Table of Contents - Volume 13 Number 2

The corrosion of metals is a serious technological problem and a variety of methods such as cathodic protection and insulating coatings has been developed to overcome it. However, the use of an active coating on metal substrates is proposed to be an innovative and effective approach. Although 2-mercaptobenzothiazole (MBT) is an efficient corrosion inhibitor for metals, its direct addition into the polymer coating or paintis not so much effective, because it is water-soluble, photodegradable and creates discontinuities in the coating layer, thus decreasingits barrier properties. A valuable approach to improve its anticorrosion performance is the entrapment of MBT into nanocarriers to be used as containers and reservoir. In the present work two different types of nanocarriers on the anticorrosion effect of 2-mercaptobenzothiazole molecule have been investigated. In particular, halloysite nanotubes (HNTs),in which MBT is loaded in the inner empty lumen through a vacuum procedure,and Zn–Al-layered double hydroxides (LDHs), in which MBT is intercalated through ionic-exchange, have been evaluated. Release tests of MBT from the obtained active particles in aqueous corrosive solution have been performed. Results have been correlated with the data obtained by visual inspection of anticorrosion effect of the active nanocarriers added into epoxy coatings and used to protect commercial steel substrate during accelerated corrosion tests.

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The interface between the reinforcement and the matrix has a significant role in enhancing the property of the composite. In this work to increase the wetting ability of the reinforcement, nickel coating is done over the carbon fiber. The process of coating is carried out through three stages. It involves sensitization time, activation time and metallization time. Using the optimized time interval of the above process coating is done, on the fiber of range 0.6 to 1 micrometer. This coated fiber has the good cohesive property within each other, which increases the wettability. Stir casting process is carried out with the stirring speed of 200 rpm and the melting temperature about 780-800⁰C is used for the manufacturing of the composite. The results of this study revealed that, as the short coated carbon content was increased, there were significant increases in the Ultimate Tensile Strength (UTS). Furthermore, Scanning Electron Microscopy (SEM) was used in order to coordinate relationships between quality of the carbon fiber and aluminium alloy bond and thereby link with tensile properties of the metal matrix composites. The metal matrix composites are  a very important role in the industries such as aerospace, automobile and sports equipment etc. The aluminium material is considered to be a light weight metal, to enhance the property of the aluminium 7075 alloy, the short coated carbon fibers added to the aluminium as a reinforcement.

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Nanoindentation is an effective way of finding mechanical properties at nanoscale. They are especially useful for thin films where elimination of the substrate effect is required. The mechanism is based upon depth sensing indentation based on Oliver and Pharr modeling. The load-depth curves as well as time on sample were analyzed. Indentation impulse was found to have significant contribution in the nature of failure zone during indentation. Fracture toughness was also related to time on the sample.

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Electro-magnetic interference (EMI) affects delicate electronic devices and living beings. Composites of a polymeric binder with fine metallic turnings (copper and brass), powders of conducting inorganic compounds (suitably fired cadmium oxide), ferroelectric powders (BaTiO₃ and orthorhombic PbNb₂O₆), and with their combinations have been prepared as cloth-like sheets, and characterized in a Vector Network Analyzer (VNA) with respect to EMI shielding and reflection capabilities. Input power (P_in) for the EMI shield (above-mentioned test materials), the reflected power (P_refl) and the transmitted power (P_out) have been measured by the VNA as a function of EM wave frequency in two technically important frequency bands - in 700 MHz to 3 GHz part of the ultra-high frequency (UHF) band and in the X-band, covering 8 to 12 GHz. From the measured data, Shielding Effectiveness in dB unit = 10 log (P_out / P_in) and Reflection Effectiveness in dB = 10 log (P_refl / P_in) have been calculated and studied for all the samples, with the results presented and discussed. In particular, our substitution of expensive metal powders by fine metallic turnings, available as waste from mechanical workshops, reduces the cost of polymer-metal composites substantially, retaining high shielding i.e. low transmission (down to -33dB in 08 to 12 GHz range).

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Magnesium AZ91D alloy is reinforced with red mud particles, is the by-product of alumina which is extracted from refining of bauxite throughbayer process to fabricate low cost novel composite by powder metallurgy technique. Reinforcement ratio was varied from 0% to 15% whereas size of the particles were kept as 30µm.The microstructure and mechanical properties such as density and microhardness of the composite were evaluated. Microstructural characterization of the sintered composite revealed a near uniform distribution of the red mud particulates with magnesium alloy metal matrix.The test results indicated that the increase in weight % of red mud particles significantly enhances the mechanical propertiesof the composite.

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Steel corrosion inhibition in acidic and alkaline medium by ethanolic extract of Milletia pinnata is described in this study. The inhibitive behavior of the inhibitor is evaluated by weight loss measurements, adsorption isotherms, and thermochemical parameters. The inhibitor exhibited a maximum of 87% and 90.5% inhibition efficiency against steel corrosion in 0.5 M NaOH and 1.0 M H₂SO₄, respectively. The weight loss linearly fit to Langmuir adsorption isotherm with correlation coefficient value close to unity. The thermochemical parameters indicated for predominant physical adsorption of the inhibitor molecules on the steel surface.

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The corrosion on smooth tinned iron material has been studied in different media.  Solutions of sulphuric acid, hydrochloric acid, acetic acid and  salt solutions of ammonium chloride and sodium chloride were prepared to investigate the corrosion on the metal plates.  The plates was immersed in the solutions for a period of time same for all the solutions in order to determine the most aggressive environment. Weight loss technique was adopted to study the rate of corrosion.  The result reveals that the material got corroded in this order sulphuric acid > hydrochloric acid > acetic acid > ammonium chloride > sodium chloride. It was therefore concluded that the rate of corrosion was high in strong acids compared to the weak acids and salts.

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The alloy Ge₁₀Se₂₀ Bi₈₀ has been prepared. Thin films of Ge₁₀Se₂₀ Bi₈₀ has been prepared via a thermal evaporation method (melt quenching technique) with 3000A thickness, and rate of deposition (4.1) A/sec at pressure 2x10-⁵ Torr. The A.C electrical conductivity of a- thin films Ge₁₀Se₂₀ Bi₈₀ has been studied as a function of frequency for annealing temperature within the range (423-623) K, the deduced exponent s values, was found to decrease with increasing of annealing temperature through the frequency of the range (10²-10⁶) Hz. It was found that, the correlated barrier hopping (CBH) is the dominant conduction mechanism. Values of dielectric constant ε₁ and dielectric loss ε₂ were found to decrease with frequency and increase with temperature. The activation energies have been calculated for the annealed thin films.

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In this study, the effect of ‘natural/self cleaning’ of ground water by precipitation after a decade of tsunami is evaluated along the coast of Kanniyakumari district, Tamil Nadu, India. The samples were collected from five stations namely Colachel, Muttom, Periyakadu, Manakudy, and Kanniyakumari. The physicochemical parameters such as turbidity, total dissolved solids, electrical conductivity, pH, alkalinity, total hardness, calcium, magnesium, sodium, potassium, chloride, and fluoride were evaluated and compared with the database of the pre-tsunami sample collected in 2004. The results indicated that the ‘natural cleaning’ has improved the quality of the ground water over the years after tsunami.

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