Hydrogen thermal dissociation

Well defined oxide phases can be obtained by thermal dissociation of oxalates, by controlled oxidation of compounds or actinide saturated ion exchangers or by reduction of higher oxides with hydrogen. Thermal dissociation of compounds often results in oxides of low density high (almost theoretical) density oxides can be prepared in sol-gel processes. 

Tantalum. Numerous methods developed to extract tantalum metal from compounds included the reduction of the oxide with carbon or calcium the reduction of the pentachloride with magnesium, sodium, or hydrogen and the thermal dissociation of the pentachloride (30). The only processes that ever achieved commercial significance are the electrochemical reduction of tantalum pentoxide in molten K TaF /KF/KCl mixtures and the reduction of K TaF with sodium. 

Qua.driva.Ient, Zirconium tetrafluoride is prepared by fluorination of zirconium metal, but this is hampered by the low volatility of the tetrafluoride which coats the surface of the metal. An effective method is the halogen exchange between flowing hydrogen fluoride gas and zirconium tetrachloride at 300°C. Large volumes are produced by the addition of concentrated hydrofluoric acid to a concentrated nitric acid solution of zirconium zirconium tetrafluoride monohydrate [14956-11-3] precipitates (69). The recovered crystals ate dried and treated with hydrogen fluoride gas at 450°C in a fluid-bed reactor. The thermal dissociation of fluorozirconates also yields zirconium tetrafluoride. 

Chlorination of Methane. Methane can be chlorinated thermally, photochemicaHy, or catalyticaHy. Thermal chlorination, the most difficult method, may be carried out in the absence of light or catalysts. It is a free-radical chain reaction limited by the presence of oxygen and other free-radical inhibitors. The first step in the reaction is the thermal dissociation of the chlorine molecules for which the activation energy is about 84 kj/mol (20 kcal/mol), which is 33 kJ (8 kcal) higher than for catalytic chlorination. This dissociation occurs sufficiendy rapidly in the 400 to 500°C temperature range. The chlorine atoms react with methane to form hydrogen chloride and a methyl radical. The methyl radical in turn reacts with a chlorine molecule to form methyl chloride and another chlorine atom that can continue the reaction. The methane raw material may be natural gas, coke oven gas, or gas from petroleum refining. 

The reason for the poor conversion efficiency to synthetic fuels is the high energy cost in liberating hydrogen from water (thermal dissociation, electroly-... 

H2 Is equal to 1 if hydrogen is at atmospheric pressure. If no interchange occurs, Qg 1. The reduction reaction will proceed effectively if log Kp g is not more than 1 or 2 units greater than log Kp Thermal dissociation is not feasible, except for iodides. 

Dahl, J. et al., Solar thermal dissociation of methane in a fluid-wall aerosol flow reactor, Int. J. Hydrogen Energ., 29, 725, 2004. 

Awareness of the very rapid migration of the H+ species provides a valuable orientation for the interpretation of many experiments. One of the most important of the examples discussed in the later parts of Section 3 has to do with the binding energy of the complexes AH that hydrogen forms with various shallow acceptors A. The lifetime of such a complex with respect to thermal dissociation into H+ and A can be measured in some types of annealing experiments, and this lifetime is related to the... 

Thermal dissociation produces ammonium fluoride and ammonia at elevated temperatures products contain ammonia and hydrogen fluoride. It forms a colorless double salt, ammonium iron fluoride SNEUF FeFs, with iron, a reaction of commercial apphcation for removing stains from fabric. It reacts with many metal oxides at elevated temperatures forming double fluorides ... 

Thermal dissociation of H2S is rapid above 850°C, producing hydrogen and sulfur. The reaction is endothermic. 

In the US, two programs were reported High Temperature Solar Splitting of Methane to Hydrogen and Carbon, and Rapid Solar-thermal Dissociation of Natural Gas in an Aerosol Flow Reactor. 

The vapour pressure ratio of actinides to noble metals is also the basis of the actinide metal preparation by thermal dissociation of intermetallic compounds. Such intermetallic compounds of An and noble metals can be prepared by hydrogen reduction of a mixture of an An oxide and a finely divided noble metal (Pt, Ir.. in the absence of noble metals, hydrogen reduction of An oxides is impossible. Am and Cm metals have been obtained by thermal dissociation of their intermetallic compounds with Pt and Ir High purity Th and Pa, the least volatile actinide metals, can be prepared by thermal dissociation of their iodides, which form readily by reaction of iodine vapour with car-... 

Fig. 23. Influence of molecular hydrogen and single H atoms (formed by thermal dissociation) on the photoelectric yield of a platinum foil, electrolytically loaded with hydrogen and brought to red heat in vacuo. Ordinate photoelectric yield I in electrons per light quantum. X = 280.3 mg T = 293°K. (a) H2 admitted,...

Also thermal dissociation reactions, such as dissociation of hydrogen,... 

Similar to ethane, propane dissociates by breakage of a C-C bond, which is weaker than the C-H bonds. In molecules such as ethylene or acetylene, with double or triple bonds between carbon atoms, a hydrogen atom is released during thermal dissociation. The following reactions, in particular, thermal dissociation of the ethyl radical (C2H5),... 

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