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Perchlorate is a threat to public health through water but also food. However, there is no effective chemical treatment process which can destroy perchlorate found in groundwater and surface water. Thus, there is growing interest in developing effective technologies, especially chemical treatments, to completely destroy trace levels of perchlorate present in drinking and groundwater. The research on perchlorate reduction by zero-valent titanium (Ti(0)) showed that perchlorate was effectively reduced to chloride using electrochemically developed pitting corrosion on Ti(0). Perchlorate reduction was believed to be caused by an active reductant (dissolved Ti(II)) during the pitting corrosion of Ti(0). The rate of perchlorate reduction was independent on the imposed potential as long as the potential was maintained above the pitting potential of Ti(0), but it was proportional to the applied current. The perchlorate reduction on the pitting developed Ti(0) was inhibited by the presence of chloride and bromide. Inhibition mechanism of perchlorate reduction inhibition was believed to be caused either by competitive adsorption of aggressive anions on bare Ti(0) surface or Ti(II) consumption by electrochemically produced chlorine. Kinetic models were developed based surface coverage of aggressive anions on bare Ti(0) and Ti(II) oxidation by chlorine. These kinetic models supported the perchlorate concentration change in the solution, but Ti(II) consumption model was not able to predict chloride concentration due to insufficient information describing complex nature of pitting on Ti(0). These results shown in this research demonstrate that pitting corrosion developed Ti(0) has the capability to chemically reduce perchlorate present in natural water and engineered systems as well as possible problems associated with electric input. This research may be a starting point for development of a new treatment process that applies titanium or titanium metal ions as a chemical reductant to abate contaminants present in natural and engineering systems. Further developments can be achieved by alloying titanium metal with other metals such as iron and aluminum, and finding a methodology producing stable Ti(II) in ambient conditions.

When the shaft current passes through the bearing under lubrication condition, the arc often occurs and the pitting can be observed on the surface of bearing. Consequently, the life of bearing is shortened. The pitting resulting from discharge is dependent upon the shaft voltage, the oil film thickness, and the insulation of lubricant. To simulate the pitting, the dynamic pitting tester is developed to investigate the effects of the kinematics parameters on the electrical pitting formation mechanism for the common material of bearing by changing the supply voltage current and the oil film thickness. Result show that in the static condition, since the arc action causes the surface melting of two specimens, and the actions of coulomb force and electrostatic force cause the specimens to attract each other, the plateau can be observed on the surfaces of specimens. The plateau is like a bridge to connect two specimens. In this moment the plateau accumulates continuously and causes two specimens to produce the repulsive force. In the dynamic condition, the formation of pitting at the initial stage is quite similar to that in the static condition. Since the effect of sliding speed, the bridge is sheared and the friction force increases. Under the actions of joule heat and friction force, the surfaces of two specimens melt and scratch continuously. When the dynamic pitting occurs, the pitting width of square specimen, the normal force and the friction force increases with increasing supply voltage, supply current, and oil film thickness. When the interface power is larger, the melting phenomenon is more obvious, and the pitting width becomes larger. Because the surface melting and the actions of Coulomb force and electrostatic force cause the material accumulates continuously, the normal force and the friction force increase with increasing the interface power. To investigate all effects of experimental parameters on the pitting width, the empirical formula for the pitting width is established in terms of supply voltage, supply current, and oil film thickness. This formula can be used to predict oil film thickness or the size of pitting width on the bearing surface for diagnosing the lubricant condition of bearing.

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A range of techniques designed to monitor copper pitting propensity were applied at two water utilities with known pitting disposition. In addition to traditional approaches including ECorr rise, chlorine decay kinetics, and surface analyses, a novel method was attempted to develop "pitting currents" between copper samples exposed to differential flow. This method allowed pitting current, potential, and resistance between "pits" and sections of copper pipe to be measured. As part of this evaluation, effects of different corrosion inhibitors and secondary disinfectants were investigated in an attempt to identify water quality modifications that might alleviate copper pitting at each utility. At a Florida utility where customers were experiencing a severe pitting problem, experiments investigated the effectiveness of corrosion inhibitors including orthophosphate, an orthophosphate-polyphosphate blend, and zinc polyphosphate. Results suggested that zinc polyphosphate provided the greatest likelihood of mitigating copper pitting corrosion, whereas orthophosphate and the orthophosphate-polyphosphate blend actually increased electrochemical indications of pitting. According to theory, orthophosphates can increase pitting intensity if applied in insufficient quantities, whereas cathodic inhibitors, such as zinc, can only reduce corrosion rates. Surface analyses determined that zinc polyphosphate produced the least amount of scale, whereas the control produced the greatest amount. Further, surface analyses also suggested that zinc and phosphorus may behave synergistically during precipitation reactions which decrease copper release. Subsequent testing at Virginia Tech laboratories confirmed that some of the benefits from the zinc polyphosphate product were directly attributed to zinc. Consistent with previous research, pitting propensity of the water in the absence of inhibitor decreased at pH 7.5 relative to pH 8.5 (Marshall, 2004). In addition, higher concentrations of chloramines increased the pitting propensity of the water, although the ratio of chlorine to ammonia had little effect. Similar experiments were also conducted at a utility in Iowa. Copper pitting has always existed in this area at some low level; however an outbreak of copper pinhole leaks recently occurred that is temporally correlated with high chlorine and chloramine concentrations. Experiments investigated combinations of disinfectant type (free chlorine or chloramines) and corrosion inhibitor (orthophosphate or zinc polyphosphate) in an attempt to decrease pitting propensity. Results indicated that the addition of zinc polyphosphate decreased pitting propensity in free chlorine systems as well as systems dosed with chloramines. In contrast, the addition of orthophosphate seemed to be ineffective in either system. Final surface analyses confirmed that inhibitors performed most effectively in the free chlorine system, whereas no clear benefits were realized in chloramine systems. / Master of Science

