The partial masking followed by the chemical etching is a well-developed method in the fabrication of microelectromechanical systems (MEMS). When there is an anisotropic chemical etching demand, the aqueous solution tends to have extremely oxidizing compounds especially hydrogen fluoride (HF). Consequently, the traditional masking methods such as photolithography which is based on the photoresist polymers may fail to protect the substrate as polymers also become removed by such a harsh etching solution. In the current study, a two-step deposition and chemical etching method is developed to form micron-sized arrays of silicon micropillars. A set of <100> silicon wafers undergoes a physical vapor deposition (PVD) of a silicon carbide (SiC) thin film. Prior to the deposition, an extremely fine mesh made of woven thin stainless steel wires is used to partially cover Si substrates. As a result, an array of micron-sized patches of SiC is deposited underneath each opening of the mesh while the rest of the substrate remains uncoated. In the next phase, the substrate is immersed in a highly corrosive solution (a mixture of hydrofluoric acid, nitric acid, and acetic acid). After giving some minutes of chemical etching, the uncoated parts of the substrate suffer from the etching process while those micron-sized patches formed previously to protect the substrate against the severe corrosive solution. Consequently, the bare silicon exposed to the solution is corroded and leaves a micron-sized pillar beneath the protective SiC coat. The etched substrates are used latterly to receive a thin film of the hydrophobic material such as polytetrafluorethylene (PTFE). The AFM analysis shows the topography of the surface and the morphology of the etched surface is studied by using the scanning electron microscopy (SEM). The results demonstrate extremely high wetting contact angle of the mentioned surface. It is proved that there is an optimum corrosion time which leads to the highest contact angle.
FIRE is committed to assist the education of young professionals and engineers of all horizons, to conceptualize, design, implement and organize efficient processes to manufacture the best refractory materials for all and specific users. FIRE education programs and the main accomplishments made since 2007 are at first briefly reviewed. In 2017, to enhance its educational mission FIRE members have undertaken the task to launch a second compendium series of books on the theme of Corrosion, to actualize the knowledge accumulated in the last three decades and to disseminate the main results for the benefit of the widest readership. The essential aspects of the 3 books to appear in 2018 are provided to illustrate the FIRE members’ role in such an endeavour.
Viscous flow is the main sintering mechanism in glass matrix composites (GMCs) and ceramic glazes and bodies. The microstructural changes that occur in the sintering of these materials include continuous development of apparent and closed pore shape, size, and volume and of the relationship between apparent and total porosity, which determines the material’s final porosity. Final porosity is probably one of the major characteristics of these materials, as it determines many resulting material performance properties. This study examines the microstructural development and sintering of glass–zircon composites with different volume fractions of rigid inclusions: f=0, 0.05, 0.11, 0.17, 0.32, 0.43, 0.53, and 0.65. The test composite sintering curves and the variation of the above characteristics with temperature and zircon grain and crystallite size were experimentally determined. The parameters relating to zircon particle connectivity were theoretically estimated with a view to interpreting the sintering of the composites via particle rearrangement by viscous flow, using the percolation theory. The zircon solution–reprecipitation mechanism was verified to only occur at temperatures above 950 °C.
The aim of this study was to validate the possibility of using the blast furnace sludge as raw material for the traditional ceramic industry. This validation occurred at the industrial level, in order to consider the maximum possible variables inherent to the industrial process, which are only possible to achieve with high production volume. For this purpose, the main focus was to determine the atmospheric pollution levels, as well as the potential leachability of hazardous components from the ceramic matrix. In addition, the main physical and mechanical properties of the products were also determined. The environmental tests showed that the investigated waste practically does not change the leaching and solubilization parameters of the ceramic product and also it brings benefit as the material particulate emission reduction due to the decrease of the combustible consumption. Additionally, the results indicated that the blast furnace sludge practically did not change the evaluated physical and mechanical properties.
Through collaboration between industry and government, we succeeded in blending synthetic seeds, evaluation seeds, and cosmetics needs and quickly established original products and sensibility studies. By controlling the average inter-surface distance in the liquid and the surface/volume precipitation in the droplet, it was possible to prepare composite particles, hollow granules and drug-encapsulating granules. Control of these microstructure improved UV shielding and optical sharpness and allowed obtaining several sustained release rates of the drug. Systematic verification of the direct shear testing method and organoleptic evaluation promoted the association between qualitative sensory parameters and physical properties and, furthermore, the standardization of the test method. Through collaboration among academia, industry and government in the powder technology field, authentication assessment (i.e., ISO, JIS) of the test methods was established.
Alkali activated materials (AAM) are obtained trough the reaction of aluminosilicate materials, preferably waste, with alkali activation solutions what results in materials with properties comparable to ceramic or concrete but at the same time with a significant lowering of CO2 footprint. One such example which could consume a huge amount of waste is production of aggregate. Alkali activated aggregate (AAA) within this research was obtained from fly ash by granulation on a pelletization plate and curing at room conditions or elevated temperature. The density, porosity, compressive strengths, and alkali silica reactivity of so obtained AAA were determined. Density is below 2000 kg/m3, what classified this aggregate into lightweight aggregates (EN 13055-1:2002). Compressive strength depends greatly on the curing regime, and it amounts to 2.6 MPa if aggregate is cured at room conditions, by application of curing at 65 °C the compressive strength is 4.7 MPa. If aggregate is fired then the corresponding compressive strength increases up to 11.4 MPa. Alkali silica reactivity test confirmed that certain expansion is to be expected if such aggregate is used in concrete.
