Biomagnetic characterization of air pollution particulates in Lahore, Pakistan

We report the characterization of anthropogenic magnetic particulate matter (MPM) collected on leaves from roadside Callistemon (bottlebrush) trees from Lahore, Pakistan, and on known sources of traffic-related particulates to assess the potential of first-order reversal curve (FORC) diagrams to discriminate between different sources of anthropogenic magnetic particles. Magnetic measurements on leaves indicate the presence of surface-oxidized magnetite spanning the superparamagnetic (<30 nm) to single domain (∼30–70 nm) to vortex size range (∼70–700 nm). Fe-bearing particles are present both as discrete particles on the surface of larger mineral dust or carbonaceous particles and embedded within them, such that their aerodynamic sizes may be decoupled from their magnetic grain sizes. FORC diagrams of brake-pad residue specimens show a distinct combination of narrow central ridge, extending from 0 to 200 mT, and a low-coercivity, vertically spread signal, attributed to vortex and multi-vortex behavior of metallic Fe. This is in agreement with scanning electron microscopy results that show the presence of metallic as well as oxidized Fe. Exhaust-pipe residue samples display a more conventional “magnetite-like” signal comprising a lower coercivity central ridge (0–80 mT) and a tri-lobate signal attributed to vortex state and/or magnetostatic interactions. The FORC signatures of leaf samples combine aspects of both exhaust residue and brake-pad endmembers, suggesting that FORC fingerprints have the potential to identify and quantify the relative contributions from exhaust and non-exhaust (brake-wear) emissions. Such measurements may provide a cost-effective way to monitor the changing contribution; of future particulate emissions as the vehicle fleet is electrified over the coming years

Magnetoelastic coupling associated with vacancy ordering and ferrimagnetism in natural pyrrhotite, Fe7S8.

Magnetoelastic coupling associated with the hexagonal-monoclinic transition in a natural sample of the mineral pyrrhotite, Fe7S8, has been analysed in terms of separate coupling of spontaneous strains with two discrete order parameters, q v for Fe/vacancy ordering and q m for magnetic ordering. Coupling of the two order parameters separately with strain gives rise to two terms for coupling between them, λ [Formula: see text] and λ [Formula: see text], and a pattern of evolution in which q v varies continuously and q m discontinuously through a single transition point. The transition is ferrimagnetic and ferroelastic but the relatively slow relaxation rate for Fe/vacancy ordering, in comparison with magnetic ordering, results in elastic and anelastic properties which are quite different from those observed in other ferroic or multiferroic materials with two instabilities. Instead of classical elastic softening, there is stiffening of the elastic constants which scales with [Formula: see text] and [Formula: see text]. Instead of the normal pattern of acoustic loss associated with the mobility and subsequent freezing for ferroelastic twin walls, the loss is consistently low throughout the temperature range 300 K-875 K

Solvation and surface effects on polymorph stabilities at the nanoscale

We explore the effects of particle size and solvent environment on the thermodynamic stability of two pairs of polymorphs subjected to ball-mill neat grinding (NG) and liquid assisted grinding (LAG). Two systems were studied: (i) forms I and II of a 1 : 1 theophylline : benzamide cocrystal and (ii) forms A and B of an aromatic disulfide compound. For both systems, the most stable-bulk polymorph converted to the metastable-bulk polymorph upon NG. LAG experiments yielded different outcomes depending on the amount of solvent used. This was further investigated by performing carefully controlled LAG experiments with increasing $\mu$L amounts of solvents of different nature. With these experiments, we were able to monitor form A to B and form I to II conversions as a function of solvent concentration and derive polymorph equilibrium curves. The concentration required for a switch in polymorphic outcome was found to be dependent on solvent nature. We propose that these experiments demonstrate a switch in thermodynamic stability of the polymorphs in the milling jar. Form B, the stable-bulk polymorph, has less stable surfaces than form A, thus becoming metastable at the nanoscale when surface effects become important. $\textit{Ex situ}$ diffraction and electron microscopy data confirm crystal sizes in the order of tens of nanometers after the ball mill grinding experiments reach equilibrium. DFT-d computations of the polymorph particles stabilities support these findings and were used to calculate cross-over sizes of forms A and B as a function of solvent. Attachment energies and surface stabilities of the various crystalline faces exposed were found to be very sensitive to the solvent environment. Our findings suggest that surface effects are significant in polymorphism at the nanoscale and that the outcomes of equilibrium ball-mill NG and LAG experiments are in general controlled by thermodynamics.Engineering and Physical Sciences Research Counci

