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Tuning pore size in a zirconium–tricarboxylate metal–organic framework
No full textThe water-stable zirconium–tricarboxylate series of frameworks, [Zr6O4(OH)4(X)6(btc)2]·nH2O, where X = formate (F), acetate (A), or propionate (P), exhibit tunable porosity by virtue of systematic modulation of the chain length of the monocarboxylate ligand X. This modification not only impacts the pore size of the framework, but provides an important avenue for the construction of mixed-linker MOFs. © 2014, The Royal Society of Chemistry
Effects of Cr substitution on structural and magnetic properties in La0.7Pr0.3Fe11.4Si1.6 compound
No full textIn an effort to explore the effect of substitution Fe by Cr in NaZn13-type La0.7Pr0.3Fe11.4−xCrxSi1.6 (x = 0, 0.06, 0.12, 0.26, and 0.34) compounds, the structure and magnetic properties have been investigated by high intensity of x-ray and neutron diffraction, scanning electron microscopy, specific heat, and magnetization measurement. It has been found that a substitution of Cr for Fe in this compounds leads to decrease in the lattice parameter a at room temperature but variation on Curie temperature (TC). While the first order nature of magnetic phase transition around TC does not change with increasing Cr content up to x = 0.34. High intensity x-ray and neutron diffraction study at variable temperatures for highest Cr concentration x = 0.34 confirmed the presence of strong magneto-volume effect around TC and indicated the direct evident of coexistence across magnetic transition as characteristic of first order nature. The values of −ΔSM around TC decrease from 17 J kg−1 K−1 for x = 0 to 12 J kg−1 K−1 for x = 0.06 and then increases with further increasing Cr content up to 17.5 J kg−1 K−1 for x = 0.34 under a change of 0–5 T magnetic field. Similar behavior on relative cooling power which is decrease from 390 J kg−1 for x = 0 to 365 J kg−1 for x = 0.06 at the beginning and then increases up to 400 J kg−1 for x = 0.34. From the point of this view with the highest Cr concentration (x = 0.34) exhibits favourable material candidate for magnetic refrigerator application therefore should inspire further study concerning on higher Cr concentration in this compound. © 2014, AIP Publishing LLC
Numerical analysis of retained residual stresses in C(T) specimen extracted from a multi-pass austenitic weld and their effect on crack growth
No full textSmall scale fracture mechanics test specimens of austenitic stainless steel weld and heat affected zone material are often extracted from non-heat-treated weldments, which contain significant weld residual stresses. Although these stresses are substantially relaxed by the process of specimen extraction, they may still reach levels that can affect subsequent testing if the applied loads are low and deformation is elastic. Long-term creep crack growth testing is one such case, where failure to take account of retained residual stresses could result in unrealistically high measurements of creep crack growth at applied load levels equivalent to those in operating plant. This paper describes a research programme to predict the start-of-creep-test levels of retained residual stress and residual stress intensity factor in compact tension C(T) specimen blanks extracted from non-post heat-treated AISI 316 weldments. The simulations were validated using neutron diffraction and slitting residual stress measurements and stress intensity factor measurement. A pass-by-pass finite element simulation of the original weldment is performed first, and followed by extraction of the C(T) specimen blank. The predicted retained residual stresses in the specimen are compared with residual stress measurements made on similar blank using neutron diffraction, and slitting techniques. The elastic stress intensity factor due to residual stress is then evaluated on the crack plane of the C(T) specimen and compared with experimental measurements made using the slitting method. Good agreement is achieved between measurement and simulation, providing validated basis for future modelling of long term creep crack growth tests. © 2014, Elsevier Ltd
In-situ neutron diffraction study of the simultaneous structural evolution of a LiNi0.5Mn1.5O4 cathode and a Li4Ti5O12 anode in a LiNi0.5Mn1.5O4||Li4Ti5O12 full cell
No full textIn this study, the application of neutron powder diffraction on studying the time-resolved structural evolution of a cell comprised with LiNi0.5Mn1.5O4 cathode and Li4Ti5O12 anode during charge–discharge cycling is demonstrated. As expected, the lattices of the LiNi0.5Mn1.5O4 cathode and the Li4Ti5O12 anode in the cell are found to simultaneously contract during charging and expand during discharging. It is found that for the LiNi0.5Mn1.5O4 cathode a solid-solution reaction is associated with the lattice change and the Ni2+/Ni3+ redox couple between 3.06 and 3.16 V (vs. Li4Ti5O12), and a two-phase reaction between LixNi0.5Mn1.5O4 and Ni0.25Mn0.75O2 is corresponding to the Ni3+/Ni4+ redox couple at voltage higher than 3.22 V (vs. Li4Ti5O12) without a corresponding change in lattice. The oxidation states of the metals in the electrodes are determined by tracking the associated change in the oxygen position. In addition, the Ti oxidation state is correlated to the intensity of the Li4Ti5O12 222 reflection at the anode, and the determined oxidation state of the Ni is correlated to the lithium occupancy within the cathode. Furthermore, the small volume changes of the cathode and the anode upon cycling suggest that the cell chemistry is favorable for practical applications. © 2013, Elsevier B.V
Experimental observation of magnetic poles inside
No full textThe pole-avoidance principle of magnetostatics results in an angular anisotropy of the magnetic neutron scattering cross section dΣM dΩ. For the case of a sintered Nd–Fe–B permanent magnet, we report the experimental observation of
a ‘spike’ in dΣM dΩ along the forward direction. The spike implies the presence
of long-wavelength magnetization fluctuations on a length scale of at least
60 nm. Using micromagnetic theory, it is shown that this type of angular anisotropy
is the result of the presence of unavoidable magnetic poles in the bulk of
the magnet and is related to the q ≠ 0 Fourier modes of the magnetostatic field.
