Increasing Sintering Temperature Research Articles

Enhancement of the Optical properties of Mg0.6 Cu0.4 FeCrO4 spinel ferrite via heat treatment

We conducted a study to analyze the structural, morphological, and optical properties of Mg0.6Cu0.4FeCrO4 spinel ferrite samples synthesized by the sol-gel method and sintered at two different temperatures, 900 °C and 1100 °C. The infrared spectrum analysis revealed the presence of only the tetrahedral stretch band (νA), which had frequencies of 585 cm−1 for 900 °C and 586 cm−1 for 1100 °C. The bandgap energy and Urbach energy values decrease with increasing sintering temperature. The bandgap energy decreases from 1.20 eV to 1.06 eV, while the Urbach energy values decrease from 1.26 eV to 1.11 eV. Emphasis has been placed on the analysis of key aspects such as refractive index(n), optical conductivity (σopt), extinction coefficient (k), penetration depth (ẟ), dielectric tangent loss, Q-factor, and dielectric constant. Optical studies have provided confirmation that Mg0.6Cu0.4FeCrO4 spinel ferrites exhibit properties suitable for optoelectronics applications.

Structure characteristics and microwave/terahertz dielectric response of low-permittivity (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr3(MoO4)9 high-entropy ceramics

Microwave dielectric ceramics play a vital role in wireless communication systems. However, it is a great challenge to obtain ideal performances of single-phase ceramics. In this work, (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr3(MoO4)9 (abbreviated as L5ZMO) high-entropy ceramics were successfully prepared by the solid-state reaction method, the pure trigonal L5ZMO structure can be synthesized in the mixture calcined at 700 °C. Rietveld refinement based on XRD data reveals that lattice parameters of L5ZMO ceramics are affected by the radius of the five rare earth elements, which indicates that the rare earth elements have been solubilized and randomly distributed in the Ln-site. The relative density illustrates a strong dependence on sintering temperature, which gradually increases with increasing sintering temperature. Based on the analysis of bond characteristics, the Mo–O bond exhibits a vital effect on the dielectric properties of L5ZMO ceramics. Besides, the infrared reflection spectrum and terahertz time-domain spectroscopy analysis show that ionic polarization is the dominant polarization in the microwave/terahertz bands. Meanwhile, the tan δ can be further reduced by optimizing process parameters. Notably, the L5ZMO high-entropy ceramics sintered at 750 °C exhibit outstanding dielectric properties of εr = 10.46, Q·f = 59,713 GHz, and τf = −21.94 ppm/°C, indicating that the high-entropy design optimizes τf (−38.8 ppm/°C) of the simple La2Zr3(MoO4)9 ceramics. The attempt provides theoretical guidance for the application of high-entropy design concepts in microwave/terahertz bands.

Optimalisasi Temperatur Sintering Pada Sintered Body Hidroksiapatit Dengan Penambahan Silika Sebagai Material Penguat

Sintered body hydroxyapatite (HA) in the form of pellets has been made by adding silica as a reinforcing material (ratio 60:40 wt.%) by varying the sintering temperature. HA and silica were subjected to a dry mixing process for 2 h, then a wet mixing process was carried out for 2 h with the addition of PVA and alcohol as a binder. The mixing process uses a rotary drum with the addition of zirconia balls with the aim of making the mixture more homogeneous. After the mixing process, the samples were dried for 48 h to remove the alcohol contained. The green body was made using the uniaxial pressing method at a pressure of 100 MPa and held for 3 minutes. The sintering process is carried out variously at temperatures of 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, and 1400°C. with a heating rate of 5ºC/minute and holding time of 4 h. Next, the temperature was lowered to 300ºC with a cooling rate of 5ºC/minute. The results showed that linear shrinkage increased significantly (weight shrinkage increased 12.83% - 25.08% and diameter shrinkage increased 3.26% - 23.21%). The results of the relative density calculation show that there is a significant increase with each variation in sintering temperature, where the increase occurs from 44.4% - 85.6%. The compressive strength value also shows an increase with increasing sintering temperature, namely from 21.2 MPa at 800 oC to 65.9 MPa at 1300 oC. Meanwhile, at a sintering temperature of 1400°C, compressive strength values decreased and oxidation occurred as evidenced by color changes. It can be concluded that the optimization of the sintering process occurs at a temperature of 1300 oC which is proven by the highest compressive strength value and no oxidation occurs.

