Microwave Sintering Method Research Articles

Low-temperature Microwave Sintering of Foam SiC for Mechanical Properties and Electromagnetic Absorption

In this work, the foam SiC ceramics were prepared by conventional and microwave sintering methods at 800 °C combined with organic template impregnation method. The microstructure, crystal structure, and mechanical properties of the samples were evaluated. Compared with conventional sintering, microwave sintering has obvious advantages such as more uniform element distribution, shorter sintering time, and better mechanical properties. Its bending strength and impact resistance reach 2.28 MPa and 4.9 kJ/m2, respectively. The dielectric constant and reflection loss of the samples were tested, and the samples sintered by microwave between room temperature and 500 °C showed better dielectric properties; as well as better microwave absorption performance at frequencies of 2-18GHz. The mechanism of microwave sintering has been elucidated, and the heating method of microwave from inside to outside is an important reason for the excellent mechanical and absorbing properties of materials.

Polaron assisted hopping mechanism in microwave processed Nd doped second layered aurivillius SrBi2Nb2O9 ceramics

The polycrystalline Sr0.8Sn0.2Bi1.75Nd0.25Nb2O9 (NdSBN) was synthesized using the green synthesis microwave sintering method, which significantly reduced the processing parameters of the NdSBN ceramics. Orthorhombic crystal structure with A21am symmetry was revealed by Rietveld refinement study, whereas the doping-induced strain and crystallite size was studied using the Williamson Hall method. Crossectional SEM micrographs confirm the plate-like structure, with an average grain size of 273.7 nm. A diffuse type of phase transition was observed at 345 °C, which usually arises due to compositional fluctuations and mobile oxygen vacancies; further, the diffusiveness of the NdSBN was studied using Uchino and Nomura function, a modified version of Curie-Weiss law (CW). The frequency and temperature-dependent dielectric study of NdSBN ceramics display a Maxwell-Wagner relaxation with a high loss in a low frequency regime, possibly due to the presence of leakage current in the solid solution. Frequency dependent AC conductivity obeys Jonscher's power law, whereas DC conductivity supports polaron assisted hopping in NdSBN composition with dual activation energies of 0.55 eV and 0.75 eV, which correspond to electrons and ions, respectively. The non-Debye type relaxation mechanism in conjunction with negative temperature coefficient of resistance (NTCR) behavior was demonstrated by temperature dependent impedance spectroscopy, while modulus spectroscopy confirmed the multiple relaxation processes in NdSBN ceramics.

Effect of applied load on wear of microwave sintered alumina-graphene ceramic composite material

The present work is mainly focussed on the preparation of alumina ceramic composite material reinforced with different weight proportions (wt%) of graphene ranging from 0.15 wt% to 0.45 wt% (with an interval of 0.1) and fabrication using microwave sintering method. Wear studies are performed on graphene reinforced alumina ceramic material samples using pin-on-disk apparatus at different loads of 5 N, 10 N, 15 N keeping speed of 0.8 m s−1 and sliding distance of 40 m constant. The obtained wear results are compared with wear performance of pure alumina samples which are prepared in the same condition. Wear tests even at higher load of 15 N revealed that the decrease in the wear rate of the ceramic composite samples reinforced with 0.35 wt% of grapheme is 35.14% and in the ceramic composite samples reinforced with 0.45 wt% of graphene is 34.85% when compared with the wear rate of samples prepared with pure alumina. The effect of different wt%s of graphene on wear properties of prepared ceramic composites is studied through SEM analysis, and observed that the abrasive wear phenomenon is found to be the dominant wear mechanism.

