M. Tech. Metallurgical Engineering / Mild steel is vulnerable to corrosion; this behaviour affects the material strength and electrochemical behaviour during industrial application. Mild steel also has poor tribological resistance; its application for the components of machines, however, requires good tribological property. The cost incurred from equipment failures, properties loss and increased production overheads makes is imperative to enhance mild steel's electrochemical and tribological properties. Electroless nickel plating has found extensive use in various industries attesting to its exceptional properties. The effect of bath parameters on the electroless plating process is of importance as this affects the adhesion, morphological behaviour, electrochemical properties and uniformity of coating. The key aim of this research is: To generally improve the understanding of the effect of electroless binary and ternary alloys on the corrosion and wear resistance of mild steel using weight loss method, potential measurement, linear polarization and tribological sliding wear tests. This work studies the effect of temperature, concentration, deposition time and the inclusion of Tin (Sn) as a third addition to the electroless bath. Corrosion and wear behaviour of the electroless plated mild steel was studied.

M. Tech. Chemical Engineering. / Discusses the corrosion of mild steel due to sulphate ions together with chloride ions in concrete reinforcement in alkaline media can be limited or even eliminated by the introduction of laser surface irradiation on the mild steel material.

Thesis (M.S.)--Ohio University, March, 2009. / Title from PDF t.p. Includes bibliographical references.

A series of homogeneous halogen containing polymers have been studied whilst sliding against mild steel and oxides present on mild steel. The degradation characteristics of P. V. C. and C1d P. V. C. have been correlated in terms of current mechano-chemical comminution theory and the process causing the wear of P. V. C., C1d P. V. C., P. T. F. E. and P. C. T. F. E. described in relation to the chemical and physical conditions at the sliding interface. In addition the potential importance of the chemical role of oxide free iron surfaces in wear processes has been demonstrated by interacting an analogue compound of P. T. F. E. (n-C5F12) with clean iron under ultra high vacuum conditions. The resulting fragmentation of the perfluorinated compound is discussed and a simplified degradation mechanism suggested.

This thesis is a contribution to research into erosion-corrosion investigating the rapid wastage of in-bed heat exchanger tubing in fluidized bed combustors. Two main new areas of research were investigated; erosion-corrosion of mild steel in a temperature gradient and erosion-corrosion modelling. It has been suggested that differences between the wastage behaviour measured in fluidized bed combustors and laboratory studies is due to laboratory tests being carried out isothermally (specimen and fluidized bed at the same temperature) whereas, in a FBC boiler, the fluidized bed is considerably hotter than the metal heat exchanger tubing. The fluidized bed test rig was modified to increase the temperature gradient between the specimen and the fluidized bed from initial tests conducted by Rogers (1992b). Tests were carried out over a range of bed temperatures (300-500° C) and cooled specimen surface temperatures (175-500° C) with a maximum temperature difference between the two of 250° C. It was discovered that the temperature of the wear scar during a test was up to 200° C hotter than the temperature at the back of the specimen where the specimen temperature was initially measured in tests by Rogers (1992b). After temperature calibration tests the wastage of the specimens in a temperature gradient were very similar to the wastage of specimens exposed isothermally at the same metal temperature. Short term oxidation experiments were conducted on mild steel to obtain oxidation kinetics for erosion-corrosion modelling. It was found that the initial apparent parabolic rate constant was an order of magnitude larger than at longer time. Erosion studies were conducted with the aim to obtain quantitative data on the particle flux and the erosive behaviour of the bed with temperature. Results were not accurate enough to yield quantitative data but provided an estimate of the particle flux in the fluidized bed test rig. Results obtained from the short term oxidation and erosion studies were used in simple erosion-oxidation models to construct erosion-corrosion regime maps which tended to predict metal erosion to higher temperatures than observed experimentally. Predictions of material wear from the combination of an oxide removal and spalling mechanism predicted sensible wastage rates which agreed with experimental results.