The effect of fission-energy Xe ion irradiation on the structural integrity and dissolution of the CeO2_2 matrix

© 2016 The Authors.This work considers the effect of fission fragment damage on the structural integrity and dissolution of the CeO₂ matrix in water, as a simulant for the UO₂ matrix of spent nuclear fuel. For this purpose, thin films of CeO₂ on Si substrates were produced and irradiated by 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate fission damage that occurs within nuclear fuels along with bulk CeO₂ samples. The irradiated and unirradiated samples were characterised and a static batch dissolution experiment was conducted to study the effect of the induced irradiation damage on dissolution of the CeO₂ matrix. Complex restructuring took place in the irradiated films and the irradiated samples showed an increase in the amount of dissolved cerium, as compared to the corresponding unirradiated samples. Secondary phases were also observed on the surface of the irradiated CeO₂ films after the dissolution experiment.The irradiation experiment was performed at the Grand Accélérateur National d’Ions Lourds (GANIL) Caen, France, and supported by the French Network EMIR. The support in planning and execution of the experiment by the CIMAP-CIRIL and the GANIL staff, especially, I. Monnet, C. Grygiel, T. Madi and F. Durantel is much appreciated. Thanks are given to I. Buisman and M. Walker from the Department of Earth Sciences, University of Cambridge for help in conducting electron probe microanalysis and polishing the samples, respectively. A.J. Popel acknowledges funding from the UK EPSRC (grant EP/I036400/1 and EP/L018616/1) and Radioactive Waste Management Ltd (formerly the Radioactive Waste Management Directorate of the UK Nuclear Decommissioning Authority, contract NPO004411A-EPS02)

Ferroelectric precursor behavior in PbSc<inf>0.5</inf>Ta <inf>0.5</inf>O<inf>3</inf> detected by field-induced resonant piezoelectric spectroscopy

A novel experimental technique, resonant piezoelectric spectroscopy (RPS), has been applied to investigate polar precursor effects in highly (65%) B-site ordered PbSc0.5Ta0.5O3 (PST), which undergoes a ferroelectric phase transition near 300 K. The cubic-rhombohedral transition is weakly first order, with a coexistence interval of ∼4 K, and is accompanied by a significant elastic anomaly over a wide temperature interval. Precursor polarity in the cubic phase was detected as elastic vibrations generated by local piezoelectric excitations in the frequency range 250–710 kHz. The RPS resonance frequencies follow exactly the frequencies of elastic resonances generated by conventional resonant ultrasound spectroscopy (RUS) but RPS signals disappear on heating beyond an onset temperature, Tonset, of 425 K. Differences between the RPS and RUS responses can be understood if the PST structure in the precursor regime between Tonset and the transition point, Ttrans=300 K, has locally polar symmetry even while it remains macroscopically cubic. It is proposed that this precursor behavior could involve the development of a tweed microstructure arising by coupling between strain and multiple order parameters, which can be understood from the perspective of Landau theory. As a function of temperature the transition is driven by the polar displacement P and the order parameter for cation ordering on the crystallographic B site Qod. Results in the literature show that, as a function of pressure, there is a separate instability driven by octahedral tilting for which the assigned order parameter is Q. The two mainly displacive order parameters, P and Q, are unfavorably coupled via a biquadratic term Q2P2, and complex tweedlike fluctuations in the precursor regime would be expected to combine aspects of all the order parameters. This would be different from the development of polar nanoregions, which are more usually evoked to explain relaxor ferroelectric behavior, such as occurs in PST with a lower degree of B-site order.RUS facilities in Cambridge were established through support from the NERC NE/B505738/1) to MAC. EKHS thanks the Leverhulme foundation (RG66640) and EPSRC (RG66344) for financial support.This is the accepted version of an original article published in Physical Review B and available online at http://link.aps.org/doi/10.1103/PhysRevB.88.174112

