Phase Transformation Studies in U–xZr (x = 2, 5, 10 wt%) Alloys Using Dynamic Calorimetry

The thermo-kinetics aspects of phase transformations in U rich U–xZr binary alloys, with x = 2, 5 and 10 wt% Zr have been investigated using dynamic calorimetry. The on-heating and cooling transformations at controlled scan rates in the range, 1–99 K min^?1, have been monitored and the following transformation sequence is obtained at slow heating (3 K min^?1) of a U–2Zr alloy: (i) α or α′ (distorted orthorhombic martensite) + δ(UZr₂) → α + γ₂ (bcc phase enriched in Zr); (ii) α + γ₂ → β (tetragonal) + γ₂; (iii) β + γ₂ → β + γ₁ (bcc phase enriched in U); (iv) β + γ₁ → γ; (v) γ (bcc) → liquid (melting). Similar transformation sequence for other compositions with varying enthalpy effects has been witnessed for 5 and 10 Zr alloys. The observed transformation characteristics are rationalized for the effect of Zr content and heating/cooling rate variations.     

Processing of Alumina-Rich Iron Ore Slimes: Is the Selective Dispersion–Flocculation–Flotation the Solution We Are Looking for the Challenging Problem Facing the Indian Iron and Steel Industry?

Beneficiation of alumina rich iron ore slimes is a major challenge for the Indian iron ore industry. Considering the limits of gravity and magnetic separation processes in the relatively finer size range in terms of achieving adequate separation efficiency, selective flotation (with and without selective flocculation) of iron ore slimes, which is being used commercially in several countries for the beneficiation of iron ores, is worth exploring for the beneficiation of Indian iron ores. Based on the extensive work carried out in our laboratories, we have concluded that the design and development of highly selective reagents to achieve satisfactory separation of hematite and goethite from alumina containing minerals (gibbsite or kaolinite) in the ore and ore slimes, is the key to solving the challenging problem of processing alumina rich iron ores. Accordingly our research work has been focused on finding/designing selective reagents for iron oxide–gibbsite–kaolinite separation based on a molecular modeling computational approach developed by us for the design of mineral processing reagents. We present in this paper the results of our density functional theory computations to evaluate the interaction energies of a wide variety of different reagent functional groups such as carboxylic acid, hydroxamic acid, phosphonic acid, iminobismethyl phosphoric acid, xanthate and starch with hematite, gibbsite and kaolinite surfaces. Among all the reagents investigated so far, starch exhibits the highest selectivity towards the hematite surface with a difference in interaction energy of ~63 kcal/mol between hematite and gibbsite surfaces. Based on our earlier work which indicated polyvinyl pyrrolidone (PVP) to be more selective dispersant for kaolinite compared to conventional sodium silicate and sodium hexametaphosphate, we have investigated selective flocculation–dispersion of natural iron ore slimes (three different samples obtained from three different mines in India) with PVP and starch reagent combination. The results are promising. While the work is still in progress, the implications of our recent results are discussed in the context of the challenging problem of processing of alumina rich iron ore slimes in India.     

A Numerical Method for Multiphase Incompressible Thermal Flows with Solid–Liquid and Liquid–Vapor Phase Transformations

ABSTRACT

A numerical method for multiphase incompressible thermal flows with solid–liquid and liquid–vapor phase transformations is presented. The flow is mainly driven by thermocapillary force and vaporization. Based on the level set method and mixture continuum model, a set of governing equations valid for solid, liquid, and vapor phases is derived, considering phase boundary conditions as source terms in the transport equations. The vaporization process is treated as a source term in the continuity equation. The model developed is applied to the laser welding process, where the flow is coupled with optical phenomena. Formation and collapse of a laser-created hole is simulated.     

Thermodynamic analysis and parametric study of an intercooled–reheat closed-cycle gas turbine on the basis of a new isentropic exponent

The thermodynamic analysis and parametric study of an intercooled–reheat closed-cycle gas turbine is presented in this paper, on the basis of a new (harmonic mean) isentropic exponent. An analytical expression is derived for the optimum pressure ratio and maximum non-dimensional net work output. It is found that the optimum pressure ratio and the maximum non-dimensional net work are high when the ratio of extreme temperatures of cycle (i.e. T _max and T _min) and isentropic efficiencies of compressor and turbine (i.e. η_c and η_t) are high. The theoretical results are also compared with the practical conditions of power plant.     

Tertiary treatment of distillery wastewater by nanofiltration

Tertiary treatment of aerobically treated distillery wastewater by nanofiltration was carried out in a spiral wound nanofiltration membrane module under different operating conditions. The results show that the percentage separation of organic and inorganic compounds was quite high, as reflected by the reduction of chemical oxygen demand (COD) and total dissolved solids (TDS) in the range of 96–99.5%, and 85–95% respectively. The color removal was in the range of 98–99.5%. The results of the effect of variation of the inlet concentration, feed circulation rate and pH conform to the mechanism of gel layer formation. Gel layer formation and Concentration polarization was found to play a major role in the treatment of distillery waste using nanofiltration (NF) membrane. It was observed that as concentration of feed solution increases the permeate flux was reduced. This change was higher compared to the separation of COD and TDS. The result indicates that the NF membrane showed very high performance efficiency for organic components (96–99.5%), as indicated by COD removal. In comparison, the separation of inorganic compounds was found to be in the range of 25–90% as estimated from relative separation of COD and TDS. The present study shows that nanofiltration is a promising technique for recovery of water from distillery waste, which could be used to achieve zero discharge status and solve a major environmental problem.     

