2. Thesis and Dissertations

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    Studies on Anionic Gemini Surfactants as Corrosion Inhibitors on AZ31 Magnesium Alloy
    (National Institute of Technology Karnataka, Surathkal, 2022) M, Gururaj Acharya; Shetty, Adka Nityananda
    The magnesium alloys are considered to be the best structural materials, because of their advantageous strength to weight ratio. But, the limitation in their real field applications lies in the fact that magnesium alloys are highly susceptible for corrosion. Hence understanding the corrosion of AZ31 alloy and developing the measures to combat the same are crucial. In the present studies, the corrosion behaviour of AZ31 alloy was investigated by electrochemical methods in sodium chloride and sodium sulphate media of different concentrations at different temperatures and followed by its inhibition studies. The corrosion rate was monitored by potentiodynamic polarization technique and electrochemical impedance spectroscopy along with SEM-EDX, and XPS. The synthesized inhibitors were subjected to theoretical studies as well. The blank corrosion studies were performed at various medium concentrations, pH and temperatures. The results revealed a trend of higher corrosion rate associated with higher medium concentration, lower pH and higher temperature. Five different long chain anionic Gemini surfactants namely, DB, DH, DO, DC and DD were synthesized and tested as corrosion inhibitors for AZ31 alloy. The calculated activation and thermodynamic parameters have been recorded in the thesis. The inhibitors were predominantly physisorbed with partial chemisorption. The adsorption of the surfactant on the surface of AZ31 alloy obeyed Langmuir adsorption isotherm. The studied surfactants were found to function as mixed-type inhibitors. The surfactants were more efficient at lower temperatures. The efficiencies of the surfactants decreased in the order: DD>DC>DO>DH>DB and this has been accredited to the reduction of chain length. The proposed mechanism attributed the cathodic inhibition to the blockage of the reaction spots by chemisorbed acetates. The anodic inhibition resulted from the compaction of porous film by precipitated magnesium- inhibitor salts.
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    Corrosion Inhibition Studies of GA9 Magnesium Alloy in Chloride and Sulphate Media
    (National Institute of Technology Karnataka, Surathkal, 2020) Shetty, Sudarshana.; Shetty, A Nityananda.; Nayak, Jagannatha
    The corrosion behaviour of GA9 magnesium alloy in two different media, namely, sodium chloride and sodium sulphate in different concentrations and temperatures have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The effect of pH of the medium on the corrosion behaviour of GA9 magnesium alloy have also been studied in both the media. The results revealed a trend of higher corrosion rate associated with higher medium concentration, lower pH and higher temperature. The corrosion rate in the sodium chloride medium was higher than that in the sodium sulphate medium. Four different alkyl sulfonates namely sodium dodecylbenzenesulfonate (SDBS), sodium 4-n-octylbenzenesulfonate (SOBS), sodium 2,4-dimethylbenzenesulfonate (SDMBS) and sodium benzenesulfonate (SBS) were tested as corrosion inhibitors for GA9. The results pertaining to the corrosion inhibition studies of four inhibitors in two different media at different temperatures in the presence of varying concentrations of inhibitors are reported in the thesis. The inhibition efficiencies of all the four inhibitors decrease with the increase in temperature and increase in the concentration of the media. Activation parameters for the corrosion of the alloy and thermodynamic parameters for the adsorption of the inhibitors have been calculated and have been documented in the thesis. The sulfonates predominately physisorbed and adsorption was in accordance with Langmuir adsorption isotherm. The studied sulfonates were found to function as mixed type inhibitors. The sulfonates were more efficient at lower temperatures in both the media. Inhibition efficiency is in the order SDBS > SOBS >SDMBS > SBS. Proposed mechanism attributed the cathodic inhibition to the blockage of the reaction spots by chemisorbed sulphonates. The anodic inhibition resulted from the compaction of the porous film by precipitated magnesium sulfonates.
