Chloride-induced corrosion of reinforcing steel is widely accepted as the primary cause of premature deterioration in concrete bridge decks (Brown, M.C., 2002). Since linear cracking in concrete cover can potentially accelerate chloride ingress to the depth of the reinforcing steel, there is reason to believe that severity of deck cracking can significantly influence the time to first repair and/or rehabilitation of the bridge deck. Surface width, orientation, and length of cracks in 38 Virginia bridge decks were investigated in order to characterize the general distribution of deck cracking in the commonwealth of Virginia. Crack data was correlated to structural/material design parameters and environmental exposure conditions in order to determine significant predictor-response relationships. The majority of surveyed bridge decks were divided into four classifications of deck type based on superstructure type and construction era, either 1968-1971 or 1984-1991. Surveyed bridge decks that did not fit into any of the four classifications were used to form more generalized subsets. These larger subsets were used to determine if significant influence factors could be translated to broader classifications of bridge decks. Transverse beam spacing, annual average daily truck traffic (AADTT), resistivity of the deck concrete, chloride exposure, and the percentage of concrete clear cover depths less than or equal to 38mm (1.5 in) were all determined to have a significant correlation with linear deck cracking. / Master of Science

As stagnant water contacts copper pipe and lead solder (simulated soldered joints), a corrosion cell is formed between the metals in solder (Pb, Sn) and copper. If the resulting galvanic current exceeds about 2 µA/cm², a highly corrosive microenvironment can form at the solder surface, with pH <2.5 and chloride concentrations 11 times higher than bulk water levels. Waters with relatively high chloride tend to sustain high galvanic currents, preventing passivation of the solder surface and contributing to lead contamination of potable water. If the concentration of sulfate increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced, and solder surfaces were readily passivated. Mechanistically, at the relatively high concentrations of lead and low pH values that might be present at lead surfaces, sulfate forms precipitates while chloride forms soluble complexes with lead. Considering net transport of anions in water, a chloride-to-sulfate mass ratio (CSMR) above 0.77 results in more chloride than sulfate transported to the lead anode surface, whereas the converse occurs below this CSMR. Bicarbonate can compete with chloride transport and buffer the pH, providing benefits to lead corrosion. Although orthophosphate is often an effective corrosion inhibitor, tests revealed cases in which orthophosphate increased lead and tin release from simulated soldered joints in potable water. Phosphate tended to increase the current between lead-tin and copper when the water contained less than 10 mg/L SO₄²⁻ or the percentage of the anodic current carried by SO₄²- ions was less than 30%. Additionally, nitrate in the potable water range of 0-10 mg/L N dramatically increased lead leaching from simulated soldered pipe joints. Chloramine decay and the associated conversion of ammonia to nitrate during nitrification could create much higher lead contamination of potable water from solder in some cases. In practical bench-scale studies with water utilities, the CSMR was affected by the coagulant chemical, blending of desalinated seawater, anion exchange, and sodium chloride brine leaks from on-site hypochlorite generators. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from lead-tin solder connected to copper. / Ph. D.

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

Aluminum is an attractive metal for use as an anode in the cathodic protection of steels in seawater due to its low cost and high current capacity. Zinc is often used for its ability to readily corrode, but it has a low current capacity and it operates at very negative voltages, leading to hydrogen generation at the steel cathode, which may cause hydrogen embrittlement. Aluminum can operate at less-negative voltages, therefore reducing hydrogen generation, but it forms a passive oxide film, preventing the anode from corroding. Ga is added to aluminum in small amounts (0.1 wt%) to destabilize this oxide film and allow for active corrosion. The mechanism of how Ga activates Al is still not well-known, though there are prevailing proposals. A previous study noted a difference in behavior between Al-Ga master heats and the alloys that were later produced by re-melting them. This study is focused on characterizing the corrosion behavior of Al-0.1 wt% Ga in synthetic seawater, with samples from a master heat and two subsequent remelts. Galvanostatic, potentiostatic, and open-circuit tests were run, as well as galvanic coupling with 1123 steel. It was found that the remelted anodes behaved more consistently and maintained stable corrosion behavior for longer times than the master heat. X-ray Photoelectron Spectroscopy analysis showed elevated concentrations of Ga inside the oxide layer. The findings support the mechanism in the literature of discrete particles of Ga forming under the oxide film but do not support the mechanism of an amalgam layer formation. This project was funded by NACE International, Virginia Tech project number 457789. / Master of Science