Multiple relaxation mechanisms in SrBi2Nb2O9 ceramic tweaked by tin and samarium incorporation in assistance with single-step microwave sintering

Non-stoichiometric lead free polycrystalline Sr0.8Sn0.2Bi1.75Sm0.25Nb2O9 (SSBSN) ferroelectric ceramics were synthesized through conventional solid step route method by incorporating ball milling and microwave sintering method. X-ray diffraction along with the Rietveld refinement technique confirms the single-phase orthorhombic structure with A21 crystal symmetry. Additionally, the short-range ordering was confirmed by Raman spectroscopy. Doping induced crystallite size and strain were further calculated from the Williamson-Hall plot, which comes around 150 nm and 1.48 × 10–3 respectively. A plate like morphology with an average grain size of 0.41 μm was confirmed by scanning electron microscopy (SEM). A diffuse type ferroelectric to paraelectric phase transition was recorded at 395 °C, mostly arising due to structural heterogeneity at the inter-ferroelectric phase boundary. The temperature and frequency-dependent dielectric measurement of SSBSN ceramic reveal a Maxwell–Wagner relaxation, with prominent dielectric loss in a low frequency regime perhaps due to the generation of leakage current in the SSBSN system. Frequency dependent ac conductivity indicates the polaron assisted hopping mechanism in SSBSN, which further obeys Jonscher’s formulation. The intra and intergranular contributions to impedance in SSBSN ceramics were probed by the complex impedance spectroscopy (CIS) technique. A non-Debye type relaxation mechanism in SSBSN ceramics was indicated by the Cole–Cole plot, whereas the conduction mechanism and transport properties were briefly studied using modulus spectroscopy.

Zr0.1Fe0.9V1.1Mo0.9O7 as Cathode for Lithium-Ion Battery

Abstract With the development of lithium-ion batteries, high capacity and high cycle stability have been the two main goals being pursued. Recent studies have shown that ZrV2O7 does not perform well in energy storage due to its low electrical conductivity and poor cycling stability. Elemental doping has proven to be an effective strategy for improving electrochemical performance. In this paper, we prepared Zr0.1Fe0.9V1.1Mo0.9O7(ZFVMO) and Zr0.1Fe0.9V1.1Mo0.9O7@c (ZFVMO@c) materials using a simple solid-phase sintering method and a fast microwave sintering method. Double ionic heterovalent substitution of Zr4+/V5+ in ZrV2O7 using Fe3+/Mo6+, Fe3+/Mo6+ gives it near-zero thermal expansion characteristics and excellent conductive properties. In electrochemical tests, the first discharge capacities of ZFVMO and ZFVMO@C are 2261 mA h g−1 and 727 mA h g−1, respectively, and the batteries were finally stabilized for 475 and 500 cycles. Compared to ZrV2O7, the electrochemical properties of ZFVMO are greatly improved.

Scope of magnesium ceria nanocomposites for mandibular reconstruction: Degradation and biomechanical evaluation using a 3-dimensional finite element analysis approach

Magnesium/Ceria nanocomposites (Mg/xCeO2 NCs (x = 0.5 %, 1 % and 1.5 %)) prepared by using powder metallurgy and microwave sintering method are assessed for their corrosion rate for a period of 28 days. As per the immersion tests results, the addition of ceria nanoparticles to pure Mg, brought about a noteworthy improvement to corrosion resistance. A corrosion rate of approximately 0.84 mm/year for Mg/0.5CeO2 and 0.99 mm/year for Mg/1.0CeO2 nanocomposites were observed. Another aspect of the study involves employing the simulation method i.e. finite element analysis (FEA) to compare the stress distribution in magnesium-ceria nanocomposite based screws and circular bars especially for Mg/0.5CeO2 and Mg/1.0CeO2. Further, the simulation also gives a perception of the impact of masticatory forces, the biting force and shear stress exerted on the Mg/0.5CeO2 and Mg/1.0CeO2 based screws. The simulations results show that the screws showed an acceptable level of stresses for a biting force up to 300 N. The circular bar as well kept its stresses at acceptable levels for the same load of 300N. The shear stress results indicated that a biting force up to 602 N can be safely absorbed by Mg/0.5CeO2 screw. The comprehensive approach allows for a better understanding of the corrosion behavior, stress distribution, and mechanical properties of the Mg/CeO2 nanocomposites, enabling the development of effective temporary implants for craniofacial trauma fixation that can withstand normal physiological forces during mastication. The study reported in this paper aims to target Mg/xCeO2 NCs for temporary implants for craniofacial trauma fixation.

