Showing papers on "Sintering published in 2014"
TL;DR: Field-assisted sintering is a low voltage, direct current (DC) pulsed current activated, pressure-assisted, and synthesis technique, which has been widely applied for materials processing in the recent years as mentioned in this paper.
Abstract: Field-assisted sintering technology/Spark plasma sintering is a low voltage, direct current (DC) pulsed current activated, pressure-assisted sintering, and synthesis technique, which has been widely applied for materials processing in the recent years. After a description of its working principles and historical background, mechanical, thermal, electrical effects in FAST/SPS are presented along with the role of atmosphere. A selection of successful materials development including refractory materials, nanocrystalline functional ceramics, graded, and non-equilibrium materials is then discussed. Finally, technological aspects (advanced tool concepts, temperature measurement, finite element simulations) are covered.
896 citations
TL;DR: Based on the results of the direct visual observations and characteristic microstructure analysis, the authors believe that spark discharge does indeed occur during the SPS process and the high-temperature spark plasma could be generated in the microgaps due to the discharge effect.
293 citations
TL;DR: A perovskite solar cell with a thin TiO2 compact film prepared by thermal oxidation of sputtered Ti film achieved a high efficiency of 15.07% and has a higher short-circuit current density and a higher fill factor.
Abstract: A perovskite solar cell with a thin TiO2 compact film prepared by thermal oxidation of sputtered Ti film achieved a high efficiency of 15.07%. The thin TiO2 film prepared by thermal oxidation is very dense and inhibits the recombination process at the interface. The optimum thickness of the TiO2 compact film prepared by thermal oxidation is thinner than that prepared by spin-coating method. Also, the TiO2 compact film and the TiO2 porous film can be sintered at the same time. This one-step sintering process leads to a lower dark current density, a lower series resistance, and a higher recombination resistance than those of two-step sintering. Therefore, the perovskite solar cell with the TiO2 compact film prepared by thermal oxidation has a higher short-circuit current density and a higher fill factor.
291 citations
TL;DR: In this article, the substitution of Li by Ga, thereby creating Li vacancies and enhancing the Li conductivity, has been investigated and it is shown that the Ga atoms are located in tetrahedral positions promoting the random distribution of lithium over the available sites, hence promoting an increase in the conductivity.
Abstract: Ga-substituted La3Zr2Li7O12 garnet is shown to be a promising Li-ion conducting electrolyte material. The strategy adopted in this study is the substitution of Li by Ga, thereby creating Li vacancies and enhancing the Li conductivity. Solid State Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) measurements have been used to identify the location of the substituted Ga in the structure and its effect on the Li distribution and mobility. In addition MAS NMR was used to follow the effect of protonation due to atmospheric moisture on the sintering behavior of these materials. In particular, it is shown that the Ga atoms are located in tetrahedral positions promoting the random distribution of lithium over the available sites, hence promoting an increase in the conductivity. Control of the sintering conditions by using a dry O2 atmosphere leads to the formation of dense ceramic materials and avoids the degradation process due to the exchange of Li+ by H+ from atmospheric moisture. Electrochemical Impe...
264 citations
TL;DR: In this paper, the thermal stability studies carried out in the temperature range of 400-600°C for duration of 2-10h in Ar atmosphere suggest that these alloys exhibit excellent thermal stability in terms of phases and crystallite size.
203 citations
TL;DR: A method is presented for the production of metal-terminated TMC nanoparticles in the 1-4 nm range with tunable size, composition, and crystal phase that opens an attractive avenue to replace PGMs in high energy density applications such as fuel cells and electrolyzers.
Abstract: Transition-metal carbides (TMCs) exhibit catalytic activities similar to platinum group metals (PGMs), yet TMCs are orders of magnitude more abundant and less expensive. However, current TMC synthesis methods lead to sintering, support degradation, and surface impurity deposition, ultimately precluding their wide-scale use as catalysts. A method is presented for the production of metal-terminated TMC nanoparticles in the 1–4 nm range with tunable size, composition, and crystal phase. Carbon-supported tungsten carbide (WC) and molybdenum tungsten carbide (MoxW1−xC) nanoparticles are highly active and stable electrocatalysts. Specifically, activities and capacitances about 100-fold higher than commercial WC and within an order of magnitude of platinum-based catalysts are achieved for the hydrogen evolution and methanol electrooxidation reactions. This method opens an attractive avenue to replace PGMs in high energy density applications such as fuel cells and electrolyzers.
