Metal Pilling-Bedworth Ratio Li 0.57 Ce 1.16 Ta 2.33 W 3.40
Pilling-Bedworth Ratio for Metal Oxidation Protection
The Pilling-Bedworth (PB) ratio helps predict how effectively a metal's oxide scale protects it during high-temperature oxidation. It compares the volume of the oxide formed to the volume of the original metal.
- A PB ratio below 1 leads to a porous oxide layer, offering poor protection.
- A PB ratio near 1 (typically 1 to 2) results in a dense, adherent oxide scale, providing excellent protection.
- A PB ratio above 1 can form a thick oxide layer, but it might be under stress, potentially causing cracks and reducing its protective effectiveness compared to ratios closer to 1.
Oxidation Data
| Metal | Pilling-Bedworth Ratio |
|---|---|
| Li | 0.57 |
| Ce | 1.16 |
| Ta | 2.33 |
| W | 3.40 |
Analysis of Metal Protection
Evaluating the PB ratios:
- Li (0.57): Ratio < 1 indicates poor protection due to a porous oxide scale.
- Ce (1.16): Ratio is close to 1. This suggests the formation of a dense, adherent oxide scale, offering superior protection.
- Ta (2.33): Ratio > 1 suggests a stressed oxide scale, potentially offering some protection but less ideal than Ce.
- W (3.40): Ratio significantly > 1 indicates a thick, stressed oxide scale, likely less protective than Ce's scale.
Most Protected Metal
Based solely on the Pilling-Bedworth ratio, Ce is the most protected metal against high-temperature oxidation because its ratio is closest to 1, favouring the formation of a dense and adherent protective oxide layer.
Important Questions from Ratios
Both the numerator and the denominator of $\frac{3}{4}$ are increased by a positive integer, x, and those of $\frac{15}{17}$ are decreased by the same integer. This operation results in the same value for both the fractions.
What is the value of x?
- Two rods P and Q of uniform circular cross section are made of same material and are subjected to identical uniaxial tensile load. The length of rod P is twice the length of rod Q and the diameter of rod P is also twice the diameter of rod Q. The ratio of elastic strain energy stored in rod P to that stored in rod Q is
- Two solid shafts P and Q made of same material transmit equal torque. Shaft P has a uniform circular cross section of area $A$ and shaft Q has a uniform circular cross section of area $4A$. If the maximum torsional shear stress developed in shaft P is 160 MPa, the maximum torsional shear stress developed (in MPa) in shaft Q is ________
