Electrochemical Study of Co-Based Alloys in Simulated Physiological Solution

The aim of the present work was to provide a better understanding of the biocompatibility of Co-based alloys in the physiological environment. Co-based alloys are widely used in orthopaedics for the manufacture of prosthetic devices. Two alloys, Co—Cr—Mo and Co—Ni—Cr—Mo, and their individual metal components were studied in simulated physiological solution at 37 °C, with and without the addition of two complexing agents, EDTA and citrate, in the concentration range from 0.1 to 50 mM. The processes were studied using electrochemical techniques: cyclic voltammetry, anodic potentiodynamic measurements, linear polarization and electrochemical impedance spectroscopy. The results are discussed in the context of the dependence of the passivation behaviour of the two alloys on their composition. Both alloys are shown to passivate very well in simulated physiological solution. The effect of complexing agents is more evident on Co—Ni—Cr—Mo than on Co—Cr—Mo alloy. This appears to be related to the presence of Ni.     

Effect of N+ ion implantation on the corrosion behaviour of Ti—6Al—7Nb and Ti—5Al—2Nb—1Ta orthopaedic alloys in Hanks solution

Ti—6Al—7Nb and Ti—5Al—2Nb—1Ta alloys were implanted with N⁺ ions with an ion energy of 75 keV at a dose rate of 1 × 10¹⁷ and 1 × 10¹⁸ ions cm^–2. Open circuit potential (OCP) and potentiodynamic cyclic polarization measurements were carried out on the titanium alloys in Hanks solution to assess their corrosion resistance. The tendency for repassivation is higher in the case of implanted alloys than in untreated alloys owing to the formation of stable passive films. The impedance data showed a decrease in the double layer capacitance and an increase in the charge transfer resistance of the treated alloys. Nitrogen ion implanted Ti—6Al—7Nb was found to be more corrosion resistant than implanted Ti—5Al—2Nb—1Ta alloy.     

SIMULTANEOUS REACTIONS OF CO, NO, O2 AND NH3 ON Pt/γA12O3 CATALYST IN A TUBULAR REACTOR

A reliable method to continuously monitor NH₃ in a gas stream containing CO—NO—O₂ and H₂O has been developed. The method is based on a quantitative oxidation of NH₃ to NO on a Pt catalyst. The extent of this reaction is affected by temperature, excess oxygen present, and space-velocity. There is a significant effect of inlet O₂ concentration on extent of various reactions in the CO—NO—O₂—H₂O system on a Pt/γAl₂O₃ catalyst. At fixed space-velocity and catalyst temperature, and for fixed reactor inlet concentrations of CO and NO. there is negligible CO—NO reaction either in the absence of oxygen or in the presence of excess oxygen. However, short of the stoichiometric amount of O₂ required for CO oxidation, there is appreciable CO—NO (and possibly also CO—NO—H₂O) reaction whose extent increases with increasing oxygen concentration. This increase is especially dramatic in a narrow window of O₂: concentrations near the stoichiometric point. Interestingly enough, near the stoichiometric point, self-sustained isothermal oscillations in the outlet CO and NO concentrations are also observed (Subramaniam and Varma. submitted for publication)     

Characterization of some aluminium alloys for application as anodes in alkaline batteries

This work deals with the evaluation and characterization of aluminium (99.61%) and some of its alloys namely, Al—Ga—In, Al—Zn, Al—In, Al—Mn and Al—Mg, as anodes in alkaline battery electrolyte. The self-corrosion rate, hydrogen evolution rate and electrochemical properties, such as open circuit potentials, polarization characteristics and anode efficiencies were examined in 4 M KOH solutions. Among the tested alloys, Al—Ga—In alloy is found to be the most promising since it exhibits high open circuit potential, minimum anodic polarization, good anode efficiency and minimum corrosion rate. On the other hand, Al—In and Al—Mn alloys show higher corrosion rate compared with the other alloys. It can be shown that, a stoichiometric correlation exists between the corrosion rate obtained by weight loss and the hydrogen evolution rate.     

Pair correlation functions and the structure of the electric double layer

The inhomogeneous Ornstein—Zernike equation for the pair correlation functions of an inhomogeneous electrolyte is solved numerically using the Lovett—Mou—Buff—Wertheim equation to relate pair and singlet functions and using the mean spherical approximation to close the Ornstein—Zernike equation. Despite the fact that the pair correlation functions can be unphysical, the resulting singlet density and charge profiles are as good as those obtained from the more complex hypernetted chain approximation and are in excellent agreement with computer simulations. In particular, the layering in the counter-ion profile and the rapid increase in the potential found at large electrode charge found in the simulations, is observed.     

Charge-transfer complexes of chloranil in solution: A conductometric study

The formation of charge-transfer complexes has been studied by conductometric measurements, in the systems aniline—chloranil and pyridine—chloranil in methyl alcohol. The stoichiometry of charge-transfer complexes formed in solution has been determined from the position of the conductivity maximum obtained during the titration of donor solution with acceptor solution. The stoichiometry of the aniline—chloranil complex is 1:1 and that of the pyridine—chloranil complex is 2:3.     

