Bedworth

Since the paper by Pilling and Bedworth in 1923 much has been written about the mechanism and laws of growth of oxides on metals. These studies have greatly assisted the understanding of high-temperature oxidation, and the mathematical rate laws deduced in some cases make possible useful quantitative predictions. With alloy steels the oxide scales have a complex structure chromium steels owe much of their oxidation resistance to the presence of chromium oxide in the inner scale layer. Other elements can act in the same way, but it is their chromium content which in the main establishes the oxidation resistance of most heat-resisting steels. 

Pilling-Bedworth Ratio the ratio of the volume of an oxide film on a metal to the volume of metal used to form that oxide. 

Formation of texture of crystalline systems differs due to the existence of phase transitions. Very important in this case is the parameter b= Vb, offered by Pilling and Bedworth in 1923 [45], This parameter is equal to the ratio of the volume, of product solid phase to the volume,... 

The ratio of the oxide formed to the metal consumed is called the Piling and Bedworth number. When the number is over 1, the metal rusts. Aluminum and magnesium are the best examples of metals that do not rust because a protective oxide coat forms that is, they have a Piling to Bedworth number of 1. Scratch an aluminum ladder and notice a bright fissure forms and quickly self-coats. The heat release in the sealing aluminum oxide is dissipated to the ladder structure. 

Pilling-Bedworth ratio of 1 96, anatase phase films can show cracks and fissures with, consequendy, a loss of mechanical stability, however a hydrogen reduction treatment above 600°C leads to phase transition from anatase (101) to rutile (110) [43] with XRD detecting TiH2 upon prolonged hydrogen treatment of titania. As shown in Fig. 4.4, introduction of vanadium increases the intensity of the anatase Ti02 peak above 700°C disappearance of the vanadium (001) peak and the simultaneous appearance of the rutile (110) peak are observed, but anatase continues to dominate even after heat treatment at 800° C. A sharp vanadium (001) peak is observed for heat treatments carried out in air, while no vanadium peak has been seen in the case of heat treatment at 600°C in presence of Ar/H2. 

The surface oxidation of a metal such as copper is accompanied by the growth of an oxide layer, the thickness of which may be measured by the method of colour interference when due allowance is made for the refractive index of the oxide formed, or by the decrease in electrical resistance of a thin wire or tube of the metal as oxidation ensues. Investigations have been made on the rate of such oxidations by Tammann (Zeit.f anorg. GJiem. cxi. 78 cxxiii. 196 cxxiv. 196), Hinshelwood (Proc. Mog. Soc. A, cii. 318), Palmer Proo. Roy. Soc. A, cm. 444) and Dunn (unpublished, see also Pilling and Bedworth, Jour. Inst. Metals, xxix. 629, 1923). It is found that the rate of increase in thickness of the oxide film oc) obeys under ideal conditions the ordinary diffusion law or CG = kt. ... 

Oxide films are often protective in the sense of hindering further oxidation, but this is not always the case. Pilling and Bedworth made an early attempt (1923) to rationalize the protective behavior of oxide films on the basis of the volume occupied by the oxide relative to the volume of metal from which it was formed. If the molar volume V° of oxide per mole of metal is less than the molar volume of the metal, the scale will be under tension as it forms and will tend to crack and so be nonprotective. An... 

However, the Pilling-Bedworth approach is of limited applicability, as is shown by the behavior of copper ... 

On which of the following metals would the oxide film be expected to be protective, according to the Pilling Bedworth principle ... 

For example, see Zweifel Steele Tetrahedron Lett. 1966,6021 Cainelli Bcrtini Grassclli Zubiani Tetrahedron Lett. 1967,1581 Takai Hoita Oshima Nozaki Bull. Chem. Soc. Jpn. 1980,5J, 1698 Knochcl Normam Tetrahedron Lett. 1986, 27, 1039 Barluenga Fernandcz-Sim6n Concell6n Yus J. Chem. Soc., Chem. Commun. 1986, 1665 Okazoc Takai Utimoio J. Am. Chem. Soc. 1987, 109, 951 Piotrowski Malpass Boleslawski Eisch J. Org. Chem. 1988, 5. , 2829 Tour Bedworth Wu Tetrahedron Lett. 1989,30, 3927 Lombardo Org. Synth. 65, 81. 

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