Publications
521 results found
Geng H, Poologasundarampillai G, Todd N, et al., 2017, Biotransformation of silver released from nanoparticle coated titanium implants revealed in regenerating bone, ACS Applied Materials and Interfaces, Vol: 9, Pages: 21169-21180, ISSN: 1944-8244
Antimicrobial silver nanoparticle coatings have attracted interest for reducing prosthetic joint infection. However, few studies report in vivo investigations of the biotransformation of silver nanoparticles within the regenerating tissue and its impact on bone formation. We present a longitudinal investigation of the osseointegration of silver nanoparticle-coated additive manufactured titanium implants in rat tibial defects. Correlative imaging at different time points using nanoscale secondary ion mass spectrometry, transmission electron microscopy (TEM), histomorphometry, and 3D X-ray microcomputed tomography provided quantitative insight from the nano- to macroscales. The quality and quantity of newly formed bone is comparable between the uncoated and silver coated implants. The newly formed bone demonstrates a trabecular morphology with bone being located at the implant surface, and at a distance, at two weeks. Nanoscale elemental mapping of the bone–implant interface showed that silver was present primarily in the osseous tissue and colocalized with sulfur. TEM revealed silver sulfide nanoparticles in the newly regenerated bone, presenting strong evidence that the previously in vitro observed biotransformation of silver to silver sulfide occurs in vivo.
Dobson KJ, Harrison STL, Lin Q, et al., 2017, Insights into ferric leaching of low grade metal sulfide-containing ores in an unsaturated ore bed using x-ray computed tomography, Minerals, Vol: 7, ISSN: 2075-163X
The distribution of the metal-bearing mineral grains within a particulate ore prepared for leaching, and the impact of this spatial heterogeneity on overall extraction efficiency is of key importance to a mining industry that must continuously target ever-reducing grades and more complex ore bodies. If accessibility and recovery of the target minerals is to be improved, a more detailed understanding of the behaviour of the system must be developed. We present an in situ analysis using X-ray computed tomography to quantify the rates of volume reduction of sulfide mineral grains in low grade agglomerated copper bearing ores during a miniature laboratory scale column leaching experiment. The data shows the scale of the heterogeneity in the leaching behaviour, with an overall reduction of sulphide mineral grains of 50%, but that this value masks significant mm3 to cm3 scale variability in reduction. On the scale of individual ore fragments, leaching efficiency ranged from 22% to 99%. We use novel quantitative methods to determine the volume fraction of the sulfide that is accessible to the leachate solution.
Nommeots-Nomm A, Labbaf S, Devlin A, et al., 2017, Highly degradable porous melt-derived bioactive glass foam scaffolds for bone regeneration, Acta Biomaterialia, Vol: 57, Pages: 449-461, ISSN: 1878-7568
A challenge in using bioactive melt-derived glass in bone regeneration is to produce scaffolds with interconnected pores while maintaining the amorphous nature of the glass and its associated bioactivity. Here we introduce a method for creating porous melt-derived bioactive glass foam scaffolds with low silica content and report in vitro and preliminary in vivo data. The gel-cast foaming process was adapted, employing temperature controlled gelation of gelatin, rather than the in situ acrylic polymerisation used previously. To form a 3D construct from melt derived glasses, particles must be fused via thermal processing, termed sintering. The original Bioglass® 45S5 composition crystallises upon sintering, altering its bioactivity, due to the temperature difference between the glass transition temperature and the crystallisation onset being small. Here, we optimised and compared scaffolds from three glass compositions, ICIE16, PSrBG and 13–93, which were selected due to their widened sintering windows. Amorphous scaffolds with modal pore interconnect diameters between 100–150 µm and porosities of 75% had compressive strengths of 3.4 ± 0.3 MPa, 8.4 ± 0.8 MPa and 15.3 ± 1.8 MPa, for ICIE16, PSrBG and 13–93 respectively. These porosities and compressive strength values are within the range of cancellous bone, and greater than previously reported foamed scaffolds. Dental pulp stem cells attached to the scaffold surfaces during in vitro culture and were viable. In vivo, the scaffolds were found to regenerate bone in a rabbit model according to X-ray micro tomography imaging.
