Instrumental Chemical Analysis of Magnesium and Magnesium Alloys

Magnesium is the lightest of all the commonly used metals. It is one of the most abundant elements in the earth's surface, amounting to a mass fraction of c.a. 2.5 %. It has been prepared for industry as metal and alloy ingots; the latter are most often made with aluminum. Various magnesium-based alloys have been developed and mainly applied to transport facilities and mobile electric devices because they have the best strength-to-weight ratio of any of the commonly used structural alloys. Practically, they are used for housing of laptop computers, mobile phones, and digital cameras, moreover, materials for acoustic diaphragm, units of vehicles, nursing-care equipments, anode for sacrificial protection, etc. Some special alloys with rare earth metals, which show high strength properties at elevated temperatures (Rokhlin, 2003), have been recently applied to aircraft and space machinery, automobile and railcar products. Accordingly, the chemical composition of magnesium and its alloys have already been standardized from major to trace quantities. International Organization for Standardization (ISO 8287, 2000; ISO 16220, 2005), American Society for Testing and Materials (ASTM B92/B92M-07, 2007; ASTM B93/B93M-07, 2007), and Japan Industrial Standard (JIS H2150, 2006; JIS H2221, 2006; JIS H2222, 2006) provide the standards of metal ingots, wrought alloys, and casting alloys separately, where vast kinds of designation, chemical constituents with permissible ranges, and chemical impurity with maximal allowable limits are denoted therein. Moreover, the wrought alloys with extruded or forged shapes to make sheets, bars, pipes, tubes, wires, etc have been specialized in ISO (ISO 3116, 2007), ASTM (ASTM B107/B107-07, 2007), and JIS as several particular standards. Table 1 shows the chemical composition of unalloyed magnesium with different purities denoted in ISO 8287. However, standardization of analytical methods to determine metal elements therein is quite insufficient. In 2006, ISO confirmed five old standards for minor analyses with gravimetry and titrimetry, and eleven ones for trace analyses with photometry and atomic absorption spectrometry, all of which were established in the 1970s and 1981. On the contrary, in 2008 ASTM withdrew the standard test methods for chemical analysis in view of a lack of information on reliability therein (ASTM E35-88, 2002), where a chill cast specimen can only be affordable to be analyzed with the ASTM test method using spark source atomic emission spectrometry (ASTM B95435-07, 2007). JIS denotes most plentiful standard methods that feature classical wet techniques and instrumental analyses corresponding with concentrations in the materials and accuracy needed, but they are standardized mostly in 1990’s with flame atomic absorption spectrometry for trace analyses. Consequently in all cases, there existed no methods for the determination of trace amounts