Showing papers on "Sintering published in 2010"
TL;DR: Microwave sintering has emerged as a new method for sinterding a variety of materials that has shown significant advantages against conventional sinterging procedures as mentioned in this paper. But microwave sinterings are not suitable for all materials.
911 citations
TL;DR: In this paper, it was shown that yttrium-stabilized zirconia can be sintered in a few seconds at ∼850°C to full density, starting from a green density of 0.5, by the application of a dc electrical field.
Abstract: We show that yttrium-stabilized zirconia can be sintered in a few seconds at ∼850°C to full density, starting from a green density of 0.5, by the application of a dc electrical field (nominally, several hours at 1450°C are needed to complete the sintering process). This finding is explained by the local Joule heating at grain boundaries, which, on the one hand, promotes grain-boundary diffusion (a kinetic effect), while at the same time restricts grain growth (a thermodynamic effect). The smaller grain size and the higher temperature at grain boundaries can then act synergistically to enhance the rate of sintering. These results have a bearing in explaining the widespread spark plasma and microwave-assisted techniques for enhanced sintering.
751 citations
TL;DR: In this paper, the main causes of catalyst deactivation in cobalt-based Fischer-Tropsch synthesis are poisoning, reoxidation of cobalt active sites, formation of surface carbon species, carbidization, surface reconstruction, sintering of crystallites, metal support solid state reactions and attrition.
514 citations
TL;DR: It was discovered that silver nanoparticles behave as soft particles when they come into contact with oppositely charged polyelectrolytes and undergo a spontaneous coalescence process, even without heating, and using this finding in printing conductive patterns, enables achieving high conductivities even at room temperature.
Abstract: A new approach to achieve coalescence and sintering of metallic nanoparticles at room temperature is presented. It was discovered that silver nanoparticles behave as soft particles when they come into contact with oppositely charged polyelectrolytes and undergo a spontaneous coalescence process, even without heating. Utilizing this finding in printing conductive patterns, which are composed of silver nanoparticles, enables achieving high conductivities even at room temperature. Due to the sintering of nanoparticles at room temperature, the formation of conductive patterns on plastic substrates and even on paper is made possible. The resulting high conductivity, 20% of that for bulk silver, enabled fabrication of various devices as demonstrated by inkjet printing of a plastic electroluminescent device.
499 citations
TL;DR: Microwave sintering has emerged as a new method for sinterding a variety of materials that has shown significant advantages against conventional sinterging procedures as discussed by the authors. But microwave sinterings are not suitable for all materials.
Abstract: Microwave sintering has emerged in recent years as a new method for sintering a variety of materials that has shown significant advantages against conventional sintering procedures. This review article first provides a summary of fundamental theoretical aspects of microwave and microwave hybrid sintering, and then advantages of microwave sintering against conventional methods are described. At the end, some applications of microwave sintering are mentioned which so far have manifested the advantages of this novel method.
325 citations
TL;DR: In this article, a summary of the development of high-temperature silicon nitride (T>1200°C) is provided, where the influence of various sintering additive systems is evaluated with focus on the high temperature potential of the resulting materials.
Abstract: In this paper, a summary of the development of high-temperature silicon nitride (T>1200°C) is provided. The high-temperature capacity of various advanced commercial silicon nitrides and materials under development was analyzed in comparison with a silicon nitride without sintering additives produced by hot isostatic pressing. Based on this model Si 3 N 4 composed of only crystalline Si 3 N 4 grains and amorphous silica in the grain boundaries the influence of various sintering additive systems will be evaluated with focus on the high-temperature potential of the resulting materials. The specific design of the amorphous grain-boundary films is the key factor determining the properties at elevated temperatures. Advanced Si 3 N 4 with Lu 2 O 3 or Sc 2 O 3 as sintering additive are characterized by a superior elevated temperature resistance caused by effective crystallization of the grain-boundary phase. Nearly clean amorphous films between the Si 3 N 4 grains comparable to that of Si 3 N 4 without sintering additives were found to be the reason of this behavior. Benefit in the long-term stability of Si 3 N 4 at elevated temperatures was observed in composites with SiC and M o Si 2 caused by a modified oxidation mechanism. The insufficient corrosion stability in hot gas environments at elevated temperatures was found to be the main problem of Si 3 N 4 for application in advanced gas turbines. Progress has been achieved in the development of potential material systems for environmental barrier coatings (EBC) for Si 3 N 4 ; however, the long-term stability of the whole system EBC-base Si 3 N 4 has to be subject of comprehensive future studies. Besides the superior high-temperature properties, the whole application process from cost-effective industrial production, reliability and failure probability, industrial handling up to specific conditions during the application have to be focused in order to bring advanced Si 3 N 4 currently available to industrial application.
