共查询到20条相似文献,搜索用时 15 毫秒
1.
Samarpita Roy Debdulal Das Tapatee Kundu Roy 《Journal of the European Ceramic Society》2021,41(10):5184-5192
High performance Er2O3 doped ZnO-V2O5 based varistors were prepared by two stage sintering (TSS) method at T1 = 1050 °C for 1/6 h and T2 = 750 and 800 °C for 2.5, 10, 20 and 40 h duration. The microstructural features and electrical properties were studied by XRD, SEM, EDS and a high voltage source unit. The combined effect of TSS and Er2O3 doping is very beneficial to restrain the grain coarsening of varistors. The effect of grain size reduction on nonlinear electrical properties was investigated. The results showed that superior electrical properties were obtained in doped samples via TSS than single stage one. A typical fine-grained (1.7 μm, 97.5 %TD) varistor with sufficiently high nonlinear exponent (α = 154), breakdown field (EB = 15.2 kV cm?1) and reasonably low leakage current density (JL = 0.13 mA cm-2) could be prepared with 0.5 mol.% Er2O3 doping at an optimum sintering condition of T1/T2 = 1050/750 °C for 40 h. 相似文献
2.
《Ceramics International》2022,48(8):10547-10554
Under high-frequency microwave irradiation, zirconia ceramics were prepared by sintering nano-CeO2 (Ce = 7 mol%) doped zirconia powder. The different effects of temperature environment on the phase structure transformation, surface functional groups, microstructure, growth process, and density of doped zirconia were analyzed, and the optimized microwave sintering process for zirconia was determined. The experimental results reveal that the tetragonal phase of zirconia is positively correlated with the temperature when the temperature reaches about 1100 °C in the studied range. The reason is that the grain grows with the increase of sintering temperature, and the surface energy of grain decreases, which leads to the fluctuation of tetragonal phase content. The density of zirconia reaches 98.03% at 1300 °C, and the growth activation energy is 27.40 kJ/mol. There is no abnormal growth of zirconia particles, and the phase transition temperature decreases, which is attributed to the efficient heating of microwave and the incorporation of nano-ceria stabilizer. 相似文献
3.
《Journal of the European Ceramic Society》2020,40(15):5504-5510
Dense alumina ceramics doped with 5 wt% 4CuO-TiO2-2Nb2O5 composite sintering aids were obtained at low sintering temperatures of 950∼975 °C. The ceramic sintered at optimal condition shows good microwave dielectric properties (εr = 12.7, Q × f = 7400 GHz), high thermal conductivity (18.4 W/m K) and high bending strength (320 MPa). TEM and EDS analysis revealed that amorphous Cu-Ti-Nb-O interfacial films with nanometer thickness formed at the grain boundaries, which could provide paths of mass transportation for densification. Al3+ ions may be involved in mass transportation through substitution by Ti3+ and Ti4+ ions near the grain boundary during the sintering process. The accumulation of copper ions at the trigeminal grain boundary was observed. The migration and reaction of copper ions in grain boundaries may also play an important role in promoting mass transportation and low-temperature densification of alumina ceramics. 相似文献
4.
《Journal of the European Ceramic Society》2014,34(10):2435-2442
We show that a two-phase 50 vol% 3YSZ-alumina ceramic flash-sinters at a furnace temperature of 1060 °C under an electrical field of 150 V cm−1. In contrast undoped, single-phase alumina remains immune to field assisted sintering at fields up to 1000 V cm−1, although single-phase 3YSZ flash sinters at 750 °C (furnace temperature). The mechanisms of field assisted sintering are divided into two regimes. At low fields the sintering rate increases gradually (FAST), while at high fields sintering occurs abruptly (FLASH). Interestingly, alumina/zirconia composites show a hybrid behavior such that early sintering occurs in FAST mode, which is then followed by flash-sintering. The specimens held in the flashed state, after they had sintered to near full density, show much higher rate of grain growth than in conventional experiments. These results are in contrast to earlier work where the rate of grain growth had been shown to be slower under weak electrical fields. 相似文献
5.
Shiva Bejugama Shibu Chameettachal Falguni Pati Ajoy Kumar Pandey 《Ceramics International》2021,47(2):1594-1601
Niobia (1 mol. %) doped Ceria Stabilized Zirconia (NbCSZ) powders were synthesized using a co-precipitation method. The synthesized powders were uniaxially compacted and sintered in air. The two-step sintering method was adopted to sinter the samples, and the sintering schedule was optimized based on density, grain size, the phase present, and the hardness of the sintered sample. It was observed that the two-step sintering method effectively suppressed the grain growth of NbCSZ samples and helped in achieving a finer grain size of 1.57 μm along with the hardness of 1195 HV10 and optimum fracture toughness value 6.20 MPa m1/2. The Low-Temperature Degradation (LTD) behavior of the sintered samples was estimated through an accelerated hydrothermal aging test, which revealed that the samples are highly resistant to LTD and shown no phase change even after 150 h of study. Moreover, the cytocompatibility of the NbCSZ was tested by culturing MG63 cells on the samples for 7 days. The NbCSZ was found to be highly biocompatible as evident from cell viability and metabolic activity assay. 相似文献
6.
