The paper reports on effect of grain-growth inhibitors MgO, Ysub.2Osub.3 and MnCOsub.3 as well as Ca modification on the microstructure, dielectric, ferroelectric and electrocaloric (EC) properties ...of Basub.0.82Srsub.0.18Snsub.0.065Tisub.0.935Osub.3 (BSSnT). Furthermore, the effects of the sintering time and temperature on the microstructure and the electrical properties of the most promising material system Basub.0.62Casub.0.20Srsub.0.18Snsub.0.065Tisub.0.935Osub.3 (BCSSnT-20) are investigated. Additions of MgO (xsub.MgO = 1%), Ysub.2Osub.3 (xsub.Y2O3 = 0.25%) and MnCOsub.3 (xsub.MnCO3 = 1%) significantly decreased the mean grain size of BSSnT to 0.4 µm, 0.8 µm and 0.4 µm, respectively. Basub.0.62Casub.0.20Srsub.0.18Snsub.0.065Tisub.0.935Osub.3 (BCSSnT-20) gained a homogeneous fine-grained microstructure with an average grain size of 1.5 µm, leading to a maximum electrocaloric temperature change |ΔTsub.EC| of 0.49 K at 40 °C with a broad peak of |ΔTsub.EC| > 0.33 K in the temperature range from 10 °C to 75 °C under an electric field change of 5 V µmsup.−1. By increasing the sintering temperature of BCSSnT-20 from 1350 °C to 1425 °C, the grain size increased from 1.5 µm to 7.3 µm and the maximum electrocaloric temperature change |ΔTsub.EC| increased from 0.15 K at 35 °C to 0.37 K at 20 °C under an electric field change of 2 V µmsup.−1. Our results show that under all investigated material systems, BCSSnT-20 is the most promising candidate for future application in multilayer ceramic (MLC) components for EC cooling devices.
Mo, TiHsub.2, Al and graphite elemental powders were used as starting materials for the activation reaction sintering process, which was employed to fabricate porous Mosub.2TiAlCsub.2. The alteration ...of phase constitution, volume expansion, porosity, pore size and surface morphology of porous Mosub.2TiAlCsub.2 with sintering temperatures ranging from 700 °C to 1500 °C were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and pore size tester. Both the pore formation mechanism and activation reaction process at each temperature stage were investigated. The experimental results illustrate that the sintered discs of porous Mosub.2TiAlCsub.2 exhibit obvious volume expansion and pore structure change during the sintering process. Before 1300 °C, the volume expansion rate and porosity increase with the increment of temperature. However, with the sintering temperature above 1300 °C, the volume expansion rate and porosity decrease. At the final sintering temperature of 1500 °C, porous Mosub.2TiAlCsub.2 with a volume expansion rate of 35.74%, overall porosity of 47.1%, and uniform pore structure was synthesized. The pore-forming mechanism of porous Mosub.2TiAlCsub.2 is discussed, and the evolution of pressed pores, the removal of molding agents, the decomposition of TiHsub.2, and the Kirkendall effect caused by different diffusion rates of elements in the diffusion reaction are all accountable for the formation of pores.
Cu.sub.2-deltaSe is an eco-friendly thermoelectric candidate owing to Cu ions migration in its high-temperature beta phase, and meanwhile the liquid-like Cu ions deteriorate the stability and ...reliability of materials. Here, Pb.sup.2+ ion was introduced into the Cu.sub.1.98Se lattice to improve the thermoelectric properties and the stability. The Pb-doped Cu.sub.1.98-xPb.sub.xSe (x = 0-0.035) compounds prepared by a facile solvothermal synthesis and microwave sintering. The obtained results reveal that the power factor of the doped samples greatly improved up to 1454 muW m.sup.-1 K.sup.-2 at 800 K, which was about 22.5% higher than that of undoped Cu.sub.1.98Se. In addition, after 3 cycles of testing, the power factor of Cu.sub.1.98Se decreased by 57% at 800 K, and that of Cu.sub.1.965Pb.sub.0.015Se decreased by less than 30%.
