Science and Technology of Materials最新文献

Preparation process and life service solicitations can cause damage on concrete's internal structure, creating cracks that tend to propagate and increase with time. This poses a risk of failure as water penetrates, corroding the rebar reducing concrete's life span. Cement can exhibit up to a certain extent a natural ability to self-heal, consequence of the long-term hydration phenomenon. Some initial cracks can be spontaneously closed if the right conditions are met (humidity). However, it will not be enough to repair major cracks formed internally over a long period of use, so strategies need to be developed to achieve an efficient level of self-healing. This need lead to a new concept – self-healing. The biological approach is a suitable alternative to achieve healing in concrete. In this work, bacteria were immobilised in expanded clay and added to concrete by aggregate replacement.

In the present work, the treatments using sodium hydroxide, flame retardant chemical and combination of both sodium hydroxide and flame retardant changed the physical properties thus reduced the mechanical properties of woven hemp fabric and fabricated composites. However, the treatments increased the fire retardant properties of fabricated composites as indicated by the burning tests, thermogravimetry analyses and limiting oxygen index tests. An assessment based on woods and engineered wood products have shown that the fabricated composites are suitable to be used for building infrastructure materials as an alternative to wood products.

A smart vehicle lighting system that combines the functions of illumination, signaling, communications, and positioning is presented. A traffic scenario is stablished, and tested under ideal environment conditions. Vehicle-to-vehicle (V2V) and infrastructure-to-vehicle (I2V) communications are analyzed. For the V2V communication study, the emitter was developed based on the vehicle headlights, whereas for the study of I2V communication system, the emitter was built on the street-lights. The VLC receivers are located at the vehicle and are used to extract the data from the modulated light beam coming from the LEDs emitters. The VLC receiver is based on a-SiC:H technology and joins the simultaneous demultiplexing operation with the photodetection and self-amplification. The receiver and the transmitters are characterized through spectral response under different optical bias. The spectral sensitivity of the receiver and its optical gain are analyzed. An algorithm to decode the information is established. The experimental results confirmed that the proposed VLC architecture is suitable for the intended applications.

In the present study, the degradation of Reactive Yellow 17 (RY17) azo dye in aqueous solution was performed using UV light and iron ions as activators of peroxydisulfate (S₂O₈²⁻ or PDS). The effect of several parameters affecting the degradation process was studied and the optimum conditions are found to be: [RY17] = 10 mg/L, [Fe²⁺] = 0.05 mM, [S₂O₈²⁻] = 1 mM and the pH = 3. The obtained results showed that the removal degrees of RY17 using different processes such as S₂O₈²⁻/Fe²⁺, S₂O₈²⁻/UV and S₂O₈²⁻/Fe²⁺/UV was 63.3%, 81.0% and 95.4% respectively within 20 min of the degradation. Based on theses removal degrees, the degradation efficiency of the RY17 increases in the order: S₂O₈²⁻/Fe²⁺/UV > S₂O₈²⁻/UV > S₂O₈²⁻/Fe²⁺ > UV > S₂O₈²⁻. The experimental data were analyzed using the first-order, second-order and Behnajady-Modirshahla-Ghanbery (BMG) kinetic models, and the kinetic data were in good agreement with the BMG model. Under the optimal conditions, the comparative study of the RY17 degradation using two salts Na₂S₂O₈ and K₂S₂O₈ showed a strong similarity. The total mineralization was monitored using COD and TOC techniques. The results showed that the peroxydisulfate activated by UV and Fe²⁺/UV system is efficient for the degradation and mineralization of RY17; it could also be an alternative for the treatment of the real wastewater contaminated by azo dyes.

In this paper, we report a study of the influence of the synthesis method on the properties of mixed metal oxides. For this, the syntheses of the mixed oxide by chemical coprecipitation and modified polymeric precursor (MPP) methods containing Ni²⁺, Zn²⁺, Al²⁺, and Zr⁴⁺ were conducted. For this purpose, the samples were characterized by X-ray powder diffraction, which showed defined peaks for the mixed metal oxides (NiO, ZnO, and ZrO₂). The interaction of H₂ with mixed oxides has been investigated using temperature-programmed reduction (H₂-TPR); this result showed that the modified polymer precursor method favored the presence of the peak at elevated temperatures. The N₂ physisorption (BET method) showed that the polymer precursor method provided higher specific surface areas and basic site numbers in relation to the coprecipitation method. Thermogravimetric analysis of the systems decomposition revealed their disintegration at ~550 °C and resulted in mixed metal oxides in both methods.

