M.A. Mousa

Electrical conduction in ?-irradiated and unirradiated Fe3O4, CdFe2O4 and Co x ZN1?x Fe2O4 (0 ?x ? 1) ferrites

The electrical conductivity of γ-irradiated and unirradiated finely divided ferrites of composition Fe3O4, CdFe2O4 and Cox Fn1−xFe2O4(0 ≤x ≤ 1) was studied in a nitrogen atmosphere as a function of temperature. Fe3O4, ZnFe2O4 and CdFe2O4 showed n-type conduction, whereas CoFe2O4 showed p-type conduction. For CoxZn1-xFe2O4 it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe3O4, and CoxZn1−xFe2O4(0 ⩽x ≤ 1) was explained by a hopping mechanism, whereas the conduction in ZnFe2O4 and in CdFe2O4 is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of γ-irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.

Mn3O4/graphene nanocomposites: outstanding performances as highly efficient photocatalysts and microwave absorbers

Mn3O4 (M) incorporated graphenes (G) synthesized by a deposition–solvothermal process, formed at various nominal weight percentages (G1M1, G3M1 and G1M3), were efficiently used for the photodegradation of methylene blue dye (MB) under visible light illumination (λ > 420 nm, 88 W, 20 ppm, 298 K) and under microwave irradiation (800 W, 2.45 GHz, 373 K). These materials were characterized using XRD, TEM-SAED, UV-Vis diffuse reflectance, N2 sorptiometry, FTIR and Raman techniques. Amongst the nanocomposites, G3M1 of polyhedral structure and an average domain equal to 10–12 nm has presented unique photo-degradation performance (100% degradation, 60 min, 0.0791 min−1 and TOC of 60%) exceeding the rest of the materials. This was mainly due to the extraordinary optical properties and to the strong interaction between Mn3O4 and graphene through which charge recombination is hampered. Based on the conduction and valence band edges together with the studied reactive species, it has been shown that ˙OH was the dominant species responsible for the MB degradation. Interestingly, the G3M1 nanocomposite has shown fascinating microwave absorption properties and is capable of degrading MB at a faster rate (0.287 min−1) than the one conducted via photocatalysis. Scavenger studies have shown that ˙OH and electrons were responsible for the excellent performance of the MB microwave degradation. The microwave results were discussed in view of the marked increase in dielectric constant (e−) and dielectric loss (e′′) in the studied frequency range of 1.0 Hz to 100 kHz, in addition to the electronic conductivity measurements. This work offers an exceptional approach for exploring high-performance microwave absorption as well as distinctive visible light photocatalytic reaction for organics degradation.

Electrical conduction in γ-irradiated and unirradiated zinc-iron ferrites

The electrical conductivity of γ-irradiated and unirradiated finely-divided spinels of composition (Zn x 2+ Fe 1−x 2+ Fe 2 3+ )O 4 2− was studied in a nitrogen atmosphere as a function of temperature. The results of both γ-irradiated and unirradiated ferrites with compositions x ⩽ 0.79 showed that the electrical conduction occurred by fast electron exchange amongst Fe2+ and Fe3+ ions situated on octahedral sites in the spinel lattice, by a hopping mechanism. For composition x > 0.79 it was found that the transition of the charge carriers through cation vacancies is the predominant mechanism. Some breaks in the conductivity-temperature curves were found near the Curie points. Seebeck voltage measurements showed that γ-irradiated and unirradiated spinels behave as n-type semiconductors. The effect of γ-irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.

Electrical conduction in some γ-irradiated and unirradiated metal-zinc ferrites

Abstract The electrical conductivity of some γ-irradiated and unirradiated metal-zinc ferrites, M0.1Zn0.9Fe2O4 (M ≡ Mn2+, Co2+, Ni2+, Cu2+ or Mg2+), was investigated as a function of temperature. The ferrites investigated showed n-type conduction. The electrical conduction in M0.1Zn0.9Fe2O4 (M ≡ Co2+, Cu2+, Mn2+, or Ni2+, can be explained by a hopping mechanism, whereas the conduction in ZnFe2O4 and Mg0.1Zn0.9Fe2O4 is interpreted on the basis of the transfer of charge carriers through the cation vacancies present in octahedral sites. The effect of γ-irradiation on the conduction process is discussed.