Prospects for improving the mechanical properties of an aluminum-zirconium composite by adding ultrafine Al2O3 powder synthesized by nitrate combustion

The paper presents the results of studying the mechanisms of sintering and properties of an Al2O3–ZrO2 composite doped with ultrafine Al2O3 powder (UFP) synthesized by burning nitrates. The material is sintered at temperatures ranging between 1450 and 1550 °C with the analysis of its physical and mechanical properties. It is shown that, as the sintering temperature and Al2O3 UFP concentration increase, linear shrinkage, microhardness, and strength naturally grow (the maximum values at 1550 °С are 27.8%, 19 GPa, and 357 MPa, respectively). The introduction of the Al2O3 UFP into the composite makes it possible to achieve an apparent density of 4.20 g/cm3 even at a sintering temperature of 1550 °С.

Endodontic Radiopacifying Application of Barium Titanate Prepared through a Combination of Mechanical Milling and Heat Treatment

Mineral trioxide aggregates (MTA) are commonly used as endodontic filling materials but suffer from a long setting time and tooth discoloration. In the present study, the feasibility of using barium titanate (BTO) for discoloration and a calcium chloride (CaCl2) solution to shorten the setting time was investigated. BTO powder was prepared using high-energy ball milling for 3 h, followed by sintering at 700–1300 °C for 2 h. X-ray diffraction was used to examine the crystallinity and crystalline size of the as-milled and heat-treated powders. MTA-like cements were then prepared using 20–40 wt.% BTO as a radiopacifier and solidified using a 0–30% CaCl2 solution. The corresponding radiopacity, diametral tensile strength (DTS), initial and final setting times, and discoloration performance were examined. The experimental results showed that for the BTO powder prepared using a combination of mechanical milling and heat treatment, the crystallinity and crystalline size increased with the increasing sintering temperature. The BTO sintered at 1300 °C (i.e., BTO-13) exhibited the best radiopacity and DTS. The MTA-like cement supplemented with 30% BTO-13 and solidified with a 10% CaCl2 solution exhibited a radiopacity of 3.68 ± 0.24 mmAl and a DTS of 2.54 ± 0.28 MPa, respectively. In the accelerated discoloration examination using UV irradiation, the color difference was less than 1.6 and significantly lower than the clinically perceptible level (3.7). This novel MTA exhibiting a superior color stability, shortened setting time, and excellent biocompatibility has potential for use in endodontic applications.

Structure, composition, microwave dielectric properties and improved ultra-low temperature sintering characteristics of Lyonsite structural Li2Mg2Mo3O12 ceramic

(1-x)Li2Mg2Mo3O12-xTiO2 (x = 0.1–0.5) composite ceramics are prepared by solid-state sintering process. And the structure, composition, microwave dielectric properties and ultra-low temperature sintering characteristics are studied. The result of two-phase (Li2Mg2Mo3O12 and TiO2) coexistence is definitely identified through XRD, mapping and Raman analysis along different regions. Furthermore, as the sintering temperature increases, the enhanced degree of densification plays a positive role in determining microwave dielectric properties. Sintering additives are used to lower sintering temperature of 0.6Li2Mg2Mo3O12-0.4TiO2 composite ceramics, where 1 wt% H3BO3 is applied to reduce the temperature from 750 °C to 700 °C and maintain excellent microwave dielectric characteristics. The cooling mechanism of sintering aids are also thoroughly studied. In all, 0.6Li2Mg2Mo3O12-0.4TiO2 composite ceramic with 1 wt% H3BO3 sintered at 700 °C displays excellent microwave dielectric properties (εr∼11.27, Q × f ∼43056 GHz, τf ∼ -3 ppm/°C). It can be served as a pioneering candidate in applications of ULTCC (ultra-low temperature co-fired ceramic).