《Ceramics International》2017,43(8):6105-6109
Alumina-MWCNT composite was densified by microwave sintering. CNTs were coated with boehmite nanoparticles to enhance their distribution in composite samples. Calcination temperature of composite powder was determined by TGA analysis (5 °C/min). Samples containing 0 and 1vol%CNT were produced by cold isostatic pressing at 180 MPa. Microwave sintering (1520 °C for 45 min) was conducted under the flow of argon. Phase analysis of the calcined composite powder showed complete transformation of boehmite into gamma-alumina. The relative densities were 99.3% and 98.1% for monolithic alumina and composite, respectively. CNT addition improved the fracture toughness of alumina by ~37%. SEM images showed that microwave sintering was successful. Also, coating CNTs improved their distribution in the alumina matrix. 相似文献
7.
《Ceramics International》2016,42(12):13888-13892
A comparative analysis of the efficiency of zirconia ceramics sintering by thermal method and high-energy electron beam sintering was performed for compacts prepared from commercial TZ-3Y-E grade powder. The electron energy was 1.4 MeV. The samples were sintered in the temperature range of 1200–1400 °C. Sintering of zirconia ceramics by high-energy accelerated electron beam is shown to reduce the firing temperature by about 200 °C compared to that in conventional heating technique. Ceramics sintered by accelerated electron beam at 1200 °C is of high density, microhardness and smaller grain size compared to that produced by thermal firing at 1400 °C. Electron beam sintering at higher temperature causes deterioration of ceramics properties due to radiation-induced acceleration of high-temperature recrystallization at higher temperatures. 相似文献
8.
AbstractFully densified Al2O3 ceramics with fine grain size were obtained by pulsed electric current sintering through a two-step heating profile (referred to as TS-PECS). Highly transparent Al2O3 polycrystals with fine grain size (400 nm) were successfully fabricated by the TS-PECS process, namely, sintering at 1000°C for 1 h and followed at 1200°C for 20 min under uniaxial pressure of 100 MPa. Effects of the first step temperature and heating rate were discussed for bulk density, grain size and transparency. The temperature in the first step strongly affects densification and grain growth of Al2O3. On the other hand, heating rate, even of 100 K min?1, in TS-PECS does not give significant influences on densification and grain growth of Al2O3. Inline transmittance at 640 nm in wavelength normalised to 1 mm in thickness is increased by decreasing heating rate even in TS-PECS. 相似文献
9.
Grain growth kinetics of dense 3 mol. % yttria-stabilized zirconia (3YSZ) ceramics during both DC flash sintering and conventional annealing were investigated using the grain size as a marker of microstructure evolution. The results indicated faster grain growth under greater current density. In contrast to conventionally annealed specimen, the grain boundary mobility was enhanced by almost two orders of magnitude with the applied electric current, revealing that joule heating alone was not sufficient to account for the experimental results. Instead, activation energy for grain growth decreased significantly due to electro-sintering. Systematic characterization of graded microstructure further indicated that local oxygen vacancies and specimen temperature were responsible for a grain size transition. Based on electrochemical reaction involved in flash sintering, grain size reduction at the cathode was proposed to be attributed to the local rearrangement of lattice cations and generated oxygen ions. 相似文献
10.
《Ceramics International》2017,43(15):12057-12060
Transparent Sm:Y2O3 ceramics were fabricated by spark plasma sintering (SPS). The effects of LiF additive and sintering temperature on the microstructure and optical transmittance of the Sm:Y2O3 ceramics were investigated. The optimal content of LiF additive and sintering temperature was found to be 0.3 wt% and 1500 ℃. The transmittance of Sm:Y2O3 ceramics with a thickness of 1.7 mm reached 75.3% at 609 nm, which is about 94% of the theoretical value. The average grain size of the sample was about 50 µm. 相似文献
11.
Aluminum-doped zinc oxide (AZO) is a potential substitute for tin-doped indium oxide due to its versatility. The properties of AZO films are related to those of the AZO sputtering target. To improve the performances of AZO targets, two-step sintering was used to densify a submicrometer zinc oxide (ZnO) powder with a size of 0.4 μm to produce both AZO and ZnO targets. 相似文献
12.
