Medium melting fraction

A number of chemical products are derived from Sasol s synthetic fuel operations based on the Fischer-Tropsch synthesis including paraffin waxes from the Arge process and several polar and nonpolar hydrocarbon mixtures from the Synthol process. Products suitable for use as hot melt adhesives, PVC lubricants, cormgated cardboard coating emulsions, and poHshes have been developed from Arge waxes. Wax blends containing medium and hard wax fractions are useful for making candles, and over 20,000 t/yr of wax are sold for this appHcation. 

Migration of fluids in a porous matrix with solid-liquid fractionation results in a process much similar to the chromatographic separation of elements (DeVault, 1943 Korzhinskii, 1970, Hofmann, 1972). This mechanism has recently been revived in the context of mantle metasomatism by Navon and Stolper (1987), Bodinier et al. (1990), Vasseur et al. (1991), in the context of hydrothermal systems by Lichtner (1985) and, for stable isotopes, by Baumgartner and Rumble (1988). Only a simplified account of this model will be given here. Let

solid matrix and melt, respectively, and vHq the fluid velocity relative... 

The simplest recording medium is a bilayer structure. It is constructed by first evaporating a highly reflective aluminum layer onto a suitable disk substrate. Next, a thin film (15-50 nm thick) of a metal, such as tellurium, is vacuum deposited on top of the aluminum layer. The laser power required to form the mark is dependent on the thermal characteristics of the metal film. Tellurium, for example, has a low thermal diffusivity and a melting point of 452 °C which make it an attractive recording material. The thermal diffusivity of the substrate material should also be as low as possible, since a significant fraction of the heat generated in the metal layer can be conducted to the substrate. For this reason, low cost polymer substrates such as poly (methylmethacrylate) or poly (vinyl chloride) are ideal. 

The slurry process is the oldest and still widely used method for manufacturing polymers of ethylene, propylene and higher a-olefins. In this process, the monomer dissolves in the polymerisation medium (hydrocarbon diluent) and forms a solid polymer as a suspension containing ca 40 wt-% of the polymer the polymerisation occurs below the melting point of the polymer. In slurry polymerisation, the temperature ranges from 70 to 90 °C, with the ethylene pressure varying between 7 and 30 atm. The polymerisation time is 1-4 h and the polymer yield is 95-98 %. The polymer is obtained in the form of fine particles in the diluent and can be separated by filtration. Removal of the catalyst residues from the polymer can be achieved by the addition of alcohol (isopropanol, methanol), followed by recovery and extraction of the catalyst residues. The polymer is freed from diluent by centrifuging and then dried. In the case of polypropylene manufacture, the atactic fraction remains in the diluent [28,37]. 

The role of sulfide-driven (chalcophile) fractionations in lunar magmatism is difficult to constrain, but sulfides presumably play a lesser role on the Moon than on Earth, because the solubility of sulfide in mafic melt increases with decreasing/o (Peach and Mathez, 1993). Compared to lithophile elements of similar volatility, sulfur is exceptionally depleted in terrestrial and martian basalts, but not so depleted in lunar basalts (Figure 6). Medium-Ti mare basalts are clearly unsaturated with sulfide, and although high-Ti mare basalts were originally believed to be sulfide-saturated (Gibson et al., 1977), Danckwerth et al. (1979) found them to be unsaturated, as well. 

Meteorites, as rocks produced in a solar nebula, have formed through a range of processes, some of which are quite different from those observed on Earth. Thus while igneous differentiation processes and metamorphism are recognized in meteorites, there also other processes operating which are not observed in terrestrial rocks. These include evaporation and condensation events related to melting in a gas-rich medium (as discussed in Section 2.3.2), impacting events, and metal-silicate fractionation. 

Despite the apparent success of the hydrothermal technique, there are a number of theoretical and practical drawbacks to this method of experimentation. Under hydrothermal conditions, some minerals dissolve excessively, melt, or react to form hydrous phases, making them unsuited to this type of investigation. Furthermore, the high vibrational frequencies of the water molecule results in complex temperature-dependencies for mineral-H20 fractionations (Fig. 3), thereby making it difficult to extrapolate fractionations outside the experimentally investigated temperature range. To overcome some of these difficulties, Clayton et al. (1989) developed a technique that uses CaCOs rather than water as the common isotope exchange medium. Rosenbaum et al. 

In the dielectric procedure developed by Ross and Frolen, the sample is made the dielectric medium between the plates of a capacitor and the change in capacitance which occurs as melting proceeds is used to determine the fraction melted... 

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