Microwave Sintering Temperature Research Articles

Dental zirconia microwave-sintering followed by rapid cooling protocol

ObjectivesThis study aimed to evaluate the effect of microwave sintering temperature and cooling rate (MS) on 3Y-TZP ceramics and its influence on the ceramic microstructure and mechanical properties. Specifically, to optimize the sintering process, reducing the total sintering time compared to conventional sintering. Materials and methodsEighty-four pre-sintered Y-TZP discs (Vipi block Zirconn, VIPI) (ISO 6872) were divided into seven groups (n = 12) according to the sintering conditions: conventional sintering (CS) at 1530 °C for 120 min and microwave sintering at 1400 °C (MS1400) and 1450 °C (MS1450) for 15 min followed by different cooling conditions: rapid cooling (RC), cooling at 400 °C (C400) and 25 °C (C25). The specimens were submitted to apparent density measurements, X-ray diffraction analysis (XRD), scanning electron microscopy, and biaxial flexural strength test. Data was statistically analyzed through two-way ANOVA, Tukey, Sidak, Dunnett and Weibull (α = 0.05). ResultsAll MS1400 groups presented lower density values than the CS and MS1450 groups. Two-way ANOVA revealed that the MS temperature and cooling rate affected the biaxial flexural strength of the Y-TZP (p < 0.01). Group MS1400RC presented lower biaxial flexural strength values (681.9 MPa) than MS1450RC (824.7 MPa). The cooling rate did not statistically decrease the biaxial strength among the groups submitted to microwave sintering at 1450 °C. XRD analysis showed that the sintering and cooling temperature did not induce tetragonal to monoclinic phase transformation. ConclusionsMicrowave sintering at 1450 °C for 15 min followed by rapid cooling can be a viable fast alternative protocol for Y-TZP sintering, compared with the conventional sintering, reducing the total sintering time by 75% and reducing the energy used for the sintering process without affecting the Y-TZP biaxial flexural strength and relative density compared to the conventional sintering. Moreover, the microwave technique promoted smaller grains and did not induce monoclinic phase formation.

Preparation of novel Ti–Y/ZrO2 ceramic by two-step of mechanical alloying and microwave-assisted sintering process

Zirconia composite ceramic materials are popular for their many excellent properties. In this study, nTi-3Y–ZrO2 composite ceramics were produced by the mechanical alloying-microwave sintering method with different Ti-doping amounts and microwave sintering temperatures. The sample's phase composition, stability rate, lattice parameters, micromorphology, relative density, and grain size are characterized. The results showed that when the sintering temperature is 1200 °C, the samples with different doping amounts are mainly mixed crystalline structures with tetragonal and cubic phases, and the stability rate remains above 90 %. As TiO2 doping increases, the lattice parameters a(Å) and b(Å)first increase and then decrease, while the lattice parameter c (Å) shows an overall increasing trend. Raman data demonstrated that the increase in Ti content promoted the generation of tetragonal phase zirconia. The average grain size is 61.33 nm, 76.23 nm, 58.77 nm, 63.35 nm, and 68.99 nm, respectively. The increase in doping is also accompanied by a narrowing of the grain size distribution, which increases the sintering activity of the sample. In addition, the relative densities of the samples were 67.85 %, 73.94 %, 84.25 %, 84.87 %, and 77.54 %, respectively, showing a gradual increasing trend overall. When the microwave sintering temperature is 1200 °C, and the doping amount is 5Ti–3Y–92Zr, the performance of the sample is superior to other groups. The preparation of nTi-3Y–ZrO2 composite ceramics can provide certain ideas for preparing ceramic materials with excellent performance in various aspects.

