In the present study, the structural modification of sand cast Al-12wt%Si alloy with sulfur/sodium and its effect on mechanical properties were investigated. Different addition levels of sulfur and sodium were used to modify and produce castings of the same shape and size from the alloy. The results indicated that the addition of sodium or sulfur to eutectic Al-Si alloy can modify the Al-Si eutectic morphology from needle-like eutectic silicon structure to fine-scale eutectic silicon structure with significant improvement in mechanical properties of the alloy. The optimum levels of modification by sodium flux (60% NaF and 40% NaCl) and sulfur were found to be 0.6%-1.0% and 0.02%-0.05% of the weight of the alloy respectively. The alloy modified with 0.6% Na flux had the best mechanical properties closely followed by the one modified with 0.02% sulfur. Over modification of the alloy with sodium produced over modification band which consisted of aluminum dendrites and coarse silicon particles in the microstructure of the alloy. Increase in concentration of sulfur decreased the degree of fineness of the eutectic silicon structure with significant decrease in mechanical properties of the alloy and this is suggested to be as a result of the presence of a brittle sulfur compound at the grain interfaces of the alloy.
The formation of carbides during the aging of a quenched steel with mass contents of 0.04% carbon was investigated by means of internal friction by measuring the carbon Snoek peak height. The aging was carried out at different temperatures ranging from 40 to 350 DC so that different types of carbides were formed. Low-temperature carbides develop after aging below 100 DC. The Johnson-Mehl equation is applied to evaluate the kinetics of precipitation and re-dissolution of the different carbides. The solubility of carbon in ferrite is influenced by the pre-existing carbides, which is, in part, the reason for the variation of thermodynamic data in previous work. Charakterislerung vonMittel· und Tieftemperaturcarbiden In einem niedriggekohlten Stahl durch innere Relbung. Die Bildung von Carbiden wahrend des Alterns eines abgeschreckten Stahles mit Kohlenstoffmassengehalten von 0,04% wurde mit Hilfe der inneren Reibung durch Messung der Hohe des Kohlenstoff-Snoek-Maximums untersucht. Die Alterung erfolgte bei verschiedenen Temperaturen von 40 bis 350 DC, so daB verschiedene Arten von Carbiden entstanden. Tieftemperaturcarbide bilden sich bei Alterungstemperaturen unter 100 DC. Die Johnson-Mehl-Gleichung diente zur Bestimmung der Kinetik der Carbidbildung und -auflosunq. Die Kohlenstofftosucnkeit im Ferrit wird von der Anwesenheit der verschiedenen Carbide beeinfluBt. Dies ist zum Teil der Grund fUr die uneinheitlichen thermodynamischen Daten in frOheren Arbeiten. 0,: Aiwu Zhu; D,: mont. Simeon Ikechukwu Neife, (now with Mechanical
ABSTRACT:The corrosion of mild steel (uncoated), galvanized steel and stainless steel (304L) have been studied using the weight loss method over a period of 98 days with measurements made at 14 days' interval in ground melon (locally called egusi), cassava pulp, mashed palm fruit, tomato pulp, and black-eyed bean pulp respectively. The results obtained show that the average corrosion rates of 304 stainless steel, galvanized steel and mild steel are in ground melon
Naval ships are constructed with mild steel. Corrosion is a major concern in a marine environment. This particular type of material degradation has recently received more attention by the marine industry. Effort is make my researchers to combat this problem. In this work, co-deposition of Zn-ZnO-Ant hill powder composite coating on mild steel was reported with the view to combat this problem. The Ant hill powder was varied from 0 to 25 g. A 10 mL of orange juice was used as an organic additive. The coating thickness, surface roughness, microstructure, hardness values, wear rate and potentiodynamic polarization in simulated sea water were determined. The addition of orange juice as an additive changed the morphological and texture of the coating, and the hardness values, wear and corrosion rate were enhanced. Maximum corrosion protection efficiency of 92.86% and 94.41% was obtained at Zn-ZnO-25gAnt hill and Zn-ZnO-25gAnt hill + orange juice, respectively. The work has established that Zn-ZnO-Ant hill powder composite coating on mild steel is promising.
This work studies the use of Amaranthus cordatus as the corrosion inhibitor for conventional mild steel in 0.5 M and 1.0 M of both H 2 SO 4 and NaCl. The effects of different concentrations of the acid and base on the inhibition efficiency of Amaranthus cordatus were tested at room temperature and at different inhibitor volumes. The experiment was set for 30 days and weight-loss corrosion technique was employed in obtaining the corrosion penetration rate using the standard equation: 87.6 w cpr At ∆ = ρ. The result shows that the rates of corrosion of the mild steel increased with an increase in concentration of the acid or base and also decreased with increasing volume of Amaranthus cordatus. Expectedly, the inhibition efficiency was found to be greater in sodium chloride than in tetraoxosulphate VI acid. Also inhibition efficiency was found to increase with increase in extracts volume and decrease in concentration of the acid or base. These findings strongly suggest that Amaranthus cordatus can be used as the inhibitor for preventing the corrosion of mild steel.
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