AA6061 is a type of precipitation-hardening aluminum alloy. Second-phase particles in precipitation hardening aluminum alloys are typically classified into three types: constituents, dispersoids, and fine strengthening precipitates. The constituent phase particles are relatively large (2– 5 μm) and primarily formed from the interaction of the alloying elements with impure elements such as Si and Fe. Dispersoids are relatively small (0.5–2 μm) and typically contain elements such as Mg, Cu, Zn, and Cr . Differences in oxidation rates between the second-phase particles and aluminum substrate cause oxidation-free crevices at the particles/substrate interface in anodic coatings. Corrosive ions can attack the substrate through such crevices. Therefore, the second-phase particles in aluminum alloys play a major role in passivity breakdown and pit morphology of aluminum alloys in seawater [14, 15]. In addition, Idrac  indicated that second-phase particles in an Al-Cu alloy resulted in pitting susceptibility in galvanic corrosion.
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The objective in this study is to investigate the effects of a surface area ratio of titanium/amalgam on the behavior of ions released from amalgams in contact with titanium and to evaluate the safety of a coexisting amalgam and titanium in the oral cavity. Conventional amalgams (Ag–25.8Sn–1.5Cu and Ag–27Sn–2Cu) and a high-copper amalgam (Ag–29Sn– 16Cu) mixed with mercury were used. Ions released from conventional and high-copper amalgams in contact with tita- nium at surface area ratios of titanium/amalgam in a range of 1/10–10/1 were qualitatively and quantitatively analyzed af- ter being immersed in 0.9 mass% sodium chloride solution with saturated dissolved oxygen at 310 K for 6 . 05 × 10 5 s (7 days). The correlation of the ions released from each amalgam in contact or not in contact with titanium was also examined to determine the relation between an increasing rate of the release of ions and the surface area ratio of tita- nium/amalgam. Furthermore, corrosion potentials, galvanic corrosion currents and potentio-dynamic polarization curves were measured under the same experimental conditions.
steel alloys, aluminum and other metals [3, 4, 6, 10–19]. They were earlier recognized as anodic inhibitors [2, 4, 9-10] in neutral and alkaline waters and as mixed inhibitors in strong acidic media . Further, molybdates are considered to promote the active–passive state on the surface of steel, which reduces the passivation current through the formation of a stable film and extends the anodic passive range [7, 10, 15, 21]. The inhibition of localized corrosion in CS and aluminum using single, binary and ternary mixtures with molybdates has also been reported [5, 7, 22–27]. Moreover, many previous authors [4, 13, 15-16] have suggested the adsorption of molybdate anions on the oxide film of the surface, which repairs the defects and pores. However, because the disadvantage of molybdate inhibition in low oxygen content solutions is its weak oxidizing power, molybdates require oxidizing agents to increase their performance [1–4, 12–14]. That said, this shortcoming could prove to be an advantage for the inhibition of galvanic corrosion .
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The electrochemical cell was allowed to stabilize before performing the electrochemical measurements. The EIS measurements for the Al2024 electrode were performed at the frequencies between 10 kHz and 0.1 Hz, with a signal potential perturbation amplitude of 10 mV. For the copper electrode the frequencies were between 10 kHz to 0.01 Hz, with a signal potential perturbation amplitude of 10 mV. The impedance data were fitted to appropriate equivalent circuits using Gamry Echam Analyst software. The potentiodynamic current-potential curves were obtained by changing the working electrode potential automatically from -200 to 200 mV versus SCE with a scan rate of 0.5 mV s -1 . For the galvanic corrosion measurements, the galvanic current density (I g ) and galvanic potential
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corrosion rates in boiling nitric acid test (ASTM A262 Practice C test). In this connection a study of possible galvanic corrosion effect at the junction of sensitized HAZ and the adjacent base metal in 304 SS in sulphuric as well as nitric acid, was undertaken. The galvanic couples were prepared using sensitized 304SS as the anodes, and the base metal as the cathodes, electrically connected in different anode to cathode ratios. Potentiodynamic anodic polarization studies were conducted in deaerated 0.5M sulphuric acid whereas electrochemical noise (ECN) experiments were performed in 3M deaerated nitric acid at room temperature as well as 60°C. The data analysis of current and potential signals was conducted using statistical methods; the data was analysed in the frequency domain using Maximum Entropy Method (MEM). The corrosion rates observed in nitric acid medium at room temperature did not show enhanced corrosion rate due to galvanic coupling. However, the corrosion rates were higher at 60°C in the same medium. Based on these results, a drastic rise in corrosion rate and the subsequent failure of the waste vault tank was not expected.
