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排序方式: 共有8867条查询结果,搜索用时 22 毫秒
1.
Víctor I. Hernández Domingo I. García-Gutiérrez Juan A. Aguilar-Garib Román J. Nava-Quintero 《Ceramics International》2021,47(1):310-319
In the current study two different batches of X7R-0603 BME-MLCCs displayed dissimilar electrical performance, despite having the same chemical composition, tape casting, and sintering conditions; with the only difference between them being the ore deposits where the raw materials were extracted from to synthesize the BaTiO3. Specifically, they presented different electrical response to highly accelerated life tests (HALT). Although the chemical analysis of each slip showed the same composition, the trace elements of the BaTiO3 sources could have acted as dopants or produced different secondary phases. A search for precipitates in the two samples was conducted by means of Scanning (SEM) and Transmission Electron Microscopy (TEM) techniques. SEM observations confirmed the presence of precipitates formed within the structure of the MLCCs exhibiting the greatest decrement in their electrical resistance results during the HALT. In order to further characterize the observed precipitates, samples were prepared by Focused Ion Beam (FIB) lift-out method, to make TEM characterization of specific precipitates feasible. TEM studies were performed on the precipitates to obtain electron diffraction patterns and complementary Energy Dispersive X-Ray Spectroscopy (EDXS) chemical analysis. Based on the crystal and chemical data obtained, it can be concluded that the precipitates are a hexagonal anhydrous silicate oxyapatite phase with a stoichiometry of Ca3Y16Si10O13, and lattice parameters of a = 0.9353 nm and c = 0.6970 nm; this phase was not found in the JCPDS data base. Differences in raw materials coming from different ore deposits can produce undesired precipitates that affect the electrical performance of MLCCs. 相似文献
2.
Xuye Wang Guopu Shi Qinggang Li Junyan Wu Hao Wu Liu Zhang Zhi Wang 《Ceramics International》2021,47(2):2280-2287
Owing to the good physicochemical compatibility and complementary mechanical properties of Ti3SiC2 and Al2O3, Ti3SiC2/Al2O3 composites are considered as ideal structural materials. However, TiC and TiSi2 typically coexist during the synthesis of Ti3SiC2/Al2O3 composites through an in-situ reaction, which adversely affects the mechanical properties of the resulting composites. In this study, Ti3SiC2/Al2O3 composites were prepared via in-situ hot pressing sintering at 1450 °C. Ge, which was used as a sintering aid, improved the purity and mechanical properties of the Ti3SiC2/Al2O3 composites. This is because Ge replaced some of the Si atoms to compensate the evaporation loss of Si to form Ti3(Si1-xGex)C2, which showed a crystal structure similar to that of Ti3SiC2. Furthermore, the molten Ge accelerated the diffusion reaction of the raw materials, increasing the overall density of the Ti3SiC2/Al2O3 composites. The optimum Ge amount for improving the mechanical properties of the composites was found to be 0.3 mol. The flexural strength, fracture toughness, and microhardness of the composite with the optimum Ge amount were 640.2 MPa, 6.57 MPa m1/2, and 16.21 GPa, respectively. The formation of Ti3(Si1-xGex)C2 was confirmed by carrying out X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy analyses. A model crystal structure of Ti3(Si1-xGex)C2 doped with 0.3 mol Ge was established by calculating the solid solubility of Ge. 相似文献
3.
《International Journal of Hydrogen Energy》2022,47(22):11500-11510
Herein, a novel ZnTe-based photocatalyst is successfully synthesized via a facile combination of water-bath and hydrothermal processes. Morphology characterization and X-ray diffraction analysis reveal that ZnTe presents irregular granular shape and cubic crystal structure. Moreover, Mott-Schottky measurement shows that the conduction band potential of ZnTe is ?0.84 V (vs NHE). With Eosin Y (EY) sensitization, ZnTe exhibits superior photocatalytic hydrogen evolution activity (223.5 μmol g?1 h?1). Meanwhile, WC-ZnTe heterojunction is constructed by depositing ZnTe nanoparticles on bulk WC and obtains the optimal H2 generation rate (559.1 μmol g?1 h?1) under EY sensitization. Electrochemical and photoluminescence results further prove that WC as electron bridge could reduce the interfacial resistance and suppress e?-h+ pairs recombination. This study explores the potential application of ZnTe as a newly active photocatalyst in photocatalytic water splitting, and emphasizes the synergistic effect of dye sensitization and bridge engineering. 相似文献
4.
