Refat M. Hassan

Thermal decomposition of some divalent metal alginate gel compounds

Abstract The thermal decomposition of divalent metal alginate gel compounds has been studied using thermogravimetry (TG) and differential thermal analysis (DTA). The compounds have been characterized by FTIR and chemical analysis. The results reveal that the decomposition of metal alginate complexes is accompanied by the formation of metal oxalates as intermediate fragments. The stabilities of these compounds correspond to the strength of chelation between the metal ions and the functional groups on the macromolecular chains. A detailed mechanism of the thermal decomposition of the complexes is given and the activation energies of the main decomposition stages have been calculated.

Kinetics and mechanism of sol-gel transformation on polyelectrolytes of nickel alginate ionotropic membranes

The kinetics and mechanism of the gelation reaction on capillary ionotropic membranes of nickel alginate complex have been studied complexometrically. It was found that the exchange between Na+ ions of the macromolecular chains of alginate sol and Ni2+ ions of the electrolyte proceed according to a sigmoidal curve with a distinct rapid period initially followed by a decrease in the rate of exchange at longer times. Second-order overall kinetics have been observed. The rate of gelation conforms to d[Gel]dt = Rj[Alg−][Ni2+] where Rj represents the second order rate of exchange of either the fast or slow exchange in such a gelation reaction. The kinetic parameters were evaluated and a tentative mechanism is discussed.

Kinetics and mechanism of oxidation of β-phenylalanine by permanganate ion in aqueous perchloric acid

The kinetics of permanganate oxidation of β-phenylalanine in aqueous perchlorate media at a constant ionic strength of 3.0 mol dm–3 has been studied spectrophotometrically. A first-order reaction in [MnO4–] and a fractional order with respect to β-phenylalanine were observed. The results obtained at various hydrogen-ion concentrations indicate that the protonated species of both the amino acid and permanganate play a role in the kinetics. Kinetic evidence for the formation of an intermediate complex between the amino acid and the oxidant is presented. The activation parameters were calculated and found to be ΔS‡=–160.14 ± 8.23 J K–1 mol–1, ΔH‡= 34.04 ± 1.02 kJ mol–1, and ΔG‡= 81.77 ± 3.47 kJ mol–1, respectively. A mechanism consistent with the kinetic results is discussed.

Kinetics and mechanism of sol-gel transformation for polyelectrolytes of capillary copper alginate ionotropic membranes

The kinetics and mechanism of sol-gel transformation on capillary ionotropic membranes of a copper alginate complex have been examined, complexometrically. Using a large excess of Cu2− ions over that of the alginate sol concentration, the pseudo-first-order plots were found to be relatively fast and curved significantly at short times, but became slow and linear at longer times. The rate law of gel formation was described by the form, (C∞ − C1) = B0exp(− Rft) + P0exp(− Rst), where these two gelation pathways showed a simple first-order dependence on both the metal ion and alginate sol. The kinetic parameters have been evaluated and a mechanism consistent with the kinetic data is suggested.

Kinetics and mechanism of sol-gel transformation on polyelectrolytes of some transition metal ions, especially cobalt alginate ionotropic membranes

Abstract The kinetics of gelation have been studied complexometrically at temperatures between 25 and 40°. The pseudo-first order plot of exchange between Na + ions of the macromolecular chains of alginate sol and Co 2+ ions gives a sigmoidal curve with two distinct portions. The initial part was fast and curved significantly at early times followed by a decrease in the rate of exchange at longer times. The rate of gelation conforms to the expression ( C ∞ - C t ) = B 0 e − Rft + P 0 e − R s t , where R f and R s are the first order rate constants of gelation for the fast and slow reactions, respectively. There is discussion of the factors which affect the rate of exchange such as the concentrations of metal ions and alginate sol, the diameter of the formed capillaries and the orientation of the macromolecular chains and the solvent molecules toward the metal ions. The kinetic parameters have been evaluated and a consistent gelation mechanism is suggested.