Thus, our observation proves the existence of such modes.© 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape
No full textThe Industries of Angkor Project (INDAP) is the first scientific study combining investigation of the chronology, supply network and technology of raw and finished iron within Angkorian (9th to 15th c. AD), Middle Period (15th to 19th c. AD) and Colonial (1863–1953) Cambodia. This paper is concerned with the production technology employed at five iron smelting sites in the northern province of Preah Vihear, three loci within the enclosure walls of the Angkorian Preah Khan complex and two, c. 30 km east, near Phnom Dek or ‘Iron Mountain’. The Phnom Dek area is a historic homeland of the ethnic minority Kuay people, who continued to smelt iron from local mineral sources into the 1940s. With the aim of testing a previously proposed ‘Angkorian Kuay’ hypothesis, that Kuay ancestors were responsible for Angkorian period iron smelting at Preah Khan of Kompong Svay (Preah Khan), the objective of this preliminary study was to establish whether any technological continuity could be detected across a 1200 year old industrial landscape, and thus if any socio-culturally homologous relations could be proposed for the ironmakers respectively responsible. Our preliminary results suggest that the iron smelting remains at Preah Khan date from Angkor's terminal phase and into the subsequent Middle Period, whereas as the two studied production sites near Phnom Dek range from the 9th–11th c. AD and to the 19th/20th c. AD. Preah Khan and Phnom Dek production systems appear to have used different iron ore sources but, in the absence of well-preserved furnace remains, statistical analysis of slag chemistry indicates a technological conservatism spanning more than a millennium. At this stage the ‘Angkorian Kuay’ model can be neither rejected nor sustained but the complexity of Preah Vihear province's settlement and industrial history is becoming increasingly apparent and will only become clearer with further excavation and study of chronologically and geographically intermediate sites. © 2014, Elsevier Ltd
Unearthing earthquakes and their tsunamis using multiple proxies: the 22 June 1932 event and a probable fourteenth-century predecessor on the Pacific coast of Mexico
No full textTsunami deposits have been widely studied in temperate latitudes, but the intrinsic difficulties associated with tropical coastal environments, and the intensity of bioturbation in these habitats, limit the possibilities of analysing these formations. Here, we investigate the deposits on the Colima coast of Mexico, which overlies the subducting Rivera and Cocos Plates, in order to reconstruct the tsunami inundation history and related hazard. We developed a multi-proxy study aimed to recognize and date historical and palaeotsunami deposits, including historical data on the effects of a known tsunami, geomorphological mapping, stratigraphic, grain size, organic matter content, diatoms, geochemical composition, magnetic susceptibility, and anisotropy of magnetic susceptibility, together with radiometric dating (210Pb and 14C). We identified two probable tsunami deposits at Palo Verde estuary including a historical event associated with the Mw 6.9 earthquake on 22 June 1932 and a palaeotsunami most likely generated by a similar event in the fourteenth century. This work shows that it is possible to identify both historical and palaeotsunamis in the tropical environment of Mexico’s Pacific coast. These data will serve to enhance our understanding of tsunami deposits in tropical environments and of the regional tsunami hazard.emperate latitudes, but the intrinsic difficulties associated with tropical coastal environments, and the intensity of bioturbation in these habitats, limit the possibilities of analysing these formations. Here, we investigate the deposits on the Colima coast of Mexico, which overlies the subducting Rivera and Cocos Plates, in order to reconstruct the tsunami inundation history and related hazard. We developed a multi-proxy study aimed to recognize and date historical and palaeotsunami deposits, including historical data on the effects of a known tsunami, geomorphological mapping, stratigraphic, grain size, organic matter content, diatoms, geochemical composition, magnetic susceptibility, and anisotropy of magnetic susceptibility, together with radiometric dating (210Pb and 14C). We identified two probable tsunami deposits at Palo Verde estuary including a historical event associated with the Mw 6.9 earthquake on 22 June 1932 and a palaeotsunami most likely generated by a similar event in the fourteenth century. This work shows that it is possible to identify both historical and palaeotsunamis in the tropical environment of Mexico’s Pacific coast. These data will serve to enhance our understanding of tsunami deposits in tropical environments and of the regional tsunami hazard. © 2020 Informa UK Limite
