Texture in dense or porous ceramics can enhance their functional and structural properties. Current methods for texturation employ anisotropic particles as starting powders and processes that drive their orientation into specific directions. Using ultra-low magnetic fields combined with slip casting, it is possible to purposely orient magnetically responsive particles in any direction. When those particles are suspended with nanoparticles, templated grain growth occurs during sintering to yield a textured ceramic. Yet, the final grains are usually micrometric, leading weak mechanical properties. Here, we explore how to tune the grain orientation size using magnetic slip casting and templated grain growth. Our strategy consists in changing the size of the anisotropic powders and ensuring that magnetic alignment and densification occurs. The obtained ceramics featured a large range of grain anisotropy, with submicrometric thickness and anisotropic properties. Textured ceramics with tunable grains dimensions and porosity are promising for filtering, biomedical or composite applications.
Bi_{4}Ti_{3}O_{12}-PVC composites were fabricated. Ceramics powders of bismuth titanate were prepared by the sol-gel method using bismuth nitrate pentahydrate Bi(NO_{3})_{3} \cdot 5H_{2}O and tetrabutyl titanate Ti(CH_{3}(CH_{2})_{3}O)_{4} as precursors. The Bi_{4}Ti_{3}O_{12}-PVC composites were fabricated from ceramics powders and polymer powders by hot-pressing method.
An aging effect due to a domain evolution in (K0.5,Na0.5)Nb0.97Sb0.03O3 <001> textured ceramics was investigated by piezoresponse force microscopy. We find that such an aging effect is pronounced in the orthorhombic single phase field. A more uniform and finer domain structure was found with aging, which was believed to originate from defect-migration. After poling, large domains with smooth boundaries were found in the aged condition.
Ceramic based materials covered with a mixture of mullite and zircon on the top, strengthened by the addition of zinc and magnesium compounds at different rates (37 % and 50 %) and made by a co-precipitation method are studied. The thermally treated and shaped materials prepared in the shape of cylindrical samples were modified to obtain different porosities. The addition of zinc to the ceramic based material leads to a significant increase and control of the density of porosity compared to the addition of magnesium. The porosity of all the materials was characterized. The permeability charact…
High performance lead zirconate titanate (PZT) ceramics with aligned porosity for sensing applications were fabricated by an ice-templating method. To demonstrate the enhanced properties of these materials and their potential for sensor and hydrophone applications, the piezoelectric voltage constants hydrostatic parameters and AC conductivity as a function of the porosity in directions both parallel and perpendicular to the freezing temperature gradient were studied. As the porosity level was increased, PZT poled parallel to the freezing direction exhibited the highest coefficients, and hydros…
Pb(Mg1/3Nb2/3)O3-PbTiO3 solid solution (PMN(1-x)-PTx) ceramics with 0 <x<1 have been prepared by homo-epitaxial templated grain growth (HTGG) using cubic PMN-PT single crystal seeds as templates and nanoparticles for thes ceramic matrix. Samples were prepared using the doctor Blade method and sintered in a controlled atmosphere. They were then analysed by DTA, TGA, optical/scanning electron microscopy, Raman spectroscopy and imaging. Relationships between Raman parameters such as band component or area versus composition (x) are proposed. Wavenumber and peak area shifts from the single crystal…
The finite element method (FEM) is used to study the influence of porosity and pore shape on the elastic properties of model porous ceramics. The Young's modulus of each model was found to be practically independent of the solid Poisson's ratio. At a sufficiently high porosity, the Poisson's ratio of the porous models converged to a fixed value independent of the solid Poisson's ratio. The Young's modulus of the models is in good agreement with experimental data. We provide simple formulae which can be used to predict the elastic properties of ceramics, and allow the accurate interpretation of…
Freeze-casting, the templating of porous structure by the solidification of a solvent, have seen a great deal of efforts during the last few years. Of particular interest are the unique structure and properties exhibited by porous freeze-casted ceramics, which opened new opportunities in the field of cellular ceramics. The objective of this review is to provide a first understanding of the process as of today, with particular attention being paid on the underlying principles of the structure formation mechanisms and the influence of processing parameters on the structure. This analysis highlig…
