Imperial College London

Professor Saiz

Faculty of EngineeringDepartment of Materials

Chair in Structural Ceramics
 
 
 
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Contact

 

+44 (0)20 7594 6779e.saiz

 
 
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Location

 

LM04.BRoyal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

203 results found

Gavalda-Diaz O, Manno R, Melro A, Allegri G, Hallett SR, Vandeperre L, Saiz E, Giuliani Fet al., 2021, Mode I and Mode II interfacial fracture energy of SiC/BN/SiC CMCs, Acta Materialia, Vol: 215, Pages: 1-11, ISSN: 1359-6454

Quantifying the mixed mode fracture toughness of interfaces in ceramic matrix composites (CMCs) is crucial for understanding their failure. In this work we use in situ micromechanical testing in the scanning electron microscope to achieve stable interfacial crack propagation in Mode I (Double Cantilever Beam) and Mode II (Push out) and measure the corresponding fracture resistances. We use this approach to measure the interfacial fracture resistance in SiC/BN/SiC CMCs and compare it to the fracture energy of the fibres. During in-situ testing, fracture paths can be observed while data is acquired simultaneously. We clearly observe debonding at the BN-fibre interface (i.e. inside adhesive debonding). The critical energy release rate of the BN-fibre interface for Mode I and II (GIc ≈ 2.1 ± 1.0 J/m2 and GIIc ≈ 1.2 ± 0.5 J/m2) are equivalent and is lower than that measured for the fibre using microscopic DCB tests (GIc ≈ 6.0 ± 2.0 J/m2). These results explain the generalized fibre debonding and pull out observed in the fracture of these CMCs. By enabling direct observation of crack paths and quantifying the corresponding fracture energies, we highlight possible routes for the optimisation and modelling of the new generation of CMC interphases.

Journal article

Cao C, Lin Z, Liu X, Jia Y, Saiz E, Wolf SE, Wagner HD, Jiang L, Cheng Qet al., 2021, Strong Reduced Graphene Oxide Coated Bombyx mori Silk, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X

Journal article

Li C, Li M, Ni Z, Guan Q, Blackman BRK, Saiz Eet al., 2021, Stimuli-responsive surfaces for switchable wettability and adhesion, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 18, ISSN: 1742-5689

Journal article

De Meyere RMG, Song K, Gale L, Harris S, Edmonds IM, Marrow TJ, Saiz E, Giuliani F, Armstrong DEJ, Gavalda-Diaz Oet al., 2021, A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites, Journal of Materials Research, Vol: 36, Pages: 2305-2314, ISSN: 0884-2914

Traditional fibre push-outs for the evaluation of interfacial properties in long fibre ceramic matrix composites present their limitations—solutions for which are addressed in this work by introducing the novel trench push-out test. The trench push-out makes use of a FIB milling system and an SEM in-situ nanoindenter to probe a fibre pushed into a trench underneath, allowing in-situ observations to be directly correlated with micromechanical events. SiCf/BN/SiC composites—candidate material for turbine engines—were used as model materials in this work. Different fibre types (Hi-Nicalon and Tyranno type SA3) were coated with BN interphases, presenting mean interfacial shear stresses of 14 ± 7 MPa and 20 ± 2 MPa, respectively, during fibre sliding. The micromechanical technique enabled visualisation of how defects in the interphase (voids, inclusions & milled notches) or in the fibre (surface asperities, non-uniform coatings) affected the variability of interfacial property measurement.

Journal article

Leung CLA, Elizarova I, Isaacs M, Marathe S, Saiz E, Lee PDet al., 2021, Enhanced near-infrared absorption for laser powder bed fusion using reduced graphene oxide, Applied Materials Today, Vol: 23, Pages: 1-10, ISSN: 2352-9407

Laser powder bed fusion (LPBF) is a revolutionary manufacturing technology that fabricates parts with unparalleled complexity, layer-by-layer. However, there are limited choices of commercial powders for LPBF, constrained partly by the laser absorbance, an area that is not well investigated. Carbon additives are commonly used to promote near infra-red (NIR) absorbance of the powders but their efficiency is limited. Here, we combine operando synchrotron X-ray imaging with chemical characterisation techniques to elucidate the role of additives on NIR absorption, melt track and defect evolution mechanisms during LPBF. We employ a reduced graphene oxide (rGO) additive to enable LPBF of low NIR absorbance powder, SiO2, under systematic build conditions. This work successfully manufactured glass tracks with a high relative density (99.6%) and overhang features (> 5 mm long) without pre/post heat treatment. Compared to conventional carbon additives, the rGO increases the powder's NIR absorbance by ca. 3 times and decreases the warpage and porosity in LPBF glass tracks. Our approach will dramatically widen the palette of materials for laser processing and enable existing LPBF machines to process low absorbance powder, such as SiO2, using a NIR beam.

