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3 Bulletin of the Polish Academy of Sciences. Chemistry

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Thermal decomposition of Sn(II), Pb(II), Cd(II) and Hg(II) cross-linked metal-alginate complexes

El-Gahami M. A., Khairou K. S., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

2003

Vol. 51, No. 2

105-113

The thermal decomposition of tin(II), lead(II), cadmium(II) and mercury(II) metal-alginate complexes has been studied using thermogravimetry (TG) and differential thermogravimetry (DTG) measurements. The TG curves showed three stages of weight loss, the DTG curves indicated the presence of a series of thermal stages associated with the TG curves. Dehydration of the coordinated water molecules occurred in the first stage, followed by decomposition of the dehydrated complexes in the next two stages. Thermal stability of these complexes in terms of the strength of chelation and coordination geometry is discussed.

Diffusion controlled relaxation time and acceleration of velocity of sol-gel transformation for cross-linked metal alginate ionotropic gel comlexes

Khairou K. S., Al-Gethami W. M., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

2003

Vol. 51, No. 3-4

207-220

The rate of gel-growth for spherical ionotropic metal alginate gel droplets has been studied. Experimental observations have shown that the relaxation time of the metal alginate ionotropic gel complexes of the droplet shapes decreased in the order Hg > Cd > Sn > Pb-alginates, whereas the velocity of sinking under gravitational acceleration decreases in the same order. The factors which affect the relaxation time and velocity of acceleration, such as the concentration and viscosity of the alginate sol, the nature and radius of the metal ion as well as the density and pH of the electrolyte solution have been examined. The activation energies indicated that the stability of these metal alginate gel complexes follows the order Hg > Cd > Pb ~ Sn alginates. A mechanism consistent with the experimental results has been discussed.

Kinetics and mechanism of sol-gel transformation on polyelectrolytes of divalent metal-alginate gel complexes with formation of capillary ionotropic polymembranes

Khairou K. S., Al-Gethami W. M., Hassan R. M.

Bulletin of the Polish Academy of Sciences. Chemistry

2002

Vol. 50, No. 3

299-308

The kinetics of gelation between Zn(II), Cd(II) and Pb(II) metal ion electrolytes and sodium alginate polysaccharide sol have been studied complexometrically at temperatures between 35 and 65°C. Using a large excess of alginate sol concentration, the pseudo first-order plots of exchange between Na+ counter ions of the macromolecular chains of alginate sol and the metal ions give sigmoidal curves with two distinct regions. The initial part was relatively fast and curved significantly at early times, followed by a slow decrease in the rates at longer times. The rate constants of gelation were found to show second-order overall kinetics and first-order in the concentration of both reac-tants. The kinetic parameters have been evaluated and a consistent gelation mechanism is suggested.