High Temperature Sintering Research Articles

Preparation of eco-friendly and high-strength ceramsite by granite scraps, granite fine mud, and phosphogypsum: Response surface methodology optimization, environmental safety assessment

Granite scraps (GS), Granite fine mud (GFM), and phosphogypsum (PG) are solid wastes containing harmful substances produced during the processing of granite and the production of phosphate fertilizer. Their resourceful and harmless utilization holds great significance in reducing environmental pollution. This study explores the preparation of eco-friendly and high-strength ceramsite using GS as the primary material, GFM as the binder, and PG as the regulator. The performance of ceramsite was studied by conducting single-factor experiments to examine the impact of the GS, GFM, and PG mass ratios. The Box-Behnken response surface methodology was utilized to optimize the effect of sintering conditions on the strength of ceramsite. The results suggested that the properties of the ceramsite are affected by the material ratios. The sintering temperature and keeping time notably influence the strength of ceramsite. Under optimal preparation conditions, the ceramsite achieved a bulk density of 1085.40kg/m3, apparent density of 2253.63kg/m3, 1-h water absorption of 0.13%, hydrochloric acid soluble rate of 0.016%, and compressive strength of 34.52MPa. Importantly, high-temperature sintering plays an essential role in fixing heavy metals and reducing the ecological risk level of heavy metals in ceramsite, which ensures excellent environmental performance and application prospects for ceramsite.

Correlation and application of thermal expansion coefficient/elastic modulus for co-sintered composite cermet/ceramic materials

Deformation and stress concentration appearing during high-temperature sintering process significantly affect production quality of solid oxide cell (SOC), due to mismatched mechanical and thermophysical properties of the sintered electrode and electrolyte. In this study, a coarse-grained molecular dynamics (CG-MD) method is developed to evaluate and correlate coefficient of thermal expansion (CTE) and elastic modulus during the entire co-sintering process (including temperature-increasing, −insulation, and -decreasing stages). It is revealed that, in the sintered porous cermet electrode, CTE primarily exhibits an increasing trend until temperature-decreasing stage. Compared to the constant values commonly applied in the literature, the elastic modulus experiences a decay trend with a reduction of 32.14 % in the porous electrode and 9.68 % reduction in the dense electrolyte. The obtained CTE and elastic modulus are correlated with the sintering parameters and further applied to a macroscopical model for predicting overall sintering warpage and stress in a co-sintered SOC half-cell composed of a thick porous electrode and a thin dense layer. The varied CTE is identified as the main factor influencing warpage deformation, while the elastic modulus as a more significant impact on the von Mises stress during the co-sintering of the half-cell. Analysis is further conducted by orthogonal testing method for sintering temperature, sintering time, material content and diameter ratio of the porous cermet nanoparticles, aiming to optimize the varied CTE and elastic modulus, particularly during the temperature-insulation process. Subsequently, the optimized properties are implemented, and it is found that, after sintering insulation for 120 min, the maximum warpage displacement is about 7.34 mm, which represents a decrease of approximately 14.11 %; while the von Mises stress is observed to be 379.24 MPa, which indicates a reduction of around 37.33 % compared with the predictions by the constant properties.

Epoxy Composite Films Filled with Sintered Multifaceted Boron Nitride for Thermal and Dielectric Applications

The miniaturization of electronic devices has led to an increase in power density and functional integration, resulting in rapid heat accumulation that adversely affects operational stability and service life. Dielectric composite films with excellent thermal conductivity and insulating properties are highly desired for addressing thermal management issues in electronic packaging applications. Hexagonal boron nitride (h-BN) is a promising filler for such composites due to its outstanding thermal conductivity, insulating properties, and chemical stability. However, the inherent platelike structure of h-BN causes significant anisotropy and poor miscibility with polymers, limiting the uniform conduction of heat. This study proposes a high-temperature sintering method that transforms flaky h-BN plates into irregular multifaceted particles. This transformation reduces thermal anisotropy and creates uniform heat conduction pathways. The resulting sintered BN/Epoxy (s-BN/EP) composite films exhibit exceptional thermal conductivity, with in-plane thermal conductivity increased by 36% to 6.0 W m-1 K-1 and through-plane thermal conductivity increased by 39% to 1.2 W m-1 K-1 compared to pristine h-BN/epoxy composites. Moreover, s-BN/EP films could maintain low dielectric constant (Dk, 3.22) and dielectric loss (Df, 0.015) at 5 GHz. This innovative approach provides a significant advancement in the development of high-performance insulating polymer composites, offering a promising solution for thermal management in high-power-density electronic packaging.

