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Evaluation of the residual stress in the cold spray technique using smooth particle hydrodynamics modelling and neutron diffraction
No full textCold spray is a material deposition technique in which powdered metals are deposited onto metallic and glass substrates as a means of improving functionality, repair or protection of the underlying substrate. The residual stress that builds up in the material during spraying is closely linked to the coating’s integrity and the bonding mechanism. Neutron diffraction residual stresses measurements were carried out at the OPAL research reactor, ANSTO, using the KOWARI strain scanner to investigate an Al-6061 sample with a fine through-thickness resolution of 0.5 mm. The experimentally determined through thickness stress profiles of the macroscopically thick coatings were used to validate FE calculations made for 100 μm thick coatings using the Smooth Particle Hydrodynamics, SPH, techniques. A pronounced plastic strain gradient was apparent in the tested and modelled samples indicative of the significant residual macro-stresses which develop in the cladding/substrate during the deposition. Around the deposited particle’s periphery (in the jetting region) the temperatures are significant, this lends itself to the presence of grain refinement at the periphery of sprayed particles and the propagation of dynamic recrystallization which is closely coupled with the thermal softening of the particle. © 2014, Trans Tech Publications
Quantification of α-particle radiation damage in zircon
No full textAnalysis of radiation damage in natural mineral analogs such as zircon is important for the evaluation of the long-term behavior of nuclear waste forms and for geochronology. Here we present results of experiments to determine the partitioning of radiation damage due to the heavy nuclear recoil of uranium and thorium daughters and the α-particles ejected in an α-decay event in zircon. Synthetic polycrystalline zircon ceramics were doped with 10B and irradiated in a slow neutron flux for 1, 10, and 28 days to achieve the reaction 10B + n → 7Li + α (+2.79 MeV), creating an α event without a heavy nuclear recoil. The 7Li atoms produced in the nuclear reaction were directly detected by NMR “spin-counting”, providing a precise measurement of the α-dose applied to each sample. The amount of damage (number fraction and volume fraction) created by each α-event (one α-event being a 7Li + α-particle) has been quantified using radiological nuclear magnetic resonance and X-ray diffraction data. The number of permanently displaced atoms in the amorphous fraction was determined by 29Si NMR to be 252 ± 24 atoms for the 10B(n,α) event when the heavy recoil is absent, which is broadly in agreement with ballistic Monte Carlo calculations. The unit-cell swelling of the crystalline fraction, determined by X-ray diffraction, is small and anisotropic. The anisotropy is similar to that observed in ancient natural samples and implies an initial anisotropic swelling mechanism rather than an anisotropic recovery mechanism occurring over geological timescales. The small unit-cell volume swelling is only ~6% of the expansion frequently attributed to α-particles associated with an actinide α-decay event. The lattice parameters indicate a volume increase as α function of a dose of 0.21 A3/1018 α-events/g, which is significantly less than the increase of 3.55 A3/1018 α-events/g seen in Pu-doped zircon and 2.18 A3/1018 α-events/g seen in natural zircon. It is concluded that the heavy recoil plays a more important role in unit-cell swelling than previously predicted. The likely mechanism for such an effect is the rapid, and thus defect-rich, recrystallization of material initially displaced by the heavy recoil. © 2014, Mineralogical Society of America
Effect of laser clad repair on the fatigue behaviour of ultra-high strength AISI 4340 steel
No full textThe fatigue behaviour of an ultra-high strength steel (>1800 MPa) was evaluated to assess the potential of using laser cladding as a repair tool for such steels in aeronautical structural applications. AISI 4340 and AerMet 100 steel powder were used to clad over a grind-out region in an AISI 4340 steel substrate using a 2.5 kW ND:YAG laser. Post-clad heat treatment (PCHT) was also investigated. Results showed very poor tensile properties and significantly reduced fatigue life of the AISI 4340 as-clad with a very high hardness and brittle fracture in the clad and HAZ zone. Residual stress results showed a compressive residual stress in the clad region and tensile residual stress in the HAZ. Changing the alloy of the clad layer to AerMet 100 steel, as well as applying a PCHT process, showed promising results as the fatigue life was improved from that of the grind-out substrate. © 2014, Elsevier B.V
Reversible pH- and Photocontrollable Carbohydrate-Based Surfactants
No full textThe parallel synthesis and properties of a library of photoswitchable surfactants comprising a hydrophobic butylazobenzene tail-group and a hydrophilic carbohydrate head-group, including the first surfactants to exhibit dual photo- and pH-responsive behavior, is reported. This new generation of surfactants shows varying micelle morphologies, photocontrollable surface tension, and pH-induced aggregation and adsorption. © 2014, WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim
Picosecond dynamics in haemoglobin from different species: A quasielastic neutron scattering study
No full textAbstract
Background
Dynamics in haemoglobin from platypus (Ornithorhynchus anatinus), chicken (Gallus gallus domesticus) and saltwater crocodile (Crocodylus porosus) were measured to investigate response of conformational motions on the picosecond time scale to naturally occurring variations in the amino acid sequence of structurally identical proteins.
