Synthesis and Characterization of Magnetite/Polyvinyl Alcohol Core–Shell Composite Nanoparticles

Magnetite (Fe₃O₄)/polyvinyl alcohol (PVA) core–shell composite nanoparticles were successfully synthesized using a coprecipitation of ferrous and ferric chloride followed by coating with PVA. The resulting nanoparticles were characterized using X‐ray diffraction, Fourier Transform Infrared Spectroscopy, Transmission Electron Microscopy, X‐ray photo electron spectroscopy, Zeta potential measurements, UV–Vis spectroscopy, Thermogravimetric Analysis, and Vibrating Sample Magnetometry (VSM). The average particle size was 13 nm. The presence of characteristic functional groups of PVA around the core of magnetite nanoparticles was confirmed by FTIR spectroscopy while the amount of PVA (%) bound to it was estimated by TGA analysis. Zeta potential measurements made by dispersing dilute sonicated samples in a Phosphate Buffer Saline (PBS pH 7.4) confirmed that the particles were negatively charged. The stability and retention of the coating material PVA in PBS (pH7.4) over a period of time were substantiated by UV–Vis spectroscopy. Room‐temperature magnetic measurements were made with a VSM which demonstrated the superparamagnetic nature of the particles with higher saturation magnetization of 56.41 emu/g. Furthermore, in vitro cytocompatibility testing of Fe₃O₄/PVA core–shell composite nanoparticles was carried out on human cervix cancer cells. This confirmed a 97% cell viability with no significant cytotoxicity and thereby substantiated their biocompatibility.     

Vinyl carbazole (VC) functionalized mesoporous silica polymer nanocomposites (SBA/VC) for the antibacterial activity studies

Vinyl carbazole (VC) functionalized ordered mesoporous silica polymer nanocomposites (SBA/VC) were synthesized by in situ radical polymerization of monomers inside the mesoporous framework and characterized for the antibacterial activity studies against gram positive and gram negative bacteria. Powder X-ray diffraction and N₂ adsorption isotherms of SBA/VC nanocomposites showed the presence of mesoporous nature. The antimicrobial activity results showed increasing trend with the increase in the concentration of vinyl carbazole (VC) and the maximum antibacterial activity was achieved with SBA/VC₆₄ nanocomposites.     

RF sources for ITER Ion Cyclotron H&CD system

The Ion Cyclotron Heating and Current Drive (IC H&CD) system for ITER will provide 20 MW to the plasma. The associated Radio Frequency (RF) source system has to be compliant with all operation modes foreseen in that frame. Their specifications are fully described in this paper and constraints on IC RF source components are detailed, in particular concerning the final stage tube of the amplifier. Results of tests performed under a collaborative work at the National Institute for Fusion Science (NIFS) facility are presented. Consequences on the procurement process by ITER India (II) are deduced.     

Conversion of wooden structures into porous SiC with shape memory synthesis

Synthesis of structured silicon carbide materials can be accomplished using wooden materials as the carbon source, with various silicon impregnation techniques. We have explored the low cost synthesis of SiC by impregnation of carbon from wood with SiO gas at high temperatures, which largely retains the structure of the starting wood (shape memory synthesis). Suitably structured, porous SiC could prove to be an important type of catalyst support material. Shape memory synthesis (SMS) has earlier been tried on high surface area carbon materials. Here we have made an extensive study of SMS on carbon structures obtained from different types of wood.     

Advances in high-k dielectric gate materials for future ULSI devices

This article discusses recent developments in high dielectric constant gate insulator materials for future ultra-large-scale integration devices below 100 nm. Since conventional gate oxide poses problems as device features are scaled down, it becomes necessary to develop new gate dielectric materials with properties similar to SiO₂ and compatible with current complementary metal-oxide semiconductor technology. As the thickness of silicon dioxide approaches less than 1.5 nm, the leakage current becomes higher than 1 A/cm² and tunnel current increases significantly. Therefore, materials are needed to provide excellent electrical characteristics such as dielectric constant higher than 30, interface-state-density less than 1 × 10¹¹/cm²-eV, tunneling current less than 10 mA/cm², and negligible hysteresis. Many high dielectric constant materials have been reported that could potentially replace SiO₂. These include SiO_xN_y, Ta₂O₅, TiO₂, Y₂O₃, CeO₂, SrTiO₃, Al₂O₃, La₂O₃, and silicates of hafnium and zirconium. These materials exhibit the desired high dielectric constants for applications as gate dielectrics in sub-100 nm silicon technology. However, detailed studies need to be performed to evaluate the compatibility of these materials with the rest of the silicon integrated-circuit manufacturing processes. For more information, contact A. Kumar, Center for Microelectronics Research, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida, 33620, (813) 974-3942; fax (813) 974-6310; e-mail akumar1@eng.usf.edu     

