Materials Sciences and Applications

  • Characterization and Cu(II) adsorption properties of activated carbons prepared from cotton stalk by one-step H3PO4 activation.

    In the present study adsorption of copper (II) ions from aqueous solution by activated carbon was produced from cotton stalks husk via thermal pretreatment preceding chemical modification with phosphoric acid was investigated under batch mode. The biosorbent was characterized by thermo-gravimetric analysis, Fourier transform infrared (FT-IR) and iodine number. The influence of copper concentration, contact time, and temperature was studied. Sorption equilibrium time was observed in 30 min. The equilibrium adsorption data were correlated with Freundlich and Langmuir adsorption isotherm models. The kinetics of the adsorption process was tested by pseudo- first-order, pseudo-second order and Intra-particle diffusion. It was shown that adsorption of copper could be described by the pseudo-second order kinetic model. Thermodynamic parameters such as Gibbs free energy (∆G0), the enthalpy (∆H0) and the entropy change of sorption (∆S0) have also been evaluated and it has been found that the adsorption process was spontaneous, feasible and endothermic in nature. The results indicated that Activated carbon was produced from cotton stalks husk can be used as an effective and low-cost adsorbent to remove copper (II) from aqueous solution.

  • Optimizing the Surface Quality of Textile Composites for Bonded Repairs

    With the accelerated use of woven composites in many industries like aerospace, marine, sports, construction, automobile and many more their repairs have become an inevitable part of it. The current problem with repairs is, even with precise machining there are bond failures due to inadequate surface quality. In this research, machining techniques like stepped and scarf repairs and abrasion techniques are used on the woven coupons to evaluate their influence on the surface characteristics. Preliminary evaluation of the surface characteristics is done using a surface profiler, to measure the topographical features like surface roughness and amplitude of the peaks and valleys. Further, the results obtained from the profiler are validated using microscopy and contact angle test to identify the trend between surface roughness and wettability. Finally, the results obtained from the various experiments helps us to identify an optimum surface quality needed prior to bonding in terms of surface roughness and contact angle. The results for 3K woven glass fibre shows an optimum surface roughness in the range of 2-4 µm and contact angle below 60˚

  • Simulation of the Dendritic Growth Velocity for Binary Alloy Al-Cu in the Undercooled System

    The phase-field model was applied to simulate the solidification kinetics to undercooled Al-Cu alloy. The relationships between material properties and model parameters are presented. The diffusivity of solute in the solid region and liquid and liquidus temperature are calculated during the simulation of solidification process. As an example, the two-dimensional computations for the dendritic growth in Al–Cu binary alloy have been performed. The dendritic morphology calculated by phase-field model showed features that are commonly found in experiments on the solidification. The concentration profiles of solute calculated in the solid region and liquid are not completely horizontal, showing evidence of microsegregation. The velocity of the dendrite tip and solute concentration at the interface front are calculated. It is found that the tip velocity is greatly concentration dependent around interface. In order to validate the growth kinetics predicted by this model tests have been performed for comparison with Stefanescu’s model. The present work based results show good agreement with those obtained by Stefanescu. The dependence of growth velocity on the initial concentration and super-cooling are also demonstrated.

  • Enhancing the liquid phase exfoliation of graphite in both aqueous and organic mixtures

    Two different solvent mixtures, aqueous and organic, were used in the graphite liquid phase exfoliation. These solvent mixtures were selected through a detailed study of Hansen Solubility Parameters. Different operational sonication parameters (sonication temperature, cycle, amplitude and time) were studied in order to analyze their influence over the exfoliation process. Exfoliated graphite obtained after different sonication conditions were further characterized by RAMAN spectroscopy and thermogravimetric techniques. Obtained results showed that, among all the studied sonication parameters, time is the most important one due to its influence over characteristics of the final exfoliated product. Thus, it was evidenced the defect formation at higher sonication times, being dominant the growth of bulk defects in the structure of exfoliated samples at sonication times superior to 5 hours. As consequence, a careful tuning of the sonication parameters is necessary in order to obtain exfoliated samples with low disorder.

