1 and 2 respectively in Fe5C2 and 0.42 mm s−1 for Fe3C. Recoil-free fractions for the two iron sites were also calculated at f300 0.785 and 0.726 for site 1 and 2 respectively

Structure and properties of Na5FeSi4O12 crystallized from 5Na2O-Fe2O3-8SiO2 glass

The phase Na5FeSi4O12 crystallizes readily from the Na2O-Fe2O3-SiO2 glass system in a relatively large compositional range. However, its crystal structure and properties have not been studied in detail since its discovery in 1930. In this work, the Na5FeSi4O12 phase is crystallized from a host glass with 5Na2O·Fe2O3·8SiO2 stoichiometry, and both the glass and crystal are studied. It is found that the Na5FeSi4O12 phase crystallizes at ~ 720°C from the glass, and melts at ~ 830°C when heated at a rate of 10°C/min. The crystal structure was solved using single crystal X-ray diffraction, and the refined data as well as the Crystallographic Information File (CIF) are reported for the first time for the Na5FeSi4O12 phase. It exhibits trigonal symmetry, space group R3 ̅c with a = 21.418, c = 12.2911 Å. The sodium atoms located between adjacent structural channels (Na5, Na51, Na52, Na53) exhibit positional disorder and splitting which was only refined by using low temperature data collection (150 K). While ~ 7% of the total Fe cations occur as Fe2+ in the glass, 4-coordinated Fe3+ constitutes ~ 93% of the total Fe cations. However, iron in the crystal, which exhibits a paramagnetic behavior, is solely present as 6-coordinated Fe3+. The magnetic and vibrational properties of the glass and crystal are discussed to provide additional insight into the structure

Doped Sr2FeIrO6 – phase separation and a Jeff ≠ 0 state for Ir5+

High-resolution synchrotron X-ray and neutron powder diffraction data demonstrate that, in contrast to recent reports, Sr2FeIrO6 adopts an I1 symmetry double perovskite structure with an a–b–c– tilting distortion. This distorted structure does not tolerate cation substitution, with low levels of A-site (Ca, Ba, La) or Fe-site (Ga) substitution leading to separation into two phases: a stoichiometric I1 phase and a cation-substituted, P21/n symmetry, a–a–c+ distorted double perovskite phase. Magnetization, neutron diffraction and 57Fe Mössbauer data show that in common with Sr2FeIrO6, the cation substituted Sr2-xAxFe1-yGayIrO6 phases undergo transitions to type-II antiferromagnetically ordered states at TN ~ 120 K. However, in contrast to stoichiometric Sr2FeIrO6, cation substituted samples exhibit a further magnetic transition at TA ~ 220 K, which corresponds to the ordering of reff ≠ 0 Ir5+ centers in the cation-substituted, P21/n symmetry, double perovskite phases

The chemical suitability for recycling of zinc contaminated steelmaking by-product dusts: The case of the UK steel plant

Basic oxygen steelmaking (BOS) dust and blast furnace (BF) dust from former and operating steelmaking facilities in the United Kingdom have been characterized by MP-AES, SEM-EDX, particle size analysis, TGA-DSC, combustion analysis, 57Fe Mössbauer spectroscopy, and powder XRD. These materials are a potentially valuable source of Fe for ironmaking, but their contamination with zinc precludes their recycling via the conventional sinter plant/BF route. XRD suggested some of the zinc present in the material is in the form of sub-stoichiometric zinc ferrites ZnxFe3-xO4, making hydrometallurgical separation less effective. BF dust contains 40 wt.% levels of fixed carbon (Cfix) indicating it could be useful as an alternative reductant in rotary hearth furnace processes such as FASTMET. The rotary hearth furnace appears to be the most suited separation technique available due to its lack of sensitivity to zinc present in zinc ferrite compounds, and reintegration of the recovered iron into the steelmaking process

Enhanced thermal stability of high-bismuth borate glasses by addition of iron

Glasses with nominal molar composition 20B2O3 – (80-x)Bi2O3 – xFe2O3 (where x = 0–40) were successfully prepared by melt-quenching. These glasses were characterised by multiple techniques including density, X-ray diffraction (XRD), X-Ray fluorescence (XRF), Raman, FT-IR and Mössbauer spectroscopies, dilatometry and differential thermal analysis (DTA). Partial replacement of Bi2O3 by Fe2O3 leads to decreasing density and molar volume and a substantial increase in thermal stability, as measured by several parameters, with maximum improvements achieved when x = 10-20. These improvements are accompanied by modest increases in dilatometric softening point. FT-IR and Raman spectra confirm the presence of BO3 and BiO6 structural units in all glasses, with glass structure apparently little affected by Fe2O3. Mössbauer spectroscopy confirms that iron is present partly as 4-fold coordinated Fe3+ in all glasses, with some 5- and / or 6- coordinated Fe3+ sites also present

The Facile and Additive-Free Synthesis of a Cell-Friendly Iron(III)-Glutathione Complex