《Advanced Powder Technology》2022,33(11):103627
Naringin (NAR), a major flavanone (FVA) glycoside, is a component of food mainly obtained from grapefruit. We used NAR as a food additive to improve the solubility and permeability of hydrophobic polyphenols used as supplements in the food industry. The spray-dried particles (SDPs) of NAR alone show an amorphous state with a glass transition temperature (Tg) at 93.2 °C. SDPs of hydrophobic polyphenols, such as flavone (FVO), quercetin (QCT), naringenin (NRG), and resveratrol (RVT) were prepared by adding varying amounts of NAR. All SDPs of hydrophobic polyphenols with added NAR were in an amorphous state with a single Tg, but SDPs of hydrophobic polyphenols without added NAR showed diffraction peaks derived from each crystal. The SDPs with NAR could keep an amorphous state after storage at a high humidity condition for one month, except for SDPs of RVT/NAR. SDPs with NAR enhanced the solubility of hydrophobic polyphenols, especially NRG solubility, which was enhanced more than 9 times compared to NRG crystal. The enhanced solubility resulted in the increased membrane permeability of NRG. The antioxidant effect of the hydrophobic NRG was also enhanced by the synergetic effect of NAR. The findings demonstrated that NAR could be used as a food additive to enhance the solubility and membrane permeability of hydrophobic polyphenols. 相似文献
5.
《International Journal of Hydrogen Energy》2022,47(43):18663-18674
Developing non-precious metal-based catalysts as the substitution of precious catalysts (Pt/C) in oxygen reduction reaction (ORR) is crucial for energy devices. Herein, a template and organic solvent-free method was adopted to synthesize Fe, B, and N doped nanoflake-like carbon materials (Fe/B/N–C) by pyrolysis of monoclinic ZIF-8 coated with iron precursors and boric acid. Benefiting from introducing B into Fe–N–C, the regulated electron cloud density of Fe-Nx sites enhance the charge transfer and promotes the ORR process. The as-synthesized Fe/B/N–C electrocatalyst shows excellent ORR activity of a half-wave potential (0.90 V vs 0.87 V of Pt/C), together with superior long-term stability (95.5% current density retention after 27 h) in alkaline media and is even comparable to the commercial Pt/C catalyst (with a half-wave potential of 0.74 V vs 0.82 V of Pt/C) in an acidic electrolyte. A Zn-air battery assembled with Fe/B/N–C as ORR catalyst delivers a higher open-circuit potential (1.47 V), specific capacity (759.9 mA h g?1Zn at 10 mA cm?2), peak power density (62 mW cm?2), as well as excellent durability (5 mA cm?2 for more than 160 h) compared to those with commercial Pt/C. This work provides an effective strategy to construct B doped Fe–N–C materials as nonprecious ORR catalyst. Theoretical calculations indicate that introduction of B could induce Fe-Nx species electronic configuration and is favorable for activation of OH1 intermediates to promote ORR process. 相似文献
6.
《International Journal of Hydrogen Energy》2022,47(91):38682-38689
A body-centered cubic equiatomic TiZrTaNbAl multi-principal element alloy (MPEA) with elemental fluctuations was investigated to further understand the relationship between the microstructure and hydrogen distribution. In this study, a composition dependence of the hydrogen distribution was observed in the TiZrTaNbAl MPEA. An inhomogeneous electron density distribution of the MPEA was revealed by advanced differential phase-contrast scanning electron microscopy (DPC-STEM) for the first time. The results showed that the electron density has a significant effect on the hydrogen distribution in TiZrTaNbAl MPEAs. This work provides new insight into the design of materials with high hydrogen storage capacity and high hydrogen embrittlement resistance. 相似文献
7.
《International Journal of Hydrogen Energy》2021,46(55):28346-28357
The effect of interstitial impurities (H and S) on the atomic, electronic structure, and mechanical properties of the γ-Fe Σ5 (021) grain boundary (GB) was investigated via first-principles calculations. H atoms act as an intergranular embrittler in the Σ5 GB due to a reduction in the charge density between the Fe atoms connected to the grains, whereas H and S co-segregation produces more pronounced embrittlement behavior, resulting in intergranular fracture. The S-induced embrittlement plays a crucial role in the H and S segregation, due to a combination of the structural and chemical effects. The fracturing of Σ5 GB due to S and H segregation is a two-step process. The first step is the breaking of Fe–Fe bonds in the GB, followed by the breaking of the remaining Fe–S bonds in the second step, resulting in the complete separation of the two grains. Moreover, the S atom can slightly compensate for the embrittlement induced by H, because some of the Fe atoms that obtain electrons from the S atoms can provide more electrons to the H atoms, and thus, they can compensate for the electrons that must be acquired from other Fe atoms. We call this “the electrons compensating effect” and this effect is helpful in the design and alloying of steels that are resistant to H embrittlement. 相似文献
8.