A Survey on Extraterrestrial Habitation Structures with a Focus on Energy-Saving 3D Printing Techniques

In the past two decades, various space agencies have shown great enthusiasm for constructing habitable structures on lunar and Martian surfaces. Consequently, several extraterrestrial structures have been proposed by different researchers. Nevertheless, only a small number of those structures are energy-efficient and cost-effective. In this research, a comprehensive review of the proposed extraterrestrial structures has been conducted. The objective is to evaluate different habitat construction techniques from technical, economic, and energy-consumption perspectives. To carry this out, different proposed structures are elaborated, and their advantages and limitations are discussed. The primary focus is on the 3D printing technique, which has demonstrated significant potential in automated manufacturing tasks. From the conducted research, it was found that the combination of 3D-printed components along with an internal breathable inflatable module is the most promising technique for habitat development on the Moon and Mars. Moreover, the microwave sintering method was identified as the most energy-saving and reliable approach for melting the on-site regolith for use in the 3D printing process. This survey has applied a multidisciplinary approach to evaluate the most energy-saving planetary construction techniques that are economically crucial for different private or government-funded space agencies.

Fabrication of hydrothermal ageing resistant of 3 mol % yttria‐stabilised tetragonal zirconia polycrystalline via microwave sintering

AbstractThe influence of microwave sintering on the densification, mechanical performances, microstructure evolution and hydrothermal ageing behaviour of pure 3 mol % yttria‐stabilised tetragonal zirconia polycrystalline (3Y‐TZP) ceramics was compared with conventional sintered samples. Green bodies were sintered via conventional pressure‐less and microwave sintering method between 1200 °C to 1400 °C with dwelling time and firing rate at 120 min, 10 °C/min and 1 min, 20 °C/min. Result showed that reduced processing temperature and holding time is possible with microwave sintering technique for fabricating good resistant zirconia sample with bulk density, Young's modulus, and Vicker's hardness that are comparable to samples sintered with conventional method. However, the microwave sintered samples suffered from hydrothermal ageing where their average grain size is above critical size. The enhancement of hydrothermal ageing resistance of the sintered samples is associated with the decreasing grain size of the sintered samples instead of sintering method.

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.

Effect of fabrication techniques on mechanical and microstructural behavior of AA7075/SiC/ZrC hybrid composite

Aluminum composites are highly sought-after in the industrial sector due to their improved mechanical properties compared to their parent metals. The choice of fabrication technique has a significant impact on the mechanical behavior of the composite. This study investigated the mechanical behavior of an optimized weight-fractioned AA7075/SiC/ZrC hybrid composite using different fabrication techniques. Stir casting, conventional sintering, and microwave sintering methods were employed to produce the composites. By optimizing the ball milling parameters, a uniform distribution of reinforcement particles was achieved throughout the matrix material. XRD, porosity, microstructural, and mechanical tests were conducted on all three composites to analyze the major changes during fabrication. Remarkably, the composites fabricated through microwave sintering exhibited significantly higher strength than the other fabrication methods. Specifically, the microwave-sintered composites displayed a compressive strength of 389 MPa, a tensile strength of 321 MPa, and a strain-to-fracture value of 26%. In contrast, the stir-cast composites showed a larger scale of secondary phases, poor mechanical performance, and elevated porosity. Moreover, when considering the overall production cost associated with the different fabrication techniques investigated in this study, microwave sintering was the most cost-effective method for large-scale production. This suggests that microwave sintering offers superior mechanical properties and economic advantages regarding manufacturing expenses.

