Microwave-sintered Samples Research Articles

Impact of microwave sintering and NiO additive on the densification and conductivity of BaCe0.2Zr0.7Y0.1O3-δ electrolyte for protonic ceramic fuel cell

This work investigated the influence of microwave sintering on the BaCe0.2Zr0.7Y0.1O3-δ phase, incorporating 2 mol% or 4 mol% NiO as sintering aid. X-ray diffraction analysis of perovskite phase detected a rhombohedral structure under both sintering heating rates (280 and 500 °C/min), also exhibiting the presence of a second phase deficient in Ba with Ni incorporated into the structure, replacing part of the Zr. Raman analysis indicated no distortions in the perovskite structure, independent of the rates and NiO concentrations. The efficacy of NiO addition as a sintering aid was demonstrated by high densification of the samples, exceeding 97 % relative density. Detailed analysis of structural, microstructural, and conductivity properties revealed that microwave sintering, particularly using a heating rate of 500 °C/min, yielded superior results compared to conventional sintering. The enhanced electrical response was attributed to a higher concentration of structural defects, oxygen vacancies, in the microwave-sintered samples, evidenced by the band at 630 cm−1 in the Raman spectrum. Among these, the BCZY sample with 2 mol% NiO, sintered under these conditions, stood out as the most promising, showcasing not only high density but also a uniform microstructure and appreciable electrical conductivity.

Ho-Mn co-doping in barium titanate piezoceramics via sol-gel process followed by microwave and conventional heating

Co-doped barium titanate (BT) piezoceramics are applied in advanced energy harvesting systems. In the present study, Ba1−2xHo2xTi1−xMnxO3 (x = 0, 0.02, 0.04, and 0.06) were produced via the sol-gel-assisted solid state co-doping technique followed by microwave and conventional heating. In the current investigation, the synthesizing and phase characterization, allotropic transition, morphological examination, elemental analysis and dielectric-piezoelectric responses were investigated by x-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Thermo-Gravimetric Analysis (TGA), Field-Emission Sanning Electron Microscope (FESEM), Energy-Dispersive x-ray Spectroscopy (EDS), Mapping analysis and inductance-Capacitance-Resistance meter (LCR meter) techniques, respectively. The XRD pattern and DSC/ TGA outcomes demonstrated that tetragonal BT phases without minor BaCO3 secondary phases are synthesized properly, and that the negligible unsolicited BaCO3 phases are thoroughly calcined by a microwave at 900 °C. Doping resulted in an increase in tetragonality (c/a) of 0.19%, 0.15%, and 0.04%, respectively, compared to the pure calcined BT. Additionally, the crystallite size of BT decreased significantly by 59%, 58%, and 52%, respectively. The results revealed that the microwave-sintered samples have higher purity, drastic delicate and finer grain size distribution, and superior tetragonality with respect to the conventionally sintered furnace samples. Furthermore, the piezoelectric constant for the microwave sintered and the conventionally sintered samples with the same value of x = 0.04 were 390 and 370 (pC/N), respectively, which established that the sintering method has satisfactory affection (approximately 6%) on the piezo function of the samples. Eventually, the prepared samples which had 0, 2, 4, and 6% moles of Ho3+-Mn2+ cations and were sintered by a microwave compared to the similar specimens fabricated by the furnace had superior dielectric constants of 2.6, 1.1, 2.2 and 2.9 times, respectively.

Mechanical, thermal, electrical, and corrosion properties of microwave-sintered Ti-0.8Ni-0.3Mo/TiB composites

