International Journal of Mechanical and Materials Engineering最新文献

The excellent clinical performance of yttria-partially stabilized zirconias (Y-SZs) makes them promising materials for indirect restorations. However, the Y-SZ phase stability is a concern, and infiltrating Y-SZs with a silica nanofilm may delay their degradation processes. In this study, we analyzed stabilities of silica-infiltrated zirconia surfaces after exposure to artificial aging (AA).

Four zirconia materials with different translucencies (n = 40) were used, including low translucency 3 mol% Y-SZ (3Y-LT, Ceramill ZI, Amann Girrbach); high translucency 4 mol% Y-SZ (4Y-HT, Ceramill Zolid); and two high translucency 5 mol% Y-SZs (5Y-HT, Lava Esthetic, 3M and 5Y-SHT, Ceramill Zolid, FX white). Sintered specimens were exposed to 40 cycles of silica (SiO₂) through room temperature atomic layer deposition (RT-ALD) using tetramethoxysilane (TMOS) and ammonium hydroxide (NH₄OH). AA was applied for 15 h in an autoclave (134°C, 2 bar pressure). Stabilities of zirconia-silica surfaces were characterized in terms of hardness and Young's modulus using nanoindentation techniques and crystalline contents using x-ray diffraction (XRD) analyses. Silica deposition was also characterized by X-ray photoelectron spectroscopy (XPS).

There was a significant effect of the interaction of materials and surface treatments on the hardness and Young's modulus values of zirconia-silica surfaces (p < 0.001). Silica deposition on zirconia surfaces improved the material resistance to degradation by AA.

Emerging challenge posed by multidrug-resistant Bacillus spp. phytopathogens on agriculture and their commodities exerts pressure on global food security. This mandates the search for other alternatives to existing antibiotics. This study reports a novel method of green synthesis of platinum nanoparticles (PtHGNM) using aqueous extract of Himalayan garlic (Allium sativum). Physicochemical characterization techniques including UV-visible spectrometry, FT-IR, XRD, DLS, zeta potential, and FESEM-EDAX disclosed the biogenic fabrication of a stable and amorphic nano platinum material. This nanoparticle exhibited high bactericidal efficacy and effectively inhibited biofilm formation by the model plant-borne pathogens used in this study. We estimated the membrane integrity, oxidative enzymes and stress parameters of bacteria to elucidate the underlying mechanism of action of PtHGNM. This research uncovered the potential of biogenic nanoparticles for sustainable plant disease management and paved the way for further analysis of its properties and mechanism of its action.

In this study, the performance of a-Si:H/μc-Si:H tandem solar cells was comprehensively assessed through two-dimensional numerical simulations. Our work involved optimizing the layer thicknesses and exploring advanced light-trapping techniques to enhance photogenerated current in both sub-cells. To reduce surface reflections on the top cell, we proposed a two-layer antireflection coating, composed of SiO₂/Si₃N₄. Additionally, we implemented a 1D photonic crystal as a broadband back reflector within the solar cell. In order to balance the current density between the sub-cells and prevent carrier accumulation at the interface, we introduced a tunnel recombination junction (TRJ). This TRJ consisted of n-μc-Si:H/p-μc-Si:H layers with a thickness of 10 nm. Under global AM 1.5G conditions, our proposed cell structure exhibited impressive electrical characteristics, including an open-circuit voltage of 1.38 V, a short-circuit current density of 12.51 mA/cm², and a fill factor of 80.82%. These attributes culminated in a remarkable total area conversion efficiency of 14%.