Methods
Protein dynamics was measured using incoherent quasielastic neutron scattering. The quasielastic broadening was interpreted first with a simple single Lorentzian approach and then by using the Kneller–Volino Brownian dynamics model.
Results
Mean square displacements of conformational motions, diffusion coefficients of internal dynamics and residence times for jump-diffusion between sites and corresponding effective force constants (resilience) and activation energies were determined from the data.
Conclusions
Modifications of the physicochemical properties caused by mutations of the amino acids were found to have a significant impact on protein dynamics. Activation energies of local side chain dynamics were found to be similar between the different proteins being close to the energy, which is required for the rupture of single hydrogen bond in a protein.
General significance
The measured dynamic quantities showed significant and systematic variations between the investigated species, suggesting that they are the signature of an evolutionary adaptation process stimulated by the different physiological environments of the respective protein. © 2014,Elsevier B.V
A comparative study of magnetic behaviors in TbNi2, TbMn2 and TbNi2Mn
No full textAll TbNi2, TbMn2, and TbNi2Mn compounds exhibit the cubic Laves phase with AB2-type
structure in spite of the fact that the ratio of the Tb to transition-metal components in TbNi2Mn is
1:3. Rietveld refinement indicates that in TbNi2Mn the Mn atoms are distributed on both the A (8a)
and B (16d) sites. The values of the lattice constants were measured to be a¼14.348A ° (space
group F-43 m), 7.618A ° , and 7.158A ° (space group Fd-3 m) for TbNi2, TbMn2, and TbNi2Mn,
respectively. The magnetic transition temperatures TC were found to be TC¼38K and TC¼148K
for TbNi2 and TbNi2Mn, respectively, while two magnetic phase transitions are detected for
TbMn2 at T1¼20K and T2¼49 K. Clear magnetic history effects in a low magnetic field are
observed in TbMn2 and TbNi2Mn. The magnetic entropy changes have been obtained. © 2014 AIP Publishing LLC
In situ diffraction studies of iron ore sinter bonding phase formation: QPA considerations and pushing the limits of laboratory data collection
No full textThe formation and decomposition of silico-ferrite of calcium and aluminium (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using in situ synchrotron and laboratory X-ray diffraction (XRD) and neutron diffraction (ND). An external standard approach for determining absolute phase concentrations via Rietveld refinement-based quantitative phase analysis is discussed. The complementarity of in situ XRD and ND in characterising sinter phase formation and decomposition is also shown, with the volume diffraction afforded by the neutron technique reducing errors in the quantification of magnetite above ~1200 °C. Finally, by collecting 6 s laboratory XRD datasets and using a heating rate of 175 °C min−1, phase formation and decomposition have been monitored under heating rates more closely approximating those encountered in industrial iron ore sintering. © 2014, International Centre for Diffraction Data
Charge-order melting in charge-disproportionated perovskite CeCu3Fe4O12