H. Sheikh M.R. Loghman-Estarki E. Mohammad Sharifi A. Alhaji J. Shakeri 《Ceramics International》2018,44(15):18235-18242
The main objective of this work is to compare the hardness, fracture toughness, and optical transparency of MgAl2O4 spinel (magnesium aluminate), MgAl2O4 spinel/ Si3N4 nanocomposite, and the heat-treated spinel/Si3N4 nanocomposite. For this purpose, the commercial spinel nanopowder and the laboratory-made spinel/ Si3N4 nanocomposite powder were sintered using spark plasma sintering (SPS). A heat treatment at 1000?°C for 4?h was carried out on the as-sintered nanocomposite. The field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX) mapping, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Nanoindentation, and Vickers microhardness analyses were used to determine microstructure, elemental analysis, functional group, hardness, and indentation toughness of the samples. The results showed that the hardness and toughness of the heat-treated sample are more than those of the as-SPSed nanocomposite as much as 15.7% and 25.7%, respectively. Also, the values of optical transmission of the nanocomposite sample in the visible range (400–800?nm) and infrared region (800–2000?nm) were lower than those of pure spinel. 相似文献
13.
《Journal of the European Ceramic Society》2023,43(5):2069-2077
Consolidating a CeO2-doped ZrO2 ceramics, free from monoclinic phase using spark plasma sintering (SPS) is a major challenge faced by previous researchers; Ce+4 → Ce+3 conversion under reducing environments was assigned as the prime factor. We report dense (> 95 % of theoretical density) 20 mol. % CeO2-doped ZrO2 ceramics, free from monoclinic phase and any of micro/ macro-cracks via SPS. The sintering temperature (1175 ℃) used for the present work was the lowest compared to previous reports on the same system. Phase analysis revealed a mixture of tetragonal (major phase) and cubic phase (minor). No depletion of cerium (Ce) from the ZrO2 matrix and no additional/impurity phases were noted after SPS; a common issue that has been observed in most of the previous works. Sintered ceramics showed appreciably high hardness (>11 GPa); the obtained toughness was in-between of tetragonal and cubic CeO2-ZrO2 ceramics. 相似文献
14.
Chih-Wei KuoYun-Hwei Shen Shaw-Bing WenHuey-Er Lee I.-Ming HungHong-Hsin Huang Moo-Chin Wang 《Ceramics International》2011,37(1):341-347
A crystalline nanopowder of 3 mol% yttria-partially stabilized zirconia (3Y-PSZ) has been synthesized using ZrOCl2 and Y(NO3)3 as raw materials throughout a co-precipitation process in an alcohol-water solution. The phase transformation kinetics of the 3Y-PSZ freeze dried precursor powders have been investigated by nonisothermal methods. Differential thermal and thermogravimetric analyses (DTA/TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) have been utilized to characterize the 3Y-PSZ nanocrystallites. When the 3Y-PSZ freeze dried powders are calcined in the range of 703-1073 K for 2 h, the crystal structure is composed of tetragonal and monoclinic ZrO2. The BET specific surface area of the 3Y-PSZ freeze dried precursor powders calcined at 703 K for 2 h is 118.42 m2/g, which is equivalent to a crystallite size of 8.14 nm. The activation energy from tetragonal ZrO2 converted to monoclinic ZrO2 in the 3Y-PSZ freeze dried precursor powders was determined as 401.89 kJ/mol. The tetragonal (T) and monoclinic (M) ZrO2 phases coexist with a spherical morphology, and based on TEM examination have a size distribution between 10 and 20 nm. When sintering green compacts of the 3Y-PSZ, a significant linear shrinkage of 8% is observed at about 1283 K. On sintering the densification cycle is complete at approximately 1623 K when a total shrinkage of 32% is observed and a final density above 99% of theoretical was achieved. 相似文献
15.
《Journal of the European Ceramic Society》2020,40(5):2050-2055
Nanocrystalline oxides exhibit exceptional resistance to plastic deformation, manifesting increased strength and hardness with reduced grain size that qualitatively follows the so-called Hall-Petch relationships. However, below a critical grain size, softening has been observed to occur, in the so-called inverse Hall-Petch regime. The mechanisms underlying these phenomena are still not well understood in oxides. Here we observe, using nanopillar compression, that the yield strength initially increases with decreasing grain size for yttria-stabilized zirconia ceramics produced by high-pressure spark plasma sintering. A hardening-to-softening transition occurs at grain sizes below ≈21 nm. The experiments indicate that this transition depends on strain rate, and the onset of the decrease in yield strength occurs before any shear fracture begins. Nanopillar compression combined with in situ electron diffraction demonstrates the onset of softening coincides with an increase in the amount of crystallographic rotation per unit strain, suggesting a change in deformation mechanism. 相似文献
16.
