Abstract: Recycled aggregates concrete (RAC) becomes an important participant in recycled materials. This study was performed in order to evaluate the effect of recycled coarse aggregates (RCA) on the chloride resistance of concretes with different coarse aggregates replacement ratio under wetting–drying cycles. Composition influence on the concrete were studied with different the addition of admixtures. The results indicate that the free chloride content decreased with the increasing of depth, whist it increased with the increasing replacement ratio of RCA at the same depth. Wetting–drying cycles accelerated the process of chloride diffusion. It was also found that the addition of admixtures can improve the ability of chloride resistance of concrete.
Abstract: The properties of alloys depend on its microstructure, such as the size of grains. In general, the balanced mechanical properties of alloys can be obtained with small grain size. While the grain size of alloys may increases under heat treatment, thermal mechanical processing and service condition of high temperature, i.e., the grain growth is inevitable. The effort of most research is to control the rate of grain growth and avoid abnormal grain growth. For example, pinning the grain boundary and reduce its mobility with the second phase particles in order to prevent grain growth. Therefore, the properties of the alloys will not decreases dramatically and the structure retains a high degree of integrity. The details of grain growth with particle pinning were investigated by phase field simulations in the present paper. It is found that, with the same size of pinning particles, the pinning effect increases with the increases of the pinning particle number. With the same pinning particle number, the pinning effect increases with the increases of pinning particle size. Under the same total volume of pinning particles while different particle size and number, the pinning effect is complicated and it will be discussed in details. The pinning effect decreases with the increases of grain boundary energy. These findings could shed light on the understanding of the grain growth kinetics with particle pinning.
Abstract: The corrosion behavior of Cr-C-deposited steel specimens, which were prepared from the Cr3+-based bath, was investigated in the 0.5 M H2SO4 solution. After electroplating, the deposited specimens were annealed at 300, 450, 600 and 700°C for 1 h. Based on the results of corrosion test, the corrosion resistance of as-plated and annealed Cr-C deposits has strongly related to the surface cracks. However, the corrosion resistance of 450°C-annealed Cr-C deposit could be obviously improved when the deposit was pre-polarized in the passive potential region. Annealed at 700°C, the corrosion resistance of Cr-C deposit is markedly raised owing to formation of Cr oxides on the crack surface during annealing.
Abstract: The lime addition in the mix asphalt became nowadays an innovative technique in the field of infrastructure. The objective of the experiences is to improve the durability of roads, especially in the United States and in Europe. In Morocco, this aspect remains in the reflecting phase, a part from some simple experiences; this technique allows, from a precise dosage of lime, to increase the service life of roads, and to optimize the maintenances costs caused by the damages.
Abstract: In present work, the influences of TiO2 nanoparticles addition on the tribological and mechanical behavior of polyphenylene sulfide (PPS) were investigated. The composites samples containing TiO2 nanoparticles at various percentages (0, 1, 3, and 6 wt. %) were prepared by melt mixing process using single screw extruder at 325 °C and 20 rpm. A pin-on-disc sliding test machine was used for measurement of wear volume and the friction coefficient. The counterface was made of steel carbide with roughness 0.1 μm Ra. The tests were run at a sliding speed of 0.4 m/s and 1 m/s, the contact pressure 0.65 Mpa with different sliding distances (5, 10, 15 and 20 km). Mechanical properties of PPS nanocomposites were studied to evaluate the influence of the nanoparticles addition, as well as examined the relation between the tribological and mechanical behavior. It was found that nanoparticles could further enhance the tribological properties. The lowest wear volume and friction coefficient was observed at 1 m/s was PPS+1wt. %, and for 0.4 m/s was observed in PPS+6wt. %. The results indicate that the mechanical of PPS nanocomposites have been improved, the impact strength and hardness increased with the incorporation of TiO2 nanoparticles. The density was also increased with TiO2 nanoparticles.
Abstract: This paper investigates the flow, thermal and mechanical properties of waste polypropylene (WPP) reinforced with silica (SiO2) nanoparticles (NPs). Recently the researches prove that the addition of NPs to the thermoplastic polymer produces significant change in its properties. SiO2 NPs of 0.001, 0.003, 0.006, 0.009, 0.012 and 0.015wt% were mixed with the WPP using twin screw extruder. The mixing process performed at 10 rpm and 190°C. The topography and particle size distribution of 0.001, 0.006 and 0.015 of SiO2 NPs concentrations samples are analyzed using atomic force microscopy (AFM). The crystallinity of nanocomposite was examined by X-ray diffraction. The melt flow rate (MFR) and melt volume rate (MVR) are tested due to SiO2 NPs concentration at standard condition using melt flow index (MFI) device. The shear viscosity and melt density are calculated using MFR and MVR values. Differential Scanning Calomitry (DSC) is used to show the effect of SiO2 NPs concentration on the thermal history of nanocomposite. Charpy impact strength and hardness are tested. The results show that the MFR and MVR increase with the NPs concentration increasing. The shear viscosity decreases with MFR and MVR increasing. The crystallinity level and the crystallinity temperature decreases with SiO2 NPs concentration increasing while impact and hardness increasing. Clear difference between solid and melt density is observed. There is a compatible between the thermal, flow and mechanical properties of different SiO2 nanocomposite samples.
Abstract: Effects of sea water immersion for palm fiber in relation to surface morphology, roughness and bonding between the fiber and sago matrix were observed. Duration of immersion varied in 1, 2, 3 and 4 weeks, and then dried at room temperature for 3 hours continued by oven at 80 °C for 6 hours. SEM and roughness arithmetic tests were applied to see surface morphology, roughness and bonding between fiber and the matrix. Result shows fiber morphology and roughness varies by the duration of immersion. The surface roughness increases as immersion continues along with fiber - matrix bonding improvement. The maximum duration of 4 weeks fiber immersion resulted in the best interlocking of matrix and fibers, as the slits between them disappear.
Abstract: Zinc oxide thin films were deposited on glass substrate at a substrate temperature of 673K by spray pyrolysis method using different concentration of 0.0125M, 0.025M and 0.05M of Zinc acetate solutions. The effect of molar concentrations on structure, surface morphology and magnetic properties of ZnO films were investigated using x-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. All deposited films were polycrystalline in nature with hexagonal wurtzite structure having a preferential growth orientation along (101) plane. An improvement of crystallinity in the deposits with increasing concentration of sprayed solution was noticed. All deposit exhibit fibrous structure which increases with increase of precursor concentration solutions. At room temperature, all deposited films were shown diamagnetic character but when cooled to 5K, they have shown paramagnetic characteristics.
Abstract: The problem of reliability prediction and assurance is characteristic of wireless devices based on nanoscale multilayer heterostructures because of the sensitivity of heterostructures’ parameters to the degradation processes due to the thinness of layers. In the current work, the degradation of the nanoscale AlAs/GaAs resonant-tunneling heterostructures due to the diffusion of the constituent elements was investigated. Analysis and comparison of data on Al and Si diffusion coefficients in GaAs shows that they strongly vary depending on the conditions of heterostructure fabrication. This happens while the defect density of the grown heterostructures depends on a large number of technological factors such as the substrate temperature during molecular beam epitaxy, chamber pressure, annealing temperature and time, defect density in the initial substrate, and many others. The values of the diffusion coefficients obtained by the authors of this article by IR spectral ellipsometry are consistent with the data of foreign researchers. This allows their use to predict the reliability of resonant tunneling diodes and nonlinear radio transmitters based on them.