323 citations
TL;DR: In this article, the authors achieved robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag-Cu interfaces.
Abstract: We achieve robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The paste is prepared by simply condensing Ag nanoparticle (NP) solution via centrifuging. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag–Cu interfaces. Both experiment and Monte Carlo simulation confirm that the melting point of joint clusters increases during sintering. This creates improved bonds for use at an elevated operating temperature using Ag NPs.
283 citations
TL;DR: In this article, the effect of various experimental conditions on the crystal structure, relative density, morphology, and total conductivity of the as-prepared BZY20 ceramic pellets were investigated in detail.
234 citations
TL;DR: In this article, a particle-compositing method was used for the first time to disperse different contents of multi-walled carbon nanotubes (CNTs) in micron sized copper powders, which were subsequently consolidated into CNT/Cu composites by spark plasma sintering (SPS).
228 citations
TL;DR: Sintering occurs when packed particles are heated to a temperature where there is sufficient atomic motion to grow bonds between the particles as mentioned in this paper, and the conditions that induce sintering depend on the material, its melting temperature, particle size, and a host of processing variables.
Abstract: Sintering occurs when packed particles are heated to a temperature where there is sufficient atomic motion to grow bonds between the particles The conditions that induce sintering depend on the material, its melting temperature, particle size, and a host of processing variables It is common for sintering to produce a dimensional change, typically shrinkage, where the powder compact densifies, leading to significant strengthening Microstructure coarsening is inherent to sintering, most evident as grain growth, but it is common for pore growth to occur as density increases During coarsening, the grain structure converges to a self-similar character seen in both the grain shape distribution and grain size distribution Coarsening behavior during sintering conforms to classic grain growth kinetics, modified to reflect the evolving microstructure These modifications involve the grain boundary coverage due to pores, liquid films, or second phases and the altered grain boundary mobility due to these phases
226 citations
TL;DR: In this article, a low-temperature sintering technique enabled by a nanoscale silver paste has been developed for attaching large-area (>100 mm2) semiconductor chips.
Abstract: A low-temperature sintering technique enabled by a nanoscale silver paste has been developed for attaching large-area (>100 mm2) semiconductor chips. This development addresses the need of power device or module manufacturers who face the challenge of replacing lead-based or lead-free solders for high-temperature applications. The solder-reflow technique for attaching large chips in power electronics poses serious concern on reliability at higher junction temperatures above 125°C. Unlike the soldering process that relies on melting and solidification of solder alloys, the low-temperature sintering technique forms the joints by solid-state atomic diffusion at processing temperatures below 275°C with the sintered joints having the melting temperature of silver at 961°C. Recently, we showed that a nanoscale silver paste could be used to bond small chips at temperatures similar to soldering temperatures without any externally applied pressure. In this paper, we extend the use of the nanomaterial to attach large chips by introducing a low pressure up to 5 MPa during the densification stage. Attachment of large chips to substrates with silver, gold, and copper metallization is demonstrated. Analyses of the sintered joints by scanning acoustic imaging and electron microscopy showed that the attachment layer had a uniform microstructure with micrometer-sized porosity with the potential for high reliability under high-temperature applications.
TL;DR: In this article, the A-site non-stoichiometry in Ba1−xZr0.8Y0.2O3−δ, a candidate electrolyte material for fuel cell and other electrochemical applications, was investigated.
Abstract: Recent literature indicates that cation non-stoichiometry in proton-conducting perovskite oxides (ABO3) can strongly influence their transport properties. Here we have investigated A-site non-stoichiometry in Ba1−xZr0.8Y0.2O3−δ, a candidate electrolyte material for fuel cell and other electrochemical applications. Synthesis is performed using a chemical solution approach in which the barium deficiency is precisely controlled. The perovskite phase is tolerant to barium deficiency up to x = 0.06 as revealed by X-ray diffraction analysis, but accommodates the non-stoichiometry by incorporation of yttrium on the A-site. The dopant partitioning can explain the decrease in cell constant with increasing x, the decrease in proton conductivity (the latter as measured by a.c. impedance spectroscopy under humidified atmosphere), and the decrease in grain size in the sintered compacts. Within the single-phase region barium deficiency also has a detrimental impact on grain boundary conductivity, as a result both of the decreased grain size, leading to a higher number density of grain boundaries and of an increased per boundary resistivity. At higher values of x, a two phase system is observed, with yttria appearing as the predominant secondary phase and the barium zirconate reverting to an undoped composition. From the relative concentrations of the observed phases and their lattice constants, the ternary phase behavior at 1600 °C (the sintering temperature) is generated. Both the bulk and grain boundary conductivities are sharply lower in the two-phase system than in the single phase compositions. The control over processing conditions demonstrates that it is possible to reproducibly prepare large-grained, stoichiometric BaZr0.8Y0.2O3−δ with a total conductivity of 1 × 10−2 Scm−1 at 450 °C, while revealing the mechanisms by which barium deficiency degrades properties.