Specific Features of the Formation of Crystalline Phases of the W—C—N System in a Cumulative Process

Results of x–ray diffractometric studies of coatings and powders of the W—C, W—N, and W—C—N systems that were obtained under conditions of a shaped–charge explosion are reported. The dependence of the phase composition on the experimental conditions is investigated. Diffusion of nitrogen to the initial polycrystalline tungsten is shown.     

Polarization-interference micromethod for the study of mutual diffusion in polymer systems

Summary A polarization-interference technique is developed for the study of mutual diffusion that is applicable to systems covering the whole concentration range from polymer — low-molecular-weight compound systems to polymer — oligomer systems. The technique is based on variations of the refraction index within the diffusion zone and is shown to have advantages over similar ones. Its accuracy in terms of wavelength is 0.04. The polybutadiene — dioctyl phtalate system is used to illustrate how the concentration distribution of the components is calculated.     

Modelling of thermal cracking effects in a two-phase concrete-like solid — a parametric investigation

Incompatibility of the physical properties of concrete constituents — the aggregate and the cement paste — gives rise to microcracking when the material is cooled to very low temperatures. The phenomenon is complex and affected by a large number of factors. An analytical model of the cracking process could be instrumental in identifying parameters for experimental investigation. A preliminary study is presented, which models concrete as a two-phase medium consisting of the coarse aggregate as inclusions in the mortar matrix. A simplified finite element procedure is employed to evaluate the effects of four parameters on crack initiating temperature and on crack volume. The parameters include two physical properties — thermal expansion coefficient and elastic modulus — and two mix factors — inclusion/matrix volume fraction and inclusion particle size. Thermal coefficient and inclusion volume fraction emerge as the major parameters affecting the fracture process, but the relationship of the two mix factors is complex.     

Soft modes and proton tunneling in PbHPO4, squaric acid and KH2PO4, type ferroelectrics

It is pointed out that the huge observed differences in the soft mode frequencies of KH₂PO₄, PbHPO₄, CsH₂PO₄ and squaric acid do not necessarily reflect a large difference in the proton 0—H———O tunneling frequencies but rather result from a difference in the short range correlations renormalizing the single proton O——H—O tunneling frequency.     

Fragments of Heterocyclic Copolyamide Phase Diagrams

Fragments of a ternary phase diagram of the system heterocyclic copolyamide—DMAA/LiCl—precipitant (H₂O and isobutanol) are obtained. The temperature—concentration boundary of the phase transition for sulfuric-acid solutions of the heterocyclic copolyamide in the region of the existence of isotropic and anisotropic phases is determined. A hypothesis is advanced concerning the relatively high thermodynamic rigidity of the copolyamide molecules, close to the rigidity of PABI but less than the rigidity of PPTA.     

Catalytic Dimerization of Alkyl Acrylates

The review deals with the chemistry of dimerization of acrylic esters in the presence of various catalysts. The article covers literature from 1963 through early 1995. The dimerization reactions are divided into three categories depending on the type of catalyst used, namely, phosphine-catalyzed, metal-catalyzed, and miscellaneous catalysts. Phosphine catalyzed dimerization leads to branched or head—tail dimers. Metal catalyzed dimerization deals with the reactions that take place in the coordination sphere of the transition metals (Ni, Pd, Ru, and Rh) complexes and are aimed at linear or tail—tail dimers. The tail—tail dimers, dialkyl hexenedioates, have a commercial potential as precursors of adipic acid, which is a raw material in the manufacture of nylon-6,6. Various strategies involved in designing the transition metal catalysts for tail—tail dimerization are highlighted. A miscellaneous catalyst section deals with systems that are not covered under the above two categories. It describes catalyst systems comprised of organic and/or inorganic compounds leading to head—tail or tail—tail dimers. The hydrodimerization reactions, which directly give dialkyl adipate from acrylic ester, are discussed separately. The mechanisms of the important dimerization reactions are outlined at appropriate places.     

Organization of contemporary systems for transport-warehouse servicing in the manufacture of man-made fibres

Conclusions -- It is necessary to begin the development of contemporary transport—warehouse systems promptly. Delay in development threatens in the future large losses and potential possibilities for new technological equipment.-- Work should be carried out in two directions: development of a complex of automated equipment for transport—warehouse systems; and performing investigative work on developing a complex of program—technical media and a mathematical—statistical model of transport—servicing systems.Translated from Khimicheskie Volokna, No. 5, pp. 50–51, September–October, 1990.     

Service of chrome — Forsterite products in the vertical channels and roofs of slaggers and regenerators of open-hearth furnaces

Conclusions Following industrial testing of thermal-shock resistant chrome -forsterite refractories in 400 ton open-hearth furnaces we established that it is possible to use them completely for replacing magnesite — chromite products in the roofs of slaggers and regenerators, and chrome — magnesite products in the structure of vertical channels.The use of chrome-forsterite products in the structure of the roofs and the walls of the lower structure of open-hearth furnaces would reduce the consumption of magnesite — chromite and chrome — magnesite products and have a substantial saving effect.Translated from Ogneupory, No. 2, pp. 22–31, February, 1970.     

