Microwave Sintering Process Research Articles

Evolution mechanism of Ti(C,N)-based cermet microstructure under microwave sintering

Experimental studies of microwave-sintered cermets were carried out at different sintering temperatures and holding times to investigate their microstructure evolution mechanism. Results of the study show that: (1) As sintering temperature increases, main microstructure evolution mechanisms of cermets are as follows: metal-phase melting, hard-phase skeleton filling of large pores in hard-phase skeletons, secondary rearrangement of the liquid phase (the liquid phase gradually fills the space between grains), and cooling down (precipitation–crystallization–reattachment); (2) As holding time increases, main microstructure evolution mechanisms of cermets are as follows: complete filling of large pores in the hard-phase skeleton, secondary rearrangement of the liquid phase, intense dissolution precipitation enhancing the formation of core-rim phase, and secondary homogeneous arrangement of the liquid phase. The special electromagnetic effects of microwave-sintered cermets and their influence on the sintering process were analyzed. It was found that both tip-discharge effect and hot-spot effect occurring during the microwave sintering process are conducive to the sintering process. The formation process of core-rim phase of cermets was also studied. Results show that: (1) Cermets form black core–white rim–grey rim structure via dissolution–precipitation and precipitation–crystallization phenomena; (2) Cermets form white core–grey rim structure through agglomeration of small particles, dissolution–precipitation, and precipitation–crystallization phenomena.

Microwave-Assisted Fabrication and Characterization of Carbon Fiber-Sodium Bismuth Titanate Composites

Lead-based piezoelectric materials cause many environmental problems, regardless of their exceptional performance. To overcome this issue, a lead-free piezoelectric composite material was developed by incorporating different percentages of carbon fiber (CF) into the ceramic matrix of Bismuth Sodium Titanate (BNT) by employing the microwave sintering technique. The aim of this study was also to evaluate the impact of microwave sintering on the microstructure and the electrical behavior of the carbon-fiber-reinforced Bi0.5Na0.5TiO3 composite (BNT-CF). A uniform distribution of the CF and increased densification of the BNT-CF was achieved, leading to improved piezoelectric properties. X-ray diffraction (XRD) showed the formation of a phase-pure crystalline perovskite structure consisting of CF and BNT. A Field Emission Scanning electron microscope (FESEM) revealed that utilizing microwave sintering at lower temperatures and shorter dwell times results in a superior densification of the BNT-CF. Raman Spectroscopy confirmed the perovskite structure of the BNT-CF and the presence of a Morphotropic Phase Boundary (MPB). An analysis of nanohardness indicated that the hardness of the BNT-CF increases with the increasing amount of CF. It is also revealed that the electrical conductivity of the BNT-CF at a low frequency is significantly influenced by the amount of CF and the temperature. Moreover, an increase in the carbon fiber concentration resulted in a decrease in dielectric properties. Finally, a lead-free piezoelectric BNT-CF showing dense and uniform microstructure was developed by the microwave sintering process. The promising properties of the BNT-CF make it attractive for many industrial applications.

Comparative study of microstructure and mechanical properties of Mg/B4C composites: Influence of sintering method and temperature

This present work compares the effect of heating methods including microwave and spark plasma sintering (SPS) process on the microstructure and mechanical properties of Mg–B4C. 5 wt%B4C mixed with Mg powders through high-energy mixer mill for 10 min at ethanol media. After mixing, the green bodies were prepared by uniaxially pressing the mixture. The microwave heating was done at sintering temperatures of 600, 650 and 700 °C without soaking time in graphite bed. While, in the case of SPS, the mixture of the powders was directly inserted into a graphite mold and sintering process was performed at 450 °C with initial and final pressures of 10 and 30 MPa at vacuum condition of 17 Pa, sequentially. The corresponding XRD patterns revealed Mg and B4C crystalline phase alongside the reaction product of MgB2 and also MgO byproduct. The FESEM investigations depict uniform distribution of B4C reinforcements at the Mg matrix. Moreover, increasing microwave sintering temperature led to decreasing pores at the microstructure of the prepared sample. The microstructure of SPSed sample revealed almost full densification compared to that of the microwave processed samples at all the sintering temperatures applied. Also, The XPS results show the presence of Mg, O, C and B elements on the surface of prepared composite, and HRTEM with HAADF-STEM images were obtained to study the interface of matrix and reinforcement. The highest bending strength and Vickers hardness of 116 ± 6 Hv and 231 ± 11 MPa were obtained for SPSed sample as well as for the highest relative density. Although the microwave sample was sintered at 700 °C at low pressure, sintering method demonstrated considerable mechanical properties in comparison to SPSed specimen, indicating a successful preparation method as a low-cost, energy- and time-saving process.