Biofouling control by hydrophilic surface modification of polypropylene feed spacers by plasma polymerisation
No full textBiofouling compromises the efficiency of membrane desalination systems, especially energy and product water quality. Feed spacers employed in conventional spiral wound membranes create turbulence to minimise concentration polarisation. Research demonstrates that feed spacers can enhance biological growth within membrane elements. In combination with the strong link between fouling and surface hydrophobicity chemical modification of feed spacers could help counteract biofouling potential. In this study, an evaluation of feed spacers coated with diglyme using plasma polymerisation was assessed. Low energy density treatment was associated with an increase in biofouling, compared with the control, consistent with insufficient cross-linking of the diglyme monomer to the spacer surface. Increasing energy density treatment resulted in fouling performance approaching that of, or slightly better than the control. It is possible that batch recirculation type experiments may not best facilitate assessment of biofouling potential in single-pass cross-flow membrane systems. The study demonstrated that plasma treatment of conventional feed spacers has potential to reduce affinity for bacterial attachment, and may provide a viable and complementary approach to direct membrane surface modification for biofouling control. Further studies to quantify changes associated with diglyme plasma polymerisation and establish optimum conditions for biofouling minimisation are recommended. © 2013, Elsevier B.V
Structural dependence of threshold displacement energies in rutile, anatase and brookite TiO2
No full textSystematic molecular dynamics simulations of low energy cascades have been performed to examine how threshold displacement events are effected by changes in crystal structure. Exploiting the structural proximity of the rutile, anatase and brookite polymorphs of TiO2, a quantitative examination of defect production has been carried out including detailed defect analysis and the determination of values of the threshold displacement energy (Ed). Across all polymorphs comparable values of Ed are reported for oxygen at around 20 eV, with the value for Ti in rutile (73 ± 2 eV) significantly higher than that in brookite (34 ± 1 eV) and anatase (39 ± 1 eV). Quantifying defect formation probability as a function of Primary Knock-on Atom (PKA) energy, simulations in rutile indicate a consistent reduction in defect formation at energies higher than Ed relative to anatase and brookite. Defect cluster analysis reveals a significant proportion of di-Frenkel pairs in anatase at Ti PKA energies around Ed. These clusters, which are stabilised by the localisation of two Frenkel pairs, are associated with a recombination barrier of approximately 0.19 eV. As such, annihilation is likely under typical experimental conditions which suggests an expected increase in the measured Ti value of Ed. Identical O defect populations produced at the threshold by the O PKA in both rutile and anatase explain the comparable values of Ed. At higher O PKA energies, the commencement of defect production on both sublattices in anatase is observed in contrast to the confinement of defects to the O sublattice in rutile. The overall trends reported are consistent with in-situ irradiation experiments and thermal spike simulations, suggesting the contrasting radiation response of the polymorphs of TiO2 is apparent during the initial stages of defect production. © 2014, Elsevier B.V
Surface exposure dating reveals MIS-3 glacial maximum in the Khangai Mountains of Mongolia
No full textThis study presents results from geomorphological mapping and cosmogenic radionuclide dating (10Be) of moraine sequences at Otgon Tenger (3905 m), the highest peak in the Khangai Mountains (central Mongolia). Our findings indicate that glaciers reached their last maximum extent between 40 and 35 ka during Marine Oxygen Isotope Stage (MIS) 3. Large ice advances also occurred during MIS-2 (at ~ 23 and 17–16 ka), but these advances did not exceed the limits reached during MIS-3. The results indicate that climatic conditions during MIS-3, characterized by a cool-wet climate with a greater-than-today input from winter precipitation, generated the most favorable setting for glaciation in the study region. Yet, glacial accumulation also responded positively to the far colder and drier conditions of MIS-2, and again during the last glacial–interglacial transition when precipitation levels increased. Viewed in context of other Pleistocene glacial records from High Asia, the pattern of glaciation in central Mongolia shares some features with records from southern Central Asia and NE-Tibet (i.e. ice maxima during interstadial wet phases), while other features of the Mongolian record (i.e. major ice expansion during the MIS-2 insolation minimum) are more in tune with glacier responses known from Siberia and western Central Asia. © 2014, University of Washington