Results in Materials最新文献

This research was based on the synthesis of new materials with capacitive properties and low cost, seeking efficient energy storage, through the manufacture and characterization of composite materials of polyvinyl alcohol (PVA)/multiwalled carbon nanotubes with carboxyl group (MWCNTs-COOH) (1 %) for electrodes. Forcespinning and electrospinning techniques were used to develop composite fiber films and compare the physical structure of the fibers and its influence on their capacitive properties. These samples were characterized by SEM, FESEM, FT-IR, XRD, TGA, Raman spectroscopy and electrochemical techniques. The characterization of the composites makes evident the structural modification that the material underwent after the treatments. The electrochemical parameters were measured by electrochemical impedance spectroscopy (EIS), with the samples immersed in H₂SO₄ 1 M as electrolyte. The PVA/MWCNTs-COOH composites with thermal treatment (340 °C) showed a considerable decrease in total impedance of up to 6 orders of magnitude (124 Ω) with respect to the blank sample (2.3 × 10⁸ Ω), as a function of the immersion time in the acid solution. As well as, an increase in the specific capacitance of up to 8 orders of magnitude (1.01×10⁻² F cm⁻²) with respect to the blank sample (5.07 × 10⁻¹⁰ F cm⁻²) for the composite manufactured by the electrospinning technique. The obtaining of fibers with directionality as a result of the forcespinning technique, the highly crossed network observed by electrospinning and the electrochemical properties shown by the structural modification of PVA/MWCNTs-COOH composite, make it, a material with potential technological applications such as electrode in electrochemical capacitors.

Autogenous shrinkage is a serious problem for high-strength concrete, which may lead to early-age cracking. Shrinkage-reducing agents are typically used to mitigate the autogenous shrinkage of concrete. However, some negative effects, such as unstable workability and the reduction of compressive strength, will be caused. In this study, emulsified or plain cooking oil is used as a shrinkage-reducing agent in low water-binder ratio concrete. Deformational behaviours of concrete with cooking oil and normal commercially available shrinkage-reducing agent are investigated. Experimental results show that the utilization of cooking oil could significantly reduce the autogenous shrinkage of high-strength concrete due to the reduction of surface tension. Additionally, emulsified cooking oil is better than normal shrinkage-reducing agents and plain cooking oil in many aspects of the concrete. Micro-structure of the concrete with different shrinkage-reducing agents is also observed. Emulsified cooking oil is considered a promising admixture for the mitigation of autogenous shrinkage of high-strength concrete.

This investigation focuses on the development and assessment of biopolymer-based green biocomposite materials that contain tamarind seed kernel powder (TKP) either in its raw or polyacrylic acid (PAA) grafted form as the reinforcing component, combined with polyvinyl alcohol (PVA) as the matrix material. The goal is to develop biopolymer TKP based green biocomposites with a biodegradable PVA matrix for food grade packaging and biomedical applications. Both raw TKP reinforced PVA and PAA grafted TKP reinforced PVA, two forms of sustainable green biocomposites, were developed. Compression molding was used to combine various raw or PAA grafted TKP loadings with PVA to produce various biocomposites. The loadings were 0 %, 0.25 %, 0.5 %, 1 %, 5 %, and 10 % in weight. To confirm the PAA grafted TKP, attenuated total reflection-fourier transform infrared (ATR-FTIR) spectrum analysis was employed. The mechanical properties of the biocomposites were examined, and it was discovered that the grafted biocomposites exhibited 4 % higher tensile strength and elongation at break (%) on average than the raw TKP reinforced PVA biocomposites. The Charpy impact strength of the biocomposites exhibited an average 28 % improvement in impact resistance with modified TKP and an 8 % increase with raw TKP when compared to pure PVA sheets. Additionally, the PAA-grafted TKP reinforced PVA biocomposites outperformed the raw TKP reinforced PVA biocomposites in water absorption tests, exhibiting an average improvement in moisture resistance of nearly 13 %. Scanning electron microscopy (SEM) tests revealed that the PAA-grafted biocomposites had a more uniform dispersion of fillers inside the PVA matrix as compared to the raw TKP/PVA biocomposites. These findings enable in the development of high-performance, environmentally friendly and green biocomposite materials for a variety of uses.