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Engineering : Chemical / M. Tech. (Chemical Engineering)

The electrochemical corrosion behavior of mild steel in apple, grape, mango, orange and the mixture of these juices was investigated in this study. Open circuit potential and weight loss analytical techniques were employed to establish the comparative corrosion rates of this material in the agro media over the interval of five days for a sixty-day immersion period at an ambient temperature. The chemical compositions of both mild steel and the agro media were determined to ascertain corrosion mechanism for the reaction. Polarization behavior of mild steel in the agro media were determined by Tafel extrapolation curves. The analysis showed that cathodic polarization curves were almost identical irrespective of the concentration of the various media while the anodic polarization curves exhibited varying active and passive corrosion behaviour due to passivating oxide films. The analysis of the results further showed that the corrosion rate of the metallic sample decreased with longer immersion periods which could be attributed to a gradual decline in acidity of these media as revealed by the pH results. Hence, the evolution of hydrogen gas and reduction of dissolved oxygen molecules from the reacting system were presumed to be major factors retarding corrosion of the solution involved. Similarly, the presence of suspended particles on the surface of the test steel sample could have also led to the impediment to corrosion rates from the surrounding atmosphere. Microscopic analysis of the corroded mild steel specimens revealed uniform and localized corrosion with Fe2O3 spotted as the main corrosion product. The result obtained from the electrochemical study showed that the corrosion rate of the mild steel sample was highest in the orange medium (1.53mm/yr), followed by grape medium (1.40mm/yr), mixture of these media (0.67mm/yr), mango medium (0.40mm/yr) while the metal corroded least in the apple medium (0.30mm/yr) over the duration of immersion. / Engineering : Chemical / M. Tech. (Chemical Engineering)

This thesis reports on the research outcome of corrosion mechanism and corrosion rate of mild steel in different environments (saline, alkaline solutions and concrete media) using potentiodynamic polarization technique. The study also included the effect of corrosion on bond strength between reinforcing steel and concrete using pull-out test. Corrosion of mild steel and 316L stainless steel with different surface conditions in 1, 3 and 5% saline (NaCl + Distilled water) was investigated. Specimens ground with 200 and 600 grit silicon carbide grinding paper as well as 1μm surface finish (polished with 1μm diamond paste) were tested. In case of mild steel specimens, reduction in surface roughness caused increase in corrosion rate, while in 316L stainless steel corrosion rate decreased as the surface roughness improved. Metallographic examination of corroded specimens confirmed breakdown of passive region due to pitting corrosion. Corrosion of mild steel was also investigated in alkaline solution (saturated calcium hydroxide, pH =12.5) contaminated with 1, 3 and 5% saline. A series of corrosion experiments were also conducted to examine the efficiency of various concentrations of calcium nitrite (CN) on corrosion behaviour of both as-received and polished mild steel in alkaline solution containing 3% saline after 1 hour and 28 days of exposure. Corrosion rate was higher for the as-received than polished mild steel surface under the same testing conditions in NaCl alkaline solution with and without nitrites due to the effect of surface roughness. Morphology investigation of mild steel specimens in alkaline solution ii containing chlorides and nitrites showed localized pits even at nitrite concentration equal to chloride concentration. Corrosion of steel bars embedded in concrete having compressive strengths of 20, 30 and 46MPa was also investigated. The effect of 2 and 4% CN by weight of cement on corrosion behaviour of steel bar in low and high concrete strengths specimens were also studied. All reinforced concrete specimens were immersed in 3% saline solution for three different periods of 1, 7 and 15 days. In order to accelerate the chemical reactions, an external current of 0.4A was applied. Corrosion rate was measured by retrieving electrochemical information from polarization tests. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel/concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and bond strength were dependent on concrete strength, amount of CN and acceleration corrosion period. As concrete strength increased from 20 to 46MPa, corrosion rate of embedded steel decreased. First day of corrosion acceleration showed a slight increase in steel/concrete bond strength, whereas severe corrosion due to 7 and 15 days corrosion acceleration significantly reduced steel/concrete bond strength. Addition of only 2% CN did not give corrosion protection for steel reinforcement in concrete with 20MPa strength at long time of exposure. However, the combination of good quality concrete and addition of CN appear to be a desirable approach to reduce the effect of chloride induced corrosion of steel reinforcement. At less time of exposure, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 days of corrosion acceleration, the higher concentration of CN gave higher bond strength in both concrete mixes. The same trend was observed at 15 days of corrosion acceleration except for the specimen with 20MPa compressive strength and 2% CN which recorded the highest deterioration in bond strength.