TL;DR: In this paper, the authors investigated the role of carbon nanotube (CNT) reinforced hydroxyapatite (HA) composite synthesized using spark plasma sintering and found that CNTs play a role in grain boundary pinning and are responsible for the improved densification and retention of nanostructure throughout the thickness of sintered pellet.
TL;DR: In this article, a series of compounds in the Li2O-Bi2O3-MoO3 ternary system were investigated with regard to the preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver (Ag) and aluminum (Al) electrodes.
Abstract: A series of compounds in the Li2O–Bi2O3–MoO3 ternary system were investigated with regard to the preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver (Ag) and aluminum (Al) electrodes. All the ceramics in this work have sintering temperatures lower than 750°C. The sintering behaviors and microwave dielectric properties of three single phases Li2MoO4, (Li0.5Bi0.5)MoO4, and Li8Bi2Mo7O28 bulk ceramics, were of particular focus in this investigation. The Li2MoO4 ceramic can be sintered to a high density at 540°C/2 h with a relative permittivity ∼5.5, a Q×f value of 46 000 GHz, and a temperature coefficient of resonant frequency (TCF) of ∼−160 ppm/°C. The (Li0.5Bi0.5)MoO4 ceramic has a scheelite structure and the largest relative permittivity of 44.4 among the ceramics studied in this work with a sintering temperature around 560°C, a Q×f value of 3200 GHz, and a large positive TCF of ∼+245 ppm/°C. The Li8Bi2Mo7O28 ceramic could be sintered at 540°C and has a relative permittivity of 13.6, a Q×f value of 8000 GHz, and a small negative TCF value of ∼−59 ppm/°C. From the X-ray diffraction analysis of cofired ceramics, the Li2MoO4 ceramic does not react with either Ag or Al powders. The Li8Bi2Mo7O28 ceramic reacts with Ag but not with Al at its densification temperature. The (Li0.5Bi0.5)MoO4 ceramic was found to strongly react with Ag powder and to a limited extent with Al powders. From this study, the Li2O–Bi2O3–MoO3 ternary system has a number of attractive new materials with low sintering temperatures, high-performing microwave dielectric properties, chemical compatibility with both Ag and Al metal electrodes, nontoxicity, and low-cost constituents. All these materials can be included in the new field of ultra-low-temperature cofiring dielectrics for multilayer applications.
TL;DR: In this article, a crack-free Cu film was obtained after sintering and the grain size reached 500nm upon grain growth, however, only agglomeration of NPs was observed at the bottom of the film, and the resistance was 0.88 Ω on average and the patterns were electrically tested by light-emitting diodes.
TL;DR: Tong et al. as mentioned in this paper investigated the mechanisms for the rapid formation of the cubic perovskite phase of BZY, pellet densification, and grain growth during SSRS synthesis using a suite of experimental techniques.
Abstract: A cost-effective solid-state reactive sintering (SSRS) method has recently been developed to synthesize high quality, fully dense, and large-grained yttrium-doped barium zirconate (BZY) ceramic pellets from the raw materials of BaCO3, ZrO2, Y2O3, and NiO, resulting in total proton conductivities as high as 3.3 × 10−2 S·cm−1at 600 °C under a wet argon atmosphere [J. Tong et al., Solid State Ionics, 2010, 181, 496]. In the present work, the mechanisms for the rapid formation of the cubic perovskite phase of BZY, pellet densification, and grain growth during SSRS synthesis are investigated in detail using a suite of experimental techniques. The pre-reaction addition of NiO to the precursor powders is confirmed to accelerate the formation of the cubic perovksite BZYphase. The rapid and full densification of NiO-modified pellets at relatively low temperature (1350 °C) is ascribed to the formation of the impure phase BaY2NiO5 and its subsequent role as a sintering aid. The dramatic further grain growth after densification is facilitated by the partial decomposition of the BaY2NiO5 (which is located primarily at grain boundaries) and its incorporation into the cubic perovskite structure of BZY.
