KINETICS OF URANIUM EXTRACTION BY MACROPOROUS BIFUNCTIONAL PHOSPHINIC ACID RESIN

ABSTRACT

The rate of extraction of uranium by macroporous bifunctional phosphinic acid (MPBPA) resin from nitric acid medium has been studied under particle diffusion controlled conditions. The internal diffusion coefficient was found to increase with increase in temperature and decrease with increase in particle size. The activation energies and entropies suggest that the extraction of uranium essentially follows ion exchange mechanism at low concentration of nitric acid while it is through linkage of >P=0 group of the resin at high concentrations.     

Determination of the Degree of Mixing in Multicomponent Ceramic Powder Compacts by Micro-Raman Spectroscopy

Powder compacts of TiO₂ and ZrO₂ were prepared from their suspensions in water at different pH values, and micro-Raman spectroscopy was used to reveal the degree of mixing in each of them, with different sizes of the focused laser spot. The change in laser intensity and particle-size distributions led to a slight variation in the average composition, as determined using three different probe sizes. The Raman-estimated volume fractions of each constituent indicated that the aqueous suspensions in which the powders were well dispersed produced the most-uniform mixing. Powders that were flocculated in suspensions before mixing also resulted in a good mixture. The most-nonuniform mixing was observed when, in the individual suspensions, one of the constituents was dispersed and the other was flocculated. These results indicated that Raman spectroscopy can be useful for the rapid determination of the degree of mixing in powder mixtures.     

Influence of different post treatments on tungsten carbide-cobalt inserts

The present work is an attempt to improve some of the mechanical properties of cemented tungsten carbide (WC) cutting tool by subjecting it to different post treatments. The different post treatments that are tried out to the tungsten carbide-cobalt (WC-Co) inserts are a) controlled cryogenic treatment, b) heating and forced air cooling and c) heating and quenching in oil bath. The response of WC-Co inserts to such different post treatments has been evaluated in terms of microhardness, microstructural changes, scanning electron microscope (SEM) micrograph and Co metal phase changes through XRD. The experimental result indicate a remarkable response to all the above mentioned post treatments and the analysis of the same are presented in this paper.     

Effect of heating mode on sintering of tungsten

Microwave heating is recognized for its various advantages, such as time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved properties. The present paper investigates the feasibility of consolidating tungsten powders through microwave sintering. A comparative analysis has also been attempted between the sintering response of pure tungsten powder compact in a microwave and conventional furnace.     

Difference in the Nature of Eu3+ Environment in Eu3+‐Doped BaTiO3 and BaSnO3

BaTiO₃ and BaSnO₃ samples doped with Eu³⁺ ions were prepared using glycine‐nitrate gel combustion method. Relative intensities and line shapes of magnetic dipole allowed ⁵D₀ → ⁷F₁ and electric dipole allowed ⁵D₀ → ⁷F₂ transitions of Eu³⁺ from the hosts, BaTiO₃ and BaSnO₃, are significantly different. Based on detailed structural investigations, it is confirmed that synthesizedBaTiO₃ sample is tetragonal with no center of symmetry around Ba²⁺ ions. Unlike this BaSnO₃ is cubic with centrosymmetric Ba²⁺ site. From X‐ray diffraction and experimentally obtained Judd–Ofelt parameters (Ω₂ and Ω₄ values), it is confirmed that in BaTiO₃ there is a decrease in the average Ba–O and Ba–Ba distances compared with that in BaSnO₃. This leads to higher Eu–O bond polarizability and adds to the distortion in its environment around Eu³⁺ in BaTiO₃:Eu compared with BaSnO₃:Eu. This is responsible for the observed difference in the luminescence properties.     

R Curves and Crack-Stability Map: Application to Ce-TZP/Al2O3

The concept of a crack-stability map is developed by considering the interaction between the crack-driving force and the rising crack-growth resistance of a toughened ceramic. The map plots normalized transition crack length as function of the ratio of the crack-initiation fracture toughness and the plateau toughness to delineate regimes of stable and unstable crack growth. The plot is used to analyze R curves and fracture stresses of a transformation-toughened Ce-TZP/Al₂O₃. It is shown that the fracture stress and the small scatter measured for this ceramic are consistent with its R- curve behavior, which enables stable growth of surface cracks from flaws (pores and second-phase particles), leading to a flaw-insensitive ceramic.     

Rate-dependent serrated flow and plastic deformation in Ti45Zr16Be20Cu10Ni9 bulk amorphous alloy during nanoindentation

The plastic deformation of Ti₄₅Zr₁₆Be₂₀Cu₁₀Ni₉ bulk metallic glass has been investigated by nanoindentation performed with loads ranging from 10 to 200 mN in a wide range of loading rates. The plastic flow in the alloy exhibited conspicuous serrations at low loading rates. The serrations, however, became less prominent as the rate of indentation increased. Atomic force microscopy showed a significant pile-up of materials around the indents, indicating that a highly localized plastic deformation occurred under nanoindentation. The possible mechanism governing the plastic deformation in bulk metallic glass specimens is tentatively discussed in terms of strain-induced free volume.     

Steady state behaviour and maintenance planning of a desulphurization system in a urea fertilizer plant

This paper presents the steady state behaviour and maintenance planning of the desulphurization process in the fertilizer industry. The process consists of four subsystems, A, B, C and D in series with three states; good, reduced and failed. One standby unit is provided for each pump. Taking constant failure and repair rates for each subsystem, mathematical modelling is done using the Chapman-Kolmogorov birth-death process. An expression for steady state availability is given. Based on the data available from a medium sized ammonia production process, the behaviour of each working unit in the process has been analysed. The computed results are discussed with the concerned plant personnel which is helpful to the management for implementing any future plan regarding design modification of the system/processes.     

Stochastic analysis and maintenance planning of the ash handling system in the thermal power plant

This paper discusses stochastic analysis of the ash handling system in a thermal power plant. The system consists of four subsystems A_i, B_j, C and D_k in series, with three possible states: good, reduced and failed. Failure and repair rates for each subsystem are taken to be constants. Using a probabilistic approach, the differential equations are generated and the expression for steady state availability is computed. Taking data from the thermal power plant, situated in North India, the behaviour of each working unit is analysed. Problems and remedies with appropriate maintenance schedules have been discussed. The results are discussed with the plant personnel and are helpful to the management in predicting the behaviour of each operating unit, so that timely decisions can be taken for maintaining the system in upstate for a long duration.