Kazantsev D, Bleichrodt F, van Leeuwen T, et al., 2017, A Novel Tomographic Reconstruction Method Based on the Robust Student's t Function For Suppressing Data Outliers, IEEE Transactions on Computational Imaging, Vol: 3, Pages: 682-693, ISSN: 2333-9403
Regularized iterative reconstruction methods in computedtomography can be effective when reconstructing frommildly inaccurate undersampled measurements. These approacheswill fail, however, when more prominent data errors, or outliers,are present. These outliers are associated with various inaccuraciesof the acquisition process: defective pixels or miscalibrated camerasensors, scattering, missing angles, etc. To account for suchlarge outliers, robust data misfit functions, such as the generalizedHuber function, have been applied successfully in the past.In conjunction with regularization techniques, these methods canovercome problems with both limited data and outliers. This paperproposes a novel reconstruction approach using a robust data fittingterm which is based on the Student’s t distribution. This misfitpromises to be even more robust than the Huber misfit as it assignsa smaller penalty to large outliers. We include the total variationregularization term and automatic estimation of a scaling parameterthat appears in the Student’s t function. We demonstrate theeffectiveness of the technique by using a realistic synthetic phantomand also apply it to a real neutron dataset.
Pilz FF, Dowey PJ, Fauchille A-L, et al., 2017, Synchrotron tomographic quantification of strain and fracture during simulated thermal maturation of an organic-rich shale, UK Kimmeridge Clay, Journal of Geophysical Research. Solid Earth, Vol: 122, Pages: 2553-2564, ISSN: 2169-9356
Analyzing the development of fracture networks in shale is important to understand both hydrocarbon migration pathways within and from source rocks and the effectiveness of hydraulic stimulation upon shale reservoirs. Here we use time‐resolved synchrotron X‐ray tomography to quantify in four dimensions (3‐D plus time) the development of fractures during the accelerated maturation of an organic‐rich mudstone (the UK Kimmeridge Clay), with the aim of determining the nature and timing of crack initiation. Electron microscopy (EM, both scanning backscattered and energy dispersive) was used to correlatively characterize the microstructure of the sample preheating and postheating. The tomographic data were analyzed by using digital volume correlation (DVC) to measure the three‐dimensional displacements between subsequent time/heating steps allowing the strain fields surrounding each crack to be calculated, enabling crack opening modes to be determined. Quantification of the strain eigenvectors just before crack propagation suggests that the main mode driving crack initiation is the opening displacement perpendicular to the bedding, mode I. Further, detailed investigation of the DVC measured strain evolution revealed the complex interaction of the laminar clay matrix and the maximum principal strain on incipient crack nucleation. Full field DVC also allowed accurate calculation of the coefficients of thermal expansion (8 × 10−5/°C perpendicular and 6.2 × 10−5/°C parallel to the bedding plane). These results demonstrate how correlative imaging (using synchrotron tomography, DVC, and EM) can be used to elucidate the influence of shale microstructure on its anisotropic mechanical behavior.
Cai B, Liu B, Kabra S, et al., 2017, Deformation mechanisms of Mo alloyed FeCoCrNi high entropy alloy: In situ neutron diffraction, Acta Materialia, Vol: 127, Pages: 471-480, ISSN: 1359-6454
A FeCoCrNiMo0.23 high entropy alloy was processed by powder metallurgy with two conditions: hot extruded and annealed. In situ neutron diffraction, together with electron microscopy, was used to study the deformation mechanisms and concomitant microstructural evolution for both conditions. The as-extruded alloy has a single face-centered-cubic structure with a calculated stacking fault energy of ∼19 mJ/m2. When the alloy is tensile deformed, nano-twins and microbands are induced, resulting in an excellent combination of strength and ductility (784 MPa ultimate tensile strength and over 50% elongation). Annealing at 800 °C for 72 h increases the strength of the alloy but decreases its ductility. This is due to the decomposition of the alloy after annealing, causing the formation of Mo-rich intermetallic particles and a decrease of the stacking fault probability. These results highlight that combined mechanisms (i.e. solute strengthening and twin/microband induced plasticity) can effectively improve both the strength and ductility of high entropy alloys.
