Open Ceramics最新文献

This paper represents the current status of the investigation into the processing of ceramic components, using Fused Filament Fabrication (“FFF”). The process chain, beginning from the additive manufacturing (“AM”), through the post processing, the debinding and sintering procedure, to the finished part is described. The examined materials are silicon nitride (Si₃N₄) and silicon carbide (SSiC), prepared by the company SiCeram/Qsil. Furthermore, comprehensive investigations on the materials are done, both in the green and in the sintered state. In addition, sources of occurring problems and defects in the process chain are pointed out and possible solutions are shown. Finally, the current status of investigations, regarding to the transfer into the industry, is discussed.

3D printing is developing rapidly and enables the production of parts manufactured using different materials. These includes zirconium dioxide (ZrO₂), which can be of particular interest for bone tissue engineering and implantology. However, highly accurate part-dimensions are a must for these applications, which is why this study addresses geometrical deviations which occur during the printing process and thermal post-processing.

Six sets of test geometries with 50 individual features were 3D printed with two different ZrO₂ slurries (3 mol% yttria-stabilized ZrO₂) and scanned with a profilometer. After debinding and sintering, the profilometer scan was repeated and the deviations and shrinkage factors were determined.

A notable difference is observed when the same ceramic is processed using two different slurries. For instance, one used ceramic slurry, LithaCon 210, exhibits shrinkage factors of $sh{r}_{XY}=21.2\pm 3.4\%$ $\left(n=78\right)$ and $sh{r}_Z=23.6\pm 0.54\%$ $\left(n=24\right)$ for protruding structures, while the other ceramic slurry, LithaCon 280, shows shrinkage factors of $sh{r}_{XY}=21.7\pm 3.3\%$ $\left(n=78\right)$ and $sh{r}_Z=24.5\pm 0.55\%$ $\left(n=24\right)$.

Geometric deviations differed for intruding (like holes and slots) and protruding (like pillars) geometries, being more pronounced in case of intruding geometries, especially where printing overhangs occur.

Although the shrinkage during sintering needs further investigation, these experimental findings are a good starting point to validate and refine simulation models for shrinkage and improve production processes of 3D printed ceramics.

The encapsulation of phase change materials (PCMs) into additive manufactured porous supports is attracting great interest for developing thermal energy storage (TES) materials with improved energy performance. Here, highly porous (86 %) self-supported 3D activated carbon/alumina supports are fabricated by direct ink writing (DIW) and, then, infiltrated with solar salt, a highly corrosive PCM with a melting temperature around 220 °C commonly employed in concentrated solar power plants. This novel, robust, chemically compatible, and lightweight infiltrated 3DTES exhibits good thermal energy storage efficiency (70 %) and thermal stability, high energy storage density (381 J g⁻¹), and avoids the liquid leakage of the molten salt. Besides, the 3D activated carbon/alumina support promotes a better ability to absorb solar energy (79 %) and enhances the thermal conductivity of the solar salt (up to 64 %). These results validate the use of DIW for manufacturing innovative TES with an enhanced energy storage behaviour.

α-tricalcium phosphate (α-TCP) is the most widespread raw material for hydraulic calcium phosphate cements (CPCs). CPCs are widely used in bone repair due to their injectability, setting ability, and osteoconductivity. This study investigated the reactivity of α-TCP powders, focusing on the impact of minor phase impurities, β-calcium pyrophosphate and hydroxyapatite, and the synthesis temperature. The α-TCP powders were synthesized via a solid-state reaction of calcium carbonate and anhydrous dicalcium phosphate, with varying Ca/P molar ratios (1.4850–1.5075) and synthesis temperatures (1175°C–1350 °C). Powders produced with a Ca/P molar ratio below 1.50 and synthesized at a temperature above the melting point of β-CPP (1296 °C) had a broader size distribution and a two to fourfold lower hydraulic reactivity. Conversely, a higher Ca/P molar ratio improved reactivity. The study underscores the importance of precise control over synthesis parameters to enhance the performance of α-TCP-based CPCs, offering insights for optimizing material design in biomedical applications.

In this study, advanced solar steam technologies are explored for their potential applications in seawater desalination and wastewater purification. We have developed a three-dimensional photothermal evaporator using MXene, luffa sponge (LS), graphitic-carbon nitride (GCN) and activated carbon (AC). The hierarchical Ti₃C₂T_x MXene/GCN/AC@LS composite photothermal evaporator exhibits superior thermostability, pH stability, and mechanical durability. The Ti₃C₂T_x MXene/GCN/AC@LS composite evaporator having a dimension of 1.25 cm displays excellent performance, leading to a high evaporation rate of 2.6 kg m⁻²h⁻¹ and a high solar-thermal conversion efficiency of 96 % under 1 sun illumination. This high efficiency is attributed to the good light absorption by the Ti₃C₂T_x MXene/GCN/AC@LS composite coupled with a better wetting through the internal microchannels of the LS, which envisages a faster water delivery and evaporation of water. The Ti₃C₂T_x MXene/GCN/AC@LS composite captures the residual heat from the sidewall surface as an additional source of energy.

