[en] In steady hydromagnetic free convection and mass transfer of an incompressible, electrically conducting, viscous stratified liquid in a porous medium past an infinite vertical, porous, isothermal plate fluctuating with time dependent suction velocity in the presence of transversely applied magnetic field of negligible magnetic Reynolds number under negligible pressure gradient has been studied. Perturbation technique followed by Pop has been used to obtain the velocity, temperature and concentration field. Skin-friction coefficient at the plate, heat transfer terms of Nusselt number and mass transfer in terms of Sherwood number have also been obtained. The effects of different parameters on velocity and skin-friction have been discussed with the help of a graph and a table respectively. (author)

[en] Theoretical investigations of the thermoelectric properties of CuI have been carried out employing first-principles calculations followed by the calculations of transport coefficients based on Boltzmann transport theory. Among the three different phases of CuI, viz. zinc-blende, wurtzite and rock salt, the thermoelectric power factor is found to be the maximum for the rock salt phase. We have analysed the variations of Seebeck coefficients and thermoelectric power factors on the basis of calculated electronic structures near the valence band maxima of these phases. (papers)

[en] In this article, β-Ga₂O₃ film was deposited on the p-Si (100) substrate using pulsed laser deposition (PLD) technique for rapidly emerging Ga₂O₃-based Schottky barrier diodes (SBDs). Although X-ray diffraction (XRD) result reveals a polycrystalline trending film, a smooth and uniform as-grown surface has been characterized by atomic force microscope (AFM) and field-emission scanning electron microscope (FESEM). Further, we have investigated metal–semiconductor (M–S) contact behavior of the fully vertical SBDs with the four different metals such as aluminum (Al), silver (Ag), gold (Au), and platinum (Pt) on Ga₂O₃ after forming ohmic contacts on the backside of the Si substrate. The barrier heights of all four metals are typically in the range of 0.51–0.69 eV and 0.72–1.41 eV as obtained from the current–voltage (I–V) and capacitance–voltage (C–V) characteristics, respectively. The carrier concentration is ~ 10¹⁶ cm⁻³ as calculated using C–V characteristics. The power device indices, namely breakdown voltage (V_BR) of 19, 26, 90, and 99 V and the on-state resistance (R_ON) values ~ 19.82, 149.19, 7.45 and 156.25 Ω cm² are also obtained for the Al/Ga₂O₃, Ag/Ga₂O₃, Au/Ga₂O₃, and Pt/Ga₂O₃ diodes, respectively. The Baliga Figure of Merits (V²_BR/R_ON) for the Au/Ga₂O₃ diode is found out to be the highest (90.73 W cm⁻²). As the SBDs are fabricated on n-Ga₂O₃/p-Si heterojunction, it is expected to have two back-to-back diodes in the device structure. However, non-existence of back-to-back diodes has been confirmed by temperature dependence I–V characteristics due to possible Poole–Frenkel (P–F) tunneling at the Ga₂O₃/Si heterojunction.

[en] Availability of energy for all aspiring population and the industry is a key factor for assessment of the growth of a nation. Fulfillment of energy demand with minimum environmental damage is the major challenge world-over. Nuclear energy serves the above purposes due to its energy sustainability and low carbon footprint. It is planned to develop a Transportable Uranium Mill (TUM) using acid leaching process. TUM will be a modular plant capable of capacity enhancement by numbering-up the process equipment and flexible enough for modification and replacement of process equipment and machineries with ease when the need arises. Many of process equipment will be of size suitable for transportation on Indian roads. The details of the characterization carried out at bench scale are presented in this paper

[en] Black shale is the unconventional resource of uranium. Recovery of uranium from black shale has been carried out by the following steps: i) size reduction, ii) leaching of uranium in the aqueous medium, iii) fluoride ion removal, iv) solvent extraction of uranium from the aqueous leach solution, v) scrubbing of the loaded solvent after extraction to remove impurities as much as possible and vi) stripping of uranium from the loaded organic into the aqueous phase. Leaching of black shale has been carried out in hydrochloric acid. Free acidity of the leach solution has been determined by potentiometric titration method. Removal of fluoride ions has been done using sodium chloride. Solvent extraction has been carried out by both tributyl phosphate and alamine-336 as extractants. Scrubbing has been tried with oxalic acid and sulphuric acid. Stripping with sodium carbonate solution has been carried out. Overall recovery of uranium is 95%. (author)

