High-temperature Sintering Process Research Articles

Polarization loss in rutile TiO2 doped with acceptor ions for microwave absorption

With an increase in electromagnetic (EM) pollution, inducing polarization loss using lattice defects has become one of the main strategies for the design and optimization of a new generation of microwave absorbers. In this study, point defects in TiO2 absorbers are designed and controlled using a sol–gel method. The influences of the electronegativity difference and the ionic valence states of the dopant ions on the microwave absorption (MA) performance of rutile TiO2 composites are investigated. The results show that the defects such as oxygen vacancy (VO∙∙) and Ti3+ can be adjusted continuously at a high-temperature sintering process. Cu2+, which has a larger electronegativity than Ti4+ (Cu2+χ = 1.90 > Ti4+χ = 1.54) promotes the localization of electrons. Furthermore, compared with Ag+, which has a similar electronegativity (Ag+χ = 1.93 ≈ Cu2+χ = 1.90), polyvalent copper ions (Cu2++e→Cu+) enhance the electron-hopping process. The formed electron-pinning defect dipole clusters (TiTi′, VO∙∙, CuTi″, CuTi″′, Ti3+→VO∙∙←Ti3+, Ti3+→VO∙∙←Cu2++e, Cu2++e→Cu+, Ti4++e→Ti3+) produce a stronger polarization relaxation process, which regulates the MA performance of TiO2 absorbers. Therefore, this study provides an essential reference for refining the EM wave attenuation performance of simple oxide absorbers.

Effect of cell sintering temperature on the performance of non-noble metal loaded cerium oxide SOEC anodes

Abstract Introducing methane oxidation reaction into the anode of the high-temperature solid oxide electrolysis cell (SOEC) can reduce the power consumption for water electrolysis. Compared to the traditional conditions of methane oxidation, the methane oxidation catalyst sintered at the SOEC anode, which is closely related to the cell sintering process. This study uses non-noble metals as active sites for methane oxidation, zirconia, and samarium oxides doped ceria as catalyst support and oxygen ion conductors. The effects of anode sintering temperature on the electrochemical performance of SOEC assisted by methane oxidation were investigated. The results indicate that the high-temperature sintering process promotes the performance of the SOEC anode with Ni as the active site, while high temperature harms the performance of the Co-loaded anode. The sintering temperature exhibits a poor effect on the Fe-loaded anode. The Ni exhibits good enhancement of methane oxidation on reducing the electrolysis voltage of SOEC, while Co only exhibits methane oxidation assistance at low-temperature sintering. Differently, Fe has almost no obvious methane oxidation assistance for SOEC, which mainly represents good oxygen evolution performance.

Breakthrough in atmospheric plasma spraying of high-density composite electrolytes: Deposition behavior and performance of plasma-sprayed GDC-LSGM on porous metal-supported solid oxide fuel cells

The potential application of plasma spraying in the preparation of ceramic electrolyte for porous metal-supported solid oxide fuel cells (SOFCs) is highlighted by its ability to eliminate the need for a high-temperature sintering process. However, the challenge of achieving highly dense electrolytes through plasma spraying remains to be addressed. In this study, a novel electrolyte for porous metal-supported SOFCs (PMS-SOFCs) is developed. This involved the preparation of a highly dense structure of gadolinium-doped ceria (GDC)-lanthanum strontium gallium magnesium oxide (LSGM) composite coating using plasma spraying under atmospheric conditions. The composite electrolyte is prepared using atmospheric plasma spraying (APS). The addition of the low-melting-point LSGM phase enhanced the microstructural densification of the GDC-based composite coating and diminished electron loss in a reducing atmosphere, thereby improving the cell's open-circuit voltage. At 36 kW plasma arc power, the single cell with composite electrolyte exhibited a maximum power density of 371 mw/cm2 at 750 °C and achieved the highest open-circuit voltage (1.03 V) at 600 °C. Moreover, the open-circuit voltage remained stable over a 100-h test. These findings suggest that using APS to deposit a composite electrolyte with added low-melting-point secondary phases presents a promising approach for achieving relatively high OCV in PMS-SOFCs based on cerium oxide electrolytes.

