Fabrication Of Ceramics Research Articles

Optimization of Ca additive and HIP condition in fabrication of the transparent MgAl2O4 ceramics

The amount of Ca addtive as well as the sintering condition on the in-line transmittance and the flexural strength of the transparent MgAl2O4 spinel ceramics were optimized. In-line transmittance and mechanical properties were also dependent on the hot-isostatic-press(HIP) temperature. Elevated HIP temperature induced the abnormal grain growth, which resulted the large trapped pores inside the grain, which resulted the in-line transmittance degraded. Elevated HIP together with larger Ca amount accelerated the generation of abnormal grain growth (AGG) and the secondary phases, hence the optical and mechanical properties degraded. The optimized condition was the addition of 800 ppm Ca with HIP at 1500 °C. Big scattering sources, pore clusters as well as the secondary calcium aluminate phases, were restricted and homogeneous microstructure without AGG was revealed. Hence, both the in-line transmittance and the strength were optimized as 84% and 323 MPa, simultaneously.

Porous SiC ceramic obtained by spark plasma sintering of preceramic paper: Microstructure, mechanical properties and gas permeability

This paper describes the fabrication and characterization of porous SiC ceramics derived from highly-filled preceramic papers. The SiC ceramics were obtained by spark plasma sintering of stacked preceramic papers at temperatures of 2100 and 2200 °C under pressures of 5–60 MPa for 10 min. The microstructure and phase composition were analyzed by scanning electron microscopy and X-ray diffraction, respectively. Gas permeation tests were performed using hydrogen permeation cell at room temperature. It is revealed that the porosity of sintered SiC can be varied from 9 to 45 % depending on the sintering parameters. The shrinkage of the materials during spark plasma sintering occurs in four stages. The linear shrinkage value of the material increases from 7 to 47 % at 2100 °C and from 20 to 50 % for the samples sintered at 2100 and 2200 °C, respectively. Correlation dependencies between porosity and mechanical properties of the fabricated SiC were established. The obtained porous SiC ceramics exhibit high bending strength of 165 MPa and gas permeation flux of 78 molH2/m2/s at the porosity of 36 % that make it suitable for ceramic-based membranes.

Enhanced Mechanical Properties of PUMA/SiO2 Ceramic Composites via Digital Light Processing.

This study aims to enhance the mechanical properties of additively manufactured polymer parts by incorporating ceramic particles (SiO2) into diluted urethane methacrylate (UDMA) photopolymer resin using digital light processing (DLP) technology. The resulting PUMA/SiO2 composites, featuring varying SiO2 contents (16.7, 28.5, and 37.5 wt%) and processed under different conditions, underwent a comprehensive series of mechanical, thermal, and chemical tests. Hardness tests showed that composites with 37.5 wt% SiO2 demonstrated superior hardness with low sensitivity to processing conditions. Bending tests indicated that elevated vat temperatures tended to degrade flexural properties, yet this degradation was mitigated in the case of the 37.5 wt% SiO2 composition. Tensile tests revealed a transition from viscoelastic to linear elastic behaviors with increasing SiO2 content, with high tensile strength sustained at low vat temperatures (<35 °C) when the SiO2 content exceeded 28.5 wt%. Thermogravimetric analysis supported these findings, indicating that increased SiO2 content ensured a more uniform dispersion, enhancing mechanical properties consequently. Thermal tests showed augmented thermal conductivity and diffusivity with reduced specific heat in SiO2-inclusive composites. This study provides guidelines for optimal PUMA/SiO2 composite utilization that emphasizes high SiO2 content and low vat temperature, offering comprehensive insights for high-performance ceramic composite fabrication in functional applications.

Ultrastrong and High Thermal Insulating Porous High-Entropy Ceramics up to 2000°C.