Microwave sintering of WC-HEA cemented carbide: Sintering process, microstructure and mechanical properties

Microwave sintering is an efficient and green material preparation technology. Ultrafine crystalline WC-CoCrFeNiCu cemented carbide were fabricated by microwave sintering using mechanically alloyed high-entropy alloy (HEA) as a binder. The effects of the microwave sintering process (sintering temperature, holding time) on grain distribution, microstructure and mechanical properties of WC-HEA cemented carbide were studied. WC-10wt%HEA showed the best mechanical properties as sintered at 1400 °C with holding time of 10 min. Its grain size, Vickers hardness and fracture toughness were 273 ± 6 nm, 17.6 ± 0.8 GPa, and 8.7 ± 0.3 MPa·m1/2, respectively. The delayed diffusion effect of HEA played significant role in inhibiting grain growth, resulting in 38% smaller than that of WC-Co cemented carbide. Improving the wettability of HEA on WC to reduce the porosity of the sintered body is the main challenge in producing cemented carbide tool materials with HEA as a binder.

Making the Case for Scaling Up Microwave Sintering of Ceramics

The densification and sintering of ceramics using microwaves is first reported in the mid‐1960s. Today, the reduced carbon footprint of this process has renewed interest as it uses less energy overall compared to conventional process heating/furnaces. However, scaling up and commercializing the microwave sintering process of ceramics remains a formidable challenge. As a contactless method, microwave sintering offers geometric flexibility over other field‐assisted sintering processes. Yet, the inability to address multiscale, multiphysics‐driven heterogeneities arising during microwave coupling limits discussions about a future scale‐up process. Herein, the case is made that unlike 60 years ago, new advances in multiscale computational modeling, materials characterization, control systems, and software open up new avenues for addressing these challenges. More importantly, the rise of additive manufacturing techniques demands the innovation of sintering processes in the ceramics community for realizing near‐net‐shaped and complex parts for applications ranging from medical implants to automotive and aerospace parts.

Function optimization of ceramic firing process and reduction of energy consumption based on CFD simulation

Microwave sintering, as an efficient and energy-saving advanced sintering method, has advantages that traditional sintering methods cannot match, such as promoting ion diffusion and refining grains. This paper uses microwave heating equipment and solid-phase reaction method combined with microwave sintering technology to prepare ceramics. The treatment process of powders and the influence of microwave sintering parameters on the reduction of energy consumption in the ceramic firing process were studied, and the microwave sintering process was optimized. This article also uses computational fluid dynamics (CFD) as a tool to establish a numerical model of hydrodynamic sedimentation based on the Euler multiphase flow model, and it uses the established numerical model to conduct engineering scale research on the classification treatment process of processing waste. Finally, this article elaborates on the process of multi-process planning and optimizes relevant process parameters. This article builds on previous research by employing a BP neural network (BPNN) to determine the correlations between the many variables involved in the production of functional ceramics and their respective quality metrics. The experimental findings demonstrate the efficacy of the proposed methodology in performing intelligent tasks like process decision-making and optimizing process parameters.

