Carbothermic process

Ferro-alloys Master alloys containing a significant amount of bon and a few elements more or less soluble in molten bon which improve properties of bon and steels. As additives they give bon and steel better characteristics (increased tensile sbength, wear resistance, corrosion resistance, etc.). For master alloy production carbothermic processes are used for large-scale ferro-sihcon, ferro-chromium, ferro-tungsten, ferro-manganese, ferro-nickel and metallothermic processes (mainly alumino and sihco-thermic) for ferro-titanium, ferro-vanadium, ferro-molybdenum, ferro-boron. 

Also, the metal can be obtained by nonelectrolytic reduction processes. In carbothermic process, alumina is heated with carbon in a furnace at 2000 to 2500°C. Similarly, in Subhalide process, an A1 alloy, Al-Fe-Si-, (obtained by carbothermic reduction of bauxite) is heated at 1250°C with AlCl vapor. This forms the subchloride (AlCl), the vapor of which decomposes when cooled to 800°C. 

Silica is reduced via a carbothermic process to silicon, which is converted to a variety of chlorosilanes. The major monomer, dimethyldichlorosilane, is produced in well over a billion pounds per year by several basic producers... 

Three compounds have been identified in the system Y-Si-N these are YSisNs, Y2Si3Ns and Y3Si6Nn (Ekstrom et al. 1997). These phases have been produced by a carbothermal process and their Si and Y NMR spectra reported (Table 4.6). 

In this procedure, extensively tested by Alcan at one time, dissolution of aluminum from the alloy using aluminum trichloride at about 1,300°C produces the volatile aluminum subhalide [19]. Cooling the subhalide moderately returns a pool of molten product aluminum, and aluminum trichloride (boiling point approximately 183°C), which serves as a working fluid and can be recycled. Despite problems with the aluminum recovery methods there remains an interest in nonelectrolytic aluminum production, such as that offered by carbothermic processes [20]. 

The carbothermic process provides metallic uranium reduction not only from dioxide (UO2) but also from a much more convenient and accessible oxide, UsOs (Wilhelm ... 

Keyword silicone-based product, high energy consumption, carbothermic process,... 

B4C pellets were fabricated by carbothermic process and characterized. 

Rice hull hydrocarbons supply the carbon source and rice hull ash the silicon source. This is an early carbothermal process (Equ. 10a). At <900°C, coking (Equ. 10b and 10c) removes water and organics and yields a mixture of silica and carbon, and at <1700°C, pyrolysis yields silicon carbide whiskers (Equation lOd). The overall yield is 1 percent. Three variants of the rice hull process are known. Compacted rice hulls can be pyrolized at 1600°C without coking [14], thus directly yielding a mixture of graphite and SiC whiskers, 10-200 pm in length and... 

If this carbothermal process is brought to only partial completion (Equation 11a and 11b), a homogeneous mixture of silicon carbide whiskers and silicon nitride powder [10] is obtained which can be fired directly to yield whisker reinforced ceramics. Silicon carbide reinforced alumina composites and silicon carbide whisker reinforced zirconia composites [31] are also products of the "chemical mixing process". The whisker growth rate in the zirconia process can be accelerated by adding metal particle catalysts such as cobalt chloride, thus potentially facilitating a VLS phase transformation. 

VLS siiicon carbide whiskers with diameters ranging from <3 to 11 jm, and lengths ranging from 5 jm to <10 cm are readily obtained by metal catalyzed chemical vapor deposition. This process facilitates an exacting control over whisker shape and dimension in a batch or a continuous process. The diameter of the catalyst determines that of the whisker. Less well-defined whiskers have been obtained by vapor deposition, chemical mixing and carbothermal processes with diameters ranging from <3 pim to >30 nm. 

Short VLS or VS whiskers are obtained with diameters ranging from 0.6 to <1.0 pm and lengths ranging from 10 to <100 pm by chemical vapor deposition, chemical mixing and carbothermal processes. Whiskers derived by the rice hull process reflect the most irregular growth habitat. Two variants have been observed, whiskers without inclusions in any part of their structure, and whiskers with nanoparticulate inclusions in the core of their structure. The sheath of these sheath/core whiskers is free of inclusions. Only their core contains nanoparticulate inclusions, such as Si-O-C phases and nanocrystalline Ca, Mn, and Fe impurities. 

Keywords Nickel Boron, Ni-based alloys. Brazing alloys, Carbothermic process... 

Ferrochrome (UK, France), or ferrochromium (USA), is a master alloy of iron and chromium containing between 40 and 75 wt.% Cr and varying amounts of carbon and silicon. It is prepared industrially by three different electrothermal processes—the carbothermic, the silicothermic, or the aluminothermic reduction of chromite ore, which is used as the main source of chromium. In the carbothermic process, a charge of chromite ore mixed with lime as fluxing agent is reduced by metallurgical coke or coal as reductant in a three-phase submerged-arc furnace. The overall chemical reaction involved is as follows ... 

The main drawback of this material is a low intrinsic electronic conductivity, which may lead to poor electrochemical performances. The synthesis procedure is aiso a sensitive point, as the oxidation of iron has to be avoided. A relatively simple method to deal with both the reducing synthesis conditions and the low conductivity of the product is to use carbon additives, also known as carbothermal process. Carbon additives have a two-fold effect. On the one hand, iron is protected against oxidation during the heating process. On the other hand, the use of carbon excess may provide an intimate mixture of LiFeP04 and carbon that has a much higher electronic conductivity than the phosphate alone. 

The raw material for the production of silicon is mostly quartz sand, silicon dioxide, which is reduced by a carbothermical process... 

When AIN was introduced for electronic packaging applications in 1985 it was considered inconsistent in properties. This inconsistency was due to problems with the AIN powders used to make sintered products. The powders were made by either of two methods direct nitridation of aluminum metal in a nitrogen gas atmosphere or carbothermal reduction of alumina, which involves the decomposition of the reaction product of aluminum trichloride with ammonia. The first process was cheaper, but the resultant powders were not especially well suited to materials for electronic applications. The carbothermal process produces powders of greater uniformity and purity, with greater control over size and shape, than the nitridation process, and is the more widely used process today." ... 

SiC whiskers can be fabricated by the reaction of silicon and carbon to form a gaseous species that can be transported and reacted in the vapor phase. This type of formation is referred to as a vapor-sohd reaction and occurs by the following multistep process 1) SiOj + C-SiO + CO and 2) SiO -I-2C-SiC -I- CO. Although the raw materials used in these carbothermal processes vary widely, nearly aU of the commercial and high-volume SiC whisker products are formed by this method. These reactions occur at temperatures greater than 1400°C and in an inert or nonoxidizing atmosphere. In addition, a catalyst is added to assure the formation of whiskers rather than particulate during the reaction. 

Figure 6 SEM photographs of AIN powders manufactured by a carbothermal process (left) and a direct...

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