Gradient fluorination engineering through interdiffusion reaction for high-voltage LiCoO2

The advancement of high charging cut-off voltage stands as a crucial avenue to enhance the energy density of LiCoO2 (LCO). However, LCO faces severe interface and bulk phase issues at high voltage (≥ 4.6 V), resulting in poor cycling stability. In this study, we reconstruct the surface structure of LCO based on the interdiffusion reaction between LCO and MgF2 in a high-temperature sintering process. Specifically, this interdiffusion reaction yields an ultra-thin LiF coating layer, artificially reinforcing the chemical structure of the cathode-electrolyte interphase (CEI) during cycling. This LiF-rich CEI not only effectively protects the surface structure of LCO, but also facilitates the lithium-ion diffusion. Furthermore, the diffusion of F and Mg into the LCO lattice significantly strengthens the structure, which inhibits unfavorable phase transitions from the O3 phase to the H1–3 phase at high voltage. Consequently, such modified LCO with concurrently enhanced interface and bulk structure exhibits outstanding long-term cycling performance within 3.0–4.6 V at 1 C, achieving a capacity retention of 84.9 % after 1000 cycles. Meanwhile, it also demonstrates excellent high-temperature performance, with a capacity retention of 85.0 % after 200 cycles under 45 °C.

Microstructure and mechanical properties of high-pressure sintered B6O-SiC nanocomposites

Boron suboxide (B6O) is recognized as a superhard material with a low mass density, high resistance to chemical wear, and excellent wear resistance. Despite its desirable properties, the limited fracture toughness of B6O restricts its application in industrial contexts. This study presents the structural and mechanical characterization of B6O-SiC nanocomposites, which were synthesized via a high-pressure high-temperature sintering process of B6O powders and SiC whiskers. The sintering process induced fragmentation of SiC whiskers, resulting in the homogenous distribution of SiC fragments within the B6O matrix. An increase in SiC content was observed to decrease the composite's hardness, while initially reducing then enhancing its toughness. The nanocomposites containing 20 wt% and 30 wt% SiC whiskers exhibited significant improvements in fracture toughness, averaging 6.5 MPa m1/2 and 7.0 MPa m1/2, respectively—approximately threefold the toughness of polycrystalline B6O—while sustaining high hardness values of 36.3 GPa and 35.6 GPa on average. Microstructural analyses revealed that the composites’ superior mechanical performance is due to the presence of strong grain boundaries, as well as a high density of nanotwins and stacking faults. The findings demonstrate a viable method for producing B6O-based nanocomposites with enhanced hardness and toughness, potentially expanding their industrial applicability.

Unraveling the conundrum of electronic leakage in protonic ceramic cells: Operation-specific insights and rational design strategies

Electronic conduction through proton-conducting electrolytes significantly impairs the efficiency of protonic ceramic cells (PCCs). In this study, we explore the electron and ion mixed transport properties of four common protonic ceramics, BaZr0.8Y0.2O3-δ (BZY82), BaZr0.7Ce0.2Y0.1O3-δ (BZCY721), BaZr04Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411), and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb1711). It marks the first instance of investigating these properties under operation-specific scenarios: fuel side of electrolysis cell, air side of electrolysis cell, fuel side of fuel cell, and air side of the fuel cell. BZCYYb1711 exhibits the highest ionic conductivity, but two to three times higher electronic leakage when exposed to oxygen-containing environments than the others. BZY82 exhibits approximately two times higher electronic leakage in a hydrogen-containing environment. BZCY721 demonstrates excellent ion transport numbers (∼0.95) across these four operating conditions. BZCYYb4411 behaves quite similarly to BZCY721. The most challenging operating environment for all candidates is the air side of fuel cell mode. This mode leads to a high initial electronic leakage, followed by a significant increase with polarization. The probable cause for this behavior is a H2-free, polarization-induced reduction that leads to the formation of VO•. The electron small polaron associated with VO• is released by the electrical field due to the Poole-Frenkel effect. ZnO and NiO sintering aids are found to be detrimental to the ionic conductivity of the electrolytes. In particular, NiO substantially lowers the ion transport number. The correlation of the operation-specific electronic leakage to full cells is discussed. It is suggested that a rational PCC design should synergistically couple BZCYYb1711 at fuel side with BZCY4411 at air side to deliver a well-balanced performance and faradaic efficiency simultaneously, and the high temperature sintering process with a NiO fuel electrode should be shortened or replaced by ultra-fast sintering techniques or using a fuel electrode scaffold-infiltration fabrication strategy.

