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Journal articleGarcia Tunon Blanca E, Machado G, Schneider M, et al., 2016,
Complex ceramic architectures by directed assembly of ‘responsive’ particles
, Journal of the European Ceramic Society, Vol: 37, Pages: 199-211, ISSN: 1873-619XSurface functionalization of alumina powders with a responsive surfactant(BCS) leads to particles that react to a chemical switch. These ‘responsive’ building blocksare capable of assembling into macroscopic and complex ceramic structures. The aggregationfollows a bottom up approach and can be easily controlled. The directed assembly ofconcentrated suspensions leads to highly dense (~99%) ceramic components with average4-point bending strength of ~200 MPa. On the other hand, the emulsification of suspensionswith concentrations from 7 to 43 vol% and 50 vol% decane results in emulsions withdifferent properties (stability, droplet size and distribution). The oil droplets provide a softtemplate confining the alumina particles in the continuous phase and at the oil/water interfaces.Aggregation of these emulsions followed by drying and sintering leads tomacroporous (pore sizes ranging from 30 to 4 µm) alumina structures with complex shapesand a wide range of microstructures, from closed cell structures to highly interconnected foams with total porosities up to 83%. Alumina scaffolds with ~55 % porosity can reachcrushing strength values above 300 MPa in compression and ~50 MPa in 4-point bending.
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Journal articleEslava S, Reynal A, Rocha VG, et al., 2016,
Using graphene oxide as a sacrificial support of polyoxotitanium clusters to replicate its two-dimensionality on pure titania photocatalysts
, Journal of Materials Chemistry A, Vol: 4, Pages: 7200-7206, ISSN: 2050-7496The nanostructure optimisation of metal oxides is of crucial importance to exploit their qualities in artificial photosynthesis, photovoltaics and heterogeneous catalysis. Therefore, it is necessary to find viable and simple fabrication methods to tune their nanostructure. Here we reveal that graphene oxide flakes, known for their nano- and two-dimensionality, can be used as a sacrificial support to replicate their nano- and two-dimensionality in photocatalytic titania. This is demonstrated in the calcination of Ti16O16(OEt)32 polyoxotitanium clusters together with graphene oxide flakes, which results in pure titania nanoflakes of <10 nm titania nanoparticles in a two-dimensional arrangement. These titania nanoflakes outperform the titania prepared from only Ti16O16(OEt)32 clusters by a factor of forty in the photocatalytic hydrogen production from aqueous methanol suspensions, as well as the benchmark P25 titania by a factor of five. These outcomes reveal the advantage of using polyoxotitanium clusters with graphene oxide and open a new avenue for the exploitation of the vast variety of polyoxometalate clusters as precursors in catalysis and photovoltaics, as well as the use of graphene oxide as a sacrificial support for nanostructure optimisation.
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Journal articleScatigno GG, Ryan MP, Giuliani F, et al., 2016,
The effect of prior cold work on the chloride stress corrosion cracking of 304L austenitic stainless steel under atmospheric conditions
, Materials Science and Engineering: A, Vol: 668, Pages: 20-29, ISSN: 0921-5093A systematic study of the effect of cold work (CW) on chloride-induced stress corrosion cracking (SCC) in 304L stainless steel was performed. CW between 0% and 40% was applied prior to corrosion of specimens at 75 °C and 70% relative humidity, for 500 h, using MgCl2 (at atmospheric pressure). Samples cracked most readily between 0.5% and 5% CW; at 20% and above no cracks were present. Additionally, above 5% CW, some specific orientation relationships become evident, with cracks primarily aligned along <111> parallel to the transverse direction. The results suggest that at levels of CW >20%, the synergistic effect of micro-mechanisms may hinder SCC in this system.
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Journal articleD'Elia E, Eslava S, Miranda M, et al., 2016,
Autonomous self-healing structural composites with bio-inspired design
, Scientific Reports, Vol: 6, ISSN: 2045-2322Strong and tough natural composites such as bone, silk or nacre are often built from stiff blocks boundtogether using thin interfacial soft layers that can also provide sacrificial bonds for self-repair. Herewe show that it is possible exploit this design in order to create self-healing structural composites byusing thin supramolecular polymer interfaces between ceramic blocks. We have built model brick-andmortarstructures with ceramic contents above 95 vol% that exhibit strengths of the order of MPa(three orders of magnitude higher than the interfacial polymer) and fracture energies that are twoorders of magnitude higher than those of the glass bricks. More importantly, these properties can befully recovered after fracture without using external stimuli or delivering healing agents. This approachdemonstrates a very promising route towards the design of strong, ideal self-healing materials able toself-repair repeatedly without degradation or external stimuli.