Green composites, renowned for their biodegradable and recyclable attributes, have recently gained substantial prominence. Their sustainability, eco-friendliness, and lightweight characteristics position them as a compelling alternative to conventional plastic-based materials. This study delves into the mechanical performance, encompassing tensile, flexural, and Charpy impact test properties, of jute and flax thermoplastic composite laminates. Additionally, it explores the flexural behavior of sandwich composites reinforced with jute and flax fabrics individually. To accomplish this, we manufactured various composite laminates, including jute/PP, flax/PP (64.2 % fiber mass fraction), flax/PP (45.0 % fiber mass fraction), and plasma-treated flax/PP (PTF/PP) composite laminates using compression molding techniques. We also crafted sandwich composites by integrating flax and jute natural fabrics as reinforcements into a polypropylene (PP) matrix for the sandwich surface layer, along with recycled polyethylene terephthalate (PET) foam as the core material. This allowed for a comprehensive comparative analysis of their functional properties. In addition to mechanical testing, the differential scanning calorimetry (DSC) analysis was conducted on various composite laminates to evaluate the crystallinity levels and melting behavior of PP within these diverse formulations. Further characterizations included Fourier transform infrared (FTIR) spectroscopy and digital imaging analysis. Our experimental results unequivocally demonstrated the superior performance of Flax/PP composite laminates over Jute/PP composite laminates in terms of flexural, tensile, and impact properties. In the context of sandwich composites, Flax/PP/PET foam exhibited the highest force resistance, along with superior bending strength and modulus when compared to Jute/PP/PET foam. Notably, Jute/PP/PET foam displayed a higher incidence of delamination and breakage. Interestingly, both sandwich composites demonstrated nearly identical properties in the impact test. Furthermore, plasma treatment of flax composite laminates had a beneficial effect on specific mechanical properties, leading to an 8.6 % enhancement in flexural strength (54.09 MPa) compared to the performance of flax/PP (45.0 % fiber mass fraction) laminate.

Multiphase nanomaterials are fascinating due to the synergistic effect between the crystalline phases that lead to improved device performance. Publications are available for the synthesis of monophasic copper oxides, such as Cu₂O and CuO, and the mixed-phase Cu₂O–CuO counterpart using different synthesis methods. However, literature report is scarce that focuses on the fabrication of bi-phase Cu₂O–CuO thin films by the spray pyrolysis technique without phase transformation to form the monophasic counterparts. The present work attempts to prepare solely mixed-phase Cu₂O–CuO films through small incremental change in substrate temperature, in steps of 20 $°C$. Structural analysis of the pyrolyzed films revealed the formation of a bi-phase Cu₂O–CuO crystal system. The crystallite size increased from 18.64 to 23.94 nm, microstrain decreased from 7.134 $\times {10}^{-4}$ to 5.625 $\times {10}^{-4}$, while stacking faults decreased from 3.753 $\times {10}^{-3}$ to 2.942 $\times {10}^{-3}$ with an increase in temperature. Microstructural analysis showed nanoaggregates with increased particle size at increasing temperature. The films exhibited a common optical bandgap of 2.61 eV. The values of the static refractive index and optical electronegativity were found to be 2.47 and 0.70, respectively. The surface roughness increased from 41.3 to 90.9 nm with substrate temperature.