Devlin-Mullin A, Todd NM, Golrokhi Z, et al., 2017, Atomic Layer Deposition of a Silver Nanolayer on Advanced Titanium Orthopedic Implants Inhibits Bacterial Colonization and Supports Vascularized de Novo Bone Ingrowth., Advanced Healthcare Materials, Vol: 6, ISSN: 2192-2640
Joint replacement surgery is associated with significant morbidity and mortality following infection with either methicillin-resistant Staphylococcus aureus (MRSA) or Staphylococcus epidermidis. These organisms have strong biofilm-forming capability in deep wounds and on prosthetic surfaces, with 10(3) -10(4) microbes resulting in clinically significant infections. To inhibit biofilm formation, we developed 3D titanium structures using selective laser melting and then coated them with a silver nanolayer using atomic layer deposition. On bare titanium scaffolds, S. epidermidis growth was slow but on silver-coated implants there were significant further reductions in both bacterial recovery (p < 0.0001) and biofilm formation (p < 0.001). MRSA growth was similarly slow on bare titanium scaffolds and not further affected by silver coating. Ultrastructural examination and viability assays using either human bone or endothelial cells, demonstrated strong adherence and growth on titanium-only or silver-coated implants. Histological, X-ray computed microtomographic, and ultrastructural analyses revealed that silver-coated titanium scaffolds implanted into 2.5 mm defects in rat tibia promoted robust vascularization and conspicuous bone ingrowth. We conclude that nanolayer silver of titanium implants significantly reduces pathogenic biofilm formation in vitro, facilitates vascularization and osseointegration in vivo making this a promising technique for clinical orthopedic applications.
Guo E, Zeng G, Kazantsev D, et al., 2017, Synchrotron X-ray tomographic quantification of microstructural evolution in ice cream - a multiphase soft solid, RSC Advances, Vol: 7, Pages: 15561-15573, ISSN: 2046-2069
Microstructural evolution in soft matter directly influences not only the material's mechanical and functional properties, but also our perception of that material's taste. Using synchrotron X-ray tomography and cryo-SEM we investigated the time–temperature evolution of ice cream's microstructure. This was enabled via three advances in synchrotron tomography: a bespoke tomography cold stage; improvements in pink beam in line phase contrast; and a novel image processing strategy for reconstructing and denoising in line phase contrast tomographic images. Using these three advances, we qualitatively and quantitatively investigated the effect of thermal changes on the ice cream's microstructure after 0, 7 and 14 thermal cycles between −15 and −5 °C. The results demonstrate the effect of thermal cycling on the coarsening of both the air cells and ice crystals in ice cream. The growth of ice crystals almost ceases after 7 thermal cycles when they approach the size of the walls between air cells, while air cells continue to coarsen, forming interconnected channels. We demonstrate that the tomographic volumes provide a statistically more representative sample than cryo-SEM, and elucidate the three dimensional morphology and connectivity of phases. This resulted in new insights including the role of air cells in limiting ice crystal coarsening.
Azeem MA, Lee PD, Phillion AB, et al., 2017, Revealing dendritic pattern formation in Ni, Fe and Co alloys using synchrotron tomography, Acta Materialia, Vol: 128, Pages: 241-248, ISSN: 1873-2453
The microstructural patterns formed during liquid to solid phase transformations control the properties of a wide range of materials. We developed a novel methodology that allows in situ quantification of the microstructures formed during solidification of high temperature advanced alloys. The patterns formed are captured in 4D (3D plus time) using a methodology which exploits three separate advances: a bespoke high temperature environment cell; the development of high X-ray contrast alloys; and a novel environmental encapsulation system. This methodology is demonstrated on Ni, Fe, and Co advanced alloy systems, revealing dendritic pattern formation. We present detailed quantification of microstructural pattern evolution in a novel high attenuation contrast Co-Hf alloy, including microstructural patterning and dendrite tip velocity. The images are quantified to provide 4D experimental data of growth and coarsening mechanisms in Co alloys, which are used for a range of applications from energy to aerospace.
Panagos P, Wang Y, McCartney DG, et al., 2017, Characterising precipitate evolution in multi- component cast aluminium alloys using small-angle X-ray scattering, Journal of Alloys and Compounds, Vol: 703, Pages: 344-353, ISSN: 1873-4669
Aluminium alloys can be strengthened significantly by nano-scale precipitates that restrict dislocation movement. In this study, the evolution of inhomogenously distributed trialuminide precipitates in two multi-component alloys was characterised by synchrotron small-angle X-ray scattering (SAXS). The appropriate selection of reference sample and data treatment required to successfully characterise a low volume fraction of precipitates in multi-component alloys via SAXS was investigated. The resulting SAXS study allowed the analysis of statistically significant numbers of precipitates (billions) as compared to electron microscopy (hundreds). Two cast aluminium alloys with different volume fractions of Al3ZrxV1-x precipitates were studied. Data analysis was conducted using direct evaluation methods on SAXS spectra and the results compared with those from transmission electron microscopy (TEM). Precipitates were found to attain a spherical structure with homogeneous chemical composition. Precipitate evolution was quantified, including size, size distribution, volume fraction and number density. The results provide evidence that these multi-component alloys have a short nucleation stage, with coarsening dominating precipitate size. The coarsening rate constant was calculated and compared to similar precipitate behaviour.