Optimisation and application of high solid loading stereolithography 3D printing ceramic cores slurry

The properties of ceramic slurry play a crucial role in the production of high-quality ceramic cores. In stereolithography 3D printing process, ceramic slurry should have high solid loading as far as possible. In this work, slurry with high solid loading and low viscosity was successfully prepared by changing the resin composition. When HDDA:TMPTA was 6:2, slurry exhibited low viscosity, high stability and excellent curing properties. Ceramic cores were successfully prepared by the optimized slurry with a solid loading of 60 vol%. The effects of sintering temperature on ceramic cores were studied. As the increase of sintering temperature, the bulk density gradually increased and the open porosity decreased. The ceramic cores exhibited excellent properties at 1250 °C. This work provided a theoretical basis for the optimisation and application of slurry on stereolithography 3D printing ceramic cores.

Low-temperature synthesis and mechanical performance analysis of single-phase high-entropy (Ti,Cr,V,Nb,Ta)B1.9 ceramics

The structural stability of non-stoichiometric TiB1.5 was assessed using first principles calculations, followed by synthesis through the mechanical alloying method. Subsequently, TiB1.5 was combined with other transition metal borides to fabricate high-entropy ceramics (HEB1.9) consisting of multi-component transition metal borides (Ti, Cr, V, Nb, Ta)B1.9 via spark plasma sintering (SPS). The sintered bodies were prepared at various temperatures ranging from 1700 °C to 1900 °C and were subjected to characterization. Simulation results indicate that TiB1.5 exhibits a negative formation energy, signifying its stability. Experimental findings reveal that at relatively low sintering temperatures, the combined influence of temperature and pressure facilitates the diffusion of several other compounds into the TiB1.5 phase, resulting in the synthesis of a single-phase high-entropy diboride ceramic (HEDC) at 1700 °C. As the sintering temperature increases, the Vickers hardness and flexural strength of the sintered body initially increase and subsequently decrease, a trend influenced by both porosity and grain size. Concurrently, fracture toughness exhibits a pattern of decreasing, increasing, and then decreasing again. At a temperature of 1850 °C, the single-phase HEDC demonstrates peak values in Vickers hardness (23.28 GPa), fracture toughness (5.33 MPa m1/2), and flexural strength (681.39 MPa).

Effect of the Firing Temperatures on the Phase Evolution and Electrical Properties of 0.85[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-0.15[Na0.73Bi0.09NbO3] Ceramics Synthesized via the Solid-State Combustion Method

In this research paper, we describe 0.85[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-0.15[Na0.73Bi0.09NbO3] (BNT-BT-NBN) ceramics fabricated by the solid-state combustion technique. The phase evolution, microstructure, dielectric, ferroelectric and energy storage properties were examined. The BNT-BT-NBN powders and ceramics were calcined and sintered between 650–900 °C and 1100–1175 °C, respectively, for 2 h. All samples showed a typical perovskite structure, as revealed by X-ray diffraction. The Rietveld refinement analysis of the ceramics suggested the samples sintered between 1100 and 1150 °C had coexisting R + T phases, while the R + T+C phases were observed in the ceramics sintered at 1175 °C. The average grain size of the samples increased from 0.52 to 1.39 μm with increased sintering temperature. The density of the ceramics increased from 5.12 to 5.45 g/cm3 when the sintering temperature increased from 1100 to 1150 °C, and then decreased. Increasing the sintering temperature from 1100 to 1150 °C caused the dielectric constant at T s (ε s) and the dielectric constant at T m (ε m) to increase from 1727 to 1945 and 1564 to 1750, respectively, and then ε s and ε m declined. All BNT-BT-NBN ceramics had good dielectric temperature stability with only a±10% change when the temperature ranged from room temperature to ∼300 °C. The optimum energy-storage properties (W rec = 0.62 J/cm3 and η = 83.2%) were obtained from the BNT-BT-NBN ceramics sintered at 1150 °C for 2 h. This data indicates that BNT-BT-NBN ceramics can be useful as lead-free materials for high density energy-storage capacitors.