In this study, Titanium boride (TiB) reinforced Ti-0.8Ni-0.3Mo/XTiB (X = 5, 10, 15, and 20 wt%) composites were successfully fabricated by microwave sintering assisted powder metallurgy process. Scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) and x-ray diffraction (XRD) analyses were used to evaluate the elemental powders individually. The distribution of TiB particles in the sintered Ti-0.8Ni-0.3Mo composites was observed using optical microscopy (OM) and SEM. The Microhardness of the microwave-sintered samples was evaluated through Micro Vicker’s hardness testing machine. Thermal characteristics were estimated for temperatures ranging from 50 to 250 °C. The electrical conductivity of Ti-0.8Ni-0.3Mo/TiB composites was calculated from the measured resistance values using the four-point probe method at room temperature. The immersion method was performed to estimate the corrosion properties by suspending the sintered samples in 3.5% NaCl solution for 60 h. The morphology of the corroded surfaces was examined using SEM. The results revealed that Ti-0.8Ni-0.3Mo/15TiB possessed optimum hardness values from 220 to 260 HV, mechanical properties such as True yield strength from 728 to 814 MPa, ultimate compression strength from 1335 to 1680 MPa, fracture strain of 6.12 to 13.81%. It also revealed less weight loss in a corrosion medium of 0.6 g. The Ti-0.8Ni-0.3Mo/TiB composites had good properties in densification aspects, which is suitable for applications such as marine and airfare components.

Effect of Europium Addition on the Microstructure and Dielectric Properties of CCTO Ceramic Prepared Using Conventional and Microwave Sintering.

In this work, Eu2O3-doped (CaCu3Ti4O12)x of low dielectric loss have been fabricated using both conventional (CS) and microwave sintering (MWS), where x = Eu2O3 = 0.1, 0.2, and 0.3, respectively. According to X-ray diffraction (XRD) and scanning electron microscope (SEM) reports, increasing the concentration of Eu3+ in the CCTO lattice causes the grain size of the MWS samples to increase and vice versa for CS. The X-ray photoelectron spectroscopy (XPS) delineated the binding energies and charge states of the Cu2+/Cu+ and Ti4+/Ti3+ transition ions. Energy dispersive spectroscopy (EDS) analysis revealed no Cu-rich phase along the grain boundaries that directly impacts the dielectric properties. The dielectric characteristics, which include dielectric constant (ε) and the loss (tan δ), were examined using broadband dielectric spectrometer (BDS) from 10 to 107 Hz at ambient temperature. The dielectric constant was >104 and >102 for CS and MWS samples at x > 0.1, respectively, with the low loss being constant even at high frequencies due to the effective suppression of tan δ by Eu3+. This ceramic of low dielectric loss has potential for commercial applications at comparatively high frequencies.

Microstructures and Properties of Cu-rGO Composites Prepared by Microwave Sintering.

This study investigated the effects of microwave sintering on the microstructures and properties of copper-rGO composites. Graphene oxide was coated onto copper particles by wet ball milling, and copper-rGO composites were formed upon microwave sintering in an argon atmosphere. Scanning electron microscopy was then used to observe the mixing in the ball-milled composite powder, and the morphology of the bulk composite after microwave sintering. Raman spectra revealed how graphene oxide changed with ball milling and with microwave sintering. The microhardness, electrical conductivity, and thermal conductivity of the composite were also measured. The results showed that graphene oxide and copper particles were well combined and uniformly distributed after wet ball milling. The overall microhardness of microwave-sintered samples was 81.1 HV, which was 14.2% greater than that of pure copper (71 HV). After microwave sintering, the microhardness of the samples in areas showing copper oxide precipitates with eutectic structures was 89.5 HV, whereas the microhardness of the precipitate-free areas was 70.6 HV. The electrical conductivity of the samples was 87.10 IACS%, and their thermal conductivity was 391.62 W·m−1·K−1.

Effect of the microstructure and properties of graphite/copper composites fabricated by microwave sintering

In this study, graphite/copper composites were prepared by microwave sintering. The microstructure and properties of the composites were characterized. The effects of different sintering temperatures on the properties of the composites were studied, and the differences between microwave sintering and conventional sintering composites were compared. The results show that after microwave sintering, the grain size of the copper matrix is refined and the graphite/copper interface is improved, and the distribution of graphite over the matrix becomes more uniform. Compared with conventional sintering, the properties of microwave-sintered samples have been further improved. Besides, with the increase in sintering temperature, the density, hardness, electrical conductivity and thermal conductivity of the composite have been improved, and some properties have become anisotropic obviously. Thus, the electrical conductivity and thermal conductivity along the direction of graphite sheet are higher than those perpendicular to the sheet.

