What is meant by Pilling-Bedworth ratio?
The Pilling-Bedworth ratio (P-B ratio), in terms of metal corrosion, is the ratio of elementary cell volume of metal oxide to the elementary cell volume of the equivalent metal where the oxide has been created.
What is the Pilling-Bedworth ratio of MgO?
The smaller thickness of the oxides film for the Mg alloy can be explained by taking into account the Pilling-Bedworth (PB) ratio. For pure MgO, the PB ratio is inferior to 1 (0.8 [1,2,57]) indicating that the oxides film cannot completely covers the metal surface.
How you can use Pilling-Bedworth rule to predict nature of oxide films explain with suitable example?
Pilling-Bedworth rule: According to it “an oxide is protective or non-porous, if the volume of the oxide is atleast as great as the volume of the metal from which it is formed”. Thus, alkali and alkaline earth metals (like Li, K, Na, Mg) form oxides of volume less than the volume of metals.
What is the significance of Pilling-Bedworth rule?
The ratio of the volume of the oxide formed to the volume of the metal consumed is called the Pilling-Bedworth rule. According to it, if the volume of the oxide layer is greater than the volume of the metal, the oxide layer is protective and non-porous.
Which of the following oxide film is protective?
Answer: zinc oxide and aluminium oxide layers are most protective against corrosion because they are amphoteric oxides i.e. they do not react with acids as well as bases.
Which metal oxide layer is non porous and protective?
) Stable – A stable layer of metal oxide is formed which is impervious and this protects the metal from further corrosion. Eg :- Al, Sn. b) Unstable- The oxide layer decomposes back to metal and oxygen.
How the specific volume ratio is related to the rate of corrosion?
Smaller the grain size and area under stress, greater will be the corrosion. volume ratio, lesser will be the oxidation corrosion. Eg: Specific volume ratio of Ni, Cr, W are 1.6, 2.0. Oxidation corrosion is least is W.
How is Pilling Bedworth ratio related to the protective capacity of an oxide layer?
The oxide layer would be unprotective if the ratio is less than unity because the film that forms on the metal surface is porous and/or cracked. Conversely, the metals with the ratio higher than 1 tend to be protective because they form an effective barrier that prevents the gas from further oxidizing the metal.
What is the value of the Pilling and Bedworth ratio of tungsten?
The Pilling–Bedworth ratio (P–B ratio), in corrosion of metals, is the ratio of the volume of the elementary cell of a metal oxide to the volume of the elementary cell of the corresponding metal (from which the oxide is created)….Values.
| Metal | Tungsten |
|---|---|
| Metal oxide | Tungsten(VI) oxide |
| Formula | WO3 |
| RPB | 3.3 |
Which oxide film is more productive?
Which oxide films is non protective?
Explanation: Porous oxide films or scales are non-protective as there is free access of oxygen to the metal surface.
Which oxide is more protective?
What is the Pilling Bedworth ratio ( p-b ratio )?
The Pilling-Bedworth ratio (P-B ratio), in terms of metal corrosion, is the ratio of elementary cell volume of metal oxide to the elementary cell volume of the equivalent metal where the oxide has been created.
How is the metal oxide P-B ratio defined?
In the paper, these two linked the metal oxide porosity to specific density 1. The metal oxide P-B ratio can be best described as the ratio of the metal oxide volume produced by the oxygen and metal reaction to the consumed value of metal. This can be further defined in the equation:
When did Pilling and Bedworth propose the classification of metals?
N.B. Pilling and R.E. Bedworth suggested in 1923 that metals can be classed into two categories: those that form protective oxides, and those that cannot. They ascribed the protectiveness of the oxide to the volume the oxide takes in comparison to the volume of the metal used to produce this oxide in a corrosion process in dry air.
Which is the correct equation for the p-b ratio?
The metal oxide P-B ratio can be best described as the ratio of the metal oxide volume produced by the oxygen and metal reaction to the consumed value of metal. This can be further defined in the equation: RPB = Voxide/Vmetal = (Moxide × Pmetal)/(n × Mmetal × Poxide)