Effect of sintering additives on the properties of alumina toughened zirconia (ATZ)

The effect of small amounts of copper oxide, manganese oxide, and stainless steel as sintering additives on the sintering behavior and mechanical properties of Alumina Toughened Zirconia (ATZ, 3Y-TZP with 20 wt% Al2O3) ceramic composites were evaluated and contrasted with that of undoped ATZ by using microwave sintering (MW) method. Green bodies were sintered at 1250°C, 1350°C, and 1500°C using a holding time of 5 min., with a heating rate of 30°C /min. In general, all ATZ samples exhibited a similar trend, as the results showed that the relative density and mechanical properties increased with increasing sintering temperature regardless of the addition of dopants. It was found that the addition of 0.2 wt% CuO, 0.5 wt% MnO2, and 0.2 wt% SS were beneficial in enhancing the densification and improving the mechanical properties of ATZ without inducing grain coarsening. The ATZ composite samples' relative density, tetragonal phase stability, microstructural evolution, Vickers hardness, and fracture toughness were revealed. The addition of 0.2 wt% CuO was the most beneficial in improving the properties of ATZ at a low sintering temperature of 1250°C since the sample obtained the highest relative density of 97%, Vickers hardness of 13.2GPa and fracture toughness of 6.5 MPa m1/2. In contrast, the undoped ATZ required a high sintering temperature to achieve comparable results to the doped samples. The ANOVA analysis revealed that the CuO-doped ATZ sample exhibited the highest significance and was the most suitable in improving both hardness (H) and fracture toughness (KIc) across all temperature conditions. This study also proved that the microwave sintering technique promotes the densification and mechanical properties of ceramic composites compared to the conventional sintering technique.Graphical abstract

Preparation and mechanical properties of SiCw-reinforced WC-10Ni3Al cemented carbide by microwave sintering

SiCw-reinforced WC-10Ni3Al cemented carbide was prepared by microwave sintering method, and the effects of the sintering temperature and SiCw content on the microstructure and mechanical properties of WC-10Ni3Al cemented carbide were investigated; the promotion effect and strengthening mechanism of SiCw were then analysed. The experimental results showed that the relative density, hardness, flexural strength and fracture toughness of WC-10Ni3Al cemented carbide increased and then decreased with increasing SiCw addition and sintering temperature. When the sintering temperature was 1500 °C and the content of SiCw was 0.3 wt%, the sample reached the highest mechanical properties and had a relative density of 96.5%, hardness of 1570 HV, flexural strength of 1275 MPa and fracture toughness of 13.1 MPa mm1/2, which were 4.0%, 23.1%, 12.5% and 8.1% higher than those of the sample without SiCw, respectively. During microwave sintering of WC-Ni3Al, the addition of an appropriate SiCw content can increase the microwave absorption of the sample, and produce many micro-high-temperature regions within the sample, which can accelerate the generation of the Ni3Al liquid phase. This promotes liquid phase flow to fill pores and rearrange the WC grains, thereby improving density and mechanical properties of the sample. The strengthening mechanisms of SiCw on microwave sintered WC-Ni3Al consist of promoting densification enhancement, fine-grained strengthening, and solid solution strengthening of Ni3Al by Si atoms.

Mechanical and thermal expansion properties of Dy2TiO5 ceramic neutron absorbers with small grains

Dy2TiO5 ceramics with small grain size range of 1.5–3 μm were successfully prepared by microwave sintering method. The phase composition, microstructure, thermal expansion, stability, corrosion resistance and neutron absorption properties of Dy2TiO5 ceramics were investigated. The results show that Dy2TiO5 ceramics possess high mechanical properties due to the small grain size, with a microhardness of 12.26 GPa. The addition of Mo significantly reduces the thermal expansion phenomenon of the sample. The oxide film formed on the surface of the Dy2TiO5 ceramic enhances its excellent corrosion resistance. In addition, the Dy2TiO5 ceramic shows excellent neutron absorption with 87.34% neutron absorption and over 94% thermal neutron absorption in 8 cm thick particles.

