Abstract
Crystal growth is a typical irreversible process due to the mutual interference of material and heat flows, which are caused by their gradients. In this report, how to measure the gradients is discussed from a technical point of view. The concentration gradient along the c axis of Rochelle salt crystal, growing in a two dimensional cell from its aqueous solution, was studied by the moire fringe method, because the tilting angle of the fringes was strictly proportional to the gradient of the refractive index along the c axis. The growth rates are well proportional linearly to the normal component of the concentration gradient at every point on the growing faces. The diffusion constants of the growth unit were obtained as a function of temperature between 12° and 40℃. The constants at 40°, 30°, 20° and 12℃ are respectively 2.85, 2.19, 1.95 and 1.70 × 10^<-6>cm^2/sec and their activation energy is 0.136eV or 3.14kcal/mol. The temperature gradient along the c axis of Rochelle salt was measured with accuracy of 0.005℃ in a two dimensional cell to eliminate thermal convection current in the cell. The growth rate was also linearly proportional to the temperature gradient at every growing interface. The thermal conductivity of saturated Rochelle salt solution was obtained by comparator method and by hot-wire method.
