Oxidation process, phenomena

While carburisation itself is not a normal corrosion process, in that there is no metal wastage, absorption and diffusion of carbon can lead to significant changes in the mechanical properties of the affected material and in particular to marked embrittlement. Furthermore, initial carburisation can produce an acceleration of the normal oxidation process, a phenomenon that is notable in nickel-chromium alloys. 

In 1961, Ashby reported the weak light emission produced from several polymers such as nylon, when heated [90], The phenomenon was termed oxylum-inescence because it was caused by oxidative processes and required the presence... 

In real systems (hydrocarbon-02-catalyst), various oxidation products, such as alcohols, aldehydes, ketones, bifunctional compounds, are formed in the course of oxidation. Many of them readily react with ion-oxidants in oxidative reactions. Therefore, radicals are generated via several routes in the developed oxidative process, and the ratio of rates of these processes changes with the development of the process [5], The products of hydrocarbon oxidation interact with the catalyst and change the ligand sphere around the transition metal ion. This phenomenon was studied for the decomposition of sec-decyl hydroperoxide to free radicals catalyzed by cupric stearate in the presence of alcohol, ketone, and carbon acid [70-74], The addition of all these compounds was found to lower the effective rate constant of catalytic hydroperoxide decomposition. The experimental data are in agreement with the following scheme of the parallel equilibrium reactions with the formation of Cu-hydroperoxide complexes with a lower activity. 

As follows from the data shown, the phenomenon of synchronous reaction coherence promotes a growth of interest in selective oxidation processes with hydrogen peroxide. This direction becomes a prime importance for modem investigations. 

It has already been mentioned that the excess potential phenomenon occurs also with the oxidation phenomena. Thus it is possible to conyert p-nitrotoluene into p-nitrobenzoic acid at lead-peroxide anodes, while at platinum anodes only the alcohol is formed. It still seems inexplicable how this peculiar action of the anode material takes place. The simplest yet sufficient. explanation is to assume that the anode is capable of influencing catalytically the oxidation process as well as the formation of molecular oxygen. If the first process is accelerated and the second retarded, we obtain the excess potential by which the evolution of oxygen occurs only at a higher potential. Inversely, the oxygen and ozone formation cart be made reversible, and the oxidizing action decreased. 

In view of this, one may ask whether in certain cases, the determination of the initiation rate (and as a consequence, of the rate constants of propagation and of termination) by the method used by Cooper and Melville was not in fact disturbed by this phenomenon of selfinhibition. In point of fact, this method is based on the investigation of the variation of the rate of oxidation as a function of time in the presence of an inhibitor (hydroquinoiie) added at the start. If, then, the reaction is self-inhibited, the experiment gives nothing but the total variation of its rate resulting from the competition between the consumption of the inhibitor added at the start and the appearance of an autoinhibitor during the course of the oxidation process. 

An adiabatic method represents the most adequate technique for determining the relative tendencies of certain coals to heat spontaneously since it simulates most closely the real phenomenon. Conceivably, a field system would be similar to the adiabatic system but with appropriate modifications to hasten the oxidation process and increase the effluent gas concentrations within a reasonable test period. This could involve a more versatile system which would allow either the study of self-heating rates, similar to a method used by Guney (10) or which may be used for adiabatic calculations of a liability index through incorporation of a constant heat input. In the latter case, the heat might be supplied exclusively from the oxidizing air stream. 

The main conclusion that could be derived from the above analysis is the ascertaining of the extraordinary complexity of the system we attempt to model. Even staying at the level of micro-chemical modeling we must accept as a fact the fundamental difference between the phenomenon and its model and, as a result, the impossibility to develop the description that reflects the reality in all its manifestations. A possible solution of the modeling problem, as applied to light alkane oxidative processing, can be found on the way of stepwise and successive execution of the basic principles stated below. 

Sillen (1966) assumes that it is not impossible that some marine biological process rapidly transforms the nitrate ions to N2. This phenomenon would use the oxygen of nitrate ions for some oxidation process in spite of the presence of 02. However, he also states, that such organisms have not been discovered. This means that the explanation of the anomalous high nitrogen content of our atmosphere remains an open question. Nevertheless we cannot exclude the possibility that this high... 

The superior photocatalytic activity of P25 makes it as a standard reference in photocatalytic oxidation processes. The mechanism of superior activity of P25 is still a controversy among the photocatalytic community [166]. When scientists realize that CO2 can also reduce by the photocatalytic phenomenon, the followers used P25 as the reference material, even though it s not a champion photocatalyst for CO2 reduction. In a process like CO2 reduction, the product yield depends on many factors interde-pendently as compared to the normal photocatalytic oxidation processes (See Table 6) [167]. The electron as well as proton transfer plays a crucial role in the thermodynamic uphill processes such as water or carbon dioxide splitting into valuable fuels that means the reaction led not alone by light irradiation. 

PEG can also contain peroxides which can initiate over time, the formation of degradants via an oxidation process. Several publications have dealt with this phenomenon. ... 

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