Oxidation Behavior of Carbon Steel: Effect of Formation Temperature and pH of the Environment

The nature of surface oxide formed on carbon steel piping used in nuclear power plants affects flow-accelerated corrosion. In this investigation, carbon steel specimens were oxidized in an autoclave using demineralized water at various temperatures (150-300 °C) and at pH levels (neutral, 9.5). At low temperatures (< 240 °C), weight loss of specimens due to dissolution of iron in water occurred to a greater extent than weight gain due to oxide formation. With the increase in temperature, the extent of iron dissolution reduced and weight gain due to oxide formation increased. A similar trend was observed with the increase in pH as was observed with the increase in temperature. XRD and Raman spectroscopy confirmed the formation of magnetite. The oxide film formed by precipitation process was negligible at temperatures from 150 to 240 °C compared to that at higher temperatures (> 240 °C) as confirmed by scanning electron microscopy. Electrochemical impedance measurement followed by Mott–Schottky analysis indicated an increase in defect density with exposure duration at 150 °C at neutral pH but a low and stable defect density in alkaline environment. The defect density of the oxide formed at neutral pH at 150-300 °C was always higher than that formed in alkaline environment as reported in the literature.     

Crystallinity,conductivity, and magnetic properties of PVDF‐Fe3O4 composite films

The formation of Fe₃O₄ nanoparticles by hydrothermal process has been studied. X‐ray Diffraction measurements were carried out to distinguish between the phases formed during the synthesis. Using the synthesized Fe₃O₄ nanoparticles, poly(vinyledene fluoride)‐Fe₃O₄ composite films were prepared by spin coating method. Scanning electron microscopy of the composite films showed the presence of Fe₃O₄ nanoparticles in the form of aggregates on the surface and inside of the porous polymer matrix. Differential Scanning calorimetry revealed that the crystallinity of PVDF decreased with the addition of Fe₃O₄. The conductitivity of the composite films was strongly influenced by the Fe₃O₄ content; conductivity increased with increase in Fe₃O₄ content. Vibration sample magnetometry results revealed the ferromagnetic behavior of the synthesized iron oxide nanoparticles with a Ms value of 74.50 emu/g. Also the presence of Fe₃O₄ nanoparticles rendered the composite films magnetic. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermodynamic Basis for Glass Formation in Cu-Zr Rich Ternary Systems and Their Synthesis by Mechanical Alloying

Topological factors such as mismatch entropy and configurational entropy, along with thermodynamic entity such as enthalpy of chemical mixing, are found to control glass formation in metallic systems. Taking both these factors into consideration, a parameter called P _HS was proposed to correlate glass forming ability successfully in the Cu-Zr-Ti system. The parameter P _HS (=?H _chem × ?S _σ /k _B ) is a product of enthalpy of chemical mixing and mismatch entropy. Our study indicates that the more negative is the P_HS value within the configurational entropy (?S _config/R) range of 0.9 to 1.0, the higher is the stability of glassy phase resulting in a larger diameter of bulk metallic glass rods. Observed theoretical predictions are supported by experimental results in which the compositions with high negative P _HS resulted in easy amorphous phase formation in comparison with less negative P _HS compositions by mechanical alloying. This criterion was extended to Cu-Zr-Al and Cu-Zr-Ag systems as well, thus establishing a strong correlation between P _HS and the glass forming ability of alloys. The role of size effect, probability of atomic arrangements, and heat of formation among constituent elements in obtaining a larger dimension bulk metallic glasses was addressed in this study.     

The Significance of the Aesthetic in Postmodern Architectural Theory

Recent postmodern suspicion of truth, objectivity, and rationality has radically transformed our understanding of architecture and its relationship to politics. In this paper, I draw upon Hilary Putnam (1981), Nelson Goodman (1968), and Satya Mohanty (1997), who propose a sophisticated account of objectivity by reexamining the "hard" sciences, and by interpreting them as complex social practices. Building upon these writers, I argue that our subjective experiences of architecture are rational. As an alternative to both modern essentialism and postmodern skepticism, this paper defends a theory of objectivity that explains the relationship of architecture to political power without abandoning rational thought.     

