Vapor Pressure of Curved Surfaces

During sintering process, there is an important matter transport through evaporation and condensation. The rate of the transport is proportional to the equilibrium vapor pressure over the surface, which has been related to the value of Ca fiy beneath the surface. If a number diVa of atoms is taken away from the vapor and added to the surface, with a corresponding decrease in the number of vacancies beneath the surface. The free energy change due to this virtual operation must be zero, so that there is  

This is called the Kelvin equation. If yswKTl kT, it becomes  

This equation means that, the vapor pressure of a given system under isothermal conditions increases with increasing curvature of the surface. 

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Table 4.1 Relative vapor pressures of curved surfaces in equilibrium at 25°C, for water drops in air and air bubbles in water...

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