Minor alloy component

Corrosion of component parts of the process plant can be readily monitored by measuring the concentrations of associated "corrosion metals (e.g. Fe, Ni, Cr, Mn, Mo) in downstream process streams or products. In view of its rapid, multi-element capability, ICPAES lends itself well to these applications, although ICP-MS with its inherently lower detection limits, can permit measurement of lower rates of corrosion and of minor alloy components which can aid in identifying which plant component is corroding. 

In addition to destroying the UO2 matrix, fuel liquefaction accelerates the release of fission products from the fuel. However, minor alloying components or impurities can have large effects on such releases. For instance, tin, which is a 1% component of zircaloy, may act as a getter for tellurium resulting in significant holdup or retention of this fission product. Both fuel liquefaction and retention of tellurium in the presence of tin illustrate that chemical reactions are crucial to the understanding of severe accidents. 

In determining the purity or percentage of lead in lead and lead-base alloys, the impurities or minor components are deterrnined and the lead content calculated by difference. Quality control in lead production requires that the concentration of impurities meet standard ASTM specifications B29 (see Table 7). Analyses of the individual impurities are performed using various wet chemical procedures and instmmental methods such as emission spectroscopy. 

The Components of Materials. The composition of most materials -whether of natural origin, such as minerals, rocks, wood, and skin, or made by humans, as for example, pottery, glass and alloys - includes several kinds of components major, minor, and trace elements (see Textbox 8). 

In the case of multi-component alloys and compounds, the surface composition may also change in addition to surface relaxation and reconstruction. For instance, the first layer of (100) plane on the surface of a nickel-aluminiim alloy enriches itself with aliuninum whose atomic size is larger than nickel. Such an enrichment of some constituents on the soUd surface is called surface segregation [Van Hove, 1993]. It is abo known that surface active minor impurities of oxygen, phosphorus and sulfur in metallic iron segregate to the clean siirface of iron [Nii-Yoshihara,... 

Zirconium alloys are chiefly used as the cladding (structural) metal in nuclear reactors. The alloys are also used as grid spacers, guide tubes, pressure tubes, calandria tubes and other minor components. 

In modern technical alloys, which almost all consist of a large number of components, the presence or absence of traces of some elements plays an extraordinarily great role in determining the mechanical properties. We have previously seen how it is just in the metals that such a great influence of traces can become manifest. The individual, typically chemical properties of the admixed elements usually play only a minor role in this (compare on the other hand de-oxidation of steel by aluminium or sodium). 

Many chondrules contain minor amounts of metals, sulfides, and oxides. These phases also occur as distinct grains and assemblages embedded in the chondrite matrix. The metallic mineral kamacite is a common chondrule component that contains significant amounts of minor elements such as cobalt, chromium, and phosphorus. Taenite is another alloy of iron and nickel. Sulfide minerals such as troilite, pyrrhotite, and pentlandite are also abundant in many chondrules. 

Vahlas and coworkers recently tested a new delivery system based on sublimation in a fluidized bed, to improve mass and heat transport. A mixture of solid Al(acac)3 (minor component) and inert alumina or silica particles was fluidized with a combination of water vapor and oxygen at 150 °C, by which amorphons AI2O3 films were obtained on Ti6242 alloy wafers immersed in the bed. Pauleau and Dnlac compared the kinetics of vaporization of Al(acac)3, Al(tfac)3 and Al(hfac)3 by isothermal TGA. The satnration vapor pressure of Al(hfac)3 is 10-fold and 100-fold higher than those of Al(tfac)3 and Al(acac)3, respectively. 

The commonest cause of impredicted corrosion problems is the failure to define, accurately, the chemistry of process streams, including startup, shutdown, and transient conditions, or to anticipate changes in chemistry at specific locations in equipment. The corrosivity of a process stream is often determined by its minor components, e.g., the presence of lOs-lOOsppm chlorides can promote localized corrosion of stainless steels and other passive alloys. It is important that minor components are defined, quantified, and evaluated at the design stage, including their possible local concentration such as in distillation and separation equipment. 

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