Influence of sintering method on microstructure, electrical and magnetic properties of BiFeO3–BaTiO3 solid solution ceramics

The (1-x)BiFeO3-xBaTiO3 (short for (1-x)BFO-xBTO, x = 0.2–0.4) ceramics were prepared by solid-state reaction with microwave sintering (MWS) and conventional sintering (CS) methods. The crystal structure, microstructures, dielectric properties, ferroelectric properties, and magnetic properties of BFO-BTO ceramics sintered by MWS and CS were systematically investigated. It is found that the MWS can effectively decrease the grain size and enhance the compactness of BFO-BTO ceramics. The X-ray diffraction (XRD) results confirm that all ceramics exhibit a single perovskite structure, and the phase transforms from rhombohedral in BiFeO3-rich compositions to pseudo-cubic phase gradually as x increases. Introducing BTO into BFO can strengthen its dielectric relaxation behavior. Compared with CS, the MWS samples have a lower remanent polarization (Pr) and a smaller coercive field (Ec) under the same electric field. Therefore, MWS contributes to the decrease of dielectric loss. Addition of BTO can contribute to the reduction of the coercive force (Hc) of BFO-based ceramic, and so decrease the hysteresisloss. At the same time, its remanent magnetization (Mr) value can be decreased by introducing BTO into BFO and using MWS method. The present research provides a route for decreasing the dielectric loss and hysteresis loss of BiFeO3-based ceramics using the MWS method.

Effects of Sintering Method and BaTiO3 Dopant on the Microstructure and Electric Properties of Bi (Fe0.9Al0.05Yb0.05) O3-Based Ceramics

The (1 − x) Bi (Fe0.9Al0.05Yb0.05) O3–xBaTiO3 (BFAYO-x BTO) ceramics were synthesized by microwave sintering (MWS) and conventional sintering (CS) methods. The crystal structure, surface morphology, dielectric and ferroelectric properties were investigated. XRD patterns show that BTO tetragonal and BFO rhombohedral phases coexist in both MWS and CS samples, and that the diffraction peaks of MWS samples shift to lower angles due to the larger ionic radius of Ba2+ compared with Bi3+. The lattice constant of BFAYO-x BTO ceramics increases with the increase of BTO content. It was found that the average grain size of the MWS ceramic is much smaller than that of the CS ceramic. Dielectric measurements reveal that the dielectric loss and dielectric constant increase with BTO content increasing. The introduction of BTO into BFAYO-based ceramic contribute to the enhancement of the dielectric relaxation behavior. The P–E hysteresis loops demonstrate that the remnant polarization (Pr) and the coercive field (EC) of the MWS samples are smaller than those of the CS samples. Pr and EC first increase, then decrease and then increase again with the increase of BTO content. The maximum and minimum values of the remnant polarization were obtained at x = 0.25 and 0.3, respectively.

Effects of Sintering Method and BiAlO3 Dopant on Dielectric Relaxation and Energy Storage Properties of BaTiO3–BiYbO3 Ceramics

(0.9 – x)BaTiO3–0.1BiYbO3–xBiAlO3 (x = 0, 0.02, 0.04, and 0.08) lead‐free ferroelectric ceramics are synthesized using conventional sintering (CS) and microwave sintering (MWS) methods. The microstructure, dielectric and ferroelectric properties, relaxation behavior, and energy storage properties are investigated systematically. X‐ray diffraction (XRD) patterns show a single perovskite phase for all samples. Scanning electron microscope (SEM) images indicate that MWS method can impede the grain growth, whereas the introduction of BiAlO3 can lead to the increase in the grain size. Dielectric measurements reveal that an obvious dielectric relaxation behavior can be strengthened by MWS, and the improvement of the dielectric constant (εr) of ceramics is realized by MWS. Incorporated with BiAlO3 contributes to enhancement of the frequency and temperature stabilities of the dielectric constant for BaTiO3–BiYbO3 ceramics. The slim hysteresis loops are observed, and the maximum polarization of the sample sintered by MWS is higher than that sintered by CS. The MWS samples possess a higher energy density which is about 2 times larger than that of CS samples, and the largest energy storage density ≈0.86 J cm−3 and energy storage efficiency ≈97.44% are, respectively, obtained at x = 0 and 0.04 for MWS ceramics.