Alginate polyelectrolyte ionotropic gels

The heterogeneous equilibrium for exchange of UO22+ counter-ions in uranyl alginate exchange resin by H+ ions has been investigated using titrimetric and spectrophotometric techniques. The thermodynamic equilibrium constant was found to be 15.51±0.33 at 25 °C. The electrical conductivity of uranyl alginate in the form of circular discs has been examined as a function of temperature. The Arrhenius plot of log δ versus 1/T showed a complicated behaviour where three regions of conduction were separated by two distinct transition zones. This behaviour was interpreted by the transfer of electrons from alginate to the cross-linked uranyl ion with formation of free radicals and uranium ions of lower oxidation states in a sequence, followed by dimerization of these radicals in the final stages. The X-ray diffraction pattern indicated that the uranyl alginate complex is amorphous in nature. Infrared absorption spectra indicated the presence of UO22+ chelated to the alginate macromolecular chains, and displayed γa CO2− and γs CO2− in the ranges of 1591 and 1410 cm−1 respectively. Two geometrical structures for chelation of UO22+ with the functional groups of alginate macromolecules have been suggested.

Thermal and electrical studies on some metal alginate compounds

Abstract The thermal decomposition of Ag—alg, Se—alg 4 and UO 2 —alg 2 compounds has been studied using thermogravimetry (TG), differential thermal analysis (DTA) and electrical conductivity measurements. The original samples are characterized by FTIR spectra. The results obtained reveal that the decomposition of these compounds proceeds via the formation of metal oxalates as intermediate fragments. The electrical conductance of these compounds at low temperature indicates that their geometric structures are non-planar and possess electrical conductivity values which lie in the range of semiconductors. Moreover, the remarkable increase in the conductance values during the decomposition of the intermediate metal oxalates is attributed to the hopping mechanism between the different valencies which exist during their thermolysis. Finally, detailed mechanisms of the various decomposition stages of the metal alginate compounds are suggested.

Kinetics of Corrosion Inhibition of Aluminum in Acidic Media by Water-Soluble Natural Polymeric Pectates as Anionic Polyelectrolyte Inhibitors

Corrosion inhibition of aluminum (Al) in hydrochloric acid by anionic polyeletrolyte pectates (PEC) as a water-soluble natural polymer polysaccharide has been studied using both gasometric and weight loss techniques. The results drawn from these two techniques are comparable and exhibit negligible differences. The inhibition efficiency was found to increase with increasing inhibitor concentration and decrease with increasing temperature. The inhibition action of PEC on Al metal surface was found to obey the Freundlich isotherm. Factors such as the concentration and geometrical structure of the inhibitor, concentration of the corrosive medium, and temperature affecting the corrosion rates were examined. The kinetic parameters were evaluated and a suitable corrosion mechanism consistent with the kinetic results is discussed in the paper.

Influence of frequency on specific conductance of polyelectrolyte gels with special correlation between strength of chelation and stability of divalent metal alginate ionotropic gels

Abstract A new technique has been used to measure the variation in the specific conductance for metal alginate gel complexes for a wide range of frequencies (0.02–800 kHz). The relationships between the specific conductance and frequency show inflection points at two different frequencies for every metal alginate complex. This behaviour is interpreted as the elimination of the relaxation effects resulting from the cleavage of the coordinate and ionic bonds between the chelated metal ions and the hydroxyl and carboxylate groups of macromolecular chains of alginate polyelectrolyte, respectively. This behaviour is discussed in terms of the strength of chelation and stability of the gel complexes.

Further evidence for detection of short-lived transient hypomanganate(V) and manganate(VI) intermediates during oxidation of some sulfated polysaccharides by alkaline permanganate using conventional spectrophotometric techniques.

Spectrophotometric evidence for the formation of hypomanganate(V), [CAR-Mn(V)O43-], and manganate(VI), [CAR-Mn(VI)O42-], intermediate complexes has been confirmed during the oxidation of iota- and lambda-carrageenan-sulfated polysaccharides (CAR) by alkaline permanganate at pHs 12 using a conventional spectrophotometer. These short-lived intermediate complexes were identified and characterized. A reaction mechanism in good consistence with the experimental results is suggested.