Effect of sliding speed and temperature on the tribological behavior of pongamia oil-based blended lubricant

The increase in industrialization has created the demand for petroleum-based lubricants throughout the world. The decrease in availability of mineral oils and their hazards related to the environment created the need to search for the alternate bio-based oils. In this work, the pongamia seed oil is blended with mineral oil (SAE20W40) at 5%, 10%, and 15% ratio for its tribological investigation at different speed and temperature. In terms of coefficient of friction and wear rate, 5% and 10% pongamia oil blends show better results at all sliding speed and temperatures. Fifteen percent of pongamia blend shows the maximum friction and wear among all the blends. Maximum friction coefficient and wear occur at 300 rpm and minimum at 1,500 rpm sliding speed. Minimum drop in the total acid number was also found in the 5% and 10% blends in comparison to 15% blend and conventional mineral. Overall, PB5 and PB10 are suitable lubricants for tribological applications.     

Tribological behavior of pongamia oil as a lubricant additive

This study assesses the friction and wear characteristics of a pongamia oil-contaminated bio-lubricant by using a pin-on-disc tribometer. To formulate the bio-lubricants, pongamia oil was blended in the ratios of 15, 30, and 50% by volume with the base lubricant SAE 20 W 40. Tribological characteristics of these blends were obtained at 1.3 and 2.5 m/s sliding velocity and the load was 150 N. Experimental results showed that the lubrication regime that occurred during the test was boundary lubrication while the main wear mechanisms were abrasive and the adhesive wear. During testing, the lowest wear was found with the addition of 15% pongamia oil, and above this contamination, the wear rate was increased considerably. With an increase in load, the viscosity of all the bio-lubricants increases and meets the International Standard Organization (ISO) VG 100 requirement at 40°C except PB 50. The addition of pongamia oil in the base lubricant acted as a very good lubricant additive which reduced the friction and wear scar diameter during the test. It has been concluded that the PB 15 can act as an alternative lubricant to increase the mechanical efficiency and contribute to reduction of dependence on the petroleum-based products.     

Design of functionally graded carbon coatings against contact damage

Three different functionally graded amorphous carbon (a-C) thin films were deposited on to aluminium substrates using a closed-field unbalanced magnetron sputtering ion plating method. The closed-field configuration prohibits the loss of secondary electrons and consequently enhances the plasma density significantly. The functional gradient of the a-C films was achieved by varying the bias voltage linearly during deposition. Three graded a-C systems possessing different variations in Young's modulus were deposited with the highest Young's modulus at the (i) top surface, (ii) interface or (iii) middle of the film. Of the three systems investigated, the one with the highest Young's modulus at the middle of the film thickness was found to exhibit significantly lower levels of cracking at higher indentation depths. Finite element models that included an embedded ring crack controlled by cohesive zone elements were developed to clarify the effect of ring cracks on the deformation of the films. This study provides guidance for the design of functionally graded coatings against contact damage.     

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO₂. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO₂/CH₄ molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO₂ molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO₂ concentration in the aqueous phase may not result in faster growth of CO₂ hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO₂, the growth for carbon dioxide hydrate was very slow in the beginning.     

Comparative study of mechanical and chemical methods for surface cleaning of a marine shell‐and‐tube heat exchanger

In this article, experimental analysis is done on shell‐and‐tube heat exchanger of a marine vessel for removal of fouling using optimum surface‐cleaning techniques. The main objective is to compare the performance of the heat exchanger before and after maintenance. Two identical deteriorated systems of heat exchangers are taken and real‐time analysis is conducted. The log data are taken before and after undergoing maintenance for the two systems. Two different cleaning techniques are used, namely, chemical cleaning and mechanical cleaning. Detailed calculations are made for the shell‐and‐tube heat exchanger. From the obtained data, comparisons are made for different parameters on the tube side such as friction factor, heat transfer coefficient and pressure drop, as well as total heat transfer rate on the shell side. From the analysis and comparison, it was found that greater heat transfer takes place for the tubes cleaned using the chemical cleaning method than for tubes cleaned by the mechanical cleaning method. Pressure drop is found to be less for chemical cleaning method than mechanical cleaning method. This indicates that the fouling effect is reduced for tubes cleaned by the chemical cleaning method, and furthermore these tubes remain corrosion‐resistant for longer periods of time.