Journal article

Gavalda-Diaz O, Lyons J, Wang S, Emmanuel M, Marquardt K, Saiz E, Giuliani Fet al., 2021, Basal Plane Delamination Energy Measurement in a Ti3SiC2 MAX Phase, JOM, Vol: 73, Pages: 1582-1588, ISSN: 1047-4838

Journal article

Azcune I, Huegun A, Ruiz de Luzuriaga A, Saiz E, Rekondo Aet al., 2021, The effect of matrix on shape properties of aromatic disulfide based epoxy vitrimers, European Polymer Journal, Vol: 148, Pages: 1-10, ISSN: 0014-3057

Aromatic disulfide based vitrimers show elasticity driven shape-memory and plastic reprocessability via associative rearrangement of dynamic covalent crosslinks. Those processess represent the two sides of a coin: the storage and relaxation of the strain energy caused by a deformation load. The key temperatures that trigger the underlying mechanisms, i.e. phase transition and disulfide exchange reaction, are extremely sensitive to the molecular structure of the polymer and under certain condition overlap. To gain insight on the relationship between the structure, dynamic and shape-changing properties, five aromatic disulfide-based epoxy networks with a range of Tg values (32–142 °C), molecular structure and crosslink densities (2252–462 mol m−3) were synthesized. The epoxy matrices were formulated combining different ratios of rigid bisphenol A diglycidyl ether (DGEBA) and flexible poly(propylene glycol) diglycidic ether (DGEPPG) epoxy monomers crosslinked by 4-aminophenyldisulfide hardener.

Journal article

Aldegaither N, Sernicola G, Mesgarnejad A, Karma A, Balint D, Wang J, Saiz E, Shefelbine SJ, Porter AE, Giuliani Fet al., 2021, Fracture toughness of bone at the microscale, Acta Biomaterialia, Vol: 121, Pages: 475-483, ISSN: 1742-7061

Bone's hierarchical arrangement of collagen and mineral generates a confluence of toughening mechanisms acting at every length scale from the molecular to the macroscopic level. Molecular defects, disease, and age alter bone structure at different levels and diminish its fracture resistance. However, the inability to isolate and quantify the influence of specific features hampers our understanding and the development of new therapies. Here, we combine in situ micromechanical testing, transmission electron microscopy and phase-field modelling to quantify intrinsic deformation and toughening at the fibrillar level and unveil the critical role of fibril orientation on crack deflection. At this level dry bone is highly anisotropic, with fracture energies ranging between 5 and 30 J/m2 depending on the direction of crack propagation. These values are lower than previously calculated for dehydrated samples from large-scale tests. However, they still suggest a significant amount of energy dissipation. This approach provides a new tool to uncouple and quantify, from the bottom up, the roles played by the structural features and constituents of bone on fracture and how can they be affected by different pathologies. The methodology can be extended to support the rational development of new structural composites.

Journal article

Cao C, Peng J, Liang X, Saiz E, Wolf SE, Wagner HD, Jiang L, Cheng Qet al., 2021, Strong, conductive aramid fiber functionalized by graphene, COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING, Vol: 140, ISSN: 1359-835X

Journal article

Petrova NL, Cai Q, Petrov PK, Saiz E, Shanahan CM, Edmonds MEet al., 2020, Can novel bone substitutes withstand the enhanced resorbing activity of Charcot osteoclasts?, Publisher: WILEY, Pages: 48-48, ISSN: 0742-3071

Conference paper

Diaz OG, Marquardt K, Harris S, Gale L, Vandeperre L, Saiz E, Giuliani Fet al., 2020, Degradation mechanisms of SiC/BN/SiC after low temperature humidity exposure, Journal of the European Ceramic Society, Vol: 40, Pages: 3863-3874, ISSN: 0955-2219