Preparation and electrochemical properties of a ceramic solid electrolyte with high ionic conductivity, Li1.3Al0.3Ti1.7(PO4)3

The emergence of lithium-ion solid electrolytes greatly increases the safety risk of liquid electrolytes. Among the many solid electrolytes, aluminum-doped Li1.3Al0.3Ti1.7(PO4)3(LATP) has become a research hotspot due to its high ionic conductivity and good air stability. However, the traditional high-temperature sintering process has the problems of lithium volatilization and secondary phase formation. Therefore, it is very difficult to prepare high-quality LATP solid electrolytes. The X-ray diffraction pattern and analysis showed that the LATP samples prepared in this paper showed rhombohedral structure and could be indexed by the R3c space group, and a new method of excess lithium compensation sintering was proposed, in which lithium compensation (LiNO3) could well reduce the impact of lithium volatilization. It can be used as a sintering additive to promote the sintering densification of LATP. In this paper, the optimal sample for sintering at 900°C was determined by measuring the microstructure and electrochemical properties of the electrolyte, and lithium doping was studied. The LATP solid electrolyte with 10 wt% lithium doped has a conductivity of 7.2× 10−4 S/cm and a low activation energy (0.278 eV). Its mechanical properties (elastic modulus and hardness) are the best, which are 103.024 GPa and 8.053 GPa, respectively, and the value of its elastic modulus is much greater than that of lithium metal shear modulus of 4.25 GPa, which can effectively inhibit the growth of lithium dendrites. And the magnitude of the grain boundary conductivity and particle size of the lithium-doped sample correspond to the dielectric constant results.

Investigation of the Effect of High-Frequency Induction Sintering on Phase Structure and Microstructure of SiC Reinforced Aluminum Matrix Composites

In this study, SiC-reinforced aluminum matrix composites were powder metallurgically (PM) prepared and sintered using high-frequency induction system (HFIS). The samples with different ratios of SiC (wt.%10, 20 and 40) added to the aluminum matrix were sintered at 660, 800, and 1000 °C. In addition, Al/SiC composites were compared by sintering with the conventional sintering (CS) method under similar sintering conditions. The heating rate for the sintering process using HFIS was 500 °C/min, while the CS method used a heating rate of 10 °C/min. The effect of the temperature and SiC ratio on the density, hardness, phase structure, and microstructure of composites was investigated. The optimum sintering temperature was determined according to the SiC additive amount. When 10%, 20%, and 40% SiC by weight were added to the aluminum matrix in the sintering process with HFIS, the required sintering temperatures were determined as 660, 800, and 1000 °C, respectively. While new phases were not formed as a result of short-term HFIS sintering, a high-temperature Al4C3 phase was detected in CS sintering. HFIS sintered Al/SiC composite samples were obtained in Al and SiC phases with high density and hardness ranging from 43-118 HV. In the high-temperature sintering process with HFIS, the formation of Al4C3 was prevented and its physical and mechanical properties were improved.

Synthesis of rGO-reinforced MgAl2O4 spinel composites by solid-state powder route mechanism: A comparative analysis between non-reinforced and rGO-reinforced spinel composites

