Metallic element concentrations, determination

The elemental concentrations determined in the metallic phase are given in Table III. The crudeness of the ceramic correction method just described adds additional uncertainty to some of these values (especially aluminum, manganese, and vanadium). Most values, however, are quite meaningful. 

Analytical Techniques. The primary method used to determine the metallic element concentration in the tailings was IX Plasma Atomic Emission Spectrometry (IXP). It was used for the determination of both major and minor components. In the former case, the analysis is straightforward, but in the case of minor constituents, it was necessary to use matrix matching, i.e., to use standard solutions having the same concentration of the major component as the unknown, to compensate for the background emission interference of the other solutes. This requires the initial determination of the major components to define the appropriate doping levels. The... 

A guide to tire stabilities of inter-metallic compounds can be obtained from the semi-empirical model of Miedema et al. (loc. cit.), in which the heat of interaction between two elements is determined by a contribution arising from the difference in work functions, A0, of tire elements, which leads to an exothermic contribution, and tire difference in the electron concentration at tire periphery of the atoms, A w, which leads to an endothermic contribution. The latter term is referred to in metal physics as the concentration of electrons at the periphery of the Wigner-Seitz cell which contains the nucleus and elecUonic structure of each metal atom within the atomic volume in the metallic state. This term is also closely related to tire bulk modulus of each element. The work function difference is very similar to the electronegativity difference. The equation which is used in tire Miedema treatment to... 

TOF-SIMS can be applied to identify a variety of molecular fragments, originating from various molecular surface contaminations. It also can be used to determine metal trace concentrations at the surface. The use of an additional high current sputter ion source allows the fast erosion of the sample. By continuously probing the surface composition at the actual crater bottom by the analytical primary ion beam, multi element depth profiles in well defined surface areas can be determined. TOF-SIMS has become an indispensable analytical technique in modem microelectronics, in particular for elemental and molecular surface mapping and for multielement shallow depth profiling. 

Ion exchange (IX) is a very useful technique for the concentration, the purification and the separation of chemically similar metallic elements present in an aqueous solution. In its most popular form of application, the metal-bearing aqueous solution is passed through a bed of solid organic resin in a particulate form wherein the sorption of the metal ions on the resin takes place by ion-exchange reactions. The pregnant resin is washed free of the entrapped feed solution and then brought into contact with an eluant of suitable composition and volume so that the resin releases the metal ions back to the eluant. The ratio of the volume of the feed and that of the eluant determines the extent of concentration that can be achieved. Purification and separation are achievable if the resin is selective or specific with respect to the metal ions of interest in comparison to impurity ions. 

The presence and concentration of various metallic elements in petroleum coke are major factors in the suitability of the coke for various uses. In the test method (ASTM D5056), a sample of petroleum coke is ashed (thermally decomposed to leave only the ash of the inorganic constituents) at 525°C (977°F). The ash is fused with lithium tetraborate or lithium metaborate. The melt is then dissolved in dilute hydrochloric acid and the resulting solution is analyzed by atomic absorption spectroscopy to determine the metals in the sample. However, spectral interferences may occur when using wavelengths other than those recommended for analysis or when using multielement hollow cathode lamps. 

Critical surface tension (Yc) of the oiled CDC Ni-plated sheets apparently is determined by the polar group concentration of oil and metallic elements (Cr and Ni). Yc increases with increasing the polar group concentration of oil and, therefore, the improvement of adhesion due to the higher polarity of oil was also supported by thermodynamical aspect (wettability). 

An interesting approach is the application of multiple ion collector mass spectrometry (MC-TIMS and MC-ICP-MS) for the determination of Cd and T1 in high purity zinc metal after trace matrix separation by the certification of reference materials from the Bureau Communie de Reference (BCR).29 Accurate and precise element concentrations in high purity zinc metal have been obtained with both mass spectrometric techniques via precise isotope ratio measurements using the isotope dilution strategy the analytical data. 

Fig. 7. Surface concentration of each metal element in the MoaBio-iCogFejO, catalyst determined by XPS analysis (41).

Electro-active labile metal contents have also been measured by using a combination of electro-deposition and analysis by graphite furnace AAS (Batley and Matousek, 1977). Metals (e.g. Pb, Co, Ni, Cr from seawater) are plated on to a short graphite tube by application of a suitable potential. At the end of the electrolysis period, the graphite cell (plus pre-concentrated metal) is placed in an electro-thermal atomiser attached to an AAS spectrometer, and the element content determined. 

In spite of its limited sensitivity, colorimetry is still useful in determination of elemental concentrations in the g range or higher (Seiler, 1988). Its main advantage is that the needed instrument, a spectrophotometer, is common in every laboratory. Colorimetric trace metal determinations are based, commonly after sample decomposition, on selective separations from interfering ions (Abbasi et al., 1988). Automated colorimetric procedures are described for the determination of N and P in trees (Stewart et al., 1990). Modern spectrophotometers provide high stability, low noise, and the advantages of computerised background control. However, for total metal determinations in environmental samples, this method is less frequently applied and has been replaced by atomic spectroscopic and electrochemical methods (Stoeppler, 1991). 

The FAAS method offers similar detection limits to NAA and is suitable for the determination of low levels of lead. Equipment costs are reasonable and the instrumentation is commonplace in many analytical laboratories. A large number of metallic elements, over a wide concentration range, extending down to ultra-trace level, can be analyzed, thus making the technique versatile and useful for other forensic applications as well as FDR detection. Apart from cost, the main advantages are simplicity, speed of analysis, and in house operation. One disadvantage of FAAS is that it is not capable of simultaneous multielement analysis. 

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