Ma L, Fauchille A-L, Dowey PJ, et al., 2017, Correlative multi-scale imaging of shales: a review and future perspectives, GEOMECHANICAL AND PETROPHYSICAL PROPERTIES OF MUDROCKS, Editors: Rutter, Mecklenburgh, Taylor, Publisher: GEOLOGICAL SOC PUBLISHING HOUSE, Pages: 175-199
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- Citations: 44
Ennis BL, Jimenez-Melero E, Mostert R, et al., 2016, Dataset concerning the analytical approximation of the Ae3 temperature., Data in Brief, Vol: 10, Pages: 330-334, ISSN: 2352-3409
In this paper we present a new polynomial function for calculating the local phase transformation temperature (Ae3 ) between the austenite+ferrite and the fully austenitic phase fields during heating and cooling of steel:[Formula: see text] The dataset includes the terms of the function and the values for the polynomial coefficients for major alloying elements in steel. A short description of the approximation method used to derive and validate the coefficients has also been included. For discussion and application of this model, please refer to the full length article entitled "The role of aluminium in chemical and phase segregation in a TRIP-assisted dual phase steel" 10.1016/j.actamat.2016.05.046 (Ennis et al., 2016) [1].
Sillekens WH, Casari D, Mirihanage WU, et al., 2016, The use of in situ X-ray imaging methods in the research and development of magnesium-based grain-refined and nanocomposite materials, JOM Journal of the Minerals, Metals and Materials Society, Vol: 68, Pages: 3042-3050, ISSN: 1047-4838
Metallurgists have an ever-increasing suite of analytical techniques at their disposition. Among these techniques are the in situ methods, being those approaches that are designed to actually study events that occur in the material during for instance solidification, (thermo)-mechanical working or heat treatment. As such they are a powerful tool in unraveling the mechanisms behind these processes, supplementary to ex situ methods that instead analyze the materials before and after their processing. In this paper, case studies are presented of how in situ imaging methods—and more specifically micro-focus x-ray radiography and synchrotron x-ray tomography—are used in the research and development of magnesium-based grain-refined and nanocomposite materials. These results are drawn from the EC collaborative research project ExoMet (www.exomet-project.eu). The first example concerns the solidification of a Mg-Nd-Gd alloy with Zr addition to assess the role of zirconium content and cooling rate in crystal nucleation and growth. The second example concerns the solidification of a Mg-Zn-Al alloy and its SiC-containing nanocomposite material to reveal the influence of particle addition on microstructural development. The third example concerns the (partial) melting–solidification of Elektron21/AlN and Elektron21/Y2O3 nanocomposite materials to study such effects as particle pushing/engulfment and agglomeration during repeated processing. Such studies firstly visualize and by that confirm what is known or assumed. Secondly, they advance science by monitoring and quantifying phenomena as they evolve during processing and by that contribute toward a better understanding of the physics at play.
Disney C, Madi K, Bodey A, et al., 2016, Visualising the 3D microscopic remodelling of mechanically loaded native tissues, Spring Meeting of the British-Society-for-Matrix-Biology (BSMB) on Grey Area - Age and the Extracellular Matrix, Publisher: WILEY, Pages: A16-A16, ISSN: 0959-9673
Guo E, Phillion AB, Cai B, et al., 2016, Dendritic evolution during coarsening of Mg-Zn alloys via 4D synchrotron tomography, Acta Materialia, Vol: 123, Pages: 373-382, ISSN: 1359-6454
The scale of solidification microstructures directly impacts micro-segregation, grain size, and other factors which control strength. Using in situ high speed synchrotron X-ray tomography we have directly quantified the evolution of dendritic microstructure length scales during the coarsening of Mg-Zn hcp alloys in three spatial dimensions plus time (4D). The influence of two key parameters, solute composition and cooling rate, was investigated. Key responses, including specific surface area, dendrite mean and Gauss curvatures, were quantified as a function of time and compared to existing analytic models. The 3D observations suggest that the coarsening of these hcp dendrites is dominated by both the re-melting of small branches and the coalescence of the neighbouring branches. The results show that solute concentration has a great impact on the resulting microstructural morphologies, leading to both dendritic and seaweed-type grains. It was found that the specific solid/liquid surface and its evolution can be reasonably scaled to time with a relationship of ∼ t−1/3. This term is path independent for the Mg-25 wt%Zn; that is, the initial cooling rate during solidification does not greatly influence the coarsening rate. However, path independence was not observed for the Mg-38 wt%Zn samples because of the seaweed microstructure. This led to large differences in the specific surface area (Ss) and its evolution both between the two alloy compositions and within the Mg-38 wt%Zn for the different cooling rates. These findings allow for microstructure models to be informed and validated to improve predictions of solidification microstructural length scales and hence strength.