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    Studies on Corrosion Inhibition of 18% Ni M 250 Grade Maraging Steel under Weld Aged Condition in Acidic Media
    (National Institute of Technology Karnataka, Surathkal, 2013) B. S., Sanatkumar; Shetty, A. Nityananda; Nayak, Jagannatha
    The corrosion behaviour of 18 % Ni M250 grade maraging steel under weld aged conditions in two different acid media, namely, hydrochloric acid and sulphuric acid in various concentrations and temperatures have been studied by Tafel polarization and electrochemical impedance spectroscopy techniques. The corrosion rate in the sulphuric acid medium was higher than in the hydrochloric acid medium. Five organic inhibitors were synthesized and characterized using spectral and elemental analysis. The five inhibitors were 1(2E)-1-(4-aminophenyl)-3-(2-thienyl) prop-2-en-1-one (ATPI), 2-(4-chlorophenyl)-2-oxoethyl benzoate (CPOB), 2-(4- bromophenyl)-2-oxoethyl- 4-chlorobenzoate (CPOM), (E)-1-(2,4-dinitrophenyl)-2-[1- (2-nitrophenyl) ethylidene] hydrazine (DNPH) and 5-diethylamino-2-{[2-(2,4- dinitrophenyl) hydrazin-1-ylidene]methyl} - phenol (DDPM). The results pertaining to the corrosion inhibition studies of five inhibitors in two different acid media at different temperatures in the presence of varying concentrations of inhibitors are reported in the thesis. Activation parameters for the corrosion of the alloy and thermodynamic parameters for the adsorption of the inhibitors have been calculated and the results have been analysed. The adsorption of first four inhibitors on the alloy was through both physisorption and chemisorption, with predominant physisorption in both the media. The mode of adsorption for the DDPM predominantly chemisorption in both the media. The adsorption of all the five inhibitors on alloy surfaces follows Langmuir adsorption isotherm. The inhibition efficiencies of first four inhibitors decrease with the increase in temperature, the inhibition efficiency of DDPM increases with the increase in temperature.
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    Study on Corrosion Behavior and Corrosion Inhibition of Magnesium Alloy Ze41
    (National Institute of Technology Karnataka, Surathkal, 2014) K, Nandini; Shetty, A. Nityananda
    The alloys of magnesium are in the spot-light lately. With applications that run the gamut from automobile parts to medical implants, this class of alloys truly deserve all the adulation coming their way. ZE41 is one such cast alloy, which is lighter than aluminium, can be cast or machined into variety of desired shapes and has good damping and shock absorption abilities. A very low resistance to corrosion puts the otherwise remarkable efficacy of ZE41 in jeopardy. Hence understanding the corrosion of ZE41 and developing the measures to combat the same are indispensable. In the present thesis the corrosion of ZE41 and its mitigation were analyzed using techniques like potentiodynamic polarization and AC impedance, along with SEM and EDX analyses. Sodium sulfate and its mixture with sodium chloride were chosen as two corrosive media. The blank corrosion studies were performed at various medium concentrations, pH and temperatures. The results revealed a trend of higher corrosion rate associated with higher medium concentration, lower pH and higher temperature. Five different long chain alkyl monocarboxylates namely stearate, palmitate, myristate, laurate and caprylate were synthesized and tested as corrosion inhibitors for ZE41. The calculated activation and thermodynamic parameters have been documented in the thesis. The carboxylates were predominantly physisorbed and adsorption was in accordance with Langmuir adsorption isotherm. The studied carboxylates were found to function as mixed-type inhibitors which predominantly suppressed anodic reaction. The carboxylates were more efficient at lower temperatures and in combined medium. At an optimum concentration the efficiencies of the carboxylates decreased in the order: stearate > palmitate > myristate > laurate > caprylate and this has been accredited to the reduction in aliphatic chain length. The proposed mechanism attributed the cathodic inhibition to the blockage of the reaction spots by chemisorbed carboxylates. The anodic inhibition resulted from the compaction of porous film by precipitated magnesium carboxylate salts.
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    Studies on corrosion inhibition of 18% Ni M 250 grade maraging steel under welded condition in acidic media
    (National Institute of Technology Karnataka, Surathkal, 2014) Kumar, Pradeep; Shetty, A. Nityananda
    The corrosion behaviour of 18% Ni M250 grade maraging steel under welded conditions in two different acid media, namely, hydrochloric acid and sulphuric acid in various concentrations and temperatures have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The corrosion rate in the sulphuric acid medium was higher than in the hydrochloric acid medium. The effect of corrosion inhibition on welded maraging steel was carried out by using five inhibitors, n a m e l y , 2,5-Bis (3,4,5-trimethoxy phenyl)-1,3,4-oxadiazole (BTPO), 1-Phenyl-4-(4-nitrophenyl) thiosemicarbazide (PNPT), 3,4,5-Trimethoxy benzoicacid(3,4,5-trimethoxy-benzylidene) hydrazide (TBTBH), 2-(5-Chloro-1Hbenzoimidazol-2-yl) phenol (CBP), 2-(4-Methoxy-phenyl)-benzo[d]imidazo[2,1-b] thiazole (MPBIT). The results pertaining to the corrosion inhibition studies of five inhibitors in two different acid media at different temperatures in the presence of varying concentrations of inhibitors are reported in the thesis. Activation parameters for the corrosion of the alloy and thermodynamic parameters for the adsorption of the inhibitors have been calculated and the results have been analysed. The adsorption of all five inhibitors on the alloy was through both physisorption and chemisorption, with predominant physisorption in both the media. The adsorption of all the five inhibitors on alloy surfaces follows Langmuir adsorption isotherm. The inhibition efficiencies of all five inhibitors decrease with the increase in temperature and increase in concentration of acidic media.