Vol.5 No.1 2012

Research paper : An analysis method for oxygen impurity in magnesium and its alloys (A. Tsuge et al.)−32−Synthesiology - English edition Vol.5 No.1 (2012) the device manufacturer (analysis lab B) based on their own disclosed conditions and those of AIST (analysis lab D) were not far apart from the CPAA results. There was a case where the measurement could not be done because the samples were boiled over the crucible (analysis lab C), and the case where low value was obtained because the Mg vapor was produced during the oxygen analysis of the residue due to incomplete evaporation of Mg leading to the return of the carbon monoxide to form the oxide again (analysis lab A). From these results, it was assumed that the relationship between the applied power and the graphite crucible temperature depends on the device and/or its manufacturing year. In other words, the crucible temperature rather than the applied power should be specified as the heating condition for standardization, and the method for obtaining the calibration curve for temperature versus applied power for each device must be described in the standard.To obtain the calibration curve, the melting of the metal particles of known melting points in the graphite crucible is monitored under gradual increase in the applied power, as shown in Fig. 12. This method is widely used to measure temperatures in the graphite ohmic-heating furnace of which direct measuring of temperature inside is difficult. Figure 13(a) shows the relationship calculated from the data of five types of metals. In general, the calibration curve exhibits curvature as shown in the figure. In the temperature range 900 °C - 2,000 °C where the Mg is evaporated off, the curvature is sufficiently small and a linear regression is applicable to the data points of the power at which the copper and chromium particles melted, as shown in figure 13(b).4 Activities for the proposal of international standard When proposing an international standard of analysis method, it is important to indicate the intention to propose the standard and to let it be known domestically and internationally that the proposal satisfies technological demands which are internationally-recognized, in parallel with the R&D to establish a method for increasing the technological reliability. Our efforts will be described below.4.1 Representing preferences of industry in Japan by the Japan Magnesium AssociationAfter establishing the elemental technologies for this analysis method, we proposed the R&D project for making the proposal of an ISO standard. To know the preferences in industry, we maintained a close relationship, from the preparatory stage of the project, with the Japan Magnesium Association (JMA), which is the industry association and Table 4. Activities for international standardizationFig. 12 Conceptual diagram of the temperature calibration of the graphite crucibleFig. 13 Relationship of applied power and graphite crucible temperature (a) Calibration curve by five kinds of metal of different melting points. (b) Calibration method in the range 900 °C ~ 2,000 °C.LowMirrorObservation of meltingHighApplied powerThe applied power when the copper or chromium particle melted is monitored654321001000200030004000Graphite crucible temperature (℃)Applied power (kW)WMoCrNiCu(a)21005001000150020002500Graphite crucible temperature (℃)Applied power (kW)W2W1CrCu2.51.50.52000 ℃900 ℃(b)NWIP votingWD deliberation OctoberJulySubmit NWIPJune★Technical cooperation to KoreaMay★Explain outline ofstandard proposalat London meetingMay★Report progressat Berlin meetingMay★Explain basic conceptat ISO/TC79/SC5Tokyo meetingMETI “Kijun Ninsho Kenkyu Kaihatsu Seido”“Standardization of Oxygen Analysis Method in Magnesium Metal and Alloy”MarchApril20122011201020092008


page 35