Gamma irradiation effects on the electrical conductivity behaviour of hexacyano-hexaamine double complexes

Abstract Gamma irradiation effects on the electrical conductivity behaviour of the double complexes [Co(NH 3 ) 6 ] [Co(CN) 6 ], [Co(NH 3 ) 6 ] [Al(CN) 6 ] and [Co(NH 3 ) 6 ] [Mn(CN) 6 ] were investigated. A comparison is made between the rates and activation energies of thermal annealing of electrical properties of pure and γ-irradiated samples. The conductivity of the solid double complexes increases with temperature, decreases with radiation dose, and remarkably increases when the transition metal of the negative component of the double complex changes from Al to Mn to Co. However, the results show that the rate constants and activation energies of thermal annealing of defects in these systems are not significantly affected by gamma irradiations.

Thermodynamic functions of the transfer of aminobenzoic acids from water to water-acetone mixtures at 25 ° C

Abstract Free energies (Δ G XXX t ) and entropies (Δ S XXX t ) of transfer of o -, m -, and p -aminobenzoic acids from water to water-acetone mixtures have been determined from solubility measurements at five temperatures (20–40 ° C). It is found that the specific solute-solvent interactions through dispersion forces play a major role on the nature of Δ G XXX t -composition profiles in the region of water-rich composition. However, in higher acetone concentration the hydrogen bonding interactions between the solvent molecules and the aminobenzoic acids as well as between the solvent molecules themselves were also considered. All these interactions have been proposed to interpret the Δ S XXX t -composition profiles and are discussed.

Electrical conduction in γ irradiated and unirradiated Fe3O4, CdFe2O4 and CoxZn1−xFe2O4 (0≤x≤1) ferrites

The electrical conductivity of γ-irradiated and unirradiated finely divided ferrites of composition Fe3O4, CdFe2O4 and Cox Fn1−xFe2O4(0 ≤x ≤ 1) was studied in a nitrogen atmosphere as a function of temperature. Fe3O4, ZnFe2O4 and CdFe2O4 showed n-type conduction, whereas CoFe2O4 showed p-type conduction. For CoxZn1-xFe2O4 it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe3O4, and CoxZn1−xFe2O4(0 ⩽x ≤ 1) was explained by a hopping mechanism, whereas the conduction in ZnFe2O4 and in CdFe2O4 is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of γ-irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.

Physicochemical studies on ZnO-Al2O3 system

Several mixed ZnO-Al2O3 systems were prepared by the impregnation method and calcined for 5 h at 300, 600 and 1000 ° C. The crystal structure, surface acidity, surface basicity, surface area, catalytic decomposition of H2O2 and the electrical conductivity of the samples prepared were studied. It was found that the decomposition of H2O2 is catalysed by the acidic sites formed on the catalyst surface at composition less than 50 mol% ZnO and by basic sites for oxides having composition higher than 50 mol% ZnO. ZnAl2O4-spinel was found to be formed at temperatures ⩾ 600 ° C and it has a catalytic activity and electrical conductivity lower than each of the pure ZnO and the oxide mixtures. The results obtained were correlated together and discussed.

Kinetic analysis of thermal decomposition reactions: Part IV: Kinetics of formation of barium titanate in crystalline mixtures of barium carbonate and titanium dioxide

Abstract The kinetics of formation of barium titanate from banum carbonate and titanium dioxide have been studied using isothermal and dynamic thermogravimetry techniques. Kinetic analysis of the isothermal data, considered from the point of view of various solid state reaction models, showed that the reaction is best described by the random nucleation Avrami equation Analysis of dynamic TG data, according to the integral methods of Coats and Redfern and of Ozawa, gave results which are not in agreement with each other or with the results obtained under isothermal conditions.

γ-Irradiation effects on the electrical conductivity of some two-dimensional complexes: RMnCl4, RCoCl4 and RMn0.5Co0.5Cl4 (R = H3N-(CH2)8-NH3)

Abstract DTA, d.c. conductivity and thermoelectric power of the compounds RMnCl 4 , RCoCl 4 and RMn 0.5 Co 0.5 Cl 4 (R = H 3 N-(CH 2 ) 8 -NH 3 ) were measured over a temperature range of 300–500 K. Both the DTA and the d.c.-conductivity results show the presence of many phase transitions in each of the complexes investigated. The conductivity results are explained on the basis of an electron-hopping mechanism. The effect of γ-irradiation on the conductivity data and the type of crystal phase are investigated and discussed.