The environmental degradation of SiC/BN/SiC CMCs under low temperature water exposure is still an unexplored field. This work shows how the effect of low temperature humid environments can be detrimental for turbostratic BN interphases, leading to a drop in mechanical properties. Furthermore, initial low-temperature humid environments can induce a faster degradation during subsequent thermal exposure. In order to understand how low temperature water exposure affects the CMC and how these changes affect the material response to subsequent exposures, intermediate temperature (800 °C) exposures have been studied before and after the low temperature humidity tests. The main challenge of this work consists of understanding how different constituents of the CMC structure (e.g. fibres and interphases) are degrading and consequently affecting the overall bulk mechanical performance and failure modes of the material. For this, linking the change in morphology and chemistry of the interphases with the micromechanical properties each constituent has been crucial.

Journal article

Rocha VG, Saiz E, Tirichenko IS, García-Tuñón Eet al., 2020, Direct ink writing advances in multi-material structures for a sustainable future, Journal of Materials Chemistry A, Vol: 8, Pages: 15646-15657, ISSN: 2050-7488

Novel manufacturing techniques such as additive manufacturing (AM, also referred to as 3D printing) will play a critical role in building a sustainable future. AM will reduce waste, energy consumption and production time by eliminating the need to assemble components. It will also enable the mass customization of complex devices. To reach their full potential, additive manufacturing technologies should be able to combine different materials in a single processing step. Although the development of multi-material printing is in its infancy, it could have a massive impact in fields as diverse as energy storage and generation, electronic devices, healthcare or structural composites to name a few. Here we provide a critical perspective on the advances and potential of multi-material printing using direct extrusion-based printing, also known as direct ink writing (DIW) or robocasting. We will show examples of devices and structures combining a wide range of materials from ceramics to metals, polymers and carbon with particular focus on three promising applications: energy storage, lightweight composites and sensors. The goals are to assess the progress made so far, to point out specific challenges and areas for further development and to provide guidelines to those interested in multi-material DIW.

Journal article

Zhou T, Wu C, Wang Y, Tomsia AP, Li M, Saiz E, Fang S, Baughman RH, Jiang L, Cheng Qet al., 2020, Super-tough MXene-functionalized graphene sheets, Nature Communications, Vol: 11, ISSN: 2041-1723

Flexible reduced graphene oxide (rGO) sheets are being considered for applications in portable electrical devices and flexible energy storage systems. However, the poor mechanical properties and electrical conductivities of rGO sheets are limiting factors for the development of such devices. Here we use MXene (M) nanosheets to functionalize graphene oxide platelets through Ti-O-C covalent bonding to obtain MrGO sheets. A MrGO sheet was crosslinked by a conjugated molecule (1-aminopyrene-disuccinimidyl suberate, AD). The incorporation of MXene nanosheets and AD molecules reduces the voids within the graphene sheet and improves the alignment of graphene platelets, resulting in much higher compactness and high toughness. In situ Raman spectroscopy and molecular dynamics simulations reveal the synergistic interfacial interaction mechanisms of Ti-O-C covalent bonding, sliding of MXene nanosheets, and π-π bridging. Furthermore, a supercapacitor based on our super-tough MXene-functionalized graphene sheets provides a combination of energy and power densities that are high for flexible supercapacitors.

Journal article

Elizarova I, Vandeperre L, Saiz Gutierrez E, 2020, Conformable green bodies: plastic forming of robocasted advanced ceramics, Journal of the European Ceramic Society, Vol: 40, Pages: 552-557, ISSN: 0955-2219

Robocasting, or the additive manufacturing of ceramics by continuous extrusion of a ceramic paste, has limited capabilities when printing complex unsupported structures such as overhangs or free standing thin artefacts. In this paper we address this limitation using a new type of paste, which allows for shaping of the green bodies after printing. To illustrate the flexibility of the paste, it was used to produce both alumina and silicon carbide parts. The paste consists of a solution of phenolic resin in methyl ethyl ketone and ceramic powders. Fabricated parts can be cut, bent, folded and draped over various objects. Once dry and fully solid, the parts become rigid and can be processed further by slow pyrolysis and sintering. Sintered samples exhibit flexural strength comparable to both conventionally produced and robocasted ceramics and shaping of the green bodies after printing does not affect the mechanical strength of the sintered parts.