This study focused on studying the possibility of using concrete with incorporation of slag from blast furnace in the filling of short steel columns. The natural sand was totally or partially replaced by the sand slag in the composition of the concrete. The characterization of these concretes was made based on their physical properties (apparent and specific densities, porosity and fineness modulus), mechanical properties (compressive and tensile strengths) and the microstructure analysis by scanning electron microscopy (SEM). The comparison with the conventional concrete was made. The experimental results show that the percentages of sand slag on the concrete composition have an important effect on the enhancement of the mechanical proprieties. The comparison of the different determined characteristics shows the benefits of the use of sand slag in the concrete composition compared with the conventional concrete.

Cohesive zone models (CZM) are a powerful tool for the design of bonded structures, but they require careful estimation of the cohesive laws for reliable results. This work experimentally evaluates by the J-integral/direct method the tensile and shear CZM laws of three adhesives with distinct ductility. Additionally, by the direct method, the precise shape of the cohesive law in tension and shear of the adhesives is defined. The double-cantilever beam (DCB) and end-notched flexure (ENF) specimens were considered to obtain the tensile and shear CZM laws of the adhesives, respectively. After obtaining the tensile and shear CZM laws, triangular, exponential and trapezoidal CZM laws were built to reproduce their behaviour. Validation of these CZM laws was undertaken with a mixed-mode geometry (double-lap joint) considering the same three adhesives and varying overlap lengths (L_O). The strength prediction by this technique revealed accurate predictions for a given CZM law shape, depending on the adhesive ductility, although all CZM law shapes were moderately accurate.

To increase the confidence in the design of adhesive structures, it is necessary to accurately predict their strength and fracture properties (critical strain energy release rate in tension, G_IC, and shear, G_IIC). It is of great importance the perception of fracture under mixed-mode, namely in which relates to the strain energy release rate in tension, G_I, and shear, G_II. This allows choosing the best failure criterion to use in cohesive zone models (CZM), to predict the joints’ behaviour. This work presents an experimental and numerical study using the Single-Leg Bending (SLB) test on bonded specimens to obtain the mixed-mode fracture properties. The analysis of G_I and G_II obtained during the experimental phase were addressed. Framing the obtained values in several fracture envelopes enable to select which failure criterion is more appropriate for each adhesive. In the numerical simulations it was possible to reproduce the observed behaviour of the experimental tests, with a positive validation of the chosen propagation criteria.

With the rising and development of material science, the application range of aluminum matrix composites is more and more extensive, and the requirements for performance are also higher. Ti₂AlC composites with both the properties of metals and ceramics have been extensively applied in various fields. In this study, highly purified Ti₂AlC which synthesized using atmospheric high-temperature calcination, and then it was mixed with Al powder and processed by pressureless sintering at 750 °C for 30 min; finally Ti₂AlC/Al composite was obtained. The obtained material was observed and analyzed using X-ray diffraction (XRD) and applied in the manufacturing of sports equipment. The surface abrasion was observed, and the frictional wear performance was analyzed. The results suggested that the friction coefficient and wear rate sharply decreased with the increase of the sliding speed, the emergence of surface oxide film and running-in; lamellar exfoliation and severe frictional wear appeared on the surface of the sports equipment when the sliding speed was low.

Several strategies have been established for the synthesis of cobalt oxide nanoparticles with tunable sizes, morphologies and magnetic properties that involve the use of environmentally malignant organic solvent and high temperature conditions. Herein, we report on a facile green approach to synthesize antiferromagnetic Co₃O₄ mesoscale particles, defect free with prism liked-anchored octahedron morphology. The structural and magnetic properties of the as-synthesized Co₃O₄ nanoparticles were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis (EDAX), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) coupled mass (MS), Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). The structural properties indicate that the as-synthesized mesostructured Co₃O₄ particles are pure crystallites of face-centred cubic phase Co₃O₄. The Co₃O₄ mesoparticles had bandgap of 2.86 and 2.54 eV and showed antiferromagnetic behaviour.