Multi-Objective Optimization in WEDM Process of Titanium Alloy (Ti-3Al-2.5V-2.0WC) using Desirability Approach

Recently, Titanium alloy (Ti-3Al-2.5V) reinforced with Tungsten Carbide (Ti-3Al-2.5V-2.0WC) developed using the microwave sintering process has plays a major role in mining industry. It has very good mechanical property and corrosion resistance. Due to its better strength and high melting point, it is difficult to machine in conventional machining process. Therefore, WEDM process give the solution to cut this high strength material in an effective manner. In this present work, the WEDM input variables such as Servo Voltage (SV), Pulse Time - On (PT-ON), Pulse Time – Off (PT-OFF) and Cutting Speed Percentage (CSP) are considered. L09 Orthogonal Array Matrix (OAM) is considered for experimental work. The output variables like Material Removal Rate (MRR) and Surface Roughness (SR) are considered to obtained the quality machining process. Multi objective optimization technique like Taguchi-Desirability Approach method is implemented to find the optimum input variables. The Improvement of MRR from 0.05978 g/min to 0.06420 g/min and SR from 3.812 μm to 3.452 μm are obtained using Desirability Approach.

Mitigating anode/electrolyte interfacial Ni diffusion by a microwave sintering method for proton-conducing solid oxide fuel cells

Although Ni-based anodes are commonly employed in proton-conducting solid oxide fuel cells (H-SOFCs), interfacial diffusion of Ni from the anode to the electrolyte is difficult to avoid, resulting in lower electrolyte and fuel cell performance. In this study, the electrolyte/anode half-cells are co-sintered using a microwave sintering process, providing a lower co-sintering temperature than the standard sintering approach. The lower co-sintering temperature minimizes Ba-evaporation at the electrolyte and mitigates anode/electrolyte interfacial Ni diffusion, resulting in decreased electrolyte and interfacial polarization resistance. The microwave-sintered cell outperforms the traditionally sintered cell in electrochemical performance, with higher fuel cell performance and lower cell resistances. Furthermore, the improved interfacial condition improves the fuel cell's long-term durability, allowing the cell to operate for 200 h without detectable degradation. This study presents an intriguing and simple way to reduce anode/electrolyte interfacial Ni diffusion, which improves fuel cell output and operational stability.

Taguchi optimization on friction stir welding of nitinol composite

The alumina welded joints with high quality is fabricated through friction stir welding. Through this experimental investigation, the friction stir welding were made between alumina and carbide based nitinol composite. The boron and titanium carbide based nitinol composite were fabricated through microwave sintering process. The tensile strength of welded joints was estimated and optimized through Taguchi approach. The substance properties of welded joint were evaluated. The interfacial layer formation and morphology of welded joint were investigated through scanning electron microscopy. The analysis of variance was provided the contribution of the friction stir welding factors. The objective of the research work is to enhance the welding strength using different input constrains and their level.

Synthesis and characterization of novel NiTi–Ni3Ti/SiC nanocomposites prepared by mechanical alloying and microwave-assisted sintering process

Equiatomic Ni–Ti alloy reinforced with 0, 2.5, 5, and 10 vol % SiC nanoparticles was synthesized through mechanical alloying and microwave sintering process. In this method, a mixture of Ti and Ni powders and SiC nanoparticles (0–10 vol%) were mechanically milled for 30 h, compressed under 1 GPa pressure, and then sintered at 900–1100 °C by microwave heating. Microstructural analysis of the synthesized samples was performed using X-ray diffraction and scanning/transmission electron microscopy, and their hardness was determined using a Vickers microhardness tester. Structural studies revealed the formation of a complex phase structure consisting of the austenite (B2–NiTi), the martensite (B19′-NiTi), and the nickel-rich (Ni3Ti) and titanium-rich (NiTi2) phases. HR-TEM investigations confirmed an increased Ni3Ti phase in the austenitic NiTi matrix nearby the martensitic NiTi phase. It was found that adding SiC nanoparticles to Ni–Ti increased the amount of hard Ni3Ti phase, promoted the stability of the martensite phase at room temperature, and retarded the matrix grain growth during the sintering process. Microhardness tests showed that when the content of SiC nanoparticles increased up to 5 vol %, the microhardness increased considerably to 9 GPa and then declined. The high microhardness of synthesized nanocomposites is due to the formation of Ni3Ti and NiTi martensitic phases and their nanocrystalline structure.