[en] The sister elements niobium (Nb) and tantalum (Ta) which belong to group V-B of the periodic table are relatively scarce in the earth's crust, the order of abundance of niobium being around 24 ppm and of tantalum only 2 ppm. On account of their close chemical similarity, the two elements invariably occur together in nature, predominantly in the form of oxide minerals, called columbites (niobite) and tantalites depending on whether the concentration of niobium or tantalum is greater corresponding to the general formula ((Fe, Mn) O. (Nb, Ta)₂O₅). Columbite-tantalite is also found to contain uranium to the order of 0.1%. This is significant in Indian context where the average uranium concentration is of the order of 0.04%. Thus, this can form an important secondary source for uranium as well in addition to being a primary source for niobium and tantalum

[en] Seawater reverse osmosis plant of 1800 m³ /day capacity is a part of 6300 m³ /day capacity Nuclear Desalination Demonstration Project, at Kalpakkam. The plant was commissioned in October 2002 and is in continuous operation. This paper deals with types of foulants, membrane cleaning procedures and the improvement in the reverse osmosis system after cleaning. This paper also describes analysis of foulants which may consist of adsorbed organic compounds, particulate matter, microorganisms, metallic oxides and chemical cleaning procedure to be adopted, which is characteristics of sea water used as the membrane foulant is very much specific with respect to the sea water constituents. The cleaning of the membranes in Kalpakkam Nuclear Desalination plant were taken up as the quality of permeate deteriorated and differential pressure across membrane had gone-up. This paper essentially deals with selection of cleaning chemicals, the experience gained in cleaning procedure adopted and effects of cleaning for the membrane system. (author)

[en] Various methods such as selective laser melting, electron beam melting, casting, friction deposition and friction stir processing are used to produce materials required by different industries. For example, low weight and high strength material is required to be produced to meet the ever increasing demand raised by fast growing aero industries. But the materials produced by these processes are found to lack in ductility and also residual and thermal stresses are formed during these processes that could adversely alter the mechanical properties of the material. Present scenario demands for the development of an eco-friendly method to produce durable materials possessing better mechanical properties. This paper presents a review on various best possible methods to produce high strength to weight ratio Ti-Al alloys. Further, it also compares the conventional and novel alloy making processes and their limitations and also explores the possibilities of making the hybrid process to get desired results. The paper can help the researchers to use the suggested hybrid processes so as to minimize the individual process limitations leading to an improved and efficient process. (paper)

[en] Desalination is one of the reliable and viable alternatives to meet the increasing requirements of safe water both for potable and industrial uses. Desalination is an energy intensive process and requires a minimum of about 0.7 kWh of energy to separate 1000 litres of water from seawater at 25 degC based on thermodynamic considerations. In practice, the energy consumption ranges from about 5 kWh to about 16 kWh per 1000 litres, depending on the type of desalination process adopted and the design philosophy. Therefore, it is desirable that the desalination plants are coupled to power stations. In view of the steadily increasing role of nuclear power in the energy sector, it was considered appropriate to demonstrate the potential and the salient features of desalination technologies in meeting the safe water demand. Accordingly, a 6300m"3/day capacity Nuclear Desalination Demonstration Project (NDDP) was set up consisting of a 4500 m"3/day capacity multistage flash (MSF) desalination plant and 1800m"3/day seawater reverse osmosis (SWRO) desalination plant coupled to Madras Atomic Power Station located at Kalpakkam. SWRO plant was commissioned in the year 2002 and MSF plant was commissioned in the year 2008. Both the plants are in round the clock shift operation since then

[en] Acid leaching process for uranium recovery from ore often generates considerable amounts of impurities into the solution. It is a challenge to separate the non-valuable impurities as manageable and stable waste products for final disposal, without losing the valuable constituents. The main impurities that come with the leach liquor are iron and sulfate. Their removal is essential for meeting the iron requirement in leaching circuit and also for making the effluent suitable for recycle. Factorial design analysis was applied to study of process variables for precipitation of iron and sulphate from leach liquor with composition using CaO as precipitation reagent