High mechanical load-carrying capability and thermal insulating performance are crucial to thermal-insulation materials under extreme conditions. However, these features are often difficult to achieve simultaneously in conventional porous ceramics. Here, for the first time, it is reported a multiscale structure design and fast fabrication of 9-cation porous high-entropy diboride ceramics via an ultrafast high-temperature synthesis technique that can lead to exceptional mechanical load-bearing capability and high thermal insulation performance. With the construction of multiscale structures involving ultrafine pores at the microscale, high-quality interfaces between building blocks at the nanoscale, and severe lattice distortion at the atomic scale, the materials with an ≈50% porosity exhibit an ultrahigh compressive strength of up to ≈337MPa at room temperature and a thermal conductivity as low as ≈0.76W m-1 K-1. More importantly, they demonstrate exceptional thermal stability, with merely ≈2.4% volume shrinkage after 2000°C annealing. They also show an ultrahigh compressive strength of ≈690MPa up to 2000°C, displaying a ductile compressive behavior. The excellent mechanical and thermal insulating properties offer an attractive material for reliable thermal insulation under extreme conditions.

Complex shapes of lithium disilicate glass-ceramics developed by material extrusion

The fabrication of high-end ceramics by additive manufacturing gained increasing research interest due to the capacity of these techniques to break through the limitations of traditional extractive manufacturing. Although efficient strategies for the processing of ceramic materials by additive manufacturing have been shown, with notable examples in the dental field, the processing of dense glass-ceramics by the same means is almost unexplored. Herein, a processing strategy for the manufacture of complex shapes of lithium disilicate glass-ceramics by material extrusion is detailed shown for the first time. An aging behaviour was observed on the glass loaded aqueous suspensions and in-deep studied, being related with the leaching of Li+ ions. Based on this, a hydrogel-based ink with high solid content (ϕ≈ 50 vol%), suitable rheological properties (G´≈106 and τ ≈ 1500 Pa) and recovery time was developed. By using the optimized ink, a propeller component with high aspect ratio and small internal connected channels, as well as a dental crown were successfully printed. A debinding schedule was tuned by the combination of differential thermal analysis and hot stage microscopy. The sintered lithium disilicate glass-ceramic parts presented good relative density (≈ 96.7 ± 0.8%) and translucency. Outstanding mechanical properties were achieved (Hv ≈5.3 GPa, KIf ≈2.1 MPa.m0.5, σ ≈ 279 ± 44 MPa), comparable to values usually attained for these materials by powder technology. The low deviation of the flexural strength data reported here is related with the absence of meaningful processing defects on the analysed fracture surfaces and the homogeneous distribution of the residual porosity as microporous, resulting in a good Weibull characteristic strength σ0 = 301 MPa. The results of the present work emphasized the potential of Direct ink Writing, a material extrusion technique, to fabricate lithium disilicate glass-ceramic parts with complex geometries, as dental crowns.

Sustainable experimental study of ceramic residues and waste fabrics

Objective: To explore feasible solutions to realize the recycling of waste materials for sustainable application in response to the existing problem of idle accumulation of large quantities of waste textile fabrics and ceramic residues. Methods: Through the experimental method, waste porcelain powder was substituted for some of the ridged raw materials in the traditional ceramic formula to make a slurry, and then mixed with waste fabrics to be fired into a new ceramic material. Then its characteristics were recorded, summarized, explored, and analyzed to explore the unique value of the material. Results: The experiments found that the mixing of the waste materials produced a good chemical reaction. The waste ceramic powder can enhance the flexural strength of the new material, reduce the deformation rate, and make the new material’s performance more stable. Waste fabrics can make the new materials enjoy the advantages of easy production, good light transmittance, and lightweight. Conclusion: This research lays a technical foundation for future entry into the design market. This contributes to the recycling of waste fabrics and ceramic residues in a sustainable way.

Research and Development of SiC Ceramic Fabrication Technologies for Optics and Fine Structures

Research and Development of SiC Ceramic Fabrication Technologies for Optics and Fine Structures

Densification of transparent hydroxyapatite ceramics via cold sintering process combined with biomineralization

We report for the first time transparent hydroxyapatite (HAp) ceramics densified using a cold sintering process and biomineralization. Under a uniaxial pressure of 800 MPa at 180 °C, granular HAp nanoparticles mixed with simulated body fluid were densified up to 98.5% relative density. During the densification, pseudo-biomineralization occurred among the HAp nanoparticles, leading to the precipitation of a new HAp phase. Additionally, the transformation of granular HAp nanoparticles into nearly circular grains produced fine microstructures with uniform and nanosized grains, reducing light scattering. As a result, the transmittance of 81.6% at λ = 550 nm was achieved. Transparent HAp exhibited Vickers hardness (3.88 ± 0.22 GPa), fracture toughness (0.62 ± 0.03 MPa·m1/2), biaxial flexural strength (41.69 ± 1.23 MPa), and Young's modulus (78.1 ± 2.04 GPa). These findings will pave the way for the fabrication and potential applications of transparent ceramics at low temperatures.

