Sintering Aid Research Articles

Enhanced optical properties and laser performance of Yb:LuScO3 transparent ceramics fabricated with ZrO(NO3)2

This work aims to fabricate the Yb:LuScO3 sesquioxides transparent ceramics for use in ultrafast and ultrashort laser technology. 1 at.% Yb:LuScO3 nanopowders were fabricated using the glycine-nitrate process. ZrO(NO3)2 was selected as the precursor of ZrO2 which functions as a sintering aid. Yb:LuScO3 transparent ceramics with different ZrO2 content were fabricated by vacuum sintering at 1780°C and HIPing at 1650°C, among which the ceramic with 7 at.% ZrO2 showed the highest transmittance, reaching 81% at 2000 nm. The ceramic achieved a maximum output power of 1.5 W at 1038 nm with a slope efficiency of 34.8% and tunable wavelength range exceeding 22 nm. The results demonstrated that Yb:LuScO3 transparent ceramics can be considered as promising materials in 1 μm solid-state laser applications.

High‐temperature behavior and self‐enhancing mechanisms of oxide‐bonded SiC porous ceramics

AbstractOxide‐bonded SiC porous ceramics (SCPCs), synthesized via reaction bonding, exhibit significant potential for high‐temperature applications. However, incorporating sintering aids inevitably results in a considerable quantity of amorphous glass phase within SCPCs, thereby introducing risks to their high‐temperature mechanical performance. In this study, we employ in‐situ characterization techniques to investigate the high‐temperature behavior of SCPCs. Our findings reveal that SCPCs demonstrate remarkable high‐temperature self‐enhancing properties, with a critical bending strength at 800°C. Beyond this temperature, the strength declines sharply. Intriguingly, the critical bending strength is 36.6% greater than at ambient temperature. Moreover, elevated temperatures enhance the elastic modulus and promote the transition of SCPCs from multilinear to nonelastic fracture. The neck phase, which imparts strength to the SCPCs, is composed of four distinct layers along the depth direction: silicate glass, oxygen‐containing, silicon‐rich, and SiC region, as revealed by FIB‐TEM. The transformation from α to β‐cristobalite in the oxygen‐containing region improves the thermal expansion match with SiC, thereby mitigating local stress concentration. Furthermore, the compressive stress within the neck region intensifies with increasing temperatures, thereby inhibiting crack propagation. This work provides a basis for the high‐temperature applications of SCPCs.

Role of Sintering Aids in Electrical and Material Properties of Yttrium- and Cerium-Doped Barium Zirconate Electrolytes

Ceramic proton conductors have the potential to lower the operating temperature of solid oxide cells (SOCs) to the intermediate temperature range of 400–600 °C. This is attributed to their superior ionic conductivity compared to oxide ion conductors under these conditions. However, prominent proton-conducting materials, such as yttrium-doped barium cerates and zirconates with specified compositions like BaCe1−xYxO3−δ (BCY), BaZr1−xYxO3−δ (BZY), and Ba(Ce,Zr)1−yYyO3−δ (BCZY), face significant challenges in achieving dense electrolyte membranes. It is suggested that the incorporation of transition and alkali metal oxides as sintering additives can induce liquid phase sintering (LPS), offering an efficient method to facilitate the densification of these proton-conducting ceramics. However, current research underscores that incorporating these sintering additives may lead to adverse secondary effects on the ionic transport properties of these materials since the concentration and mobility of protonic defects in a perovskite are highly sensitive to symmetry change. Such a drop in ionic conductivity, specifically proton transference, can adversely affect the overall performance of cells. The extent of variation in the proton conductivity of the perovskite BCZY depends on the type and concentration of the sintering aid, the nature of the sintering aid precursors used, the incorporation technique, and the sintering profile. This review provides a synopsis of various potential sintering techniques, explores the influence of diverse sintering additives, and evaluates their effects on the densification, ionic transport, and electrochemical properties of BCZY. We also report the performance of most of these combinations in an actual test environment (fuel cell or electrolysis mode) and comparison with BCZY.