TL;DR: In this paper, a chemical precursor mediated process was used to form catalyst nanoparticles (NPs) with an extremely high density (1014 to 1016 m−2), controllable size distribution (3−20 nm), and good thermal stability at high temperature (900 °C).
Abstract: A chemical precursor mediated process was used to form catalyst nanoparticles (NPs) with an extremely high density (1014 to 1016 m−2), controllable size distribution (3−20 nm), and good thermal stability at high temperature (900 °C). This used metal cations deposited in layered double hydroxides (LDHs) to give metal catalyst NPs by reduction. The key was that the LDHs had their intercalated anions selected and exchanged by guest−host chemistry to prevent sintering of the metal NPs, and there was minimal sintering even at 900 °C. Metal NPs on MoO42− intercalated Fe/Mg/Al LDH flakes were successfully used as the catalyst for the double helix growth of single-walled carbon nanotube arrays. The process provides a general method to fabricate thermally stable metal NPs catalysts with the desired size and density for catalysis and materials science.
TL;DR: In order to improve the fracture toughness, SiC whiskers or SiC chopped fibers were added to a ZrB 2 matrix in volumetric fraction of 10 and 20 vol.%. The composites were hot-pressed between 1650 and 1730°C and their final relative densities were higher than 95 as mentioned in this paper.
Abstract: In order to improve the fracture toughness, SiC whiskers or SiC chopped fibers were added to a ZrB 2 matrix in volumetric fraction of 10 and 20 vol.%. The composites were hot-pressed between 1650 and 1730 °C and their final relative densities were higher than 95%. Even at the lowest sintering temperature, the whiskers showed an evident degradation. On the other hand, the fibers maintained their initial shape and a strong interface formed between matrix and reinforcement. The fracture toughness of the composites increased from 30 to 50% compared to the baseline material, with the fibers showing a slightly higher toughening effect. In the whiskers-reinforced composites, the room-temperature strength increased when 10 vol.% whiskers were added. In the fibers-reinforced composites, the room-temperature strength decreased regardless the amount of fibers added. The high-temperature strength of the composites was higher than that of the baseline material for both types of reinforcement.
TL;DR: In this article, the critical processing temperature required to obtain very low resistivity of polymer nanocomposites has been identified for Ag nanoparticles with different surface properties, and the results indicate that the decomposition temperature of surface residues played a key role in the sintering of Ag particles and thus the electrical resistivity.
Abstract: Highly conductive polymer nanocomposites with very low resistivity (4.8 × 10−5 Ω cm) were prepared by thermal sintering of silver nanoparticles with silver flakes dispersed in a polymer matrix at 180 °C. By comparative studies of thermal behavior of Ag nanoparticles, the critical processing temperature required to obtain very low resistivity of polymer nanocomposites has been identified for Ag nanoparticles with different surface properties. The results indicate that the decomposition temperature of surface residues on Ag nanoparticles plays a key role in the sintering of Ag nanoparticles and thus the electrical resistivity of the polymer nanocomposites. Electrical measurements of the polymer nanocomposites showed that morphological changes induced by sintering of Ag nanoparticle with Ag flakes considerably contribute to the reduction of the contact resistance between conductive fillers, increasing the nanocomposite conductivity.
01 Dec 2010
TL;DR: In this article, the authors show that even 5 s of sintering, a temperature of 225 °C, or a pressure as low as 2 MPa is sufficient to generate bonds comparable to solder and high pressure sinter joints if the remaining parameters (p, t and T, respectively) are set correctly.
Abstract: For decades soldering has been the technology of choice in die bonding. However, due to worldwide health protection regulations, the most common solder alloys, which contain lead, have been banned. Furthermore, standard solders cannot fulfil the reliability requirements of future power electronic devices. New interconnection technologies have to be developed. One of them is pressure sintering (p=30‥50 MPa) of silver flakes below 300 °C. It forms a strong, highly electrically and thermally conductive bond. In order to lower the level of pressure, silver nanoparticles can be used. Shear tests have shown that even 5 s of sintering, a temperature of 225 °C, or a pressure as low as 2 MPa is sufficient to generate bonds comparable to solder and high pressure sinter joints if the remaining parameters (p, t and T, respectively) are set correctly. However, strength is only a necessary criterion as aging comes into play. Therefore, reliability tests using thermal cycling and power cycling were run. These returned superior reliability of the sintered samples. 160 million of the power cycles between +45 and +175 °C run in this work can be extrapolated using a Coffin-Manson model. Solder joints failed at about 40,000 cycles.
