Volumen 66 (2019): Heft 3 (December 2019)

The alloys from Al–Mg–Si system provide an excellent combination of mechanical properties, heat treatment at extrusion temperature, good weldability, good corrosion resistance and formability. Owing to the high casting speed of rods or slabs, the solidification is rather non-equilibrium, resulting in defects in the material, such as crystalline segregations, the formation of low-melting eutectics, the unfavourable shape of intermetallic phases and the non-homogeneously distributed alloying elements in the cross-section of the rods or slabs and in the entire microstructure. The inhomogeneity of the chemical composition and the solid solution negatively affects the strength, the formability in the warm and the corrosion resistance, and can lead to the formation of undesired phases due to segregation in the material. In this experimental investigation, the cross-sections of the rods from two different alloys of the 6xxx group were investigated. From the cross-sections of the rods, samples for differential scanning calorimetry (DSC) at three different positions (edge, D/4 and middle) were taken to determine the influence of inhomogeneity on the course of DSC curve. Metallographic sample preparation was used for microstructure analysis, whereas the actual chemical composition was analysed using a scanning electron microscope (SEM) and an energy dispersion spectrometer (EDS).

The world energy demand has become higher with the growing population, which has translated into an increase in emission of greenhouse gases into the atmosphere. For this reason, CO₂ capture and storage has been undertaken to purify the atmosphere. For storing this CO_2, it is necessary to have wells to inject it (deeper than 800 m); moreover, these wells need to have stability over time, and one of the stability aspects is the protection of steel against corrosion. Considering this aspect, the most common steels (focussed on American Petroleum Institute [API] steels) that can be used in an injector well were studied. The best performance was obtained using a high alloy content of Cr and Ni. Furthermore, the most important parameter analysed when corrosion is studied is the test time, which was modelled to stabilise the corrosion rates. The experiments were undertaken after a general review of different studies that investigated the corrosion of steel when in contact with CO₂ in the vapour phase and under supercritical conditions.

Field, mineralogical and petrochemical studies of the Precambrian Basement Complex rocks around Akungba-Akoko were carried out with the aim of determining their petrology, petrochemical characteristics and petrogenesis. The petrology of Akungba-Akoko area comprises migmatite, granite gneiss and biotite gneiss intruded by biotite granite, charnockite and minor felsic and basic rocks. Seventeen representative samples of the granite gneiss, biotite gneiss, biotite granite and charnockite were collected during field geological mapping of the area for petrographic and geochemical analyses. Modal mineralogy revealed that the granite gneiss, biotite gneiss and granite have assemblages of quartz + feldspar + mica + hornblende + opaques and are granitic in composition. The charnockite is characterized by anhydrous mineral assemblage of quartz + feldspar + biotite + hornblende + pyroxene + opaques. Petrochemical data of the rocks revealed that they are moderately to highly enrich in SiO₂, sub-alkaline, peraluminous, magnesian to ferroan and calcic and have K/Rb < 283. The geochemical characteristics and discrimination of the rocks indicated that the granite gneiss and biotite gneiss are orthogneisses formed by metamorphism of igneous protoliths of granitic composition and the biotite granite and charnockite are of igneous/magmatic origin. The biotite granite, charnockite and the igneous protoliths of the biotite gneiss are I-type granitoids formed from crustal igneous-sourced melt(s), while the igneous protoliths of the granite gneiss is a S-type granitoid probably derived from shallow crustal or sedimentary-sourced melt(s). Tectonic discrimination of the rocks indicated that they were formed during a phase of magmatic activity related to collision and subduction.

Heavy mineral component of 13 samples from the Lokoja and Patti Formations, Bida Basin have been studied for their textural characteristics, compositional abundance, maturity and provenance determinations. The suite of heavy minerals encountered is classified as opaque and non-opaque constituents. The non-opaque components include zircon, tourmaline, rutile, garnet, staurolite, epidote, kyanite, titanite, lawsonite, cassiterite, sillimanite, hornblende, hypersthene and andalusite. The assemblage is generally dominated by zircon and tourmaline in the two formations. The constituent heavy minerals identified are dominated by ultra-stable and stable classes, whereas the ZTR indices indicate mineralogical immaturity coupled with textural immaturity of the constituent grains. This suggests the possible dominance of chemical weathering of the source rock. The suites of minerals recovered have been linked to both metamorphic and non-metamorphic crystalline rock origins.

Hydrogeological assessment of groundwater resources was carried out with a view to evaluate the potential of the aquifers to provide portable water supply and access the distribution of electrical parameters of hydrogeologic units in some areas in Odeda, Ogun State, Nigeria. A geophysical survey using vertical electrical sounding (VES) with the Schlumberger electrode array, with half-current electrode spacing (AB/2) varying from 1 to 132 m was carried out at 30 different stations in the study area. The VES data were interpreted qualitatively and quantitatively. Three-to-five sub-surface layers consisting of topsoil, weathered layer consisting of clay, sandy clay, clayey sand and sand layers, and fractured/fresh basement were delineated. Layer resistivities and thicknesses obtained on the curves within the study area showed one main aquifer type, which is the fractured basement. The longitudinal unit conductance (ranging from 0.049720 to 1.4520000 mhos) of the study area aided the protective capacity to be rated into good, moderate and weak. About 33% of the study area falls within the weak protective capacity, 57% falls within the moderate protective capacity and 10% falls within the good protective capacity.