Mechanical behaviour of ceramic materials shaped by robocasting additive manufacturing and traditional extrusion processes has been compared with the aim of analysing the suitability of printing 3D traditional ceramic artefacts to withstand high mechanical strengths as traditional ceramic tiles show. Extruded artefacts by both methodologies were characterized using X-ray diffraction, mercury porosimetry and mechanical strength tests. Although traditional extruded samples presented higher mechanical strength and lower global porosity when comparing similar compositions and shaping techniques, 3D printed artefacts by robocasting showed interesting mechanical properties within the range of the extrusion process. This feature along with their characteristic closed porosity make them be considered as light ceramic artefacts with a remarkable hardness to withstand specific designs in which moderated mechanical resistance could be required.
Additive manufacturing of alkali-activated materials currently attracts a lot of attention, because of the possibility to produce customized high-performance elements for a range of applications, potentially being more resource-efficient than conventionally produced parts. Here, we describe a new additive manufacturing process for alkali-activated materials that is based on selective laser-heating of lithium aluminate/microsilica slurries. The new process-material combination allows to manufacture elements with complex geometries at high building rates and high accuracy. The process is versatile and transferrable to structures of sizes differing by orders of magnitude. The mechanical strength of the obtained materials was in the range of values reported for conventional metakaolin-based geopolymers, and superior to what has been hitherto reported for alkali-activated materials produced by additive manufacturing. This mechanical performance was obtained despite the fact that the degree of reaction of the lithium aluminate and the microsilica was low, suggesting that significant reactions took place only at the surface of the microsilica particles.
Technological progress in the field of additive manufacturing (AM) as a shaping method is inexorably advancing. In particular, AM provides the possibility to manufacture functionally graded components using a voxel model method. In medical technology, especially in implantology, these new structures can open new applications. In order to increase the ingrowth of cells into an implant, a function-optimized structure with a defined porosity gradient seems to be advantageous. In addition, ceramic implants are known for their excellent biocompatibility. From the material side, alumina toughened zirconia is a particularly interesting material. In combination with AM processes, completely new possibilities arise for the production of novel implants. Vat photo polymerization of ceramics (CerAM VPP), also known as lithography-based ceramic manufacturing (LCM), is suitable to realize defined and filigree structures. This article will show results from the process development for CerAM VPP of ATZ components with a defined graded porosity.
Direct ink writing (DIW) facilitates the fabrication of three-dimensional (3D) green structures through the layer-by-layer deposition of colloidal gel-based inks. Several gel designs have been developed for aqueous systems. Here, we report a facile gelation method for a non-aqueous system: Y2O3-stabilized ZrO2 (YSZ) particles dispersed in ethanol. First, fluidic and concentrated YSZ colloids were prepared using polyethyleneimine (PEI) as a dispersant. Then, a fluid-to-gel transition was triggered by adding polyvinyl butyral (PVB) as a free polymer. The resulting colloidal gels had a viscoelastic response adequate for DIW. Further analysis revealed that the depletion flocculation mechanism plays an important role on this gelation. Moreover, using the non-aqueous colloidal gel, a helical coil structure of ~100 µm dimeter was patterned via the deposition of a continuous filament extrusion through a cylindrical nozzle in a water reservoir. During the deposition, a PVB film was formed in situ on the surface of the filament because of the poor solubility of PVB in water, which was used to avoid variations in the ink rheology owing to unexpected ethanol evaporation. The present methodology may be a useful route for the engineering of 3D green structures.
In general, micromilled mould inserts made of steel, aluminum or brass are used today for ceramic injection moulding (CIM) processes. However, tool making via mechanical subtractive manufacturing processes as micromilling is time- and cost-effective and the use of 3D printed mould inserts becomes an attractive alternative to metal mould inserts. In this paper, we report about the use of 3D printed mould inserts for CIM of alumina microreactor parts. It was observed that mould inserts printed using the Polyjet technology were very well suited for functional prototyping via CIM. The mould inserts surface was found without visible thermally introduced damage after twenty CIM process cycles. In contrast to the high quality of mould inserts printed using the PolyJet technology, mould inserts made via fused deposition modeling (FDM) technology revealed as not applicable for the purpose of this study. The mould inserts manufactured using FDM-printer exhibit significantly higher surface roughness, larger longitudinal deflection and manufacturing-related undercuts along the edges of the 3D printed microstructure.
3D printing is the iconic technology of the fourth industrial revolution, characterized by a merger of diverse technologies that is blurring the boundaries between physics, digital technology and biology. Previously associated with prototyping only, additive manufacturing has won acclaim by adapting to a wide variety of materials and industrializing its processes. But what about the most technically challenging materials such as ceramics? Technical ceramics take benefit of this new technology also: 3D printing enables new innovative development in various market field, the production of Solid Oxide Fuel Cells (SOFC) being the most meaningful use case.