Corrosion behaviour of structural materials in sodium influenced by formation of ternary oxides

Fast breeder reactors use liquid sodium metal as the coolant in their primary and secondary circuits. Corrosion behaviour and compatibility of structural materials in sodium at the operating temperature of the reactors has been found to be influenced by oxygen impurity in sodium even at parts per million level. The compatibility of structural materials in sodium influenced by oxygen in the liquid metals has been dealt with previously on the basis of formation of binary oxides of the solid metals. Since then many of the structural metals have been found to form ternary oxides in sodium. Several three phase equilibria and free energy of formation data for the ternary oxides of structural metals with sodium are reviewed in this paper. Threshold oxygen levels in sodium for the formation of binary oxides and ternary oxides on structural metals are derived from the relevant thermodynamic data. Many of the structural metals are found to form ternary oxides at much lower oxygen levels in sodium than required for the formation of respective binary oxides. Threshold oxygen levels in sodium for the formation of ternary oxides of major constituents of stainless steel are also presented. Corrosion behaviour of the structural metals and austenitic steels influenced by formation of ternary oxides is discussed.     

Anisotropic particle synthesis in dielectrophoretically controlled microdroplet reactors

The miniaturization of chemical and biological processes in microfluidic devices and bioarrays is a major technological achievement. Microchips performing multiphase material synthesis operations could be a future step in this trend of miniaturizing technology. Here we show how electrically controlled chips can be used for the synthesis and manipulation of new types of particles with advanced structure. The method is based on a technique that allows freely suspended droplets and particles to be entrapped and transported using electric fields. The fields that hold and guide the droplets and particles are applied through arrays of electrodes submerged in the oil. Each of the microdroplets suspended on the surface of fluorinated liquid serves as a microscopic reactor, where the particles are formed by solidification of the carrier droplets. Controlled on-chip assembly, drying, encapsulation and polymerization were used to make anisotropic 'eyeball' and striped particles, polymer capsules and semiconducting microbeads.     

Ultra-violet absorption spectra: 4-hydroxy coumarins

The ultra-violet absorption, in the range 250 mμ—350 mμ, of twelve 4-hydroxy coumarins in methanol and in 10% aqueous methanol over a range of pH, has been studied and discussed.     

Energy conservation in fossil-fuel-fired systems: Three case studies

This paper reports the results of energy analysis of oil- and coal-fired systems in a sodium silicate industry, in a mechanized bakery and in silk filatures. In all, seven systems (three oil-fired and four coal-fired units) were evaluated and energy conservation measures were suggested. It is shown that in most cases, the fuel consumption can be reduced by over half. The recommendations for fuel savings and mathematical simulations are valid for similar systems elsewhere.     

The Use of a Flow Microcalorimeter to Characterise Powder Surfaces

When a material is exposed to air at a definite temperature and humidity, it will gain or lose moisture until on equilibrium moisture content is attained. This value depends on the chemical and physical properties of the material and is generally lower for non-porous solids and higher but more variable for fibrous or colloidal organic substances. In pharmaceutical powders the sorption of moisture poses many problems for the formulator. Moisture uptake can have a profound effect on both the physical and chemical stability of the powder. The presence of a film of moisture can provide a medium where chemical reactions such as hydrolysis can take place. This in turn affects the powder properties such as the potency of the drug or may result in the formation of insoluble products on the surface thus affecting drug availability. It can also lead to changes in coloration of the drug. From a manufacturing point of view, moisture uptake has an added adverse effect in terms of the handling properties of the material. This is because an increase in moisture content generally causes- a free-flowing powder to cohere, thus causing inefficient mixing with other powders, blocking of machinery and resultant non-uniformity of the product. On the other hand a very fine dry powder may become easier to handle when a little moisture is present and may also reduce the dustiness of the powder and increase the powder's capacity to consolidate.

Moisture usually condenses on the surface of the substance exposed to the atmosphere. However in porous powders, it may penetrate the depth of the powder bed. At a given temperature condensation increases with an increase in the partial pressure of water vapour in the atmosphere. Powder surfaces in general are very reactive and the amount of moisture adsorbed increases as the surface area of a powder increases, because moisture uptake is essentially a surface phenomenon (Sprowls²). For the measurement of adsorption at liquid/solid interfaces, Groszek³developed the flow microcalorimeter. This instrument has been used to measure the lubricating action of solid lubricants such as graphite^4,5 and more recently for the study of dental enamel surfaces⁶ In addition the instrument has been used for the measurement of specific surface area^7,8 The flow micro-calorimeter has been modified and adapted for use in the present work in order to evaluate heats of adsorption and desorption of moist air at various powder surfaces.