Effect of Firing Temperatures on Phase Formation, Microstructure, Dielectric and Magnetic Properties of Ni0.6Zn0.4Fe2O4 Ceramics Synthesized by the Solid-State Combustion Technique

In this study, the effect of firing temperatures on phase formation, microstructure dielectric and magnetic properties of Ni0.6Zn0.4Fe2O4 (NZFO) ceramics were investigated. The NZFO powder were synthesized by the solid-state combustion technique using glycine as a fuel to reduce the reaction temperature. All samples were calcined in the range of 900 °C–1100 °C for 2 h and sintered in the range of 1175 °C–1275 °C for 2 h. A pure ferrite phase was found in the powders calcined above 1000 °C and the average particle size of NZFO powders was increased from 0.39 µm to 0.59 µm when the calcination temperature was increased. The x-ray diffraction (XRD) analysis results confirmed the formation of pure spinel structure with cubic phase in all the ceramic samples. The average grain size (5.54–2.80 µm) was slightly decreased, and the dielectric constant (239–13) tended to decrease with increasing sintering temperature. As the sintering temperature increased to 1250 °C, it was found that the lattice parameters (8.366–8.387 Å), the density (5.29–5.35 g/cm3), and saturation magnetization (81.51–93.92 emu/g) tended to increase after that decrease.

Sintering Temperature Effect on Phase Formation, Microstructure and Electrical Properties of Modified KNLNTS Solid Solution Prepared via the Solid-State Combustion Technique

In this study, the effect of sintering temperature (1000–1100 °C for 2 h) on phase formation, phase transition, microstructure and electrical properties of lead-free piezoelectric (K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3 (KNLNTS) solid solution with 0.3 wt%Bi2O3 + 0.4 wt%Fe2O3 + 0.2 wt%CuO additive (abbreviate as modified KNLNTS) was investigated. Modified KNLNTS ceramics were synthesized by the solid-state combustion technique using glycine as fuel. The modified KNLNTS powders were prepared using the calcination condition of 650 °C for 2 h. The XRD pattern of all sintered ceramics exhibited a pure perovskite phase. Using Rietveld refinement to analyze the phase formation showed that the modified KNLNTS ceramics had co-existing phases of orthorhombic and tetragonal in all sintered ceramics and the orthorhombic phase increased when the sintering temperature increased. The average grain size, TO-T, Tc, Pr and Ec increased with increasing sintering temperature. At the sintering temperature of 1025 °C, the modified KNLNTS ceramic showed the best electrical properties (Cε ≈ 6745, Smax ≈0.274% and d*33 ≈ 548 pm/V). The good electrical properties of the modified KNLNTS ceramics makes them good candidates for lead-free applications to replace Pb-based ceramics.

Study on Microstructure, Mechanical Performance and Thermal Shock Resistance of Diffusion Welded Joint of ODS-W and TZC Alloy

