The electrochemical corrosion of pure magnesium in 1 N NaCl

An electrochemical investigation was carried out to study the corrosion of pure magnesium in 1 N NaCl at different pH values involving electrochemical polarisation, scanning tunnel microscopy (STM), measurement of hydrogen gas evolution and measurement of the elements dissolved from the magnesium specimen which were determined by inductively coupled plasma atomic emission spectrophotometry (ICPAES). A partially protective surface film was a principal factor controlling corrosion. Film coverage decreased with increasing applied electrode potential. Application of a suitable external cathodic current density was shown to inhibit magnesium dissolution whilst at the same time the hydrogen evolution rate was relatively small. This showed that cathodic protection could be used to significantly reduce magnesium corrosion. A new definition is proposed for the negative difference effect (NDE). (C) 1997 Elsevier Science Ltd.

Alloying of pure magnesium with Mg-33.3 wt-%Zr master alloy

To capitalise on the strengthening potential of zirconium as a potent grain refiner for magnesium alloys, the mechanisms of adding zirconium to magnesium and its subsequent grain refining action need to be understood. Using a Mg-33.3Zr master alloy (Zirmax supplied by Magnesium Elektron Ltd) as a zirconium alloying additive, the influence of different alloying conditions on the dissolution of zirconium in magnesium was investigated. It was found that owing to the highly alloyable microstructure of Zirmax, the dissolution of zirconium was generally complete within a few minutes in the temperature range 730 to 780degreesC. Prolonging and/or intensifying stirring were found to have no conspicuous influence on further enhancing the dissolution of zirconium. In all cases studied, the average grain size increased with increasing holding time at temperature while the total zirconium content decreased. The finest grain structure and highest total zirconium content corresponded to sampling immediately after stirring. Pick up of iron by molten magnesium from the mild steel crucibles used for melting and holding, was significantly delayed or avoided in the temperature range 730 to 780degreesC by coating the crucibles with boron nitride. It is therefore feasible to conduct zirconium alloying at 730degreesC without the need of a considerable excess of Zirmax addition using a properly coated or lined steel crucible.

Corrosion behaviour of pure magnesium in a simulated body fluid

The corrosion behaviour of pure magnesium in Hank's simulated body fluid (SBF) was investigated. It was found that the polarization of Mg in the SBF solution was similar to that in a NaCl aqueous solution. However, AC impedance analysis suggested that the detailed dissolution steps involved in the corrosion of Mg in the SBF could be different in terms of their rates or contributions to corrosion damage of Mg. Moreover, the corrosion rate of Mg in the SBF solution was found to be increasing with time and significant hydrogen evolution and alkalization of the SBF solution resulting from corrosion of Mg were measured in the study. The results suggested that after some proper measures are taken to retard corrosion reaction, Mg can be successfully employed as a degradable and absorbable implant material.

Production and Evaluation of Calcium Magnesium Acetate, HR-243, 1982

Calcium magnesium acetate (CMA) has been identified by Bjorksten Research Laboratories as an environmentally harmless alternative to sodium or calcium chloride for deicing highways. Their study found CMA to be noncorrosive to steel, aluminum and zinc with little or no anticipated environmental impact. When used, it degrades into elements found in abundance in nature. The deicing capabilities were found to be similar to sodium chloride. The neutralized CMA they produced did cause scaling of PC concrete, but they did not expect mildly alkaline CMA to have this effect. In the initial investigation of CMA at the Iowa DOT laboratory, it was found that CMA produced from hydrated lime and acetic acid was a light, fluffy material. It was recognized that a deicer in this form would be difficult to effectively distribute on highways without considerable wind loss. A process was developed to produce CMA in the presence of sand to increase particle weight. In this report the product of this process, which consists of sand particles coated with CMA, is referred to as "CMA deicer". The mixture of salts, calcium magnesium acetate, is referred to as "CMA". The major problems with CMA for deicing are: (1) it is not commercially available, (2) it is expensive with present production methods and (3) there is very little known about how it performs on highways under actual deicing conditions. In view of the potential benefits this material offers, it is highly desirable to find solutions or answers to these problems. This study provides information to advance that effort. The study consisted of four principal tasks which were: 1. Production of CMA Deicer The objective was to further develop the laboratory process for producing CMA deicer on a pilot plant basis and to produce a sufficient quantity for field trials. The original proposal called for producing 20 tons of CMA deicer. 2. Field Evaluation of CMA Deicer The objective was to evaluate the effectiveness of CMA deicer when used under field conditions and obtain information on application procedures. Performance was compared with a regular 50/50 mixture of sand and sodium chloride. 3. Investigation of Effects of CMA on PC Concrete The objective was to determine any scaling effect that mildly alkaline CMA might have on PC concrete. Comparison was made with calcium chloride. 4. Determine Feasibility of Producing High Magnesium CMA The objective was to investigate the possibility of producing a CMA deicer with magnesium acetate content well above that produced from dolomitic lime. A high magnesium acetate content is desirable because pure magnesium acetate has a water eutectic of -22 F° as compared with +5 F° for calcium acetate and is therefore a more effective deicer.