Intelligent Optimization and Impact Analysis of Energy Efficiency and Carbon Reduction in the High-Temperature Sintered Ore Production Process

The coordinated optimization of energy conservation, efficiency improvement, and pollution reduction in the sintering production process is vital for the efficient and sustainable development of the sintering department. However, previous studies have shown shortcomings in the multi-objective collaborative optimization of sintering systems and the quantification of pollutant impacts. To address these, this paper proposes a multi-objective optimization method integrated with the NSGA-III algorithm and establishes an integrated system optimization model for sintered ore production and high-temperature waste heat recovery. The results demonstrate significant improvements: energy utilization efficiency increased by 0.67%, energy consumption decreased by 17.3 MJ/t, production costs were reduced by 11.45 CNY/t, and the emissions of CO2, SO2, and NOx were reduced by 0.464 kg/t, 0.034 kg/t, and 0.008 kg/t, respectively. Additionally, the study identified optimal configuration parameters and analyzed the quantitative impact of several key factors on multiple indicators. The results also show that reducing the water content of the mixture, decreasing the middling coal content in the fuel, and increasing the thickness of the material layer are effective strategies to reduce energy consumption and pollutant emissions in the sintering process. Overall, implementing these optimizations can bring significant economic and environmental benefits to the steel industry.

Additive manufacturing of high-performance SiO2-Al2O3-K2O (Na2O) ceramic components via binder jetting technology

To resolve issues such as high sintering temperatures and relatively low relative densities and bending strengths of sintered bodies during the preparation of ceramic parts using binder jetting (BJ) additive manufacturing (AM) technology. In this study, high-performance SiO2-Al2O3-K2O (Na2O) ceramics were fabricated using quartz, kaolin, potassium feldspar, and sodium feldspar as raw materials through BJ technology. Initially, the sintering process of the BJ ceramics was studied by adjusting the ratio of potassium feldspar to sodium feldspar and the sintering temperature, which enhanced the relative density and bending strength of the silicate ceramics. Subsequently, using response surface methodology (RSM), the effects of print layer thickness (A), scraper speed (B), and ink volume per unit area (C) on the performance of the ceramics after sintering were investigated. Results indicated that the optimal parameters of the BJ printing process were determined using RSM: A was 250 μm, B was 3.44 mg cm−3, and C was 35 mm s−1. Under these conditions, the sintered ceramics achieved optimal relative densities, closed porosities, and flexural strengths of 89.05 %, 10.85 %, and 69.19 MPa for relative density, closed porosity, and flexural strength, respectively.

Honeycombed pomegranate-like sludge ceramsite particles: Preparation with fly ash floating beads as the pore-forming template and performance optimization

Ceramsite used in construction and building are typically limited by high water absorption rates, the contradiction between lightweight and high strength, and severe performance fluctuations. This can be attributed to the fact that ceramsites are currently prepared by high-temperature sintering expansion, wherein viscosity and surface tension of the liquid phases shall perfectly match with the gas generation rate. On the other hand, sand washing sludge and fly ash are common solid wastes in construction and building and their environmentally friendly disposal are of great significance. In this study, honeycombed pomegranate-like sludge ceramsites with low density (packing density = 733.2–968.3 kg/m3), high strength (cylinder compressive strength = 11.2–18.8 MPa), and low water absorption rate (one-hour water absorption rate = 1.2–2.8 %) were prepared with sand washing sludge and fly ash floating beads as the raw material and the pore-forming template, respectively. Also, the effects of particle size and content of fly ash floating beads on the structure and performance of the as-prepared ceramsite were investigated. The results indicated that the pore structure of the as-prepared ceramsite was directly dependent on size and content of the fly ash floating beads, suggesting that the performance of the as-prepared ceramsite can be customized by tuning size and content of the beads. Additionally, lightweight aggregate concrete prepared by using the as-prepared ceramsites exhibited improved 7-day and 28-day compressive strengths and reduced thermal conductivity compared with concrete prepared by using commercially available ceramsites. Overall, this study presents the preparation of ceramsite particles with both high strength and low density by using fly ash and sand washing sludge, both of which are abundant solid wastes in constructions, thus contributing to solid waste recycling in construction.