Journal article

Peng J, Huang C, Cao C, Saiz E, Du Y, Dou S, Tomsia AP, Wagner HD, Jiang L, Cheng Qet al., 2020, Inverse Nacre-like Epoxy-Graphene Layered Nanocomposites with Integration of High Toughness and Self-Monitoring, MATTER, Vol: 2, Pages: 220-232, ISSN: 2590-2393

Journal article

Feilden E, Glymond D, Saiz E, Vandeperre Let al., 2019, High temperature strength of an ultra high temperature ceramic produced by additive manufacturing, Ceramics International, Vol: 45, Pages: 18210-18214, ISSN: 0272-8842

In this study hafnium diboride was fabricated using the additive manufacturing technique robocasting. Parts have been successfully produced with complex shapes and internal structures not possible via conventional manufacturing techniques. Following pressureless sintering, the monolithic parts reach densities of 94–97% theoretical. These parts exhibit bending strength of 364 ± 31 MPa at room temperature, and maintain strengths of 196 ± 5 MPa up to 1950 °C, which is comparable to UHTC parts produced by traditional means. These are the highest temperature mechanical tests that a 3D printed part has ever undergone. The successful printing of the high density HfB2 demonstrates the versatile range materials that can be produced via robocasting using Pluronic pastes.

Journal article

Wat A, Ferraro C, Deng X, Sweet A, Tomsia AP, Saiz E, Ritchie ROet al., 2019, Bioinspired nacre-like alumina with a metallic nickel compliant phase fabricated by spark-plasma sintering, Small, Vol: 15, ISSN: 1613-6810

Many natural materials present an ideal "recipe" for the development of future damage-tolerant lightweight structural materials. One notable example is the brick-and-mortar structure of nacre, found in mollusk shells, which produces high-toughness, bioinspired ceramics using polymeric mortars as a compliant phase. Theoretical modeling has predicted that use of metallic mortars could lead to even higher damage-tolerance in these materials, although it is difficult to melt-infiltrate metals into ceramic scaffolds as they cannot readily wet ceramics. To avoid this problem, an alternative ("bottom-up") approach to synthesize "nacre-like" ceramics containing a small fraction of nickel mortar is developed. These materials are fabricated using nickel-coated alumina platelets that are aligned using slip-casting and rapidly sintered using spark-plasma sintering. Dewetting of the nickel mortar during sintering is prevented by using NiO-coated as well as Ni-coated platelets. As a result, a "nacre-like" alumina ceramic displaying a resistance-curve toughness up to ≈16 MPa m½ with a flexural strength of ≈300 MPa is produced.

Journal article

D'Elia E, Ahmed HS, Feilden E, Saiz Eet al., 2019, Electrically-responsive graphene-based shape-memory composites, Applied Materials Today, Vol: 15, Pages: 185-191, ISSN: 2352-9407

Shape memory materials can open new design opportunities in fields as diverse as healthcare, transportation or energy generation. In this respect, shape memory polymers (SMPs) have attracted much attention due to their advantages over metals in terms of weight and reliability. However, they are still marred by slow reaction times and poor mechanical performance. In this work we show how, by integrating a graphene network in a SMP matrix, it is possible to create composites with very low carbon contents (below 1 wt%) able to change shapes in short times (10 s of seconds) in response to low electric voltages (<10 V). This is possible because the conductive network is highly interconnected at the microscopic scale, acting as a very efficient Joule heater. The composites exhibit excellent shape fixity (>0.95 ± 0.03) and shape recovery ratios (>0.98 ± 0.03). Due to the 2D nature of graphene, this network directs crack propagation during fracture resulting in materials that retain bending strengths close to 100 MPa and exhibit significant extrinsic toughening (with toughness that reach values up to 3 times the initiation value). Furthermore, changes in conductivity can be used to follow the formation and growth of damage in the material before catastrophic failure, allowing the use of this material as a damage sensor. These results provide practical guidelines for the design of reliable shape memory composites for structural and sensing applications.