A hydrothermal-sintering process for metakaolin-based geopolymers was exploited to immobilize simulated .sup.137CsCl. Pollucite phase is easily formed from geopolymers containing NaOH under 200 â ...hydrothermal conditions. An additional 1200 â-sintering process step not only retained the pollucite phase in the sintered geopolymers, but also increased the density of the microstructures. The leached ion fraction from the geopolymers prepared using the hybrid hydrothermal-sintering process was obviously lower than that of geopolymers prepared using only the 200 â hydrothermal processing steps. Especially, the hybrid hydrothermal-sintering process lowered the Cs.sup.+ volatilization during sintering due to the presence of the pollucite phase precursor in the geopolymers.
Strontium and cobalt-free LaNisub.0.6Fesub.0.4Osub.3–δ is considered one of the most promising electrodes for solid-state electrochemical devices. LaNisub.0.6Fesub.0.4Osub.3–δ has high electrical ...conductivity, a suitable thermal expansion coefficient, satisfactory tolerance to chromium poisoning, and chemical compatibility with zirconia-based electrolytes. The disadvantage of LaNisub.0.6Fesub.0.4Osub.3–δ is its low oxygen-ion conductivity. In order to increase the oxygen-ion conductivity, a complex oxide based on a doped ceria is added to the LaNisub.0.6Fesub.0.4Osub.3–δ. However, this leads to a decrease in the conductivity of the electrode. In this case, a two-layer electrode with a functional composite layer and a collector layer with the addition of sintering additives should be used. In this study, the effect of sintering additives (Bisub.0.75Ysub.0.25Osub.2–δ and CuO) in the collector layer on the performance of LaNisub.0.6Fesub.0.4Osub.3–δ-based highly active electrodes in contact with the most common solid-state membranes (Zrsub.0.84Scsub.0.16Osub.2–δ, Cesub.0.8Smsub.0.2Osub.2–δ, Lasub.0.85Srsub.0.15Gasub.0.85Mgsub.0.15Osub.3–δ, Lasub.10(SiOsub.4)sub.6Osub.3–δ, and BaCesub.0.89Gdsub.0.1Cusub.0.01Osub.3–δ) was investigated. It was shown that LaNisub.0.6Fesub.0.4Osub.3–δ has good chemical compatibility with the abovementioned membranes. The best electrochemical activity (polarization resistance about 0.02 Ohm cmsup.2 at 800 °C) was obtained for the electrode with 5 wt.% Bisub.0.75Ysub.0.25Osub.1.5 and 2 wt.% CuO in the collector layer.
Mg.sub.3Sb.sub.2 compounds were synthesized via low-temperature solid-state reaction (SSR) and ball milling (BM), respectively, followed by spark plasma sintering (SPS) process. The effects of ...possible sintering pressure-induced orientation in the SPS process have been investigated in terms of the microstructure and thermoelectric transport properties. The results indicate that BM technique causes more severe Mg loss than pure SSR method, leading to distinct Sb phase existing in the product after SPS consolidation process. On the contrary, a single phase of Mg.sub.3Sb.sub.2 is easily obtained with the combination of SSR and SPS techniques. Besides, these BM-SPS and SSR-SPS samples exhibit the similar microstructure as well as the same electrical and thermal transport properties parallel or perpendicular to the direction of sintering pressure. The study suggests that SSR method embodies the advantages of both the composition control and the orientation elimination in Mg.sub.3Sb.sub.2 compound as compared to BM method with the specific parameters in the current work. This investigation is quite favorable for this material fabrication and the future application of thermoelectric modules and devices.
