Corrosion behavior of metals and alloys in marine-industrial environment

This work deals with atmospheric corrosion to assess the degrading effects of air pollutants on ferrous and non-ferrous metals and alloys, which are mostly used as engineering materials. An exposure study was conducted in the Tuticorin port area located on the east coast of South India, in the Gulf of Mannar with Sri Lanka to the southeast. Common engineering materials, namely mild steel, galvanized iron, Zn, Al, Cu and Cu–Zn alloys (Cu–27Zn, Cu–30Zn and Cu–37Zn), were used in the investigation. The site was chosen where the metals are exposed to marine and industrial atmospheres. Seasonal 1 to 12 month corrosion losses of these metals and alloys were determined by a weight loss method. The weight losses showed strong corrosion of mild steel, galvanized iron, Cu and Zn and minor effect on Al and Cu–Zn alloys. Linear regression analysis was conducted to study the mechanism of corrosion. The composition of corrosion products formed on the metal surfaces was identified by x-ray diffraction and Fourier transform infrared spectroscopy.     

Shape-tailoring of gold nanostructures: can a detergent act as the reducing or protecting agent?

A commercially available detergent was found to be an effective reducing as well as stabilizing agent for the synthesis of differently shaped gold nanoparticles in an aqueous solution at an ambient condition and the as-prepared gold nanoparticles behave as an efficient catalyst for the reduction reaction of 4-nitrophenol at room temperature.     

Hollow MgNi1.4Zn0.6/CaCu2.79Fe4.21O12 nanocomposite synthesis via ultrasonic high‐temperature spray pyrolysis

In this study, a distinctive hollow MgNi_1.4Zn_0.6/CaCu_2.79Fe_4.21O₁₂ nanocomposite was synthesized for the first time using ultrasonic high‐temperature spray pyrolysis method controlled at 1200°C. Effect of various concentrations (0.01, 0.1, and 1 mol L^?1) of the precursor solution on particle size and crystalline phase of nanocomposites was also analyzed. XRD and SEM results confirmed the difference in the particle size and crystalline pattern of the synthesized nanocomposite arisen due to the difference in concentrations. The results of antibacterial and antioxidant studies showed that the nanocomposites possessed remarkable antibacterial and antioxidant activities. Thus, the prepared hollow MgNi_1.4Zn_0.6/CaCu_2.79Fe_4.21O₁₂ metal oxide nanocomposite via ultrasonic high‐temperature spray pyrolysis can be an excellent material in various biomedical applications.     

The effect of B4C addition to MnO2 in a cathode material for battery applications

Boron carbide (B₄C) added manganese dioxide (MnO₂) used as a cathode material for a Zn-MnO₂ battery using aqueous lithium hydroxide (LiOH) as the electrolyte is known to have higher discharge capacity but with a lower average discharge voltage than pure MnO₂ (additive free). The performance is reversed when using potassium hydroxide (KOH) as the electrolyte. Herein, the MnO₂ was mixed with 0, 5, 7 and 10 wt.% of boron carbide during the electrode preparation. The discharge performance of the Zn|LiOH|MnO₂ battery was improved by the addition of 5-7 wt.% boron carbide in MnO₂ cathode as compared with the pure MnO₂. However, increasing the additive to 10 wt.% causes a decrease in the discharge capacity. The performance of the Zn|KOH|MnO₂ battery was retarded by the boron carbide additive. Transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy analysis (EDS) results show evidence of crystalline MnO₂ particles during discharging in LiOH electrolyte, whereas, manganese oxide particles with different oxygen and manganese counts leading to mixture of phases is observed for KOH electrolyte which is in agreement with X-ray diffraction (XRD) data. The enhanced discharge capacity indicates that boron atoms promote lithium intercalation during the electrochemical process and improved the performance of the Zn|LiOH|MnO₂ battery. This observed improvement may be a consequence of B₄C suppressing the formation of undesirable Mn(III) phases, which in turn leads to enhanced lithium intercalation. Too much boron carbide hinders the charge carrier which inhibits the discharge capacity.     

