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.     

Isothermal Grain Growth Studies on Nanostructured 9Cr-1Mo and 9Cr-1W Ferritic Steels Containing Nano-sized Oxide Dispersoids

Analysis of isothermal grain growth kinetics of nanocrystalline Fe-9Cr-1Mo and Fe-9Cr-1W-based ferritic oxide dispersion strengthened alloys is reported. Fe-9Cr-1Mo-0.25Ti-0.5Y₂O₃ alloy exhibited ~900 and ~250 pct enhancement in grain-coarsening resistance at 1073 K (800 °C) in comparison with Fe-9Cr-1Mo-0.5Y₂O₃ alloy and Fe-9Cr-1W-0.5Y₂O₃ alloy, respectively. Comparison of grain growth time exponents also revealed that addition of Ti and Y₂O₃ to nanocrystalline Fe-9Cr alloy has significantly enhanced the grain growth resistance. This is attributed to the possible presence of Y-Ti-O-based nanoclusters (<5 nm).     

Bioefficacy of EPA–DHA from lipids recovered from fish processing wastes through biotechnological approaches

The effect of fish oil recovered from fish visceral waste (FVW-FO) on serum and liver lipids, activity of HMG-CoA reductase in liver microsomes and EPA + DHA incorporation in liver, heart and brain were evaluated. Rats were fed different concentrations of FVW-FO providing 1.25%, 2.50%, 5.0% EPA + DHA recovered by either fermentation or enzymatic hydrolysis for 8 weeks. Feeding FVW-FO reduce triacylglycerols (5.96–20.3%), total cholesterol (7.9–21.5%) and LDL (7.39–21.7%) cholesterol levels in serum compared to group fed on a control diet (groundnut oil). The activity of HMG-CoA reductase was reduced (p < 0.05) in the FVW-FO fed groups compared to the control. EPA + DHA level in serum, liver, brain and heart increased with increments in dietary EPA + DHA. Results show the hypolipidemic property of FVW-FO and reduced HMG-CoA reductase activity which is proportional to the incorporation of EPA + DHA. Recovery of FVW-FO will address the increasing demand for fish oil and reduce pollution problems.     

Identification of Fouling Mechanism During Ultrafiltration of Stevia Extract

Stevioside is one of the naturally occurring sweetener, which can be widely applied in food, drinks, medicine, and daily chemicals. Membrane separation has potential application in clarification of stevioside from pretreated stevia extract by ultrafiltration. In the present study, namely 5-, 10-, 30-, and 100-kDa molecular weight cutoff membranes have been used. Quantification of membrane fouling during ultrafiltration is essential for improving the efficiency of such filtration systems. A systematic analysis was carried out to identify the prevailing mechanism of membrane fouling using a batch unstirred filtration cell. It was observed that the flux decline phenomenon was governed by cake filtration in almost all the membranes. For 100 kDa membrane, both internal pore blocking and cake filtration are equally important. Resistance in series analysis shows that the cake resistance is several orders of magnitude higher than the membrane resistance. The cake resistance is almost independent of transmembrane pressure drop, which indicates the incompressible nature of the cake. A response surface analysis was carried out to quantify the development of cake resistance with time during ultrafiltration of various membranes. Quality parameters show that the 30-kDa membrane is better suited for clarification purposes. Identification of the fouling mechanism would aid in the process of design and scaling up of such clarification setup in future.     