Microwave sintering coupled with sintering aids for proton-conducting oxide membranes

The BaCe0·4Zr0·4Y0·2O3 (BCZY) was modified with the NiO sintering aid and prepared by a microwave sintering (MVS) method as the electrolyte for proton-conducting solid oxide fuel cells (H–SOFCs). The incorporation of NiO into the BCZY lattice improves the sinterability of the material, leading to the increase of the shrinkage from 3% to 26% after the high-temperature sintering. The dense BaCe0·4Zr0·4Y0·15Ni0·05O3 (BCZYN) pellet can be obtained after sintering at 1500 °C, whereas the Ni-free BCZY is porous after sintering at the same condition. By further using the MVS method, the BCZYN can be densified at 1300 °C, which is 200 °C lower than conventional sintering. Furthermore, the microwave-sintered BCZYN has a higher conductivity than the conventionally sintered one due to the larger grain size. Using the MVS method in the H–SOFCs fabrication, the high porosity of the anode substrate can be retained. In contrast, the cell prepared by the conventional sintering (CS) method has a relatively dense anode, which is detrimental to gas fuel transportation. As a result, the microwave sintered cell exhibits an output of 1010 mW cm−2 at 700 °C, which is significantly larger than that for the conventionally sintered cell, being 535 mW cm−2 at the same testing condition, suggesting the advantage of using the MVS method for the fuel cell fabrication.

Ball milling assisted preparation of nano La–Y/ZrO2 powder ternary oxide system: Influence of doping amounts

Zirconia powder with good dispersion, fine particle size, and stability is used as high-quality raw material in many fields, such as ceramic materials and refractories. In this paper, the influence of lanthanum oxide (La2O3) and yttrium oxide (Y2O3) co-doped zirconia (ZrO2) on its phase transformation behavior, phase stability, and microstructure were investigated. The ball milling method is applied to fabricate different amounts of La2O3-doped yttrium oxide stabilized zirconia oxide. Then, the powder obtained from ball milling was roasted using the microwave sintering method. The samples were characterized using XRD, FT-IR, Raman, SEM and BET to determine the optimal conditions for La2O3–Y2O3 co-doped ZrO2 powder. The results showed that replacing part of Y2O3 with La2O3 increases zirconia powder's tetragonal and cubic phase, enhancing the fracture strength of the subsequent synthesized materials. At the same time, the stability of zirconia stabilized with La2O3 doping is significantly improved compared to that of Y2O3 alone. According to all analysis methods, when the doping amount is 2.8Y0.2La, the powder's phase composition, stability, particle size distribution, and dispersion degree are the best compared with other doping amounts in our study. The obtained powder has a smaller specific surface area, a lower surface energy, a smaller porosity, and a higher density. The samples under this condition can be better used in subsequent materials. The enhancement of various properties of zirconia can significantly prolong the service life of materials in practical applications.

Rapid solidification of simulated radioactive contaminated soil by continuous microwave sintering: Effects of temperature and doping level

In order to find a rapid, efficient, safe and reliable treatment technology for radioactive contaminated soil, the microwave sintering method was used to sinter the simulated radioactive contaminated soil with different CeO2 content at 1100 °C, 1200 °C and 1300 °C for 30 min to achieve vitrification. The phase, microstructure, morphology, mechanical properties, and chemical durability of the sintered samples were investigated. XRD and SEM-EDS results showed that Ce4+ did not participate in the formation of the glass network, but was fixed in the glass network structure. The amorphous fraction of the samples sintered at 1300 °C can reach up to 98%. EDS results showed that the element distribution was uniform. In addition, the density and hardness values of the sintered matrices were in the range of 1.875–2.543 g/cm3 and 6.667–7.112 GPa, respectively. Our results show that the density and hardness values are related to the sintering temperature and CeO2 content. The normalized leaching rate of Ce in samples reached 10−7 g/(m2·d) after 28 d.

