The corrosion pathways in AA2024-T3, AA5083-O and AA6082-T6 alloys have been investigated. The objective of the investigation is to further the understanding of the complex localised corrosion mechanism in aluminium a...The corrosion pathways in AA2024-T3, AA5083-O and AA6082-T6 alloys have been investigated. The objective of the investigation is to further the understanding of the complex localised corrosion mechanism in aluminium alloys. The investigation was carried out by examining the corroded surfaces of the alloys after potentiodynamic polarization tests in a 3.5% NaCl solution with the aid of a scanning electron microscope, and by analysing the flow of anolyte solution using the scanning vibrating electrode technique. The results revealed that the overall corrosion pathways in the alloys are distinctively different and are influenced by the flow of anolyte solution. Also revealed, was the fact that corrosion propagates in two ways （particularly in the AA5083-O and AA6082-T6 alloys）： an overall pathway in the corrosion front （filiform-like pathway in the AA5083 alloy and organized linear pathways in AA6082 alloy）; and the crystallographic channelling along the （100） directions. These are dependent on the grain distinct features of the AA5083-O and AA6082-T6 alloys and are not influenced by the presence of coarse second phase particles in these alloys, compared with the AA2024-T3 alloy, where the corrosion pathways are more dependent on the presence of second phase particles and grain boundary character.展开更多
Repassivation behaviour of the passive film formed on lean duplex stainless steel UNS S32101 and austenitic stainless steel UNS S30403 in a CO2-saturated oilfield environment has been studied. The native passive film ...Repassivation behaviour of the passive film formed on lean duplex stainless steel UNS S32101 and austenitic stainless steel UNS S30403 in a CO2-saturated oilfield environment has been studied. The native passive film on the alloys was thinned/removed by stepping the potential of the alloy to ﹣850 mV/Ag/AgCl for 30 minutes. Potentiostatic measurements were then taken at potentials of ﹣200, ﹣100, 0, 100 and 200 mV versus Ag/AgCl. Results show that the passive film repassivates at potentials of ﹣200 and ﹣100 mV and 0 mV for both alloys at 50°C. The current density however continues to rise for potentials of 100 and 200 mV. This shows that both alloys are susceptible to pitting at potentials above 100 mV at the test temperature of 50°C.展开更多
The use of rice husk and corn cob ashes as aggregates for foundry moulding sand has been studied. 5-12.5 weight percent of rice husk and corn cob ashes were added to the sand mixture and the sand properties determined...The use of rice husk and corn cob ashes as aggregates for foundry moulding sand has been studied. 5-12.5 weight percent of rice husk and corn cob ashes were added to the sand mixture and the sand properties determined. A mixture of equal proportion of rice husk and corn cob ashes was also used. In each case, four weight percent water and clay were added to the sand mixture. Some of the properties of the sand tested are: permeability, green compression strength, dry compression strength, green shear strength, dry shear strength, moisture content and permeability. The results showed that the green compression strength, green shear strength, moisture content and permeability decrease with increase in the additives (rice husk ash, corn cob ash, and (50% rice husk and 50% corn cob ashes). While dry compression strength and dry shear strength increase with increase in weight percent of the additives.展开更多
The characterization of five different Nigerian clay deposits has been carried out by employing three different characterization techniques (X-ray Diffraction, X-ray Fluorescence and Scanning Electron Microscopy/EDX)....The characterization of five different Nigerian clay deposits has been carried out by employing three different characterization techniques (X-ray Diffraction, X-ray Fluorescence and Scanning Electron Microscopy/EDX). The clays obtained from the various deposits were carefully prepared for the analyses and the results obtained were compared to confirm the consistency and reliability of the different methods employed. The results revealed the various desirable (SiO2 and Al2O3) and deleterious (Fe3O4, K2O, MgO, MnO and Na2O) elements and compounds contained in the clay samples in the various proportions and the appropriate purification technique required for preparing the clays for high temperature applications. Consequent upon the identification of the deleterious impurities, oxalic acid at different concentrations was used to leach the impurities out of the various clays. However, three out of the five deposits were chosen for purification because they possess the least quantities of the most deleterious (Fe2O3) of the impurities.展开更多
基金EPSRC for financial support through the LATEST2 Programme grant (EP/H020047/1)
文摘The corrosion pathways in AA2024-T3, AA5083-O and AA6082-T6 alloys have been investigated. The objective of the investigation is to further the understanding of the complex localised corrosion mechanism in aluminium alloys. The investigation was carried out by examining the corroded surfaces of the alloys after potentiodynamic polarization tests in a 3.5% NaCl solution with the aid of a scanning electron microscope, and by analysing the flow of anolyte solution using the scanning vibrating electrode technique. The results revealed that the overall corrosion pathways in the alloys are distinctively different and are influenced by the flow of anolyte solution. Also revealed, was the fact that corrosion propagates in two ways （particularly in the AA5083-O and AA6082-T6 alloys）： an overall pathway in the corrosion front （filiform-like pathway in the AA5083 alloy and organized linear pathways in AA6082 alloy）; and the crystallographic channelling along the （100） directions. These are dependent on the grain distinct features of the AA5083-O and AA6082-T6 alloys and are not influenced by the presence of coarse second phase particles in these alloys, compared with the AA2024-T3 alloy, where the corrosion pathways are more dependent on the presence of second phase particles and grain boundary character.
文摘Repassivation behaviour of the passive film formed on lean duplex stainless steel UNS S32101 and austenitic stainless steel UNS S30403 in a CO2-saturated oilfield environment has been studied. The native passive film on the alloys was thinned/removed by stepping the potential of the alloy to ﹣850 mV/Ag/AgCl for 30 minutes. Potentiostatic measurements were then taken at potentials of ﹣200, ﹣100, 0, 100 and 200 mV versus Ag/AgCl. Results show that the passive film repassivates at potentials of ﹣200 and ﹣100 mV and 0 mV for both alloys at 50°C. The current density however continues to rise for potentials of 100 and 200 mV. This shows that both alloys are susceptible to pitting at potentials above 100 mV at the test temperature of 50°C.
文摘The use of rice husk and corn cob ashes as aggregates for foundry moulding sand has been studied. 5-12.5 weight percent of rice husk and corn cob ashes were added to the sand mixture and the sand properties determined. A mixture of equal proportion of rice husk and corn cob ashes was also used. In each case, four weight percent water and clay were added to the sand mixture. Some of the properties of the sand tested are: permeability, green compression strength, dry compression strength, green shear strength, dry shear strength, moisture content and permeability. The results showed that the green compression strength, green shear strength, moisture content and permeability decrease with increase in the additives (rice husk ash, corn cob ash, and (50% rice husk and 50% corn cob ashes). While dry compression strength and dry shear strength increase with increase in weight percent of the additives.
文摘The characterization of five different Nigerian clay deposits has been carried out by employing three different characterization techniques (X-ray Diffraction, X-ray Fluorescence and Scanning Electron Microscopy/EDX). The clays obtained from the various deposits were carefully prepared for the analyses and the results obtained were compared to confirm the consistency and reliability of the different methods employed. The results revealed the various desirable (SiO2 and Al2O3) and deleterious (Fe3O4, K2O, MgO, MnO and Na2O) elements and compounds contained in the clay samples in the various proportions and the appropriate purification technique required for preparing the clays for high temperature applications. Consequent upon the identification of the deleterious impurities, oxalic acid at different concentrations was used to leach the impurities out of the various clays. However, three out of the five deposits were chosen for purification because they possess the least quantities of the most deleterious (Fe2O3) of the impurities.