Ceramic materials are ubiquitous in technologies operating under high mechanical, thermal or chemical constrains. Research in ceramic processing aims at creating ceramics with properties that are still challenging to obtain, such as toughness, transparency, conductivity, among others. Magnetic slip casting is a ceramic process where an external magnetic field is used to align the ceramic grains along preferential crystallographic directions, thereby creating controlled texture. Over the past 20 years of research on magnetic slip casting, ceramics of multiple chemistry were found to exhibit enh…
Textured alumina ceramics were obtained by Spark Plasma Sintering (SPS) of undoped commercial a-Al2O3 powders. Various parameters (density, grain growth, grain size distribution) of the alumina ceramics, sintered at two typical temperatures 1400°C and 1700°C, are investigated. Quantitative textural and structural analysis, carried out using a combination of Electron Back Scattering Diffraction (EBSD) and X-ray diffraction (XRD), are represented in the form of mapping, and pole figures. The mechanical properties of these textured alumina ceramics include high elastic modulus and hardness value …
Effect of interfacial Fe3O4 nanoparticles on the microstructure and mechanical properties of textured alumina densified by ultrafast high-temperature sintering
We demonstrate a facile method to produce crystallographically textured, macroporous materials using a combination of modified ice templating and templated grain growth (TGG). The process is demonstrated on alumina and the lead-free piezoelectric material sodium potassium niobate. The method provides macroporous materials with aligned, lamellar ceramic walls which are made up of crystallographically aligned grains. Each method showed that the ceramic walls present a long-range order over the entire sample dimensions and have crystallographic texture as a result of the TGG process. We also pres…
The formation of regular patterns is a common feature of many solidification processes involving cast materials. We describe here how regular patterns can be obtained in porous alumina and hydroxyapatite (HAP) by controlling the freezing of ceramic slurries followed by subsequent ice sublimation and sintering, leading to multilayered porous ceramic structures with homogeneous and well-defined architecture. These porous materials can be infiltrated with a second phase of choice to yield biomimetic nacre-like composites with improved mechanical properties, which could be used for artificial bone…
A 3-D porous apatite scaffold (B-HA), recently obtained through biomorphic transformation of a natural wood, is investigated on its multi-scale porous structure determining superior mechanical properties and biological behaviour. B-HA shows hierarchical pore architecture with wide aligned channels interconnected with smaller tubules, thus recapitulating in detail the lymphatic network of the original wood template. As induced by its biomimetic architecture, B-HA displays values of compression and tensile strength and stiffness, higher than the values usually measured in sintered ceramics with …
Preparation of particle-loaded foams, followed by drying, sintering and/or cross-linking are widely explored routes for developing lightweight ceramics with high mechanical strength. The non-sintered dry ceramic foams are less studied due to their intricate production and the assumed poor mechanical strength of the obtained "green" materials. Here we produce lightweight ceramics from foamed particle suspensions containing spherical silica particles with radii varied between 4.5 nm and 7 μm. The wet foams were prepared in the presence of cationic surfactant and were dried at ambient conditions …
Macroscopic fibers of carbon nanotubes (CNT) have emerged as an ideal architecture to exploit the exceptional properties of CNT building blocks in applications ranging from energy storage to reinforcement in structural composites. Controlled synthesis and scalability are amongst the most pressing challenges to further materialize the potential of CNT fibers. This workshows that under floating catalyst chemical vapor conditions in the direct spinning method, used both in research and industry,the ceramic reactor tube plays an unsuspected active role in CNT growth, leading for example to doublin…
A Brazilian disk geometry of an alumina layered composite with alternating dense and porous layers was dynamically loaded using a Split-Hopkinson Pressure Bar (SHPB)apparatus under compression. High-speed imaging and transmitted force measurements were used to gain an insight into stress wave propagation and mitigation through such a layered system. Uniformly distributed porosities of 20 and 50 vol % were introduced into the interlayers by the addition of fine graphite particles which volatilized during heat treatment. Brazilian disk samples were cut from the cylinders which were drilled out o…