Influence of microwave sintering temperatures on mechanical and microstructural Behavior of Al/SiC/snail shell hybrid composite synthesized through powder metallurgy technique

This study emphasizes the synthesis of hybrid aluminum composite reinforced with SiC and Snail Shell (S-Shell) particles through the powder metallurgy technique. The hybrid composite corresponding to the optimized volume fraction of SiC and Snail shell powder (Al-6%SiC-6%S-Shell) was subjected to microwave-assisted sintering (MAS) by varying the sintering temperatures from 400°C to 550°C in steps of 50°C. Results concluded that microwave-sintered composites show superior mechanical characteristics than the composites sintered through conventional sintering techniques. The maximum ultimate tensile strength (U.T.S) of 316 MPa, and compression strength of 396 MPa were obtained for microwave sintered Al-6%SiC-6%Snail shell powder composite sintered at 500°C. However, increasing the sintering temperature above 500°C leads to a reduction in U.T.S and Compression strength due to the formation of coarse grains by absorbing the microwaves at higher temperatures. The U.T.S, Compression strength and Vickers hardness of the microwave sintered Al-6%SiC-6%Snail shell powder hybrid composite sintered at 500°C was enhanced by 42.08%, 42.4%, and 35.5% compared to conventionally sintered hybrid composite. The grain size was found to be increased with an increase in microwave sintering temperature due to the enhancement in the absorption capability of the microwaves with the temperature rise. The results of this study also suggest that choosing materials with a high microwave response helps to achieve improved mechanical properties for microwave-sintered composites.

Microstructural characteristics and mechanical behavior of microwave-assisted sintered ferromagnetic FeCoNi1.5CrCu HEAp/Al matrix composites

The preparation of metal particle reinforced aluminum matrix composites by powder metallurgy has been widely studied in recent years. In this work, the effect of microwave sintering temperature on the microstructure and mechanical behavior of high-entropy alloys (HEAs) reinforced aluminum matrix composites prepared by powder metallurgy was investigated. Due to the outstanding microwave absorbing property of ferromagnetic HEAs particles, the composites sintering proceeded efficiently. At 480 °C, the aluminum matrix in the composite material is more compact, and the HEAs particles in the composite material are more evenly distributed, and the interface between HEAs particles and aluminum matrix is smooth. At 500 °C, the intensity of HEAs diffraction peak in the composite material changes significantly. At 520 °C, AlNi solid solution phase with BCC structure appears in the HEAs region, and the HEAs structure changes from FCC to FCC + BCC, and Al5Cr8, Al5Co2 and Al2Cu phases precipitate. At 480 °C, the nanohardness and elastic modulus at the interface reaches 1245.31 MPa and 72.45 GPa, respectively, showing relatively excellent interfacial bonding strength. The elastic modulus of both HEAs reinforcement and aluminum matrix decrease at a sintering temperature above 480 °C, and the composites have hard and brittle characteristics. At 480 °C, the macroscopic compression and yield strengths of composites are ~ 421.2 MPa and ~ 289.5 MPa, and the maximum shrinkage rate is ~65.3%, exhibiting excellent strength and toughness.

Investigation of the Effects of Reduced Sintering Temperature on Dielectric, Ferroelectric and Energy Storage Properties of Microwave-Sintered PLZT 8/60/40 Ceramics

In this study, (Pb0.92La0.08) (Zr0.60Ti0.40) O3 (PLZT 8/60/40) ceramics were synthesized using a high-energy ball-milling technique followed by microwave sintering at different temperatures from 900 °C to 1200 °C. The optimal microwave sintering temperature for the PLZT 8/60/40 ceramics was found to be 1150 °C, which is relatively low compared with conventional sintering temperature. The sintered ceramics show the pure perovskite phase, uniform grain microstructure (1.2 µm) and high density (~99.5%). The polarization vs. electric field (P-E) hysteresis curves were used to investigate the ferroelectric and energy storage properties. The switching characteristic in P-E loops and occurrence of domain switching current in current vs. electric field (I-E) loops confirms their ferroelectric nature. The PLZT ceramics, which were sintered at 1150 °C, show the highest remnant polarization (Pr) of ~32.18 μC/cm2 and domain switching current (Imax) of ~0.91 mA with a low coercive field (Ec) of ~10.17 kV/cm. The bipolar and unipolar strain vs. electric field (S-E) hysteresis loops were also measured and the highest unipolar strain was found to be ~0.26% for the PLZT ceramics sintered at 1150 °C. The unipolar S-E curves were used to derive the piezoelectric coefficient (d33~495 pm/V) and a strain hysteresis loss (~5.8%).