Microstructure and mechanical properties of 5.8 GHz microwave-sintered ZrO2/Al2O3 ceramics

Aim of the present study is to sinter zirconia nanocomposite powders doped with ceria and toughened with alumina (10Ce-TZP/Al2O3) by non-conventional means, i.e. microwave sintering technology. The sintering effects of various microwave applicators and frequency generators were evaluated using an optimised experimental set-up. The microwave-sintered samples were compared with the composites sintered by the conventional method. The mechanical properties of the ceramic composites were evaluated by their hardness, fracture toughness and Young's modulus. Likewise, their density and microstructure were analysed.

Enhanced dielectric and piezoelectric properties in microwave sintered ( $$\hbox {Ba}_{0.997}\hbox {Nd}_{0.003})\hbox {TiO}_{3}$$ Ba 0.997 Nd 0.003 ) TiO 3 ceramic when compared to conventional sintered ceramics

Dielectric, conductivity and piezoelectric properties have been studied on (\(\hbox {Ba}_{0.997}\hbox {Nd}_{0.003})\hbox {TiO}_{3}\) ceramic samples prepared through microwave sintered (MWS) and conventional sintered (CS) routes and the results are presented in this paper. The room temperature dielectric constant at 10 kHz for CS and MWS samples are 1245 and 5250 respectively. Room temperature dielectric constant in MWS sample was almost four times higher than that of the CS sample. The value of \(K_{\mathrm{t}}\) is found to be 0.998 and 0.997; whereas the value of \(d_{33}\) is \(7.72 \hbox { nm V}^{-1}\) (573 K) and \(444.66 \hbox { nm V}^{-1}\) (573 K) for CS and MWS samples, respectively. In the present study almost 57 times enhancement in piezoelectric charge constant (\(d_{33}\)) is observed for the MWS \(\hbox {Ba}_{0.997}\hbox {Nd}_{0.003}\hbox {TiO}_{3}\) ceramic when compared to the CS ceramic.

Superior electrical and magnetic properties of microwave-sintered NiMgCuZn nanoferrites in comparison to their conventionally sintered counterparts

Microwave technique was employed for sintering a series of Ni0.5−xMgxCu0.3Zn0.2Fe2O4 nanoferrites (x = 0.05, 0.10, 0.15, 0.20) synthesized by citrate precursor method. The samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), LCR meter, and Fourier-transform infrared spectroscopy (FTIR). A comparative analysis was performed for the microwave-sintered specimens and conventionally sintered specimens. This work highlights the significant reduction in sintering duration for microwave technique and remarkable improvement in electromagnetic properties like higher dc resistivity and higher initial permeability for microwave-sintered samples as compared to conventionally sintered ones, thereby making microwave-sintered samples more suitable for high frequency and multilayer chip inductor (MLCI) applications.

Microstructure, dielectric and ferroelectric properties of (1−x) BaTiO3–xBiYbO3 ceramics fabricated by conventional and microwave sintering methods

(1−x) BaTiO3–xBiYbO3 (abbreviated as (1−x) BT−xBY, x = 0, 0.03, 0.06 and 0.09) ferroelectric ceramics have been fabricated by conventional sintering (CS) and microwave sintering (MWS) methods. The microstructure, dielectric and ferroelectric properties of (1−x) BT–xBY ceramics have been investigated systematically. X-ray diffraction patterns indicate all samples possess single perovskite phase and the crystal structure transforms from tetragonal to pseudo-cubic phase with increasing x. It can be also found that denser microstructure and finer grains can be obtained by MWS compared to CS as indicated by scanning electron microscopy. Dielectric measurements reveal that the addition of BY can lead to an obvious relaxation behavior in all samples, and the relaxation characteristics of MWS samples are stronger than those of CS samples. Moreover, the dielectric constant decreases with increasing BY content and the temperature stability and frequency stability of dielectric properties can be enhanced by using MWS method and addition of BY. P–E hysteresis loops become slimmer with the increase of BY content, and the ferroelectric properties of MWS samples are similar to those of CS samples. The leakage current of MWS sample is smaller than that of CS sample from J–E curve. The energy storage efficiency (η) increases with increasing BY content, while the energy storage density (U) increases and then decreases, Umax is obtained at x = 0.06. These results demonstrate that MWS technique and moderate BY content are effective methods to prepare materials for energy storage application.