Journal Article•
TL;DR: The conventional cold compaction-and-sinter powder metallurgy (PM) approach offers an efficient solution to the near-net shape or preform fabrication of titanium and its alloys for cost reduction and improved chemical homogeneity and refined microstructures as discussed by the authors.
Abstract: The conventional cold-compaction-and-sinter powder metallurgy (PM) approach offers an efficient solution to the near-net shape or preform fabrication of titanium and its alloys for cost reduction and improved chemical homogeneity and refined microstructures. The methods for compacting titanium powder are similar to those used for other ductile powders. The high-purity titanium in the most ductile state is similar to annealed copper in terms of elastic modulus, hardness, elongation, and ultimate tensile strength. The properties of titanium are sensitive to the impurity level, in particular to nitrogen, oxygen, carbon, and iron. Hardness is a convenient measure of the quality of a titanium sponge product. Dilatometric studies of the sintering of titanium-nickel alloys show similar observations and confirm that oxide films on titanium powder surfaces do not need to be reduced by the atmosphere or disrupted by a chemical additive.
TL;DR: In this article, a single-phase multiferroic BiFeO3 powder was prepared by improved solid-state synthesis, and dense BiO3 ceramics were fabricated by a spark plasma sintering (SPS) process.
Abstract: Single-phase multiferroic BiFeO3 powder was prepared by improved solid-state synthesis, and dense BiFeO3 ceramics were fabricated by a spark plasma sintering (SPS) process. The sintering temperature of SPS ranged from 650 to 800 °C under 50 MPa. It is found that the sample is not only single phased but also of high density when sintered at 650 °C. The dielectric constant and loss of the samples were tested between 100 Hz and 20 MHz at several temperatures. Oxygen and vacuum annealing conditions impact the dielectric behaviour of the BiFeO3 ceramics prepared by the SPS technique obviously. The piezoelectric coefficient d33 of the sample annealed in vacuum is 4.2 pC N−1 at room temperature.
TL;DR: The surface diffusivity is determined from measurements obtained from STEM images acquired during the initial stages of sintering and is in reasonable agreement with measurements made on the surface of nanoparticles, using other techniques.
Abstract: An aberration-corrected JEOL 2200FS scanning-transmission electron microscope (STEM), equipped with a high-angle annular dark-field detector (HAADF), is used to monitor the coalescence and sintering of Pt nanoparticles with an average diameter of 2.8 nm. This in situ STEM capability is combined with an analysis methodology that together allows direct measurements of mass transport phenomena that are important in understanding how particle size influences coalescence and sintering at the nanoscale. To demonstrate the feasibility of this methodology, the surface diffusivity is determined from measurements obtained from STEM images acquired during the initial stages of sintering. The measured surface diffusivities are in reasonable agreement with measurements made on the surface of nanoparticles, using other techniques. In addition, the grain boundary mobility is determined from measurements made during the latter stages of sintering.
TL;DR: In this paper, the authors developed a low energy consuming and green process for the catalytic oxidation of HCl to Cl2, especially when compared with the electrolysis process, by using ultra-fine RuO2 crystallites that cover the surface of the TiO2 primary particles with strong interaction.
Abstract: Sumitomo Chemical has developed a low energy consuming and green process for the catalytic oxidation of HCl to Cl2, especially when compared with the electrolysis process. The RuO2/rutile-TiO2 catalyst has high catalytic activity and thermal stability due to ultra-fine RuO2 crystallites that cover the surface of the TiO2 primary particles with strong interaction. In addition, the silica modified RuO2/rutile-TiO2 catalyst shows higher thermal stability by preventing the RuO2 sintering due to using dispersed SiO2 particles. With these catalysts, high reaction rates required for industrial applications are achieved, even at low temperatures.
TL;DR: In this paper, a dc electric field of 20 V/cm shifts the densification curve to a lower temperature in constant heating rate experiments with yttria-stabilized tetragonal zirconia powder (3Y-TZP).
Abstract: We show, for the first time, that a dc electric field of 20 V/cm shifts the densification curve to a lower temperature in constant heating rate experiments with yttria-stabilized tetragonal zirconia powder (3Y-TZP). The enhanced sintering rate is ascribed, at least in part, to the reduced rate of grain growth under the applied field, consistent with earlier experiments on the influence of such fields on grain size in superplastic deformation and isothermal grain growth in zirconia polycrystals.
