Pilling and 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. 

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 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 A, cm. 444) and Dunn (unpublished, see also Pilling and Bedworth, Jour.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... 

The Pilling and Bedworth ratio [11] compares the volume of oxide produced to the volume of metal consumed. It is an important parameter in predicting the oxide protection properties. In their model, PiUing and Bedworth [11] assumed a mechanism in which the oxide growth occurs at the metal-oxide interface by the difHision of oxygen through the oxide. If the volume of the oxide layer is smaller than the volume lost by the metal, then the oxide layer will be subjected to high tensile stresses. On the other hand, if the volume... 

Pilling and Bedworth ratios closest to unity are the most suited for protection, while those that deviate from unity would suggest an oxide layer that wiU crack or do not adhere effectively. The PB ratio is defined as ... 

The parabolic rate law, which is named after Tammann [48] and Pilling and Bedworth [11 ], is by... 

The mechanism and the theories of linear oxidation must be discussed with reference to specific examples. This will shortly be done, but it will be helpful to return first of all to the theories of Pilling and Bedworth. 

High-temperature corrosion is a form of corrosion that does not require the presence of a liquid electrolyte. Sometimes, this type of damage is called dry corrosion or scaling. The first quantitative approach to oxidation behavior was made in the early 1920s with the postulation of the parabolic rate theory of oxidation by Tanunaim and, independently, by Pilling and Bedworth. 

The simplest is obviously the linear law, which was found for the first time in experiments of metal oxidations by oxygen gas at high temperature on massive samples in the form of thin plates and made it possible to neglect the attack of the faces with lower areas of the plates. It was introduced by Pilling and Bedworth [PIL23]. 

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