Utilization of handheld LIBS and XRF analyzers for impurity detection in 3D-printed ultra-high-temperature ceramics

In this study, we implement handheld laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence (XRF) analyzers to detect elemental impurities in additively manufactured ultra-high-temperature ceramics (UHTCs). Spectral data were collected from digital light processing (DLP) 3D-printed alumina (Al2O3) samples at various processing stages. These stages included high-temperature debinding and sintering phases used to bake out organic impurities and improve grain cohesion of the ceramic. Spectral analysis revealed the presence of organic impurities such as H and C together, with inorganic impurities such as Na, Si, Ca, and Fe. A reduction in elemental impurities in the spectra was observed as the ceramic samples were processed, validating the effectiveness of handheld analyzers for in situ rapid impurity detection and quality control in the manufacturing of 3D-printed UHTCs.

Catalytic combustion of 1,2-dichloroethane over highly active and stable oxygen vacancy-enriched Ru/Co3O4 catalysts: The unique etching strategy through calcium doping

A series of Ru/XCaCo-N catalysts with different Ca to Co3O4 mass ratios were synthesized using doping-etching strategy and the catalytic combustion performance of 1,2-dichloroethane (EDC) was investigated. Consequently, Ru/5CaCo-N-450 catalyst exhibited the excellent activity for the EDC elimination in different reaction conditions, as well as stability against high temperature. The characteristic results revealed that the existing of abundant oxygen vacancies in Ru/5CaCo-N-450 catalyst significantly improved the redox and acidity property and enhanced the high-temperature sintering stability through the interaction of Ru species with Co3O4. The results of in-situ DRIFTS spectra indicated the promoted contribution of oxygen vacancies that facilitated the adsorption and activation of EDC, and synergistic effect between Ru species and Co3O4 benefited to the elimination of absorbed Cl species as well as the ability of deep oxidation for intermediates. Thus, an excellent catalyst with high activity and stability has been investigated in detail using a doping-etching strategy, and the relatively simple and environmentally friendly synthesis method provides a broad prospect for potential industrial applications.

Efficient synthesis of FeVO4 cathode materials in high specific energy thermal batteries

Thermal batteries, which are essential for applications in extreme environments, require cathode materials with high specific energy and thermal stability. In this study, metal vanadates were synthesized via a chemical precipitation method followed by high-temperature sintering, offering a promising alternative for conventional transition metal sulfides. The synthesized FeVO4 exhibits phase purity, while copper and nickel vanadates show secondary phases, indicating challenges in achieving pure-phase synthesis of metal vanadates. Electrochemical evaluations reveal that FeVO4 cathode delivers an initial discharge voltage of 2.65 V and a specific capacity of 190 mAh/g. Whereas the FeVO4/CNTs composite cathode demonstrates an enhanced specific capacity of 253.66 mAh/g, which is attributed to prolonged discharge plateaus. Phase evolution studies indicated that FeVO4 reacts with molten salts during high-temperature discharge, leading to the formation of Fe2O3 and Li0.3V2O5, which contribute to the observed stepwise discharge behavior. These results emphasize the importance of optimizing the interactions between cathode materials and molten salts to improve the performance of high-temperature thermal batteries.