The straightfoward creation of an unreported glutathione-stabilised iron(III) complex is disclosed. In contrast to previous reports, glutathione was shown to coordinate and stabilise iron directly under physiological conditions in the absence of additional sulfur containing molecules, such as sodium sulfide. The complex was extensively characterised; the molecular geometry was determined as two inequivalent octahedra, approximately 2/3 of which is slightly distorted towards more tetrahedral in character, with the remaining 1/3 more regularly octahedral. The dispersion of the iron(III)-glutathione complex in aqueous solution yielded particles of 255±4 nm in diameter that enhanced the growth and proliferation of L929 fibroblast cells over 7 days, and inhibited the activity of matrix metalloproteinase-13. Consequently, the unprecedented glutathione-stabilised iron(III) complex disclosed has potential use as a simple-to-prepare growth factor for inclusion within cell culture media, and is an excellent candidate as a therapeutic for the treatment of metalloproteinase-13-associated diseases

An injectable, self-healing and MMP-inhibiting hyaluronic acid gel via iron coordination

Regulating the activity of matrix metalloproteinases (MMPs) is a potential strategy for osteoarthritis (OA) therapy, although delivering this effect in a spatially and temporally localised fashion remains a challenge. Here, we report an injectable and self-healing hydrogel enabling factor-free MMP regulation and biomechanical competence in situ. The hydrogel is realised within one minute upon room temperature coordination between hyaluronic acid (HA) and a cell-friendly iron-glutathione complex in aqueous environment. The resultant gel displayed up to 300% in shear strain and tolerance towards ATDC 5 chondrocytes, in line with 21 the elasticity and biocompatibility requirements for connective tissue application. Significantly enhanced inhibition of MMP-13 activity was achieved after 12 hours in vitro, compared with a commercial HA injection (OSTENIL® PLUS). Noteworthy, 24-hour incubation of a clinical synovial fluid sample collected from a late-stage OA patient with the reported hydrogel was still shown to downregulate synovial fluid MMP activity (100.0±17.6 % à 81.0±7.5 %), with at least comparable extent to the case of the OSTENIL® PLUS-treated SF group (100.0±17.6 % à 92.3±27.3 %). These results therefore open up new possibilities in the use of HA as both mechanically-competent hydrogel as well as a mediator of MMP regulation for OA therapy

Complex magnetic ordering in the oxide selenide Sr2Fe3Se2O3

Sr2Fe3Se2O3 is a localised-moment iron oxide selenide in which two unusual coordinations for Fe2+ ions form two sublattices in a 2:1 ratio. In the paramagnetic region at room temperature the compound adopts the crystal structure first reported for Sr2Co3S2O3, crystallising in space group Pbam with a = 7.8121 Å, b = 10.2375 Å, c = 3.9939 Å and Z = 2. The sublattice occupied by two thirds of the iron ions (Fe2 site) is formed by a network of distorted mer-[FeSe3O3] octahedra linked via shared Se2 edges and O vertices forming layers, which connect to other layers by shared Se vertices. As shown by magnetometry, neutron powder diffraction and Mössbauer spectroscopy measurements, these moments undergo long range magnetic ordering below TN1 = 118 K, initially adopting a magnetic structure with a propagation vector (½–δ, 0, ½) (0 ≤ ≤ 0.1) which is incommensurate with the nuclear structure and described in the Pbam1’(a01/2)000s magnetic superspace group, until at 92 K (TINC) there is a first order lock-in transition to a structure in which these Fe2 moments form a magnetic structure with a propagation vector (½ , 0, ½) which may be modelled using a 2a × b × 2c expansion of the nuclear cell in space group 36.178 Bab21m (BNS notation). Below TN2 = 52 K the remaining third of the Fe2+ moments (Fe1 site) which are in a compressed trans-[FeSe4O2] octahedral environment undergo long range ordering, as is evident from the magnetometry, the Mössbauer spectra and the appearance of new magnetic Bragg peaks in the neutron diffractograms. The ordering of the second set of moments on the Fe1 sites results in a slight re-orientation of the majority moments on the Fe2 sites. The magnetic structure at 1.5 K is described by a 2a × 2b × 2c expansion of the nuclear cell in space group 9.40 Iab (BNS notation)

From acrylates to silicones: A review of common optical fibre coatings used for normal to harsh environments.

The full realisation of optical fibres in devices such as sensors is reliant on the stability of their polymer coating under in-service conditions. Depending on the application, resistance to several environmental factors may be required, such as high or low humidity level, temperature, pressure, or exposure to aggressive solids, liquids or gases. Changes in mechanical or chemical properties as a result of harsh environments can lead to stresses in the coating and subsequent deterioration of the physical or optical properties of the optical fibre. A variety of coating materials are available on the global market, offering optical fibre manufacturers a plethora of options. This review provides a comparison among four most utilised, commercially available types of coating material: conventional and specialty acrylates, polyimides and silicones. It details the history of their development, reported physiochemical properties and some of their main limitations in the context of optical fibre coating applications