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  • Journal article
    Ferraro C, Garcia-Tuñon E, Rocha VG, Barg S, Fariñas MD, Alvarez-Arenas TEG, Sernicola G, Giuliani F, Saiz Gutierrez Eet al., 2016,

    Light and strong SiC networks

    , Advanced Functional Materials, Vol: 26, Pages: 1636-1645, ISSN: 1616-301X

    The 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.
  • Journal article
    Vandeperre 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: 1873-619X

    The 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.
  • Journal article
    Chabi S, Rocha VG, Garcia-Tunon E, Ferraro C, Saiz E, Xia Y, Zhu Yet al., 2016,

    Ultralight, Strong, Three-Dimensional SiC Structures

    , ACS NANO, Vol: 10, Pages: 1871-1876, ISSN: 1936-0851
  • Conference paper
    Hatt O, Larsson H, Giuliani F, Crawforth P, Wynne B, Jackson Met 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
  • Journal article
    Boix M, Eslava S, Machado GC, Gosselin E, Ni N, Saiz E, De Coninck Jet 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
  • Journal article
    Glymond D, Vick M, Pan M-J, Giuliani F, Vandeperre LJet al., 2015,

    Creep of mullite zirconia composites

    , JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 35, Pages: 3607-3611, ISSN: 0955-2219
  • Journal article
    Ni N, Barg S, Garcia-Tunon E, Macul Perez F, Miranda M, Lu C, Mattevi C, Saiz Eet al., 2015,

    Understanding Mechanical Response of Elastomeric Graphene Networks

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    Ultra-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.
  • Journal article
    D'Elia E, Barg S, Ni N, Rocha VG, Saiz Eet al., 2015,

    Self-healing graphene-based composites with sensing capabilities

    , Advanced Materials, Vol: 32, Pages: 4788-4794, ISSN: 1521-4095

    A 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.
  • Journal article
    Wang D, Romer F, Connell L, Walter C, Saiz E, Yue S, Lee PD, McPhail DS, Hanna JV, Jones JRet 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: 2050-7518

    Inorganic/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.
  • Journal article
    Al Nasiri N, Ni N, Saiz E, Chevalier J, Giuliani F, Vandeperre LJet 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: 0955-2219

    Silicon 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.
  • Journal article
    Chen Z, Wang X, Giuliani F, Atkinson Aet al., 2015,

    Microstructural characteristics and elastic modulus of porous solids

    , Acta Materialia, Vol: 89, Pages: 268-277, ISSN: 1359-6454

    Porous 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).
  • Journal article
    Rodriguez-Florez N, Garcia-Tunon E, Mukadam Q, Saiz E, Oldknow KJ, Farquharson C, Millan JL, Boyde A, Shefelbine SJet 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
  • Journal article
    Weekes HE, Vorontsov VA, Dolbnya IP, Plummer JD, Giuliani F, Britton TB, Dye Det al., 2015,

    In situ micropillar deformation of hydrides in Zircaloy-4

    , Acta Materialia, Vol: 92, Pages: 81-96, ISSN: 1873-2453

    Deformation 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.
  • Journal article
    Chen Z, Wang X, Giuliani F, Atkinson Aet 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 article
    Al Nasiri N, Saiz E, Giuliani F, Vandeperre LJet 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 article
    Garcia-Tunon E, Barg S, Franco J, Bell R, Eslava S, D'Elia E, Maher RC, Guitian F, Saiz Eet al., 2015,

    Printing in three dimensions with graphene

    , Advanced Materials, Vol: 27, Pages: 1688-1693, ISSN: 1521-4095

    Responsive 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.
  • Journal article
    Bourtsalas A, Vandeperre LJM, Grimes SM, Themelis NJ, Cheeseman CRet al., 2015,

    Production of pyroxene ceramics from the fine fraction of incinerator bottom ash

    , Waste Management, Vol: 45, Pages: 217-225, ISSN: 0956-053X

    Incinerator 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.
  • Journal article
    Proctor JE, Bhakhri V, Hao R, Prior TJ, Scheler T, Gregoryanz E, Chhowalla M, Giulani Fet al., 2015,

