[en] The problem of the dynamics of condensation of potassium additive in a porous insulator of an MHD generator under the conditions on a temperature gradient is studied. The temporal evolution of the process in described with the help of an equation determining the rate of change of porosity as a result of condensation and the equation of motion on the condensation boundary. The obtained solutions are used to estimate the characteristics condensation and evaporation times of the additive and to calculate the change in the resistance of the insulating gap