Crack-healing ability of structural ceramics and a new methodology to guarantee the structural integrity using the ability and proof-test

Recently, the authors developed Si₃N₄, Al₂O₃ and mullite ceramics with good self-crack-healing abilities. It was shown that the optimized crack-healing condition to get high temperature strength was: 1573 K, 1 h, in air, and the healed zone exhibited the same strength as the base material up to about 1573 K (Si₃N₄ and Al₂O₃) and 1473 K (mullite), respectively. Using this good crack-healing ability, a new methodology to guarantee the reliability of ceramic components [crack-healing + proof test] was proposed. It was shown that reliability could be guaranteed before service by this technique, using about 200 samples. However, if a crack initiated during service, reliability would be severely impaired. Therefore, if a material can heal a crack during service, and if the healed zone has enough strength at the temperature of healing, it would be very desirable for structural integrity. From the above points of view, a new methodology to guarantee the structural integrity of ceramic components using in situ crack-healing ability was proposed and the usefulness is discussed using the test results in terms of crack-healing behavior and proof test theory by the authors.     

A facile one-step synthesis and fabrication of hexagonal palladium-carbon nanocubes (H-Pd/C NCs) and their application as an efficient counter electrode for dye-sensitized solar cell (DSSC)

Hexagonal palladium-carbon nanocubes (H-Pd/C NCs) were prepared using a simple one-step chemical synthesis protocol and subsequently the prepared materials were used as the counter electrode (CE) in dye sensitized solar cell (DSSC) to replace the platinum (Pt) electrode. The H-Pd/C NCs were characterized by a variety of suitable analytical techniques including powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analysis to evaluate the crystalline, structural, morphological, compositional, chemical state and surface area. The BET nitrogen adsorption /desorption analysis shows that the as-prepared H-Pd/C NCs sample had a large surface area (568.8 m² g⁻¹) with average pore size of ∼3 nm. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses indicate that the H-Pd/C NCs have low charge-transfer resistance on the electrolyte/electrode interface and high electrocatalytic activity for the reduction of triiodide to iodide redox electrolyte and hence it is used as a CE in DSSC. The H-Pd/C NCs showed an overall power conversion efficiency (PCE) of 4.1% which performance is comparable with the conventional Pt CE (4.0%) under the identical condition.     

CaAlSiN3:Eu2+ phosphors bonding with bismuth borate glass for high power light excitation

The CaAlSiN₃:Eu²⁺ red phosphor-in-glass was prepared using bismuth borate glass as the binder for high power light excitation. B₂O₃–Bi₂O₃–Al₂O₃–ZnO glass powder showed good sintering behavior with CaAlSiN₃:Eu²⁺ phosphors at around 550 °C. The phosphor-in-glass has flat surface with a thickness of about 100 μm. From the images of FE-SEM and confocal laser scanning microscope, the uniform distribution of phosphor particles inside the phosphor-in-glass was vividly and clearly observed. And the luminescent property of phosphors was not greatly affected by glasses, as shown in fluorescence spectra. When the volume radio of CaAlSiN₃:Eu²⁺ phosphors was 50%, the sample exhibited low thermal quenching and high flexural strength of 28.5 MPa. Compared YAG:Ce³⁺ phosphor-in-glass with CaAlSiN₃:Eu²⁺ phosphor-in-glass, we found bismuth borate glass had better wettability on YAG:Ce³⁺ particles, which caused a higher flexural strength of the YAG:Ce³⁺ phosphor-in-glass.     

Numerical study on bubble trapping in UV-nanoimprint lithography

Bubble trapping in the template pattern during the resist filling process is one of the most serious issues in UV-nanoimprint lithography. The mechanism of bubble trapping is studied based on a numerical analysis of the resist flow in a simple model. Flow behavior of water-like low viscosity liquid as a resist is investigated for particular structures of the template and the contact angles for the template and the substrate. Time evolutions of the flow of the resist are simulated and the mechanism of bubble trapping is demonstrated. The results show that large contact angle between the resist and the template causes bubble trapping, however the contact angle between the resist and the substrate does not greatly influence the results.     

Effect of pre-deformation on the stress corrosion cracking susceptibility of aluminum alloy 2519

The effects of pre-deformation and strain rate on the stress corrosion cracking （SCC） behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension （SSRT）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones （PFZ） become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.     

Activated carbon-supported catalyst loading of CH4N2O for selective reduction of NO from flue gas at low temperatures

Selective catalytic reduction of nitrogen oxides with loaded CH₄N₂O (low-temperature urea-SCR) is a novel and promising technology to remove nitrogen oxides from low-temperature oxygen-containing flue gas, which can avoid the problem of NH₃ escape. In the present study, a series of industrial-grade biomass-based activated carbon (AC)-supported transition metal oxide catalysts with urea loading were prepared by ultrasound-assisted impregnation, and the physicochemical properties of the catalysts were observed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), graphite furnace atomic absorption spectroscopy (GFAAS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The influences of the AC type, reaction temperature, AC particle size, metal oxide loading, urea load level and loaded active element type on the catalytic activity were studied through experiments. Moreover, the NO adsorption capacities of the AC carrier at different temperatures were also tested and calculated. The results of NO adsorption tests show that the adsorption capacity of AC decreased with increasing temperature. The results of the catalytic performance tests indicate that the copper- and manganese-based catalysts with 6 wt% urea exhibited better activity than the other catalysts. The copper-based catalyst, in particular, yielded better than 93% NO conversion at low temperatures (50–100 °C). Finally, on the basis of the combined characterization results and thermodynamics analysis, a NO removal mechanism of the copper- and manganese-based catalysts was proposed and discussed; the electron transfers of Mn⁴⁺ ⇌ Mn²⁺ and Cu²⁺ ⇌ Cu⁰ promoted the low-temperature urea-SCR method.     