Investigating non-metallic inclusions within ultra-high-strength-steel via conventional methods is a known: however, the challenge is to obtain chemical information of such inclusions at the sub-micrometer level. In this context, probing Fe-based oxide in inclusions is a vital aspect for guiding steel’ performance. The vibrational properties of sub micrometer size Fe-based oxides were investigated by Raman mapping along with chemometric analysis with the aim of probing their chemical composition. Highly contrasted Raman spectra were recorded from several inclusions embedded at different spatial locations. The observed spectral features were identified as specific markers of hematite (α-Fe₂O₃) and magnetite (Fe₃O₄). Principal Component Analysis was used to confirm the presence of these markers and potentially revealing additional patterns. Their unambiguous assignment has been inferred by comparing our experimental findings with the literature data recorded either in single crystals of iron oxides or oxyhydroxides. Micro-Raman spectroscopy is proven to be a reliable, cost-effective, and non-invasive tool for the unambiguous identification of subsurface regions of steel.

In this research, the Zn-Yb-Sb materials in the form Zn_1-xYb_xSb; x = 0.02 to 0.8, were composed by a solid-state microwave method. These samples were examined to determine the crystal structure by XRD analysis, which indexed to the orthorhombic phase. The dominant peak (112) had a clearly shift in Bragg angle from 28.536° to 28.784° with increasing Yb content. The Yb content (x) effects on the thermoelectric properties (TE) was measured at the temperature reach to 500 K. Increased the Yb content (the sample with x = 0.8) in Zn_1-xYb_xSb caused an increase in the Seebeck coefficient (486 μV/K at 433 K) and a decrease in each of the hole concentration (3.02 × 10²¹ cm⁻³) and the electrical conductivity (5320 S/m). Ascribing to the increased Seebeck coefficient, the higher value of the power factor measured in this research was 1257 μW/mK² at 473K for the sample of Zn_0.92Yb_0.08Sb (x = 0.08).). These experimental results suggest that a clear idea of the application of the Zn_1-xYb_xSb for TE modules.

This study employs the sol-gel auto combustion technique fueled by diethanolamine (DEA) to synthesize nanocrystalline magnesium ferrite (MgFe₂O₄) powders. During the study, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL), and vibrating sample magnetometry (VSM) were then used in order to determine how differing calcination temperatures influence the structure, chemical bonding, surface texture, morphology, optical, fluorescence, and magnetic properties of the resulting MgFe₂O₄ powders. The findings from the XRD and FT-IR analysis indicate that a single-phase spinel structure is formed in each of the MgFe₂O₄ samples. According to UV-DRS analysis, optimal calcination improved sample reflection levels in comparison to the visible and infrared spectral findings for the as-synthesized sample. The calcined samples exhibited bandgap energy (E_g) ranging from 2.11 eV to 2.14 eV, which was greater than the 2.02 eV of the as-synthesized sample. Examination of the PL spectra in the range of 380–700 nm revealed various light emission bands for the samples, which increased significantly in intensity at higher calcination temperatures. Furthermore, higher calcination temperatures also increased the magnetization of the MgFe₂O₄ spinel powders, while coercivity dropped significantly.

The heat of hydration is fundamental in understanding the hydration mechanism of cementitious materials, and temperature can significantly affect the heat of hydration. A recent study has shown that coal-derived char can be used as a green additive for improving the engineering properties of conventional cement grout. However, the impact of temperature on heat of hydration of char-cement grout is currently unknown. In this study, the heat of hydration (with degree of hydration) of cement and char-cement grouts at 5, 23, and 35 °C are investigated. This study reveals that incorporating char into the cement grout enhances its degree of hydration at temperatures ranging from 5 to 35 °C, highlighting the potential advantages of using coal char in grouting applications, especially at low temperature.

This study explores the effect of preheating before rolling on the microstructural and mechanical properties of an AA5052/Ti/AA5052 lamellar composite fabricated by roll bonding. The roll bonding was done in two ways: conventional rolling and preheating before rolling. Preheating was done before rolling for 7 min at 350 °C. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness, and tensile tests were used for microstructural and mechanical investigations. By performing preheating, the strength increased from 468 MPa to 511 MPa, elongation changes were insignificant, and hardness decreased in aluminum and titanium layers from 108 to 100 HV and 234 to 212 HV, respectively. By preheating, aluminum diffusion in titanium and metallurgical connection occurred. Therefore, SEM showed better bonding in preheated specimens.