Microstructures using RF sputtered PSG film as a sacrificial layer in surface micromachining

In this paper, we explore RF magnetron sputtered Phosphor-silicate-glass (PSG) film as a sacrificial layer in surface micromachining technology. For this purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by conventional solid-state reaction route using P₂O₅ and SiO₂ powders. The PSG films were prepared in a RF (13·56 MHz) magnetron sputtering system at 300 watt RF power, 20 mTorr pressure and 45 mm target-to-substrate spacing without external substrate heating. Microstructures of sputtered silicon dioxide film were fabricated using sputtered PSG film as sacrificial layer in surface micromachining process.     

Optimal heat extraction from an updraft biomass reactor

This paper presents the design of gas-water and gas-air heat exchangers for extraction of thermal energy from updraft biomass gasifiers in the firing rate range 10–120 kg/h. Mathematical models are developed to study the sensitivity of the heat exchanger efficiency and effectiveness to geometric and flow variables. Optimal parameters to suit the biomass reactor have been evolved. The calculated heat transfer coefficients have been compared with experimental results obtained in test gas-water and gas-air heat exchangers with an observed deviation between −25 and + 17%. In conclusion, system efficiencies of about 75–80% can be achieved by choice of appropriate operating flow regimes and heat exchanger sizes.     

Nanomaterials based biofuel cells: A review

Biofuel cells (BFCs) are the devices made to transform the chemical energy of organic matter to electrical energy utilizing metabolic reactions occurring in microorganisms during degradation of organic contaminants. In spite of having many applications such as waste water treatment, biosensors and portable uses of BFCs, promoting the uses of BFCs is very challenging because of short life-time and low-power density. Most of the BFC developed till date is only capable to fulfill energy needs of biomedical short-term implanted devices. Use of materials with nano dimensions in the construction of BFCs has been studied extensively and reported as a worthwhile strategy to increase its efficiency. Usually, it is difficult to achieve efficient electron transfer on planar electrode from biocatalyst due to its non-specific orientational the interface. Nonmaterials provide close wiring for the electron transfer between biocatalyst and electrode. Use of various nanomaterials is the most effective way to decrease the gap between active sites (electron producing area)deep inside the enzyme or proteins and the electrodes to achieve better electron transfer. Also, various nanomaterials are utilized to improve the membrane materials for better electron barrier. Many carbon nanostructures, conducting polymers, metal and metal oxides are promising nonmaterials to enhance the current output from BFC. This review highlights recent progress registered in the development of various nanomaterials for construction of electrode and membranes of biofuel cells for better efficiency. It also emphasized the utilization of different metallic nanomaterials, inorganic nanomaterials, conducting polymer-based nanomaterials and carbon-based nanomaterials such as graphene, fullerenes, and carbon nanotubes.     

Screw-theoretic analysis framework for cooperative payload transport by mobile manipulator collectives

In recent times, there has been considerable interest in creating and deploying modular cooperating collectives of robots. Interest in such cooperative systems typically arises when certain tasks are either too complex to be performed by a single agent or when there are distinct benefits that accrue by cooperation of many simple robotic modules. However, the nature of both the individual modules as well as their interactions can affect the overall system performance. In this paper, we examine this aspect in the context of cooperative payload transport by robot collectives wherein the physical nature of the interactions between the various modules creates a tight coupling within the system. We leverage the rich theoretical background of analysis of constrained mechanical systems to provide a systematic framework for formulation and evaluation of system-level performance on the basis of the individual-module characteristics. The composite multi-degree-of-freedom (DOF) wheeled vehicle, formed by supporting a common payload on the end-effectors of multiple individual mobile manipulator modules, is treated as an in-parallel system with articulated serial-chain arms. The system-level model, constructed from the twist- and wrench-based models of the attached serial chains, can then be systematically analyzed for performance (in terms of mobility and disturbance rejection). A two-module composite system example is used throughout the paper to highlight various aspects of methodical system model formulation, effects of selection of active, passive or locked articulations on system performance, and experimental validation on a hardware prototype test bed.