Investigation of curing behavior and mechanical properties of SiC ceramics prepared by vat photopolymerization combined with pressureless liquid-phase sintering using Al2O3-coated SiC powder

Preparation of SiC ceramics via vat photopolymerization can enhance the use of SiC ceramics in defense, aerospace, and other fields. However, the high ultraviolet absorbance and refractive index of SiC powder present challenges in achieving the desired curing depth for SiC slurry in vat photopolymerization. Additionally, the low sintering activity of SiC powder hinders the densification of 3D-printed SiC ceramics. Consequently, the fabrication of SiC ceramics using vat photopolymerization 3D printing technology encounters significant challenges. This study proposes a method of improving the curing properties of SiC slurry with Al2O3-coated SiC powder. The gap between SiC particles was optimized by incorporating small particle β-SiC with enhanced sintering activity. The effects of Al2O3 coating modification and β-SiC percentage in SiC powder system on the UV absorbance of SiC powder, rheology and curing properties of SiC slurries, and sintering properties of SiC ceramics were thoroughly investigated. Furthermore, the density, flexural strength, and elastic modulus of the sintered parts prepared by vat photopolymerization combined with the pressureless liquid-phase sintering process achieve 2.82 ± 0.07 g/cm3, 225.3 ± 13.6 MPa, and 94.9 ± 5.5 GPa, respectively. These properties are comparable to those of other currently available 3D-printed SiC ceramics but are easier to manipulate and achieve, showcasing its competitiveness.

Fabrication of high-strength magnetocaloric Fe2AlB2 MAB phase ceramics via combustion synthesis and hot pressing

The work focuses on the study of the structure, phase composition, mechanical, electrical, and thermophysical properties, as well as the heat resistance and magnetocaloric effect of Fe2AlB2 MAB phase obtained by combining the self-propagating high-temperature synthesis and hot pressing. An investigation of the phase composition and structure of a consolidated sample disclosed that the main component of the ceramic is plate-like Fe2AlB2 grains with a thickness of 170–200 nm and a length of 2–5 μm. The resulting single-phase hot-pressed ceramics exhibited hardness values up to 12.8 GPa, fracture toughness up to 5.2 MPa∙m1/2, bending strength up to 429 MPa, and a thermal conductivity coefficient up to 7.47 W/(m∙K). A differential scanning calorimetry analysis revealed that at a temperature of 1284 °C the complete decomposition of Fe2AlB2 occurred. The magnetocaloric effect measured by the direct method was 0.92 K at a Curie temperature of 291 K. The heat resistance of Fe2AlB2 was studied at 1000 °C. It has been established that the oxidation process is governed by a linear law, whereby a multilayer structure of a heterogeneous oxide film is formed on the surface of the sample. The surface layer of the oxide film consisted of hematite α-Fe2O3, while the inner layer comprised boron-containing oxides in the form of iron warwickite Fe2BO4 and a porous layer of aluminum borate Al4B2O9, formed as needle/wire-shaped crystals. The formation of a FeB-based sublayer at the interface with the substrate has been established. The calculated oxidation rate after 30 h of testing was 5.55∙10−4 mg/(cm2∙s).