Tailoring BaCe0.7Zr0.1(Dy0.1|Yb0.1)0.2O3−δ electrolyte through strategic Cu doping for low temperature proton conducting fuel cells: Envisioned theoretically and experimentally

This study addresses the challenge of high sintering temperatures in proton-conducting fuel cells (PCFCs) with BaCeO3-doped electrolytes. We demonstrate that 1 mol% copper (Cu) doping at the B-site of BaCe0.7Zr0.1(Dy0.1|Yb0.1)0.2O3−δ (BCZDYb) improves sintering behavior, enabling densification at 1400 °C. However, Cu doping disrupts stoichiometry, creating barium vacancies and reducing proton-accepting cations, affecting overall conductivity. This mechanism is confirmed through density functional theory (DFT) calculations and various experimental techniques, including crystal structure analysis using X-ray diffraction (XRD) and morphology and elemental analysis via field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS). Electrochemical measurements are performed using the electrochemical impedance spectroscopy (EIS). The ionic conductivity of 1 mol% Cu-doped BCZDYb (BCZDYb-1) is 1.49 × 10−2 S cm−1 at 650 °C, which is ∼3.58 times higher than that of BCZDYb sintered at 1200 °C. The BCZDYb-1 exhibits ∼16 times higher grain boundary conductivity when sintered at 1400 °C, compared to undoped BCZDYb. The single cell employing BCZDYb-1 as the electrolyte achieved a power density of ∼606 mW cm−2 at 550 °C. These results indicate that a controlled amount of Cu doping can enhance densification while maintaining high ionic conductivity, making it suitable for practical applications in PCFCs operating at lower temperatures.

Sintering of Copper Nanoparticles using Intense Pulsed Light for screen-printed films on flexible substrate

Abstract Rapid growth in applications involving large area flexible electronics has led to wide adoption of the technique of sintering printed films using intense pulsed light (IPL) due to its pulse mode operation and ability to reach high sintering temperatures without affecting the underlying substrate significantly. We study sintering mechanisms of screen-printed thin films of copper nanoparticles on polyethylene terephthalate (PET) plastic substrate by varying irradiance energy over a wide range to monitor conductivity and associated microstructure changes. We obtain optimized parameters which indicate existence of a sharp threshold irradiance energy to kickstart sintering, and two distinct regimes beyond that. The low temperature regime has a high energy barrier while the high temperature regime has a substantially reduced energy barrier with change of phase due to local melting.

Exploring the Potential of Cold Sintering for Proton-Conducting Ceramics: A Review.

Proton-conducting ceramic materials have emerged as effective candidates for improving the performance of solid oxide cells (SOCs) and electrolyzers (SOEs) at intermediate temperatures. BaCeO3 and BaZrO3 perovskites doped with rare-earth elements such as Y2O3 (BCZY) are well known for their high proton conductivity, low operating temperature, and chemical stability, which lead to SOCs' improved performance. However, the high sintering temperature and extended processing time needed to obtain dense BCZY-type electrolytes (typically > 1350 °C) to be used as SOC electrolytes can cause severe barium evaporation, altering the stoichiometry of the system and consequently reducing the performance of the final device. The cold sintering process (CSP) is a novel sintering technique that allows a drastic reduction in the sintering temperature needed to obtain dense ceramics. Using the CSP, materials can be sintered in a short time using an appropriate amount of a liquid phase at temperatures < 300 °C under a few hundred MPa of uniaxial pressure. For these reasons, cold sintering is considered one of the most promising ways to obtain ceramic proton conductors in mild conditions. This review aims to collect novel insights into the application of the CSP with a focus on BCZY-type materials, highlighting the opportunities and challenges and giving a vision of future trends and perspectives.

Enhanced energy storage performance in NBT-based MLCCs via cooperative optimization of polarization and grain alignment

Dielectric ceramics possess a unique competitive advantage in electronic systems due to their high-power density and excellent reliability. Na1/2Bi1/2TiO3-based ceramics, one type of extensively studied energy storage dielectric, however, often experience A-site element volatilization and Ti4+ reduction during high-temperature sintering. These issues may result in increased energy loss, reduced polarization and low dielectric breakdown electric field, ultimately making it challenging to achieve both high energy storage density and efficiency. To address these issues, we introduce a synergistic optimization strategy that combine polarization engineering and grain alignment engineering. First principles calculations and experimental analyses show that the doping of Mn2+ can suppress the reduction of Ti4+ in Na1/2Bi1/2TiO3-based ceramics and enhance ion off-centering displacements, thereby reducing energy loss and improving polarization. In addition, we prepared multilayer ceramic capacitors with grains oriented along the <111> direction using the template grain growth method. This approach effectively reduces electric-field-induced strain by 37% and markedly enhances breakdown electric field by 42% when compared with nontextured counterpart. As a result of this comprehensive strategy, <111 >-textured Na1/2Bi1/2TiO3-based multilayer ceramic capacitors achieve an ultra-high energy density of 15.7 J·cm−3 and an excellent efficiency beyond 95% at 850 kV·cm−1, exhibiting a superior overall energy storage performance.