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Journal articleBhowmik A, Dolbnya I, Britton TB, et al., 2016,
Using coupled micropillar compression and micro-Laue diffraction to investigate deformation mechanisms in a complex metallic alloy Al13Co4
, Applied Physics Letters, Vol: 108, ISSN: 0003-6951In this study, we have used in-situ micro-Laue diffraction combined with micropillar compression of focused ion beam milled Al13Co4 complex metallic alloy to investigate the evolution of deformation in Al13Co4. Streaking of the Laue spots shows that the onset of plastic flow occurs at stresses as low as 0.8 GPa, although macroscopic yield only becomes apparent at 2 GPa. The measured misorientations, obtained from peak splitting, enable the geometrically necessary dislocation density to be estimated as 1.1 1013 m-2.
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Journal articleNasiri NA, Saiz E, Giuliani F, et al., 2016,
Grain bridging locations of monolithic silicon carbide by means of focused ion beam milling technique
, Materials Letters, Vol: 173, Pages: 214-218, ISSN: 1873-4979A slice and view approach using a focused ion beam (FIB) milling technique was employed to investigate grain bridging near the tip of cracks in four silicon carbide (SiC) based materials with different grain boundary chemistries and grain morphologies. Using traditional observations intergranular fracture behaviour and hence clear evidence of grain bridging was found for SiC based materials sintered with oxide additives. More surprisingly, in large grain materials, the FIB technique reveals evidence of grain bridging irrespective of the grain boundary chemistry, i.e. also in materials which macroscopically fail by transgranular failure. This helps to explain why the toughness of large grained materials is higher even if failure is transgranular.
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Journal articleFerraro C, Garcia-Tuñon E, Rocha VG, et al., 2016,
Light and strong SiC networks
, Advanced Functional Materials, Vol: 26, Pages: 1636-1645, ISSN: 1616-301XThe directional freezing of microfiber suspensions is used to assemble highly porous (porosities ranging between 92% and 98%) SiC networks. These networks exhibit a unique hierarchical architecture in which thin layers with honeycomb‐like structure and internal strut length in the order of 1–10 μm in size are aligned with an interlayer spacing ranging between 15 and 50 μm. The resulting structures exhibit strengths (up to 3 MPa) and stiffness (up to 0.3 GPa) that are higher than aerogels of similar density and comparable to other ceramic microlattices fabricated by vapor deposition. Furthermore, this wet processing technique allows the fabrication of large‐size samples that are stable at high temperature, with acoustic impedance that can be manipulated over one order of magnitude (0.03–0.3 MRayl), electrically conductive and with very low thermal conductivity. The approach can be extended to other ceramic materials and opens new opportunities for the fabrication of ultralight structures with unique mechanical and functional properties in practical dimensions.
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Journal articleVandeperre LJ, Wang X, Atkinson A, 2016,
Measurement of mechanical properties using slender cantilever beams
, Journal of the European Ceramic Society, Vol: 36, Pages: 2003-2007, ISSN: 1873-619XThe measurement of mechanical properties of materials only available in the form of thin sheets requires the use of load cells and displacement sensors of high sensitivity at low applied loads. These are available in testing platforms such as instrumented nano-indenters. In the current work, the elastic modulus and fracture toughness of thin cantilever beams of a representative brittle thin sheet material (300 μm thick NiO/YSZ support for a solid oxide fuel cell) were measured using a micro-/nano-indenter. The Young’s modulus and KIC were determined to be 139 ± 4 GPa and 2.13 ± 0.27 MPa m0.5 respectively using this method.