Enhancing the sustainable production of cost-effective ceramics with high strength using kaolin, sewage sludge and blast-furnace slag

Solid waste treatment remains an unavoidable environmental burden for modern cities. Currently, the multipurpose utilization of solid waste in construction and building materials is worth in-depth research as it furnishes high-value commercialization pathways with environmental and economic benefits for managing waste and addressing resource scarcity. This study explored the cost-effective ceramic fabrication from 40 % sewage sludge, 10 % blast-furnace slag and 50 % kaolin through in-situ sintering method, which enhanced the sustainable production of ceramic materials. The influences of firing temperature on the ceramic sintering effects, including mineral composition, micromorphology, pore structure and process performance, were systematically investigated. Results showed that the particle consolidation and sintering degrees of finished ceramics continuously increased as the firing temperature raised, presenting different surface, cross-sectional and pore structure characteristics. This was because increasing the firing temperature changed natures of the formed glass phase, such as content and viscosity. Moreover, variations in the ceramic structure would further affect its process performance. The ceramics prepared at 1250 °C were determined to have best firing effects with the densest structure and excellent performance, and the corresponding water absorption, bulk density, apparent porosity and compressive strength were 0.97 %, 2.32 g/cm3, 2 % and 70 MPa, respectively. Finally, comparisons with other researches confirmed that the developed ceramics possessed strong competitiveness in process performance. The presented study provided data support for the value-added application and sintering optimization of waste slag and sludge in ceramic production.

Wolframite-type MnMoO4: Magnetization, sintering by Cool-SPS, and magnetodielectric effect

Dense ceramic samples of wolframite-type MnMoO4 (w-MnMoO4) have been prepared by Cool-SPS (Spark Plasma Sintering) for the first time with the goal of investigating the magnetic, dielectric, and magneto-electric properties of this thermally fragile polymorph of MnMoO4. Earlier studies found that w-MnMoO4 converts to the structurally different α-MnMoO4 phase if heated in air at 873 K, thus hindering fabrication of w-MnMoO4 ceramics by conventional high-temperature sintering. Unsintered powder samples, which were prepared via a hydrothermal method, and dense ceramics elaborated by Cool-SPS have the same magnetic properties. Magnetic susceptibilities display Curie-Weiss behaviour, χ = C/(T-θ), with effective moments for Mn2+ ion μeff ≈ 5.9 μB/Mn-atom and negative Weiss temperatures θ ≈ - 96 to - 98 K. Unlike the isostructural multiferroic compounds MnW1-xMoxO4 (0 ≤ x < 0.3) which exhibits at least two successive magnetic transitions below 15 K, w-MnMoO4 undergoes only one paramagnetic-to-antiferromagnetic transition at TN ≈ 32 K. The field-dependent magnetization at 2 K shows a spin-flop transition at μ0HSF ≈ 2 T. Capacitance and dielectric losses obtained for a ceramic between 2 and 300 K in zero field and in a field of 9 T reveal several weak anomalies. Dielectric anomalies are observed at the magnetic phase transition, suggesting a magnetoelectric coupling. Qualitatively different dielectric and magnetodielectric behaviours occur in α-MnMoO4 ceramics at low temperature.

Ceramic shell fabrication via Stereo Lithography Apparatus: Recent progress on cracking problems and preventive measures

Stereo Lithography Apparatus (SLA) has demonstrated improvements on surface-roughness and dimensional-accuracy of the precision casting prototypes in recent years, which however is still far from being satisfactory in industrial. One primary problem is the easy crack of the ceramic shell at sintering process originated from the high thermal expansion coefficient of the photosensitive resin. Herein, this paper aims to find a solution for the cracking problem of the SLA-prototyped ceramic shells. This paper introduces recent studies mainly focusing on the aspect of photosensitive resin modification, the hollow structure improvement inside the photosensitive resin prototype, the wax sheet pasting method on the weak part of ceramic shells, and the sintering process design of the photosensitive resin in ceramic shells. The performance of ceramic shells through these studies are evaluated, and a fundamental solution to the cracking problem of ceramic shells is thereafter prospected.