Reduced Graphene Oxide (rGO)-reinforced MgAl2O4 spinel composite was successfully synthesized by a solid-state powder route mechanism via high-energy planetary ball milling of corresponding metal oxide precursors followed by a high-temperature single-stage sintering process. The effect of rGO on the homogeneity, phase development, morphology, chemical composition, rate of formation of spinel, and cation anti-site formation of the composites was methodically investigated. For comparison, a stoichiometric non-reinforced MgAl2O4 spinel was also synthesized. The addition of 0.2 wt% and 0.4 wt% of rGO as reinforcement increased the homogeneity of the ball-milled composite powder, with Polydispersity Index (PDI) values of 0.19 and 0.15 respectively, as compared to 0.24 obtained in non-reinforced spinel composite. The X-ray diffraction pattern and IR spectrum of 1650 °C sintered composites confirmed the formation of highly crystalline phases with spinel structure. The microstructural analysis revealed that the addition of rGO led to a reduction in porosity and improved the process of sintering. Calorimetric studies showed that spinelization started to occur at 858 °C and 880 °C for 0.2 wt% and 0.4 wt% rGO-reinforced composites respectively, which was faster than non-reinforced composite. 27Al solid-sate nuclear magnetic resonance (SS-NMR) analysis depicted that ceramic composite reinforced with rGO exhibited lesser inversion parameter of 0.09 (for 0.2 wt% rGO) and 0.055 (for 0.4 wt% rGO), as compared to 0.145 obtained in non-reinforced composite, indicating lesser cation anti-sites formation in rGO-reinforced spinel composite.

Improved Performance of QDSSCs Can Be Achieved by Constructing a Transparent Anatase TiO2@MWCNT Photoanode Based on the Bionic Mountain Lotus.

In this research, the structural characteristics of the mountain holly leaf were emulated. It was observed that after the initially uneven surface of the petals is filled with infiltrated water, it exhibits a distinctive transparent beauty after rainfall. Furthermore, the presence of leaf veins enhances the structural strength of the petals and facilitates nutrient transport. Inspired by previous studies on double-layer spin-coated films, we further developed and designed the TA TiO2@MWCNT photocathode thin film. This innovative film incorporates multiwalled carbon nanotubes (MWCNT) into a previously established TA TiO2 photocathode thin film. The inclusion of MWCNT results in the formation of a three-dimensional highway structure, where MWCNT intertwines within the TA TiO2 film. Under the operational state of immersion in the electrolyte, it maintains a level of transparency similar to that of the TA TiO2 photoanode thin film. The high-temperature sintering process results in the oxidation and depletion of MWCNTs on the surface of the film, leaving behind uniformly dispersed concave defects, thereby greatly enhancing the specific surface area. The findings demonstrate that the optoelectrode of high transparency and high specific surface area, TA TiO2@MWCNT, comprehensively enhances the performance of the solar cells. The transparent QDSSC surpasses its counterparts for the first time, achieving a power conversion efficiency (PCE) of 6.335%. This sets the stage for new materials and innovative approaches in the field of solar cells and other titanium dioxide film-related areas.

Heterogeneous diamond–TiC composites with high fracture toughness and electrical conductivity

The concurrent enhancement of toughness, electrical conductivity, and thermal stability in polycrystalline diamond composites represents a formidable challenge. Here, a novel diamond-TiC composites (referred to as DTC) with high fracture toughness and conductivity were synthesized through a high-temperature and high-pressure reaction sintering process utilizing two precursors: diamond mixtures containing TiH2 and Ti-coated diamonds. On the one hand, the inherent bonding and encasing of TiC onto the diamond matrix form a heterogeneous structure, providing high strength and excellent fracture toughness up to 11.6 MPa·m1/2. On the other hand, the established oxygen barrier and current pathway offer a thermal stability of 765 °C and high conductivity up to 837 S·m−1. Remarkably, this rare combination of mechanical, electrical, and thermal properties has been realized within a single material under relatively moderate sintering conditions, thus positioning diamond-TiC composites as a promising ceramic for electrical applications in high-stress environments.