Wreckage of ‘Carnauba’, a 1930s vintage Sikorsky S-38 aircraft, a beloved icon of SC Johnson's early history, was found on July 5, 2000, in seawater off of an Indonesian island of West Irian Jaya. The company decided to recover this aircraft from seawater, conserve it, and display it in its museum, as part of their rich heritage. The objective was to study the aluminum alloy used on the aircraft for its chemical and mechanical properties, suggest the corrosion mechanism of aluminum alloy 2024 in seawater, and recommend preservation methods for the same. Chemical analysis performed on the samples collected from the site revealed that copper was the primary alloying element. Copper is responsible for increasing the strength. However, copper is also the reason for pitting corrosion of the aluminum alloy, causing material loss and reducing the structural stability of the wreckage. Copper forms intermetallics with other elements, such as magnesium and aluminum, and is distributed in the aluminum matrix heterogeneously. In order to study the corrosion mechanism of aluminum alloy 2024, it was subjected to potentiodynamic tests in sodium chloride solution. In the presence of an electrolyte like seawater, the difference between the potentials of these intermetallics and the surrounding aluminum matrix creates a galvanic cell. The galvanic cells serve as sites for localized corrosion. Chloride ions are responsible for pitting of alloy 2024. A pitting potential of around -600mV was observed when sodium chloride was used as an electrolyte. The average corrosion rate measured for wrought aluminum alloys was around 0.05 mm/year. The thesis provides guidelines or recommendations for the procedure to be followed in recovering aircraft from seawater, and retain it in its as found condition. Recommendations about various measurements like pH, dissolved oxygen, salinity, pressure, temperature, and velocity need to be taken and the visual assessment needs to be done before the aircraft is hauled from the seawater were specified. After the aircraft has been recovered, recommendations for handling, cleaning, and prevention of corrosion using coatings such as carnauba wax and inhibitors such as chromates, have been stated.

Made available in DSpace on 2014-06-11T19:28:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T20:37:40Z : No. of bitstreams: 1 silva_jwj_me_guara.pdf: 1820882 bytes, checksum: 7e96fbad2b277d2b628c44604b9cf46d (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Foram caracterizados os comportamentos eletroquímicos e avaliadas as resistências à corrosão das ligas aeronáuticas 2024-T351 e 7050-T7451 em soluções aquosas de cloreto contendo cromato, molibdato e tungstato. Foram realizados ensaios de corrosão não-eletroquímicos de imersão prolongada acompanhados de análise metalográfica de superfície por microscopia óptica e identificação dos produtos de corrosão por difratometria de raios-X. A análise quantitativa de superfícies das ligas após a imersão, indica que os pites formados têm áreas médias similares. Os pites são mais largos do que profundos e de geometria, predominantemente, cônica ou quase-cônica e irregular. Em todos os produtos de corrosão de cada liga foi encontrado hidróxido de alumínio, em suas diferentes formas cristalinas. Medidas de perda de dureza, como uma conseqüência da deterioração superficial, também foram determinadas. Além disso, ensaios eletroquímicos como medidas de potencial em circuito aberto, curvas de polarização e voltametria cíclica complementaram este estudo. Em meio aerado os resultados obtidos mediante medidas eletroquímicas são consistentes com aqueles obtidos nos ensaios de imersão, em particular o efeito do CrO42- e do MoO42-. O WO42- mostrou-se agressivo em períodos prolongados de imersão. Apesar dos ensaios revelarem uma redução parcial de MoO42- em ambas as ligas, o efeito desse oxi-ânion parece ser diferente sobre cada liga. Em meio desaerado as ligas apresentam passivação em todos os eletrólitos. A adição dos oxi-ânions não modificou significativamente o potencial de pite para a liga 7050, enquanto que para a liga 2024 ele foi deslocado levemente para valores mais positivos. / It has been characterized the electrochemical behavior and evaluated the 2024-T351 and 7050-T7451 aircraft alloys corrosion resistance in chloride aqueous solutions containing chromate, molybdate and tungstate. It has been carried out non-electrochemical long immersion corrosion testings accompanied by surface metalography analysis achieved by light microscopy and corrosion products identification by X-ray difratometry. Surfaces quantitative analysis upon the alloys after immersion, indicates that formed pits have similar average area. Pits are widther than deeper and own predominantly a conical or quasi-conical and irregular geometry. In all corrosion products of each alloy it has been found aluminum hydroxide in its different crystalline ways. Hardness loss measurements have also been determined. In addition, electrochemical testings such as open circuit potential measures, polarization curves and cyclical voltammetry have completed this study. In aerated means the obtained results before electrochemical mesurements are similar to those obtained in the immersion tests, in particular CrO42- and MoO42- effects. WO42- has been found to be aggressive in very long immersion period. Though tests display a MoO42- partial reduction in both alloys, this oxi-anion effect seems to be different upon each alloy. In de-aerated means alloys present passivation in all eletrolytes. Oxi-anion addition has not changed significantly pit potential for 7050 alloy, while for 2024 alloy it has been dislocated, slightly, for more positive values.