Piezoelectric ceramics with hierarchical macro- and micro-pore channels for sensing applications

Piezoelectric sensors have attracted increasing attention due to their high sensitivity to forces, pressures and acceleration. The use of porous piezoelectric ceramics with aligned pores formed by freeze casting for sensing application also exhibit advantages due to their combination of a high piezoelectric charge coefficient and low permittivity, which leads to an enhancement in sensor sensitivity compared to dense materials. To fabricate porous materials, the process of direct ink writing (DIW) exhibits superiority in terms of structural design as a result of its ability to provide layer-by-layer and mold-free rapid prototyping. This work provides the first demonstration of the fabrication of lead zirconate titanate (PZT) piezoelectric ceramic scaffolds with sophisticated hierarchical porous structures by simultaneous DIW and freeze casting. The morphology of the porous cells and individual layers of the hierarchical porous PZT ceramic scaffolds were designed by adjusting the rheological properties and optimizing the printing path. The effect of cell structure and number of layers on sensing performance was investigated in detail. Manufactured scaffolds with a sandwich structure exhibited a high output voltage (191 V) under the application of 1 N external force, with a sensitivity of 8.98 V·kPa−1. This work provides a new approach to structural design of piezoelectric sensors to inform future efforts in the fabrication of high-performance piezoelectric ceramics with hierarchical porosity with complex and bespoke geometries.

Fabrication of fine‐grained Li2TiO3 ceramic with enhanced performance using high‐energy ball milling

AbstractNumerous efforts have been made to fabricate Li2TiO3 tritium breeding ceramics with satisfactory density and mechanical strength while maintaining a fine grain structure. In this study, high‐energy ball milling was performed to promote grain refinement and amorphization of TiO2 and Li2CO3 powders, thereby preparing Li2TiO3 ceramic at a reduced sintering temperature. In the presence of high‐energy ball milling, powder mixtures with particle sizes of 24–29 nm were obtained, and the formation of β‐Li2TiO3 occurred at 400°C. The relative density and crushing load of Li2TiO3 ceramic pebbles improved as the ball‐to‐powder ratio and milling time increased. The Li2TiO3 ceramic pebbles sintered at 900°C exhibited a tiny grain size, satisfactory relative density (89%), and excellent crushing load (121 ± 13 N). The results also demonstrated that Li2TiO3 ceramic possessed the maximum thermal conductivity and ionic conductivity under the conditions of a 20:1 ball‐to‐powder ratio and 20 h milling time, that is, 5.028 W/m·K and 1.87×10−2 S/m at room temperature. Overall, the high‐energy ball milling process has shown advantages in the fabrication of tritium breeding ceramics with fine‐grained structure and excellent comprehensive performance.

Fabrication and metrology of SiC cladding and seals for containment and heat transfer applications

Background SiC is a candidate material for high-temperature nuclear applications due to its high corrosion resistance, thermomechanical strength, and low neutron cross-section. Traditional manufacturing methods include sintering to a near-net shape with post-sinter finish machining. Methods Analysis of the metrology from fabricated SiC casings was conducted. SiC was fabricated using spark plasma sintering (SPS) under constant temperature and pressure (~2,000K; ~10MPa). Samples were then sandblasted to remove excess graphite and underwent metrological evaluation. Results Metrology indicates that dimensions may not be sufficiently predictable for net-shape fabrications. The process of mass dosing, human input, and sinter-forging lead to standard deviations of up to ~7%, suggesting that alternative tooling approaches are required to decrease the amount, and subsequent cost, of post-sinter machining. Dimensional compatibility trials using surrogate pellets show that machining is required. Conclusions The consequences of poor tolerances are discussed with respect to theoretical applications. This is an expected outcome for a ceramic fabrication process.

Fabrication of broadband wave-transparent Si3N4 ceramics with octet-truss lattice structure by vat photopolymerization 3D printing technology

Vat photopolymerization 3D printing of Si3N4 ceramics has attracted great attention recently. To overcome the low curing depth limitation caused by α-Si3N4, β-Si3N4 with low absorbance and large particle size was selected in this paper. After printing, the effects of pressureless sintering temperatures on mechanical and dielectric properties were systematically investigated. At 1800 °C, the real permittivity of Si3N4 ceramics was 7.37, and the maximum bending strength was 367 ± 75 MPa. Considering the application of Si3N4 ceramics in radomes/windows, the dielectric constant of Si3N4 ceramics should be further reduced. Therefore, the octet-truss lattice structure was introduced to optimize the porosity of ceramics. As the porosity increased from 25% to 36%, the real permittivity decreased from 5.56 to 4.42, and the bending strength ranged from 98 ± 7–62 ± 13 MPa. It shows that vat photopolymerization 3D printing can be a promising technology for the fabrication of wave-transparent Si3N4 ceramics.

