Metallurgical characterization of pulsed current gas tungsten arc,friction stir and laser beam welded AZ31B magnesium alloy joints

This paper reports the influences of welding processes such as friction stir welding (FSW), laser beam welding (LBW) and pulsed current gas tungsten arc welding (PCGTAW) on mechanical and metallurgical properties of AZ31B magnesium alloy. Optical microscopy, scanning electron microscopy, transmission electron microscopy and X-Ray diffraction technique were used to evaluate the metallurgical characteristics of welded joints. LBW joints exhibited superior tensile properties compared to FSW and PCGTAW joints due to the formation of finer grains in weld region, higher fusion zone hardness, the absence of heat affected zone, presence of uniformly distributed finer precipitates in weld region.     

Developing Temperature–Time and Pressure–Time diagrams for diffusion bonding AZ80 magnesium and AA6061 aluminium alloys

The principal difficulty when joining magnesium (Mg) and aluminium (Al) lies in the existence of formation of oxide films and brittle intermetallic in the bond region. However diffusion bonding can be used to join these alloys without much difficulty. In this investigation, an attempt was made to develop Temperature–Time and Pressure–Time diagrams for diffusion bonding of AZ80 magnesium (Mg) and AA6061 aluminium (Al) dissimilar materials. The bonding quality of the joints was checked by microstructure analysis and lap shear tensile testing. Based on the results Temperature–Time and Pressure–Time diagrams were constructed. These diagrams will act as reference maps for selecting appropriate diffusion bonding process parameters to join AZ80 magnesium alloy and AA6061 aluminium alloy without trial experiments.     

Developing an empirical relationship to predict the corrosion rate of friction stir welded AZ61A magnesium alloy under salt fog environment

Magnesium (Mg) alloys shows the lowest density among other engineering metallic materials. As a consequence, this light alloy has a promising future. However, these alloys have great affinity for oxygen and other chemical oxidizing agents. The limitation of low corrosion resistance restricts their practical applications. Extruded Mg alloy plates of 6 mm thick of AZ61A grade were butt welded using friction stir welding (FSW) process. Corrosion behavior of the welds was evaluated by conducting salt fog test in NaCl solution at different chloride ion concentrations, pH value and spraying time. Also an attempt was made to develop an empirical relationship to predict the corrosion rate of friction stir welded AZ61A magnesium alloy. Three factors and a central composite design were used to minimize the number of experimental conditions. Response surface method was used to develop their relationship. The developed relationship can be effectively used to predict the corrosion rate of friction stir weld AZ61A magnesium alloy at 95% confidence level.     

Nondisruptive material sampling and mechanical testing

The aging and inservice degradation of industrial equipment has underscored a need for efficient and reliable evaluation of the suitability of such equipment for continued service. The structural components of traditional energy production facilities, such as fossil- and nuclear-fueled electric power plants, are prime examples of aging equipment for which integrity during extended service is of major concern. The paper describes a recently developed nondisruptive miniature material sample removal and test approach that is being applied to a range of operating electric power plant components from turbine generators to pressure vessels, and to petrochemical plant reactor vessels for inservice integrity assessment. Thein situ removal of a thin wafer-like sample (less than 25 mm in diameter and 2.5 mm in thickness) from the component surface generally has no effect on component integrity. The miniature specimen small punch (disk bend) test has been developed to mechanically test the as-removed material, and is being used to estimate the material tensile behavior and fracture properties (ductile-to-brittle transition temperature and fracture toughness) required for a reliable component integrity assessment.     

Optimal cycle time and production rate in a family production context with shelf life considerations

This paper considers the problem of determining the optimal production rate for each item and the optimalcycle time for the family of items in a family production context with restrictions on the shelf life of the various items in the family. An algorithm that determines the optimal production rate for all the items as well as the optimal cycle time is proposed. This is an improvement over the existing method by Silver (1995) that can determine the optimal production rate only for one item for which the shelf life constraint is binding. Examples are provided to illustrate the proposed method.     

Inhalable liposomes of Glycyrrhiza glabra extract for use in tuberculosis: formulation,in vitro characterization,in vivo lung deposition,and in vivo pharmacodynamic studies

Objective: The current study involves the development of liposomal dry powder for inhalation (LDPI) containing licorice extract (LE) for use in tuberculosis.

