Hydrazines decomposition

The mechanism of hydrazine decomposition has been studied much less than that of hydrogen peroxide, and the mechanism actually is not known. We may take some clues however from studies of its oxidation in aqueous solution by metal salts, in which kinetic and isotope labelling techniques were used. As the main mechanism for the oxidation of hydrazine by ferric ion the following was proposed 57)  

This is a typical reaction of Class B, which may be expected to be pH dependent however, because of the formation of a proton during the reaction. The products in this case are ammonia and nitrogen. To convert this mechanism into a catalytic reaction some other step would have to be proposed, in which the ferrous ion is reoxidized into the ferri-ion, but no studies on this have been done up to now. 

Hydrazine is also known to decompose into nitrogen and hydrogen over metallic catalysts like platinum or palladium, and the intermediate has been shown by mass spectrometry 58 to be the di-imid N2H2  

This is probably also a reaction of Class B, which however may be expected not to be pH dependent. Therefore, taking into account the scanty evidence available, we may propose that the catalytic activity for this reaction is also dependent on the redox properties of the catalyst, but that the direction of the reaction, either into ammonia and nitrogen or into nitrogen hydrogen respectively, may be connected with acid/base properties. 

Phthalocyanine complexes, deposited as a film on a metal of the same kind as their central metal ion, appeared to be active for hydrazine decomposition 48)-Wholly organic polymers, prepared by the dechlorination of poly vinylidene chloride 62 were also shown to be active, but the ammonia and hydrogen produced reacted with the catalyst, a problem also encountered with the polychelate catalysts. 

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This is the dominant overall reaction for the decomposition on platinum or tungsten at 200 and 380 °C, respectively40. Most workers on hydrazine decomposition flames41-44, in which the reactions are homogeneous, report a stoichiometric equation similar to (b) for final flame temperatures up to 1900 °K. Measurements of MacLean and Wagner45 on decomposition flames and of Husain and Norrish37 on the flash photolysis of hydrazine indicate the contribution of the overall reaction... 

Ammonia Synthesis, Ammonia Decomposition and Hydrazine Decomposition... 

In this case the hydrazine is the sole source of the working gas, which is expanded by the heat released by the oxidation of aluminum, whereas in the unmetallized system a significant part of the hydrogen from hydrazine decomposition furnishes energy by oxidation as well as part of the working gas in the form of water. 

Equilibrium concentrations of carbon or ammonia are not found in short combustion chambers used in rocket motors. The reason for this non-equilibrium situation is that the rate of formation of soot is very slow and carbon does not have time to form. Similarly the dissociation of NH3 is very slow. Thus in ethylene oxide monopropellant rocket motors one finds very little carbon, whereas equilibrium considerations predict carbon as a predominant product and in hydrazine decomposition chambers one finds an excess of NH3 over that predicted by equilibrium considerations. In ethylene oxide motors carbon forms from the decomposition of methane, not the reaction represented above, thus both non-equilibrium situations give higher performance than expected, since the endothermic reactions do not have time to take place. Of course, carbon also could form in cool reactions which take place in boundary layers along the walls where velocities are slow. 

Because of the relatively low temperatures of decomposition of monopropellants, the attainment of non-equilibrium products is observed in some cases. The specific impulse and equilibrium combustion temperature of several monopropellants, are summarized in table IV. C. 1 and IV. C. 2. The non-equilibrium character of hydrazine decomposition was discussed previously in section m. A. The methyl substituted hydrazines are observed to behave in the same manner (32). These characteristics are summarized in table IV.C. 3. The non-equilibrium decomposition of the hydrazine is particularly interesting because it results in combustion temperatures and performances which are higher than those which are predicted from equilibrium considerations. 

The Raschig hydrazine synthesis can be extended one further step. Reaction of chloramine with hydrazine in ether yields triazanium chloride, which decomposes instantaneously. This is responsible for hydrazine decomposition during the Raschig synthesis (see Section 5.2.1) ... 

For a first order dependence such as that observed for a hydrazine decomposition flame, As will be shown in Section 4.C.5, although hydrocarbon-air... 

Hydrazine has been studied extensively for use in monopropellant thrusters for space flights of long duration. Thrusters are used or altitude control of communication satellites. Here the decomposition of hydrazine over a packed bed of alumina-supported iridium catalyst is of interest. " In a proposed study, a 2% hydrazine in 98% helium mixture is to be passed over a packed bed of cylindrical particles 0.25 cm in diameter and 0.5 cm in length at a gas-phase velocity of 15m/s and a temperature of 750 K. The kinematic viscosity of helium at this temperature is 4.5 X 10 nF/s. The hydrazine decomposition reaction is believed to be externally mass transfer-limited under these conditions. If the packed bed is 0.05 m in length, what conversion can be expected Assume isothermal operation. 

Lee S, Fan CY, Wu TP, Anderson SL (2005) Hydrazine decomposition over Ir /Al O model catalysts prepared by size-selected cluster deposition. J Phys Chem B 109 381... 

When N2H4 was studied by flash photolysis, absorptions attributable to NH2 and NH radicals were observed, together with a continuous absorption, whose intensity increases in the u.v., which was suggested to be produced by N2H3.67 Hydrazine decomposition has been studied in the... 

Diphenylaminyl radicals, In, produced in tetraphenyl-hydrazine decomposition, react with the formation of diphenyl amine and oligomeric semidienes. Diphenyl amine is formed in the reaction of In with labile dimers, AmAm, with iminoquinone structure. The rate constant of Am recombination measured by flash photolysis technique (FTP) was found to be 1.8x10 l.mole s (cyclohexane, 293°K). The combination of In and ROj was studied by FPT using monitoring at two different avelengt s. It runs with the rate constant of 6x10 l.mole s (cyclohexane,... 

Hydrazine decomposition Ir/f-CNF 30%Ir/f-CNF presents far better performances than a commercial Ir/AEOs catalyst (Shell 405). 355,356... 

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