Si3N4-Assisted Densification Sintering of Na3Zr2Si2PO12 Ceramic Electrolyte toward Solid-State Sodium Metal Batteries

The solid-state metal battery with solid-state electrolytes has been considered the next generation of energy storage technology owing to its superior safety and high energy density. But, unfavorable ionic conductivity and interfacial problems make it difficult to widely use in practice. In this work, Si3N4 was rationally introduced into the NASICON matrix as a sintering aid, and the influence of Si3N4 on the crystal phase, microstructure, electrochemical and electrical performance of Na3Zr2Si2PO12 (NZSP) ceramic was systematically studied. The results demonstrate that the introduction of Si3N4 can effectively lower the densification sintering temperature of Na3Zr2Si2PO12 electrolyte and enhance the room temperature ionic conductivity of the NZSP to 3.82 × 10−4 S cm−1. In addition, since Si3N4 has a high thermal conductivity and can inhibit the transmission of electrons between the grains of the electrolyte matrix, it will effectively hinder the generation of sodium metal dendrites and relieve the concentration of the heat source. Moreover, owing to the desirable interface compatibility of the Na and NZSP-Si3N4 electrolyte, the Na/NZSP-1150-1%Si3N4/Na symmetric battery exhibits excellent stability, and the electrode/electrolyte interface still maintains good integrity even after long-term cycling. The assembled Na/NZSP-1150-1%Si3N4/Na3.5V0.5Mn0.5Fe0.5Ti0.5(PO4)3 cell manifests an initial specific capacity of 152.5 mA h g−1, together with an initial Coulombic efficiency of 99.8%. Furthermore, after 200 cycles, the battery displays a capacity retention rate of 82%.

Static and dynamic mechanical properties of aluminum nitride-silicon carbide whisker composites

AlN composites reinforced with SiC whiskers and Y2O3 sintering aids were fabricated using the hot-pressing technique to investigate static and dynamic mechanical properties. Microstructure analysis revealed that increasing SiC whisker content yielded grain refinement and decreasing relative density. The Vickers hardness increased from 10.29 to 14.47 GPa, while the fracture toughness improved from 3.03 to 4.39 MPa·m1/2 with 30 wt% SiC whiskers. A numerical approach for evaluating the dynamic modulus and loss factor is presented utilizing the wave propagation characteristics. The dynamic properties showed decreasing dynamic modulus and increasing loss factor with higher SiC content, attributed to increased porosity and interphase boundaries. Thermal conductivity, however, decreased from 139.53 to 49.95 W/m·K as SiC whisker content increased, primarily due to enhanced phonon scattering at grain and interphase boundaries. These findings suggest that AlN-SiCw composites are promising candidates for heat dissipation ceramic substrates, which offer superior mechanical strength and reliable thermal management.

Cathode-supported SOFCs enabling redox cycling and coking recovery in hydrocarbon fuel utilization

Although cathode-supported solid oxide fuel cells (SOFCs), characterized by significantly thinner anode layers than anode-supported SOFCs, are known to have unique advantages in ensuring stability and reliability against redox operating conditions and carbon deposition, they have received relatively less attention due to their lower performance. Furthermore, there is a lack of in-depth theoretical and experimental studies on their outstanding redox cycle characteristics than the anode-supported cells. Here, applying a sintering aid to the electrolyte considerably reduces the sintering temperature of the electrolyte, with the shrinkage and microstructure of the cathode effectively controlled to lower the diffusion resistance. Consequently, the operating temperature was lowered by more than 100 °C compared to previously reported cathode-supported SOFCs; moreover, at 650 °C, a maximum power density more than twice that reported in previous reports. The redox stability of the cathode-supported cells was demonstrated experimentally and theoretically through a redox cycling test and a 3-D finite element method-based SOFC structure model. Moreover, the outstanding redox cycle property of cathode-supported cells has been experimentally demonstrated for the first time to have the potential to mitigate carbon deposition that occurs when utilizing methane fuel. Hence, this study presents new insights for achieving stable and reliable SOFC operation.

