Diffusivity of Cadmium Vapor in Air

Cadmium vapor is a toxic substance whose diffusivity in air is not readily available in the literature. It is desired to calculate its diffusivity at its boiling point of 1038 K and a pressure of 1 atm. Because an empirical atomic volume is not available, we use the reported value for its liquid volume of 14 cm / mol for an atomic weight of 112.4. We obtain, using Equation 3.2  

Atomic and Molecular Volume Contributions for Diffusivity Calculations 

A data point for the diffusivity of Cd in N2 at 273 K is available for comparison. Its value is 0.15 crxP/s and we obtain, by applying a temperature correction in line with Equation 3.2, 

This is in good agreement with the calculated value of 1.6 cm /s. Comments  

Some remarks are in order regarding the magnitude of gas phase diffusivi-ties. We note from Table 3.1 that at 25dC and a pressure of 1 atm, most diffusivities cluster arotmd a value of 0.1 cm /s. This includes metal vapors, as well as medium-sized organic molecules such as DDT and the PCBs. The reason for this lies in the relatively weak dependence of on molar volume 

---