Significance: The current epidemiology of tuberculosis along with the increasing emergence of resistant forms of tuberculosis necessitates the need for developing alternative efficacious medicines for treatment. Licorice is a medicinal herb with reported activity against Mycobacterium tuberculosis.

Methods: Liposomes with LE were prepared by thin film hydration technique and freeze dried to obtain LDPI. The comprehensive in vitro and in vivo characterization of the LDPI formulation was carried out.

Results: The particle size of liposomes was around 210?nm with drug entrapment of almost 75%. Transmission electron microscopy revealed spherical shape of liposome vesicles. The flow properties of the LDPI were within acceptable limits. Anderson Cascade Impactor studies showed the mean median aerodynamic diameter, geometric standard deviation and fine particle fraction of the LDPI to be 4.29?µm, 1.23, and 54.68%, respectively. In vivo lung deposition studies of LDPI in mice showed that almost 46% of the drug administered reaches the lungs and 16% of administered drug is retained in the lungs after 24?hours of administration. The in vivo pharmacodynamic evaluation of the LDPI showed significant reduction in bacterial counts in lungs as well as spleen of TB-infected mice.

Conclusions: LE LDPI thus has a promising potential to be explored as an effective anti-tubercular medicine or as an adjunct to existing anti-tubercular drugs.     

Rational model for comparing vulnerability to environmental health risks at different locations.

Many factors must be considered in correlating the environmental quality of a location with the disease pattern. Therefore, an attempt is made to identify the rationale needed to correlate human disease patterns with pollutant loads and a simple, though arbitrary, and qualitative model for distinguishing areas more prone to environmental health risks is suggested.     

Influence of pulse reversal on the performance of pulse electrodeposited copper indium sulphide solar cells

This paper reports for the first time influence of pulse reversal on the properties and performance of pulse electrodeposited CuInS₂ films. The films exhibited single phase chalcopyrite structure. The intensity of the X-ray diffraction peaks become sharp and increase in intensity with increase of pulse reversal time. The crystallite size increases with pulse reversal time. Resistivity of the films decreases from 2.0 to 0.05 Ω cm with increase of pulse reversal time. The mobility and carrier density increase with pulse reversal time. Solar cells fabricated with Mo/CuInS₂/CdS/Ag have yielded reasonable photo outputs.     

Life-assessment technology for fossil power plants

During the last decade, construction of new fossil power plants has come to a virtual halt in the United States. The main factors responsible for this situation are: (1) industry perception of the existence of sufficient reserve margins, (2) uncertainty in forecasting load growth, (3) cost of borrowing for new plant construction, (4) siting and licensing problems for new plants, and (5) the applicability of more stringent environmental standards for new plants. Unfortunately, by the year 2000 it is estimated that nearly 20% of all the fossil units will be more than 40 years old, and almost 44% will be more than 30 years old. Based on historical trends, nearly half of all fossil plants have been retired before their fortieth year and three quarters before serving 50 years. In the future this trend is unlikely because of the shrinking reserve margins and the long lead time for new capacity addition. If the life of these aging plants can be extended by 20–30 years, utilities can have a viable low-cost alternative to building new plants while at the same time circumventing some of the regulatory, siting and licensing constraints. In view of this, plant life extension has become an integral part of the planning strategy for many US utilities. A critical component of the Electric Power Research Institute’s (EPRI) efforts in formulating life extension strategies for fossil power plants is the development of techniques to assess the current condition of high-temperature components. These techniques are necessary not only for assessment of the remaining life, but also for avoiding catastrophic failures and forced outages, for setting up inspection intervals and for optimizing the operating procedures. The components that are being addressed at present are boiler pressure parts, steam pipes and steam turbine rotors. This paper will provide a brief overview of current concerns and areas of research where significant progress has been made to address these concerns from a phenomenological point of view.     

Near-edge X-ray absorption fine structure spectroscopy as a tool for investigating nanomaterials

We have demonstrated near-edge X-ray absorption fine structure (NEXAFS) spectroscopy as a particularly useful and effective technique for simultaneously probing the surface chemistry, surface molecular orientation, degree of order, and electronic structure of carbon nanotubes and related nanomaterials. Specifically, we employ NEXAFS in the study of single-walled carbon nanotube and multi-walled carbon nanotube powders, films, and arrays, as well as of boron nitride nanotubes. We have focused on the advantages of NEXAFS as an exciting, complementary tool to conventional microscopy and spectroscopy for providing chemical and structural information about nanoscale samples.