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kind of low alloy steels, the corrosion process of 907A should also damage its function as a component of facilities, especially, the main servicing environment for 907A is the ocean with high content of different aggressive particles. Moreover, in order to meet some special demands from the industrial products design [5, 7], 907A has to be coupled with other metals, especially titanium (Ti) and copper (Cu), the galvanic corrosion caused by the mutual electron transfer (through the combination) between the two coupled partners is inevitable , which also undoubtedly accelerate the corrosion process of 907A and markedly degrade its properties. Therefore, the study of the corrosion behaviors for 907A and its galvanic couple with Ti in seawater is of important significance.
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DU acted as anode in a galvanic corrosion system. In oxidizing conditions, uranium corrodes rapidly. Galvanic corrosion behavior of DU alloys exposed to ASTM or natural seawater are studied for each metal or alloy coupled to remaining test materials as one group(AISI 304 SS, T621, Al, AA 7075-T6, bare AISI 4340 steel etc.)[14,15]. Theoretically, galvanic corrosion can be eliminated by insulating or blocking the direct electrical contact between DU and its coupled metal. However, in most practical utilizing situations, direct contact is required to meet the mechanical joint demands. For example, in a special applicational situation, the DU parts need to be connected with 40Cr steel bolt. Galvanic corrosion for the couple of DU and 40Cr steel may occur when the bolt connected parts is exposed to corrosive atmosphere. However, no report related to galvanic corrosion of DU/40Cr couple is available and the galvanic corrosion data are lack to evaluate the reliability of the bolt connected structure in special atmosphere. Therefore, it is vitally important and valuable to study the galvanic corrosion behaviors of DU/40Cr steel in corrosive mediums.
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So far, the study on galvanic corrosion among dissimilar metals is still a relevant topic [1,3,4]. A number of researches have been conducted to investigate the effects of various operating parameters, such as cathode /anode area ratio , temperature , dissolved oxygen[8-10], seawater flow rate, etc., on the galvanic corrosion. Galvanic corrosion is a dynamic process [12,13], involves several coupled phenomena such as electrochemical reactions, electro-migration, ionic diffusion, oxide layer formation and dissolution . Beyond doubt, during the galvanic corrosion process, an irreversible thermodynamic process accompany with the dissipation of energy will occur meanwhile. Up to now, the energy dissipation regulation in the galvanic corrosion has been researched few , moreover, the relationships between crystal energy variation and corrosion process are still unclear .
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Galvanic corrosion between AISI304 stainless steel and carbon steel in mortars has been studied by open circuit potential, electrochemical impedance spectroscopy, and galvanic coupling currents. The corrosion state of the coupling rebar was also examined after removing the mortars. The results suggest that the carbon steel presents a high risk of galvanic corrosion in the initial stage when it is electrically coupled with stainless steel in the chloride-contaminated mortars. However, for the stainless steel promotes the passivation of carbon steel, the risk of galvanic corrosion on carbon steel significantly decreased as the time extends. In addition, the water-cement ratio of mortars does not have a dramatic influence on the galvanic corrosion between stainless steel and carbon steel in the chloride-contaminated environment.
