On the kinetics of crystallization of zinc oxalate (III). Effect of supersaturation

Abstract

The crystallization kinetics of zinc oxalate a t different supersaturations was studied by a turbidimetry method. It was found that the curves optically registered by this method can be quantitatively characterized a t initial supersaturations lower than 4.51. The graphically differentiated curves showed that the maximum crystallization rate could be fitted by equation Vmax z K ( C -Co)2, where C and C, are the initial and the equilibrium concentrations, respectively. The crystallization rates after the maximum follow the same equation depending on the absolute supersaturation a t a given moment. A linear dependence between the rate constants and the supersaturations a t the maximum crystallization rates is found, This dependence is determined by the inversely proportional correlation of the distances between the steps of growth with the supersaturation given by equation (8). The activation growth energy E* = 7.1 kcal/mole is determined from the straight line obtained. Die Kristallisationskinetik von Zinkoxalat bei verschiedenen Ubersattigungen wirdanhand einer turbidimetrisehen Methode untersucht. Es wird festgestellt, da8 die nach dieser Methode optisch registrierten Kurven bei Ausgangsiibersattigungen unter 4,51 quantitativ charakterisiert werden konnen. Die graphisch differenzierten Kurven zeigen, daB fur die maximale Kristallisationsgeschwindigkeit die Gleichung Vmax = K ( C -C,)2 giiltig ist, in der C und C, die Ausgangs-bzw. Gleichgewichtskonzentration bezeichnen. Nach dem Maximum folgen die Kristallisationsgeschwindigkeiten derselben Gleichung in Abhiingigkeit von der absoluten Ubersattigung in einem bestimmten Augenblick. Zwischen den Geschwindigkeitskonstanten und den Ubersattigungen bei den maximalen Kristallisationsgeschwindigkeiten besteht eine lineare Abhiingigkeit, die durch das umgekehrt proportionale Verhiiltnis der Abstiinde zwischen den Wachstumsstufen zu der von Gleichung (8) angegebenen Ubersiittigung bestimmt wird. Die Aktivierungsenergic des Kristallwachstums E * = 7 , l kcal/mol wird aus der erhaltenen Gerade bestimmt,

Reverse Micelle Based Growth of Zincophosphate Sodalite: Examination of Crystal Growth

“…12 Examples include ZnC 2 O 4 ‚2H 2 O, whose crystals have different habits in different supersaturation ranges. 14 In the case of CaHPO 4 , with increasing supersaturation, rhombohedral, intergrown, and twinned crystals of CaHPO 4 ‚2H 2 O and ultimately, spherical agglomerates of CaHPO 4 are formed. 15 To the best of our knowledge, the influence of supersaturation on growth of microporous frameworks has not been systematically examined.…”

Investigation of nucleation and crystal growth kinetics of nickel manganese oxalates

“…Moreover, the comparison of these results with previously published nucleation rates for different oxalate salts is ambiguous. Very few results concerning the particle number concentration, the critical nucleus or the induction period of oxalates (Pb(C 2 O 4 ), Zn(C 2 O 4 ),y) have been published [1,3]; and no nucleation rate expressions presented.…”

“…A literature review about the crystal growth of others simple oxalates shows that barium, cadmium [15], yttrium [16], zinc [3], lead [17] and magnesium [18] oxalates have been studied. However, the comparison of results is ambiguous.…”

“…A better control of the precipitation process should help produce the powder quality desired for ceramic processing. Very few kinetic data concerning the particle number concentration, the critical nucleus, the induction period and the precipitation rate of oxalate systems have been published [1,3]. No previous data have been reported concerning the nucleation and the crystal growth rates of Ni-Mn mixed oxalates.…”