Discovery of a maximum damage structure for Xe-irradiated borosilicate glass ceramics containing powellite

In order to increase the waste loading efficiency in nuclear waste glasses, alternate glass ceramic (GC) materials are sought that trap problematic molybdenum in a water-durable CaMoO4 phase within a borosilicate glass matrix. In order to test the radiation resistance of these candidate wasteforms, accelerated external radiation can be employed to replicate long-term damage. In this study, several glasses and GCs were synthesized with up to 10 mol% MoO3 and subjected to 92 MeV Xe ions with fluences ranging between 5 × 10^12 to 1.8 × 10^14 ions/cm2. The main mechanisms of modification following irradiation involve: (i) thermal and defect-assisted diffusion, (ii) relaxation from the ion's added energy, (iii) localized damage recovery from overlapping ion tracks, and (iv) the accumulation of point defects or the formation of voids that created significant strain and led to longer-range modifications. Most significantly, a saturation in alteration could be detected for fluences greater than 4 × 10^13 ions/cm2, which represents an average structure that is representative of the maximum damage state from these competing mechanisms. The results from this study can therefore be used for long-term structural projections in the development of more complex GCs for nuclear waste applications.EPSRC (Grant No. EP/K007882/1

Biomagnetic Characterization of Air Pollution Particulates in Lahore, Pakistan

Funder: Cambridge Trust (Cambridge Commonwealth, European & International Trust); Id: http://dx.doi.org/10.13039/501100003343Abstract: We report the characterization of anthropogenic magnetic particulate matter (MPM) collected on leaves from roadside Callistemon (bottlebrush) trees from Lahore, Pakistan, and on known sources of traffic‐related particulates to assess the potential of first‐order reversal curve (FORC) diagrams to discriminate between different sources of anthropogenic magnetic particles. Magnetic measurements on leaves indicate the presence of surface‐oxidized magnetite spanning the superparamagnetic (<30 nm) to single domain (∼30–70 nm) to vortex size range (∼70–700 nm). Fe‐bearing particles are present both as discrete particles on the surface of larger mineral dust or carbonaceous particles and embedded within them, such that their aerodynamic sizes may be decoupled from their magnetic grain sizes. FORC diagrams of brake‐pad residue specimens show a distinct combination of narrow central ridge, extending from 0 to 200 mT, and a low‐coercivity, vertically spread signal, attributed to vortex and multi‐vortex behavior of metallic Fe. This is in agreement with scanning electron microscopy results that show the presence of metallic as well as oxidized Fe. Exhaust‐pipe residue samples display a more conventional “magnetite‐like” signal comprising a lower coercivity central ridge (0–80 mT) and a tri‐lobate signal attributed to vortex state and/or magnetostatic interactions. The FORC signatures of leaf samples combine aspects of both exhaust residue and brake‐pad endmembers, suggesting that FORC fingerprints have the potential to identify and quantify the relative contributions from exhaust and non‐exhaust (brake‐wear) emissions. Such measurements may provide a cost‐effective way to monitor the changing contribution; of future particulate emissions as the vehicle fleet is electrified over the coming years

Structural effects in UO2_2 thin films irradiated with fission-energy Xe ions

Uranium dioxide thin films have been successfully grown on LSAT (Al$_{10}$La$_3$O$_{51}$Sr$_{14}$Ta$_7$) substrates by reactive magnetron sputtering. Irradiation by 92 MeV $^{129}$Xe$^{23+}$ ions to simulate fission damage that occurs within nuclear fuels caused microstructural and crystallographic changes. Initially flat and continuous thin films were produced by magnetron sputtering with a root mean square roughness of 0.35 nm determined by AFM. After irradiation, this roughness increased to 60-70 nm, with the films developing discrete microstructural features: small grains (~3 $\mu$m), along with larger circular (up to 40 $\mu$m) and linear formations with non-uniform composition according to the SEM, AFM and EDX results. The irradiation caused significant restructuring of the UO$_2$ films that was manifested in significant filmsubstrate mixing, observed through EDX analysis. Diffusion of Al from the substrate into the film in unirradiated samples was also observed.Engineering and Physical Sciences Research Council (Grant ID: EP/ I036400/1), Radioactive Waste Management Ltd (formerly the Radioactive Waste Management Directorate of the UK Nuclear Decommissioning Authority, contract NPO004411A-EPS02), Russian Foundation for Basic Research (projects 13-03-90916), CSAR, Grand Accelélérateur National d’Ions Lourds (GANIL) Caen France, French Network EMIR, CIMAP-CIRIL, M.V.Lomonosov Moscow State University Program of Development, CKP FMI IPCE RA