High‐entropy ceramics with excellent energy storage performance via screening sintering aids

High‐entropy ceramics with excellent energy storage performance via screening sintering aids

Vat photopolymerization of complex-shaped silicon nitride ceramics with high mechanical and thermal performance by optimization sintering aids and kinetics

In this study, the impact of sintering aid content and sintering time on the density, phase composition, microstructure, thermal conductivity, and mechanical properties of silicon nitride (Si3N4) ceramics through vat photopolymerization (VPP) was systematically investigated. The results revealed that an increase in sintering aid amount promoted the network distribution of the grain boundary phase along with densification, grain coarsening and microstructure uniformity. The extension of sintering time improved density, thermal conductivity, and mechanical properties of the material. Superior performance with density of 99.4%, thermal conductivity of 64.4W·m-1·K-1, flexural strength of 879 ± 37MPa, and hardness of 15.0 ± 0.4GPa was achieved in sample containing 8wt.% MgO/Y2O3 sintered for 12h. Finally, high-precision Si3N4 ceramic heat sink elements were successfully fabricated via VPP, opening up new prospects in thermal management applications associated with electronics and automotive industries.

Influence of Ti3AlC2 additions on CMAS corrosion resistance of porous LaMgAl11O19 abradables

The corrosion of calcium-magnesium-aluminosilicate (CMAS) is a critical degradation mechanism for the hot sections of aircraft engines, particularly affecting abradable components where inherent defects complicate the prevention of rapid CMAS melt penetration. To address this challenge, Ti3AlC2 was incorporated into the porous LaMgAl11O19 abradables at concentrations of 5–20 wt% as both a self-healing agent and sintering aid. Annealing at 1200 °C markedly improved crack closure and pore isolation within the coating, with these effects intensifying with higher Ti3AlC2 concentrations, and resulted in the retention of excess TiO2. CMAS interaction tests conducted at 1300 °C demonstrated that only the abradables with 20 wt% Ti3AlC2 addition significantly reduced the penetration of CMAS melt. This effect is attributed to the densification of the abradables caused by self-healing, which blocks the propagation of CMAS along defect channels, and the role of TiO2 as a nucleating agent that facilitates the crystallization of CMAS and the precipitation of CaAl2Si2O8. The La/Ca ratio in the solid solutions related to LaMgAl11O19 and LaTi2Al9O19 can be used to reflect the corrosion level of platelet-like grains, where a value below 1 is likely to trigger their dissolution.

Flash sintering of AlN ceramics with Y2O3 additive

This study demonstrates the fabrication of dense AlN-based ceramics through the flash sintering technique for the first time. Flash sintering was performed at a furnace temperature of 1500 °C with 10 wt% Y2O3 as a sintering aid in a nitrogen atmosphere. The effects of the current density and holding time on the microstructure evolution and mechanical properties were investigated. The results show that the relative density, grain size and Vickers hardness of specimens increase with increasing current density and holding time. The specimen showed the highest relative density of 98.6% and a Vickers hardness of 12.68 GPa when a current density of 100 mA/mm2 and a holding time of 60 min were used. Additionally, the grain sizes at the positive side of the electrodes were found to be larger than those at the negative side. These findings suggest that dense AlN-based ceramics can be fabricated in a rapid and efficient way through the flash sintering technique.

Effect of ZrSiO4 as additive on the mechanical properties of DLP printing porous mullite ceramics

In order to satisfy the demand for mullite porous ceramics with complex geometries in the engineering field, the digital light processing (DLP) technology is employed to prepare mullite porous ceramics in this study. However, the poor mechanical properties of the mullite porous ceramics prepared using the DLP technology limits its further application in engineering field. In this work, the microstructure of mullite crystals was regulated by adding the sintering aid ZrSiO4 to enhance the mechanical properties of the mullite ceramics, and the effects of sintering aid ZrSiO4 content and sintering temperature on the internal microstructure evolutions of mullite porous ceramics were investigated. Results showed that the decomposition of ZrSiO4 promoted the generation of the silica-rich liquid phase at high temperatures, which effectively promoted the nucleation and growth of needle-like mullite crystals. When the sintering temperature was 1600 °C and the ZrSiO4 content was 10 wt%, the well-developed elongated crystals formed an interlocking nonwoven structure. The corresponding mullite porous ceramics exhibited a compressive strength of 2.52 MPa and a porosity of 74.51%. The strategy of this study can be a feasible route for preparing lightweight and high-strength mullite porous ceramics via digital light processing.