  • Role of Dispersion and Functionalization on Mechanical Properties in Carbon Nanotube-Polymer Composites

    Carbon nanotubes (CNTs) exhibit excellent mechanical and thermal properties. Designing composites that employ CNTs as the reinforcing or filler material offer the potential to create bulk materials with greatly enhanced mechanical and thermal properties. Unfortunately, the resulting property enhancement in CNT, and other carbon nanomaterial, enhanced composites vary greatly. In macroscale composites, like carbon fiber/epoxy composites, the large interface area and relatively low surface area to volume ratio of the carbon fiber/epoxy results in excellent transfer of load or thermal energy across the interface, thus allowing the carbon fiber to enhance the mechanical or thermal properties of the composite. In nanocomposites, the high surface area to volume ratio between the reinforcing and matrix materials requires tightly coupled interactions at the interface. Additionally, due to the high surface area to volume ratio of the nanomaterial filler, there is added difficulty in ensuring the reinforcing materials are uniformly dispersed. These two major differences between macroscale and nanoscale composites results in the existing predictive models failing to predict the effective composite properties. To improve the understanding of the roles that interface bonding and the dispersion of the reinforcing material play on the effective properties, we present the results of a detailed experimental study. To study the role of the reinforcing material/matrix interface bonding, we fabricate CNT/polymer composites where the CNTs are functionalized with different functional groups. To study the role of the nanoparticle filler dispersion, we fabricate CNT polymer composites with different dispersing techniques. This work shows that CNT dispersion is critical for fabricating CNT composites with enhanced mechanical properties.

  • Eutectic Carbides in Damascus steel Ledeburite Class (Wootz)

    Considered the nature of the change of the morphology of excess carbides in Damascus steel (Wootz), depending on the degree of supercooling of the melt, heat treatment and plastic deformation. Discovered that some of blades Damascus steel has an unusual nature of origin of the excess cementite, which different from the redundant phases of secondary cementite, cementite of ledeburite and primary cementite in iron-carbon alloys. It is revealed that the morphological features of separate particles of cementite in Damascus steels lies in the abnormal size of excess carbides having the shape of irregular prisms. Considered three hypotheses for the formation of excess cementite in the form of faceted prismatic of excess carbides. The first hypothesis is based on thermal fission of cementite of a few isolated grains. The second hypothesis is based on the process of fragmentation cementite during deformation to the separate the pieces. The third hypothesis is based on the transformation of metastable cementite in the stable of angular eutectic carbide. It is shown that the angular carbides are formed within the original metastable colony ledeburite, so they are called “eutectic carbide”. It is established that high-purity white cast iron is converted into of Damascus steel during isothermal soaking at the annealing. It was revealed that some of blades Damascus steel ledeburite class do not contain in its microstructure of crushed ledeburite. It is shown that the pattern of carbide heterogeneity of Damascus steel consists entirely of angular eutectic carbides. Believe that Damascus steel refers to non-heat-resistant steel of ledeburite class, which have similar structural characteristics with semi-heat-resistant die steel or heat-resistant high speed steel, differing from them only in the nature of excess carbide phase.

  • Evaluation of commercial and fresh-picked Origanum vulgare after dehydration

    Origanum vulgare Lamiaceae is one of the most used condiments in many countries, and is used in the perfume industry and also in folk medicine. To evaluate the composition of this plant due to its heterogeneity, the main objective was analyze origanum in commercial form and fresh picked after treated at different temperatures, using mainly solid-state NMR techniques, as well as FTIR, XRD and TGA were applied, showing possible existence of larger molecules and structures with low molar mass due to difference of mobility presented by molecules. We observed the carbon-13 signals’ intensity and the signals detection or not varied according to kind of oregano studied as well as the thermal treatment temperature. The techniques are efficient in determining the compounds present in such heterogeneous material, although they are difficult to apply. The HR-MAS confirmed the existence of major compounds such as water, fixed oils, terpenes and polysaccharides.

  • Vinyl Ester/Glass Microballoon Syntactic Foams with Low Density

    In this study, the synthesis and characterization of vinyl ester/glass microballoon syntactic foams with different weight percentages are investigated. Both the tensile and compressive properties of the syntactic foams are characterized. Generally, the results show that the compressive strength and moduli of several syntactic foam compositions are comparable to those of pure vinyl ester as a matrix resin. Due to the lower density of syntactic foams, the specific compressive properties of SCFT-01 (2wt.%) are higher than all other specimens and closer to neat resin. Similar trends are also observed in the tensile properties. The results show that syntactic foams with vinyl ester matrix possess strength behaviour that varies with different content of glass microballoons. This difference is related to the possibility of particle fracture in the stress range where modulus is calculated from the compressive stress–strain curves. In addition, tensile modulus is found to be 70–80% higher than the compressive modulus for all syntactic foam compositions, but both of them are still lower than neat resin. The results also show that the content of glass microballoons in the syntactic foams should be controlled to obtain a good combination of compressive strength and tensile strength. The reasons are discussed in detail.