Dopant-vacancy binding effects in Li-doped magnesium hydride

We use a combination of ab initio calculations and statistical mechanics to investigate the substitution of Li+ for Mg2+ in magnesium hydride (MgH2) accompanied by the formation of hydrogen vacancies with positive charge (with respect to the original ion at the site). We show that the binding energy between dopants and vacancy defects leads to a significant fraction of trapped vacancies and therefore a dramatic reduction in the number of free vacancies available for diffusion. The concentration of free vacancies initially increases with dopant concentration but reaches a maximum at around 1 mol % Li doping and slowly decreases with further doping. At the optimal level of doping, the corresponding concentration of free vacancies is much higher than the equilibrium concentrations of charged and neutral vacancies in pure MgH2 at typical hydrogen storage conditions. We also show that Li-doped MgH2 is thermodynamically metastable with respect to phase separation into pure magnesium and lithium hydrides at any significant Li concentration, even after considering the stabilization provided by dopant-vacancy interactions and configurational entropic effects. Our results suggest that lithium doping may enhance hydrogen diffusion hydride but only to a limited extent determined by an optimal dopant concentration and conditioned to the stability of the doped phase.

Understanding magnesium corrosion - A framework for improved alloy performance

The purpose of this paper is to provide a succinct but nevertheless complete mechanistic overview of the various types of magnesium corrosion. The understanding of the corrosion processes of magnesium alloys builds upon our understanding of the corrosion of pure magnesium. This provides an understanding of the types of corrosion exhibited by,magnesium alloys, and also of the environmental factors Of most importance. This deep understanding is required as a foundation if we are to produce magnesium alloys much more resistant to corrosion than the present alloys. Much has already been achieved, but there is vast scope for improvement. This present analysis can provide a foundation and a theoretical framework for further, much needed research. There is still vast scope both for better fundamental understanding of corrosion processes, engineering usage of magnesium, and also on the corrosion protection of magnesium alloys in service.

Corrosion behaviour of magnesium in ethylene glycol

Corrosion of magnesium engine components by coolant is an important issue in the automotive industry where magnesium alloys may be used. It is of significance to understand the corrosion behaviour of pure magnesium in ethylene glycol solutions, as this can provide a basis for developing new coolants for magnesium alloy engine blocks. In this paper, through corrosion and electrochemical tests, it was found that the corrosion rate of magnesium decreased with increasing concentration of ethylene glycol. Individual contaminants, such as NaCl, NaHCO3, Na2SO4 and NaCl can make aqueous ethylene glycol solution more corrosive to magnesium. However, in NaCl contaminated ethylene glycol, NaHCO3 and Na2SO4 showed some inhibition effect. The solution resistivity played an important role in the corrosion of magnesium in ethylene glycol solutions, and the competitive adsorption of ethylene glycol and the contaminants on the magnesium surface was also responsible for the observed corrosion behaviours. The corrosion of magnesium in ethylene glycol can be effectively inhibited by addition of fluorides that react with magnesium and form a protective film on the surface. (C) 2003 Elsevier Ltd. All rights reserved.

A critical review of the stress corrosion cracking (SCC) of magnesium alloys

This review aims to provide a foundation for the safe and effective use of magnesium (Mg) alloys, including practical guidelines for the service use of Mg alloys in the atmosphere and/or in contact with aqueous solutions. This is to provide support for the rapidly increasing use of Mg in industrial applications, particularly in the automobile industry. These guidelines should be firmly based on a critical analysis of our knowledge of SCC based on (1) service experience, (2) laboratory testing and (3) understanding of the mechanism of SCC, as well as based on an understanding of the Mg corrosion mechanism.

Effect of Mg-Ga powder addition on the superconducting properties of MgB2 samples

MgB2 bulk samples containing different proportions of Mg-Ga powder were prepared by an in situ reaction technique. The Mg-Ga powder was obtained via high energy ball milling of a Mg-10 at.% Ga composite, which was fabricated by melting of pure magnesium and gallium metals inside encapsulated stainless steel tube at 655 °C in a controlled atmosphere. The MgB2 samples containing 0, 1, 3, 5 and 7 wt.% of MgGa addition were sintered at 650 °C for 30 min in argon atmosphere. Magnetic measurements performed at 5 K and 20 K showed improved critical current density, Jc, in the low magnetic field range for samples with MgGa addition. The critical temperature, Tc, for all samples with gallium additions is consistently higher when compared to the pure MgB2. © 2007 Elsevier B.V. All rights reserved.

Estudo de propriedades anelásticas de MgB2

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