Investigation on the microwave sintering heating process and mechanism of h-BN/ZrO2/SiC composites

To explore the potential of microwave sintering's application in the preparation of h-BN/ZrO2 based side sealing plate, h-BN/ZrO2/SiC composites were sintered using above technology. The effect of feedstock material composition and input microwave power regulation rate on the microwave sintering process was emphatically analyzed. The phase composition, microstructure and related physical properties of sintered composites were examined. The results indicated that ZrB2 was generated in microwave sintered h-BN/ZrO2/SiC. The fracture strength and apparent porosity were 42 MPa and 11%, respectively, when the composite was sintered at 1550 °C for 30 min. Regarding the heating process of sample during microwave sintering, larger input power in the heating stage could increase the heating rate and ensure the sample obtain higher sintering temperature. After reaching the sintering temperature, the highest sintering temperature could be maintained even if the input power was greatly reduced in the holding stage. When the temperature exceeded a critical value, the sintering temperature of the sample would decrease obviously even if the input power greatly increased. The above phenomenon could be attributed to the power redistribution effect of microwave sintering. Based on this effect, the change of SiC content also had a significant impact on the microwave sintering process, which mostly depended on the variations of dielectric loss and electroconductibility of SiC due to the evolution of temperature.

Influence of sintering temperature on mechanical and tribological characteristics of copper based composite reinforced by 2D hybrid material

The effect of sintering temperature on the mechanical and tribological characteristics of 2D phase reinforced copper-based composite has been investigated in the present study. The Cu-based composites containing 2 wt. % of(GO + MoS2)NP were sintered at different temperatures (1023, 1073, 1123, and 1173 K) by microwave sintering process. The microstructural features observed by SEM and HRTEM of composites suggest that as the sintering temperature increases (GO + MoS2)NP pocket formation tendency also increases, which also governs the mechanical and tribological characteristics of composites. As the sintering temperature elevated, the ultimate tensile strength of the composite decreases, whereas friction and wear rate decrease with increase in temperature up to 1123 and beyond 1123 increase in friction and wear has been observed. The decrease in strength with increasing sintering temperature has been attributed to the grain size increment and increase in (GO + MoS2)NP pocket size at the grain boundaries. However, the decrease in friction and wear rate has been ascribed to the ease of extrusion of (GO + MoS2)NP from the pockets for the composites sintered at high temperature, rather than extrusion of (GO + MoS2)NP of fillers from the intra-grainular sites, i.e., for the composites sintered at lower temperature.

Metallographical characterization of Al-SiCP metal matrix composites processed through microwave sintering technique

Al-MMCs are termed to be favourable lightweight component with improved functional stability. Al-MMCs were identified as very good alternative to conventional metals for locomotives and aerospace elements due to favourable properties compared to others. MMCs are produced by different techniques, among them a unique method of low cost processing by microwave technique is waving the researchers to think about it. Microwave processing leads to direct interaction of radiations at molecular level which benefits in obtaining high temperature rate. Because of its cost effectiveness and speed of processing, microwave method is increasingly being explored for processing particulate reinforced MMCs via powder metallurgy. The present work involves fabrication of Al-SiC MMCs by microwave sintering process with different percentage of reinforcement materials. The Metallographical characteristics of microwave processed material have been investigated. Metallographic investigation highlights the reinforcement materials that are spread out in the matrix in uniform way, this leads to betterment of the bonding of the matrix and the selected reinforcement material (SiC) which further leads to enhance the mechanical properties of processed materials.