Enhancing oxidation resistance of silicon nitride using a Ca2+ stabilizer

Silicon nitrides are widely used in ceramic heaters for combustion engines due to their high strength and wear resistance. However, their poor oxidation resistance at elevated temperatures limits their reliability. Oxidation products, such as silica and intermediate compounds from sintering additives, often suffer from microcracks due to phase transformation and volume expansion mismatch during thermo-mechanical cycles. Use of cation dopants to chemically stabilize the transformation of the oxidation front is proposed. This study investigated the effect of Ca2+ treatment on Si3N4 with MgO and Y2O3 sintering aids. The Si3N4 samples were coated with CaO and the phase composition, microstructure, and chemical distribution of the oxidation products were analyzed using XRD, SEM, TEM, STEM, and EDS. The oxidation coupon tests revealed that the CaO coating effectively protected Si3N4 from oxidation at 1300 ºC for 40h. Moreover, the microstructure analysis showed that CaO coating created more favorable microstructures which reduced oxidation reactions.

Low sintering temperature, interface characteristic and microwave/terahertz dielectric properties of ternary-phase Nd2O3-P2O5 based ceramics for patch antenna application

In this work, LiF was chosen as a sintering aid to lower the sintering temperature required for monoclinic NdPO4 (NPO) ceramic. A comprehensive investigation was conducted to analyze the impact of LiF on the sintering characteristics, microstructures, phase compositions, crystalline structures, interface characteristics, and microwave dielectric properties of NPO ceramic. Structure-property relationships were discussed based on the density, crystallite size, and lattice strain. The complex impedance spectroscopy revealed the mechanism underlying the interface characteristics of LiF on NPO ceramic. Additionally, far-infrared reflectance spectra and THz time-domain spectra revealed the intrinsic dielectric properties of NdPO4–1 wt.%LiF (NPO1). Notably, 1 wt.% LiF effectively reduced the sintering temperature from 1300 °C to 850 °C, significantly improving densification and dielectric properties. Typical properties such as Q × f = 55,840 GHz (at 9.58 GHz), εr = 10.4, and τf = −43.1 ppm °C−1 were obtained for NPO1 ceramic after sintering at 850 °C. Furthermore, its compatibility with Ag was explored as a prerequisite for LTCC applications. Finally, the NPO1 ceramic was designed as a microstrip antenna with high gain (6.83 dB) and low return loss (−18.85 dB) at a centre frequency of 2.56 GHz, demonstrating its potential for Wi-Fi and Bluetooth applications. This work provides a theoretical foundation and practical guidance for developing orthophosphate ceramics.

Wettability and infiltration of Si drop on Si3N4 ceramic containing BaSiO3 as sintering aid

As container for the photovoltaic (PV) Si growth, fused silica crucible can only be used once owing to crystallization breakage, which inevitably reduces the quality and yield of Si. To develop re-useable crucible, Si3N4 ceramics were successfully fabricated using novel BaSiO3 (0-8 wt%) as sintering aid. Higher BaSiO3 content promotes the densification and sintering of Si3N4 ceramic. Then, the wetting/infiltration behaviors of Si/Si3N4 binary systems were systematically investigated by sessile drop test and microstructural analysis technology. With 8 wt% BaSiO3 introduction, the Si3N4 ceramic displayed larger contact angle of Si drop and excellent Si infiltration resistance, which was determined by de-oxidation rate. Moreover, three type of infiltrations, including infiltrations under Si drop and beyond Si drop (on/under substrate surface), were found and systematically analyzed. In this work, novel sintering aid (BaSiO3) was developed for Si3N4 ceramic fabrication at relatively lower sintering temperature. Additionally, the data of wetting/infiltration behavior for Si/Si3N4 binary system can be used to guide the application of Si3N4 crucible in PV Si manufacture.

