Development of P/M Fe–P soft magnetic materials

Phosphorous is treated as an impurity in conventional steels owing to segregation of phosphorous and formation of brittle phosphides along the grain boundaries. It is responsible for cold and hot shortness in wrought steels. In conventional powder metallurgy, involving compaction and sintering, high phosphorous content (up to 0·7%) in Fe-based alloys exhibit attractive set of mechanical and magnetic properties. These powder-processed alloys suffer from increasing volumetric shrinkage during sintering as phosphorous is increased beyond 0·6%. Thus both cast as well as conventional powder metallurgy routes have their own limitations in dealing with iron?Cphosphorous alloys. Hot-powder forging was used in the present investigation for the development of high-density soft magnetic materials containing 0·3?C0·8% phosphorous to overcome these difficulties. It was observed that phosphorous addition improves the final density of the resulting product. It was further observed that hot-forged iron?Cphosphorous alloys have excellent hot/cold workability and could be easily shaped to thin strips (0·5?C1·0?mm thick) and wires (0·5?C1·0?mm diameter). The powder hot-forged alloys were characterized in terms of microstructure, porosity content/densification, hardness, soft magnetic properties and electrical resistivity. Magnetic properties such as coercivity 0·35?C1·24?Oe, saturation magnetization 14145?C17490 G and retentivity 6402?C10836 G were observed. The obtained results were discussed based on the microstructures evolved.     

Pressure Leaching Kinetics of Multimetallic Sulphide Concentrates in H2SO4 + O2 Solution

Abstract

A multimetallic sulphide concentrate containing sphalerite, galena, chalcopyrite and silver in the matrix of pyrite was decomposed at elevated temperature and oxygen pressures in dilute sulphuric acid solutions for sufficient residence time to yield 95% of the zinc in the pregnant solution while most of the lead and silver remained in the residue together with most of the pyrite. The selective leaching process appeared to follow the diffusion controlled mechanism. The effects of concentration of the leachant, temperature and time of leaching, particle size, oxygen pressure and agitation on the leaching process were investigated. Results indicate the prospect of extracting not only all the metals but also appreciable amounts of elemental sulphur under optimized experimental conditions.     

Synthesis,structure and low temperature study of electric transport and magnetic properties of GdSr<Subscript>2</Subscript>MnCrO<Subscript>7</Subscript>

The layered perovskite oxide, GdSr₂MnCrO₇, has been prepared by the standard ceramic method. The powder X-ray diffraction studies suggest that the phase crystallizes with tetragonal unit cell in the space group I4/mmm. The electrical transport properties show that the phase is an electrical insulator and the electrical conduction in the phase occurs by a 3D variable range hopping mechanism. The magnetic properties suggest that the ferromagnetic interactions are dominant in the high temperature region.     

Joint effect of test effort and learning factor on software reliability and optimal release policy

This paper presents a realistic approach for software reliability growth modelling incorporating the joint effect of test effort and learning factor. The error detection process in software is described using a non-homogeneous Poisson process. Maximum likelihood estimates of the reliability growth parameters are obtained using a numerical method. Optimal release policies for cost and reliability are discussed. Finally, an example using real-life data is presented for illustration and comparison     

Monte Carlo simulation for reliability evaluation of complex systems

A complex system of s-dependent and s-independent units is considered in this paper for system reliability evaluation. It is also assumed that failure of any unit in the dependent set increases the failure probabilities of the remainder in the set. A general ease of partial redundant subsystems is considered. A computational algorithm to compute effective failure rates of the remaining components which fail sequentially, is explained for programme implementation. Fault-tree logic for the system failure is used as one of the subprogrammes. The advantage of this approach is that it can be used for a large complex system without any difficulty, besides many advantages normally associated with the fault-tree technique.     

Flow of a micropolar fluid in a micro-channel under the action of an alternating electric field: Estimates of flow in bio-fluidic devices

The paper is devoted to a study of the electro-osmotic flow of a micropolar bio-fluid, when the flow takes place between two plates that are in a state of periodic vibrations. Considering blood as a micropolar fluid, it is found that the amplitude of oscillation of the microparticles of blood increases when the micropolar effect is pronounced more and more and that a rise in DebyeHückel parameter enhances both the velocity and microrotation gradient. The results provide guidelines for the improvement of design of bio-sensing and micro-fluidic devices. The study leads to the conclusion that electrical double layers formed in the vicinity of the wall can significantly alter the flow dynamics of physiological fluids in micro-bio-fluidic devices.     

SECOND LAW ANALYSIS OF A SOLAR THERMAL POWER SYSTEM

This communication presents second law analysis based on exergy concept for a solar thermal power system. Basic energy and exergy analysis for the system components (viz. parabolic trough collector/receiver and Rankine heat engine etc.) are carried out for evaluating the energy and exergy losses as well as exergetic efficiency for typical solar thermal power system under given operating conditions. Relevant energy flow and exergy flow diagrams are drawn to show the various thermodynamic and thermal losses. It is found that the main energy loss takes place at the condenser of the heat engine part whereas the exergy analysis shows that the collector-receiver assembly is the part where the losses are maximum. The analysis and results can be used for evaluating the component irreversibilities which can also explain the deviation between the actual efficiency and ideal efficiency of solar thermal power system.     

Formulation optimisation of a whey lemon beverage using a blend of the sweeteners aspartame and saccharin

Product formulations based on combinations of two sweeteners were optimised in a sweetened paneer whey lemon beverage (WLB) by organoleptic panels. The binary sweetener blend aspartame/saccharin (70:30, 0.0425%) scored the highest based upon comparison with the best‐optimised single sweetener aspartame (0.07%) in WLB and had nonsignificant differences with the control WLB sweetened with sucrose in all sensory attributes. This best binary blend showed maximum synergy in sweetness intensity (14.4%) and overall acceptability (7.5%) in respect of a single sweetener aspartame. The multiple‐sweetener approach involving use of binary blend (0.0425%) resulted in 39% reduction of usage level when compared with single sweetener aspartame (0.07%).