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Journal articleChabi S, Rocha VG, Garcia-Tunon E, et al., 2016,
Ultralight, Strong, Three-Dimensional SiC Structures
, ACS NANO, Vol: 10, Pages: 1871-1876, ISSN: 1936-0851 -
Conference paperHatt O, Larsson H, Giuliani F, et al., 2016,
Predicting chemical wear in machining titanium alloys via a novel low cost diffusion couple method
, 3rd CIRP Conference on Surface Integrity, Publisher: ELSEVIER SCIENCE BV, Pages: 219-222, ISSN: 2212-8271- Author Web Link
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- Citations: 20
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Journal articleGlymond D, Vick M, Pan M-J, et al., 2015,
Creep of mullite zirconia composites
, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 35, Pages: 3607-3611, ISSN: 0955-2219- Author Web Link
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- Citations: 2
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Journal articleBoix M, Eslava S, Machado GC, et al., 2015,
ATR-FTIR measurements of albumin and fibrinogen adsorption: Inert versus calcium phosphate ceramics
, JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, Vol: 103, Pages: 3493-3502, ISSN: 1549-3296- Author Web Link
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- Citations: 10
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Journal articleNi N, Barg S, Garcia-Tunon E, et al., 2015,
Understanding Mechanical Response of Elastomeric Graphene Networks
, Scientific Reports, Vol: 5, ISSN: 2045-2322Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.
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Journal articleD'Elia E, Barg S, Ni N, et al., 2015,
Self-healing graphene-based composites with sensing capabilities
, Advanced Materials, Vol: 32, Pages: 4788-4794, ISSN: 1521-4095A self-healing composite is fabricated by confining a supramolecular polymer in a graphene network. The network provides electrical conductivity. Upon damage, the polymer is released and flows to reform the material. Healing is repeatable and autonomous. The composite is sensitive to pressure and flexion and recovers its mechanical and electrical properties even when rejoining cut surfaces after long exposure times.
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Journal articleWang D, Romer F, Connell L, et al., 2015,
Highly flexible silica/chitosan hybrid scaffolds with oriented pores for tissue regeneration
, Journal of Materials Chemistry B, Vol: 3, Pages: 7560-7576, ISSN: 2050-7518Inorganic/organic sol–gel hybrids have nanoscale co-networks of organic and inorganic components that give them the unique potential of tailored mechanical properties and controlled biodegradation in tissue engineering applications. Here, silica/chitosan hybrid scaffolds with oriented structures were fabricated through the sol–gel method with a unidirectional freeze casting process. 3-Glycidoxypropyl trimethoxysilane (GPTMS) was used to obtain covalent inorganic/organic coupling. Process variables were investigated such as cooling rate, GPTMS and inorganic content, which can be used to tailor the mechanical properties and hybrid chemical coupling. Structural characterization and dissolution tests confirmed the covalent cross-linking of the chitosan and the silica network in hybrids. The scaffolds had a directional lamellar structure along the freezing direction and a cellular morphology perpendicular to the freezing direction. Compression testing showed that the scaffolds with 60 wt% organic were flexible and elastomeric perpendicular to the freezing direction whilst behaving in an elastic-brittle fashion parallel to the freezing direction. The compressive strengths are about one order of magnitude higher in the latter direction reaching values of the order of 160 kPa. This behaviour provides potential for clinicians to be able to squeeze the materials to fit tissue defect sites while providing some mechanical support from the other direction.
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Journal articleAl Nasiri N, Ni N, Saiz E, et al., 2015,
Effect of microstructure and grain boundary chemistry on slow crack growth in silicon carbide at ambient conditions
, Journal of the European Ceramic Society, Vol: 35, Pages: 2253-2260, ISSN: 0955-2219Silicon carbide (SiC) is being used increasingly as a room temperature structural material in environments where moisture cannot always be excluded. Unfortunately, there have been almost no reports on slow crack growth (SCG) in SiC at room temperature. To address this gap, SCG in SiC was studied using constant stress rate and double torsion tests in water. SiC based materials were produced with a wide range of grain boundary chemistries and microstructures, which may affect their slow crack growth behaviour. To clarify the role of chemistry and microstructure respectively, solid state (SS) sintering with carbon and boron along with liquid phase (LP) sintering using oxides additives were used to produce materials with fine and coarse grains. The LP-SiC was three times more sensitive to SCG than SS-SiC materials. Moreover, the larger grained material with a higher toughness was less sensitive to SCG than the materials with fine grains.
