Some polishing experiments on copper in a hyperbolic cell

Some polishing experiments have been carried out on copper anodes in a hyperbolic cell designed by Gilmont and Walton, using orthophosphoric acid as the electrolyte. The results obtained have been compared to those obtained in similar experiments in a Hull cell. It has been found that very similar bands of different reflectivity and polishes are found to form in both the cells. These bands shift with time and a study of such displacements has been made. The results are briefly discussed.     

Conductometric determination of carbon in uranium carbide and its solution in nitric acid

A simple but accurate method has been developed for the determination of carbon in uranium carbide powders/pellets as well as in solutions of uranyl nitrates. The methodology involves quantitative conversion of carbon present in the sample to carbon dioxide that is subsequently absorbed in a dilute solution of barium hydroxide. The conductivity shift of the barium hydroxide solution is monitored on-line continuously using a laboratory-built PC-based conductivity measurement system that has been developed in-house based on the direct conversion of conductance to the digital pulse frequency. A new gas absorption cell has been designed to ensure quantitative absorption during the residence time of the gas in the cell. The method is sensitive, accurate and precise to 1-3% at 600-1000 mug of carbon in samples of uranium carbide.     

Size effect study in magnetoelectric BiFeO3 system

In this paper, we report for the first time finite size effects on Néel temperature (T _N) of magnetoelectric BiFeO₃ system. Novel wet chemical route has been developed to produce fine particles of BiFeO₃ with controlled size and size distribution. Unlike other oxide systems, lattice volume contraction has been observed with decrease in particle size. The decrease in T _N is co-related to unit cell volume contraction occurring with reduction in particle size.     

Empirical modelling of hydrazoic acid distribution in nitric acid-TBP/n-dodecane biphasic system

During reductive partitioning, hydrazoic acid is produced by the reaction of hydrazine and nitrous acid. In this paper an empirical model for the extraction of hydrazoic acid and its temperature dependence is reported.     

Polarisation and polishing studies on copper in a Hull cell

In continuation of our previous work,^1–2 the effects of polishing time, sp. gr. of the electrolyte, addition of EDTA, electrolyte level, etc., on the position, size and shape of the variously polished bands obtained in a Hull cell have now been studied. I–V measurement when carried out showed that total cell voltage increases regularly with total cell current, thereby affording no explanation for the variously polished bands. However, with a specially designed probe electrode,³ it has been possible to study the current distribution as existing during polarisation at different points of the anode surface and thus offer some explanation for the appearance of variously polished bands which could not be interpreted earlier in terms of electrode potentials.     

Synthesis of surfactant-templated silica films with orthogonally aligned hexagonal mesophase

Thin silica films with orthogonally aligned hexagonal close-packed cylindrical structure are synthesized by dip coating silica precursors and poly(ethylene oxide)-polyproplyene oxide (PEO-PPO) triblock surfactants (P123) onto modified glass slides. All films cast from this sol display 2D hexagonal pore structures (a approximately 6.2 nm) under transmission electron microscopy (TEM). However, X-ray diffraction (XRD) shows that confining freshly deposited films between two chemically neutral modified slides completely aligns the pores toward the direction orthogonal to the substrate. Equally effective alignment is obtained by using slides modified with either a random PEO-PPO copolymer or P123 itself. The channels in films cast onto unmodified slides, onto modified slides which are exposed to air, or onto modified slides which are exposed to unmodified glass slides align at least partially parallel to the substrate. Parallel mesophase alignment is also observed in a control experiment with a sol containing the nonionic surfactant template decaethelyne glycol hexadecyl ether (Brij-56) sandwiched between copolymer-modified slides because the surfaces are not chemically neutral toward Brij-56. This study confirms that it is possible to use substrate surface chemistry to control the orientation of mesophases in mixtures of reactive silicates and low molecular weight nonionic surfactant templates.     

Development of a continuous homogeneous process for denitration by treatment with formaldehyde

Removal of nitric acid from high level liquid wastes (HLLW) of nuclear fuel reprocessing plants is warranted for simplifying the procedure for waste fixing. Chemical denitration aims to reduce the waste volume by destroying the acidity and subsequent concentration by adding suitable reductants. Reduction of nitric acid to gaseous products is an attractive way to accomplish denitration. Nitric acid reduction with formaldehyde proceeds with the formation of CO₂, NO₂, NO or N₂O depending on the reaction conditions and all the reaction products except water can be eliminated from the system in gaseous form. The HNO₃–HCHO reaction is governed by a complex mechanism of exhibiting relatively long induction period, depending upon the temperature, concentration of reactants and nitrous acid reaction intermediate. In the present work, a homogeneous denitration process with formaldehyde which offers safety and is governed by controlled kinetics was demonstrated on a laboratory scale. The induction period before commencement of the reaction was eliminated by maintaining the reaction mixture at a pre determined temperature of 98 °C. Based on the results accrued from lab scale experiments, the equipment for pilot plant scale operation was designed, the reaction efficiency for continuous denitration was determined and the investigation of nitric acid destruction was extended to full-scale plant capacity. The role of organics in the waste in foaming up of the reaction mixture was also studied using a synthetic waste solution.