The diffusion welded joint of oxide dispersion strengthened tungsten (ODS-W) and Mo-Ti-Zr-C alloy (TZC) was successfully fabricated with the use of spark plasma sintering (SPS) at a vacuum level of 10 Pa. This study systematically investigates the microstructure, mechanical performance, and thermal shock resistance of the ODS-W/TZC connector at four different temperatures, ranging from 1300 to 1600 °C. The diffusion distance between the W and Mo atoms at the interface of ODS-W/TZC joint raises as the sintering temperature increases, with a maximum diffusion distance of up to 2 μm at 1500 °C, but then slightly decreases at 1600 °C. The ODS-W/TZC connector bonded at 1500 °C exhibits the best tensile performance, with tensile strengths of 459 MPa and 786 MPa at room temperature and 500 °C, respectively. A maximum hardness of 446 HV is obtained at the interface when the sample is sintered at 1600 °C. Thermal shock tests are conducted on the surface and interface of the ODS-W/TZC connector sintered at various temperatures. ODS-W/TZC samples prepared below 1500 °C were severely damaged, leading to exfoliation after laser thermal shock, while samples prepared above 1500 °C produced fewer damage cracks. Confocal laser scanning microscope (CLSM) analysis demonstrated that the ODS-W/TZC joint fabricated at 1500 °C exhibited substantially reduced height perturbation of both its surface and interface compared to that of ODS-W, providing evidence for its superior thermal shock resistance.

Microstructure and mechanical properties of WC–TiC–Co cemented carbides produced by spark plasma sintering (SPS) method

Cemented carbide 91 wt% WC–3 wt% TiC–6 wt% Co was sintered by spark plasma sintering at different temperatures of 1200 °C, 1300 °C, and 1400 °C and the effect of sintering temperature on the microstructure and properties of this type of composites, such as total density, apparent density, hardness, and fracture surface were measured and observed using Field Emission-Scanning Electron Microscopy, Optical Microscopy, X-ray diffractometry and mechanical test instruments. The results showed that the apparent density of the samples increased with increasing sintering temperature from 1200 to 1300 °C from 13.98 to 14.23 g/cm3, respectively. But in the sample sintered at 1400 °C, the density was reduced to 14.20 g/cm3. An increase in the fluidity of the cobalt phase and capillary pressure is the cause of the increase in density at higher temperatures, the cobalt phase has evaporated and the density has decreased slightly. Also, Vickers micro-hardness results showed that the hardness of sintered samples increased with the increase of sintering temperature. For the sample sintered at 1200 °C the hardness value of 1746.41 kgf/mm2 was obtained which increased with increasing sintering temperature from 1300 to 1400 °C from 2094.33 to 2280.97 kgf/mm2, respectively. The amount of core–shell structure [including TiC-core and (W, Ti)C-shell] increased with increasing the sintering temperature process. As a result, the hardness also increased. At the optimum sintering temperature, it was found that TiC inhibited the grain growth of tungsten carbide. In addition, as expected, the grain growth of tungsten carbide increased with increasing sintering temperatures. Examination of the fracture surface of sintered samples at different temperatures also showed that brittle fracture involves fracture.

Simultaneous optimization of the tensile strength, bending strength, hardness and wear resistance of W[sbnd]Cu composite produced by sintering process

In this research, the mechanical properties of tungsten‑copper (WCu) composite fabricated by the sintering technology were optimized by design of experiments. The parameters of sintering temperature, sintering time and weight percentage of copper were selected to optimize the tensile strength, bending strength, wear resistance and hardness of the WCu composite using the response surface method combined with desirability process. The microstructure of the WCu composite was also examined by SEM, TEM, XRD and EDS analyses. The results showed that a rise in the sintering temperature from 1000 to 1150 °C improved the tensile strength of WCu composite, while a rise in the sintering temperature from 1150 to 1300 °C deteriorated the tensile strength. Moreover, the bending strength, wear resistance and hardness of the WCu composite continuously enhanced with the increase of sintering temperature from 1000 to 1300 °C. An increase in the amount of Cu from 20 to 40 wt% resulted in a reduction in the wear resistance and hardness of the WCu composite, while the increase of Cu content improved the tensile and bending strengths. It was also showed that mechanical properties of the WCu composite can be improved simultaneously by using 23 wt% Cu at sintering temperature of 1220 °C and sintering time of 2.5 h.