Journal article

Caballero SSR, Saiz E, Montembault A, Tadier S, Maire E, David L, Delair T, Gremillard Let al., 2019, 3-D printing of chitosan-calcium phosphate inks: rheology, interactions and characterization, Journal of Materials Science: Materials in Medicine, Vol: 30, ISSN: 0957-4530

Bone substitute fabrication is of interest to meet the worldwide incidence of bone disorders. Physical chitosan hydrogels with intertwined apatite particles were chosen to meet the bio-physical and mechanical properties required by a potential bone substitute. A set up for 3-D printing by robocasting was found adequate to fabricate scaffolds. Inks consisted of suspensions of calcium phosphate particles in chitosan acidic aqueous solution. The inks are shear-thinning and consist of a suspension of dispersed platelet aggregates of dicalcium phosphate dihydrate in a continuous chitosan phase. The rheological properties of the inks were studied, including their shear-thinning characteristics and yield stress. Scaffolds were printed in basic water/ethanol baths to induce transformation of chitosan-calcium phosphates suspension into physical hydrogel of chitosan mineralized with apatite. Scaffolds consisted of a chitosan polymeric matrix intertwined with poorly crystalline apatite particles. Results indicate that ink rheological properties could be tuned by controlling ink composition: in particular, more printable inks are obtained with higher chitosan concentration (0.19 mol·L−1).

Journal article

Wang X, Peng J, Zhang Y, Li M, Saiz E, Tomsia AP, Cheng Qet al., 2018, Ultratough Bioinspired Graphene Fiber via Sequential Toughening of Hydrogen and Ionic Bonding, ACS NANO, Vol: 12, Pages: 12638-12645, ISSN: 1936-0851

Journal article

Zhang Y, Peng J, Li M, Saiz E, Wolf SE, Cheng Qet al., 2018, Bioinspired supertough graphene fiber through sequential interfacial interactions., ACS Nano, Vol: 12, Pages: 8901-8908, ISSN: 1936-0851

Natural nacre exhibits extraordinary functional and structural diversity, combining high strength and toughness. The mechanical properties of nacre are attributed to (i) a highly arranged hierarchical layered structure of inorganic minerals (95 vol %) containing a small amount only of organic materials (5 vol %), (ii) abundant synergistic interfacial interactions, and (iii) formation under ambient temperature. Herein, inspired by these three design principles originating from natural nacre, the supertough bioinspired graphene-based nanocomposite fibers (BGNFs) are prepared under room temperature via sequential interfacial interactions of ionic bonding and π-π interactions. The resultant synergistic effect leads to a super toughness of 18.7 MJ m-3 as well as a high tensile strength of 740.1 MPa. In addition, the electrical conductivity of these supertough BGNFs is as high as 384.3 S cm-1. They can retain almost 80% of this conductivity even after 1000 cycles of loading-unloading testing, which makes these BGNFs promising candidates for application in flexible and stable electrical devices, such as strain sensors and actuators.

Journal article

Pelissari PIBGB, Bouville F, Pandolfelli VC, Carnelli D, Giuliani F, Luz AP, Saiz E, Studart ARet al., 2018, Nacre-like ceramic refractories for high temperature applications, Journal of the European Ceramic Society, Vol: 38, Pages: 2186-2193, ISSN: 0955-2219

High-temperature ceramics, so-called refractories, are widely used for the manufacturing of metals, for energy generation and aerospace applications. Refractories are usually strong and stiff but fragile due to the lack of plastic deformation and other intrinsic toughening mechanisms. This inherent brittleness limits their use in applications where catastrophic failure is not tolerated. The present work reports the design and fabrication of refractories with a bio inspired nacre-like microstructure comprising aligned alumina platelets, separated by an aluminium borate interphase, obtained through transient liquid phase sintering. The bioinspired composites exhibit high strength, 672 MPa, toughness, 7.4 MPa m1/2, and stable crack propagation at high temperatures, above 600 °C, due to the aluminium borate interlayer. This makes nacre-like ceramic refractories sintered with a transient liquid phase good candidate for high temperature applications, competing favourably with ceramic matrix composites and following a simpler and cheaper processing route.

Journal article

Saiz E, Boccaccini AR, Chevalier J, Peroglio Met al., 2018, Editorial on Bioceramics for Bone Repair, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 38, Pages: 821-822, ISSN: 0955-2219

Journal article

Ferraro C, Meille S, Réthoré J, Ni N, Chevalier J, Saiz Eet al., 2018, Strong and tough metal/ceramic micro-laminates, Acta Materialia, Vol: 144, Pages: 202-215, ISSN: 1359-6454

