Atmosphere initial composition 5, 6

It was assumed that fluoride-containing precursors undergo partial hydrolysis by atmospheric moisture. For instance, for an initial composition corresponding to x = 0.05, the final composition was found, using mass loss and chemical analyses, to be Lio.goCMgo.osoTao 9s)02.79sF0.o9o(OH)o.o6o. 

Case 2. The raindrop falls on a limestone rock and comes to equilibrium with calcite, while remaining in equilibrium with the PCO2 of the atmosphere. This process results in dissolution of the rock, and addition of calcium and alkalinity to the raindrop. The knowns are Pc02> the initial composition of the solution, and that it must be in equilibrium with calcite. In this case, as in all others, electroneutrality must apply, but mass balance will not because of CO2 exchange with the atmosphere. First the equations will be written for calcium. 

Figure 7 The relationship between the xenon isotope compositions of the atmosphere, initial atmosphere, and the upper mantle as sampled by MORE. The line connecting the initial atmosphere (fractionated U-Xe) and the present atmosphere has a slope equal to the ratio of plutonium-derived Xe to radiogenic Xe ( Xe/ Xe) in the atmosphere. Any xenon that remained in the solid reservoir from where this was degassed must have a greater value for this ratio and so he in the shaded region (Ozima et al, 1985). While measured MORBs do so, upper-mantle compositions that have been corrected for U-derived Xe (based on MORE data of Kunz et al, 1998 and on CO2 weU gas data of Phinney et al, 1978) do not, indicating that upper-mantle xenon is not the residual left from atmosphere degassing.

A suitable initial composition for the atmosphere has been deduced from meteorites. Multi-dimensional isotopic correlations of chondrite data have been used to constrain a range of compositions that, when mass-fractionated, yields the light-isotope ratios of terrestrial Xe. In order to match the terrestrial heavy Xe isotope ratios, addition of radiogenic I and a heavy Xe isotope component is required. Constraining the composition of the heavy isotope component to known fission spectra then defines the U-Xe composition and identifies " Tu-derived fissiogenic Xe as the heavy isotope component (see Primordial Xe section). This is compatible with meteorite data that... 

Figure 9. Xe isotope compositions of terrestrial precursors and present reservoirs. U-Xe, fractionated to match the light Xe isotopes (Fig. 7), provides an initial composition of the atmosphere, to which radiogenic Xe and fissiogenic e have been added. Similar fractionation of solar wind (SW) Xe produces Xe that is too heavy to supply the atmosphere. MORE typically have Xe/ °Xe and e/ °Xe ratios that are greater than the atmosphere due to radiogenic and fissiogenic additions and are correlated, with the range likely due to variable atmospheric contamination of samples. The most precise measurement of mantle Xe is for CO2 well gas. When uranogenic Xe is subtracted, the...

Of course, if the protective scale of chromia or alumina is not penetrated by SO2, sulphide cannot form at the scale-metal interface. This was found for Ni-20 wt% Cr, Co-35 wt% Cr and Fe-35 wt% Cr alloys exposed to pure SO2 at 900 °C and emphasizes the resistance of a chromia scale to permeation. On the other hand, alloys in the Fe-Cr-Al, Ni-Cr-Al and Co-Cr-Al systems were exposed to atmospheres in the H2-H2S-H2O system. These atmospheres had compositions that supported the formation of chromia or alumina together with the sulphides of Fe, Ni and Co at the scale-metal interface. In these cases, a protective layer of chromia or alumina that formed initially was penetrated by sulphur to form iron, nickel, and cobalt sulphides at the scale-metal interface. Furthermore, iron, nickel, and cobalt ions apparently diffused through the oxide layer to form their sulphides on the outside of the protective scale. Thus the original protective scale was sandwiched between base-metal sulphides. 

Some important key words are provided with a number of subordinate entries these are indented and printed with a lower-case initial letter (example Atmospheric air / composition). 

Once initiated, zirconium and carbon powders react exothermically in a vacuum or inert atmosphere to form zirconium carbide. With the greater availabiHty of relatively pure metal powders, this technique is coming into common use for the production of several refractory carbides. Zirconium carbide is not a fixed stoichiometric compound, but a defect compound with a single-phase composition ranging from ZrCQ to ZrCQ at 2400°C. 

A number of patents describe accelerators that will reduce the time required for stabilization (24,27,28). The accelerators are often inherent to the polymer or precursor but may be added to the gas phase during stabilization. For example, it is common to have an acid group present as comonomer such as itaconic acid [97-65-4] or methacrylic acid [79-41-4]. The acid groups provide initiation sites for cyclization. Alternatively, the stabilization atmosphere composition can be modified to accelerate stabilization (29). 

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