β-Irradiation Effects on the Formation and Stability of CaMoO4_{4} in a Soda Lime Borosilicate Glass Ceramic for Nuclear Waste Storage

Molybdenum solubility is a limiting factor to actinide loading in nuclear waste glasses, as it initiates the formation of water-soluble crystalline phases such as alkali molybdates. To increase waste loading efficiency, alternative glass ceramic structures are sought that prove resistant to internal radiation resulting from radioisotope decay. In this study, selective formation of water-durable CaMoO$_{4}$ in a soda lime borosilicate is achieved by introducing up to 10 mol % MoO$_{3}$ in a 1:1 ratio to CaO using a sintering process. The resulting homogeneously dispersed spherical CaMoO$_{4}$ nanocrystallites were analyzed using electron microscopy, X-ray diffraction (XRD), Raman and electron paramagnetic resonance (EPR) spectroscopies prior to and post irradiation, which replicated internal β-irradiation damage on an accelerated scale. Following 0.77 to 1.34 GGy of 2.5 MeV electron radiation CaMoO$_{4}$ does not exhibit amorphization or significant transformation. Nor does irradiation induce glass-in-glass phase separation in the surrounding amorphous matrix, or the precipitation of other molybdates, thus proving that excess molybdenum can be successfully incorporated into a structure that it is resistant to β-irradiation proportional to 1000 years of storage without water-soluble byproducts. The CaMoO$_{4}$ crystallites do however exhibit a nonlinear Scherrer crystallite size pattern with dose, as determined by a Rietveld refinement of XRD patterns and an alteration in crystal quality as deduced by anisotropic peak changes in both XRD and Raman spectroscopy. Radiation-induced modifications in the CaMoO$_{4}$ tetragonal unit cell occurred primarily along the c-axis indicating relaxation of stacked calcium polyhedra. Concurrently, a strong reduction of Mo$^{6+}$ to Mo$^{5+}$ during irradiation is observed by EPR, which is believed to enhance Ca mobility. These combined results are used to hypothesize a crystallite size alteration model based on a combination of relaxation and diffusion-based processes initiated by added energy from β-impingement and second-order structural modifications induced by defect accumulation.Univ. of Cambridge, Dept. of Earth Sciences, and EPSRC (Grant No. EP/K007882/1) for an IDS

The role of microbial sulfate reduction in calcium carbonate polymorph selection

Microbial sulfate reduction is a dominant metabolism in many marine sedimentary environments. The influence of this metabolism on the kinetics of CaCO3 growth, as well as the dominant polymorphs precipitated, is poorly understood. To investigate the role of microbial metabolism on CaCO3 precipitation and polymorph selection, we conducted growth experiments with the sulfate reducing bacteria (D. bizertensis) in media with varying Mg/Ca and different seeding materials (calcite and kaolinite). Our results suggest that sulfate reducing bacteria both induce carbonate mineral precipitation through an increase in alkalinity and serve as a nucleation sites for the growing carbonate mineral; the majority of the carbonate minerals produced were on cell material rather than mineral seeds. We also find the Mg/Ca and presence of phosphate in the media play a key role in controlling the rates of carbonate mineral precipitation and calcium carbonate polymorph selection. In media where the Mg/Ca is greater than 2, crystalline monohydrocalcite (MHC) is the primary carbonate mineral produced. Although phosphate concentrations have a lesser effect on which polymorph initially precipitates, a series of transformation experiments suggests that the presence of phosphate stabilizes MHC crystals and prevents its transformation to more stable calcium carbonate polymorphs. Collectively, these results suggest that the polymorph of microbially-mediated calcium carbonate cements is determined by the solution chemistry upon nucleation.Ministry of Education Malaysia, SLAI (Skim Latihan Akademik IPTA) scholarship to CY