Synthesis and characterization of chitosan/poly(acrylic acid) polyelectrolyte complex

Polyelectrolyte complex based on chitosan and acrylic acid monomer by photoinitiated free‐radical polymerization in the absence of crosslinker showed a large transition in swelling in response to changes in pH of surrounding medium. Their ability to swell arises from polyelectrolyte interactions and molecular structure of the complex. The main properties of interest that related to the molecular structure, swelling volumes, glass transition temperature, and elastic modulus of the complex were investigated. The effect of water content, the only variable in the sample component, played an important role in molecular structure of the complex and as a consequence, the extent of intermolecular linkage, especially amide bonds which in turn governed the degree of swelling of the polyelectrolyte complex in this study. The decreased degree of swelling and higher temperature shift of glass transition temperature was found with increased water content, whereas increased modulus of elasticity of dry complex was found in lower water content of synthesis component. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1025–1035, 2002     

Hydrogen-assisted cracking

This article reviews a number of case studies involving hydrogen-assisted cracking in steels. Before the case studies are presented, the current state of understanding of hydrogen-assisted cracking is briefly reviewed. At present there are two leading approaches to the development of a mechanism of hydrogen-assisted cracking, one based upon bond weakening, and the other upon strain localization. As the case studies illustrate, hydrogen-assisted cracking can lead to failures in perhaps unexpected circumstances. The need for the wider dissemination of information about hydrogen cracking to design engineers is indicated.     

Temperature-induced phase change in a fat. A study by electron spin resonance

Electron Spin Resonance, Differential Scanning Calorimetry and rheological techniques have been used to study the physical changes induced by temperature in lard and in the solid and liquid fractions obtained by fractionation of lard at 15 C. The mobilization process of a C18 fatty acid nitroxide derivative dispersed in the molten fat has been observed in the temperature range −50 to +70 C. The mobilization of the probe seemed to be concomitant with the melting of the low melting point glycerides. Above this temperature, all the probes were in the liquid phase and their mobility reflected the viscosity of their liquid environment, or the viscosity of the bulk fat when crystal was no longer present. Probe mobility was temperature dependent, and it was identical for the three fats at the same temperature, despite their different triglyceride compositions.     

Utilisation de couples d'hydrocarbures dans les frigopompes et les thermofrigopompes à absorptionUtilisation of hydrocarbon pairs in absorption heat pumps in cooling applications

The performances of two systems using hydrocarbon pairs are compared. The first system is an absorption heat pump, comprising a rectification column separator and a mixer comprising a single-stage cell. In this case, five hydrocarbon pairs are used. In the second system, the authors compare the performances of three hydrocarbon pairs in two heat pumps with one or two stages in the mixer. It was shown that the best performances are obtained using pairs with the most similar chemical compositions.     

Studies of palladium electrodeposition from baths based on Pd(NH3)2X2 Part II: X=Br and X=NO2

The chemistry and electrochemistry of electroplating baths based on Pd(NH₃)₂Br₂ and Pd(NH₃)₂(NO₂)₂ has been investigated and compared with that previously reported for Pd(NH₃)₂Cl₂. It is shown that electroactive species in all the baths is Pd(NH₃) ₄ ²⁺ and, hence, the mechanisms and current efficiencies for the cathodic deposition of palladium metal are similar in all three media. On the other hand, only in bromide electrolytes is the palladium found to dissolve anodically.     

Electrocatalyst performance in industrial water electrolysers

Electrocatalyst materials used in industrial water electrolysis equipment must meet stringent requirements for long-term stability. Low electrode overvoltages must be sustained over prolonged periods of normal operation, including power interruptions. This paper presents an overview of the catalyst systems currently favoured for use in alkaline electrolyte. Performance data covering test periods exceeding 30 000 h are presented for representative commercial electrocatalysts. Results obtained in 100 000-A unipolar cells are correlated in detail with expectations based on measurements in laboratory and pilot-plant equipment.Particular attention is given to the effects of open-circuit conditions on electrode stability. An accelerated reverse-potential cycling test is described which allows identification of materials expected to withstand industrial operating conditions. It is found that the better materials which have been identified can be used with confidence, at least in electrolysers of the unipolar design in which potential variations encountered during current interruptions are modest.     

Multitemporal passive microwave mapping in MACHYDRO'90

MACHYDR0'90 was an experiment conducted in Pennsylvania in 1990 to study the synergistic use of remote sensors in multitemporal hydrologic studies. As part of this mission the pushbroom microwave radiometer was flown and used to produce brightness temperature maps. Verification studies and vegetation algorithms for mixed land cover areas are described