High-performance, stable buffer-layer-free La0.9Sr0.1Ga0.8Mg0.2O3 electrolyte-supported solid oxide cell with a nanostructured nickel-based hydrogen electrode

La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) with an extraordinary oxygen-ion conductivity has been extensively studied as an electrolyte material for intermediate temperature solid oxide cells (SOCs). However, the conventional high-temperature sintering process of electrodes results in detrimental reaction between LSGM and Ni-based hydrogen electrode and microstructural coarsening of the electrode. Herein, a buffer-layer-free LSGM electrolyte-supported single cell with a nanostructured Ni-Gd0.1Ce0.9O1.95 (GDC) electrode is developed using a sintering-free fabrication approach. The cell exhibits a peak power density of 1.23 W cm−2 at 800 °C and an electrolysis current density of 1.85 A cm−2 at 1.5 V with excellent operating stability. The good performance and durability is owing to the synergistic effects of the elimination of elemental interdiffusion at the electrode/electrolyte interface, polarization induced in situ formation of hetero-interfaces between Ni-GDC and LSGM, and remarkable structural stability of Ni-GDC. This study provides an innovative means for the development of efficient and durable buffer-layer-free LSGM-supported SOCs.

Facile Route to Synthesize a Highly Sinterable Li1.3Al0.3Ti1.7(PO4)3 Solid Electrolyte.

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a widely used solid electrolyte in solid-state lithium batteries, owing to its excellent chemical stability against moisture and high total ionic conductivity. However, traditionally, densification of LATP has been achieved through a high-temperature sintering process (approximately 1000 °C) owing to its poor sinterability. Herein, we report a facile synthesis route to obtain highly sinterable LATP solid electrolyte using tetrabutyl titanate (C16H36O4Ti) as the titanium source and incorporating the traditional solid-state reaction method. The synthetic LATP powder mixed with a low ratio of LiTiPO5 exhibited a hybrid crystalline-amorphous phase structure, which facilitated grain fusion, promoted structural homogeneity, and facilitated structural densification under low-temperature sintering. The sintered LATP pellet, which exhibited an interconnected structure and indistinct grain boundaries, achieved a relative density of >90% and an ionic conductivity of 0.667 mS/cm at a sintering temperature of only 750 °C. Additionally, we systematically studied and demonstrated the synthesis reaction mechanism, sintering behavior, and ionic diffusion kinetics of LATP electrolytes. Our study paves the way for synthesizing highly sinterable LATP solid electrolytes using a simple, additive-free, and cost-effective method.

Cold sintering process for densification of Fe3O4 ceramic magnets with improved properties

Iron oxide-based ferrite ceramics, widely applied in high-frequency applications, are conventionally produced through high-temperature sintering processes, often resulting in grain growth and phase transformation. In this study, we used a cold sintering process (CSP) with oxalic acid (OA) as a solvent to consolidate iron oxide (Fe3O4) ceramics at a low temperature of 160 °C. The OA-assisted CSP technique has demonstrated a remarkable capacity to facilitate the dissolution and redeposition of iron oxide ions, leading to the interconnection of Fe3O4 particles, forming densely packed ceramics even at low-temperature sintering. Importantly, CSP maintained particle sizes and hindered phase transitions of Fe3O4. The OA concentrations in CSP had a minimal impact on crystal structure and magnetic properties, but it significantly enhanced microstructural features, density, hardness, and electrical resistance. Compared to reference samples prepared without an aqueous solution or with water alone, the CSP-prepared Fe3O4 ceramics with OA exhibited substantially improved density (a relative density of ∼80 %), mechanical properties (Vickers hardness of 3.5–4.0 GPa), magnetic properties (saturation magnetization >70 emu/g), and electrical resistance (electrical conductivity ∼10−3 S/cm at 102–106 Hz). These findings demonstrate a novel approach to fabricating Fe3O4 ceramics at significantly lower temperatures while still achieving properties comparable to those sintered at high temperatures.

Comparison between Lithium Substitution and Doping on the Physical and Piezoelectric Properties of Lead-Free BCZT Ceramics

Defects generation in ceramics by element substitution or doping may improve their properties. However, different results will be obtained even though the same element is involved due to different mechanisms. Ceramics Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) is one of the potential candidates to replace lead-based material PZT. However, the conventional method requires high-temperature calcination and sintering process to synthesize this material. Thus, Lithium (Li) can act as the sintering aid to lower the temperature at the same time, the properties of piezoelectric can be enhanced. In this paper, the structural, physical, and piezoelectric performance of lead-free Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) ceramics with Lithium Li substitution and doping, synthesized by the solid-state reaction method were studied. The substitution of Li increases the density, ρ and piezoelectric coefficient, d33 of BCZT which are 4.075 g/cm3 and 304.6 pC/N, respectively. These results demonstrate that Li substitution is more beneficial to the piezoelectric properties than doping because it produces higher grain boundary resistance and activation energy and has lower conductivity than doping. This can provide a definite strategy during the chemical composition design and manufacture of BCZT ceramics.

