Pilling-Bedworth ratio

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In chemistry and materials science, the Pilling-Bedworth ratio (PBV, or PBR from Pilling-Bedworth ratio ) is the ratio of the molar volumes of a metallic element and its oxide. The PBV can be used to estimate whether a metal is permanently resistant to dry air through the formation of a protective oxide layer ( passivation ). Since the oxide formation sometimes takes place in several stages and mixed oxides can be formed in alloys, the PBV does not allow any reliable statements. This applies in particular to atmospheric corrosion, which almost always occurs via hydroxides due to the ubiquitous water.


M denotes the molar mass , ρ the density , V the (molar) volume and n the number of metal atoms in the empirical formula of the oxide.


The following relationship can be shown on the basis of measurements:

Schematic representation of the oxide structure and the Pilling-Bedworth ratio
PBV <1: tearing of the oxide layer, no protective effect (example magnesium oxide on magnesium )
PBV> 2: flaking of the oxide layer, no protective effect (example rust on iron )
PBV = 1 ... 2: Formation of a permanent, passivating oxide layer (examples aluminum , titanium , chrome layer on steel)

Numerical values

metal Metal oxide PBV
magnesium Magnesium oxide 0.81
aluminum Alumina 1.28
Zirconium Zirconium (IV) oxide 1.56
nickel Nickel (II) oxide 1.65
iron Iron (II) oxide 1.7
titanium Titanium (IV) oxide 1.73
chrome Chromium (III) oxide 2.07
iron Iron (II, III) oxide 2.10
iron Iron (III) oxide 2.14
iron Iron (III) oxide hydroxide ( rust ) 3.6
Silicon Silicon dioxide 2.15
Tantalum Tantalum (V) oxide 2.47
Vanadium Vanadium (V) oxide 3.25

Web links


  • Ralf Bürgel: Handbook high temperature material technology basics. Page 272ff. ISBN 3528231076
  • NB Pilling, RE Bedworth: The Oxidation of Metals at high Temperatures. J. Inst. Met 29 (1923), pp. 529-591.
  • ND Tomashov: Theory of Corrosion and Protection of Metals (The Science of Corrosion). Translated and edited by BH Tyrtell, I. Geld, HS Preiser, New York (1965).


  1. ^ A b "ASM Handbook Vol.13 Corrosion", ASM International, 1987.