    Stabilization of boron carbide via silicon doping

    , Journal of Physics: Condensed Matter, Vol: 27, ISSN: 0953-8984

    Boron 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.
  • Journal article
    Menzel R, Barg S, Miranda M, Anthony DB, Bawaked SM, Mokhtar M, Al-Thabaiti SA, Basahel SN, Saiz E, Shaffer MSPet al., 2015,

    Joule Heating Characteristics of Emulsion-Templated Graphene Aerogels

    , ADVANCED FUNCTIONAL MATERIALS, Vol: 25, Pages: 28-35, ISSN: 1616-301X
  • Conference paper
    Chen 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
  • Conference paper
    Varanasi VG, Russias J, Saiz E, Loomer PM, Tomsia APet 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 article
    Chen Z, Wang X, Giuliani F, Atkinson Aet 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
  • Journal article
    Wegst UGK, Bai H, Saiz E, Tomsia AP, Ritchie ROet al., 2015,

    Bioinspired structural materials

    , NATURE MATERIALS, Vol: 14, Pages: 23-36, ISSN: 1476-1122
  • Journal article
    Spathi C, Young N, Heng JYY, Vandeperre LJM, Cheeseman CRet al., 2014,

    A simple method for preparing super-hydrophobic powder from paper sludge ash

    , Materials Letters, Vol: 142, Pages: 80-83, ISSN: 1873-4979

    Paper 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.
  • Journal article
    Zhang T, Vandeperre LJ, Cheeseman CR, 2014,

    Formation of magnesium silicate hydrate (M-S-H) cement pastes using sodium hexametaphosphate

    , Cement and Concrete Research, Vol: 65, Pages: 8-14, ISSN: 0008-8846

    Magnesium silicate hydrate (M-S-H) gel is formed by the reaction of brucite with amorphous silica during sulphate attack in concrete and M-S-H is therefore regarded as having limited cementing properties. The aim of this work was to form M-S-H pastes, characterise the hydration reactions and assess the resulting properties. It is shown that M-S-H pastes can be prepared by reacting magnesium oxide (MgO) and silica fume (SF) at low water to solid ratio using sodium hexametaphosphate (NaHMP) as a dispersant. Characterisation of the hydration reactions by x-ray diffraction and thermogravimetric analysis shows that brucite and M-S-H gel are formed and that for samples containing 60 wt.% SF and 40 wt.% MgO all of the brucites react with SF to form M-S-H gel. These M-S-H cement pastes were found to have compressive strengths in excess of 70 MPa.
  • Journal article
    Kuenzel C, Li L, Vandeperre L, Boccaccini AR, Cheeseman CRet al., 2014,

    Influence of sand on the mechanical properties of metakaolin geopolymers

    , CONSTRUCTION AND BUILDING MATERIALS, Vol: 66, Pages: 442-446, ISSN: 0950-0618
  • Journal article
    Barg S, Perez FM, Ni N, Pereira PDV, Maher RC, Garcia-Tunon E, Eslava S, Agnoli S, Mattevi C, Saiz Eet al., 2014,

    Mesoscale assembly of chemically modified graphene into complex cellular networks

    , Nature Communications, Vol: 5, Pages: 1-10, ISSN: 2041-1723

    The widespread technological introduction of graphene beyond electronics rests on our ability to assemble this two-dimensional building block into three-dimensional structures for practical devices. To achieve this goal we need fabrication approaches that are able to provide an accurate control of chemistry and architecture from nano to macroscopic levels. Here, we describe a versatile technique to build ultralight (density ≥1 mg cm−3) cellular networks based on the use of soft templates and the controlled segregation of chemically modified graphene to liquid interfaces. These novel structures can be tuned for excellent conductivity; versatile mechanical response (elastic-brittle to elastomeric, reversible deformation, high energy absorption) and organic absorption capabilities (above 600 g per gram of material). The approach can be used to uncover the basic principles that will guide the design of practical devices that by combining unique mechanical and functional performance will generate new technological opportunities.
  • Journal article
    Poologasundarampillai G, Yu B, Tsigkou O, Wang D, Romer F, Bhakhri V, Giuliani F, Stevens MM, McPhail DS, Smith ME, Hanna JV, Jones JRet al., 2014,