201 citations
TL;DR: The highly dispersed Ni nanoparticles in mesoporous silica were achieved via using polyol as new delivery conveyors and removable carbon templates to exhibit excellent coking- and sintering-resistance in dry reforming of methane.
194 citations
TL;DR: An equiatomic CoCrFeNiAl high-entropy alloy was synthesized by mechanical alloying, and phase evolutions, microstructure, thermal properties and annealing behaviors were investigated as discussed by the authors.
193 citations
TL;DR: In this paper, the deactivation by coke deposition of Ni and Co catalysts in the steam reforming of ethanol has been studied in a fluidized bed reactor under the following conditions: 500 and 700°C; steam/ethanol molar ratio, 6; space time, 014g catalyst ǫ/g ethanol, partial pressure of ethanol in the feed, 011bar, and time on stream up to 20h The decrease in activity depends mainly on the nature of the coke deposited on the catalysts, as well as on the physical-chemical properties (B
180 citations
TL;DR: In this article, the authors focus on the hydrothermal stability of the heterogeneous catalysts in order of the increasing severity of the reaction medium: superheated steam, liquid water at temperatures below 200 °C, sub-and supercritical liquid water, and supercritical water.
173 citations
TL;DR: In this article, the influence of the composition of the composite starting powder and the SLS parameters on the density and strength of composite SLS parts was investigated, allowing realizing SLS part with a relative density of 36%.
Abstract: Thermally induced phase separation (TIPS) was used to produce spherical polypropylene–zirconia composite powder for selective laser sintering (SLS). The influence of the composition of the composite starting powder and the SLS parameters on the density and strength of the composite SLS parts was investigated, allowing realizing SLS parts with a relative density of 36%. Pressure infiltration (PI) and warm isostatic pressing (WIPing) were applied to increase the green density of the ZrO 2 –PP SLSed parts. Infiltrating the SLS parts with an aqueous 30 vol.% ZrO 2 suspension allowed to increase the sintered density from 32 to 54%. WIPing (135 °C and 64 MPa) of the SLS and SLS/infiltrated complex shape green polymer–ceramic composite parts prior to debinding and sintering allowed raising the sintered density of the 3 mol Y 2 O 3 stabilized ZrO 2 parts to 92 and 85%, respectively.
TL;DR: In this paper, the dependence of density and conductivity of solid electrolytes on sintering under different oxygen partial pressures is discussed, and an effective method to improve the relative density of lithium oxide ceramics is proved.
TL;DR: In this paper, the compatibility of Li-La-(Zr-Ta)-O garnet related lithium ion conductors with all solid state battery (ASSB) systems processed by spark plasma sintering (SPS) is reported.
TL;DR: In this paper, Li7La3Zr2O12 (LLZO) pellets with a grain size of 100-200 μm and a relative density of 94% were prepared by conventional solid-state processing at a sintering temperature of 1100 °C, 130 °C lower than previously reported.
Abstract: Al-substituted Li7La3Zr2O12 (LLZO) pellets with a grain size of 100–200 μm and a relative density of 94% were prepared by conventional solid-state processing at a sintering temperature of 1100 °C, 130 °C lower than previously reported. Morphological features and the presence of impurities were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Femtosecond Laser Induced Breakdown Spectroscopy (LIBS) was used to visualize the distribution of impurities. The results suggest that chemical composition of the powder cover strongly affects morphology and impurity formation, and that particle size control is critical to densification. These properties, in turn, strongly affect total ionic conductivity and interfacial resistance of the sintered pellets.
TL;DR: In this paper, the effect of sintering temperature on the phase compositions, microstructure and Li ionic conductivity is systematically investigated, and the results show that pure cubic phase LLZO can be obtained at a range of temperatures from 1100 to 1180°C for no more than 10min.
TL;DR: In this paper, the effect of DC electric field on sintering, and on the electrical conductivity of undoped rutile, TiO2 (99.99%), has been investigated at fields ranging from 0 V to 1000 V/cm.