Study on the preparation of ceramic membrane support and its Fe migration rule by high‐aluminum fly ash as raw material

AbstractIn order to reduce the cost of ceramic membrane support, ceramic membrane support was prepared using high‐aluminum fly ash as raw material, and its Fe migration rules during the preparation process are studied. The effects of sintering temperature, pore forming agent content, and binder content on the properties of support, such as porosity, pore size, bending strength and water flux have been investigated. The optimum contents of high‐aluminum fly ash, pore forming agent and binder in the ceramic membrane support are 95%, 4%, and 1% respectively, and its sintering temperature is 1300°C. The porosity, bending strength, pore size, and water flux of the prepared support are 37%, 22 MPa, 665 nm, and 2800 L/h·m2·MPa, respectively. X‐ray powder diffractometer, X‐ray fluorescence spectrometer, X‐ray photoelectron spectrometer, inductively coupled plasma spectrometer, transmission electron microscope, spherical aberration corrected transmission electron microscopy, and laser Raman spectroscopy were used to characterize the support and Fe existing morphology in it. The results show that the main phases of sintered support are mullite, corundum, and silica. Massive mullite is produced when the sintering temperature reaches 1200°C. The content of mullite increases with increasing sintering temperature. About 7.7 % content of total Fe in the support exists in the form of Fe2O3. About 92.3% content of total Fe is dissolved into mullite. Fe is evenly distributed in mullite, and it is enriched at the grain boundary by element segregation. Fe in mullite is difficult to dissolve under strong acid conditions, so its stability is very strong.

Hybrid Sol–Gel and Spark Plasma Sintering to Produce Perovskite-like SrTiO3 Ceramics for Radioactive Waste Isolation

The paper presents a reliable technology combining sol–gel synthesis and spark plasma sintering (SPS) to obtain SrTiO3 perovskite-type ceramics with excellent physicomechanical properties and hydrolytic stability for the long-term retention of radioactive strontium radionuclides. The Pechini sol–gel method was used to synthesize SrTiO3 powder from Sr(NO3)2 and TiCl3 (15%) precursors. Ceramic matrix samples were fabricated by SPS in the temperature range of 900–1200 °C. The perovskite structure of the synthesized initial SrTiO3 powder was confirmed by X-ray diffraction and thermal analysis results. Scanning electron microscopy revealed agglomeration of the nanoparticles and a pronounced tendency for densification in the sintered compact with increasing sintering temperature. Chemical homogeneity of ceramics was confirmed by energy dispersive X-ray analysis. Physicochemical characteristic studies included density measurement results (3.11–4.80 g·cm−3), dilatometric dependencies, Vickers microhardness (20–900 HV), and hydrolytic stability (10−6–10−7 g·cm−2·day−2), exceeding GOST R 50926-96 and ISO 6961:1982 requirements for solid-state matrices. Ceramic sintered at 1200 °C demonstrated the lowest strontium leaching rate of 10−7 g/cm2·day, optimal for radioactive waste (RAW) isolation. The proposed approach can be used to fabricate mineral-like forms suitable for RAW handling.

Microstructure and properties of porous Si3N4 ceramics fabricated by digital light processing combined with spark plasma sintering