Blacklight sintering of BaZrO3-based proton conductors

Acceptor-doped BaZrO3, a ceramic proton conductor, is well researched for use in solid oxide fuel cells due to its proton conductivity and chemical stability. A major drawback of the material is the difficulty of sintering as it requires high sintering temperatures and long heating times (> 1600 °C, 24 h). An emerging sintering technology to mitigate this challenge is blacklight sintering, which uses a high-powered blue or UV light source to heat ceramics extremely fast leading to short sintering times and reduced energy demand. In this work, BaZr0.8Y0.2O3-δ (BZY20) and BaZr0.8Y0.1Sc0.1O3-δ (BZY10Sc10) were blacklight-sintered with a high-power blue laser in under four minutes. Even though the resulting samples have a gradient from large to small grains and structurally disordered grain boundaries, the proton conductivity is comparable to conventionally sintered samples. Hence, blacklight sintering is a promising technology with the potential to sinter BaZrO3 much faster, while saving energy.

Fine-Grain High-Performance Densified Oxide Fibers Produced by Open Ultrafast High-Temperature Sintering.

The considerable grain growth occurring during the long-term high-temperature sintering of polycrystalline oxide fibers negatively affects their mechanical properties, which highlights the need for alternative sintering methods. Herein, open ultrafast high-temperature sintering (OUHS) in air, characterized by rapid heating/cooling (>10000 K min-1) and a short high-temperature holding time (<10 s), is used to produce 3 mol% yttria-stabilized zirconia continuous fibers with coherent boundaries forming robust connections between fine grains. The tensile strength of these fibers (2.33GPa on average, sintering temperature = 1673 K) notably exceeds that of their counterparts produced by traditional sintering (1.17GPa). The effects of pores on fiber mechanicalproperties are analyzed using experimental and theoretical methods. For a versatility demonstration, OUHS is applied to several types of polycrystalline oxide fibers (HfO2, Al2O3, TiO2, Y2O3, and La2Zr2O7), considerably improving their mechanical properties and enabling crystalline phase control, which demonstrates the suitability of this procedure for the development of high-performance materials.

Acceleration of grain boundary diffusion during ultra-fast firing (UHS) of alumina powder compacts

The sintering rate of a ceramic at a given temperature and relative density is often higher if the heating to that sintering temperature is more rapid. This has previously been explained in terms of microstructural coarsening during slow heating, which degrades the sinterability of the body before it reaches the sintering temperature. In this work the sintering of pure alumina with conventional heating rates (CS, 100–900 °C/hour) was compared with ultra-fast firing, using the method known as ultrafast high-temperature sintering (UHS, 120–140 °C/s). Despite the wide difference in heating rate, the SEM microstructures for a given density were similar and a modified Master Sintering Curve analysis of the results showed that the small pore size reduction observed was not sufficient to account for the acceleration in sintering of UHS samples compared with CS. There remained an additional acceleration by a factor of up to ∼20 that was attributed to a higher grain boundary diffusion coefficient in UHS. It is suggested that this is the result of the boundaries forming between powder particles not having time to relax to their lowest energy, most compact structures during UHS, i.e. non-equilibrium grain boundaries. In support of this hypothesis, it is shown that powder compacts that were first partially pre-sintered with conventional heating rates and then subjected to UHS did not show the same acceleration of sintering displayed by UHS of green bodies. The implication is that the slow pre-sintering allowed relaxation of the grain boundaries to low energy structures with low diffusion coefficients.