Abstract: The effect of DC electric field on sintering, and on the electrical conductivity of undoped rutile, TiO2 (99.99%), has been investigated at fields ranging from 0 V to 1000 V/cm. The experiments were carried out at a constant heating rate of 10°C/min with the furnace temperatures reaching up to 1150°C. The sintering behavior falls into two regimes: at lower fields, up to 150 V/cm, sintering is enhanced, but densification occurs gradually with time (Type A or FAST sintering). At higher fields sintering occurs abruptly, and is accompanied by a highly nonlinear increase in conductivity, which has been called flash sintering (Type B or FLASH sintering). Arrhenius plots of conductivity yield an activation energy of 1.6 eV in Type A and 0.6 eV in Type B behavior; the first is explained as ionic and the second as electronic conductivity. The evolution of grain size under both types of sintering behavior are reported. These results highlight that the dominant mechanism of field-assisted sintering can change with the field strength and temperature. We are in the very early stages of identifying these mechanisms and mapping them in the field, frequency, and temperature space.
TL;DR: In this paper, it was shown that undoped yttria-stabilized zirconia can be sintered nearly instantaneously to nearly full density at furnace temperature of 1133°C under a DC applied field of 500 V/cm.
Abstract: Conventional sintering of undoped Y 2 O 3 requires temperatures above 1400 °C for a few hours. We show that it can be sintered nearly instantaneously to nearly full density at furnace temperature of 1133 °C under a DC applied field of 500 V/cm. At 1000 V/cm sintering occurs at 985 °C. The FLASH event, when sintering occurs abruptly, is preceded by gradually accelerated field-assisted sintering (FAST). This hybrid behaviour differs from earlier work on yttria-stabilized zirconia where all shrinkage occurred in the flash mode. The microstructure of flash-sintered specimens indicated that densification was accompanied by rapid grain growth. The single-phase nature of flash-sintered Y 2 O 3 was confirmed by high-resolution transmission electron microscopy. The non-linear rise in conductivity accompanying the flash led to Joule heating. It is postulated that densification and grain growth were enhanced by accelerated solid-state diffusion, resulting from both Joule heating and the generation of defects under the applied field.
TL;DR: In this article, the authors compared several alternative sintering methods compared to traditional thermal Sintering as high temperature and long process time of thermal sinterings are increasing the costs of inkjet-printing and preventing the use of this technology in large scale manufacturing.
TL;DR: In this paper, the conditions for laser sintering of copper nanoparticle (NP) inks in ambient conditions while avoiding oxidation were studied and determined the regime for stable, low resistivity copper (< × 3 bulk resistivity value) generation in terms of laser irradiance and exposure duration.
Abstract: Copper nanoparticle (NP) inks serve as an attractive potential replacement to silver NP inks in functional printing applications However their tendency to rapidly oxidize has so far limited their wider use In this work we have studied the conditions for laser sintering of Cu-NP inks in ambient conditions while avoiding oxidation We have determined the regime for stable, low-resistivity copper (< × 3 bulk resistivity value) generation in terms of laser irradiance and exposure duration and have indicated the limits on fast processing The role of pre-drying conditions on sintering outcome has also been studied A method, based on spectral reflectivity measurements, was used for non-contact monitoring of the sintering process evolution It also indicates preferred spectral regions for sintering Finally, we illustrated how selective laser sintering can generate high-quality, fine line (<5 µm wide) and dense copper circuits
TL;DR: In this paper, the relationship between the long-term phase transformation and mechanical properties was investigated, which facilitates the simulation and prediction of properties under operating conditions, and a nano/micro hybrid structure was observed as the phase transformation developed.
TL;DR: In this article, a low-cost porous mullite ceramic membrane supports were fabricated from recycling coal fly ash with addition of natural bauxite, and the fabricated membrane supports feature high porosity without mechanical strength degradation.