When the corrosion time is shorter than 76 h, only one distinct phase-angle peak (Peak I) is observed in the high frequency domain except the data drift in the ultra-high frequency region. The latter phenomenon has been ascribed either to the atomic scale inhomogeneities (rather than the geometry roughness of the solid electrode) , or the effect of reference electrode geometry/position , or the high resistance capillary effect of the reference electrode . Both the peak height of the phase-angle (Peak I) and the diameter of the corresponding capacitive loop decrease with immersion time (< 76 h), which indicates the more uneven distribution of corrosion current on the corroding surface .
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The galvanic cell consisting of two non-noble alloys, such as, Wiron ® 88|Remanium 2000+ presents very low cell potential (a few mV), while the galvanic cell, between the Wiron ® 88 and the noble alloy V-Gnathos ® Plus, showed a greater cell potential. After 10 minutes the values were -18 and -104 mV, respectively. In both cases the release of cations was detected: Co 2+ and Ni 2+ for the Wiron ® 88|Remanium 2000+ and Wiron ® 88|V-Gnathos ® Plus galvanic couples, respectively, with the ionic concentrations, increasing almost exponentially during the 1 st week, reaching values of 12.15 for the Co 2+ and 7.30 μg L -1 , for the Ni 2+ , after the 25 days period of immersion, in the artificial saliva solution, at 37 °C. However, it shall be emphasized, that the concentration of ions delivered into the solution is quite low (levels of ppb).
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I am grateful to the Shoesmith, Noël, and Wren groups for their valuable feedback and input and for creating such an enjoyable working atmosphere. In particular, thank you to Dr. Dmitrij Zagidulin for getting me started in the lab, for assisting with synchrotron X-ray micro-CT experiments, and for the countless times he has answered my questions and helped me solve problems with instruments, experimental setups, software, data storage, and programming. I would like to thank Lindsay Braithwaite for her valuable assistance and contributions to this thesis and for being such a wonderful summer student and labmate. Thank you to Dr. Shannon Hill for teaching me how to perform Raman spectroscopy and for answering my questions about Fe corrosion products. I would also like to thank Dr. Anna Dobkowska for the helpful discussions about metallurgy and mechanical properties of materials and for her assistance with metallographic porosity analysis. Thank you to I would also like to thank David Noël for creating and debugging the program to calculate the shortest path—his assistance is greatly appreciated—and Dr. Fraser Filice for his help troubleshooting the program.
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The Pontor ® 2 | Ti and Pontor ® 2 | Ti6Al4V couples present the more negative galvanic voltages, starting with values of -0.143 and -0.129 V and then keeping an almost constant value, over a period of 10 minutes, -0.120 and -0.104 V, respectively. The galvanic voltage for the of Pagalin | Ti couple starts with a value of -0.175 V and changes abruptly to +0.050 V, during the first 5 min, then varies less abruptly reaching +0.100 V, after the 10 minutes. The higher and more positive values of the galvanic cell potential for the Pagalin | Ti couple is in agreement with previous data. Effectively, the Pagalin corrodes easily due to the high percentage of Ag.
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however, these metal oxides are dissolvable. Corrosion in molten fluorides mainly occurs through the dissolution of alloying elements into the melt [10-12]. The key driving force for the corrosion is the difference in the free energy between the salt constituents and the corresponding fluorides of the alloy compositions. The free energy of salt constituents such as LiF, NaF, and KF, is more negative than those of the fluorides for any constituents of alloys, thus corrosion of alloys can hardly occur in pure molten fluoride salts. However, in actual system, several kinds of corrosion reactions may occur. The main driving forces for the corrosion in molten fluorides generally involve impurities in the fluorides, temperature gradients and galvanic corrosion.
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The experimental results in this study showed the corrosion resistance of different types of samples, which had clear distinguishing characteristics. The corrosion of EN 6061-T6 connected with hot-galvanized IF steel via the tox punching method had galvanic corrosion that was more severe than that of the SPR joints. This contrast was due to the difference in potential (ΔE = 0.54 V) between the stretched hot-galvanized IF steel and EN 6061-T6 sheets. In addition, an intense contact corrosion effect was induced between a large cathode coupling a small stretched Zn coating anode. The EIS of the stressed area showed obvious distinction contrast to IF steel/aluminum sheets, especially the stretched region. Strained condition produced during the tox punching assembly, such as extrusion and stretching, should be taken into consideration because of their potential effect on electrochemical and corrosion performance in the presence of a depolarizer in an aggressive environment.