Drop Calorimetry Studies on 9Cr–1W–0.23V–0.06Ta–0.09C Reduced Activation Steel

The temperature dependence of enthalpy increment (H _T − H ₂₉₈) of 9 mass% Cr–1 mass% W–0.23 mass% V–0.06 mass% Ta–0.09 mass% C reduced activation steel has been measured by inverse drop calorimetry in the temperature range 400 K to 1273 K. A critical comparison of present isothermal enthalpy measurements with the results of our previous dynamic calorimetry studies has been made to reveal clearly the occurrence of various diffusional phase transformations that occur at high temperature. These phase changes are marked by the presence of distinct inflections or cusps in an overall nonlinear variation of enthalpy values with temperature. The principal thermal relaxation step of the martensitic microstructure obtained through quenching from the high-temperature γ-austenite phase is observed around 793 K. The ferromagnetic-to-paramagnetic transition of the α-ferrite phase is found to occur at 1015 K. The equilibrium values of γ-austenite start (Ae ₁) and finish (Ae ₃) temperatures are found to be 1063 K and 1148 K, respectively. A value of 12 J · g⁻¹ has been estimated for Δ°H ^α→γ the latent heat associated with the α → γ transformation. The measured enthalpy increment variation of the α-ferrite phase with temperature has been fitted to a suitable empirical function to estimate the temperature-dependent values of the specific heat. A comparison of the drop calorimetry-based indirect estimate of the specific heat with the direct differential scanning calorimetry-based values revealed that the drop calorimetry estimates are systematically lower than its dynamic calorimetry counterpart. This difference is attributed to the fact that, under finite heating rate conditions that are typical of dynamic calorimetry, measurements are made under nonequilibrium conditions. Notwithstanding this limitation, there is a good overall agreement between the two C _p values and also among the phase transformation temperatures so that a reliable assessment of thermal properties and phase transformation characteristics of reduced activation steel can be determined by a combined analysis of the results of drop and differential scanning calorimetry.     

Synthesis and spectroscopy of transparent colloidal solution of Gd2O3: Er3+, Yb3+ spherical nanocrystals by pulsed laser ablation

The synthesis and the spectroscopy of upconverting nanocolloidal solutions have recently generated considerable interest due to their potential application as biolevels and in biological assays. This paper reports the synthesis of lanthanides doped transparent colloidal solution via pulsed laser ablation (PLA) which is highly fluorescing. Er³⁺, Yb³⁺ co-doped Gd₂O₃ phosphor has been laser ablated to synthesize the colloidal solution in triply distilled water. Spherical shaped nanoparticles of the average diameter in the range of 8–26 nm have been synthesized and characterized. Efficient multicolor upconversion (UC) emission has been observed and possible UC mechanism has been suggested. This approach will provide a method to synthesize highly UC efficient, non-agglomerated, pure transparent nanocolloidal solution for biological applications from already reported efficient phosphors.     

CTAB-assisted hydrothermal synthesis of single-crystalline copper-doped ZnO nanorods and investigation of their photoluminescence properties

A simple CTAB-assisted hydrothermal synthesis of undoped and copper-doped ZnO nanorods is reported. The phase and structural analysis carried out by X-ray diffraction, shows the formation of hexagonal wurtzite structure of ZnO. Morphology of the ZnO nanorods was investigated by electron microscopy techniques which showed the formation of well dispersed regular shape ZnO nanorods of 100 ± 10 nm in diameter and 900 ± 100 nm in length. However, size of the copper doped ZnO nanorod slightly increased with increasing copper concentration. Furthermore, the selected area electron diffraction pattern and high resolution transmission electron microscopy reveal that both the undoped and copper doped ZnO nanorods were single crystalline in nature and preferentially grew up along [0001] direction. Optical property was investigated by photoluminescence spectroscopy. The effects of copper doping on the photoluminescence property of ZnO nanorods were investigated.     

Influence of sludge disintegration by high pressure homogenizer on microbial growth in sewage sludge: an approach for excess sludge reduction

Excess sludge treatment and disposal is currently a challenge in wastewater treatment plant due to socio-economic and environmental regulation factors. Therefore, it is necessary to explore and develop technology for reduction of excess sludge in wastewater treatment plants rather than treating the generated sludge. This paper discusses technologies for excess sludge growth reduction using high pressure homogenizer treatment which causes cell lysis. The cell lysis and the microbial cellular maintenance energy requirement increases as a result of applied stress. This causes the energy required for non-growth reactions to increase with simultaneous increase in substrate conversion into carbon dioxide rather than microbial cell multiplication.