No full textA novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. (57)Fe Mössbauer spectroscopy displays a charge disproportionation transition of 4Fe(3.5+) → 3Fe(3+) + Fe(5+) below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured. Electron and X-ray diffraction studies reveal that the body-centered cubic symmetry (space group Im3̅, No. 204) is retained at temperatures as low as 100 K, indicating the absence of any types of charge-ordering in the charge-disproportionated CeCu3Fe4O12 phase. The magnetic susceptibility and neutron powder diffraction data illustrate that the antiferromagnetic ordering of Fe ions is predominant in the charge-disproportionated CeCu3Fe4O12 phase. These findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu3Fe4O12 series and that the melting of the charge-ordering in CeCu3Fe4O12 is caused by the substantial decrease in the Fe valence and the resulting large deviation from the ideal abundance ratio of Fe(3+):Fe(5+) = 1:1 for rock-salt-type charge-ordering. © 2014, American Chemical Society
Band alignments of different buffer layers (CdS, Zn(O,S), and In2S3) on Cu2ZnSnS4
No full textThe heterojunctions of different n-type buffers, i.e., CdS, Zn(O,S), and In2S3 on p-type Cu2ZnSnS4
(CZTS) were investigated using X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray
Absorption Fine Structure (NEXAFS) Measurements. The band alignment of the heterojunctions
formed between CZTS and the buffer materials was carefully measured. The XPS data were used
to determine the Valence Band Offsets (VBO) of different buffer/CZTS heterojunctions. The
Conduction Band Offset (CBO) was calculated indirectly by XPS data and directly measured by
NEXAFS characterization. The CBO of the CdS/CZTS heterojunction was found to be cliff-like
with CBOXPS¼ 0.2460.10 eV and CBONEXAFS¼ 0.1860.10 eV, whereas those of Zn(O,S) and
In2S3 were found to be spike-like with CBOXPS¼0.9260.10 eV and CBONEXAFS¼0.8760.10 eV
for Zn(O,S)/CZTS and CBOXPS¼0.4160.10 eV for In2S3/CZTS, respectively. The CZTS
photovoltaic device using the spike-like In2S3 buffer was found to yield a higher open circuit
voltage (Voc) than that using the cliff-like CdS buffer. However, the CBO of In2S3/CZTS is
slightly higher than the optimum level and thus acts to block the flow of light-generated electrons,
significantly reducing the short circuit current (Jsc) and Fill Factor (FF) and thereby limiting the
efficiency. Instead, the use of a hybrid buffer for optimization of band alignment is proposed. © 2014, AIP Publishing LLC
AMS dating of ancient plant residues from experimental stone tools: a pilot study
No full textResidue analyses on stone artefacts have contributed to resolving functional questions in stone tool research. Although identifying the function of tools through the analysis of their micro-residues is possible, the establishment of a sound numerical chronology for stone tools lacking a clear stratigraphic sequence, such as surface scatters, remains a challenge. While radiocarbon dating of blood residue on stone artefacts has been published previously (Loy 1987, 1990, 1993; Loy et al., 1990; Nelson et al.1986), this paper reports on an experiment designed to assess the possibility of directly dating residues on stone artefacts by accelerator mass spectrometry (AMS) based radiocarbon measurements. Innovative with this approach is (1) the use of mid and late Holocene pre-dated plant material (wood and peat), processed with contemporarily manufactured stone flakes under controlled laboratory conditions and (2) the use of very small carbon masses (less than 22 μg) for radiocarbon dating. The 14C results of the wood residues are in excellent agreement with the original sample, whereas the 14C results of the peat residues yield a wider age variation as expected due to the inhomogeneity of the material, but nevertheless, provided dates within an expected age range. Preliminary results demonstrate the feasibility of dating very small amounts of plant residue on lithics directly when contaminants are confined.© 2013, Elsevier Ltd