The gaseous reduction of solid calciowustites in Co/Co2 and H2/H2O gas mixtures

The reduction of calciowustites has been carried out in CO/CO₂ and H₂/H₂O gas mixtures at temperatures between 1073 and 1373 K. The effect of lime additions to the wustite is to extend considerably the range of gas conditions over which porous iron morphologies are observed compared to those found on reduction of pure wustite. The products obtained at low oxygen potentials consisted of porous iron containing a dispersion of CaO particles, at intermediate oxygen potentials a two phase structure consisting of porous iron and dicalcium ferrite was formed, and at high oxygen potentials a dense iron layer over the oxide surface is observed throughout reduction. F. NAKIBOGLU, formerly Graduate Student, Department of Mining and Metallurgical Engineering, University of Queensland, Brisbane, Australia D.H. St. JOHN, formerly Postdoctoral Fellow, University of Queensland     

A Simple Converse of Burnashev's Reliability Function

In a remarkable paper published in 1976, Burnashev determined the reliability function of variable-length block codes over discrete memoryless channels (DMCs) with feedback. Subsequently, an alternative achievability proof was obtained by Yamamoto and Itoh via a particularly simple and instructive scheme. Their idea is to alternate between a communication and a confirmation phase until the receiver detects the codeword used by the sender to acknowledge that the message is correct. We provide a converse that parallels the Yamamoto-Itoh achievability construction. Besides being simpler than the original, the proposed converse suggests that a communication and a confirmation phase are implicit in any scheme for which the probability of error decreases with the largest possible exponent. The proposed converse also makes it intuitively clear why the terms that appear in Burnashev's exponent are necessary.     

The effect of sulfur on the gaseous reduction of solid calciowustites

Investigations have been carried out into the effects of sulfur on the reduction of solid calciowustites in CO/CO₂ gas mixtures. It has been shown that the presence of calcium in the oxide and sulfur in the gas leads to catastrophic swelling through iron whisker growth. The various mechanisms of iron growth in these systems are also discussed. D. H. St. JOHN, formerly Postdoctoral Fellow, University of Queensland F. NAKIBOGLU, formerly Graduate Student, Department of Mining and Metallurgical Engineering, University of Queensland, Brisbane, Australia     

Synthesis and electrochemical,electrical and gas sensing properties of novel mononuclear metal-free,Zn(II), Ni(II), Co(II), Cu(II), Lu(III) and double-decker Lu(III) phthalocyanines substituted with 2-(2H-1,2,3-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl) phenoxy

A new mono substituted phthalonitrile derivative 3 was prepared by a nucleophilic displacement reaction of 4-nitrophthalonitrile with 2-(2H-1,2,3-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol. Novel metallophthalocyanines 4–8 (M = Zn, Ni, Co, Cu, Lu, respectively), metal free 9 and double decker Lu(III) phthalocyanine 10 with four peripheral 2-(2H-1,2,3-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenoxy groups were synthesized by cyclotetramerisation of the phthalonitrile and characterized by elemental analyses, FTIR, ¹H NMR, UV–vis and MALDI-TOF MS spectral data. Cyclic voltammetry, differential pulse voltammetry and in situ spectroelectrochemistry of the phthalocyanine compounds have been studied. This allowed us to identify and compare metal- and phthalocyanine ring-based redox processes of the complexes. Impedance spectroscopy (IS) and dc conductivity measurements were performed as a function of temperature (300–430 K) and frequency (40–10⁵ Hz.). The sensing properties of the films for toluene were also investigated. The dc results showed an activated conductivity dependence on temperature for all films. While room temperature impedance spectra consist of a curved line, a transformation into a full semicircle with increasing temperature was observed. The analysis of ac conductivity data showed that the CBH model is the dominant conduction mechanism for the electron transport in the films. While exposure to toluene has no effect on the conductivity of the film of 8–10 completely reversible sensor response to toluene only were obtained for compounds 4–7. It was also observed that the operating temperature had a considerable effect on sensing characteristics of the films.