Ennis BL, Jimenez-Melero E, Atzema EH, et al., 2016, Metastable austenite driven work-hardening behaviour in a TRIP-assisted dual phase steel, International Journal of Plasticity, Vol: 88, Pages: 126-139, ISSN: 1879-2154
The mechanically-induced transformation behaviour of the metastable austenite phase in a high-strength industrial TRIP-assisted Dual Phase steel was monitored in situ using high-energy synchrotron diffraction under uniaxial loading. This allowed direct quantification of the impact of the transformation of the metastable austenite phase (16 vol %), embedded in a ferrite-bainite-martensite matrix, on the work hardening behaviour of this steel. Our results show that the mechanically induced transformation of austenite does not begin until the onset of matrix yielding. We provide experimental evidence which demonstrates for the first time that the austenite transformation increases the work-hardening contribution, σw thereby supporting a driving force approach to transformation induced plasticity. The transformation work required leads to an increase in the macroscopic work-hardening rate after matrix yielding and continues to offset the decrease in the work-hardening rate in the ferrite and martensite phases up to the UTS. Further we show conclusively that martensite yielding does not occur until the completion of the mechanically induced transformation of austenite. Plastic deformation of martensite is immediately followed by local plastic instability leading to necking and ultimate failure of this material.
Saucedo-Mora L, Lowe T, Zhao S, et al., 2016, In situ observation of mechanical damage within a SiC-SiC ceramic matrix composite, Journal of Nuclear Materials, Vol: 481, Pages: 13-23, ISSN: 1873-4820
SiC-SiC ceramic matrix composites are candidate materials for fuel cladding in Generation IV nuclear fission reactors and as accident tolerant fuel clad in current generation plant. Experimental methods are needed that can detect and quantify the development of mechanical damage, to support modelling and qualification tests for these critical components. In situ observations of damage development have been obtained of tensile and C-ring mechanical test specimens of a braided nuclear grade SiC-SiC ceramic composite tube, using a combination of ex situ and in situ computed X-ray tomography observation and digital volume correlation analysis. The gradual development of damage by matrix cracking and also the influence of non-uniform loading are examined.
Godinho JR, Gerke KM, Stack AG, et al., 2016, The dynamic nature of crystal growth in pores, Scientific Reports, Vol: 6, ISSN: 2045-2322
The kinetics of crystal growth in porous media controls a variety of natural processes such as ore genesis and crystallization induced fracturing that can trigger earthquakes and weathering, as well as, sequestration of CO2 and toxic metals into geological formations. Progress on understanding those processes has been limited by experimental difficulties of dynamically studying the reactive surface area and permeability during pore occlusion. Here, we show that these variables cause a time-dependency of barite growth rates in microporous silica. The rate is approximately constant and similar to that observed on free surfaces if fast flow velocities predominate and if the time-dependent reactive surface area is accounted for. As the narrower flow paths clog, local flow velocities decrease, which causes the progressive slowing of growth rates. We conclude that mineral growth in a microporous media can be estimated based on free surface studies when a) the growth rate is normalized to the time-dependent surface area of the growing crystals, and b) the local flow velocities are above the limit at which growth is transport-limited. Accounting for the dynamic relation between microstructure, flow velocity and growth rate is shown to be crucial towards understanding and predicting precipitation in porous rocks.
Archilha NL, Missagia RM, Hollis C, et al., 2016, Permeability and acoustic velocity controlling factors determined from x-ray tomography images of carbonate rocks, AAPG Bulletin, Vol: 100, Pages: 1289-1309, ISSN: 0149-1423
Carbonate reservoir rocks exhibit a great variability in texture that directly impacts petrophysical parameters. Many exhibit bi- and multimodal pore networks, with pores ranging from less than 1 μm to several millimeters in diameter. Furthermore, many pore systems are too large to be captured by routine core analysis, and well logs average total porosity over different volumes. Consequently, prediction of carbonate properties from seismic data and log interpretation is still a challenge. In particular, amplitude versus offset classification systems developed for clastic rocks, which are dominated by connected, intergranular, unimodal pore networks, are not applicable to carbonate rocks.Pore geometrical parameters derived from digital image analysis (DIA) of thin sections were recently used to improve the coefficient of determination of velocity and permeability versus porosity. Although this substantially improved the coefficient of determination, no spatial information of the pore space was considered, because DIA parameters were obtained from two-dimensional analyses. Here, we propose a methodology to link local and global pore-space parameters, obtained from three-dimensional (3-D) images, to experimental physical properties of carbonate rocks to improve P-wave velocity and permeability predictions. Results show that applying a combination of porosity, microporosity, and 3-D geometrical parameters to P-wave velocity significantly improves the adjusted coefficient of determination from 0.490 to 0.962. A substantial improvement is also observed in permeability prediction (from 0.668 to 0.948). Both results can be interpreted to reflect a pore geometrical control and pore size control on P-wave velocity and permeability.