Spherical granular structures of Ag/Co nanoparticles: Synthesis, characterization and magnetic properties

Ag/Co bimetallic nanoparticles in the form of hierarchical spherical structures were prepared by the polyol process using oleic acid and oleylamine as surfactants. The Ag/Co nanoparticles so obtained were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), UV-vis spectroscopy (UV-Vis), small angle X-ray scattering (SAXS), vibrating sample magnetometer (VSM) and super-conducting quantum interference device (SQUID). The XRD results in complement with the UV-vis studies indicated the absence of Ag-Co alloy formation during the synthesis. The FESEM observations depicted dense and uniform spherical granular structures for the Ag/Co nanoparticles; while the TEM studies apparently revealed a bimodal distribution of nanoparticles exist in the Ag/Co samples. The SAXS analysis on the Ag/Co colloids further validated the TEM results. The VSM studies showed typical ferromagnetic characteristics for the Ag/Co nanoparticles at room temperature; whereas the SQUID measurements demonstrated superparamagnetic nature for these nanoclusters with a blocking temperature close to 250 K. The synthetic route presented in this work represents a simple means of producing bimetallic composite superstructures of Ag/Co nanoparticles in the form of spherical granules on a large scale. These spherical aggregates have the potential to be important building blocks for more complex nanostructures and would be interesting for magnetic studies and catalytic applications.     

Strength anomaly of the B2 phase in Ti–25Al–25Zr alloy

Mechanical behaviour of the single B2 phase in the alloy Ti–25Al–25Zr has been studied under compression with different strain rates at elevated temperatures. The alloy Ti–25Al–25Zr exhibits yield strength anomaly similar to those of the typical B2 intermetallics such as FeAl. The stress–strain curves of the alloy tested at 400 °C show type C serrations which are considered to be due to dislocation unlocking. Intersecting and straight slip lines are observed in specimens tested at 400 °C and 600 °C, respectively.     

Nonlocal strain gradient finite element analysis of nanobeams using two-variable trigonometric shear deformation theory

In the present paper, a new trigonometric two-variable shear deformation beam nonlocal strain gradient theory is developed and applied to investigate the combined effects of nonlocal stress and strain gradient on the bending, buckling and free vibration analysis of nanobeams. The model introduces a nonlocal stress field parameter and a length scale parameter to capture the size effect. The governing equations derived are solved employing finite element method using a 3-nodes beam element, developed for this purpose. The predictive capability of the proposed model is shown through illustrative examples for bending, buckling and free vibration of nanobeams. Comparisons with other higher-order shear deformation beam theory are also performed to validate its numerical implementation and assess its accuracy within the nonlocal context.

     

Self-catalyzed chemical vapor deposition method for the growth of device-quality metal thin films

Deposition of metals and alloys was demonstrated using thermal chemical vapor deposition starting from commercially available precursors in the absence of molecular hydrogen. The adopted chemical strategy relies solely on the selective reactivity of alcohols with metal complexes at deposition temperature. In this report, particular interest was given to the growth of nickel and silver. This process allows the optimization of the growth of single hcp and fcc phases of nickel starting from Ni(acac)₂, whereas several silver precursors allow the deposition of the fcc crystalline structure of silver. Steady growth kinetics, without incubation time, was noticed for all investigated precursors. The electrical conductivity of hcp-Ni, fcc-Ni and fcc-Ag shows the typical decay to the bulk value with increased film thickness, and the temperature resistivity coefficients are similar to the corresponding bulk material.     

Holographic interferometric study of heat transfer to a sliding vapor bubble

Heat transfer associated with a vapor bubble sliding along a downward-facing inclined heater surface was studied experimentally using holographic interferometry. Volume growth rate of the bubbles as well as the rate of heat transfer along the bubble interface were measured to understand the mechanisms contributing to the enhancement of heat transfer during sliding motion. The heater surface was made of polished silicon wafer (length 185 mm and width 49.5 mm). Experiments were conducted with PF-5060 as test liquid, for liquid subcoolings ranging from 0.2 to 1.2 °C and wall superheats from 0.2 to 0.8 °C. The heater surface had an inclination of 75° to the vertical. Individual vapor bubbles were generated in an artificial cavity at the lower end of the heater surface. High-speed digital photography was used to measure the bubble growth rate. The temperature field around the sliding bubble was measured using holographic interferometry. Heat transfer at the bubble interface was calculated from the measured temperature field. Results show that for the range of parameters considered the bubbles continued to grow, with bubble growth rates decreasing with increasing liquid subcooling. Heat transfer measurements show that condensation occurs on most of the bubble interface away from the wall. For the parameters considered condensation accounted for less than 12% of the rate heat transfer from the bubble base. In this study the heater surface showed no drop in temperature as a result of heat transfer enhancement during bubbles sliding.