Abstract: Low-cost porous mullite ceramic membrane supports were fabricated from recycling coal fly ash with addition of natural bauxite. V 2 O 5 and AlF 3 were used as additives to cause the growth of mullite crystals with various morphologies via an in situ reaction sintering. Dynamic sintering, microstructure and phase evolution of the membrane supports were characterized in detail and open porosity, pore size, gas permeation and mechanical properties were determined. It showed the membrane support with 3 wt.% V 2 O 5 and 4 wt.% AlF 3 addition exhibits an open porosity of ∼50%, mechanical strength of 69.8 ± 7.2 MPa, an interlocking microstructure composed of anisotropically grown mullite whiskers with an aspect ratio of 18.2 ± 3.6 at 1300 °C. Addition of more V 2 O 5 lowered the secondary mullitization temperature, resulting in more mullite formation at lower temperatures. The fabricated membrane supports feature high porosity without mechanical strength degradation, possible strengthening mechanism of the mullite whiskers was further discussed.
TL;DR: In this paper, Al-nano MgO composites using A356 aluminum alloy and mgO nanoparticles were fabricated via stir casting and powder metallurgy (PM) methods.
Abstract: In the present work, Al–nano MgO composites using A356 aluminum alloy and MgO nanoparticles (1.5, 2.5, and 5 vol.%) have been fabricated via stir casting and powder metallurgy (PM) methods. Different processing temperatures of 800, 850, and 950 °C for stir casting and 575, 600, and 625 °C for powder metallurgy were considered. Powder metallurgy samples showed more porosity portions compare to the casting samples which results in higher density values of casting composites (close to the theoretical density) compare to the sintering samples. Introduction of MgO nanoparticles to the Al matrix caused increasing of the hardness values which was more considerable in casting samples. The highest hardness value for casting and sintering samples have been obtained at 850 and 625 °C respectively, in 5 vol.% of MgO. Compressive strength values of casting composites were higher than sintered samples which were majorly due to the more homogeneity of Al matrix, less porosity portions, and better wettability of MgO nanoparticles in casting method. The highest compressive strength values for casting and sintered composites have been obtained at 850 and 625 °C, respectively. Scanning electron microscopy images showed higher porosity portions in sintered composites and more agglomeration and aggregation of MgO nanoparticles in casting samples which was due to the fundamental difference of two methods. Generally, the optimum processing temperatures to achieve better mechanical properties were 625 and 850 °C for powder metallurgy and stir-casting, respectively. Moreover, casting method represented more homogeneous data and higher values of mechanical properties compare to the powder metallurgy method.
TL;DR: Sintering zirconia using long cycles and high temperatures will result in reduction of ΔE and CR, and biaxial flexural strength is not affected by changes in the evaluated sintering parameters.
TL;DR: In the present work, the (Bi1-xCex)VO4 ceramics were prepared via a solid-state reaction method and all the ceramic samples could be densified below 900 °C and infrared spectral analysis supported that the dielectric contribution for this system at microwave region could be attributed to the absorptions of structural phonon oscillations.
Abstract: In the present work, the (Bi1–xCex)VO4 (x ≤ 0.6) ceramics were prepared via a solid-state reaction method and all the ceramic samples could be densified below 900 °C. From the X-ray diffraction analysis, it is found that a monoclinic scheelite solid solution can be formed in the range x ≤ 0.10. In the range 0.20 ≤ x ≤ 0.60, a composite region with both monoclinic scheelite and tetragonal zircon solid solutions was formed and the content of the zircon phase increased with the calcined or sintering temperature. The refined lattice parameters of (Bi0.9Ce0.1)VO4 are a = 5.1801(0) A, b = 5.0992(1) A, c = 11.6997(8) A, and γ = 90.346(0)° with the space group I112/b(15). The VO4 tetrahedron contracts with the substitution of Ce for Bi at the A site, and this helps to keep the specific tetrahedron chain stable in the monoclinic structure. The microwave dielectric permittivity was found to decrease linearly from 68 to about 26.6; meanwhile, the quality factor (Qf) value increased from 8000 GHz to around 23900 GHz ...
TL;DR: In this paper, phase pure hydroxyapatite (HA) was successfully prepared using calcined eggshells as a calcium precursor via the wet chemical precipitation method, and the sintering of eggshell-derived HA compacts was carried out in air over a temperature range of 800-1400°C.
TL;DR: In this paper, the sintering behavior of nanocrystalline zinc oxide under external AC electric field between 0 and 160 V/cm was analyzed, where high current densities flow through the sample at high electric fields, entailing a sudden increment of the temperature estimated to several hundreds of K and an exaggerated grain growth.
