Thermal reduction process

Pldgeon Process. The Pidgeon (46—49) process (Fig. 6) was the first commercial thermal reduction process usiag siUcoa, and was developed ia the 1940s. This process is used by Timminco (Haley, Oatario, Canada) and Ube Industries (Japan). The overall reaction for this process is... 

This reaction occurs in a vacuum and the gaseous metal is condensed in a cooler part of the apparatus. AH strontium metal is produced commercially by the thermal reduction process in aUoy steel retorts. 

Metallic Mg is produced industrially using both electrolytic and thermal reduction methods. The electrolytic processes differ primarily in the choice of electrolyte—anhyd MgClj, partially hydrated MgClj x HjO and MgO. The more important thermal reduction processes use FeSi, A1 alloys or C as reducing agents. 

The most widely employed thermal reduction process for preparing Mg metal uses PeSi as reducing agent. Mixtures of the substrate, usually calcined dolomite (i.e., MgO, CaO) and PeSi are fabricated into briquettes with a hydrocarbon binder and loaded into Ni-Cr steel (15/28) retorts. After evacuation the retort is subjected to a temperature gradient Mg distills from the hot mixture (at 1150°C) and high-purity Mg crystals collect at the water-cooled end of the retort ... 

Aluminum or one of its alloys (Al-Si, Al-Ca-Si, Al-Ca-Pe-Si) can be substituted for PeSi in this process. The alternative thermal reduction process is based on the reduction of pure MgO by carbon in an arc furnace at temperatures above 1800°C. Since the reaction ... 

In the principal thermal reduction process, CaO, obtained by calcination of high-purity CaCOj, is reduced with A1 or one of its alloys ... 

Briquettes of CaO with 5-20% excess powdered A1 are heated under vacuum to 1170°C in a Ni-Cr steel (15/28) retort in which the Ca vapor, produced by reduction of solid CaO by A1 vapor, is condensed in a zone at 680-740 C. Any Mg impurity is condensed in a zone at 275-350°C a mixture of the two metals condenses in an intermediate zone. The A1 content of the product can be reduced by passing the metal vapor, before it condenses, through a vessel filled with solid CaO. The adaptation of the FeSi thermal reduction process for Mg production (see 7.2.3.2.1) to Ca manufacture has also been described but is not economically viable in comparison with the above process. The thermal reduction of CaO with carbon has been proposed as for Mg production, however, the reversibility of the equilibrium ... 

Fig. 3 Potential energy profiles for the concerted and the stepwise mechanism in the case of a thermal reductive process. E is the electrode potential for an electrochemical reaction and the standard potential of the electron donor for a homogeneous reaction. For an oxidative process, change - into + and donor into acceptor.

The main challenge with storing in terms of oxidation of reactive metals is the reversibility and the control of the thermal reduction process in order to produce the metal in a solar furnace, where Na and Li have a gravimetric hydrogen derrsity of 3 mass% and 6.3 mass%, respectively. 

Currently, thermal reduction processes have replaced the electrolysis method. The starting material in these methods is limestone, which is calcined to produce calcium oxide. The latter is ground, mixed and compacted with aluminum, and reduced at temperatures between 1,000° to 1,200°C under vacuum. Calcium vapors formed in low yield under such thermodynamic conditions are transferred from the reactor and condensed in cool zones, thus shifting the equilibrium to allow formation of more calcium vapors. The reactions are as follows ... 

Chromium metal is produced hy thermal reduction of chromium(III) oxide, Cr203 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr203 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with A1 powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen. 

Thermal reduction processes are not being practiced anywhere in the world at present for large-scale production of sodium. Such methods, however, can he conveniently adapted for laboratory preparation of metalhc sodium. Sodium can be prepared by thermal reduction of its hydroxide, carbonate, or chloride at elevated temperatures. These salts are heated with carbon, calcium carbide, iron carbide, ferrosilicon, or other reducing agents at temperatures above 800°C under vacuum ... 