Quantitative studies on the coal—oil agglomeration process

This paper summarises the work carried out at the Indian School of Mines on the quantification of the coal—oil agglomeration process for the purpose of modelling. The growth of agglomerates in the coal—oil agglomeration process follows a self-preserving behaviour. Using this, a characteristic curve, which is independent of the levels of the process variables, has been developed. It has also been found that the growth of agglomerates follows a second-order kinetics. The kinetic equation can be used for predicting the size (d₅₀) which passes 50% of the agglomertes. The prediction of the size distribution of the agglomerates needs the estimation of d₅₀ and the shape of the characteristic curve. The characteristic curve has been quantified using the equation Y = 1 — exp (—0.693x^m) and the d₅₀ values of the agglomerates have been evaluated through the kinetic equation and also through direct correlation of d₅₀ with the process variables. The percentage yield of agglomerates has been found to follow a relationship of the form Y = k₃{1 — exp[;—k₄(d₅₀ — x₀)^m]} with d₅₀.

The significance of these equations in modelling the process is outlined.     

A COMPARATIVE ANALYSIS OF THE DERIVATION OF INFINITE DILUTION ACTIVITY COEFFICIENTS FROM ΔT— x AND ΔP — x DATA

The experimental determination of infinite dilution activity coefficients (γ^∞) of liquid mixtures is carried out by gas chromatographic and ebulliometric techniques. Both methods show inaccuracies due to experimental difficulties.

This paper provides a comparative analysis of the influence of errors in measurements on the evaluation of γ^∞ using ΔT — x and ΔP — x experimental data. It is shown that the errors in the determination of γ^∞ from ΔP — x data are generally lower than those from ΔT — x ones     

Refractory concrete lining in open-hearth y-shaped pouring spouts

Conclusions The life of concrete linings in y-shaped pouring spouts is threefold that of chamotte linings. The main wear of the concrete lining is accounted for by the mechanical removal of the 8 to 10 mm thick slag — concrete contact layer during cleaning operations.The applicating of coatings of different composition substantially affects the structure of the concrete — slag contact layer.There was no difference in quality between metal poured through chamotte lined spouts and concrete — lined spouts.The use of concrete lining for y-shaped pouring spouts is warranted for technical and economic reasons. Further increase in the service life of this type of lining requires more testing and extensive adaption to industrial furnaces.     

AIRLIFT REACTORS: CHARACTERISTICS, APPLICATIONS AND DESIGN CONSIDERATIONS

Bioreactors of the airlift type are a promising design for aerobic fermentations. The basic knowledge required for understanding and predicting the performance of these reactors is only now beginning to emerge. In this review we present our observations and those of other investigators in an attempt to build up a coherent picture of airlift devices. All the major aspects—mixing and hydrodynamics, mass and heat transfer—in these reactors are considered. Comparisons between bubble columns and airlift systems are made where analogies, similarities and/or differences between them provide insight into airlift systems. Throughout, the areas of particular concern and those in need of further research in this field are mentioned. Extensive work on all forms of airlift reactors, particularly in non-Newtonian media—homogeneous and suspensions—remains to be done. Current knowledge does not permit airlift reactor design with a high degree of confidence. However, the technical feasibility of all types of fermentations—plant cell, tissue culture, bacterial, fungal, and those utilizing yeasts—in airlift vessels has been demonstrated.     

Bile acids bound to polymers

Summary Bile acids are steroids containing one — lithocholic acid, two — desoxycholic acid, and three — cholic acid hydroxyl groups, respectively. The hydroxyl group in position 3 of the steroid skeleton after esterification of the carboxyl group at C-24 under suitable conditions selectively reacts with methacryloyl chloride to give the corresponding methacrylic ester derivatives which undergo radically initiated uni- and copolymerizations to yield high molecular weight polymers.This paper is dedicated to Professor Georg Manecke on the occasion of his 70th birthday     

COMPLEX DYNAMIC BEHAVIOR IN THE CASE OF CO—NO—O2—H2O REACTION SYSTEM ON Pt/γAl2O3 CATALYST

Self-sustained, isothermal oscillations in outlet species concentrations were observed under certain steady inlet conditions in the case of the CO—NO—O₂—H₂O reaction system on Pt/γAl₂O₃ catalyst in a fixed-bed tubuiar reactor. The oscillations were mostly aperiodic, and for fixed inlet concentrations of the other species, they occurred in a rather narrow window of inlet oxygen concentrations near the stoichiometric point. The amplitude and frequency of these oscillations were affected by temperature and by the inlet concenlrations of CO and NO. Systemalic experiments, conducted to understand the cause of these oscillations, revealed that the catalyst aging procedure and the presence of water vapor induced the complex dynamic behavior observed in the CO—NO—O₂—H₂O system. The oscillations are explained qualitatively in terms of the competition among the various reactants for adsorption and subsequent reaction on the catalyst surface.