Reduction of Chlorides

Metallothermic reduction of chlorides has been the basis of some very important processes for reactive metals production. Examples include the Kroll and Hunter processes for the preparation of zirconium and titanium, and calcium or lithium reduction processes for the rare earths. 

The famous Kroll process is based on the following reaction (in the case of zirconium)  

The Kroll reactor is, therefore, designed to keep away air and moisture from the reaction system. 

Manual bleeder valve Argon purge line 

The above reaction shows that the oxychloride decomposes at the sublimation temperature into the volatile tetrachloride and the nonvolatile oxide. Reduction starts as soon as the chloride vapour contacts the molten magnesium, and this exothermic reaction raises the temperature of the reaction mixture. The temperature of the reduction crucible is maintained in the range of 800 to 875 °C. The process is carefully controlled by matching the sublimation rate of zirconium tetrachloride with the reduction rate. The conclusion of the reduction is indicated by a fall in temperature and pressure. 

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Similar graphs can be plotted for the reduction of any metal oxide and also for the reduction of chloride and sulphide ores. 

The most usual synthetic routes to the derivatives of platinum group metals are the exchange reactions of the complexes containing halide ligands with alkali metal alkoxides (method 5), alcoholysis of the same kind derivatives (usually by phenols, method 4), alcoholysis of hydroxide complexes (method 3), and redox reactions — reduction of chlorides or 0s04 in alcohol media (method 7) (Table 12.25). 

Reduction of chlorides 142a,c,d with an excess of LiAlH4 affects two reaction centers and yields the corresponding hydrides EtN(R)CH2GeHMe2 (R = Me, CH2CH=CH2, Ct GeHMe. The latter was also isolated by reduction of digermamorpholine 151485. 

The pure metal is much more difficult to obtain because of its reactivity with C, N2, H2, and 02- There are four different routes to its production reduction of chlorides, reduction of the oxide, thermal dissociation of the iodide, and an electrochemical process. ... 

The mechanisms of action through which RCAs act are not completely understood. One explanation for the toxic effects of RCAs is the production of hydrochloric acid through reduction of chloride ions on mucosal membranes (Worthington and Nee, 1999). This may help explain the... 

A brilliant steel-coloured form of the metal is obtained by reduction of chlorides of molybdenum at a red heat in a glass tube by hydrogen. It is found that molybdenum tetra- and penta-chlorides, on heating below 1330° C., yield metallic molybdenum. 

Chatgilialoglu studied (MesSijsGeH as a new radical hydrogen donor, and found that reduction of chlorides, bromides, and iodides, deoxygenation of secondary alcohols via a thiono ester (Barton-McCombie reaction), deamination of primary amines via isocyanides, removal of PhSe group, and replacement of a tertiary nitro group by hydrogen were extremely effective (Scheme 11.15) [31]. 

Hydrogen reduction of chlorides in thermal plasma can be apphed not only to produce powder of individual metals but also to produce different intermetalhc compounds. The composition of the generated crystals copies the composition of the chloride mixture in the gas phase. This effect permits the production of the intermetallic compounds with the required composition. Refractory intermetallic compounds based on niobium and vanadium were synthesized from their chlorides (conversion close to 100%) in a hydrogen plasma jet generated by RF-ICP discharge (Bashkirov Medvedev, 1968). The reaction products were crystallized on a substrate sustained at a temperature of about 1000°C. The plasma-metallurgical technology is proven to be effective in the synthesis of vanadium-Hsilicon... 

The reduction of chloride 237 by LiALD, as well as its methanolysis with sodium methylate result in a mixture of tricyclic (mainly) and bicyclic products 383,4.ii>. 

Extended research. Made beryllium by reduction of chloride by sodium as a white metal, specific gpravity 2.1, and describes properties. Could not make the sulpiiide... 

In general, it can be concluded that hydrophobic treatment of concrete is an effective and low-cost preventative measure against corrosion that may be caused by chloride ingress. The beneficial effect is mainly a strong reduction of chloride ingress, both in semi-permanent contact and in wetting/drying situations. The effective life in fully exposed atmospheric conditions is at least five years and more, probably much more, when protected from UV radiation by a layer of asphalt... 

The first test results after 28 days of storage under water already show a reduction of chloride migration coefficients for the mortars with polymer additives (Fig. 4). When compared to the reference mortar composition, a reduction in the chloride-migration-coefficient from 1.55x10-12 mVs to 0.80x10-12 mVs was achieved, by using styrene-acrylate of 20 % concentration. 

The reaction takes place on reduction of chlorides of titanium in oxidation state (m) or (iv) by metallic potassium or alkyl-lithium with subsequent decomposition of the organo-titanium species on warming. Titanium metal alkoxide radical anion systems have also been shown to act as catalysts in the conversion of elemental nitrogen to hydrazine ... 

These reactions include the decarboxylation of formate in aqueous alkaline solutions at Pt, Pd or Au anodes[376], formation of azone[377], and anodic oxidation or cathodic reduction of chloride and bromide complexes of Pt and Pd[378-380]. In [381] the mechanism of oxidation of graphite at low anodic potentials was explained by assuming a barrierless reaction similar to the electrochemical desorption of CO2. So far, it has not been possible to draw a more definite conclusion about the mechanism of these processes. 

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