Contribution of texture to the strengthening and fracture in hot-rolled magnesium-12.7 at % cadmium alloy

The grain size dependencies of the yield and fracture stresses in hot rolled Mg-12.7 at % Cd alloy have been measured in the temperature range 77 to 420 K and are found to be in accordance with HalI-Petch type of equations. In hot rolled Mg-12.7 Cd alloy, the HalI-Petch intercept a w is higher than that in hot rolled magnesium, while the slope ky is comparable. The fracture is intercrystalline at 77 K, mixed mode at 300 K and ductile at 420 K. The above flow and fracture behaviours are interpreted in terms of the complimentary effects of texture hardening and solid solution strengthening.

Texture strengthening in warm-rolled cadmium-1% silver alloy

The variation in the tensile properties at 77 K and 300 K in warm-rolled (300 K) Cd-1% Ag alloy with deformation has been studied in longitudinal as well as transverse specimens. The low-temperature yield strength increases with warm rolling without much loss in ductility. The strength at 300 K, however, decreases with heavy warm deformation. From microstructural studies and X-ray investigations, it was observed that changes in grain size and texture occur during warm rolling. Both these changes are found to be important in deciding the tensile properties. The longitudinal and transverse strengths at 77 K vary linearly with l-frac12, where l is the average grain diameter, and thus they obey the Hall-Petch relation. The Hall-Petch slope, k, is lower in specimens with favourable lcub1013rcub texture while the intercept σo is higher when the lcub0002rcub texture is less favourable.

A field investigation of solubility and food chain accumulation of biosolid-cadmium across diverse soil types

One of the pathways for transfer of cadmium (Cd) through the food chain is addition of urban wastewater solids (biosolids) to soil, and many countries have restrictions on biosolid use to minimize crop Cd contamination. The basis of these restrictions often lies in laboratory or glasshouse experimentation of soil-plant transfer of Cd, but these studies are confounded by artefacts from growing crops in controlled laboratory conditions. This study examined soil to plant (wheat grain) transfer of Cd under a wide range of field environments under typical agronomic conditions, and compared the solubility and bioavailability of Cd in biosolids to soluble Cd salts. Solubility of biosolid Cd (measured by examining Cd partitioning between soil and soil solution) was found to be equal to or greater than that of soluble Cd salts, possibly due to competing ions added with the biosolids. Conversely, bioavailability of Cd to wheat and transfer to grain was less than that of soluble Cd salts, possibly due to addition of Zn with the biosolids, causing reduced plant uptake or grain loading, or due to complexation of soluble Cd2+ by dissolved organic matter.

Surface oxidation of cadmium, indium, tin and antimony by photoelectron and Auger spectroscopy

Surface oxidation of Cd, In, Sn and Sb has been investigated by employing valence bands, metal 4d levels and plasmon bands in X-ray photoelectron spectra. O(KLL), metal M4N45N45, and plasmon transitions in electron-induced Auger spectra as well as Auger transitions due to the metal (metal oxide) and plasmons in X-ray-induced Auger spectra. The surface oxides are In2O4, CdO and a mixture of SnO and SnO2 in the case of In. Cd and Sn respectively. The facility of surface oxidation is found to vary as In>Cd>Sn>Sb. Inter-atomic Auger transitions involving oxygen valence bands have been identified on oxidized surfaces of Cd and In.

Electrode kinetics of a nickel/cadmium cell and failure-mode prediction. Estimation of equivalent resistance of an internal short

A quantitative expression has been obtained for the equivalent resistance of an internal short in rechargeable cells under constant voltage charging.

Texture strengthening in warm-rolled cadmium-1% silver alloy

The variation in the tensile properties at 77 K and 300 K in warm-rolled (300 K) Cd-1% Ag alloy with deformation has been studied in longitudinal as well as transverse specimens. The low-temperature yield strength increases with warm rolling without much loss in ductility. The strength at 300 K, however, decreases with heavy warm deformation. From microstructural studies and X-ray investigations, it was observed that changes in grain size and texture occur during warm rolling. Both these changes are found to be important in deciding the tensile properties. The longitudinal and transverse strengths at 77 K vary linearly with l-frac12, where l is the average grain diameter, and thus they obey the Hall-Petch relation. The Hall-Petch slope, k, is lower in specimens with favourable lcub1013rcub texture while the intercept σo is higher when the lcub0002rcub texture is less favourable.

