H2O content

Solvent Preparation. The most critical aspect of the solvent is that it must be dry (less than 0.02 wt % of H2O) and free of O2. If the H2O content is above 0.02 wt %, then the reaction of Mg and RX does not initiate, except for an extremely reactive RX species, such as benzyl bromide. Although adventitious O2 does not retard the initiation process, the O2 reacts with the Grignard reagent to form a RMg02X species. Furthermore, upon hydrolysis, the oxidized Grignard reagent forms a ROH species that may cause purification problems. 

The effect of increasing pressure is to move the average hydrocarbon content towards the heavier species, but increasing temperature seems to favour the production of lighter species. The final proportions are also determined by the state of the catalyst, and the physical anangement of tire reactor. The formation of the oxygenated compounds could also involve reactions between the H2O content of tire gas in the form of adsorbed OH radicals and hydrocarbon radicals since the production of these molecules is also well beyond the thermodynamic expectation. 

As the CH4 component of the fuel reforms to CO and H2, H2O is consumed. This favors the reversal of Equation (8-16), which allows Si02 to be deposited downstream, possibly on exposed nickel surfaces. Oxygen-blown coal gas, however, has an H2O content of only -13%, and this is not expected to allow for significant Si transport. 

At low 2Ot, DH20n, may be treated as roughly independent of H2O content. Hence, the diffusion equation becomes... 

In summary, the diffusion behavior of both H2O and CO2 demonstrates the importance of understanding the role of speciation in diffusion, and the very different consequences due to that role. Diffusion of a single-species component (such as Ar) usually does not depend on its own concentration (when the concentration is low), but depends on the melt composition. For a multispecies component, speciation affects the diffusion behavior. For H2O, speciation makes the diffusion behavior very complicated even at low H2O concentrations, total H2O diffusivity still depends on H2O content (because the species concentrations are not proportional), in addition to the dependence on melt composition. If species concentrations are proportional to each other and hence to the total concentration of the component, then the diffusivity is independent of the concentration of the component, as in the case of CO2 diffusion. Many multispecies components probably satisfy this condition that the concentrations of... 

It has been observed that water dramatically enhances oxygen diffusion in silicate melts as well as in many crystalline silicates. Furthermore, in systems studied in more detail, it has been observed that the diffusivity is roughly proportional to H2O pressure (Farver and Yund, 1990), or H2O content in the phase. This has been... 

Figure 3-28 H2O diffusion profile for a diffusion-couple experiment. Points are data, and the solid curve is fit of data by (a) error function (i.e., constant D) with 167 /irn ls, which does not fit the data well and (b) assuming D = Do(C/Cmax) with Do = 409 /im ls, which fits the data well, meaning that D ranges from 1 /rm /s at minimum H2O content (0.015 wt%) to 409 firn ls at maximum H2O content (6.2 wt%). Interface position has been adjusted to optimize the fit. Data are adapted from Behrens et al. (2004), sample DacDC3.

Figure 3-37 Compositional dependence of diffusivities. (a) Fe-Mg interdiffusivity along the c-axis in olivine as a hinction of fayalite content at P — O.l MPa and log /b2 =-6.9 0.1. Diffusion data are extracted using Boltzmann analysis. Some of the nonsmoothness is likely due to uncertainty in extracting interdiffusivity using the Boltzmann method. Data are from Chakraborty (1997). (b) Ar and CO2 diffusivity in melt as a function of H2O content. Data are from Watson (1991b) and Behrens and Zhang (2001).

In silicate melts, the diffusivity is strongly affected by the H2O concentration the diffusivities of Ar, CO2, and molecular H2O all increase roughly exponentially with increasing H2O content. That is, InD increases linearly with H2O content. Figure 3-37b displays the dependence of CO2 and Ar diffusivity on H2O content. 

When the viscosity is a function of H2O content and hence varies as a function of r, the pressure in the bubble may be found as follows (Proussevitch and Sahagian, 1998) ... 

The above set of equations can be solved numerically given input parameters, including initial bubble radius Uo, temperature, ambient pressure Pf, surface tension a, solubility relation, D and p as a function of total H2O content and temperature, and initial total H2O content in the melt. 

Silica makes up 12.6 mass-% of the Earth s crust as crystalline and amorphous forms. It was found that both modifications show similar main luminescence bands, namely a blue one centered at 450 nm ascribed to which substitutes for Si, red centered at 650 nm linked with non-bridge O, and dark-red at 700-730 nm linked with Fe. Time-resolved luminescence of hydrous volcanic glasses with different colors and different Fe, Mn, and H2O contents were measured and interpreted (Zotov et al. 2002). The blue band with a short decay time of 40 ns was connected with T2( D)- Ai ( S) and Ai C G)- Ai ( S) ligand field transitions of Fe " ", the green band with a decay time of approximately 250 ps with a Ti( G)- Ai( S) transition in tetrahedrally coordinated Mn ", while the red band with a much longer decay time of several ms with T1 (4G)- Ai( S) transitions in tetrahedrally coordinated Fe ". We detected Fe " " in the time-resolved luminescence spectrum of black obsidian glass (Fig. 4.43d). 

Crystal stability is related to the amount of barium and water in the zeolite. Single crystal data by their number tend to indicate a decrease in the crystal quality of zeolite A at higher and lower H2O contents. Although hydrated Bag-A had... 

For the synthesis of zinc ferrite (ZnFe204) of stoichiometric composition CFD and HPS samples were mixed in an appropriate ratio. From the chemical analysis the Fe/Zn molar ratio of the mixture was 2.18. To override the problem of the coohng effect of volatiles on the plasma (mentioned above), prior to mixing HPS sample was preheated at 300 °C to reduce its volatile (H2O) content. Conditions of the plasma treatments can be seen in Table 3. In order to improve heat transport between the hot gases... 

Figure 2. Overall batch composition of faujasite syntheses reported by several investigators (H2O content not shown).

Other than the main Bunsen reaction, the other three steps in this section involve separation of gases and H2O from the flowing chemical stream. O2, which forms as a result of water splitting, is removed from the recycled stream to avoid formation of complexes in the rest of the section. SO2 is washed/separated from the Bunsen reactor output to prevent any side reaction downstream. The last step in Section I involves the extraction of H2O from the HI product stream before it is sent to Section III. This will reduce the energy requirement, as H2O evaporation processes impose a high heat demand based on the current flow sheet. Hence, any reduction in H2O content in the Bunsen reaction products will be beneficial to the overall cycle efficiency. 

Hacker B. R. (1996) Eclogite formation and the rheology, buoyancy, seismicity, and H2O content of oceanic crust. In Subduction Top to Bottom, Geophys. Monogr. 96 (eds. G. Bebout, D. Scholl, S. Kirby, and J. Platt). AGU, Washington, DC, pp. 337-346. 

In an extensive review of the geochemistry of volatile-bearing minerals in mantle xenoliths, Ionov et al (1997) have pointed out that although minerals such as mica, amphibole, and apatite are often referred to as hydrous, in many cases they have very low H2O contents (Boettcher and O Neill, 1980). In such cases, these minerals may have significant amounts of fluorine, chlorine and CO2. Mica, amphibole, and apatite, together with the oxide phases, are important hosts for titanium, potassium, rubidium, strontium, barium, and niobium (Table 9). 

---