Mechanical properties of a novel tungsten fiber-reinforced tungsten composite prepared through powder extrusion printing and high-pressure high-temperature sintering

Tungsten is one of the most promising candidate materials for plasma-facing materials (PFM) because of its high melting point, superior thermal conductivity, and low sputtering rate. However, its significant brittleness and high ductile-to-brittle transition temperature constrain its broader engineering applications. To address these limitations, we developed a novel tungsten fiber-reinforced tungsten (Wf//W) composite. This composite utilizes commercially available black tungsten wire mesh as the fiber reinforcement phase with a mass ratio of 1 %. The material was synthesized through a combined Powder Extrusion Printing and High-Pressure, High-Temperature sintering process, achieving a relative density exceeding 99 %. Additionally, the composite exhibits a maximum hardness of 589 ± 10 HV, attributable to the presence of high-density dislocations in the matrix. Its compressive strength reaches up to 1530 MPa, and the plastic deformation strain is as high as 15.8 %, both of which are outstanding compared to existing research. These findings offer an alternative route for producing high-density Wf//W materials, in addition to chemical vapor deposition method and powder metallurgy technique.

Structure, thermal and mechanical properties of mid-entropy thermal barrier ceramic (Y0.3Gd0.3Yb0.4)4Hf3O12 prepared by ultrafast high-temperature sintering

Thermal barrier coatings (TBCs) have an important role to play in the development of aero engines. In this paper, mid-entropy rare-earth hafnate (Y0.3Gd0.3Yb0.4)4Hf3O12(YGYbH) ceramic material was designed based on rRE3+/rHf4+ and was successfully fabricated in only 7 min using an ultrafast high-temperature sintering (UHS) process. The YGYbH ceramic bulk exhibits a single homogeneous fluorite structure and excellent high temperature phase stability, which can remain phase constant for 80 h at 1500 °C due to its unique cation radius ratio and high-entropy effect. YGYbH possesses sluggish grain growth characteristics and great anti-sintering properties, and when annealing at 1500 °C for 30 h, its grain size only grows from the initial 1.19 μm–1.61 μm, which is conducive to stabilizing the mechanical properties of YGYbH at higher service temperature. YGYbH has a low thermal conductivity of 0.89 W/(m·k) at 1100 °C, which is much lower than that of 6%–8%Y2O3 partially stabilized ZrO2(YSZ) (∼2.5 W/(m·k)), while having a high coefficient of thermal expansion (CTE), from 8.8 × 10−6/K at room temperature to 11.0 × 10−6/K at 1500 °C which is nearly to that of the YSZ. Furthermore, YGYbH has a high hardness (11.94 GPa) and a low elastic modulus (147.4 GPa), but a slightly lower fracture toughness (1.26 MPa m½) than that of 8YSZ, exhibiting great overall mechanical properties. Based on the results of this work, YGYbH with excellent overall performance exhibits great potential as the next-generation TBC material.

Enabling long-term oxide based solid-state lithium metal battery through a near room-temperature sintering process

The huge Li ion transport resistance through the grain boundaries (GBs) among rigid oxide particles forces the adoption of high-temperature sintering (HTS) process over 1000 °C. Nevertheless, the severe side reactions and uncontrollable lithium loss are always companied during the high-cost HTS process, which slows down the pace of oxide solid electrolyte (OSE) for practical application and accelerates the exploration of a new OSE sintering process. Herein, a near-room-temperature (60 °C) cold-sintering process is proposed by filling the GBs with a low-melting-point plastic crystal electrolyte (PCE). Due to the soft property and high-ionic conductivity of PCE, the Li ion transport rate through the GBs is 10 times faster than the bulk phase, endowing the OSE (Li1.5Al0.5Ge1.5(PO4)3 chosen as a representative) with a room temperature ionic conductivity of 0.25 mS cm−1. As proof of the concept, the assembled Li symmetrical cells perform a low over-potential of 50 mV with a capacity of 1 mA h cm−2 and full cells delivers a capacity retention of roughly 70% after 820 cycles (1.5 years) at 0.1C.

