A. Al Rawas

Identification of Corrosion Products Due to Seawater and Fresh Water

Mossbauer and X-ray diffraction (XRD) measurements were performed on corrosion products extracted from the inner surface of two different metal tubes used in a desalination plant in Oman. One of the tubes corroded due to the seawater while the second was corroded due to fresh water. The corrosion products thus resulted due to seawater were scrapped off in to two layers, the easily removable rust from the top is termed outer surface corrosion product and the strongly adhered rust as internal corrosion product. The Mossbauer spectra together with the XRD pattern of the outer surface showed the presence of magnetite (Fe3O4), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), goethite (α-FeOOH) and hematite (Fe2O3). The inner surface however showed the presence of akaganite, goethite, and magnetite. On the other hand, the corrosion products due to the fresh water showed only the presence of goethite and magnetite. The mechanism of the corrosion process will be discussed based on the significant differences between the formation of the iron components of the corrosion products due to seawater and the fresh water.

The electronic and magnetic structure of bcc iron-nickel alloy

The first principles discrete variational method and the local density approximation are used to calculate the electronic and magnetic properties of clusters of iron and nickel atoms representing the bcc iron-nickel alloy with nickel concentration up to about 30%. It is found that the presence of nickel atoms at sites neighbouring iron increases the iron local magnetic moment but decreases the magnitude of the magnetic hyperfine field. The magnetic hyperfine field at the iron site increases with increasing number of nickel atoms at the next-nearest-neighbour sites. Consequently, the experimentally observed maximum in both magnetization and hyperfine field versus nickel concentration is attributed to different iron sites. The 3d local densities of states at iron and nickel sites are calculated. The average density of states is found to remain unaltered for the majority sub-band, whereas it exhibits large deformation for the minority sub-band. An energy diagram is deduced from the density of states and is used to explain the formation of magnetic moment at iron and nickel sites. We deduce the following from these calculations. The observed increase in the local magnetic moment in the iron site is attributed to the reduction in the weight of the bonding d states and the accompanying constancy of the weight of the antibonding states, which ar driven by sd interaction.

Magnetic properties of nanocrystalline FexCu1-x alloys prepared by ball milling

X-ray diffraction, Mossbauer and magnetization measurements were used to study FexCu1−x alloys prepared by ball-milling. The X-ray data show the formation of a nanocrystalline Fe—Cu solid solution. The samples with x ≥ 0.8 and x ≤ 0.5 exhibit bcc or fcc phase, respectively. Both the bcc and fcc phases are principally ferromagnetic for x ≥ 0.2, but the sample with x = 0.1 remains paramagnetic down to 78 K. The influence of the local environment on the hyperfine parameters and the local magnetic moment are discussed using calculations based on the discrete-variational method in the local density approximation.

Mössbauer Studies of Fe0.7−xSi0.3Mnx Alloys

In this work we present Fe57 Mössbauer study for the alloy system Fe0.7−xSi0.3Mnx, where 0≤x≤0.3. Mössbauer spectroscopic results show that all the samples studied are magnetically ordered at 77 K, and at room temperature, except for x=0.3 at 300 K where it shows paramagnetic behavior. The average magnetic hyperfine field is found to decrease with increasing the manganese concentration at 77 K and 300 K. The average magnetic hyperfine field is found to increase with decreasing the temperature from 300 K to 77 K for all samples under investigation. The average isomer shift is found to decrease with increasing the manganese concentration.

Mössbauer Studies of Fe 0.7− x Si 0.3 Mn x Alloys

In this work we present Fe57 Mossbauer study for the alloy system Fe0.7− x Si0.3Mn x , where 0 ≤ x ≤ 0.3. Mossbauer spectroscopic results show that all the samples studied are magnetically ordered at 77 K, and at room temperature, except for x = 0.3 at 300 K where it shows paramagnetic behavior. The average magnetic hyperfine field is found to decrease with increasing the manganese concentration at 77 K and 300 K. The average magnetic hyperfine field is found to increase with decreasing the temperature from 300 K to 77 K for all samples under investigation. The average isomer shift is found to decrease with increasing the manganese concentration.

Agnetic Properties of Iron-Copper Alloys

The discrete-variational method in the local density approximation is used to calculate the local properties at the iron central site in iron-copper alloys. The local magnetic moment, hyperfine field and the isomer shift at iron sites are calculated versus the number of copper atoms at the neighboring shells. It is found that the magnetic moment increases with increasing number of copper atoms in the first coordination shell, whereas the magnetic hyperfine field decreases. Assuming a binomial distribution of copper atoms the average properties are calculated and compared to experimental results.