Effect of the addition of sintering aid on densification behaviour of alumina ceramic

ABSTRACT Alumina ceramic densified using microwave sintering (2.45 GHz, 2800 W) process at temperature of 1500℃ for 1 h. The consolidation of alumina particles (≈2 µm) was assisted by MgO and TiO2 additives in various proportions. The influence of MgO and TiO2 additives on densification mechanism and physical property of alumina has been studied. It has been observed that the density attained a maximum value of 3.95 g/cm3 for sample doped with MgO (0.25 vol %) and TiO2 (0.25 vol %). The microstructure study and microhardness results reveal that the addition of optimum amount of doping i.e. 0.25 vol % MgO and 0.25 vol % TiO2 is the feasible way to improve the densification of alumina and physical properties.

Effect of cold and hot compactions on corrosion behavior of p- and n-type bismuth telluride-based alloys developed through microwave sintering process

Bismuth Telluride (BiTe) based p-type and n-type alloys exhibit superior thermoelectric (TE) performance covering energy requirements for specialized and home utilization. The main challenge nowadays is the sustainability of their adequate TE performance in corrosive environments, which might activate the corrosion reactions, leading to the degradation of p/n semiconductors, and then failure of the TE device. This study investigates the electrochemical responses of cold and hot compacted, microwave-sintered p- and n-type BiTe alloys in a saline medium (3.5 wt% NaCl solution). XRD analysis of microwave-sintered cold- and hot-compacted BiTe pellets confirmed their phase purity and uniform crystal structure. Potentiodynamic polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) data showed enhancements in the corrosion behavior of hot-compacted p-type and cold-compacted n-type BiTe pellets. The study also proposes a corrosion resistance mechanism with an equivalent electrical circuit (EEC) to fit the experimental EIS data of both BiTe pellets. FE-SEM analysis showed visible microstructural evolutions of the BiTe pellets and their passive films. It revealed a remarkable improvement in the microstructure and blocking effect caused by the formed passive films coating the surfaces of the pellets and acting as a physical barrier preventing the passing of destructive Cl- ions. EDX spectra have proved the presence of p-type and n-type BiTe alloys, each with the corresponding dopant element of Antimony (Sb) or Selenium (Se), respectively, and in the same weight compositions for either hot or cold compacted pellets. AFM analysis examined the surface topography of developed pellets. It showed an increment in the surface roughness-mean-square (RMS) values with the development of passive films on p- and n-type BiTe alloys.

Microstructure and mechanical properties of aluminum matrix composites with bimodal-sized hybrid NbC-B4C reinforcements

Aluminum (Al) is an earth-abundant metal recognized with superior properties for vital applications in the aerospace and transportation industries. Structural components of Al exhibit poor performance due to its inherent low mechanical strength. In this work, the mechanical properties of Al are enhanced by reinforcing with bimodal micron-sized Niobium Carbide (NbC) and nano-sized Boron Carbide (B4C) ceramic particles. Al-NbC-B4C hybrid composites have been synthesized via ball milling followed by cold compaction and microwave sintering. NbC micro-reinforcement composition has been kept fixed (5 wt%), while B4C nano-reinforcement composition varied from 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%. XRD patterns revealed the high crystallinity with no detected new phases formed in the sintered composites. TEM micrographs presented the microstructure evolutions with uniform distribution of (micron + nano) hybrid bimodal-sized ceramic reinforcements in the Al matrix. FE-SEM micrographs and corresponding elemental mapping demonstrated the homogeneity in the elemental distribution of synthesized Al-NbC-B4C composites through the ball milling and microwave sintering processes. Roughness values and AFM images showed the formation of insoluble secondary phases dispersed in the Al matrix enhancing its surface resistance towards localized plastic deformations. Al-5 wt%NbC-2.0 wt%B4C composite has exhibited an ultrahigh improvement in the mechanical properties compared to pure Al. It showed enhancements in microhardness (46%), nanohardness (54%), and Young’s modulus (31%). It also showed high ultimate compression strength of 328 MPa and a low engineering failure strain of 0.64. FE-SEM compressive fractography confirmed the strengthened dispersion hardening effect from bimodal-sized ceramic particles obstacle multi-length cracks and resisting fracture failure.