A barium-based perovskite structured ceramic with five different B-site cations was prepared by a solid-state synthesis method. The phase and chemical homogeneity of the synthesised material was verified using x-ray diffraction and energy dispersive x-ray spectroscopy, showing the successful synthesis of a single-phase perovskite structure with Ba A-site and Ti, Hf, Zr, Y, Nb, B-site cations. Ultra-high vacuum x-ray photoelectron spectroscopy was used to reveal the valence states of the constituent elements. Conventional, two-step and spark plasma sintering were used to form dense pellets with limited grain growth. The room temperature electrical characteristics of the sintered pellets were investigated by electrochemical impedance spectroscopy where a conductivity increase of two orders of magnitude was observed in a water-bearing atmosphere. Synchrotron-based ambient-pressure x-ray photoelectron spectroscopy performed under water-bearing and dry conditions suggest that the conductivity increase is related to the incorporation of hydroxyl groups into the perovskite structure.

Managing the vast quantities of waste constantly generated by mining activities is one of the major environmental and economic problems facing mankind today. Fluorapatite is separated from the associated gangue minerals by a series of crushing and screening, washing, and flotation processes. These processes produce a significant amount of phosphate sludge, which is stored on the mine site in drift rock and large surface ponds. One possible environmental option is to reuse it as an alternative raw material in ceramics and building materials. Consequently, two phosphate sludges from two different Moroccan towns, Youssoufia and Khouribga, were studied. Due to the complexity of these raw materials resulting from long geological processes, in-depth physical, chemical, mineralogical, and thermal characterization is required. Dry compressed powder pellets were sintered at 900 °C, 1000 °C, and 1100 °C for 2 h. The study focuses on the effect of sintering temperature on mineralogical transformations and ceramic properties such as apparent porosity, water absorption, and mechanical strength. At 1100 °C, a slight increase in density was observed for both phosphate sludges. Water absorption was reduced by 2.51 % in both sludges for pellets sintered at 1100 °C compared to those sintered at 900 °C. Mechanical strength improved significantly, with an increase of about 60 % for samples sintered at 1100 °C, recording 227 N for Youssoufia sludge and 247 N for Khouribga sludge. This work has provided new data on the physical, chemical, mineralogical, and thermal changes in ceramics as the sintering temperature increases. These data will be useful for the manufacture of high-value ceramics.

Silicon nitride and boron nitride (Si₃N₄/h-BN) based ceramic composites were prepared by Spark Plasma Sintering (SPS) using aluminium oxide (Al₂O₃) and/or yttrium oxide (Y₂O₃) as sintering additives. The amount of h-BN introduced varied from 0 vol.% to 20 vol.% in order to study its influence on ceramic properties. In the same way, the amount of oxide additives has been controlled and the influence of the additive's nature on the final properties has been underlined. The sintering temperature has been selected in order to obtain equivalent relative densities. The formation of β-SiAlON has been underlined by XRD and TEM analysis. Moreover, due to the fast-sintering process, amorphous secondary phase has been formed. Mechanical properties (hardness, fracture toughness, Young modulus) and thermal diffusivity have been evaluated. It appears that the nature of the oxide additive used plays an important role on the mechanical and thermal behaviour of Si₃N₄/h-BN composites.

This study proposes the use of Al-added Si–Mg composite fillers for low-temperature joining of SiC while maintaining high-temperature reliability of the joints. SiC was brazed at 1100 °C using the fillers with various compositions, based on Mg-evaporation-induced isothermal solidification of Si. The interfacial microstructure and mechanical properties of the joint were determined for different Al and Mg compositions in the filler. The added Al promoted Mg evaporation during joining, which increased the joint strength by mitigating the brittleness of the Si-based bonding layers. However, metallic Al remained in the bonding layers, which deteriorated the high-temperature joint strength. Higher Mg and Al concentrations in the filler promoted MgAl₂O₄ formation in the bonding layers that correlated with Al particle refinement. This contributed to an improvement of the joint properties, with the flexural strength at 1200 °C in air exceeding 60 MPa.

This in vitro study examines the electrochemical responses and surface degradation of alumina and feldspar dental ceramic materials in acidic environments using cyclic polarization and electrochemical impedance spectroscopy (EIS). Alumina and feldspar demonstrate balanced responses in both Fusayama Artificial Saliva and acidic solutions, indicating effective passivation. SEM/EDX analyses after 168-h immersion reveal significant elemental variations, suggesting complex surface phenomena and chemical reactions leading to oxide layer formation. Alumina exhibits increased Si, O, Al, Na, K, and C counts, while feldspar shows increased Si, O, Al, Na with reduced C and Ca levels, indicating complex reactions. Immersion induces notable elemental composition modifications, with alumina showing remarkable corrosion resistance and feldspar undergoing selective dissolution. This study provides insights into the electrochemical and surface degradation of these materials, emphasizing long-term stability and the need for continuous monitoring of protective layer dynamics in future research on corrosion-resistant dental biomaterials.