Carbonaceous refractory materials

Refractory materials in primitive meteorites were investigated first as they have the best chance of escaping homogenization in the early solar system. Inclusions in C3 carbonaceous chondrites exhibit widespread anomalies for oxygen and the iron group elements. Only a few members, dubbed FUN (for Fractionated and Unknown Nuclear effects), also display anomalous compositions for the heavy elements. Anomalies in inclusions have generally been connected with explosive or supernova nucleosynthesis. 

Heterogeneous accretion models for the formation of the Earth advocate the initial accretion of refractory, less-oxidized components that make up the bulk of the planet (some 50-80%), followed by the accretion of a lower-temperature, more oxidized component (e.g., perhaps comparable to carbonaceous chondrites). The overall nature of the initially refractory material is not well characterized, but it could have affinities to ordinary or enstatite chondrites. These two-component mixing models seek to reconcile the observational constraints from chemical and isotopic studies of the silicate Earth. As of early 2000s, we do not have sufficient data to identify in detail the nature of these two components of accretion if they existed. 

For the solar industry, impurity control and alternative raw materials are of great interest. In the normal metallurgical silicon production furnace, silica is charged into the form of quartz lumps. The carbonaceous materials have many forms like charcoal coke, coal, and wood chips. The charge is carefully composed and the raw materials are selected to give best possible yield with respect to Si and to avoid unwanted impurities. Also, the refractory materials and the consumable electrodes are source of impurities. The Si from the arc... 

The quanitity of the raw material necessary to produce a reliable estimate of any element will depend on the selected detection instrument. In general, samples for uranium analysis are preconcentrated by evaporation, air-, freeze-, or oven-drying to remove water, and dry-ashing or wet-ashing to remove carbonaceous matter. For vegetation and soil, acid or alkali fusion followed by acid dissolution of the fusion cake is required to ensure dissolution of refractory materials. Aerosol, water, soft tissues, blood, and dry-ashed bone samples may be solubilized with mineral acids. 

There is no industry-wide standard for designating the various grades of carbonaceous materials that are commercially available. Each manufacturer has its own method and nomenclature to describe the available grades and varieties that are made for specific purposes or properties. The following will help introduce carbonaceous products typically utilized as refractory materials. 

Tables 5 and 6 describe other parameters that have a direct effect on the properties of graphite materials. Table 5 illustrates the difference in material properties of graphite from two different manufacturers that reflects differing raw materials and processing methods or techniques. As can be seen from Table 5, the manufacturer has a profound influence on graphite properties due to differing manufacturing procedures, proprietary methods, and processes. This is primarily why there is no industry-wide standard for carbonaceous refractories.

Typical ceramic refractory materials used in the hearth wearing surface are shown in Table 8. Note that the thermal conductivities of ceramic refractories (insulating) are significantly lower than any carbonaceous refractory. The properties and characteristics of all ceramic refractories depend on the type, quality, and source of the raw materials utilized in their mix and the particle size makeup. 

PROP Soot is defined as a brown-to-black substance incidentally produced during the incomplete and uncontrolled combustion of any carbonaceous material. It is a mixture of colloidal carbon, organic tars, and refractory inorganics whose composition depends on combustion conditions. It is not unusual for the tarry component to account for more than 50 weight percent of the soot, particularly, when produced by inefficient combustion of coal or wood. Can be distinguished from carbon black on the basis of differences in physical and chemical properties. 

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