《International Journal of Hydrogen Energy》2021,46(62):31623-31633
In this paper, Pt nanoparticles (Pt NPs) deposited hybrid carbon support is prepared by modifying double-layered hollow carbon spheres(DLHCs)with poly(3,4-ethylenedioxythiophene) (PEDOT) and used as anode catalyst of methanol oxidation. The structure of nanocomposites is characterized by SEM, TEM, FT-IR, XRD and XPS, confirming the greatly enhanced synergistic effect between the PEDOT and DLHCs, and illustrating the uniform distribution of Pt NPs on the PEDOT/DLHCs composite surface with a small particle size (~2.63 nm). Cyclic voltammetry, chronoamperometry and impedance spectroscopy applied to determine the electrocatalytic activity of catalysts, it is found that the synthesized PEDOT/DLHCs/Pt possesses excellent characteristics such as large electrochemically active surface area and high mass activity of 59.45 m2 g−1 and 807 mA mg−1 in 0.5 M H2SO4 containing 1 M methanol solution, which is almost 1.24 and 2.8 times greater than those of commercial Pt/C, and the catalyst exhibits superior stability after 500 durability cycles. The enhanced electrocatalytic behavior can be ascribed to the excellent electronic conductivity of PEDOT-modified DLHCs and the strong binding of PEDOT/DLHCs to Pt NPs, suggesting that the PEDOT/DLHCs/Pt is a promising electrocatalyst for direct methanol fuel cell. 相似文献
9.
《Ceramics International》2022,48(2):1814-1819
Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ (x = 0, 0.2, 0.4) long persistent phosphors were prepared via solid-state process. The pristine Sr3Al2O5Cl2:Eu2+, Dy3+ phosphor exhibits orange/red broad band emission around 609 nm, which can be attributed to the electric radiation transitions 4f65 d1→4f7 of Eu2+. Upon the same excitation, the B3+-doped Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ phosphors display red-shift from 609 nm to 625 nm with increasing B3+ concentrations. The XRD patterns show that Al3+ can be replaced by B3+ in the host lattice at the tetrahedral site, which causes lattice contraction and crystal field enhancement, and thereafter achieves the red-shift on the emission spectrum. The XPS investigation provides direct evidence of the dominant 2-valent europium in the phosphor, which can be ascribed for the broad band emission of the prepared phosphors. The afterglow of all phosphors show standard double exponential decay behavior, and the afterglow of Sr3Al2O5Cl2:Eu2+, Dy3+is rather weak, while the sample co-doped with B3+shows longer and stronger afterglow, as confirmed after the curve simulation. The analysis of thermally stimulated luminescence showed that, when B3+ is introduced, a much deeper trap is created, and the density of the electron trap is also significantly increased. As a result, B3+ ions caused redshift and enhanced afterglow for the Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ phosphor. 相似文献
10.
Ashkan Farazin Saeid Sahmani Maryam Soleimani Amin Kolooshani Saeed Saber-Samandari Amirsalar Khandan 《Ceramics International》2021,47(13):18339-18350
Porous bony scaffolds are utilized to manage the growth and migration of cells from adjacent tissues to a defective position. In the current investigation, the effect of titanium oxide (TiO2) nanoparticles on mechanical and physical properties of porous bony implants made of polymeric polycaprolactone (PCL) is studied. The bio-nanocomposite scaffolds are prepared with composition of nanocrystalline hydroxyapatite (HA) and TiO2 powder using the freeze-drying technique for different weight fractions of TiO2 (0 wt%, 5 wt%, 10 wt%, and 15 wt%). In order to identify the microstructure and morphology of the fabricated porous bio-nanocomposites, the X-ray diffraction (XRD), atomic force microscope (AFM) and scanning electron microscopy (SEM) are employed. Also, the biocompatibility and biodegradability of the manufactured scaffolds are examined by placing them in a simulated body fluid (SBF) for 21 days, their weight and pH changes are measured. The rate of degradation of the PCL-HA scaffold can be controlled by varying the percentage of its constituent components. Due to an increasing growth and activity of bone cells and the apatite formation on the free surface of the fabricated bio-nanocomposite implants as well as their reasonable mechanical properties, they have the potential to be used as a bone substitute. Additionally, with the aid of the experimentally extracted mechanical properties of the scaffolds, the vibrational characteristics of a beam-type implant made of the proposed porous bio-nanocomposites are explored. The results obtained from SEM image indicate that the scaffolds produced by the employed method have high total porosity (70%–85%) and effective porosity. The pore size is obtained between 60 and 200 μm, which is desirable for the growth and propagation of bone cells. Also, it is revealed that the addition of TiO2 nanoparticles leads to reduce the rate of dissolution of the fabricated bio-nanocomposite scaffolds. 相似文献