Cement production for concrete is one of the main reasons why the building industry contributes significantly to carbon dioxide emissions. This paper investigates an innovative approach to utilizing CO₂ by incorporating mixed biochar in mortar. Various dosages (0%, 3%, 5%, and 10%) of mixed biochar were explored to assess their impact on the structural properties and environmental sustainability. In this study, mixed biochar was prepared using the pyrolysis method, in which biomasses (rice husk and sawdust) were heated in the absence of oxygen for 2 h in a muffle furnace at the heating rate of 10 ℃/min to 550 ℃ with a 2-h holding time. The replacement of biochar was done with cement in a mortar mixture for casting the cubes followed by putting them in the carbonation chamber for 28 days curing. After that, the cured samples were tested for mechanical strength, porosity, density, and water absorption. X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) showed that biochar supplementation promoted cement hydration products. Field emission scanning electron microscope (FESEM) analysis showed that several cement hydrates such as C-S–H, Ca(OH)₂, and CaCO₃ were formed with different doses of biochar and increased mechanical strength. Addition of 10 wt. % biochar increased the compressive strength of the composite by 24.2% than the control respectively, and successfully promoted the CO₂ sequestration with 6% CO₂ uptake after 28 days of accelerated CO₂ curing. The present research has shown the benefits of optimally integrating mixed biochar with cement in the development of low-carbon, sustainable cementitious materials that have the potential to convert building materials like concrete in the future.

In the present work, the enhancement of photoinduced optical activity in a photosensitive nanolayer of AgCl doped by Ag nanoparticles, using bi-periodic crisscrossed self-organized periodic nanostructures (C-SPNs) is achieved. We found that the formation of two non-identical SPNs (i.e., with different periods), which crisscrossed each other, enhances the rotation of the polarization plane of the linear polarized probe beam, compared to the case when the two nanostructures are identical (i.e., having the same period). The difference in periods of the two C-SPNs increases the anisotropy of the medium, which in turn boosts the optical chirality produced by the formation of complex crisscrossed gratings made of Ag nanoparticles. The angle between the two gratings can be a control parameter for the amount and sign of rotation of the polarization plane of the probe beam. The enhanced optical activity of the bi-periodic C-SPNs, compared to the identical C-SPNs, can be attributed to the formation of more intricate chiral building blocks at the intersections of the two gratings.

Porous solids are commonplace in engineering structures and in nature. Material properties are inevitably affected by the internal inhomogeneity. The effective thermal conductivity of porous materials has been and remains to be a subject of extensive research. Less attention has been devoted to thermal conductivity impacted by internal cracks. This study is devoted to theoretical analyses of the combined effects of pores and cracks on the effective thermal conductivity. Systematic numerical simulations using the finite element method are performed based on two-dimensional models, with periodic distributions of internal pores and cracks. The parametric investigations seek to address how individual geometric layout can influence the overall thermal conduction behavior. In addition to circular pores and isolated cracks, angular pores with cracks extending from their sharp corners are also considered. It is found that both isolated cracks and cracks connected to existing pores can significantly reduce the effective thermal conductivity in porous materials. Since it is much easier to microscopically detect internal pores than thin cracks, care should be taken in using the apparent porosity from microscopic images and density measurements to estimate the overall thermal conductivity. Quantitative analyses of the detailed geometric effects are reported in this paper.

Bismuth ferrite (BFO) nanoparticles have emerged as a non-toxic catalyst with remarkable potential for the photodegradation of various environmental pollutants. A notable departure from conventional approaches, where cations are added as dopant, this study achieved enhanced catalytic performance through anion substitution. Specifically, replacing oxygen atoms with nitrogen introduces spin-polarized defect states within the BFO’s energy gap, resulting in a notable reduction in the energy band gap. Nitrogen doping of bismuth ferrite yields a novel material with exceptional capabilities for the photodegradation of methylene blue dye and the reduction of 4-nitrophenol. Comprehensive characterization, including X-ray diffraction, Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, has unequivocally confirmed the successful incorporation of nitrogen into the BFO nanoparticle lattice. Interestingly, field emission scanning electron microscopy analysis revealed no significant alteration in nanoparticle size after nitrogen doping. Meanwhile, UV-diffuse reflectance spectroscopy unveiled a distinct decrease in the energy gap upon nitrogen incorporation. The observed improvements in catalytic activities can be attributed to nitrogen ions, introduced as substitutes, effectively occupying the oxygen defects within the sample, thereby diminishing recombination centers for photogenerated charge carriers and decreasing recombination rates. Additionally, adsorption kinetics studies underscore the efficacy of the catalyst surface in adsorbing methylene blue and/or 4-nitrophenol, conforming to the Ho pseudo-second-order model. This study not only highlights the exciting potential of nitrogen-doped bismuth ferrite nanoparticles in environmental remediation but also sheds light on the intricate interplay between anion substitution, band structure modification, and catalytic performance enhancement.

