Abstract: Zinc oxide (ZnO) nanoparticleswere successfully synthesized by chemical precipitation method at different hydroxyl concentrations. The resulting nanoparticles are characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectroscopy. From TEM images, the measured average sizes of the nanoparticles were 4.45 nm to 5.26 nm. Selected area diffraction(SAED) patternsconfirmed that the nanoparticles were of highly crystalline ZnO having wurtzitephase structure.The energy band gap values red-shifted from 3.79 to 3.64 eV based from excitonic absorption peaks. All the samples exhibited a strong visible emission and decreasing peak intensity in increasing OH- concentration.
Abstract: Unique urchin-like CuO nanostructures were successfully synthesized by a simple chemical bath deposition method at low temperature of 70°C in a short reaction time of 1h. XRD pattern revealed the presence of pure crystalline monoclinic CuO. Morphological analysis revealed the formation of spherical structures composed of numerous hair-like structures arranged in an urchin-like fashion. A plausible growth mechanism was proposed in this paper. Antibacterial test revealed that the nanostructures successfully inhibited the growth of both S. aureus and E. coli.
Abstract: Cellulose and TiO2 nanoparticles were coated on the surface of cotton fabric for photocatalytic self-cleaning. Cellulose-TiO2 dispersion was prepared by mixing TiO2 in cellulose solution (Cellulose in 60%H2SO4 solution). Surface morphology of Cellulose-TiO2 nanoparticles coated sample was analyzed in specimen by SEM. White particles appeared on the surface of the cotton fabrics confirmed that TiO2 was coated successfully. Orange II dye was used as stain and its degradation was observed under UV light. Washing study showed that self-cleaning properties are stable with 1, 3 and 5% TiO2 coated samples. Air and water vapor permeability was not decreased significantly after coating. Tensile strength also was increased significantly after coating.
Abstract: In the present paper, water glass was used to synthesize silica aerogels and calcium magnesium silica aerogels. The present research was aimed to investigate the effect of gel aging time (1 and 24 hours) on the physical and surface properties of aerogels. Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, Fourier Transform Infrared spectroscopy and scanning electron microscopy techniques were used to characterize aerogels. Successful formation of nanopores (2.8-4.4 nm) was approved by N2 adsorption/desorption isotherms. The aerogels contained porous network structure with different surface areas (388.9-729.9 m2 g-1). Aging for longer times led to an ability to decrease the density of the aerogels. The bulk density was higher in silica aerogels than in calcium magnesium silica aerogels. The well-tailored network matrix with high BET surface area (729.9 m2 g-1) and low density (0.116 g cm-3) was achieved via 24 hours gel aging of calcium magnesium silica aerogel.
Abstract: The effect of microwave sintering on the densification of forsterite ceramic was investigated. Forsterite powder was prepared via solid-state reaction method with the application of attrition milling and heat treatment. The forsterite compacts were microwave sintered at 1100 °C to 1250 °C with 30 min holding and a ramping rate of 50 °C/min. The samples were then characterized in terms of phase stability, relative density and microstructure evaluation. This work revealed that microwave sintering is beneficial in producing dense forsterite at lower sintering temperature with shorted operating hour (< 1 hr). Highest relative density of 87.9% was successfully obtained at 1250 °C with estimated grain size of lesser than 1 μm as compared to conventional sintering.
Abstract: The identification of the material models which are used in the finite element analysis for the forming operation and springback are very important in terms of accurate predictions. The aim of this paper is to characterize both the anisotropy and the hardening of the ultra-high strength steel such as martensitic steel (MS steel) in order to identify material parameters of constitutive equation, which able to reproduce the mechanical behavior. Uniaxial tensile tests were carried out for characterizing the anisotropic plastic behavior of the MS steel. Cyclic tests under tension-compression load were also carried out for characterizing the Bauschinger effect during reverse deformation. Yoshida-Uemori hardening model associated with orthotropic yield criterion Hill’s 1948 is used to represent the in-plane mechanical behavior of the martensitic steel. The resented results show a very good agreement between model predictions and experiments: flow stresses during loading and reverse loading are well reproduced.
Abstract: The pitting corrosion behavior of AISI 202 stainless steel (SS) – a low-nickel, austenitic SS grade, was investigated by means of cyclic voltammetry (CV) technique complemented by Scanning Electron Microscopy (SEM). From the starting potential, the current density decreases and changes its sign at the corrosion potential (Ecorr). The anodic response exhibits a well-defined anodic peak followed by a passive region. A noticeable increase in the anodic current density was observed after reaching the breakdown potential (Eb). The second anodic peak which may be attributed to onset of oxygen evolution was also observed. Moreover, the cyclic voltammograms revealed that hysteresis loop is absent for all the studied concentrations, indicating that AISI 202 SS in citric acid is highly resistant to pitting corrosion as also supported by the results of SEM. It was found out that the critical current density (icrit) increases with increasing citric acid concentration.
Abstract: Band structures with pearlite and ferrite aligned as stripes can be created during the heat treatment of carbon steel. Since band structures undermine the mechanical quality of end products, it is highly important to select a process condition that will not create band structures as a result of heat treatment. This study verified the effect of temperature and cooling rate on the creation of band structures during heat treatment of 35MnB and 25Mn steel tubes for drive shafts and also considered the optimal process conditions to remove band structures or prevent their creation. The experimental results suggest that, during heat treatment of 35MnB and 25Mn steel tubes, it is most effective to ensure a cooling rate faster than furnace cooling in order to prevent band structures.
Abstract: The desire to mitigate climate change due to greenhouse gas emissions has led to the exploration of plant fibers as alternative materials for various industrial applications acoustics inclusive. In this investigation, sound absorption properties of barkcloth, a nonwoven fabric from Antiaris toxicaria were characterized. Theoretical empirical sound absorption models based on Delany and Bazley such as Miki, Wu and Allard – Champoux were utilized to validate the experimental data. The empirical models were in agreement with experimental data; Incorporation of an air-gap between the fabric layers had a positive influence on the overall sound absorption behavior of barkcloth fabrics rendering the fabric a good sound absorption material.
Abstract: This paper addresses the problem of the speed of plane waves of dilatation, in which the impacted end is sustained so as to maintain constant strain behind the wave front, through auxetic solids considering density correction; the importance of this work can be inferred from the lack of knowledge on this type of material. Results for the dimensionless wave speed reveal that the Poisson’s ratio magnitude and the strain play primary and secondary roles, respectively. In addition, there is better control of wave speed in the auxetic region than in the conventional region due to a more gradual change of the wave speed in the former. Hence the use of auxetic materials facilitates better passive control of wave propagation in bulk solids.