Abstract: We report the sintering behavior of nanocrystalline zinc oxide under external AC electric field between 0 and 160 V/cm. In situ acquisition of density by means of laser dilatometry, evaluation of specimen temperature, real-time measurement of electric field and current help analyze this peculiar behavior. Field strength and blocking electrodes significantly affect densification and microstructure, which was evaluated in the vicinity of the flash event and for the fully sintered material. High current densities flow through the sample at high electric fields, entailing a sudden increment of the temperature estimated to several hundreds of K and an exaggerated grain growth. In contrast, low current density flows through the sample at lower electric fields, which guarantees normal grain growth and highest final density. Macroscopic photoluminescence measurements give insights into the development of the defect structure. Electric fields are expected to enhance defect mobility, explaining the high densification rates observed during the sintering process.
TL;DR: In this article, the authors compared the effects of different sintering methods on the microstructure and anti-ferroelectric properties of lead-free 0.5 NbO 3 ternary system ceramics.
TL;DR: In this paper, the porosity of boron carbide was measured and the effect of porosity on mechanical properties (hardness, fracture toughness, and elastic modulus) was investigated.
Abstract: The densification behavior of boron carbide without sintering additives is reported for temperatures in the range of 1100 °C to 1800 °C by spark plasma sintering (SPS) technique together with the sintering parameters (Holding Time and Pulsed DC). The influence of porosity on mechanical properties (hardness, fracture toughness and elastic modulus) of boron carbide prepared by SPS is measured. Pulsed DC current is found to play a dominant role in the densification of boron carbide and in achieving near theoretical density at lower sintering temperature compared to conventional sintering techniques. Hardness, fracture toughness and elastic modulus of fully dense B 4 C are measured as 37.2 GPa, 2.8 MPa.m 1/2 and 570 GPa respectively. Microstructural analysis indicates the presence of deformation twins in boron carbide grains.
TL;DR: It is demonstrated by means of combining noninvasive in situ indirect nanoplasmonic sensing and ex situ scanning transmission electron microscopy that monomodal size-selected platinum cluster catalysts on different supports exhibit remarkable intrinsic sintering resistance even under reaction conditions.
Abstract: Employing rationally designed model systems with precise atom-by-atom particle size control, we demonstrate by means of combining noninvasive in situ indirect nanoplasmonic sensing and ex situ scanning transmission electron microscopy that monomodal size-selected platinum cluster catalysts on different supports exhibit remarkable intrinsic sintering resistance even under reaction conditions. The observed stability is related to suppression of Ostwald ripening by elimination of its main driving force via size-selection. This study thus constitutes a general blueprint for the rational design of sintering resistant catalyst systems and for efficient experimental strategies to determine sintering mechanisms. Moreover, this is the first systematic experimental investigation of sintering processes in nanoparticle systems with an initially perfectly monomodal size distribution under ambient conditions.
TL;DR: In intense pulsed light (IPL) sintering of inkjet-printed CuO layers on a primer-coated porous PET substrate to convert the electrically insulating CuO into conductive Cu, conductive layers are obtained in less than 1 s after the printing process.
Abstract: We demonstrate intense pulsed light (IPL) sintering of inkjet-printed CuO layers on a primer-coated porous PET substrate to convert the electrically insulating CuO into conductive Cu. With this approach, conductive layers are obtained in less than 1 s after the printing process. The IPL sintering was performed for high productivity with minimum duration and repetition of IPL irradiation to evaluate the effect of pulse number and energy output on the conductivity and morphology of the sintered Cu layers. Depending on the energy output, sheet resistances were measured as 0.355, 0.131, and 0.121 Ω·□–1 by exposure energy of 5.48 (single pulse), 7.03 (double pulse), and 7.48 J·cm–2 (triple pulse), respectively. In contrast, an excessive energy with relatively short pulse duration causes a delamination of the Cu layer. The lowest resistivity of about 55.4 nΩ·m (corresponds to about 30% conductivity of bulk Cu) was obtained by an IPL sintering process of 0.26 s after the printing, which was composed of 2 ms trip...