Rapid microwave sintering of functional electroceramic materials

Rapid microwave sintering processes with heating rates of up to 300 °C/min and zero isothermal hold have been implemented using a 5 kW 24 GHz gyrotron system for high-temperature microwave processing of materials. ZnO-based varistor ceramics, BaTiO3/SrTiO3 dielectric ceramics and Gd:CeO2 ceramics for solid electrolyte applications have been sintered to densities of up to 96% of the theoretical value. Using in situ optical dilatometry, correlation between the development of thermal instability under intense volumetric microwave heating and the early onset of densification has been revealed. The influence of the absorbed microwave power on densification and grain growth has been studied by comparing direct and susceptor-assisted microwave heating processes. The possibility of tailoring the microstructure and functional properties of the obtained materials by choosing optimal regimes of rapid microwave sintering is discussed.

Study on Preparation and Properties of Sintered Brick from Multi-Source Solid Waste

The recycling of construction waste and the use of a new sintering process in the field of sintered bricks can greatly solve the problems of clay resource depletion, soil structure destruction, and high CO2 emissions that always limit the development of the sintered brick field. The study was carried out using an orthogonal experiment to derive the optimal mix ratio for the preparation of sintered bricks, and subsequently, the sintered bricks were prepared using the optimal mix ratio. The experimental results show that the maximum compressive strength of construction waste sintered brick (MRB sintered brick) prepared using high-temperature sintering is 8.1 MPa, and the water absorption is 11. When the waste glass slag is mixed with 10%, it can show a better fluxing effect in the preparation of sintered bricks by mixing construction waste with waste glass slag (MGB sintered bricks), so that the MGB sintered bricks have a higher densification. The compressive strength is 32.9% higher and the water absorption is 3.5% lower than that of MRB sintered brick. MGS sintered bricks were prepared by mixing Yellow River sedimentary sand into MGB sintered bricks. The strength of MGS sintered bricks increased with the replacement rate of Yellow River sedimentary sand, and when the replacement rate of Yellow River sedimentary sand reached 16%, the strength of the MGS sintered bricks increased by 88.9%, and the water absorption rate was reduced by 4.6% compared with the MGB sintered bricks. The sintering mechanism had significant effects on the compressive strength, weathering resistance, and frost resistance of the sintered brick. The microwave sintering process has the characteristics of high efficiency, uniform heating, selective heating, and low thermal inertia, which can increase the compressive strength of MGS sintered brick by 4.6%, reduce the water absorption by 12.9%, shorten the sintering time by 43.6%, and improve the frost resistance.

(Invited) A Novel, Ultra-Fast Fabrication of SOFCs By Flash Light Sintering Process