Tokudome Y, Fukui M, Tarutani N, et al., 2016, High-Density Protein Loading on Hierarchically Porous Layered Double Hydroxide Composites with a Rational Mesostructure, Langmuir, Vol: 32, Pages: 8826-8833, ISSN: 1520-5827
Hierarchically porous biocompatible Mg-Al-Cl-type layered double hydroxide (LDH) composites containing aluminum hydroxide (Alhy) have been prepared using a phase-separation process. The sol-gel synthesis allows for the hierarchical pores of the LDH-Alhy composites to be tuned, leading to a high specific solid surface area per unit volume available for high-molecular-weight protein adsorptions. A linear relationship between the effective surface area, SEFF, and loading capacity of a model protein, bovine serum albumin (BSA), is established following successful control of the structure of the LDH-Alhy composite. The threshold of the mean pore diameter, Dpm, above which BSA is effectively adsorbed on the surface of LDH-Alhy composites, is deduced as 20 nm. In particular, LDH-Alhy composite aerogels obtained via supercritical drying exhibit an extremely high capacity for protein loading (996 mg/g) as a result of a large mean mesopore diameter (>30 nm). The protein loading on LDH-Alhy is >14 times that of a reference LDH material (70 mg/g) prepared via a standard procedure. Importantly, BSA molecules pre-adsorbed on porous composites were successfully released on soaking in ionic solutions (HPO4(2-) and Cl(-) aqueous). The superior capability of the biocompatible LDH materials for loading, encapsulation, and releasing large quantities of proteins was clearly demonstrated.
Shuai S, Guo E, Phillion AB, et al., 2016, Fast synchrotron X-ray tomographic quantification of dendrite evolution during the solidification of Mg-Sn alloys, Acta Materialia, Vol: 118, Pages: 260-269, ISSN: 1873-2453
The evolution of dendritic microstructures during the solidification of a Mg-15 wt%Sn alloy was investigated in situ via fast synchrotron X-ray microtomography. To enable these in situ observations a novel encapsulation method was developed and integrated into a fast, pink beam, imaging beamline at Diamond Light Source. The dendritic growth was quantified with time using: solid volume fraction, tip velocity, interface specific surface area, and surface curvature. The influence of cooling rate upon these quantities and primary phase nucleation was investigated. The primary dendrites grew with an 18-branch, 6-fold symmetry structure, accompanied by coarsening. The coarsening process was assessed by the specific surface area and was compared with the existing models. These results provide the first quantification of dendritic growth during the solidification of Mg alloys, confirming existing analytic models and providing experimental data to inform and validate more complex numeric models.
Cai B, Wang J, Kao A, et al., 2016, 4D synchrotron X-ray tomographic quantification of the transition from cellular to dendrite growth during directional solidification, Acta Materialia, Vol: 117, Pages: 160-169, ISSN: 1873-2453
Solidification morphology directly impacts the mechanical properties of materials; hence many models of the morphological evolution of dendritic structures have been formulated. However, there is a paucity of validation data for directional solidification models, especially the direct observations of metallic alloys, both for cellular and dendritic structures. In this study, we performed 4D synchrotron X-ray tomographic imaging (three spatial directions plus time), to study the transition from cellular to a columnar dendritic morphology and the subsequent growth of columnar dendrite in a temperature gradient stage. The cellular morphology was found to be highly complex, with frequent lateral bridging. Protrusions growing out of the cellular front with the onset of morphological instabilities were captured, together with the subsequent development of these protrusions into established dendrites. Other mechanisms affecting the solidification microstructure, including dendrite fragmentation/pinch-off were also captured and the quantitative results were compared to proposed mechanisms. The results demonstrate that 4D imaging can provide new data to both inform and validate solidification models.