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Journal articleChen Z, Wang X, Giuliani F, et al., 2015,
Microstructural characteristics and elastic modulus of porous solids
, Acta Materialia, Vol: 89, Pages: 268-277, ISSN: 1359-6454Porous La0.6Sr0.4Co0.2Fe0.8O3−δ ceramic films with different porosities were fabricated by constrained sintering on dense substrates of Gd-doped ceria at 900-1200 °C. The actual digital three dimensional microstructures of the as-sintered films were reconstructed using focused ion beam/scanning electron microscope tomography and their elastic moduli were calculated using finite element modelling based on the reconstructed microstructures. The calculated moduli were found to be in good agreement with experimental results. Porosity was found to be the primary factor influencing the elastic modulus. In order to explore the influence of microstructural features other than porosity the real microstructures, and artificial microstructures based on spherical mono-size particles, were coarsened numerically at constant porosity using a cellular automaton method. The simulation results showed that in the initial stages of sintering, when interparticle necks are small, the modulus increases with the neck size. However, as the coarsening increases further, the modulus becomes insensitive to the details of the microstructure and only depends on porosity. The results also show that simulation gives inaccurate results if the ratio of characteristic length of the simulated volume to the characteristic length of the microstructure is too small (less than approximately a factor of 8).
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Journal articleRodriguez-Florez N, Garcia-Tunon E, Mukadam Q, et al., 2015,
An Investigation of the Mineral in Ductile and Brittle Cortical Mouse Bone
, JOURNAL OF BONE AND MINERAL RESEARCH, Vol: 30, Pages: 786-795, ISSN: 0884-0431- Author Web Link
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- Citations: 45
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Journal articleWeekes HE, Vorontsov VA, Dolbnya IP, et al., 2015,
In situ micropillar deformation of hydrides in Zircaloy-4
, Acta Materialia, Vol: 92, Pages: 81-96, ISSN: 1873-2453Deformation of hydrided Zircaloy-4 has been examined using in situ loading of hydrided micropillars in the scanning electron microscope and using synchrotron X-ray Laue microbeam diffraction. Results suggest that both the matrix and hydride can co-deform, with storage of deformation defects observed within the hydrides, which were twinned. Hydrides placed at the plane of maximum shear stress showed deformation within the hydride packet, whilst packets in other pillars arrested the propagation of shear bands. X-ray Laue peak broadening, prior to deformation, was associated with the precipitation of hydrides, and during deformation plastic rotation and broadening of both the matrix and hydride peaks were observed. Post-mortem TEM of the deformed pillars has indicated a greater density of dislocations associated with the precipitated hydride packets, while the observed broadening of the hydride electron diffraction spots further suggests that plastic strain gradients were induced in the hydrides by compression.
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Journal articleChen Z, Wang X, Giuliani F, et al., 2015,
Fracture toughness of porous material of LSCF in bulk and film forms
, Journal of the American Ceramic Society, Vol: 98, Pages: 2183-2190, ISSN: 1551-2916 -
Journal articleGarcia-Tunon E, Barg S, Franco J, et al., 2015,
Printing in three dimensions with graphene
, Advanced Materials, Vol: 27, Pages: 1688-1693, ISSN: 1521-4095Responsive graphene oxide sheets form non‐covalent networks with optimum rheological properties for 3D printing. These networks have shear thinning behavior and sufficiently high elastic shear modulus (G′) to build self‐supporting 3D structures by direct write assembly. Drying and thermal reduction leads to ultra‐light graphene‐only structures with restored conductivity and elastomeric behavior.
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Journal articleAl Nasiri N, Saiz E, Giuliani F, et al., 2015,
Effect of microstructure and slow crack growth on lifetime prediction of monolithic silicon carbide
, Materials Science and Engineering A - Structural Materials Properties Microstructure and Processing, Vol: 627, Pages: 290-295, ISSN: 0921-5093 -
Journal articleBourtsalas A, Vandeperre LJM, Grimes SM, et al., 2015,
Production of pyroxene ceramics from the fine fraction of incinerator bottom ash
, Waste Management, Vol: 45, Pages: 217-225, ISSN: 0956-053XIncinerator bottom ash (IBA) is normally processed to extract metals and the coarse mineral fraction is used as secondary aggregate. This leaves significant quantities of fine material, typically less than 4mm, that is problematic as reuse options are limited. This work demonstrates that fine IBA can be mixed with glass and transformed by milling, calcining, pressing and sintering into high density ceramics. The addition of glass aids liquid phase sintering, milling increases sintering reactivity and calcining reduces volatile loss during firing. Calcining also changes the crystalline phases present from quartz (SiO2), calcite (CaCO3), gehlenite (Ca2Al2SiO7) and hematite (Fe2O3) to diopside (CaMgSi2O6), clinoenstatite (MgSiO3) and andradite (Ca3Fe2Si3O12). Calcined powders fired at 1080°C have high green density, low shrinkage (<7%) and produce dense (2.78g/cm3) ceramics that have negligible water absorption. The transformation of the problematic fraction of IBA into a raw material suitable for the manufacture of ceramic tiles for use in urban paving and other applications is demonstrated.