Silicon nitride (Si3N4) is a potentially good ceramic material for industrial heat exchangers. However, at elevated temperatures and in coal combustion atmospheres its lifetime is severely reduced by oxidation. To increase its corrosion resistance, the formation of a protective oxidation barrier layer was promoted by the deposition of oxide thin films. Homogeneous and crack-free oxide coatings of calcium magnesium zirconium phosphate (CMZP) and magnesium doped aluminum titanate (Mg-doped Al2TiO5) were successfully deposited on Si3N4 using the sol-gel and dip-coating technique. Coated and uncoated samples were then exposed to a sodium containing atmosphere at 1000*C for 360 hours to simulate typical industrial environment conditions. Structural post-exposure analyses based on weight loss measurements and mechanical tests indicated better corrosion resistance and strength retention for CMZP coated Si3N4 compared to as received and Mg-doped Al2TiO5 coated Si3N4. This difference was attributed to the protective nature of the corrosion layer, which in the case of CMZP, significantly impeded the inward diffusion of oxygen to the Si3N4 surface. / Master of Science

Concrete corrosion has serious societal and economic impacts and is an important concern in a utility's overall corrosion control strategy. Though concrete based pipes and linings are only restricted to the distribution mains, they still make up a large percentage of the drinking water infrastructure at about 17% of its total length. An improved understanding of the corrosion mechanisms involved steps that can be taken to mitigate concrete corrosion are very important. This study examined the role of phosphate chemicals, water chemistry, temperature and gaseous cavitation on the degradation of cement-based pipes and linings. It also provides information for utilities to make informed decisions regarding the use, effectiveness, and application of phosphate corrosion inhibitors relative to concrete corrosion control. Under low alkalinity and low pH conditions, considered to be highly aggressive in the literature, we noticed very substantial corrosion of concrete in laboratory experiments. At high pH and high alkalinity conditions, the buildup of scale (e.g., calcium carbonate) on the inside of the pipe is the major concern. The addition of phosphate inhibitors strongly influenced both concrete corrosion and scaling. At low alkalinity the addition of zinc orthophosphate or polyphosphate reduced corrosion of concrete. The addition of orthophosphate under low alkalinity conditions increased aluminum leaching and could push aluminum concentrations above the EPA SMCL threshold. At high alkalinity conditions the addition of orthophosphate is highly effective at reducing scaling, and aluminum leaching was not a concern. The presence of high concentrations of magnesium and silicon could form magnesium aluminum oxyhydroxides and magnesium silicates which could act as a protective scale on the concrete surface. However, this precipitate forms only at pH values above 9.5. The effectiveness of this protective scale in reducing corrosion of concrete was not established unambiguously in this research. Temperature plays a key role in corrosion of concrete. Calcite solubility increases at lower temperatures however at higher temperatures corrosion of concrete increases, which implies that corrosion of concrete is not driven by calcite solubility. At higher alkalinities scaling of concrete is higher at lower temperatures. This indicates that calcite solubility controls scaling of concrete at higher alkalinities. Tests with gaseous cavitation indicate that corrosion of concrete does not increase in the presence of gaseous cavitation. Vaporous cavitation is more detrimental to concrete than gaseous cavitation. / Master of Science

Glass corrodes in aqueous environments. The corrosion process is well-understood for many circumstances involving long periods of time at room temperature as well as processes that involve conventional heating, but the effect of microwave energy on glass corrosion has never been fully investigated. It was suspected that microwaves may alter or accelerate the aqueous corrosion processes that occur in glass which contribute to migration into foods or other materials. Lithium disilicate (Li2O-2SiO2) and commercial soda-lime glass were corroded using both conventional and microwave heating in this study. The results did not clearly show substantial differences in corrosion under the test conditions, but leave open the possibility of an altered mechanism in some circumstances. These findings suggest the need for testing at a lower microwave frequency, specifically 2.45 GHz. / Master of Science

No description available.