Xu W, Horsfield AP, Wearing D, et al., 2016, Diversification of MgO//Mg interfacial crystal orientations during oxidation: A density functional theory study, Journal of Alloys and Compounds, Vol: 688, Pages: 1233-1240, ISSN: 1873-4669
In this work we use computer simulations to explain the variety of crystal orientations observed at interfaces between MgO and Mg when Mg single crystals are oxidized. Using first-principles density functional theory simulations we investigate the interfacial stability of MgO//Mg interfaces, and find that a combination of interfacial chemical bonding energy and epitaxial strain stored in the oxide layers can change the relative stability of competing MgO//Mg interfaces. We propose that a combination of the oxygen chemical potential at the interface plane and the epitaxial strain energy stored in the oxide layers is responsible for the differences in observed interfacial crystal orientations–a key insight for the design and development of Mg alloys reinforced by MgO particles.
Shuai S, Guo E, Wang M, et al., 2016, Anomalous alpha-Mg dendrite growth during directional solidification of a Mg-Zn alloy, Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, Vol: 47, Pages: 4368-4373, ISSN: 1543-1940
Dendritic morphology was investigated in a directionally solidified magnesium-zinc alloy using synchrotron X-ray tomography and electron backscattered diffraction. Unexpectedly, primary dendrites grew along ⟨213¯¯¯1⟩⟨213¯1⟩ , rather than the previously reported ⟨112¯¯¯0⟩⟨112¯0⟩ and ⟨224¯¯¯5⟩⟨224¯5⟩ directions. Further, seven asymmetric sets of side branches formed, instead of six-fold symmetric arms, evolving with three coexisting morphologies per trunk of: traditional, seaweed structure, and free growth. The anomalous growth is attributed to the imposed thermal gradient and zinc-induced interfacial energy anisotropy variations.
Lin Q, Neethling SJ, Courtois L, et al., 2016, Multi-scale quantification of leaching performance using X-ray tomography, Hydrometallurgy, Vol: 164, Pages: 265-277, ISSN: 0304-386X
The performance of heap leaching is dictated by a large number of processes acting at a wide range of length scales. One important scale is that of the individual particles, where the interaction between the rate kinetics at the surfaces of the individual mineral grains and the mass transport through the particle combine to give the overall apparent particle scale kinetics. It has been recognised for a long time that variability in the mineralogy, size and spatial distribution of the mineral grains within the particle are likely to have a large effect on the leach performance and its variability and thus, ultimately, the performance of the heap. In this paper a new method for quantifying this behaviour and its variability at scales from the particle through to the grain and down to the surface kinetics is presented. This method is based on the use of a series of XMT (also called micro-CT) images of a column taken at regular intervals over 168 days of leaching. The key development in the analysis of this data is an algorithm that has allowed every single one of the hundreds of thousands of mineral grains within the column to be individually tracked across all the time points as they undergo dissolution. This has allowed the dependency of the mineral grain leach rate on its size and position in the particle to be decoupled from one another. It also meant that the variability in the surface kinetics of the grains could be assessed, with mineralogical variability being the key source of this variability. We demonstrate that understanding and quantifying this underlying kinetic variability is important as it has a major impact on the time evolution of the average kinetics of the leaching.
Kazantsev D, Ovtchinnikov E, Withers PJ, et al., 2016, Sparsity seeking total generalized variation for undersampled tomographic reconstruction, IEEE 13th International Symposium on Biomedical Imaging (ISBI), Publisher: IEEE, Pages: 731-734, ISSN: 1945-8452
Here we present a novel iterative approach for tomographic image reconstruction which improves image quality for undersampled and limited view projection measurements. Recently, the Total Generalized Variation (TGV) penalty has been proposed to establish a desirable balance between smooth and piecewise-constant solutions. Piecewise-smooth reconstructions are particularly important for biomedical applications, where the image surface slowly varies. The TGV penalty convexly combines the first and higher order derivatives, which means that for some regions (e.g. uniform background) it can be more challenging to find a sparser solution due to the weight of the higher order term. Therefore we propose a simple heuristic modification over the Chambolle-Pock reconstruction scheme for TGV which consists of adding the wavelet thresholding step which helps to suppress aliasing artifacts and noise while preserve piecewise-smooth appearance. Preliminary numerical results with two piecewise-smooth phantoms show strong improvement of the proposed method over TGV and TV penalties. The resulting images are smooth with sharp edges and fewer artifacts visible.
