Pure oxygen theory

Chapman (1930a, b) showed successfully that the characteristics of the height of the ozone layer and ozone density in the earth s atmosphere can be described by assuming only oxygen is present as a reactive species in the atmosphere, and this reaction scheme is called pure oxygen theory or Chapman mechanism. Photolysis of O2 occurs by the solar radiation of wavelength shorter than 242 nm (see Sect. 4.3.1). Only the photolytic process. 

The first point is due to the incomplete treatment of the pure oxygen theory, ignoring trace constituents other than O, O2 and O3, which will be described in detail below. The second point is due to the transport of ozone within the stratosphere and into the troposphere. Photochemical lifetime of stratospheric O3 is the order of 10 min at the altitude of 45 km and the diurnal cycle is observed. On the... 

Autothermal reforming is a combination of SR and POX, which in theory can be totally heat balanced. When air is used instead of pure oxygen, the reaction can be represented by the following equation ... 

The work was of immense importance to the field, but let s note some interesting little flaws that prove that even Lavoisier was not infallible. First, he names vital air as oxygene, which means acid maker. This was reasonable to Lavoisier since combustion of carbon, sulfur, and phosphorus in pure oxygen each produced acids. His oxygen theory of acids was well accepted. This included... 

The only important chlorate is chlorate of potash, the theory of the production of which has been already explained (see p. 77). It forms tabular crystals, of a pearly lustre. It is chiefly used as a convenient source of very pure oxygen gas, and as an oxidising agent. Its formula is KO, Cl 0, or K, CIO,. 

The nature of the mobile ionic species was questionable for a long period of time. For passive Al, Verwey [47] assumed in 1935 that exclusive transport of Al-cations occurs in a fixed oxygen matrix. The idea of mobile cations dominated the oxide formation theories for the next 30 years. It seemed to be reasonable, as the volumes of cations are much smaller than -anions (e.g. by a factor of 20 for AP+), even if the experimental results indicated a combined transport. Marker experiments in the sixties proved cation-transference numbers in the range from 0.3 to 0.7 for many systems (Al, Be, Nb, Ta, Ti, V, W) coming closer to 0.5 with increasing current density, that is, cations and anions move in fact simultaneously (Table 1). This indicates that effects of charge distribution become more important than individual ion properties like size or polarizability [25]. Exceptions are the crystalline oxides on Hf and Zr, which are pure oxygen conductors. 

Two facts established by these experiments impressed on me the conviction that Berthelot might have found the true theory of explosions first the close coincidence between the rates of explosion of hydrogen (both with oxygen and nitrous oxide) and the calculated mean velocities of the products of combustion and, secondly, the great discordance between the found and calculated rates for carbonic oxide with both oxygen and nitrous oxide, for I had previously discovered that pure carbon monoxide cannot be exploded either with pure oxygen or pure nitrous oxide/... 

Determination of the water composition became a major advance of the oxygen theory. In 1781 H. Cavendish observed that inflammable air upon combustion is transformed almost completely (together with dephlogisticated air) into pure water. But he published his results only in 1784. Lavoisier knew about these experiments and, after repeating them, he concluded that water is not a simple substance but a mixture of inflammable and invigorating air. Since the conclusion was made in 1783, Lavoisier is held by many to be the first one to have established the composition of water. In reality, however, H. Cavendish was the first. Determination of the composition of water made it possible to get an insight into the nature of hydrogen. 

An important aspect of any theory of the oxidation of a pure metal is that it enables us to see how the protective power of the oxide layer can be altered by the introduction of alloying constituents into the metal. According to Wagner s theory, the parabolic rate constant for the system Ni/NiO for example depends upon the concentration of cation vacancies in the oxide in equilibrium with oxygen gas. If this concentration can be reduced, the oxidation rate is reduced. Now this can be done if cations of lower valency than Ni can be got into the oxide (Fig. 1.77). Suppose, for example, that a little Li is added to the Ni. Each Li ion which replaces Ni is a negative... 

The complex Sn(OH)+ given here is purely formal since a further reaction could result in Sn(OH)2 or in the dehydrated form SnO. What shall be emphasized is that the theories explaining the catalytic effect of tin through oxygen-containing species can be justified by taking into account the chemical properties of Sn(II). 

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