Zinc, cadmium and lead resistance mechanisms in bacteria and their contribution to biosensing

In bacteria resistance to heavy metals is mainly achieved through active efflux, but also sequestration with proteins or as insoluble compounds is used. Although numerous studies have dealt with zinc, cadmium and lead resistance mechanisms in bacteria, it has still remained unclear how different transporters are integrated into an effective homeostasis/resistance network and whether specific mechanisms for lead sequestration exist. Furthermore, since metals are toxic not only to bacteria but to higher organisms as well, it is important to be able to estimate possible biological effects of heavy metals in the environment. This could be done by determining the bioavailable amount of the metals in the environment with bacterial bioreporters. That is, one can employ bacteria that respond to metal contamination by a measurable signal to assess the property of metals to cross biological membranes and to cause harmful effects in a possibly polluted environment. In this thesis a new lead resistance mechanism is described, interplay between CBA transporters and P-type ATPases in zinc and cadmium resistance is presented and finally the acquired knowledge is used to construct bacterial bioreporters for heavy metals with increased sensitivity and specificity. The new lead resistance model employs a P-type ATPase that removes Pb2+ ions from the cytoplasm and a phosphatase that produces inorganic phosphate for lead sequestration in the periplasm. This was the first study where the molecular mechanism of lead sequestration has been described. Characterization of two P-type ATPases and two CBA transporters showed that resistance mechanisms for Zn2+ and Cd2+ are somewhat different than for Pb2+ as these metals cannot be sequestered as insoluble compounds as easily. Resistance to Zn2+ was conferred merely by the CBA transporter that could export both cytoplasmic and periplasmic ions; whereas, full resistance to Cd2+ required interplay of a P-type ATPase that exported cytoplasmic ions to periplasm and a CBA transporter that further exported periplasmic ions to the outside. The knowledge on functionality of the transporters and metal-inducible promoters was exploited in bioreporter technology. A transporter-deficient bioreporter strain that lacked exporters for Zn2+/Cd2+/Pb2+ could detect up to 45-fold lower metal concentrations than its wild type counterpart due to the accumulation of metals in the cell. The broad specificity issue of bioreporters was overcome by using Zn-specific promoter as a sensor element, thus achieving Zn-specific bioreporter.

On the orientation of grain boundaries in cadmium recrystallized during hot deformatio

The authors are grateful to Professor K. P. Abraham for the provision of facilities and encouragement. One of us (PRR) acknowledges the award of a National Associateship by the UGC which facilitated a short-time visit to the Indian Institute of Science.

Cadmium stress alters the redox reaction and hormone balance in oilseed rape (Brassica napus L.) leaves

In order to understand the physiological response of oilseed rape (Brassica napus L.) leaves to cadmium (Cd) stress and exploit the physiological mechanisms involved in Cd tolerance, macro-mineral and chlorophyll concentrations, reactive oxygen species (ROS) accumulation, activities of enzymatic antioxidants, nonenzymatic compounds metabolism, endogenous hormonal changes, and balance in leaves of oilseed rape exposed to 0, 100, or 200 μM CdSO4 were investigated. The results showed that under Cd exposure, Cd concentrations in the leaves continually increased while macro-minerals and chlorophyll concentrations decreased significantly. Meanwhile, with increased Cd stress, superoxide anion (O 2 • − ) production rate and hydrogen peroxide (H2O2) concentrations in the leaves increased significantly, which caused malondialdehyde (MDA) accumulation and oxidative stress. For scavenging excess accumulated ROS and alleviating oxidative injury in the leaves, the activity of enzymatic antioxidants, such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), was increased significantly at certain stress levels. However, with increased Cd stress, the antioxidant enzyme activities all showed a trend towards reduction. The nonenzymatic antioxidative compounds, such as proline and total soluble sugars, accumulated continuously with increased Cd stress to play a long-term role in scavenging ROS. In addition, ABA levels also increased continuously with Cd stress while ZR decreased and the ABA/ZR ratio increased, which might also be providing a protective role against Cd toxicity.

