2887.     ROGINSKIĬ, S. Z., AND TSELLINSKAYA, T. F.  Experimental Investigation of the Role of Supersaturation in the Preparation of Catalysts.  Acta physicochim, U.R.S.S., vol. 19, 1944, pp. 225-247 (in English); Jour. Phys. Chem. (U.S.S.R.), vol. 18, 1944, p. 477-492; Chem. Abs., vol. 39, 1945, p. 2447.

        Pyrolytic decomposition of NiCO3 is a centripetal topochemical reaction.  The decomposition was affected in an apparatus in which the CO2 pressure (pT) was controlled by freezing out CO2 in a cryostat maintained at various temperatures.  the supersaturation (A) of the genetic reaction is defined as A=RT in (pT/pTí), in which pT is the equilibrium pressure of CO2 at the surface of the solid.  The decomposition of NiCO3 is autocatalytic; the reaction velocity increases with increasing supersaturation.  This decomposition is extremely rapid at CO2 partial pressures of 10-4 to 10-2 mm. of Hg; near the equilibrium pressure the decomposition is slow.  The rate constant varies exponently with the temperature.  The apparent activation energies for the decomposition are 11,000 cal. per mol. for Δ F=constant, 17,000 for pco2=3X10-3 mm., 15,000 for p=2 mm., and 11,000 for p=10 mm.  Up to its maximum, the reaction velocity obeys an approximate quadratic law; hence the process involves primarily the development of formerly existing initiation centers, as is true for the decomposition of Ni formate (abs. 703). The values of the reciprocals of the times needed to attain a definite degree of decomposition increase almost linearly with the supersaturation.  A plot of velocity versus % of decomposition shows a maximum for each temperature and CO2 pressure; this maximum is at 5-10% decomposition and is only slightly dependent on the experimental conditions.  The H2O content of the sample of NiCO3 has a peculiar, and as yet unexplained, effect on the kinetics of the decomposition.

        ROĬTER, V. A.  See abs. 1164, 1165.