Ajoy Kumar PandeyKoushik Biswas 《Ceramics International》2011,37(1):257-264
Nano-structured ceria stabilized zirconia powder was synthesized from their respective nitrate salts using a wet chemical co-precipitation method. Dried powder was calcined at different temperatures. Particle size of calcined powders was measured by X-ray diffraction (Scherrer equation) and high resolution transmission electron microscopy. Relative quantities of phases (e.g. monoclinic, tetragonal and cubic) were estimated using rigorous Rietveld analysis. The powder was compacted and sintered conventionally following different time and temperature schedules in order to optimize the sintering schedule for fabrication of dense material. The microstructures of the sintered samples were observed by field emission scanning electron microscopy. Vickers hardness (∼945 VHN) showed appreciable increase (>35%) in the hardness value compared to earlier reported ones. Fretting wear of some of the selected samples was carried out in un-lubricated condition. Wear volume and specific wear rate were estimated and correlated with the microstructure. Fatigue microcrack formation, plastic deformation, grain pull-out and abrasion were found to be the main wear mechanisms. 相似文献
17.
《Ceramics International》2020,46(17):27175-27183
The fabrication of silicon nitride (Si3N4) ceramics with a high thermal conductivity was investigated by pressureless sintering at 1800 °C for 4 h in a nitrogen atmosphere with MgO and Y2O3 as sintering additives. The phase compositions, relative densities, microstructures, and thermal conductivities of the obtained Si3N4 ceramics were investigated systemically. It was found that at the optimal MgO/Y2O3 ratio of 3/6, the relative density and thermal conductivity of the obtained Si3N4 ceramic doped with 9 wt% sintering aids reached 98.2% and 71.51 W/(m·K), respectively. EDS element mapping showed the distributions of yttrium, magnesium and oxygen elements. The Si3N4 ceramics containing rod-like grains and grain boundaries were fabricated by focused ion beam technique. TEM observations revealed that magnesium existed as an amorphous phase and that yttrium produced a new secondary phase. 相似文献
18.
《Ceramics International》2020,46(9):13240-13243
Zirconia ceramics were prepared by oscillatory pressure sintering (OPS) and hot pressing (HP). The result revealed that OPS could enhance densification compared to HP when sintering temperature was higher than a critical value. The onset temperature for rapid grain growth was found to be same for both techniques. However, rate of grain growth in OPS was lower than that in HP. Furthermore, the result also showed that samples prepared by OPS exhibited higher hardness than those prepared by HP when sintering temperature was higher than the critical value. The improved hardness was solely due to the higher density of the samples prepared by OPS. 相似文献
19.
《Ceramics International》2017,43(11):8525-8530
Commercial Y2O3 powder was used to fabricate Y2O3 ceramics sintered at 1600 °C and 1800 °C with concurrent addition of ZrO2 and La2O3 as sintering aids. One group with different contents of La2O3 (0–10 mol%) with a fixed amount of 1 mol% ZrO2 and another group with various contents of ZrO2 (0–7 mol%) with a fixed amount of 10 mol% La2O3 were compared to investigate the effects of co-doping on the microstructural and optical properties of Y2O3 ceramics. At low sintering temperature of 1600 °C, the sample single doped with 10 mol% La2O3 exhibits much denser microstructure with a few small intragranular pores while the samples with ZrO2 and La2O3 co-doping features a lot of large intergranular pores leading to lower density. When the sintering temperature increases to 1800 °C, samples using composite sintering aids exhibit finer microstructures and better optical properties than those of both ZrO2 and La2O3 single-doped samples. It was proved that the grain growth suppression caused by ZrO2 overwhelms the acceleration by La2O3. Meanwhile, 1 mol% ZrO2 acts as a very important inflection point with regard to the influence of additive concentration on the transmittance, pore structure and grain size. The highest in-line transmittance of Y2O3 ceramic (1.2 mm in thickness) with 3 mol% of ZrO2 and 10 mol% of La2O3 sintered at 1800 °C for 16 h is 81.9% at a wavelength of 1100 nm, with an average grain size of 11.2 µm. 相似文献
20.
《Ceramics International》2016,42(15):16640-16643
Transparent Y2O3 ceramics were fabricated by the solid-state reaction and vacuum sintering method using La2O3, ZrO2 and Al2O3 as sintering aids. The microstructure of the Y2O3 ceramics sintered from 1550 °C to 1800 °C for 8 h were analyzed by SEM. The sintering process of the Y2O3 transparent ceramics was optimized. The results showed that when the samples were sintered at 1800 °C for 8 h under vacuum, the average grain sizes of the ceramics were about 3.5 µm. Furthermore, the transmittance of Y2O3 ceramic sintered at 1800 °C for 8 h was 82.1% at the wavelength around the 1100 nm (1 mm thickness), which was close to its theoretical value. Moreover, the refractive index of the Y2O3 transparent ceramic in the temperature range from 30 °C to 400 °C were measured by the spectroscopic ellipsometry method. 相似文献