Synergistic effects of ZrO2 and La2O3 on the phase stability and optical–electronic properties of Y2O3

AbstractYttrium oxide has the potential to be used as a host material for creating polycrystalline transparent ceramics (PTCs). This paper presents an experimental study on opto‐electrical properties of using zirconium oxide and lanthanum oxide as sintering aids via the co‐precipitation technique. The sintering aids improve the properties, sintering process, and lower the sintering temperature. Five different compositions of were synthesized and they were then used to analyze for their structural, morphological, physio‐chemical, and electrical characteristics. For the system studied, the addition of and does not change the phase of pure , but an increase in the crystal and grain size from to and 10.2 µm to 16.4 µm was noticed. The thermal characterization over thermogravimetric analysis/differential thermal calorimetry (TGA/DSC) determines the temperature at which pure undergoes a phase transition, specifically over 700°C. A reduction in the band gap due to strain induced by the dopant resulted in a decrease in energy from to . The dielectric constant of doped with exhibits a significant increase of .

Effects of ZnO additive on the electrical and densification properties of A-site deficient barium cerate perovskite

The dual strategies of A-site deficiency and addition of ZnO sintering aid have been employed to optimise stability and densify the high-temperature proton conductor Ba0.95Ce0.8Y0.2O3-δ at 1200 °C (B95CYZn-1200). Structural analysis performed by Rietveld refinement based on X-ray diffraction data indicated perovskite phase with monoclinic symmetry (space group, I2/m). Raman spectroscopy revealed the presence of ZnO for material sintered at 1200 °C, which most likely partially resides in grain-boundary regions, leading to enhanced electrical transport observed by impedance spectroscopy at low temperature. Anomalous and reproducible frequency-dependent impedance behaviour below 500 °C, observed in various atmospheres, is suggested to be attributable to the varistor-type properties of ZnO. The electrical conductivity of B95CYZn-1200 in the range 500–900 °C is typical of perovskite proton conductors but with greater conductivity than both Ba-stoichiometric BaCe0.8Y0.2O3-δ and ZnO-free Ba0.95Ce0.8Y0.2O3-δ in wet O2 and N2, reaching ∼ 1.1 S m−1 at 550 °C in wet O2. Resistance to carbonate formation and mechanical breakdown was demonstrated via prolonged impedance measurements in CO2- and H2-containing atmospheres in the range 600–700 °C.

Influence of germanium concentration on the microstructure and optical transparency of terbium gallium garnet ceramics

AbstractIn recent years, transparent terbium gallium garnet (TGG) ceramics have garnered significant interest for their application in high‐power Faraday isolators. However, challenges in achieving high transparency have led researchers to explore the addition of various sintering aids as a key strategy to enhance the optical quality of TGG ceramics. Through this work, the effect of germanium (Ge) addition on the microstructure and optical transparency of TGG magneto‐optical ceramics was investigated. TGG powders were synthesized by the co‐precipitation method, and the source Ge was Ge ethoxide added through a ball‐milling step. Transparent TGG ceramics were prepared by air pre‐sintering combined with hot isostatic pressing post‐treatment and subsequent annealing. The ceramics containing 200 ppm Ge exhibit optimal transmittance of 81.3% at 1064 nm (a value of theoretical transmittance), the Verdet constant was −133.0 rad·T−1·m−1 at 633 nm. When the addition of Ge reaches 600 ppm, a secondary phase can be observed on the surface of ceramic. Subsequently, TGG ceramics prepared from 1425°C to 1500°C with 200 ppm of Ge were analyzed, which revealed that the optimal pre‐sintering temperature is 1450°C.

Mechanical Properties of Silicon Nitride in Different Morphologies: In Situ Experimental Analysis of Bulk and Whisker Structures.

