Refractory components

THE ISOTOPIC HETEROGENEITY IN THE REFRACTORY COMPONENTS OF THE EARLY SOLAR-SYSTEM... 

Roozeboom type I is obtained whenever the Gibbs free energy curve of the melt initially touches that of the mixture in the condition of pure component. This takes place at the melting temperature of the more refractory component (T2 in... 

The amoeboid descriptor for amoeboid olivine aggregates refers to their irregular shapes. AOAs tend to be fine-grained and porous, and have comparable sizes to CAIs in the same meteorite. They consist mostly of forsterite and lesser amounts of iron-nickel metal, with a refractory component composed of anorthite, spinel, aluminum-rich diopside, and rarely melilite. The refractory component is sometimes recognizable as a CAI embedded within the AOA. The AOAs show no evidence of having been melted, but some contain CAIs that have melted. 

To estimate the destruction rate of TOC, it is assumed that the decomposition rate of humic substances is proportional to Clx which is the TOC of refractory components produced (Kusakabe et al., 1990). Consequently, the decomposition rate of humic compounds measured in the recirculating system is expressed as the sum of the rate in the bubble column and in the UV reactor (VR + VB) as follows ... 

Hertkorn, N., Benner, R., Frommberger, M., Schmitt-Kopplin, P., Witt, M., Kaiser, K., Kettrup. A., and Hedges, J. I. (2006). Characterization of a major refractory component of marine dissolved organic matter. Geochim. Cosmochim. Acta 70, 2990-3010. 

The question as to what is the active site of Cu-based catalysts in MSR is still unclear and debated in the literature. Similar to the methanol synthesis reaction, either metallic Cu° sites, oxidized Cu+ sites dispersed on the oxide component or at the Cu-oxide interface, or a combination of both kinds of sites are thought to contribute to the active ensembles at the Cu surface. Furthermore, the oxidic surface of the refractory component may take part in the catalytic reaction and provide adsorption sites for the oxygenate-bonded species [126], whereas hydrogen is probably adsorbed at the metallic Cu surface. Similar to methanol synthesis, factors intrinsic to the Cu phase also contribute to the MSR activity in addition to SACu- There are two major views discussed in the literature relating these intrinsic factors either to the variable oxidation state of Cu, in particular to the in situ adjustment of the Cu°/Cu+ ratio at the catalyst s surface [102, 107, 127 132], or to the defect structure and varying... 

Carbon/carbon composites are also used as refractory components in gas-cooled high-temperature nuclear reactors, e.g., in the heat exchanger between the primary and secondary helium cooling circuits (13). 

In many cases, the most appropriated use of AOP may be as a stage of a combined biological/chemical process. AOP can be used as pre-treatment step to enhance biodegradability of the waste or as a complementary treatment to remove residual bio-refractory component if the biological treatment is not adequate to ensure the water-quality standards. 

The latter reaction can form long chain phosphates, where n is theoretically infinite. Being formed by heat treatments, these phosphates are excellent candidates for high-temperature ceramics and glasses. Because the subject of this volume is low-temperature ceramics, we will not discuss the condensed phosphates in detail, except in one case in Chapter 15, where cements for geothermal wells are discussed with sodium metaphosphate. However, bear in mind that CBPCs can be precursors to high temperature phosphates and glasses. For this reason, as we have seen in the literamre survey presented in Chapter 3, early interest in CBPCs was the formation of refractory shapes at room temperature, which were then fired to produce the final refractory components. 

Despite these limitations, the detailed molecular information of EI-FTIR-MS promises an important increase in our knowledge of the most murky of DOM components. The few studies that have so far been done on ocean waters use some form of SPE with acidified samples to simultaneously achieve both ends (e.g., Koch et al., 2005 Kujawinski et al., 2004), while at the same time hkely removing much of the DON (Koch et al., 2005). For investigating the humic fraction of DON, this selectivity may actually be an advantage. SPE isolates the smaller MW components that make up majority of ocean DOM, and also likely account for the most refractory components (Amon and Benner, 1994). 

In Figure 3, aluminum is representative of refractory elements in general and the Al/Si ratios indicate the size of the refractory component relative to the major fraction of the meteorite. It is clear from this figure that the Al/Si ratio of Cl meteorites agrees best with the solar ratio, although the ratios in CM (Type 2 carbonaceous chondrites) and even OC (ordinary chondrites) are almost within the error bar of the solar ratio. The errors of the meteorite ratios are below 10%, in many cases below 5%. A very similar pattern as for aluminum would be obtained for other refractory elements (calcium, titanium, scandium, REEs, etc.), as ratios among refractory elements in meteorites are constant in all classes of chondritic meteorites, at least within —5-10%. The average Sun/CI meteorite ratio of 19 refractory lithophile elements (Al, Ca, Ti, V, Sr, Y, Zr, Nb, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Lu, see Table 2) is... 

CAI E38 from Efremovka with an accretionary rim (b)-(d) backscattered electron images from regions marked in elemental map. This CAI consists of melilite (mel), aluminum, titanium-diopside (fas), spinel (sp), and anorthite (an) and is surrounded by a multilayered Wark-Lovering rim composed of spinel, perovskite (pv), anorthite, aluminum-diopside, and forsterite, and a thick outer forsterite-rich accretionary rim (red in (a)). The accretionary rim consists of forsterite (ol) and refractory components composed of spinel, aluminum-diopside, and anorthite. 

Tests. These models have chondritic Th/U, subchondritic K/Th, and relatively low contents of refractory components compared to the more extreme cases described above. A typical magma produced from these compositions would have a low-FeO basaltic composition. The mineralogy of the basalt would be quartz normative for the Morgan and Anders bulk composition and consist of plagioclase and high-calcium pyroxene. 

The refractory component comprises the elements with the highest condensation temperatures. There are two groups of refractory elements the refractory lithophile elements (RLEs)—aluminum, calcium, titanium, beryllium, scandium, vanadium, strontium, yttrium, zirconium, niobium, barium, REE, hafnium, tantalum, thorium, uranium, plutonium—and the refractory siderophile elements (RSEs)—molybdenum, ruthenium, rhodium, tungsten, rhenium, iridium, platinum, osmium. The refractory component accounts for —5% of the total condensible matter. Variations in refractory element abundances of bulk meteorites reflect the incorporation of variable fractions of a refractory aluminum, calcium-rich component. Ratios among refractory lithophile elements are constant in all types of chondritic meteorites, at least to within —5%. 

In Figure 1 aluminum is representative of the refractory component. AU types of carbonaceous chondrites are enriched in refractory elements, whereas ordinary and enstatite chondrites are depleted. Variations in Mg/Si (Figure 1) are smaller and may be the result of preferred accumulation or loss of olivine as discussed... 

The two elements calcium and aluminum are RLEs. The assumption is usually made that aU RLEs are present in the primitive mantle of the Earth in chondritic proportions. Chondritic (undifferentiated) meteorites show significant variations in the absolute abundances of refractory elements but have, with few exceptions discussed below, the same relative abundances of lithophile and siderophile refractory elements. By analogy, the Earth s mantle abundances of refractory lithophile elements are assumed to occur in chondritic relative proportions in the primitive mantle, which is thus characterized by a single RLE/Mg ratio. This ratio is often normalized to the Cl-chondrite ratio and the resulting ratio, written as (RLE/Mg)N, is a measure of the concentration level of the refractory component in the Earth. A single factor of (RLE/Mg) valid for all RLEs is a basic assumption in this procedure and will be calculated from mass balance considerations. 

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