Research activity on ceramic/graphene composites and hybrids has increased dramatically in the last decade. In this review, we provide an overview of recent contributions involving ceramics, ...graphene, and graphene-related materials (GRM, i.e., graphene oxide, reduced graphene oxide, and graphene nanoplatelets) with a primary focus on applications. We have adopted a broad scope of the term ceramics, therefore including some applications of GRM with certain metal oxides and cement-based matrices in the review. Applications of ceramic/graphene hybrids and composites cover many different areas, in particular, energy production and storage (batteries, supercapacitors, solar and fuel cells), energy harvesting, sensors and biosensors, electromagnetic interference shielding, biomaterials, thermal management (heat dissipation and heat conduction functions), engineering components, catalysts, etc. A section on ceramic/GRM composites processed by additive manufacturing methods is included due to their industrial potential and waste reduction capability. All these applications of ceramic/graphene composites and hybrids are listed and mentioned in the present review, ending with the authors' outlook of those that seem most promising, based on the research efforts carried out in this field.
The ability of boehmite to form printable inks has sparked interest in the manufacturing of 3D alumina (Al2O3) and composite structures by enabling direct ink writing methods while avoiding the use ...of printing additives. These materials may exhibit high porosity due to the printing and sintering procedures, depending on the intended application. The 3D-printed porous composite structures of γ-Al2O3 and α-Al2O3 containing 2 wt.% of carbon nanotubes or reduced graphene oxide ribbons were fabricated from boehmite gels, followed by different heat treatments. The reinforcing effect of these carbon nanostructures was evidenced by compression tests carried out on the different alumina structures. A maximum relative increase of 50% in compressive strength was achieved for the γ-Al2O3 composite structure reinforced with reduced graphene oxide ribbons, which was also accompanied by an increase in the specific surface area.
Geometrically complex, three‐dimensional (3‐D) structures of SiC were produced by a colloidal printing method known as robocasting, followed by low‐pressure spark plasma sintering (SPS) to produce ...dense ceramic bodies. A concentrated, aqueous colloidal ink consisting of SiC, Al2O3, and Y2O3 particles in a dilute polymer solution with a total solids volume fraction of 0.44 was developed to have pseudoplastic behavior with yield stress rheology. Lattice structures consisting of extruded filaments deposited in an overall cylindrical or cuboid shape were printed through nozzles ranging in diameter from 150 to 330 μm. After printing, drying and calcining processes, the structures were sintered at 1700°C in argon by SPS. The final average grain size was 1–2 μm and samples displayed above 97% of theoretical density, showing ~22.8% linear shrinkage from green to sintered state.
The remarkable tunability of 2D carbon structures combined with their non-toxicity renders them interesting candidates for thermoelectric applications. Despite some limitations related to their high ...thermal conductivity and low Seebeck coefficients, several other unique properties of the graphene-like structures could out-weight these weaknesses in some applications. In this study, hybrid structures of alumina ceramics and graphene encapsulated alumina nanofibers are processed by spark plasma sintering to exploit advantages of thermoelectric properties of graphene and high stiffness of alumina. The paper focuses on thermal and electronic transport properties of the systems with varying content of nanofillers (1-25 wt.%) and demonstrates an increase of the Seebeck coefficient and a reduction of the thermal conductivity with an increase in filler content. As a result, the highest thermoelectric figure of merit is achieved in a sample with 25 wt.% of the fillers corresponding to ~3 wt.% of graphene content. The graphene encapsulated nanofibrous fillers, thus, show promising potential for thermoelectric material designs by tuning their properties via carrier density modification and Fermi engineering through doping.
Rare‐earth zirconates have been identified as a class of low‐thermal‐conductivity ceramics for possible use in thermal barrier coatings (TBCs) for gas‐turbine engine applications. To document and ...compare the thermal conductivities of important rare‐earth zirconates, we have measured the thermal conductivities of the following hot‐pressed ceramics: (i) Gd2Zr2O7 (pyrochlore phase), (ii) Gd2Zr2O7 (fluorite phase), (iii) Gd2.58Zr1.57O7 (fluorite phase), (iv) Nd2Zr2O7 (pyrochlore phase), and (v) Sm2Zr2O7 (pyrochlore phase). We have also measured the thermal conductivity of pressureless‐sintered 7 wt% yttria‐stabilized zirconia (7YSZ)—the commonly used composition in current TBCs. All rare‐earth zirconates investigated here showed nearly identical thermal conductivities, all of which were ∼30% lower than the thermal conductivity of 7YSZ in the temperature range 25°–700°C. This finding is discussed qualitatively with reference to thermal‐conductivity theory.
