The acid-catalysis of chromic acid oxidation of carboxymethyl cellulose (CMC) as a polysaccharide in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm−3 have been investigated spectrophotometrically. The experimental results showed first-order kinetics in chromic acid and fractional first-order dependence with respect to [CMC]. A kinetic evidence for the formation of 1:1 complex between chromic acid and CMC was revealed. The hydrogen ion dependence of the reaction rates showed that the oxidation process is acid-catalyzed. Induced polymerization of acrylonitrile indicated that the oxidation process proceeds by free-radical mechanism. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is suggested.

The oxidative status and the morphological changes of liver of rats exposed to cadmium (5 mg Cd/kg body weight subcutaneously) for 22 days and the protective role of melatonin (10 mg/kg b.w.) against the toxicity of cadmium was studied. The concentration of malondialdehyde (MDA), as an indicator of lipid peroxidation, activity of the antioxidant enzyme superoxide dismutase (SOD) as well as the concentration of glutathione (GSH) was measured in the liver. The morphological changes were investigated using both light and electron microscopes. The exposure to Cd led to an increase of MDA levels and a decrease of both the activity of SOD and GSH concentration in the liver. In contrast, melatonin administration restored the previous changes to nearly the normal levels. Morphologically, Cd led to different histopathological changes such as loss of normal architecture of the parenchymatous tissue, cytoplasmic vacuolization, cellular degeneration and necrosis, congested blood vessels, destructed cristae mitochondria, fat globules, severe glycogen depletion, lipofuscin pigments, and collagenous fibers formation. Again, melatonin administration counteracts all changes and the tissue appears more or less normal. The rate of recovery was faster when melatonin was administered for treatment after the exposure to cadmium than if the animals left without any treatment. The results suggest that melatonin may be useful as an antioxidant in combating free radical-induced oxidative stress and tissue injury that is a result of cadmium toxicity.

The oxidative status and the morphological changes of liver of rats exposed to cadmium (5 mg Cd/kg body weight subcutaneously) for 22 days and the protective role of melatonin (10 mg/kg b.w.) against the toxicity of cadmium was studied. The concentration of malondialdehyde (MDA), as an indicator of lipid peroxidation, activity of the antioxidant enzyme superoxide dismutase (SOD) as well as the concentration of glutathione (GSH) was measured in the liver. The morphological changes were investigated using both light and electron microscopes. The exposure to Cd led to an increase of MDA levels and a decrease of both the activity of SOD and GSH concentration in the liver. In contrast, melatonin administration restored the previous changes to nearly the normal levels. Morphologically, Cd led to different histopathological changes such as loss of normal architecture of the parenchymatous tissue, cytoplasmic vacuolization, cellular degeneration and necrosis, congested blood vessels, destructed cristae mitochondria, fat globules, severe glycogen depletion, lipofuscin pigments, and collagenous fibers formation. Again, melatonin administration counteracts all changes and the tissue appears more or less normal. The rate of recovery was faster when melatonin was administered for treatment after the exposure to cadmium than if the animals left without any treatment. The results suggest that melatonin may be useful as an antioxidant in combating free radical-induced oxidative stress and tissue injury that is a result of cadmium toxicity.

The influence of Rb in the triple sulfate LiK(1−x)RbxSO4 (0 ≤ x ≤ 0.2) compound on the structural and thermal properties of the bulk material is discussed. Samples were prepared by fusing the sulfates in stoichiometric ratios in a platinum crucible at 1273 K for 30 min. The x-ray powder diffraction measurements were performed at ambient temperature. The crystal structure parameters were refined by the Rietveld method using the FullProf program. The analysis indicated a single-phase having a hexagonal symmetry with space group P63 regardless of the Rb content. Thermal analysis by differential scanning calorimetry shows a considerable shift of the phase transition point towards lower temperatures with increasing Rb content. A pre-transitional effect is observed by differential thermal analysis of the sample without Rb contribution while for the sample with 20% Rb the transition is represented by double endothermic peaks. The energy of transition has been estimated using the Kissinger method for samples with different concentrations of Rb

The kinetics of hardening precipitates of Al-1.12 wt.% Mg2Si-0.35 wt.% Si (excess Si) and Al-1.07 wt.% Mg2Si-0.33 wt.% Cu (balanced + Cu) alloys have been investigated by means of differential scanning calorimetry and hardness measurements. The excess Si enhances the precipitation kinetics and improves the strength of the material. On the other hand, however addition of Cu assist formation of the Q phase which positively changed the alloy strength. The high binding energy between vacancies and solute atoms (Si and Mg) enhances the combination of Si, Mg and vacancies to form Si-Mg-vacancy clusters. These clusters act as nucleation sites for GP-zones. The coexistence of the β'- and Q'-precipitates in the balanced + Cu alloy results in a higher peak age hardening compared to the alloy with Si in excess