Midha S, Tripathi R, Geng H, et al., 2016, Elucidation of differential mineralisation on native and regenerated silk matrices, Materials Science and Engineering C, Vol: 68, Pages: 663-674, ISSN: 1873-0191
Bone mineralisation is a well-orchestrated procedure triggered by a protein-based template inducing the nucleation of hydroxyapatite (HA) nanocrystals on the matrix. In an attempt to fabricate superior nanocomposites from silk fibroin, textile braided structures made of natively spun fibres of Bombyx mori silkworm were compared against regenerated fibroin (lyophilized and films) underpinning the influence of intrinsic properties of fibroin matrices on HA nucleation. We found that native braids could bind Ca(2+) ions through electrostatic attraction, which initiated the nucleation and deposition of HA, as evidenced by discrete shift in amide peaks via ATR-FTIR. This phenomenon also suggests the involvement of amide linkages in promoting HA nucleation on fibroin. Moreover, CaCl2-SBF immersion of native braids resulted in preferential growth of HA along the c-axis, forming needle-like nanocrystals and possessing Ca/P ratio comparable to commercial HA. Though regenerated lyophilized matrix also witnessed prominent peak shift in amide linkages, HA growth was restricted to (211) plane only, albeit at a significantly lower intensity than braids. Regenerated films, on the other hand, provided no crystallographic evidence of HA deposition within 7days of SBF immersion. The present work sheds light on the primary fibroin structure of B. mori which probably plays a crucial role in regulating template-induced biomineralisation on the matrix. We also found that intrinsic material properties such as surface roughness, geometry, specific surface area, tortuosity and secondary conformation exert influence in modulating the extent of mineralisation. Thus our work generates useful insights and warrants future studies to further investigate the potential of bone mimetic, silk/mineral nanocomposite matrices for orthopaedic applications.
Ennis BL, Jimenez-Melero E, Mostert R, et al., 2016, The role of aluminium in chemical and phase segregation in a TRIP-assisted dual phase steel, Acta Materialia, Vol: 115, Pages: 132-142, ISSN: 1873-2453
In this work we demonstrate that micro-segregation patterns of alloying elements present in a high-strength TRIP-assisted DP steel after casting are retained in the microstructure throughout processing, and lead to anisotropy (banding) in the final microstructure. In particular, we have assessed the role of Al on the chemical segregation of Mn, Cr and Si during casting, and their impact on the phase transformations occurring during thermo-mechanical processing of the as-cast material. We have derived the elemental partition coefficients, based on the experimentally determined dendrite spacing and chemical profiles in the as-cast structure, and used them to derive the local austenite-to-ferrite transformation temperature. Our cellular automaton methodology to simulate phase transformations allows reliable prediction of the formation or suppression of banding in the intermediate and final microstructures for different heating or cooling rates. Our results reveal that aluminium exerts the largest individual effect of the substitutional elements on the formation of banding in these steels. Controlling micro-segregation during solidification in advanced high-strength multiphase steels is therefore critical for obtaining homogeneous mechanical properties in the final product, as it controls the phase transformations occurring during thermo-mechanical processing and therefore the final microstructure.
Hughes AE, Trinchi A, Chen FF, et al., 2016, Structure and Transport in Coatings from Multiscale Computed Tomography of Coatings-New Perspectives for Eelectrochemical Impedance Spectroscopy Modeling?, ELECTROCHIMICA ACTA, Vol: 202, Pages: 243-252, ISSN: 0013-4686
Poologasundarampillai G, Lee PD, Lam C, et al., 2016, Compressive strength of bioactive sol-gel glass foam scaffolds, International Journal of Applied Glass Science, Vol: 7, Pages: 229-237, ISSN: 2041-1294
Larry Hench's 45S5 Bioglass® has been used in more than a million patients as a synthetic bone graft, in the form of a particulate. Bioglass is able to stimulate more bone regeneration than other bioactive ceramics. However, it is not commercially available as a porous scaffold with amorphous glass structure because the 45S5 composition crystallizes during sintering. The sol–gel foaming process was developed in Hench's laboratory to overcome this problem. Here, we concisely review the work on scaffold development from Hench's group and report new data that show maximum compressive strengths in excess of 5 MPa can be achieved while maintaining the interconnected pore networks required for vascularized bone ingrowth. This was achieved through optimization of sintering of the sol–gel foams. Sintering of the sol–gel foams was correlated to the network connectivity and silanol content. Changes in strength after immersion in simulated body fluid were found to be small over the times investigated. Relating the dissolution results to in vivo studies indicates that the scaffolds degrade more rapidly in vivo than in vitro.
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