Electrophoretic Deposition of One- and Two-Layer Compacts of Holmium and Yttrium Oxide Nanopowders for Magneto-Optical Ceramics Fabrication

In this work, the possibility of fabricating composite magneto-optical ceramics by electrophoretic deposition (EPD) of nanopowders and high-temperature vacuum sintering of the compacts was investigated. Holmium oxide was chosen as a magneto-optical material for the study because of its transparency in the mid-IR range. Nanopowders of magneto-optical (Ho0.95La0.05)2O3 (HoLa) material were made by self-propagating high-temperature synthesis. Nanopowders of (Y0.9La0.1)2O3 (YLa) were made by laser synthesis for an inactive matrix. The process of formation of one- and two-layer compacts by EPD of the nanopowders from alcohol suspensions was studied in detail. Acetylacetone was shown to be a good dispersant to obtain alcohol suspensions of the nanopowders, characterized by high zeta potential values (+29–+80 mV), and to carry out a stable EPD process. One-layer compacts were made from the HoLa and YLa nanopowders with a density of 30–43%. It was found out that the introduction of polyvinyl butyral (PVB) into the suspension leads to a decrease in the mass and thickness of the green bodies deposited, but does not significantly affect their density. The possibility of making two-layer (YLa/HoLa) compacts with a thickness of up to 2.6 mm and a density of up to 46% was demonstrated. Sintering such compacts in a vacuum at a temperature of 1750 °C for 10 h leads to the formation of ceramics with a homogeneous boundary between the YLa/HoLa layers and a thickness of the interdiffused ion layer of about 30 μm.

Influence of Grain Size on Dielectric Behavior in Lead-Free 0.5 Ba(Zr0.2Ti0.8)O3-0.5 (Ba0.7Ca0.3)TiO3 Ceramics.

Fine-tuning of grain sizes can significantly influence the interaction between different dielectric phenomena, allowing the development of materials with tailored dielectric resistivity. By virtue of various synthesis mechanisms, a pathway to manipulate grain sizes and, consequently, tune the material's dielectric response is revealed. Understanding these intricate relationships between granulation and dielectric properties can pave the way for designing and optimizing materials for specific applications where tailored dielectric responses are sought. The experimental part involved the fabrication of dense BCT-BZT ceramics with different grain sizes by varying the synthesis (conventional solid-state reaction route and sol-gel) and consolidation methods. Both consolidation methods produced well-crystallized specimens, with Ba0.85Ca0.15O3Ti0.9Zr0.1 (BCTZ) perovskite as the major phase. Conventional sintering resulted in microstructured and submicron-structured BCT-BZT ceramics, with average grain sizes of 2.35 μm for the solid-state sample and 0.91 μm for the sol-gel synthesized ceramic. However, spark plasma sintering produced a nanocrystalline specimen with an average grain size of 67.5 nm. As the grain size decreases, there is a noticeable decrease in the maximum permittivity, a significant reduction in dielectric losses, and a shifting of the Curie temperature towards lower values.

Preceramic Polymers for Additive Manufacturing of Silicate Ceramics.

The utilization of preceramic polymers (PCPs) to produce both oxide and non-oxide ceramics has caught significant interest, owing to their exceptional characteristics. Diverse types of polymer-derived ceramics (PDCs) synthesized by using various PCPs have demonstrated remarkable characteristics such as exceptional thermal stability, resistance to corrosion and oxidation at elevated temperatures, biocompatibility, and notable dielectric properties, among others. The application of additive manufacturing techniques to produce PDCs opens up new opportunities for manufacturing complex and unconventional ceramic structures with complex designs that might be challenging or impossible to achieve using traditional manufacturing methods. This is particularly advantageous in industries like aerospace, automotive, and electronics. In this review, various categories of preceramic polymers employed in the synthesis of polymer-derived ceramics are discussed, with a particular focus on the utilization of polysiloxane and polysilsesquioxanes to generate silicate ceramics. Further, diverse additive manufacturing techniques adopted for the fabrication of polymer-derived silicate ceramics are described.