Ramachandran, M. (1987) Studies on diffusion controlled periodic phenomena of precipitation. PhD thesis, Madurai-Kamaraj University.

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Abstract

After exploring a large number of sparingly soluble systems, the author obtained good rings with the following materials in the agar agar gel a) Lead silicate, b) silver molybdate, c) thorium oxinate, d) cadmium oxinate, e) cupric chromate and f) thorium carbonate. Out of these systems, Liesegang rings of cupric chromate are found to be reported in the past literature. Since no quantitative studies were made on this system and this system was found to be one of the best, from the view point of possessing detailed macro and micro structures, it has been purposely included in this thesis to reflect more light on the mechanism of formation of Liesegang rings. Out of six systems, four systems were of white colour and two systems were of greenish yellow and scarlet red cum dark yellow colour respectively. White rings system of lead silicate and thorium carbonate were very similar to one another in appearance and in their large number, produced in the test tubes. These rings were of thin discs nature separated by medium spacing, just somewhat micro spicing reported in some systems. Contrary to these two systems, thorium and cadmium oxinate produced a few number somewhat thicker rings separated by large void spaces. Cupric chromate system produced one category of system with M/20 concentration of internal electrolyte, but largely different in the remaining lower concentrations of internal electrolyte. Rings obtained with M/20 internal electrolyte had all the combinations of the three types of structures, viz. Revert type alternate coloured band followed by clear spaces and in between these precipitate rings occurred the micro structure fringes. In these studies the distances between the consecutive rings were measured with the help of a cathetometer. The data obtained are processed as per equation Log (Xn – Xn-1) = A + α Xn And plotted in various figures. These figures were used for the verification of the validity of logarithmic equation and thus the indirectly the validity of Mathur’s Damped Harmonic Wave Diffusion Theory. Different curves drawn for different concentrations of external and internal electrolytes for each system depicted the influence of the concentrations on the rings spacing obeying the following relationship. (Xn – Xn-1) = [P(S/CoC’o)] eαxn In some of the systems like lead silicate and thorium carbonate the number of rings was fairly large and uniformly distributed. Hence, in these two cases the ring points were falling more precisely on straight line curves than in some other systems in which the number of rings produced were less and the disturbance effect of temperature etc., sometime is more pronounced as in the case of silver molybdate. In some systems which produced broad rings separated by large void spaces such as the one thorium oxinate, it could be observed that even the thickness of the precipitate rings changes from ring to ring and also from test tube to test tube for the nth ring with respect to the concentration of the electrolyte. Data on thickness of the rings are also recorded in this particular case. The author investigated qualitatively and quantitatively in detail six different systems of periodic precipitations and verified the validity of Wave Harmonic Diffusion Theory of Mathur for Liesegang Rings are found that the data obtained on these few systems studied for under the present research work fits in the theory and the equations derived by Mathur

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Periodic phenomena
Subjects:	Electrodics and Electrocatalysis
Divisions:	UNSPECIFIED
Depositing User:	Dr. N Meyyappan
Date Deposited:	13 Jun 2012 04:56
Last Modified:	13 Jun 2012 04:56
URI:	http://cecri.csircentral.net/id/eprint/2828

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