The present work explores the strength enhancement via minor modifications of the pattern design in pure light SiC woodpile structures created by filament printing. In particular, the effect of the ...filament stacking angle on both the compression resistance and the elastic modulus of these structures are evaluated. Different patterns were designed while maintaining the bulk structure density, therefore the differences in the mechanical data (strength and elastic modulus) are not attributable to density variations. All of these materials were partially sintered at intermediate temperature for additional porosity enhancement. Moreover, SiC specimens made by full filament overlapping were produced to serve as reference massive material. Remarkably, the massive SiC printed material displays ordered spherical porosity and a closed-pore foam appearance, thus revealing a novel route for producing these type of porosity. Results evidence that the structure robustness can be tuned through slight design modification, which thus offers the possibility of further structure lightening without reducing the target strength.
El presente trabajo explora la mejora de la resistencia mecánica de estructuras ligeras formadas por apilamiento de rodillos de SiC puro, procesadas por impresión directa de tinta, a través de modificaciones menores del patrón de diseño. En particular, se evalúa el efecto del ángulo de apilamiento de los filamentos sobre la resistencia a la compresión y el módulo elástico de estas estructuras. Los diferentes patrones fueron diseñados manteniendo similares densidades aparentes de las estructuras, por lo tanto, las diferencias observadas en los resultados mecánicos (resistencia y módulo elástico) no son atribuibles a variaciones de densidad. Todas las estructuras se sinterizaron parcialmente para mantener una elevada porosidad. Además, se produjeron muestras de SiC macizas creadas por la superposición de filamentos utilizadas como material masivo de referencia. Curiosamente, este material muestra una porosidad esférica y ordenada, y presenta la apariencia típica de esponjas con porosidad cerrada, mostrando en consecuencia una ruta alternativa para la fabricación de este tipo de materiales celulares. Dado que la robustez de estructuras 3D se puede maximizar a través de una ligera modificación del diseño, esto permitiría alternativamente aligerar aún más las estructuras sin perjudicar su resistencia.
The promising applications of metal-organic frameworks (MOF) can be widened if these materials were additive manufactured to develop three-dimensional (3D) MOF architectures. In this work, iron-based ...MOF/silicon carbide (SiC) composite aqueous inks with a high solids content (64 wt%) are printed into 3D periodic lattices by a direct ink writing technique (Robocasting). MOF appear fully integrated within the cellular architectures, which display total porosities in the range of 74–78% depending on the scaffold design. The 3D MOF-Fe/SiC structures exhibit good mechanical strength (~4.6 MPa) and a semiconductor-like behaviour. The structures show a remarkable response in the hydroxylation of phenol with hydrogen peroxide, demonstrating high selectivity and yield to dihydroxybenzene species.
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•3D cellular MOF-Fe/SiC architectures are direct ink written from pseudoplastic inks.•MOFs appear fully integrated within the printed scaffolds.•The scaffolds exhibit good mechanical strength and semiconductor-like behaviour.•Good catalytic performance in the hydroxylation of phenol.•High selectivity and yield to dihydroxybenzene species.
A revision on ceramic/graphene composites is presented. The more representative results for a wide number of bulk composites are compared, making special emphasis on their mechanical (fracture ...toughness, strength) and elastic properties, along with wear and friction topics. The electrical functionality boosted by the contacted graphene network is critically assessed for conducting and dielectric ceramic matrices. Regarding thermal transport, the enhancement or depletion of thermal conductivity is reviewed for different materials and specific orientations. Furthermore, new developments on layered materials and coatings, as well as on three-dimensional cellular composites, which certainly widen the scope of applications for this remarkable group of ceramic materials, are looked over.
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