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This paper presents the effect of size reduction of palm oil fuel ash (POFA) in the nanoscale to improve the mortar strength. In this work, three different particle sizes of POFA prepared using the LA abrasion machine were used as a cement replacement. The physical and chemical properties, mineralogy, and morphology of all POFA specimens were studied. The effect of size reduction on the pozzolanic reactivity of POFA is also studied. The mortar mix design that contained micro and nano POFA was prepared and evaluated for its compressive and flexural properties at the ages of 7, 28, 56, and 90 days. Response surface methodology was used to evaluate the relationship between the factors (cement replacement) and responses (compressive and flexural strength), aiming to find the best mix design. The grinding method in this work produced POFA as small as 110 nm. The nano POFAs were observed to have better pozzolanic reactivity compared to micro POFA. The results show that nano POFA increased the mortar strength activity index by up to 20% compared to micro POFA. The best mix design was found using a combination of 10 and 3% of micro and nano POFA as cement replacement. The best mix design shows excellent early compressive strength (7 days) compared to other mixes, although the difference in long-term compressive strength is insignificant. Similar findings were observed for the flexural strength, whereby the best mix design was obtained using a combination of 10 and 3% of micro and nano POFA. This work may provide useful insight into the effect of size reduction on the pozzolanic reactivity of POFA.

This study presents a novel and eco-friendly approach for synthesizing silver nanocomposite at room temperature. The method utilizes chitosan derived from snail (Archachatina marginata) shell waste crosslinked with EDTA as a combined reducing and capping agent. The existence of silver nanoparticles in the composite was confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive X-ray (EDX), energy dispersive X-ray fluorescence (EDXRF) and thermogravimetric analysis (TGA). The TEM, SEM, XRD, and analyses revealed that the silver nanoparticle has a face-centered cubic structure with an average size of 45.30 nm respectively. EDX and EDXRF showed characteristic silver peaks confirming the formation of silver nanoparticles in the composite while TGA indicated that silver nanoparticles contributed to good thermal stability of the composite. The formation of silver nanoparticles was indicated by a brown color transformation and an ultraviolet visible (UV Vis) absorption peak at 435 nm. The synthesized nanocomposite demonstrated promising antibacterial activity against both Staphylococcus saprophyticus DSM 18669 and Escherichia coli O157 strains, with S. saprophyticus showing higher susceptibility. This highlights the potential of chitosan-EDTA silver nanocomposites as alternative antimicrobial agents.

Polymer patterns are promising for many applications due to their high stability and superior chemical and physical properties. By functionalizing various surfaces with polymer patterns, it is possible to detect and prevent many common infections. Treatment of resistant bacteria with antibiotics is limited and they can spread quickly. For this reason, it was designed a surface that can prevent contamination by functionalizing polymer patterns. In the study, a polymer pattern model obtained by combining gallic acid with gold nanoparticles (GA@AuNP) synthesized through green chemistry was designed. Polymer-patterned structures were obtained on silicon wafers using Poly(ethylene glycol) (PEG) polymer and were self-assembled with GA@AuNPs. Diagnosis and inhibition of bacterial cells in a short time were demonstrated with the prepared modified PEG polymer pattern. Surface-enhanced Raman scattering effects were used to optimize the stability of surfaces patterned with self-assembled GA@Au NPs. By modification of PEG polymer patterns, a biomarker design that can be used in many different bioapplications is proposed.