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1.
High-purity mullite ceramics, promising engineering ceramics for high-temperature applications, were fabricated using transient liquid phase sintering to improve their high-temperature mechanical properties. Small amounts of ultrafine alumina or silica powders were uniformly mixed with the mullite precursor depending on the silica-alumina ratio of the resulting ceramics to allow for the formation of a transient liquid phase during sintering, thus, enhancing densification at the early stage of sintering and mullite formation by the reaction between additional alumina and the residual glassy phase (mullitization) at the final stage of sintering. The addition of alumina powder to the silica-rich mullite precursor resulted in a reaction between the glassy silica and alumina phases during sintering, thereby forming a mullite phase without inhibiting densification. The addition of fine silica powder to the mullite single-phase precursor led to densification with an abnormal grain growth of mullite, whereas some of the added silica remained as a glassy phase after sintering. The resulting mullite ceramics prepared using different powder compositions showed different sintering behaviors, depending on the amount of alumina added. Upon selecting an optimum process and the amount of alumina to be added, the pure mullite ceramics obtained via transient liquid phase sintering exhibited high density (approximately 99%) and excellent high-temperature flexural strength (approximately 320 MPa) at 1500 °C in air. These results clearly demonstrate that pure mullite ceramics fabricated via transient liquid phase sintering with compositions close to those of stoichiometric mullite could be a promising process for the fabrication of high-temperature structural ceramics used in an ambient atmosphere. The transient liquid phase sintering process proposed in this study could be a powerful processing tool that allows for the preparation of superior high-temperature structural ceramics used in the ambient processing atmosphere. 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(100):42280-42292
In this study, the separation of hydrogen from gas mixtures using a palladium membrane coupled with a vacuum environment on the permeate side was studied experimentally. The gas mixtures composed of H2, N2, and CO2 were used as the feed. Hydrogen permeation fluxes were measured with membrane operating temperature in the range of 320–380 °C, pressures on the retentate side in the range of 2–5 atm, and vacuum pressures on the permeate side in the range of 15–51 kPa. The Taguchi method was used to design the operating conditions for the experiments based on an orthogonal array. Using the measured H2 permeation fluxes from the Taguchi approach, the stepwise regression analysis was also employed for establishing the prediction models of H2 permeation flux, followed by the analysis of variance (ANOVA) to identify the significance and suitability of operating conditions. Based on both the Taguchi approach and ANOVA, the H2 permeation flux was mostly affected by the gas mixture composition, followed by the retentate side pressure, the vacuum degree, and the membrane temperature. The predicted optimal operating conditions were the gas mixture with 75% H2 and 25% N2, the membrane temperature of 320 °C, the retentate side pressure of 5 atm, and the vacuum degree of 51 kPa. Under these conditions, the H2 permeation flux was 0.185 mol s?1 m?2. A second-order normalized regression model with a relative error of less than 7% was obtained based on the measured H2 permeation flux. 相似文献
3.
《International Journal of Hydrogen Energy》2022,47(66):28645-28654
The introduction of catalyst on anode of solid oxide fuel cell (SOFC) has been an effective way to alleviate the carbon deposition when utilizing biogas as the fuel. A series of La0.6Sr0.4Co1-xNixO3-δ (x = 0, 0.2, 0.4, 0.6, 0.8) oxides are synthesized by sol-gel method and used as catalysts precursors for biogas dry reforming. The phase structure of La0.6Sr0.4Co1-xNixO3-δ oxides before and after reduction are characterized by X-ray diffraction (XRD). The texture properties, carbon deposition, CH4 and CO2 conversion rate of La0.6Sr0.4Co1-xNixO3-δ catalysts are evaluated and compared. The peak power density of 739 mW cm?2 is obtained by a commercial SOFC with La0.6Sr0.4Co0.4Ni0.6O3-δ catalyst at 850 °C when using a mixture of CH4: CO2 = 2:1 as fuel. This shows a great improvement from the cell without catalyst for internal dry reforming, which is attributed to the formation of NiCo alloy active species after reduction in H2 atmosphere. The results indicate the benefits of inhibiting the carbon deposition on Ni-based anode through introducing the La0.6Sr0.4Co0.4Ni0.6O3-δ catalyst precursor. Additionally, the dry reforming technology will also help to convert part of the exhaust heat into chemical energy and improve the efficiency of SOFC system with biogas fuel. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(76):32359-32371
On-site hydrogen production through steam-methane reforming (SMR) from city gas or natural gas is believed to be a cost-effective way for hydrogen-based infrastructure due to high cost of hydrogen transportation. In recent years, there have been a lot of on-site hydrogen fueling stations under design or construction in China. This study introduces current developments and technology prospects of skid-mounted SMR hydrogen generator. Also, technical solutions and economic analysis are discussed based on China's first on-site hydrogen fueling station project in Foshan. The cost of hydrogen product from skid-mounted SMR hydrogen generator is about 23 CNY/kg with 3.24 CNY/Nm3 natural gas. If hydrogen price is 60 CNY/kg, IRR of on-site hydrogen fueling station project reaches to 10.8%. While natural gas price fall to 2.3 CNY/Nm3, the hydrogen cost can be reduced to 18 CNY/kg, and IRR can be raised to 13.1%. The conclusion is that skid-mounted SMR technology has matured and is developing towards more compact and intelligent design, and will be a promising way for hydrogen fueling infrastructures in near future. 相似文献
5.