Thermal reduction processes have been apphed successfully in making the metal from salts. In one such process, potassium fluotantalate is reduced with sodium metal at high temperatures to form tantalum powder of high purity and small particle size. Also, tantalum oxide can be reduced at high temperatures in vacuum with aluminum, silicon, or tantalum carbide. When the oxide is reduced by tantalum carbide, a metal sponge is obtained which can be embrittled with hydrogen to form powder metal. 

In a careful study of the long wavelength behavior of Co(C204)33 ", Adamson demonstrated that racemization of this complex could accompany its reduction. At 450 mpt, for example, with optically active Co(C204)33, O optical activity/O reduction = 1.15 thus fl> racemization = 0.0018 and Ored = 0.012.5 It was shown by Adamson that this result could be accommodated by assuming reaction (22) was reversible and was driven forward photochemically. The observed ratio of d>rao to bred could then be rationalized in terms of the well-known thermal reduction processes.75... 

A gas-reaction purification process also has attracted attention over the years. This is based on aluminum trichloride gas reacting with molten aluminum at about 1000°C to produce aluminum monochloride gas. Aluminum fluoride gas may he substituted for the aluminum monochloride gas in the process. Raw materials for the process may be scrap aluminum, aluminum from thermal-reduction processes, aluminum carbide, or aluminum nitride. As of the beginning of 1987, none of these other processes are fully commercial. 

In spite of these major limitations, considerable progress has been made in understanding many of the important factors that influence subsurface water chemistry. Na+, Ca2+ and Cl- account for the major portion of dissolved components in most brines (Figure 8.6). Ca2+, which can comprise up to 40% of the cations, usually increases relative to Na+ with depth (Figure 8.7). Br and organic acids are commonly found at concentrations of 1 to 2 g L1 (Land, 1987). The bicarbonate concentration is largely limited by carbonate mineral solubility, and sulfate is generally found in low concentrations as a result of bacterial and thermal reduction processes. 

In the early 1990 s it was reported that N2O emissions from adipic acid producers could contribute to atmospheric ozone depletion and global warming [I]. It was estimated that adipic acid production may account for up to 10% of the annual increase in the atmospheric N2O. Ihls report sparked an abatement initiative among the major adipic acid producers. Successes have been announced and implementations are scheduled for 1996-98 [2]. However, Monsanto was already practicing complete abatement by a thermal reduction process and elected to pursue a more desirable path of value-added utilization. 

In the thermal reduction process, reaction (14.4), magnesium oxide (as a component of dolime) reacts with a metal such as silicon, which is present in ferrosilicon, to produce magnesium metal. The two thermal methods in operation today are the Pidgeon and Magnetherm processes. The Pidgeon process is a batch process in which dolime and silicon (usually ferrosilicon) are briquetted and fed into a gas-fired or electrical heat retorts. The retort is... 

CaClj was chosen as a melt for the metal-thermal reduction process, as much CaO can be dissolved in it, which is required for an anode process with oxygen evolution. In addition electrolysis of CaCl2 can be conducted at high temperatures without danger of considerable evaporation and high temperatures are necessary for operation of a TiOj anode. The possibility of electrolysis of CaCl2-CaO melt with a ceramic anode was shown earlier [3]. 

Hong I et al (2013) Mesoporous Si/C composite anode for Li battery obtained by magnesium-thermal reduction process. Solid State Ionics 232 24-28 Huachao T et al (2013) Preparation of porous Si/C anode materials by magnesiothermic reduction method. J Chin Ceram Soc 41(8) 1046-1050... 

The deposition of boron phosphide by CVD was carried out in a gas flow system by the thermal decomposition of diborane-phosphine mixtures in a hydrogen atmosphere and the thermal reduction of boron tribromide-phosphorus trichloride mixtures with hydrogen (37). The hydrides are thermodynamically unstable at room temperature and decompose rapidly at above 500°C, which tends to promote homogeneous nucleation by pyrolysis in the gas phase. The halides are thermally more stable than the hydrides, and higher substrate temperatures may be used in the thermal reduction process with essentially no gas-phase reactions. At high substrate temperatures, a phosphorus pressure equal to or greater than the vapor pressure of boron phosphide must be present over the substrate surface to maintain the stoichiometry of the deposit. 

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