There is a growing interest in the development of composites with complex structures designed to generate enhanced mechanical properties. The challenge is how to implement these structures in practical materials with the required degree of control. Here we show how freeze casting of ceramic preforms combined with metal infiltration can be used to fabricate Al2O3/Al-4wt% Mg micro-laminated composites. By manipulating the solid content of the suspension and the morphology of the ceramic particles (from platelets to round particles) it is possible to access a range of structures with layer thickness varying between 1 and 30 μm and metallic contents between 66 and 86 vol%. The mechanical response of the materials is characterized by combining bending tests with observation of crack propagation in two and three dimensions using different imaging techniques. These composites are able to combine high strength and toughness. They exhibit a rising R-curve behaviour although different structures generate different toughening mechanisms. Composites fabricated with Al2O3 particles exhibit the highest fracture resistance approaching 60 MPa m1/2, while laminates prepared from Al2O3 platelets exhibit higher strengths (above 700 MPa) while retaining fracture resistance up to ∼40 MPa m1/2. The results provide new insights on the effect of structure on the mechanical properties in metal-ceramic composites as well as on the design of appropriate testing procedures.

Journal article

Rocha VG, Garcia-Tunon E, Botas C, Markoulidis F, Feilden E, D'Elia E, Ni N, Shaffer M, Saiz Eet al., 2017, Multimaterial 3D Printing of Graphene-Based Electrodes for Electrochemical Energy Storage Using Thermoresponsive Inks, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 37136-37145, ISSN: 1944-8244

The current lifestyles, increasing population, and limited resources result in energy research being at the forefront of worldwide grand challenges, increasing the demand for sustainable and more efficient energy devices. In this context, additive manufacturing brings the possibility of making electrodes and electrical energy storage devices in any desired three-dimensional (3D) shape and dimensions, while preserving the multifunctional properties of the active materials in terms of surface area and conductivity. This paves the way to optimized and more efficient designs for energy devices. Here, we describe how three-dimensional (3D) printing will allow the fabrication of bespoke devices, with complex geometries, tailored to fit specific requirements and applications, by designing water-based thermoresponsive inks to 3D-print different materials in one step, for example, printing the active material precursor (reduced chemically modified graphene (rCMG)) and the current collector (copper) for supercapacitors or anodes for lithium-ion batteries. The formulation of thermoresponsive inks using Pluronic F127 provides an aqueous-based, robust, flexible, and easily upscalable approach. The devices are designed to provide low resistance interface, enhanced electrical properties, mechanical performance, packing of rCMG, and low active material density while facilitating the postprocessing of the multicomponent 3D-printed structures. The electrode materials are selected to match postprocessing conditions. The reduction of the active material (rCMG) and sintering of the current collector (Cu) take place simultaneously. The electrochemical performance of the rCMG-based self-standing binder-free electrode and the two materials coupled rCMG/Cu printed electrode prove the potential of multimaterial printing in energy applications.

Journal article

Feilden E, Ferraro C, Zhang Q, García-Tuñón E, D'Elia E, Giuliani F, Vandeperre L, Saiz Eet al., 2017, 3D printing bioinspired ceramic composites, Scientific Reports, Vol: 7, ISSN: 2045-2322

Natural structural materials like bone and shell have complex, hierarchical architectures designed to control crack propagation and fracture. In modern composites there is a critical trade-off between strength and toughness. Natural structures provide blueprints to overcome this, however this approach introduces another trade-off between fine structural manipulation and manufacturing complex shapes in practical sizes and times. Here we show that robocasting can be used to build ceramic-based composite parts with a range of geometries, possessing microstructures unattainable by other production technologies. This is achieved by manipulating the rheology of ceramic pastes and the shear forces they experience during printing. To demonstrate the versatility of the approach we have fabricated highly mineralized composites with microscopic Bouligand structures that guide crack propagation and twisting in three dimensions, which we have followed using an original in-situ crack opening technique. In this way we can retain strength while enhancing toughness by using strategies taken from crustacean shells.