Synthesis,characterization, and drug release properties of poly(N-isopropylacrylamide) gels prepared in methanol–water cononsolvent medium

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol–water mixture. A scanning electron microscopy study revealed that the freeze-dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X_0.43>X_0.21>X_0.76 ≈ X_0.57>X_0.31>X_0.13>X_0.06>X₀, where X_m denotes a gel prepared in a methanol–water mixture with m mole fraction of methanol (x_m). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol–water mixtures with different x_m values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X_0.43> X_0.31> X_0.21> X_0.57> X_0.76 ≈ X_0.13> X_0.06> X₀. The reswelling rates of these hydrogels decreased in the following order: X₀> X_0.31> X_0.06 ≈ X_0.13 > X_0.76> X_0.57> X_0.21> X_0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug-loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Covulcanization of LLDPE/EMA blends using dicumyl peroxide

The effect of dicumyl peroxide (DCP) content on the gel fraction, mechanical, dynamic mechanical, and thermal properties of linear low‐density polyethylene (LLDPE)/ethylene‐co‐methyl acrylate (EMA) blends were studied. Gel content of the blends increases with increasing DCP content, and EMA is more prone to crosslinking than LLDPE. Wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) were used to study the effect of DCP crosslinking on percent crystallinity and crystalline structure of the blends and individual components. At lower level of DCP loading, crosslinking process does not have significant effect on the crystalline structure of the LLDPE, which was confirmed from the percent crystallinity and lattice distance value. However, at higher DCP content, percent crystallinity decreases significantly. At lower EMA concentration (<50%), percent crystallinity and lattice distance remain unchanged up to 2 wt % of DCP. For EMA contents of more than 50 wt %, increasing DCP content reduces the crystallinity of the blends and increases the lattice distance. The highest level of mechanical and dynamic mechanical properties was observed for 60/40 LLDPE/EMA blends at 2 wt % DCP. Addition of LLDPE‐g‐MA (3 wt %) as a compatibilizer enhances the properties of the vulcanizates. Blends crosslinked with DCP up to 0.3 wt % can easily be reprocessed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Epoxy—Polyester IPNs modified with aromatic amines

Semi-interpenetrating polymer networks (Semi-IPNs) based on epoxy and unsaturated polyester resin (UPR; added in 5.9 and 11.1 wt %) have been prepared by chemical route. Room temperature curing was attempted using triethylene tetramine as a hardener. Blend with 11.1% UPR is found to exhibit best mechanical properties. Further, blends were also prepared by adding aromatic amines such as diphenylamine (DPA, secondary amine) and benzidine (Bz, primary amine). Structural elucidation of the samples through identification of functional groups was carried out with the help of Fourier transform infra red spectroscopy. Absence of peak at 915 cm⁻¹ (characteristic of epoxy ring) confirmed complete curing in all the blends. The mechanical properties such as hardness, izod impact and tensile strength of blends were compared. The co-cured blends show decrease in shore hardness (≈ 1–6%), while, the izod impact exhibits an opposite trend. Blends with 10% DPA and Bz show an increase in izod impact by 268.6% and 38.8% respectively. Further, the tensile strength is observed to be enhanced by 45% in case of DPA while addition of Bz reduces it by 32.8%. Thermal properties were studied by thermogravimetric (TGA) and differential scanning calorimetric (DSC) analysis. TGA shows no significant change in onset and decomposition temperature but temperature at which it melts is lowered almost by 100–150°C together with the onset temperature (by ≈ 200°C) observed in DSC. Scanning electron micrographs reveal granular nature of the samples. The homogeneity of blends appears to be good. The blends co-cured with DPA are relatively crystalline compared with others. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

QoS‐aware routing and power control algorithm for multimedia service over multi‐hop mobile ad hoc network

This paper presents a QoS (quality of service) aware routing and power control algorithm consuming low transmission power for multimedia service over mobile ad hoc network. Generally, multimedia services need stringent QoS over the network. However, it is not easy to guarantee the QoS over mobile ad hoc network since its network resources are very limited and time‐varying. Furthermore, only a limited amount of power is available at mobile nodes, which makes the problem more challenging. We propose an effective routing and power control algorithm for multimedia services that satisfies end‐to‐end delay constraint with low transmission power consumption. The proposed algorithm supports the required bandwidth by controlling each link channel quality over route in a tolerable range. In addition, a simple but effective route maintenance mechanism is implemented to avoid link failures that may significantly degrade streaming video quality. Finally, performance comparison with existing algorithms is presented in respect to traditional routing performance metrics, and an achievable video quality comparison is provided to demonstrate the superiority of the proposed algorithm for multimedia services over mobile ad hoc network. Copyright © 2010 John Wiley & Sons, Ltd.