Influence of Li2O–MgO–ZnO–B2O3–SiO2 glass doping on the microwave dielectric properties and sintering temperature of Li3Mg2NbO6 ceramics

Li3Mg2NbO6 + x wt% Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS, x = 2, 4, 6, 8, 10) microwave dielectric ceramics with the rock-salt structure were primarily investigated by the traditional solid-state method. The microstructures, microwave dielectric properties, and sintering characteristics were studied systematically according to the doping concentration and sintering temperature. It could be seen that the LMZBS glass effectively lower the sintering temperature of Li3Mg2NbO6 ceramics from 1250 to 925 °C with microwave dielectric properties changing as a function of the amounts of the LMZBS glass. The experimental results showed that 4 wt% LMZBS glass enabled Li3Mg2NbO6 ceramics sintered at 925 °C for 4 h to have excellent microwave dielectric properties: er = 16.02, Q × f = 56,455 GHz, τf = − 18.81 ppm/°C. Therefore, Li3Mg2NbO6 ceramics doped with LMZBS glass meet the requirements of low-temperature co-fired ceramics.

Transparent MgAl2O4 ceramics prepared by microwave sintering and hot isostatic pressing

Transparent MgAl2O4 ceramics have been successfully fabricated by microwave sintering and hot isostatic pressing (HIP) from high purity spinel nanopowders. The influence of microwave sintering temperature on densification and microstructure was studied, choosing 1400 °C as the sintering temperature. The comparative study of microwave sintering and pressureless sintering of MgAl2O4 ceramics was made to investigate the difference between the two sintering methods. Compared to the conventional pressureless sintering, the microwave sintered MgAl2O4 ceramics reach relative high density at lower temperature and much shorter time. The in-line transmittance of the transparent 1.5 mm thick MgAl2O4 ceramic obtained by microwave sintering (1400 °C, 80 min) and HIP (1650 °C/180 MPa/3 h) was 86.4% at 1064 nm and 80.2% at 400 nm, respectively. The samples have a Vickers hardness of 13.7 GPa.

Stability properties and structural characteristics of CaO-partially stabilized zirconia ceramics synthesized from fused ZrO2 by microwave sintering

Partially stabilized zirconia (PSZ) ceramics play a significant role as fundamental ceramics and refractory materials. In this work, a CaO-PSZ ceramics material was synthesized from fused ZrO2 by microwave sintering. The stability properties and structural characteristics of the products were characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated that in a microwave field, the duration and sintering temperature presented similar influence trends for the stability properties of ZrO2 ceramics materials, which the finding was assigned to the phase transformation of ZrO2 with temperature change. In addition, following the microwave treatment of the fused zirconia sample at 1450 °C for 2.0 h, a cubic and monoclinic mixed phase was formed. These outcomes corresponded to the results from the SEM and energy dispersive X-ray (EDAX) analysis, demonstrating the successful preparation of the CaO-PSZ ceramics. The toughness of the ceramics was improved, which could be attributed to the formation of CaO-stabilizer-precipitated acicular crystals. The theoretical fundamentals and the practical cases presented in this paper are beneficial for the application of the microwave sintering technology in the synthesis of CaO-PSZ ceramics.

Study on ZnO Varistors Doped with Y2O3 by Microwave Two-step Sintering

The zinc oxide varistor prepared in this paper is mainly composed of submicron zinc oxide powder and dopants, and is prepared by two-step sintering method, which is in contrast with traditional sintering method and ordinary microwave sintering method. The effects of microwave sintering temperature and holding time on the microstructure and electrical properties of ZnO varistors were investigated. The results show that the potential gradient of microwave sintering is higher than that of traditional sintering, but the leakage current also increases. Compared with ordinary microwave sintering, the two-step sintering can further effectively reduce the grain size, enhance densification, not only improve the potential gradient, but also reduce leakage current. In two-step sintering, increasing sintering temperature can effectively reduce leakage current and non-linear coefficient, but the potential gradient is also greatly reduced. When the holding time is more than 1 hour, there is little difference in electrical performance. When the holding time is too small, its electrical performance is weak overall.