Solid oxide fuel cells (SOFCs) have strong potential for next-generation energy conversion systems because of their high energy conversion efficiency, fuel flexibility and low emission of pollutant. In the last decades, the SOFC technology has rapid progress in terms of performance and durability aspect, expanding its application ranges from stationary system to portable devices. In the fabrication of SOFCs, a simple and mass productive fabrication process such as screen-printing, tape casting and sol-gel method are widely used in the industry because it is easy, scalable and economical process. However, a high temperature post heat-treatment process is required to ensure material properties of the ceramic electrolyte and electrode in these processes. In particular, to achieve a highly dense electrolyte layer, a high sintering temperature above 1300oC is usually employed in the fabrication process, which causes considerable amount of time and significant manufacturing costs. Therefore, reducing the sintering temperature and long process time is one of the major challenges to reduce the fabrication cost and facilitate the commercialization of SOFCs. To overcome this problem, many efforts have been made to demonstrate alternative sintering process to reduce the sintering temperature and process time. For example, several researchers proposed spark plasma sintering process as an alternative sintering process because of the high heating rate within a short time based on Joule heating mechanism [1, 2]. However this process has a limitation of complex vacuum system configuration and high equipment cost for commercialization. In addition, excimer laser ablation annealing and microwave sintering process have been also suggested but there are still limitations such as extremely narrow spot size and complexity of microwave interactions with materials respectively [3, 4]. On the other hand, the flash light sintering process presented here uses a white flash light generated by a xenon arc lamp discharge as a heat treatment sources and has many advantages of an extremely short process time, scalability and simple process condition as standard ambient and temperature. Most of all, because this process conducted within a few seconds, it can significantly improve the productivity and cost-effectiveness of the SOFCs. Our previous works successfully demonstrated that the solution-based YSZ thin films was annealed by flash light sintering and it showed comparable material properties to the conventional thermal sintering process [5]. Nevertheless, due to the low light absorption property and difficulty to sinter the ceramic particles, studies on the flash light sintering process for the powder-based films are still limited. In this work, we demonstrate for the first time rapid fabrication of SOFCs using a novel flash light sintering process. The ceramic electrolyte and electrode was fabricated by using mass productive screen-printing method and flash light sintering process was employed as an alternative sintering process of conventional thermal sintering method. In the sintering process, the effect of various pulse conditions on the sinterbility of the ceramic components were investigated, and the material properties such as microstructure, crystallinity and electrochemical property were analyzed. The optimized ceramic components were employed to fabricate SOFC unit cell and their cell performance and impedance behavior was evaluated to demonstrate the flash light sintering process. Reference [1] Deepash Shekhar Saini et al. “Improved conductivity of spark plasma sintered Ho-Substituted Ba-ZrO3 electrolyte ceramics for IT-SOFCs.” ACS Applied Energy Materials. 1, 7, 3469-3478 (2018)[2] Tatiana L. Simonenko et al. “Spark plasma sintering of nanopowders in the CeO2-Y2O3 system as a promising approach to the creation of nanocrystalline intermediate-temperature solid electrolytes.” Ceramics International, 44, 16, 19879-19884 (2018)[3] Hao, H., Xu, L., Huang, Y., Zhang, X. & Xie, Z. “Kinetics mechanism of microwave sintering in ceramic materials.” Science in China Series E: Technological Sciences 52, 2727–2731 (2009).[4] Bayati, R. et al. “Modifcation of properties of yttria stabilized zirconia epitaxial thin flms by excimer laser annealing.” ACS applied materials & interfaces 6, 22316–22325 (2014).[5] Park, J.S. et al. Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films. Scientific reports 7, 12458 (2017)

Development and activity enhancement of zirconium/vanadium oxides as micro-heterogeneous ceramic electrocatalyst for ORR in low temperature fuel cell

A porous nano-metal oxide composite consisting of zirconium oxide and vanadium oxide (ZrVNPs) was prepared using precipitation hydrothermal technique, followed by microwave sintering process in order to enhance the catalytic activity toward oxygen reduction reaction (ORR) which is a key reaction in the development of low-temperature fuel cell technology. Microwave sintering process conditions were optimized using response surface methodology models (RSM) and the optimized produced material was called ZrV-T. The physiochemical and electrochemical activities of the fabricated materials were investigated and the results elucidated that, the catalytic efficiency of prepared samples is influenced by morphology, lattice structure, and porosity, as well as metal–support interactions and interfacial structural changes that affect oxygen molecules adsorption and activation. The thermally treated composite (ZrV-T) exhibits higher oxygen reduction performance than the non-sintered material (ZrVNPs). Both materials have different half-wave potentials (E1/2 = −0.36 V) and (E1/2 = −0.29 V) for ZrVNPs and ZrV-T respectively. In addition, ZrV-T has a higher stability than the Pt/C catalyst in 0.1 M KOH solution by 4% after 120 min. Using ZrV-T is likely to reduce costs in FCs and promote the use of electrochemical energy devices and it may also be beneficial in other systems that promote catalytic activity.