Sintering process is an important factor affecting the properties of porous Si3N4 ceramics. However, there are few studies on the properties of porous Si3N4 ceramics fabricated by combining digital light processing (DLP) technology and spark plasma sintering (SPS) technology. In this study, a method to prepare porous Si3N4 ceramics by combining DLP with SPS technology was proposed, and ceramic samples were successfully prepared. The effect of sintering temperature and holding time of SPS technology on the microstructure and properties of porous Si3N4 ceramics prepared by DLP technology was discussed. With the increase of sintering temperature from 1600 °C to 1700 °C, the conversion content of α-Si3N4 phase to β-Si3N4 phase increased from 19.19% to 76.72%. The fracture mode of porous Si3N4 ceramics gradually transformed from intergranular to transgranular. The porosity of Si3N4 ceramics gradually decreased from 40.34 ± 4.9% to 30.54 ± 2.7% with opposite trend in bulk density. And the flexural strength increased from 109.1 ± 7.6 MPa to 249.5 ± 4.0 MPa. When the sintering temperature was 1700 °C, the content of β-Si3N4 increased first and then remained essentially constant with the increase of holding time from 5 min to 15 min. The porosity increased from 30.54 ± 2.7% to 35.15 ± 2.5%, while the variation in bulk density were opposite. And the flexural strength severely decreased from 249.5 ± 4.0 MPa to 126.1 ± 7.2 MPa. This research provides valuable insights into the DLP-forming ceramic materials sintered by SPS technology.

Effective post-processing strategies of inkjet-printed ceramic cathodes for improved fuel cell performance

The reluctant effectiveness of the post-processing strategies of the inkjet-printed ceramic components in solid oxide fuel cells (SOFCs) limits the realization of high-power density. We herein report the detailed study on the influences of post-processing strategies including drying and sintering of inkjet-printed cathode layers on their final microstructural, mechanical and electrochemical properties. Results showed that the maximum power density at 0.7V achieved through furnace drying was 2.3 times that of the freeze-dried one, which was due to the high effective porosity of the inkjet-printed layer. The furnace-dried cell was further found to have better mechanical strength (H=2.14GPa, E=93.56GPa). With increased sintering temperature, the power density first increased and then decreased, contrary to its ohmic resistance and polarization resistance. The highest power density of 1084.70 mW cm−2 was reached when sintered at 900°C. This study offers effective post-processing strategies of drying and sintering for the inkjet-printed SOFC components for higher energy conversion efficiency.

Large area bare Cu-Cu interconnection using micro-Cu paste at different sintering temperatures and pressures

The microstructure evolution, shear strength, and fracture behavior of large area (10 mm × 10 mm) bare Cu-Cu interconnection sintered using micro-Cu paste at different sintering temperatures (180, 200, 250, and 300 °C) and assistant pressures (0, 2, 5, and 10 MPa) were investigated in this study. The results showed that, as sintering temperature and assistant pressure increased, the microstructure of the sintered joints became denser, and the bonding quality of both the Cu dummy chip/Cu paste and Cu paste/Cu substrate interfaces was elevated, while more small crack or blind hole generated at the former interface. Moreover, the shear strength of the sintered joints increased with increasing sintering temperature and assistant pressure, a robust joint could be obtained under an assistant pressure of 10 MPa regardless of the sintering temperature as well as under an assistant pressure of 5 MPa at 250 and 300 °C. The fracture preferred at the Cu dummy chip/Cu paste interface, and the ductility of the sintered joint increased with increasing sintering temperature and assistant pressure. Accordingly, the optimized sintering temperature and assistant pressure are 250 °C and 10 MPa, respectively.

Phase Transformation of YSZ Electrolyte in Anode-Supported SOFCs

The addition of nickel oxide (NiO) to 8 mol% yttria-stabilized zirconia (8YSZ) accelerates the phase transformation from cubic phase to tetragonal phase when exposed to a reducing atmosphere at relatively high temperatures such as 900 ℃, resulting in the degradation of oxide ion conductivity.In this study, NiO-related phase transformation of 8YSZ electrolyte is investigated for anode-supported cells (ASCs). 8YSZ electrolyte co-sintered with NiO-YSZ anode at high temperatures exhibited NiO dissolution into the 8YSZ electrolyte during the sintering process and the amount of dissolved NiO increased with increased sintering temperatures. After reducing the cells at 900 ℃, phase transformation is observed in the 8YSZ electrolyte and resulted in a decrease of the oxide ion diffusion coefficient (D*). On the other hand, no phase transformation is observed for the cells reduced at 700 ℃for 5 hours.