The kinetics of hardening precipitates of Al-1.12 wt.% Mg2Si-0.35 wt.% Si (excess Si) and Al-1.07 wt.% Mg2Si-0.33 wt.% Cu (balanced + Cu) alloys have been investigated by means of differential scanning calorimetry and hardness measurements. The excess Si enhances the precipitation kinetics and improves the strength of the material. On the other hand, however addition of Cu assist formation of the Q phase which positively changed the alloy strength. The high binding energy between vacancies and solute atoms (Si and Mg) enhances the combination of Si, Mg and vacancies to form Si-Mg-vacancy clusters. These clusters act as nucleation sites for GP-zones. The coexistence of the β'- and Q'-precipitates in the balanced + Cu alloy results in a higher peak age hardening compared to the alloy with Si in excess

The kinetics of hardening precipitates of Al-1.12 wt.% Mg2Si-0.35 wt.% Si (excess Si) and Al-1.07 wt.% Mg2Si-0.33 wt.% Cu (balanced + Cu) alloys have been investigated by means of differential scanning calorimetry and hardness measurements. The excess Si enhances the precipitation kinetics and improves the strength of the material. On the other hand, however addition of Cu assist formation of the Q phase which positively changed the alloy strength. The high binding energy between vacancies and solute atoms (Si and Mg) enhances the combination of Si, Mg and vacancies to form Si-Mg-vacancy clusters. These clusters act as nucleation sites for GP-zones. The coexistence of the β'- and Q'-precipitates in the balanced + Cu alloy results in a higher peak age hardening compared to the alloy with Si in excess

The kinetics of hardening precipitates of Al-1.12 wt.% Mg2Si-0.35 wt.% Si (excess Si) and Al-1.07 wt.% Mg2Si-0.33 wt.% Cu (balanced + Cu) alloys have been investigated by means of differential scanning calorimetry and hardness measurements. The excess Si enhances the precipitation kinetics and improves the strength of the material. On the other hand, however addition of Cu assist formation of the Q phase which positively changed the alloy strength. The high binding energy between vacancies and solute atoms (Si and Mg) enhances the combination of Si, Mg and vacancies to form Si-Mg-vacancy clusters. These clusters act as nucleation sites for GP-zones. The coexistence of the β'- and Q'-precipitates in the balanced + Cu alloy results in a higher peak age hardening compared to the alloy with Si in excess

Polycrystalline LiK1-xRbxSO4 mixed crystals (with x=0.1 and 0.2) have been synthesized by air quenching of the melt and characterized by X-ray powder diffraction and DSC measurements. Their ionic conductivity has been measured as a function of temperature over a wide frequency range. From an analysis of the frequency-dependent conductivity at different temperatures below and above the reconstructive phase transition, the dc conductivity, the hopping frequency of mobile ions and the exponent n of the ac dispersive regime are determined. The values of the activation energy for the ac and dc conductivities and that of the hopping process are found to be almost the same, implying that the charge-carriers concentration is independent of temperature. The power-law exponent n of the conductivity spectra has average values of 0.57 and 0.66 in the room- and high-temperature phases, respectively, indicating different conduction properties in the two phases. Moreover, scaling of the conductivity spectra at the room- and high-temperature phases points to the structural influence on the microscopic dynamics of mobile ions

The dc conductivity (σ) along the polar b-axis of ammonium zinc chloride (AZC) crystals in its four hightemperature phases has been measured as a function of temperature. Doping with Mn2+ in different concentrations changed strongly both values of σ at all temperatures and the dependence of ln σdc on 1/T in the phase transition regions. The activation energy of conduction was calculated from the linear portions of this dependence in each phase. The results were discussed in the light of the decomposition of (NH4)2 in the high-temperature normal phase, the discommensuaration (DC) formation/annihilation in the incommensurate phase and domain wall motion and stripples nucleation in the commensurate- and antiferroelectric-phases. Pinning of DC’s in the crystal lattice and/or by the structural defects and the possibility of dislocation formation was also discussed. The bulk- and the electrode-limited conduction mechanisms were also considered. The current density-voltage gradient relationship according to the usual Richardson-Schottky (RS) equation shows disagreement between extracted parameters and experimentally measured ones. A modified equation was used to solve this difficulty which, in addition, facilitated the calculation of the electronic mobility (μ), the barrier height (ϕ) at the electrode-dielectric interface and the R-S constant (βRS). The effect of Mn2+-content on values of μ, ϕ and βRS in different phases of AZC was also considered