Shape memory characteristics of microwave sintered porous Ti–30 at.%Ta alloy for biomedical applications

In this work, the influence of microwave sintering time and temperature on the microstructure characterisation, and thermal and mechanical behaviours of Ti–30Ta were investigated. The relative densities of Ti–30Ta samples were in the range of 65–72% and as the sintering times/temperatures increased, the relative density decreased. The pore size averages were in the range of 6–17 µm with different sintering parameters, for instance the smallest pore size of 6.8 µm was observed after being sintered at 900 ℃ for 30 min (Ta2). Two morphologies of plate-like (P) and needle-like (N) structures were observed, as well as two regions – dark region (Ti-rich region) and bright region (Ta-rich region), also two phases – β and α. The DSC results revealed that the Ms to Mf transformation range was 98.86 to 80.5 ℃, respectively, while the range of As to Af transformation was about −22.35 to 92 ℃, respectively. The maximum fracture strength and its strain were acquired in the sintered sample of 900 ℃ for 30 min. The total strain recovery (ɛT) was improved linearly as the sintering temperature increased, correspondingly, the best ɛT was implied in Ti–Ta shape memory alloys after being sintered at 1000 ℃ for 30 min (Ta4).

Synthesis and formation mechanism of high‐purity Ti3AlC2 powders by microwave sintering

AbstractHigh‐purity titanium aluminum carbide (Ti3AlC2) powders were synthesized by a microwave sintering method using different titanium sources as raw materials. The prepared products were characterized by differential scanning calorimetry (DSC), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicated that the synthesized Ti3AlC2 powders have high purity (97.5%) and even distribution of the grain size when using a 3TiH2/1.2Al/2C mixture as raw materials when the microwave sintering temperature and time were 1300°C and 30 minutes, respectively. The formation mechanism of the Ti3AlC2 is described as proceeding via four stages. The solid‐phase reaction between titanium and aluminum occurs below the melting point of aluminum and the main product is a Ti3Al phase, which is an observed intermediate compound for the formation of Ti2AlC and Ti3AlC2. Thus, this study provides a beneficial approach to low‐temperature synthesis of high‐purity Ti3AlC2 materials.

Effects of Microwave Sintering Temperature and Holding Time on Mechanical Properties and Microstructure of Si3N4/n-SiC ceramics.

The n-SiC (nanometer SiC) is added to be the additive in order to improve the mechanical performance of Si3N4 ceramics. A microwave sintered the ceramics at different temperature and holding times. The results shows that the Si3N4/n-SiC ceramics (85 wt% Si3N4 + 5 wt% n-SiC + 5 wt% Al2O3 + 5 wt% Y2O3) have the best mechanical properties at 1600 °C, which is beneficial to the densification and β-Si3N4 phase formation for 10 min: the density, hardness, and fracture toughness were 97.1%, 14.44 GPa, and 7.77 MPa·m1/2, which increased by 2.8%, 7.0%, and 13.1%, respectively, when compared with the ceramics (90 wt% Si3N4 + 5 wt% Al2O3 + 5 wt% Y2O3).