Preparation of VZrHfNbTa High-Entropy Alloy-Based High-Temperature Oxidation-Resistant Coating and Its Bonding Mechanism.

Ultra-high Temperature Oxidation-Resistant Alloys (UTORAs) have received a lot of attention due to the increased research demand for deep space exploration around the world. However, UTORAs have the disadvantages of easy oxidation and chalking. So, in this study, a UTORAs is prepared by hot-press sintering on VZrHfNbTa (HEA: High Entropy Alloys can generally be defined as more than five elements by the equal atomic ratio or close to the equal atomic ratio alloying, the mixing entropy is higher than the melting entropy of the alloy, generally forming a high entropy solid solution phase of a class of alloys.) a substrate coated with hafnium. The bonding mechanism, resistance to high-temperature oxidation, and hardness of the sample tests are carried out. The results show that zirconium in the matrix will diffuse into the hafnium coating during the high-temperature sintering process and form the HfZr alloy transition layer, the coating thickness of the composite is about 120 μm, and the diffusion distance of zirconium in the hafnium coating is about 60 μm, this transition layer chemically combines the hafnium coating and the HEA substrate into a monolithic alloy composite. The results of high-temperature oxidation experiments show that the oxidation degree of the hafnium-coated VZrHfNbTa composite material is significantly lower than that of the VZrHfNbTa HEA after oxidation in air at 1600 °C for 5 h. The weight gain of the coated sample after oxidation is 56.56 mg/cm2, which is only 57.7% compared to the weight gain of the uncoated sample (98.09 mg/cm2 for uncoated), and the surface of the uncoated HEA shows obvious dents, oxidation, and pulverization occurred on the surface and interior of the sample. In contrast, the coated composite alloy sample mainly undergoes surface oxidation sintering to form a dense HfO2 protective layer, and the internal oxidation of the hafnium-coated VZrHfNbTa composite alloy is significantly lower than that of the uncoated VZrHfNbTa HEA.

A Simple Preparation of Electrolyte Powder for Stoichiometric Electrolyte in Protonic Ceramic Cells

Among various eco-friendly energy conversion technologies, solid oxide cells (SOCs) exhibit superior energy conversion efficiency and performance owing to the kinetic and thermodynamic advantages. Recently, protonic ceramic cells (PCCs) have begun to attract attention with expectation that the operating temperature of SOCs can be lowered around 500oC, thereby achieving better durability with maintaining higher conversion efficiency. However, the promising proton conducting electrolytes in PCCs are mostly Ba-containing perovskites exhibiting highly refractory property, thus substantially have challenges associated with barium volatilization during high-temperature sintering process. At the same time, Ni-containing transient phases generated at the electrode and supplied to the electrolyte during sintering of electrode/electrolyte bilayer not only facilitate the sintering of electrolyte, but also induce the compositional change owing to the residue thereof. Such off-stoichiometry indeed degrades the electrical properties, and thus most of all reported performance of PCCs could not fully reflect the intrinsic property of electrolytes.Here, we describe a simple but effective strategy to realize the highly conductive electrolyte in PCCs via suppression of barium volatilization as well as minimization of supplied amount of transient phases; a low-temperature calcination process. The electrolyte powder calcined at the relatively lower temperature, which is high enough to react all the precursors without residue, but low enough to suppress the Ba volatilization. The PCCs fabricated using this low-temperature calcined electrolyte powder shows the reduced ohmic resistance, and in turn, enhanced electrochemical performance. While the research on PCCs, up to now, have mainly been focused on processing technique or new materials for the better performance, the result of this study implies that the status of initial electrolyte powder can significantly influence the overall cell characteristics.