Effect of Dopants and Sintering Method on the Properties of Ceria-Based Electrolytes for IT-SOFCs Applications

Doped and co-doped ceria ceramics are used as electrolyte materials in solid oxide fuel cells. In this work, ceria-based oxides, Ce0.90Gd0.06Y0.02M0.02O2−δ (M = Ca, Fe, La, and Sr) were prepared by conventional as well as microwave processing from the precursors prepared by the mixed oxide method. The consolidated calcined powders in pellet form were sintered in microwave energy at 1400°C for 20 min and in an electric furnace of IR radiation at 1400°C for 6 h. The x-ray diffraction analysis confirmed that all the compositions were crystallized into a cubic fluorite structure. Surface morphology of the sintered products was studied using scanning electron microscopy and the microhardness was investigated using the Vickers hardness test. The comparative results analysis shows that the microwave-sintered samples have uniform grain growth, higher density and higher microhardness than the corresponding conventionally sintered products. The microwave-sintered sample of composition Ce0.90Gd0.06Y0.02Sr0.02O2−δ was found to have the highest microhardness among the four compositions due to its high density and smallest grain size.

A comparative study of lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.08Sn0.02)O3 ceramics prepared by conventional sintering and microwave sintering techniques

A comparative study on the lead-free ((Ba0.85Ca0.15) (Ti0.9Zr0.08Sn0.02)O3 (BCZTS)) piezoelectric ceramics prepared by conventional sintering (CS) and microwave sintering (MWS) techniques has been conducted. Samples fabricated by CS and MWS techniques showed pure ABO3 perovskite structure in XRD patterns. High-density ceramic materials were obtained in both CS and MWS ceramics. The microstructure of MWS samples is more homogeneous and less porous than CS samples. In addition, the grain size of MWS specimens is larger than the CS one at the same temperature. The piezoelectric property of both samples was measured, the result showed that both d33 and kp were higher for MWS samples compared to CS samples. The dielectric property of both samples was measured in the frequency range of 100Hz–1MHz. The typical relaxor behavior was observed in both types of samples confirmed by diffuse phase transition and frequency dispersion. Tc of MWS ceramics was lower than CS ceramics when 1220°C ≤ T ≤ 1340°C, while Tc of MWS ceramics was higher than CS ceramics when T = 1380°C. The ferroelectric property was tested at 3kV and 1Hz, the result exhibited that both CS and MWS ceramics were good ferroelectric materials.

Structural, Magnetic, and Dielectric Properties of Conventional- and Microwave-Sintered Ni0.6Zn0.4−xCu x Fe2O4

In the present work, structural, magnetic, and dielectric properties of conventional- and microwave-sintered Ni0.6Zn0.4-xCu x Fe2 O 4 (x = 0.0 to 0.4 in steps of 0.1) are studied. X-ray diffraction measurements confirm the formation of a single spinel phase. Crystallite size estimated from Scherrer’s method found between 30–41 nm and 36–28.5 nm in conventional- and microwave-sintered samples respectively. The lattice constant decreases with Cu substitution, suggesting the incorporation of Cu into the spinel lattice. SEM images reveal that microwave sintering results in larger grains with intragranular pores. Saturation magnetization was found to decrease with Cu content. Cation distribution estimated from the magnetization data supports the observed changes in magnetic parameters. A significant influence on microstructure and cation redistribution on dielectric properties are observed for microwave-sintered samples.

Microwave sintering behavior of FeCuCo based metallic powder for diamond alloy tool bit

A novel method of microwave pressureless sintering to fabricate FeCuCo based diamond alloy tool bits was proposed. The characteristic of densification, mechanical properties and microstructural development of the microwave-sintered samples were investigated. Compared to the traditional sintering method in resistance furnace in this work, the microwave sintering displayed distinct advantages, including shorter sintering time, lower sintering temperature, more homogeneous element diffusion, more excellent holding force between in diamond and alloyed matrix. The result demonstrated that the designed metallic powders could be quickly heated to 850 °C in microwave field and heating rate for compacted mixed powder could even reach up to 30 °C/min. And also the relative density and hardness of samples were estimated to be 95.14% and 98.5 HRB by microwave sintering at 850 °C. Additionally, the microstructure analysis manifested microscopic texture was more uniform, which indicated that the microwave sintering was beneficial to the decrease of void defect in FeCuCo and diamond sintered compact. The possible microwave sintering mechanism was also discussed. This work will provide novel perspective of the sintering strategy for the metallic matrix superhard material tool field.