《International Journal of Hydrogen Energy》2022,47(80):33919-33937
Development of efficient, low cost and multifunctional electrocatalysts for water splitting to harvest hydrogen fuels is a challenging task, but the combination of carbon materials with transition metal-based compounds is providing a unique and attractive strategy. Herein, composite systems based on cobalt ferrite oxide-reduced graphene oxide (Co2FeO4) @(rGO) using simultaneous hydrothermal and chemical reduction methods have been prepared. The proposed study eliminates one step associated with the conversion of GO into rGO as it uses direct GO during the synthesis of cobalt ferrite oxide, consequently rGO based hybrid system is achieved in-situ significantly, the optimized Co2FeO4@rGO composite has revealed an outstanding multifunctional applications related to both oxygen evolution reaction (OER) and hydrogen counterpart (HER). Various metal oxidation states and oxygen vacancies at the surface of Co2FeO4@rGO composites guided the multifunctional surface properties. The optimized Co2FeO4@rGO composite presents excellent multifunctional properties with onset potential of 0.60 V for ORR, an overpotential of 240 mV at a 20 mAcm?2 for OER and 320 mV at a 10 mAcm?2 for HER respectively. Results revealed that these multifunctional properties of the optimized Co2FeO4@ rGO composite are associated with high electrical conductivity, high density of active sites, crystal defects, oxygen vacancies, and favorable electronic structure arisinng from the substitution of Fe for Co atoms in binary spinel oxide phase. These surface features synergistically uplifted the electrocatalytic properties of Co2FeO4@rGO composites. The multifunctional properties of the Co2FeO4@ rGO composite could be of high interest for its use in a wide range of applications in sustainable and renewable energy fields. 相似文献
6.
《International Journal of Hydrogen Energy》2022,47(93):39639-39653
Metals that are exposed to high pressure hydrogen gas may undergo detrimental failure by embrittlement. Understanding the mechanisms and driving forces of hydrogen absorption on the surface of metals is crucial for avoiding hydrogen embrittlement. In this study, the effect of stress-enhanced gaseous hydrogen uptake in bulk metals is investigated in detail. For that purpose, a generalized form of Sievert's law is derived from thermodynamic potentials considering the effect of microstructural trapping sites and multiaxial stresses. This new equation is parametrized and verified using experimental data for carbon steels, which were charged under gaseous hydrogen atmosphere at pressures up to 1000 bar. The role of microstructural trapping sites on the parameter identification is critically discussed. Finally, the parametrized equation is applied to calculate the stress-enhanced hydrogen solubility of thin-walled pipelines and thick-walled pressure vessels during service. 相似文献
7.
《International Journal of Hydrogen Energy》2022,47(94):39961-39972
Micro-cracks commonly occur on the catalyst layers (CLs) during the manufacturing of catalyst coated membranes (CCMs). However, the crack shape parameters effect on CLs in-plane (IP) electronic conductivity λs is not clear. In this work, the relationship between crack parameters and the λs is obtained based on the two-dimensional (2D) multiple-relaxation time (MRT) lattice Boltzmann method (LBM). The LBM numerical model is validated by the normalized λs experiment applied on three different home-made cracked CLs, and the parameter study focus on crack width, length, quantity and phase angle are carried out. The results show that the decrease of λs has different sensitivity |k| to the parameters above. The crack width has little effect on λs decrease, and the |kw| is 0.038. However, crack arm length and quantity show more significant impact, which |kl| and |kN| are 0.753 and 0.725, respectively. The CLs with different crack propagation directions show significant anisotropy on λs, and a 53.53% decrease in λs is observed between 0° and 90° crack phase angle change. To manufacture a high electronic conductivity CL, crack initiation and migration mitigation are highly encouraged. 相似文献
8.