Microwave sintering and fracture behavior of zirconia ceramics

Yttria and Lanthana co-stabilized zirconia ceramics were successfully prepared by microwave hybrid sintering with a multi-mode cavity at 2.45 GHz. Microhardness, bending strength, fracture toughness, and relative density were tested. The fracture behavior of 3Y–ZrO2 ceramics was studied after sintering. The results showed the average toughness values of 1550 °C microwave sintered and conventional sintered samples were 7.68 MPa m1/2 and 4.31 MPa m1/2 respectively. The average grain size of microwave sintered samples was 500 nm which was smaller than that (700 nm) of conventional sintered samples. The microstructure of fracture samples showed that the intergra1nular fractures were main features for microwave sintered samples, whereas the numerous transgranular fractures were observed in conventional sintered samples. The XRD results revealed that content of monoclinic phase gradually increase with the increasing of microwave sintering temperature in 3Y–ZrO2 samples. It was proposed that the grain boundary diffusion and induced phase transformation worked together weakening the grain boundary bonding strength under the effect of microwave field.

Influence of microwave processing and sintering temperature on the structure and properties of Sr/Zr doped hydroxyapatite

Abstract Among the different cations that are substituted to modify the properties of calcium hydroxyapatite, Sr and Zr have gained interest because of their effect on bone formation and mechanical properties, respectively. In the present work, Sr and Zr substituted hydroxyapatite, Ca9·39Zr0·11Sr0·5(PO4)6(OH)2 are synthesized by conventional and microwave sintering at different temperatures. The effect of different sintering techniques and temperatures are investigated on the structural and morphological properties of as-synthesized samples. The X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) is used to study the variation in structural properties and scanning electron microscopy (SEM) is used to investigate the morphology with the variation in sintering conditions. The changes in lattice parameters clearly show that Sr and Zr are incorporated into hydroxyapatite lattice. Microwave sintered samples retain the higher amount of hydroxyapatite and experience higher density levels as compared to conventional sintering. As compared to conventional sintering, the grain size is more uniform and low percentage of secondary phase is observed in microwave sintered sample.

Microstructure, enhanced electric and magnetic properties of Bi0.9La0.1FeO3 ceramics prepared by microwave sintering

Bi0.9La0.1FeO3 (short for BLFO) ceramics was fabricated by conventional solid-state reaction and microwave sintering. Effects of microwave sintering temperature on microstructure, electric and magnetic properties have been systematically investigated. The XRD results indicate that BLFO ceramics sintered at 800 °C and 820 °C are single rhombohedral distortion perovskite phase, and there is small amount of secondary phase (Bi2Fe4O9) in the ceramic sample sintered at 780 °C. As microwave sintering temperature rises, the densification of BLFO ceramics enhances and the grain size increases, but the homogeneity of grain becomes worse. Microwave sintering temperature has little effect on room-temperature dielectric constant. The leakage current density decreases with the rise of sintering temperature, which is closely related to enhanced densification. The leakage mechanism of BLFO ceramics changes from bulk-limited Poole-Frenkel emission to space-charge-limited bulk conduction as sintering temperature rises. The remnant polarization of BLFO ceramics sintered at 820 °C is much higher than that of the samples sintered at 800 °C and 780 °C, and the coercive electric field changes little with sintering temperature. The results indicate the higher sintering temperature is benefit for the ferroelectricity of BLFO ceramics. The magnetic hysteresis loops of BLFO ceramics indicate that the ceramic samples sintered at 800 °C and 820 °C show a typical ferromagnetic behavior at room temperature. Compared with BLFO ceramics sintered at 800 °C, the spontaneous magnetization and saturation magnetization of BLFO ceramics sintered at 820 °C are higher, and its remnant magnetization and coercive magnetic field are lower.

Analysis of Strength and Microstructural Characteristics of Heat Treated Al Alloy Composites

Metal matrix composites (MMC’s) consist of a metallic matrix combined with dispersed particulate phases as reinforcement. In this study mechanical behaviour and tensile characteristics of 2024 and 2900 alloy matrix composites produced by a powder metallurgy process are investigated as a function of microstructure-strength properties. Two different Samples of Al alloy composites are prepared using 6 wt% Al2O3 and 6 wt% SiC as reinforcement phase in each. Hardness and tensile properties of these samples are investigated using Instron testing machine. The results indicated that tensile properties of the composites significantly improved in the yield strength, UTS and elastic modulus, on incorporation of hard, brittle ceramic particles as compared to unreinforced counterparts. The analysis of mechanical behaviour has revealed that the strength improves significantly with increase in microwave sintering temperature.