Preparation and Characterization of Glass-Ceramic Basalt Fiber

Basalt fiber(BF) is widely applied in the construction industry to improve the mechanical properties of construction materials. Recent studies show that BF has the potential to further enhance its performance via a crystallization approach. In this work, the glass-ceramic basalt fibers(GCBFs) were prepared through nucleation and crystallization treatments according to the crystallization kinetics calculations. Results from XRD and SEM show that GCBFs have main crystalline phases of Diopside and ...     

In vitro cytotoxicity,corrosion and antibacterial efficiencies of Zn doped hydroxyapatite coated Ti based implant materials

Ti6Al4V alloy is successfully used as implant material in dental and orthopedic surgeries for years due to its much better compatibility, lower density, corrosion resistance, etc. compared to the other metals. Meantime, modification of the surface of these alloys is needed to enhance material-tissue interaction and osteointegration between the implant and the bone. In this study, Ti6Al4V alloy surfaces were modified by application of RF magnetron sputtering technique and coated with zinc (Zn) doped hydroxyapatite (HAp). The obtained coating was very stable with highly crystalline structure, demonstrated enhanced corrosion resistance, osteointegration and antimicrobial effectiveness against Escherichia coli (E. coli) bacteria.     

Realizing particle population inversion of 2.7 μm emission in heavy Er3+/Pr3+ co-doped low hydroxyl fluorotellurite glass for mid-infrared laser

In this work, the population bottleneck of Er³⁺: ⁴I_11/2 → ⁴I_13/2 was overcome for the first time in heavy Er³⁺/Pr³⁺ co-doped TeO₂–BaF₂–La₂O₃–LaF₃ (TBLL) low hydroxyl fluorotellurite glasses. Infrared emission spectra and fluorescence lifetime decay curves reveal that Pr³⁺ ions could deplete the electrons from the Er³⁺: ⁴I_13/2 level faster than those from the Er³⁺: ⁴I_11/2 under 980 nm excitation. Specifically, the energy transfer (ET) efficiency of the Er³⁺: ⁴I_13/2 → Pr³⁺: ³F_3,4 process (ET1) reached 96.27%, while that of the Er³⁺: ⁴I_11/2 → Pr³⁺: ¹G₄ process (ET2) is only 2.17% in the Er³⁺/Pr³⁺ co-doped glass. Additionally, the energy transfer mechanism of Er³⁺ and Pr³⁺ ions was investigated using the Dexter theory, where the energy transfer microscopic parameters C_D-A are 13.21 × 10⁻⁴⁰ cm⁶/s and 0.89 × 10⁻⁴⁰ cm⁶/s for the ET1 and ET2 processes, respectively. Finally, a numerical simulations laser model was developed to discuss the laser properties of the Er³⁺/Pr³⁺ co-doped TBLL fibers. The simulation results indicate that a 2.7 μm laser with a maximum output power of 2.26 W and slope efficiency of 13.89% could be achieved when the fiber background loss is reduced to 0.5 dB/m. The above results suggest that the Er³⁺/Pr³⁺ co-doped TBLL glass has great potential applications in mid-infrared fiber lasers.     

Microstructural evolution and microwave transmission/absorption transition in polymer-derived SiOC ceramics

Herein, we present the structural evolution of polymer-derived SiOC ceramics with the pyrolysis temperature and the corresponding change in their microwave dielectric properties. The structure of the SiOC ceramics pyrolyzed at a temperature lower than 1200 °C is amorphous, and the corresponding microwave complex permittivity is pretty low; thus, the ceramics exhibit wave transmission properties. The Structural arrangement of free carbon in the SiOC ceramics mainly happens in the temperature range of 1200 °C-1300 °C due to the separation from the Si–O–C network and graphitization, while the structural arrangement of the Si-based matrix mainly occurs in the range of 1300 °C-1400 °C owing to the separation of SiC₄ from the Si–O–C network to form nanocrystalline SiC. In pyrolysis temperature range of 1200 °C-1400 °C, the microwave permittivity of SiOC shows negligible change. At a pyrolysis temperature exceeding 1400 °C, the carbothermal reaction of free carbon and the Si–O backbone becomes significant, leading to the formation of crystalline SiC. The as-formed SiC and residual defective carbon improve the polarization loss of SiOC ceramics. In this case, the SiOC ceramics show significantly increased complex permittivity, exhibiting electromagnetic absorption characteristics. These characteristics promote the application of polymer-derived SiOC ceramics to high-temperature electromagnetic absorption materials.