Vol.5 No.1 2012

Research paper : An analysis method for oxygen impurity in magnesium and its alloys (A. Tsuge et al.)−26−Synthesiology - English edition Vol.5 No.1 (2012) several large companies that manufacture basic materials such as sheets by twin-roll and rods by extrusion.On the other hand, as shown in Fig. 1, about 85 % of the world share for Mg metal is dominated by the Chinese heat refined metal. Although China is currently positioned as the “raw-material-exporting country,” it is expected to put more effort in the manufacture of alloys and components[2] in the future. Currently, the major East Asian countries are entering the global market in various ways, and one of the characteristics of the Mg material industry is that although these three countries are rivals, there is potential for getting together to build a cooperative and collaborative relationship.From the perspective of environment protection, there is no question that the use of Mg material should be expanded. The prevalence of the oxygen analysis method is expected to facilitate the verification of quality and reliability of the materials and components and eventually leading to the improvement thereof. At the same time, it is possible to appeal the excellence of the products of Japan, which has an advantage in Mg components manufacturing technology. Therefore we began to develop an easy yet highly reliable oxygen analysis method that can be used for process management at manufacturing plants. In this study, disseminating research results to industry was built into its objectives from the beginning. At the start of the R&D project, we set the final goal to proposing a developed method as an international standard. It was expected that the international standard would serve as a yardstick for product properties in the global market. In this paper, we will present the development of the element technologies of the oxygen analysis method, the process in which the reliability of the method was verified, and the background to international cooperation for the proposal of the standard. 2 Element technologies and remaining issues for international standardization2.1 Development of the basic technologyIn standardizing the analysis method of industrial materials, versatility is a factor to be considered in addition to a stand point only from analysis technology. For example, radio activation analysis that is known as the analysis method for oxygen is excellent in terms of the accuracy of results, but the use of nuclear reactors and accelerators for activation is strictly regulated, and hence this method cannot be used for routine on-site analysis. Also, the wet chemical analysis, which was mainstream in the past, tends to be avoided because the analysis personnel must be highly skilled, and such method is adopted in a standard only when no other instrumental analysis is available.Under these circumstances, inert gas fusion infrared absorptiometry (IGF-IRA) is generally employed as the industrial measurement method of oxygen content in metals.[6] The oxygen analysis by IGF-IRA is used widely in industries including iron and steel, and there are many commercially available automated devices. There are also many companies that can contract the oxygen analysis. From these points, this method is considered to be promising one for the standardization of oxygen analysis for Mg.Figure 2 shows the schematic of the measurement principle of IGF-IRA method. The sample is placed in a graphite crucible in an inert gas flow such as helium, and heated by applying a current in the crucible. The oxygen in the sample is reduced by reaction with the carbon in the crucible material, and the carbon monoxide formed by the reduction reaction is extracted eventually. The carbon monoxide concentration in the helium flow is measured and accumulated by the infrared absorption detector to determine the oxygen content in the sample. The analysis is done by the reduction reaction of the sample by carbon, and this is the same reaction used in refining iron from iron ore. This derives from the fact that IGF-IRA method was originated and developed in the iron and steel industry.It is expected to respond quickly to the demand for oxygen analysis in Mg, if the measurement of oxygen in Mg is enabled using an established method. However, in general, the IGF-IRA method has not been considered applicable to Fig. 1 Share of international market of magnesium metalFig. 2 Conceptual diagram of the inert gas fusion methodSource: “Mineral Commodity Summaries, January2011,” US Geological SurveyChinaIsraelOthersBrazilKazakhstanRussiaGraphite crucible+ N2(Thermal conductivity detector )2500 ℃<+ CO(Infrared detector )HeHe


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