Adsorption-desorption and photocatalytic properties of inorganic-organic hybrid cadmium thiosulfate compounds

Three inorganic-organic hybrid framework cadmium thiosulfate phases have been investigated for adsorption and photodegradation of organic dye molecules. Different classes of organic dyes, viz., triaryl methane, azo, xanthene, anthraquinone, have been studied. The anionic dyes with sulfonate groups appear to readily adsorb on the cadmium thiosulfate compounds in an aqueous medium. The adsorption of the dye molecules, however, does not create any structural changes on the cadmium thiosulfate compounds, though weak electronic interactions have been observed. The adsorbed dyes have been desorbed partially in an alcoholic medium, suggesting possible applications in scavenging specific anionic dyes from the aqueous solutions. Langmuir adsorption/desorption isotherms have been used to model this behavior. UV-assisted (lambda(max) = 365 nm) photocatalytic decomposition studies on the cationic dyes indicate reasonable activity comparable with that of Degussa P-25 (TiO2) catalyst. Sunlight assisted photocatalyti studies have been carried out in detail employing hybrid framework compounds. The Langmuir-Hinshelwood kinetics model, employed to follow the degradation profile of the organic dyes, indicates that the photocatalytic degradation follows the order: triaryl methane > azo > xanthene.

Microsphere Bouquets of Bismuth Telluride Nanoplates: Room-Temperature Synthesis and Thermoelectric Properties

We report the synthesis and properties of sphere-shaped microscale aggregates of bismuth telluride nanoplates. We obtain porous microspheres by reducing bismuth chloride and orthotelluric acid with hydrazine in the presence of thioglycolic acid-which serves as the shape-and size-directing agent-followed by room-temperature aging-which promotes nanoplate aggregation. Thin film assemblies of the nanoplate microspheres exhibit n-type behavior due to sulfur doping and a Seebeck coefficient higher than that reported for assemblies of chalcogenide nanostructures. Adaptation of our scalable approach to synthesize and hierarchically assemble nanostructures with controlled doping could be attractive for tailoring novel thermoelectric materials for applications in high-efficiency refrigeration and harvesting electricity from heat.

Thermoelectric Power Under Strong Magnetic Field in Quantum Dots and Quantized Superlattices: Simplified Theory and Relative Comparison

In this paper, we study the thermoelectric power under strong magnetic field (TPSM) in quantum dots (QDs) of nonlinear optical, III-V, II-VI, GaP, Ge, Te, Graphite, PtSb2, zerogap, Lead Germanium Telluride, GaSb, stressed materials, Bismuth, IV-VI, II-V, Zinc and Cadmium diphosphides, Bi2Te3 and Antimony respectively. The TPSM in III-V, II-VI, IV-VI, HgTe/CdTe quantum well superlattices with graded interfaces and effective mass superlattices of the same materials together with the quantum dots of aforementioned superlattices have also been investigated in this context on the basis of respective carrier dispersion laws. It has been found that the TPSM for the said quantum dots oscillates with increasing thickness and decreases with increasing electron concentration in various manners and oscillates with film thickness, inverse quantizing magnetic field and impurity concentration for all types of superlattices with two entirely different signatures of quantization as appropriate in respective cases of the aforementioned quantized structures. The well known expression of the TPSM for wide-gap materials has been obtained as special case for our generalized analysis under certain limiting condition, and this compatibility is an indirect test of our generalized formalism. Besides, we have suggested the experimental method of determining the carrier contribution to elastic constants for nanostructured materials having arbitrary dispersion laws.

Si, CdTe and CdZnTe radiation detectors for imaging applications

The structure and operation of CdTe, CdZnTe and Si pixel detectors based on crystalline semiconductors, bump bonding and CMOS technology and developed mainly at Oy Simage Ltd. And Oy Ajat Ltd., Finland for X- and gamma ray imaging are presented. This detector technology evolved from the development of Si strip detectors at the Finnish Research Institute for High Energy Physics (SEFT) which later merged with other physics research units to form the Helsinki Institute of Physics (HIP). General issues of X-ray imaging such as the benefits of the method of direct conversion of X-rays to signal charge in comparison to the indirect method and the pros and cons of photon counting vs. charge integration are discussed. A novel design of Si and CdTe pixel detectors and the analysis of their imaging performance in terms of SNR, MTF, DQE and dynamic range are presented in detail. The analysis shows that directly converting crystalline semiconductor pixel detectors operated in the charge integration mode can be used in X-ray imaging very close to the theoretical performance limits in terms of efficiency and resolution. Examples of the application of the developed imaging technology to dental intra oral and panoramic and to real time X-ray imaging are given. A CdTe photon counting gamma imager is introduced. A physical model to calculate the photo peak efficiency of photon counting CdTe pixel detectors is developed and described in detail. Simulation results indicates that the charge sharing phenomenon due to diffusion of signal charge carriers limits the pixel size of photon counting detectors to about 250 μm. Radiation hardness issues related to gamma and X-ray imaging detectors are discussed.