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Journal articleProctor JE, Bhakhri V, Hao R, et al., 2015,
Stabilization of boron carbide via silicon doping
, Journal of Physics: Condensed Matter, Vol: 27, ISSN: 0953-8984Boron carbide is one of the lightest and hardest ceramics, but its applications are limited by its poor stability against a partial phase separation into separate boron and carbon. Phase separation is observed under high non-hydrostatic stress (both static and dynamic), resulting in amorphization. The phase separation is thought to occur in just one of the many naturally occurring polytypes in the material, and this raises the possibility of doping the boron carbide to eliminate this polytype. In this work, we have synthesized boron carbide doped with silicon. We have conducted a series of characterizations (transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and x-ray diffraction) on pure and silicon-doped boron carbide following static compression to 50 GPa non-hydrostatic pressure. We find that the level of amorphization under static non-hydrostatic pressure is drastically reduced by the silicon doping.
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Journal articleMenzel R, Barg S, Miranda M, et al., 2015,
Joule Heating Characteristics of Emulsion-Templated Graphene Aerogels
, ADVANCED FUNCTIONAL MATERIALS, Vol: 25, Pages: 28-35, ISSN: 1616-301X- Author Web Link
- Open Access Link
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- Citations: 97
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Journal articleChen Z, Wang X, Giuliani F, et al., 2015,
Analyses of microstructural and elastic properties of porous SOFC cathodes based on focused ion beam tomography
, JOURNAL OF POWER SOURCES, Vol: 273, Pages: 486-494, ISSN: 0378-7753- Author Web Link
- Open Access Link
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- Citations: 26
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Journal articleWegst UGK, Bai H, Saiz E, et al., 2015,
Bioinspired structural materials
, NATURE MATERIALS, Vol: 14, Pages: 23-36, ISSN: 1476-1122- Author Web Link
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- Citations: 2812
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Conference paperChen Z, Giuliani F, Atkinson A, 2015,
DETERMINATION OF ELASTIC MODULI FOR POROUS SOFC CATHODE FILMS USING NANOINDENTATION AND FEM
, 38th International Conference on Advanced Ceramics and Composites (ICACC), Publisher: AMER CERAMIC SOC, Pages: 111-128- Author Web Link
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- Citations: 1
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Conference paperVaranasi VG, Russias J, Saiz E, et al., 2015,
NOVEL PLA- AND PCL-HA POROUS 3D SCAFFOLDS PREPARED BY ROBOCASTING FACILITATE MC3T3-E1 SUBCLONE 4 CELLULAR ATTACHMENT AND GROWTH
, Next Generation Biomaterials and Surface Properties of Biomaterials Symposia during the Materials Science and Technology Conference and Exhibition (MS and T), Publisher: JOHN WILEY & SONS INC, Pages: 175-186, ISSN: 1042-1122 -
Journal articleSpathi C, Young N, Heng JYY, et al., 2014,
A simple method for preparing super-hydrophobic powder from paper sludge ash
, Materials Letters, Vol: 142, Pages: 80-83, ISSN: 1873-4979Paper sludge ash (PSA) is a readily available waste material generated by the paper recycling industry. This work reports on the production of hydrophobic powders by dry milling PSA in the presence of a fatty acid surface functionalising agent. Optimum laboratory processing involves dry milling for 8 h with a 4 wt.% addition of stearic acid and this produced a super-hydrophobic powder with a water contact angle of 153°. Different chain length fatty acids were investigated but stearic acid produced the highest hydrophobicity. The super-hydrophobicity of PSA results from the micro-particulate texture induced by dry milling with simultaneous formation of calcium stearate self-assembling surface monolayers chemically bonded to fracture surfaces.
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