Sintering polycrystalline silicon carbide composite ceramics with ultra-high hardness under high pressure

Silicon carbide (SiC) is an important structural ceramic material, exhibiting exceptional comprehensive properties that are unmatched by metals and other structural materials. In this study, a combination of α-SiC micron powder and β-SiC nanopowder was utilized as precursor materials for high pressure and high temperature (HPHT) sintering. Under a pressure of 5.0 GPa, polycrystalline SiC samples with mixed grain size were sintered within a temperature range from 1000 to 1700 °C, and compared with SiC samples sintered from single micron powder under identical temperature and pressure conditions. The microstructures of the two sets of SiC samples were observed using scanning electron microscopy. Additionally, the stress states and strengthening mechanisms among SiC grains with mixed grain size under HPHT were further analyzed in conjunction with X-ray diffraction results. The polycrystalline SiC composite ceramics sintered at 1700 °C exhibited superior mechanical and thermal properties, achieving a Vickers hardness of 35.2 GPa that is 23.5 % higher than that obtained by conventional spark plasma sintering and even surpassing the hardness of single crystal SiC, demonstrating thermal stability up to 1405 °C in air environment. Transmission electron microscopy was employed to analyze defects and plastic deformation in these samples. The study suggests that the primary strengthening mechanisms of the sintered polycrystalline SiC composite ceramics under HPHT include the increase in micro defects induced by in-situ plastic deformation at elevated temperatures and the effects of high-temperature creep. This study provides new insights into the HPHT sintering of hard materials.

Yb:YSAG ceramics: An attractive thin-disk laser material alternative to a single crystal?

The 8.3 at.% Yb-doped yttrium-scandium-aluminum garnet (YSAG) ceramics were fabricated by a modified reverse co-precipitation method followed by uniaxial and cold isostatic pressing, annealing in air and high-temperature sintering in vacuum. Spectroscopic and lasing properties were investigated in dependence on Y/Sc/Al ratio in ceramic composition. Optical transmission of Yb:YSAG ceramics in visible and near-infrared spectral range exceeds 80 % that indicates a high quality of the Yb:YSAG samples. Among all the ceramics, the Y2.35Yb0.25Sc1.00Al4.40O12 composition demonstrates the best lasing performance and the highest slope efficiency up to 75 %.

Effects of binary sintering additives (SmF3-Sm2O3) and sintering temperature on β-SiAlON ceramic tool materials

β-SiAlON ceramic tool materials were fabricated via spark plasma sintering using binary sintering additives (SmF3-Sm2O3). The effects of SmF3 addition and sintering temperature on the densification, phase composition, microstructure and mechanical properties were studied. Furthermore, the corrosion behavior of β-SiAlON ceramic tool materials due to excessive SmF3 at high sintering temperatures (≥1700 °C) was revealed. The results indicated that SmF3 could promote the densification and generation of β-SiAlON. Higher SmF3 content and sintering temperature increased the aspect ratio and average grain size of β-SiAlON, which made fracture toughness increase and Vickers hardness decrease. The best density, fracture toughness and hardness of β-SiAlON ceramic tool materials were 3.204 g/cm3, 6.45 ± 0.07 MPa m1/2 and 16.72 ± 0.09 GPa. However, β-SiAlON was corroded by excessive SmF3 during high temperature sintering, resulting in deterioration in densification and properties.

Mechanism and process study of spent lithium iron phosphate batteries by medium-temperature oxidation roasting strategy

In this study, we determined the oxidation roasting characteristics of spent LiFePO4 battery electrode materials and applied the iso-conversion rate method and integral master plot method to analyze the kinetic parameters. The ratio of Fe (II) to Fe (III) was regulated under various oxidation conditions. The results showed that 95.50 % of LiFePO4 was oxidized to Li3Fe2(PO4)3 and Fe2O3 under the most cost-effective roasting conditions (500°C, 1000 mL/min, 30 min, air atmosphere) and only approximately 18 % graphite was involved in the reaction. More than 99 % of the lithium was leached under these roasting conditions, with minimal impurities. Medium-temperature selective oxidation roasting effectively avoided the high-temperature sintering phenomenon that affects the crystal structure of the product. Instead, a fine, uniform oxidized phase was formed, and the polyvinylidene fluoride impurity that typically persists throughout the recycling process was avoided. This study provides a sufficient theoretical basis and experimental prerequisites for selective, time-efficient, and economical lithium leaching or reductive regeneration of the cathode materials.