Microwave sintering of Ti(C, N)-based cermet cutting tool material

A Ti(C, N)-based cermet cutting tool material with satisfactory properties was fabricated in an energy-efficient way by microwave sintering. The effect of microwave singtering process and the component ratio of carbide (WC, Mo2C) on phase composition, microstructure and mechanical properties were studied. The cermet containing 5wt% WC and 15wt% Mo2C microwave sintered at 1400℃ for 10min, got the optimal mechanical properties. The relative density, fracture toughness and Vicker's hardness were 97.2 ± 0.5%, 8.24 ± 0.49MPam1/2 and 17.54 ± 0.66GPa, respectively. The microwave sintering temperature and holding time decreased by 1.4~15.25% and 66.7~96.1% in comparison with conventional sintering. Solid solution (Ti, Mo)C2 and (W, Ti)C without nitrogen formed, which was different from the carbonitride solid solution that formed in conventional sintering. Additionally, long holding time brought about the formation of whisker-like materials, which benefited the fracture toughness.

Transformation of waste crystalline silicon into submicro β-SiC by multimode microwave sintering with low carbon emissions

This paper presents a novel method for the transformation of waste crystalline silicon, including waste polysilicon (photovoltaic industry), single crystal silicon (waste chip), and activated carbon (AC) into submicro β-SiC in timescales of minutes using a multimode microwave rotary tube reactor under open-air conditions. This research addressed the difficult problem of microwave sintering temperature measurement by using light conducted by a quartz tube wall. The synthesis underwent a liquid-solid reaction at 1450±50°C for 6–8min, which is a noticeable improvement when compared to industrial processes, where a heating time of 30h and temperatures of 2200–2400°C are commonly needed. Theoretical calculations show that the new synthesis method for β-SiC consumes 4.1–4.8 times less energy than modern production methods using quartz sand (SiO2) as the raw material, and CO2 emission using this method is reduced by 76–79%.

Synthesis and reaction evolution of high-purity Ti2SC powder by microwave hybrid heating at low temperature

Highly pure Ti2SC was synthesised by microwave hybrid heating. The effects of composition and processing parameters, such as microwave output power, sintering temperature and dwell time on the formation process and morphology of Ti2SC were studied. The purity of Ti2SC is sensitive to the content of sulphur and sintering temperature. The results indicated that the optimum condition for synthesising Ti2SC was using a mixture of 1.15TiS2/2.85Ti/2C powders irradiated under a 100% microwave output power sintering at 1100°C for 3 min at Ar atmosphere. In addition, the reaction evolution of Ti2SC was discussed in details.

Effect of Microwave Sintering on Electrical Properties of PLZT Ceramics

Lead lanthanum zirconate titanate(PLZT) powders synthesized by partial co-precipitation method were used to fabricate PLZT ceramics by conventional muffle furnace or by microwave muffle furnace. The crystal structure, microstructure, electrical properties of PLZT ceramics prepared by these two methods were investigated. The results show that the PLZT ceramics sintered by these two methods are pure perovskite structure. Microwave sintered PLZT ceramics possess smaller grain, more uniform size and less holes than do the conven tional prepared. The microwave sintering temperature is much lower than that by the conventional method, and the duration time is also much less, while the electrical properties of the ceramics sintered by these two methods are similar. The best properties of PLZT ceramics can be gained by microwave sintering at 1000℃ with dielectric constant and piezoelectric constant of 2512 and 405 p C/N. The remnant polarization is 16.5 k V/cm, and the coercive field is 8.2 μC/cm2. The dielectric constant and piezoelectric constant of PLZT ceramics sintered by conventional method at 1250 ℃reach the maximum values of 2822 and 508 p C/N. The remnant polarization is 21.6 k V/cm and the coercive field is 9.6 μC/cm2.