《International Journal of Hydrogen Energy》2022,47(45):19758-19771
In this study, the effects of cell temperature and relative humidity on charge transport parameters are numerically analyzed. In order to perform this analysis, three-dimensional and anisotropic numerical models are developed. The numerical models are integrated into the experimental values for anisotropic electrical conductivities, as depending on cell temperature and relative humidity, that were obtained from our previous study. The achieved results indicate that the values of current densities in the in-plane direction increase with increasing cell temperature and relative humidity, while the current densities reach a maximum in the rib regions for both the numerical model at the through-plane direction. The behaviors of electrolyte potentials are similar with changes in the cell temperature and relative humidity. In addition, the cathode electrical potentials in both the in-plane direction and through-plane direction do not change to a considerable amount with increasing cell temperature and relative humidity. 相似文献
9.
《Advanced Powder Technology》2022,33(12):103847
We investigate synthesis, phase evolution, hollow and porous structure and magnetic properties of quasi-amorphous intermediate phase (QUAIPH) and hematite (α-Fe2O3) nanostructure synthesized by annealing of akaganeite (β-FeOOH) nanorods. It is found that the annealing temperature determines the phase composition of the products, the crystal structure/size dictates the magnetic properties whereas the final nanorod morphology is determined by the starting material. Annealing of β-FeOOH at ~300 °C resulted in the formation of hollow QUAIPH nanorods. The synthesized material shows low-cytotoxicity, superparamagnetism and good transverse relaxivity, which is rarely reported for QUAIPH. The QUAIPH nanorods started to transform to porous hematite nanostructures at ~350 °C and phase transformation was completed at 600 °C. During the annealing, the crystal structure changed from monoclinic (akaganeite) to quasi-amorphous and rhombohedral (hematite). Unusually, the crystallite size first decreased (akaganeite → QUAIPH) and then increased (QUAIPH → hematite) during annealing whereas the nanorods retained particle shape. The magnetic properties of the samples changed from antiferromagnetic (akaganeite) to superparamagnetic with blocking temperature TB = 84 K (QUAIPH) and finally to weak-ferromagnetic with the Morin transition at TM = 244 K and high coercivity HC = 1652 Oe (hematite). The low-cytotoxicity and MRI relaxivity (r2 = 5.80 mM?1 s?1 (akaganeite), r2 = 4.31 mM?1 s?1 (QUAIPH) and r2 = 5.17 mM?1 s?1 (hematite)) reveal potential for biomedical applications. 相似文献
10.
《International Journal of Hydrogen Energy》2022,47(72):30830-30842
Carbon dioxide (CO2) and methane (CH4) are the primary greenhouse gases (GHGs) that drive global climate change. CO2 reforming of CH4 or dry reforming of CH4 (DRM) is used for the simultaneous conversion of CO2 and CH4 into syngas and higher hydrocarbons. In this study, DRM was investigated using Ag–Ni/Al2O3 packing and Sn–Ni/Al2O3 packing in a parallel plate dielectric barrier discharge (DBD) reactor. The performance of the DBD reactor was significantly enhanced when applying Ag–Ni/Al2O3 and Sn–Ni/Al2O3 due to the relatively high electrical conductivity of Ag and Sn as well as their anti-coke performances. Using Ag–Ni/Al2O3 consisting of 1.5 wt% Ag and 5 wt% Ni/Al2O3 as the catalyst in the DBD reactor, 19% CH4 conversion, 21% CO2 conversion, 60% H2 selectivity, 81% CO selectivity, energy efficiency of 7.9% and 0.74% (by mole) coke formation were achieved. In addition, using Sn–Ni/Al2O3, consisting of 0.5 wt% Sn and 5 wt% Ni/Al2O3, 15% CH4 conversion, 19% CO2 conversion, 64% H2 selectivity, 70% CO selectivity, energy efficiency of 6.0%, and 2.1% (by mole) coke formation were achieved. Sn enhanced the reactant conversions and energy efficiency, and resulted in a reduction in coke formation; these results are comparable to that achieved when using the noble metal Ag. The decrease in the formation of coke could be correlated to the increase in the CO selectivity of the catalyst. Good dispersion of the secondary metals on Ni was found to be an important factor for the observed increases in the catalyst surface area and catalytic activities. Furthermore, the stability of the catalytic reactions was investigated for 1800 min over the 0.5 wt% Ag-5 wt% Ni/Al2O3 and 0.5 wt% Sn-5 wt% Ni/Al2O3 catalysts. The results showed an increase in the reactant conversions with an increase in the reaction time. 相似文献