Pilling-Bedworth 1923 ratio PBR = V_oxide / V_metal: PBR < 1 (Mg, Ca) porous non-protective; 1 < PBR < 2 (Al, Cr, Si) protective adherent; PBR > 2 (Fe-rust) compressive-stress + spallation; basis of high-T-corrosion design.
Pilling-Bedworth 1923 ratio PBR = V_oxide / V_metal: PBR < 1 (Mg, Ca) porous non-protective; 1 < PBR < 2 (Al, Cr, Si) protective adherent; PBR > 2 (Fe-rust) compressive-stress + spallation; basis of high-T-corrosion design.