LIESEGANG RING-TYPE STRUCTURES AND BIFURCATION IN SOLID-VAPOR AND LIQUID-PHASE REACTIONS BETWEEN COBALT NITRATE AND AMMONIUM HYDROXIDE

New results on the reaction between (i) cobalt nitrate (A) and ammoniu m hydroxide (B) in gelatin and (ii) cobalt nitrate (solid) and ammonia vapor are reported. Spatial bifurcation of the blue wave into a numbe r of normal Liesegang type bands is observed in a one-dimensional tube in gel media depending on the concentration of electrolytes and gel, Similar bifurcation is also observed when the reaction was carried out in gel media between two microslides, Results show that K-sp (solubil ity product), as envisaged in recent theories, plays a significant rol e in initiating bifurcation depending on K, the magnitude of the produ ct of concentration of A and B, which determines the degree of supersa turation. The value of K at the instant of bifurcation, when (i) conce ntration of Co(NO3)(2) is alone changed or when (ii) concentration of NH4OH alone is changed, is similar when uncertainties are taken into a ccount. The bifurcation behavior when gel concentration is changed sug gests that in case of high gel concentration pore size is affected, th ereby influencing the diffusion of ions. The results satisfy the spaci ng law. The results further satisfy the relation d(2) = m't + C' at an y time t, where d is the distance between the lower front of the preci pitate and the junction and m' and C' are constants, thereby suggestin g that the role of diffusion is vital, as envisaged in various theorie s of the phenomenon. A colored banded structure separated by air gaps (vacant spaces) is formed when the solid cobalt nitrate reads with amm onia vapor, This type of behavior has not been reported earlier. Initi ally, a single band is formed in a one-dimensional experiment, but in the course of time (similar to 1 month) several bands are formed simul taneously, The diffusion kinetics in the initial stages of the solid-v apor reaction has been studied in a one-dimensional tube. The data obe y the relation xi(2) = kt, where xi is the thickness of the product la yer at any time t and k is some constant. Similar studies were made on microslides which showed that during the reaction, a colored product is formed which undergoes change in the sequence pink --> blue --> bro wn. Results in the one-dimensional case support recent theories which postulate nucleation followed by aggregation. (C) 1997 Academic Press.