Microwave sintering of zirconia-toughened alumina (ZTA)-TiO2-Cr2O3 ceramic composite: The effects on microstructure and properties

This paper focuses on the development of a zirconia-toughened alumina ZTA-TiO2-Cr2O3 ceramic composite by means of microwave sintering at 2.45 GHz within the range 1200 °C–1400 °C, with a dwell time of 5–20 min. It is aimed at attaining improved microstructure and properties at a lower sintering temperature and shorter soaking time, compared to using a conventional heating method. Consequently, the effects of sintering temperature and soaking time on densification, properties and microstructural behaviour of the composite, are investigated. XRD analysis reveals that the microwave-sintered samples possess a higher crystallinity at a higher sintering temperature. Microstructural analysis confirms the uniform distribution of particles and controlled grain growth; with the lowest AGI value being 1.28 grains/μm. The sample that is microwave-sintered at 1350 °C with 10 min of soaking time achieves a high density (95.74% of the theoretical density), elevated hardness (1803.4 HV), and excellent fracture toughness (9.61 MPa m1/2), and intergranular cracks. This proves that the microwave sintering technique enhances densification, microstructural evolution and the properties of the ceramic composite at a lower temperature and shorter soaking time, compared to conventional heating. Overall, the improved mechanical properties of the microwave-sintered ceramics, compared to conventionally-sintered ceramics, are attributed to the enhanced densification and finer and more homogeneous microstructure that is achieved through the use of a microwave sintering method. The results reveal that microwave sintering is effective in improving the microstructure and density of materials, and will be useful for enhancing the mechanical properties of ZTA-TiO2-Cr2O3 ceramic composites.

Vanadium carbide reinforced aluminum matrix composite prepared by conventional, microwave and spark plasma sintering

The effect of sintering method on the structure and mechanical properties of aluminum −10 wt% VC composite was investigated. Aluminum-VC metal matrix composite was prepared successfully by conventional (at 600 °C), microwave (at 600 °C) and spark plasma sintering (at 450 °C). The obtained results indicate that the aluminum −10 wt% VC composite prepared by SPS had the highest relative density (99 ± 0.6 ± %TD), bending strength (295 ± 15 MPa) and microhardness (232 ± 16 Vickers). The XRD investigations showed the decomposition of VC phase and the formation of Al3V intermetallic phase in the microwave-sintered samples. The SEM micrographs and EDS analyses revealed uniform distribution of reinforcement particles in SPS method and the formation of Al3V phase in microwave-sintered sample.

Microwave sintering of ceria-doped scandia stabilized zirconia as electrolyte for solid oxide fuel cell

In this work, the effect of microwave sintering on the properties of 1 mol% ceria-doped scandia stabilized zirconia (10Sc1CeSZ) was investigated. The sintering was carried out at temperatures 1300 °C and 1350 °C for 15 min using a 2.45 GHz microwave furnace. The sintering behavior of the microwave sintered ceramics was compared with that obtained via the conventional sintering at temperatures ranging from 1300 °C to 1550 °C with 2 h holding time. It was found that both sintering processes yielded highly dense samples with minimum density of 98% theoretical value. Phase analysis by X-ray diffraction revealed the presences of only cubic phase in all sintered samples. All sintered pellets possessed high Vickers hardness (13–14.6 GPa) and fracture toughness (∼3 MPa m1/2). Microstructural examination by using the scanning electron microscope showed that the grain size varied from 2.9 to 9.8 μm for the conventional sintered samples whereas the grain size of the microwave sintered ceramics was below 2 μm. Electrochemical Impedance Spectroscopy study recorded the maximum ionic conductivity of 0.280 S/cm at 800 °C for the conventional-sintered sample at 1550 °C whereas a high value of 0.314 S/cm was measured for the microwave-sintered sample at 1350 °C.