Presence Of Alkaline Earth Ions Research Articles

Viscoelastic behavior of alkali and alkaline earth aluminophosphate glasses

• Viscoelasticity of alkali and alkaline-earth aluminphosphate glass was investigated. • Activation energy of stress relaxation changed with aluminum content. • Different change in two series would be due to existence of AlO 4 . The viscoelastic behavior of alkali and alkaline earth aluminophosphate glasses was studied. The energetic interpretation was based on the Arrhenius behavior of the relaxation modulus. With increasing aluminum content, the activation energy of the relaxation increased in the alkali series but decreased in the alkaline earth series. Dynamic viscoelasticity measurements revealed that the loss modulus, E ”(ω), showed a crossover of the relaxation process at the glass transition temperatures. The activation energy below the transition temperature was close to the energies of internal friction or ionic self-diffusion. The energy above the transition temperature corresponded to the dissociation energies of alkali-oxygen or alkaline earth-oxygen single bonds. The different behavior in the energy of the relaxation modulus between alkali and alkaline earth series was due to weak bonds caused by adding alkali ions and the formation of crosslinking by low-coordinate aluminum polyhedra because of the presence of alkaline earth ions.

The addition effects of alkaline earth ions in the chemical synthesis of ε-Fe2O3 nanocrystals that exhibit a huge coercive field

An iron oxide/silica composite material, which was prepared by combining reverse-micelle and sol-gel techniques, exhibited a huge coercive field Hc of 20kOe (1.6×105Am−1) in our previous work. The key of this synthetic procedure was the added Ba2+ ions that created a single phase of ε-Fe2O3. In the present work, the addition effect of Ca2+ ions to this procedure was investigated. Consequently, rod-shape ε-Fe2O3 nanocrystals (40–120nm×15–20nm) were obtained and a Hc value of 20kOe was observed. Thermodynamical analysis that considered the surface energy of nanoparticle suggested that a single ε-Fe2O3 phase was generated by retarding the crystal growth of Fe2O3 particles under the presence of alkaline earth ions.

Catalytic Activity of Titanium Silicates Synthesized in the Presence of Alkali-Metal and Alkaline-Earth Ions

Titanium containing aluminum-free ZSM-5 (TS-1) synthesized in the presence and absence of alkali metal and alkaline earth ions are investigated as catalysts for the selective oxidation of alkanes and alkenes using aqueous H2O2 as oxidant at temperatures below 100°C. Sodium-exchanged TS-1 is not active for alkane oxidations. Similarly, no catalytic activity is observed for TS-1 synthesized in the presence of high concentrations of alkali metal ions (Si/Na <20). For both cases, the catalytic activity can be restored by washing the solid with acid solution prior to catalytic evaluation. Similar results are obtained for TS-1 synthesized in the presence of other alkali metal ions, e.g., Li, K. However, the presence of alkaline earth ions, e.g., Mg, in the synthesis gel does not have a significant effect on the catalytic activity of TS-1. Based on the catalytic data and the physicochemical properties of the samples, a plausible explanation for the above results is described. The acid treatment may be useful in overcoming the problems of synthesizing TS-1 from reagents that contain alkali metal ions, e.g., TPAOH solutions. More importantly, this treatment opens the possibility of synthesizing other titanium-containing silicate structures that require the presence of alkali metal ions in the synthesis gel for their formation.

Crystal destruction of zeolite NaA during ion exchange with magnesium and calcium ions

AbstractExtreme conditions of ion exchange like, for instance, highly concentrated solution, high temperature and a long time of exchange can cause destructions of crystals. Zeolites NaMgA are structurally degraded much more than zeolites NaCaA. Reason for the reduced stability of crystals in presence of alkaline earth ions is the proton concentration increased beyond the dissociation equilibrium of water owing to the formation of weakly dissociated alkaline earth ion hydroxides. The zeolite lattice is destroyed hydrolytically by the influence of protons.

The Effect of Slow Two‐Electron Transfers and Disproportionation on Cyclic Voltammograms

The EE mechanism (two‐electron transfer) for cyclic voltammetry was investigated in considerable detail along with the effect of disproportionation. The theory was developed for either the first or second electron transfer being slow while the other one was reversible. It was possible to develop generalized working curves for the height and shape of the wave regardless of the difference in 's and the values of α and . This theory was then applied to the analysis of the reduction of benzil in the presence of alkaline earth ions in dimethylformamide.