Journal article

Ferraro C, Garcia-Tunon E, Barg S, Miranda M, Ni N, Bell R, Saiz Eet al., 2017, SiC porous structures obtained with innovative shaping technologies, Journal of the European Ceramic Society, Vol: 38, Pages: 823-835, ISSN: 0955-2219

SiC structures with porosities ranging between 20–60% have been fabricated using two methods emulsification and freeze casting. While emulsification results in foam-like isotropic materials with interconnected pores, freeze casting can be used to fabricate highly anisotropic materials with characteristic layered architectures. The parameters that control the pore size and final porosity have been identified (solid content in the initial suspensions, emulsification times or speed of the freezing front). We have found that liquid state sintering (suing Al2O3 and Y2O3 as additives) at 1800 °C on a powder (SiC/Al2O3) bed provides optimum consolidation for the porous structures. The mechanical strength of the materials depends on their density. Freeze casted materials fabricated with bimodal particle size distributions (a controlled mixture of micro and nanoparticles) exhibit higher compressive strengths that can reach values of up to 280 MPa for materials with densities of 0.47.

Journal article

Garcia-Tunon E, Feilden E, Zheng H, D'Elia E, Leong A, Saiz Eet al., 2017, Graphene Oxide: An All-in-One Processing Additive for 3D Printing, ACS Applied Materials and Interfaces, Vol: 9, Pages: 32977-32989, ISSN: 1944-8244

Many 3D printing technologies are based on the development of inks and pastes to build objects through droplet or filament deposition (the latter also known as continuous extrusion, robocasting, or direct ink writing). Controlling and tuning rheological behavior is key for successful manufacturing using these techniques. Different formulations have been proposed, but the search continues for approaches that are clean, flexible, robust and that can be adapted to a wide range of materials. Here, we show how graphene oxide (GO) enables the formulation of water-based pastes to print a wide variety of materials (polymers, ceramics, and steel) using robocasting. This work combines flow and oscillatory rheology to provide further insights into the rheological behavior of suspensions combining GO with other materials. Graphene oxide can be used to manipulate the viscoelastic response, enabling the formulation of pastes with excellent printing behavior that combine shear thinning flow and a fast recovery of their elastic properties. These inks do not contain other additives, only GO and the material of interest. As a proof of concept, we demonstrate the 3D printing of additive-free graphene oxide structures as well as polymers, ceramics, and steel. Due to its amphiphilic nature and 2D structure, graphene oxide plays multiple roles, behaving as a dispersant, viscosifier, and binder. It stabilizes suspensions of different powders, modifies the flow and viscoelasticity of materials with different chemistries, particle sizes and shapes, and binds the particles together, providing green strength for manual handling. This approach enables printing complex 3D ceramic structures using robocasting with similar properties to alternative formulations, thus demonstrating the potential of using 2D colloids in materials manufacturing.

Journal article

Leong AYL, Mahtar MA, Mattevi C, Leong KH, Saiz E, Sum WSet al., 2017, Graphene filled epoxy coatings for enhanced corrosion protection, 21st International Conference on Composite Materials (ICCM-21)

© 2017 International Committee on Composite Materials. All rights reserved. The ability of graphene oxide derived fillers to enhance the moisture barrier performance of epoxy coating has been investigated. Films and coatings of virgin and modified graphene oxide (GO) were produced with different dispersion methods. Water vapour transmission rate (WVTR) was evaluated. Reduction in WVTR of GO/epoxy films were less than predicted and in one case, was higher than unfilled epoxy film. However, moisture barrier and corrosion protection performance were improved by reducing the graphene oxide. Films with reduced GO (rGO) have smaller WVTR while corrosion rate of rGO/epoxy coating was also lowered.

Conference paper

Ni H, Xu F, Tomsia AP, Saiz E, Jiang L, Cheng Qet al., 2017, Robust Bioinspired Graphene Film via pi-pi Cross-linking, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 24987-24992, ISSN: 1944-8244

Graphene composite films inspired by nacre are the subject of ongoing research efforts to optimize their properties for applications in flexible energy devices. Noncovalent interactions do not cause interruption of the delocalized conjugated π-electron system, thus preserving graphene’s excellent properties. Herein, we synthesized a conjugated molecule with pyrene groups on both ends of a long linear chain (AP-DSS) from 1-aminopyrene (AP) and disuccinimidyl suberate (DSS). The AP-DSS molecules are used to cross-link adjacent graphene nanosheets via π–π interfacial interactions to improve properties of graphene films. The tensile strength and toughness of resultant graphene films were 4.1 and 6.4 times higher, respectively, than that of pure rGO film. More remarkably, the electrical conductivity showed a simultaneous improvement, which is rare to be achieved in other kinds of covalent or noncovalent functionalization. Such integration demonstrates the advantage of this work to previously reported noncovalent functionalization of graphene.

Journal article

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