(K, Na)NbO3 lead-free piezoceramics prepared by microwave sintering and solvothermal powder synthesis

Low temperature and short processing time are favorable for fabricating (K, Na)NbO3 (KNN) lead-free piezoelectric ceramics with a drawback of easy alkali metal volatilization during the powder synthesis and sintering processes. This study revealed that microwave sintering (MS) in addition to microwave solvothermal synthesis (MSS) of powder can lead to short-time fabrication of KNN ceramics with high density and fine grains. It was found that when the concentration of KOH/NaOH exceeds 1 M, KNN powder with single perovskite structure can be synthesized successfully by MSS method, which can be densified by MS to a high relative density close to 97% at 1050 °C even using 2/9 shorter time than conventional sintering (CS) at the same temperature. Importantly, the MSed KNN ceramics show better piezoelectric and ferroelectric properties than CSed counterparts. Without any dopants, the piezoelectric coefficient (d33) of the MSed pure KNN ceramics is 132 pC/N, and the remnant polarization (Pr) is 26.3 μC/cm2. The results show that the MS method is a promising method for preparing KNN-based ceramics.

Preparation of SiC nanowires based on graphene as the template by microwave sintering

In this study, silicon carbide was prepared by microwave sintering method with graphene as carbon source and ethyl orthosilicate as the silicon source. First, SiO2 particles were in situ covered on the surface of graphene by sol-gel method, and then one-dimensional silicon carbide nanowires were obtained by carbothermal reduction reaction. The macro morphology of SiC nanowires with different sintering temperatures was observed, and the samples were characterized and analyzed by XRD, FTIR, and SEM. From the XRD results, we can see there were sharp diffraction peaks of SiC sintering at1500 °C, indicating that β-SiC was generated at 1500 °C via microwave sintering. It can be shown that one-dimensional SiC nanowires were interwoven into the two-dimensional SiC nanonetworks due to using graphene sheets as the templates. The results showed that SiC nanowires could be successfully prepared by microwave sintering using graphene/SiO2 as precursors; the optimal sintering temperature is 1500 °C, and the keeping time is 40 min. Therefore, using microwave sintering to synthesize SiC is a more appropriate way to reduce manufacturing energy consumption, save cost and improve production efficiency.

Effect of microwave sintering on KNN-based lead free ceramics

Microwave sintering has been known as the effective method to prepare ceramics. In this study, the microwave sintering method was used to synthesize 0.96(K0.5Na0.5)0.95Li0.05Nb0.93Sb0.07O3-0.04CaZrO3 ceramics. The effect of holding time on the properties of ceramics was investigated. With the holding time of 30 min, the excellent piezoelectric properties (d 33 = 286 pC/N) can be achieved.

Effect of Kaolin Geopolymer Ceramics Addition on the Microstructure and Shear Strength of Sn-3.0Ag-0.5Cu Solder Joints during Multiple Reflow.

Solder interconnection in three-dimensional (3D) electronic packaging is required to undergo multiple reflow cycles of the soldering process. This paper elucidates the effects of multiple reflow cycles on the solder joints of Sn-3.0Ag-0.5Cu (SAC305) lead (Pb)-free solder with the addition of 1.0 wt.% kaolin geopolymer ceramics (KGC). The samples were fabricated using powder metallurgy with the hybrid microwave sintering method. Apart from using conventional cross-sectioned microstructure imaging, advanced synchrotron real-time in situ imaging was used to observe primary IMC formation in SAC305-KGC solder joints subjected to multiple reflow soldering. The addition of KGC particles in SAC305 suppressed the Cu6Sn5 IMC’s growth as primary and interfacial layers, improving the shear strength after multiple reflow soldering. The growth rate constant for the interfacial Cu6Sn5 IMC was also calculated in this study. The average growth rate of the primary Cu6Sn5 IMCs decreased from 49 µm/s in SAC305 to 38 µm/s with the addition of KGC particles. As a result, the average solidified length in the SAC305-KGC is shorter than SAC305 for multiple reflow soldering. It was also observed that with KGC additions, the growth direction of the primary Cu6Sn5 IMC in SAC305 changed from one growth to two growth directions. The observed results can be attributed to the presence of KGC particles both at grains of interfacial Cu6Sn5 IMCs and at the surface of primary Cu6Sn5 IMC.