    Poly(gamma-glutamic acid)/Silica Hybrids with Calcium Incorporated in the Silica Network by Use of a Calcium Alkoxide Precursor

    , Chemistry-A European Journal, Vol: 20, Pages: 8149-8160, ISSN: 1521-3765

    Current materials used for bone regeneration are usually bioactive ceramics or glasses. Although they bond to bone, they are brittle. There is a need for new materials that can combine bioactivity with toughness and controlled biodegradation. Sol-gel hybrids have the potential to do this through their nanoscale interpenetrating networks (IPN) of inorganic and organic components. Poly(γ-glutamic acid) (γ-PGA) was introduced into the sol-gel process to produce a hybrid of γ-PGA and bioactive silica. Calcium is an important element for bone regeneration but calcium sources that are used traditionally in the sol-gel process, such as Ca salts, do not allow Ca incorporation into the silicate network during low-temperature processing. The hypothesis for this study was that using calcium methoxyethoxide (CME) as the Ca source would allow Ca incorporation into the silicate component of the hybrid at room temperature. The produced hybrids would have improved mechanical properties and controlled degradation compared with hybrids of calcium chloride (CaCl2), in which the Ca is not incorporated into the silicate network. Class II hybrids, with covalent bonds between the inorganic and organic species, were synthesised by using organosilane. Calcium incorporation in both the organic and inorganic IPNs of the hybrid was improved when CME was used. This was clearly observed by using FTIR and solid-state NMR spectroscopy, which showed ionic cross-linking of γ-PGA by Ca and a lower degree of condensation of the Si species compared with the hybrids made with CaCl2 as the Ca source. The ionic cross-linking of γ-PGA by Ca resulted in excellent compressive strength and reduced elastic modulus as measured by compressive testing and nanoindentation, respectively. All hybrids showed bioactivity as hydroxyapatite (HA) was formed after immersion in simulated body fluid (SBF).
  • Journal article
    Jones NG, Humphrey C, Connor LD, Wilhelmsson O, Hultman L, Stone HJ, Giuliani F, Clegg WJet al., 2014,

    On the relevance of kinking to reversible hysteresis in MAX phases

    , Acta Materialia, Vol: 69, Pages: 149-161, ISSN: 1359-6454

    This paper examines the idea that reversible hysteresis in MAX phases is caused by the formation, growth and collapse of unstable, or incipient, kink bands. In situ X-ray diffraction of polycrystalline Ti3SiC2 in compression showed that residual elastic lattice strains developed during the first loading cycle and remained approximately constant afterwards. These residual strains were compressive in grains with a low Schmid factor and tensile in grains with a high Schmid factor, consistent with previous observations of plastically deformed hexagonal metals. In contrast, incipient kink bands would be expected to collapse completely, without any residual strain. Elastoplastic self-consistent simulations showed that reversible hysteresis is predicted if some grains yield by slip on the basal plane, while others remain predominantly elastic, giving both the experimentally observed magnitude of the work dissipated and its dependence on the maximum applied stress. The reversible hysteresis in single crystals was studied by cyclically indenting thin films of Ti3SiC2 and Ti3SiC2/TiC multilayers on Al2O3 substrates. The work dissipated in the multilayer films was greater than in Ti3SiC2 alone, despite the reduction in volume fraction of Ti3SiC2. Reversible hysteresis was also observed during indentation of single-crystal cubic MgO, demonstrating that this behaviour can occur if there are insufficient slip systems to accommodate the strain around the indentation. These results show that reversible hysteresis is associated with conventional dislocation flow, without the need for unstable kinking.
  • Journal article
    Chen Z, Wang X, Giuliani F, Atkinson Aet al., 2014,

    Surface quality improvement of porous thin films suitable for nanoindentation

    , CERAMICS INTERNATIONAL, Vol: 40, Pages: 3913-3923, ISSN: 0272-8842

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