Ternesite is synthesized through sintering a mixture of CaCOsub.3, SiOsub.2, and CaSOsub.4 in a molar ratio of 4:2:1. Ternesite has a hydration rate between ye’elimite and belite in an ...aluminum-containing environment, and is considered to be a new material that can be used to enhance the performance of calcium sulphoaluminate cements. This experiment investigated the influence of different particle sizes of SiOsub.2 on ternesite formation. Controlled partial pressure sintering was employed within the temperature range from 1100 °C to 1200 °C, with a 72 h incubation period. The highest purity of ternesite in the samples reached 99.47% (500 nm SiOsub.2 sample). The analysis results from scanning electron microscopy and an energy dispersive spectrometer indicated that the particle size of SiOsub.2 exerted a significant influence on the formation of ternesite. In the preparation of ternesite from 10 μm particle size SiOsub.2, traces of calcium silicate were found in the product. The results of a thermal analysis further demonstrated significant distinctions in the thermal stability of ternesite prepared with SiOsub.2 of different particle sizes. Additionally, the crystallinity of ternesite was influenced by the particle size of SiOsub.2, consequently impacting the hydration performance of ternesite–calcium sulphoaluminate cement.
With the massive penetration of electronics into human life, higher demands are placed on electrical contacts. Among them, the lifetime of electrical contacts and safety are the most concerning. In ...this research, Alsub.2Osub.3-Cu/25Mo5Ta and 0.5Ysub.2Osub.3/Alsub.2Osub.3-Cu/25Mo5Ta composites were prepared by using ball milling and powder metallurgy methods. The two composites were subjected to 10,000 contact opening and closing electrical contact experiments and the arc duration and arc energy were analyzed. The results show that the addition of Ysub.2Osub.3 has a slight effect on the mechanical properties of the Alsub.2Osub.3-Cu/25Mo5Ta composites but has a significant effect on the electrical contact performance. Ysub.2Osub.3 can reduce the mass loss of the electrical contacts during the electrical contact process, which prolongs their service life. The addition of Ysub.2Osub.3 decreased the average arc duration and arc energy of the electrical contact material by 21.53% and 18.02%, respectively, under the experimental conditions of DC 30 V, 10 A. TEM results showed that nanoscale YTaOsub.4 with excellent thermal stability was generated during the sintering process, which has a positive effect on the electrical contact performance of the composites.
Flash sintering of ceramics Biesuz, Mattia; Sglavo, Vincenzo M.
Journal of the European Ceramic Society,
February-March 2019, 2019-02-00, Volume:
39, Issue:
2-3
Journal Article
Peer reviewed
Open access
Flash sintering is a novel densification technology for ceramics, which allows a dramatic reduction of processing time and temperature. It represents a promising sintering route to reduce economic, ...energetic and environmental costs associated to firing. Moreover, it allows to develop peculiar and out-of-equilibrium microstructures.
The flash process is complex and unusual, including different simultaneous physical and chemical phenomena and their understanding, explanation and implementation require an interdisciplinary approach from physics, to chemistry and engineering. In spite of the intensive work of several researchers, there is still a wide debate as for the predominant mechanisms responsible for flash sintering process.
In the present review, the most significant and appealing mechanisms proposed for explaining the “flash” event are analyzed and discussed, with the aim to point out the level of knowledge reached so far and identify, at least, possible shared theories useful to propose future scientific activities and potential technological implementations.
Flash sintering has evolved into touch‐free sintering, where free‐standing workpieces can be sintered without attaching electrodes. Instead, the flash is transmitted from the surface of a reactor ...into the workpiece with superimposition of a magnetic field. Thus, sintering now depends on two independent parameters: the current used to sustain the flash in the reactor and the current flowing through the induction coil. We present a first report on the influence of these two parameters on the quality of the sintered workpiece. The specimens were made from whiteware, consisting of aggregates of ceramic particles interspersed with particles of a glass phase. The results are presented in a map with the reactor current and the induction current as the control variables. Three regimes are identified: insufficient sintering, good sintering, and the formation of defects. The reactor current emerges as an important variable: densification is poor if it is too low, and defects form if it is too high, with high density achieved in the intermediate regime. High induction currents are needed to achieve good sintering. Touch‐free flash sintering has also been shown to sinter and at the same time transform powders of elemental oxides into a single‐phase multicomponent ceramic.