Silicon nitride (Si3N4) is widely used in structural ceramics and advanced manufacturing due to its excellent mechanical properties and high-temperature stability. These applications always involve deformation under mechanical loads, necessitating a thorough understanding of their mechanical behavior and performance under load. However, the mechanical properties of Si3N4, particularly at the micro- and nanoscale, are not well understood. This study systematically investigated the mechanical properties of bulk Si3N4 and Si3N4 whiskers using in situ SEM indentation and uniaxial tensile strategies. First, nanoindentation tests on bulk Si3N4 at different contact depths ranging from 125 to 450 nm showed significant indentation size effect on modulus and hardness, presumably attributed to the strain gradient plasticity theory. Subsequently, in situ uniaxial tensile tests were performed on Si3N4 whiskers synthesized with two different sintering aids, MgSiN2 and Y2O3. The results indicated that whiskers sintered with Y2O3 exhibited higher modulus and strength compared to those sintered with MgSiN2. This work provides a deeper understanding of the mechanical behavior of Si3N4 at the micro- and nanoscale and offers guidance for the design of high-performance Si3N4 ceramic whiskers.

Effects of Bi2O3–CuO addition on the dielectric properties of MgO–TiO2(w) ceramics sintered at low temperatures

Herein, MgO–12 % TiO2(w) ceramics with different contents of Bi2O3–CuO sintering aid were prepared using a solid-state method. The effects of the sintering aid content on the sintering temperature and the dielectric and mechanical properties of the ceramics were studied. The material was characterized using scanning electron microscopy and X-ray diffraction and Precision LCR tester and universal testing machine and Archimedes drainage method. When the Bi2O3–CuO content was less than 9 wt%, the ceramic sample has higher dielectric properties. When the Bi2O3–CuO content was greater than 9 wt%, the dielectric properties will deteriorate. This is because Bi2O3 participates in the chemical reaction between MgO and TiO2, forming a high dielectric loss Bi4Ti3O7 phase. At high temperatures, Cu2+ can easily change valence to Cu+, promoting oxygen vacancies and increasing dielectric loss in ceramic samples. The introduction of Bi2O3–CuO produces new MgTiO3, Mg2TiO4, and Bi4Ti3O12 phases in the sample structure, resulting in a structure in which the MgO grains in the sample are surrounded by the new phases that appear around them. This structure fills the pores, increases density, enhances mechanical properties. The dielectric properties of the ceramics were the when the sintering temperature was 1050 °C, and the Bi2O3–CuO content was 3 wt%. The dielectric constant and dielectric loss were 11.19 and 1.17 × 10−4, respectively. The bending strength of the ceramic sample increased from 138.72 MPa to 179.64 MPa when the Bi2O3–CuO content was increased from 3 wt% to 15 wt%. The Bi2O3–CuO sintering aid enables MgO to be better applied in ceramic substrates.

Effect of Y2O3 on thermophysical parameters and mechanical properties of Al-Al2O3 composites and compatibility with high temperature Al-Si alloys

Abstract Al-Al2O3 is a crucial encapsulation composite used in solar thermal storage systems. This study utilized Al and Al2O3 powders as raw materials, with Y2O3 serving as a sintering aid, to prepare Al-20Al2O3-xY2O3 composites (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) through the cold pressure sintering method. The latent heat, thermal conductivity, and bending strength of the Al-20Al2O3-xY2O3 composites were measured. The compatibility of the composites with Al-12 wt%Si alloys was analyzed. Furthermore, the relationships between thermophysical parameters, mechanical properties, compatibility, and microstructure were explored. The oxidation mechanism of Al and the wetting angle of the composites with Al-12Si were simulated using LAMMPS software. It was concluded that with an increase in Y2O3 content, the bending strength, thermal conductivity, and compatibility of the composites initially increased and then decreased. The Al-20Al2O3-0.2Y2O3 composite exhibited the least porosity, highest bending strength (76.32 MPa), and thermal conductivity (46.82 W/(m·K)). In compatibility testing, the diffusion distance of Si atoms was shortest (90 μm) in the Al-20Al2O3-0.2Y2O3 composite. Moreover, this composite had the largest wetting angle (88°) with the Al-12Si alloy, resulting in good compatibility between them.