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However, in actual steam generators, the degree of galvanic effect is expected to be more severe and the corrosion rate of Alloy 600 coupled with the magnetite will increase. These results can be explained by the following two reasons. First, operating temperature of steam generator in PWRs is the high temperature ranges up to 553 K. In addition, a local temper- ature increase is expected within the magnetite deposited on the surface of Alloy 600 tubing, since heat transfer though the tubing is hindered by the deposits. The porosity of passive ﬁlm increases with temperature and intrinsic modiﬁcation of the chemical composition and/or physical structure of the passive ﬁlm takes places. These changes lead to an increase of defects in the passive ﬁlm and generate higher galvanic corrosion rate. 32) Second, the ratio of the cathodic to anodic
2) A galvanic corrosion process may be considered at the welding joints regions. This type of corrosion oc- curs because of potential differences between metallic materials, when in contact and in presence of an electro- lyte. The material with more negative potential acts as an anode and exhibited a corrosion process. For this spe- cific case, apparently the welding joint acted as anode in the corrosion reaction. However, the galvanic corrosion was less evident in the site where the failure occurred, because of the effect of the erosion corrosion. At the 12 technical hours position, the erosion corrosion effect is less evident and the galvanic corrosion is clearly ob- served (Figure 17).
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A satellite in orbit becomes too hot when exposed to direct sun light and experiences low temperature when it dives in to earth shadow. The thermal cycling test is designed to evaluate the effect of cycling temperature on the deposit that is likely to be encountered throughout the life span of a spacecraft. The test was conducted in thermo statistically controlled hot and cold chambers. A total of 100 cycles were applied. A cycle consists of placing the samples in to a chamber operating at -45 ° C for 5 minutes, bringing them to an ambient temperature with a dwell of 15 minutes then shifting them to a hot chamber at 85 ° C for another 5 minutes. After thermal cycling test, specimens were inspected visually and their optical properties were measured. The α s and ε IR for different samples before and after thermal cycling test is tabulated in Table 5. No change in color and degradation of the coating was observed in case of chromate and galvanic black anodizing. Further no change in optical properties was observed. In case of cerium conversion coating visually no degradation was noticed but a slight increase in α s and ε IR value ~0.003 and 0.02 was observed. However, in case of stannate coating darkening and black spots were observed with increase in α s and ε IR value by ~ 0.042 and 0.11, respectively.
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With water being the most common fluid used in heat transfer systems and having very effective electrolytic qualities, corrosion has long been a significant issue in cooling systems. Through extensive and ongoing research across many industries, chemicals have been identified that have specific qualities of inhibiting corrosion when added to the cooling water. Whilst these chemicals generally have beneficial corrosion inhibition qualities, many have significant characteristics which have been identified as hazardous to health and the environment. Of the chemicals in use today, the most significant for the purpose of this research are nitrites, in the form of sodium nitrite, and azoles, in the form of sodium mercaptobenzothiazole, both of which are passivation inhibitors.
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This experiment will investigate of corrosion rate by using the type 316 stainless steel with different thickness. These investigations have been made using other materials of alloy steel and carbon steel. The material is dissolved under solution sodium chloride (Mehdipour, Naderi, & Markhali, 2014). For this experiment will be carried out using the stainless steel 5cm x 5cm and the range of thickness is 0.2 mm to 0.5 mm. A 3mm thickness plate for the hydrogen production process has been researched by Mahrous (Mahrous, Sakr, Balabel, & Ibrahim, 2010)(“HHO Dry Cell Kits,” 2009). Recent studies showed that the different specimen size will get the different corrosion rate and reasonable for us to reduce the specimen size in order to attain excellent corrosion resistance (Wu et al., 2014)(Mirzaee Sisan, Abdolahi Sereshki, Khorsand, & Siadati, 2014).
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