01 Jan 2010
TL;DR: In this paper, the fundamentals of grain growth and densification, and related microstructural evolution during liquid phase sintering (LPS), are described and their theoretical treatments are described.
Abstract: This chapter describes the fundamentals of grain growth and densification, and related microstructural evolution during liquid phase sintering (LPS). Two different types of grain growth behavior, stationary (conventionally called normal) and nonstationary in terms of the relative grain size distribution, and their theoretical treatments are described. Particular emphasis is placed on the prediction of nonstationary grain growth with the suggestion of general principles of microstructural evolution during LPS. Fundamental differences between the two densification mechanisms, contact flattening and pore filling, are described and their validities discussed. Model calculations of densification kinetics by pore filling theory are also provided.
TL;DR: Experimental results and theoretical analyses revealed that the interfacial thermal resistance between the CNTs and the Cu matrix plays a crucial role in determining the thermal conductivity of bulk composites, and only small interfacialthermal resistance can induce a significant degradation in thermal Conductivity for CNT/Cu composites.
Abstract: Carbon nanotube–copper (CNT/Cu) composites have been successfully synthesized by means of a novel particles-compositing process followed by spark plasma sintering (SPS) technique. The thermal conductivity of the composites was measured by a laser flash technique and theoretical analyzed using an effective medium approach. The experimental results showed that the thermal conductivity unusually decreased after the incorporation of CNTs. Theoretical analyses revealed that the interfacial thermal resistance between the CNTs and the Cu matrix plays a crucial role in determining the thermal conductivity of bulk composites, and only small interfacial thermal resistance can induce a significant degradation in thermal conductivity for CNT/Cu composites. The influence of sintering condition on the thermal conductivity depended on the combined effects of multiple factors, i.e. porosity, CNTs distribution and CNT kinks or twists. The composites sintered at 600°C for 5 min under 50 MPa showed the maximum thermal conductivity. CNT/Cu composites are considered to be a promising material for thermal management applications.
TL;DR: The noncontact printable polymer nanocomposites with superior electrical conductivity and fast processing are promising for the future of printed electronics.
Abstract: We show the fast preparation of printable highly conductive polymer nanocomposites for future low-cost electronics. Highly conductive polymer nanocomposites, consisting of an epoxy resin, silver flakes, and incorporated silver nanoparticles, have been prepared by fast sintering between silver flakes and the incorporated silver nanoparticles. The fast sintering is attributed to: 1) the thermal decomposition of silver carboxylate—which is present on the surface of the incorporated silver flakes—to form in situ highly reactive silver nanoparticles; 2) the surface activation of the incorporated silver nanoparticles by the removal of surface residues. As a result, polymer nanocomposites prepared at 230 °C for 5 min, at 260 °C for 10 min, and using a typical lead-free solder reflow process show electrical resistivities of 8.1 × 10−5, 6.0 × 10−6, and 6.3 × 10−5 Ω cm, respectively. The correlation between the rheological properties of the adhesive paste and the noncontact printing process has been discussed. With...
TL;DR: In this paper, a CNT/Al 2 O 3 composites can be densified by pressureless sintering without damage to the CNTs, achieving relative densities as high as 99%.
Abstract: Alumina ceramics reinforced with 1, 3, or 5 vol.% multi-walled carbon nanotubes (CNTs) were densified by pressureless sintering. Commercial CNTs were purified by acid treatment and then dispersed in water at pH 12. The dispersed CNTs were mixed with Al 2 O 3 powder, which was also dispersed in water at pH 12. The mixture was freeze dried to prevent segregation by differential sedimentation during solvent evaporation. Cylindrical pellets were formed by uniaxial pressing and then densified by heating in flowing argon. The resulting pellets had relative densities as high as ∼99% after sintering at 1500 °C for 2 h. Higher temperatures or longer times resulted in lower densities and weight loss due to degradation of the CNTs by reaction with the Al 2 O 3 . A CNT/Al 2 O 3 composite containing 1 vol.% CNT had a higher flexure strength (∼540 MPa) than pure Al 2 O 3 densified under similar conditions (∼400 MPa). Improved fracture toughness of CNT–Al 2 O 3 composites was attributed to CNT pullout. This study has shown, for the first time, that CNT/Al 2 O 3 composites can be densified by pressureless sintering without damage to the CNTs.
TL;DR: In this paper, a composite electrolyte containing a Li/Na carbonate eutectic and a doped ceria phase is employed in a direct carbon fuel cell (DCFC).