Ruthenium, proposed as a new candidate of diffusion barrier, has three different kinds of oxides, which are native oxide, electrochemical reversible oxide and electrochemical irreversible oxide. Native oxide was formed by naturally exposed to air. Electrochemical reversible oxide was formed at lower anodic potential region, and irreversible oxides were formed at higher anodic potential region. In this study, we were focusing on the effect of copper electrodeposition on each type of oxides. From decreased charge of anodic stripping peaks and underpotential deposition (UPD) waves in cyclic voltammetry (CV), efficiency of Cu deposition dropped off indicating that interfacial binding strength between Cu and Ru oxides was weakened when the Ru surface was covered with irreversible oxide and native oxide. Also, Cu UPD was hindered by both O2 and H2 plasma modified Ru surfaces because the binding strength between Cu and Ru was weakened by O2 and H2 plasma treatment. Cu/Ru and Cu/Ta bimetallic corrosion was studied for understanding the corrosion behavior between diffusion barrier (Ta and Ru) and Cu interconnects under the post chemical mechanical planarization (CMP) process in semiconductor fabrication. Gallic acid is used in post CMP slurry solution and is known well as antioxidant which is supposed to oxidize itself to prevent other species from oxidizing. However, in this study under the observation of Cu microdot corrosion test, copper was corroded only in gallic acid at specific pH region of alkaline condition which is close to the pH region for post CMP solution formula. With different pH alkaline condition, gallic acid formed different oxidized products which are characterized by cyclic voltammetry and UV-Vis spectroscopy. Therefore, the specific oxidized product from particular pH region condition caused the Cu corrosion. Also, the corrosion rate of Cu microdots was influenced by substrate effect (Cu/Ru and Cu/Ta) and ambient control, which was included in this study.

<p>U ovom radu efikasnost odabranih derivata tiazola u inhibiciji korozije bakra u kiseloj<br />sulfatnoj sredini određena je u funkciji koncentracije inhibitora metodom merenja<br />gubitka mase, elektrohemijskom impedansnom spektroskopijom i potenciostatskom<br />polarizacijom. Polarizacionim merenjima takođe je određena zavisnost inhibitorske<br />efikasnosti od&nbsp; temperature i kinetički parametri procesa korozije bakra&nbsp; kao i&nbsp; model<br />adsorpcione izoterme prema kojem se odigrava proces adsorpcije&nbsp; inhibitora i&nbsp;odgovarajući termodinamički parametri. Merenjima kvarc kristalnom mikrovagom&nbsp;<em>in&nbsp;</em><br /><em>situ&nbsp; </em>je praćen proces elektrohemijskog rastvaranja bakra i adsorpcije ispitivanih<br />inhibitora. SEM/EDX analizom&nbsp; proučavana&nbsp; je promena morfologije bakarne povr&scaron;ine<br />usled dejstva korozione sredine i rastvora inhibitora.&nbsp; Rezultati eksperimentalnih<br />ispitivanja korelirani su&nbsp; sa teorijskim proračunima na nivou teorije funkcionala<br />gustine.</p> / <p>In this work, the efficiency of selected thiazole derivatives in&nbsp; the inhibition of corrosion of copper in the acidic sulfate solution is determined in&nbsp; the function ofthe inhibitors&nbsp; concentration by weight loss method,&nbsp; electrochemical impedance spectroscopy and potentiostatic polarization. The dependence of the inhibition efficiency of temperature and kinetic parameters of the process of corrosion ofcopper&nbsp; as well as&nbsp; adsorption isotherm model&nbsp; according to which takes place the process of adsorption of inhibitors and the corresponding thermodynamic parameters were also&nbsp; determined by polarization measurements.&nbsp; A process of electrochemical copper&nbsp; dissolution and&nbsp; adsorption of tested inhibitors is followedin situ&nbsp; by&nbsp; quartz crystal microbalance&nbsp; measurements Changes in the morphology of the copper surface due to the effects of corrosive environment and the solutions of the&nbsp; inhibitors were studied by SEM/EDX analysis.The experimental results were correlated with theoretical calculations at the density functional theory level.</p>