Corrosion Report Lab 5

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Jan 9, 2024

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Corrosion Lab Report MIE270 Kai Henderson 1008990790 E2 TA: Mayesha Binte Mahmud Lab 5 Corrosion of Metals Abstract: The corrosion presents a prominent and persuasive issue in modern society, as it continually erodes the structures to which modern society is built upon. This lab seeks to provide a comprehensive overview of the mechanism that motivate corrosion and the influence different materials have on such mechanisms. This was achieved by conducting the Corrosion of Metals lab which provided the experimental data necessary substantiate to describe the mechanism of corrosion. In this lab student were required to determine, the potentials of different galvanic couples, the oxidation potential of different material relative to standard electrode, and the resistance caused by an oxidant filament. The data collected was used to answer subsequent discussion questions detailing different sections of lab and corrosion mechanisms. Using the knowledge attained during the lab students were then tasked with the determining the design flaw of a hypothetical container, given cathodic and anodic tendencies of materials involved. After identification and explanation student’s were then required to purpose and justify improvements to the current design.

1.0 Introduction In the field of Engineering and Material Science understanding a process of corrosion and its corresponding effect on materials, is crucial element in materials selection and design. On average 3-4% of a countries annual GDP is spent on corrosion prevention or associated maintenance [1], representing a sizable and expensive problem for many nations. Thus, when engineers are designing new products, important consideration must be given to corrosion prevention, as this may affect the product’s life cycle, performance, and safety. Such forms of corrosion prevention include utilizing corrosion restraint materials, inhibiting the corrosiveness of the surrounding environment or utilizing a mechanism that mitigates materials corrosion [3]. Before implementing or designing such devices/materials it is vital in understanding the fundamental mechanisms motivating corrosion, as to best assure its prevention. Corrosions is deteriorative mechanism that typically consists of the electrochemical reaction between two reactive species. This transfer of electrons is facilitated by the electrochemical half reactions of oxidation and reduction, that release and gain electrons respectively. The region to which oxidation and reduction occur are also known as the anode and cathode respectively. Corrosion is governed by the amount free energy within the system, which itself dependent on temperature, concentration of reactants and the specific electrode pairs. Different electrode pairs influence the standard electrode potential reactions as each electrode possesses is own unique electrode potential, representing is tendency to lose electrons. As to readily find the standard electrode potential the EMF series was established which normalized the different materials’ electrode potentials to that of Hydrogen. The standard electrode potential is an indicator for the tendency of corrosion that will occur, for ideal (ATM) conditions, while the Nerst equation may be utilized for non-standard conditions to determine corrosion [3]. Using this knowledge student’s may effectively complete the objective of the Lab 5. Lab 5 possessed three main objectives, which were, to determine the potential associated to each galvanic couple specified in the produce section. The goal of this objective was demonstrating how different materials influence the potential created by each galvanic couple The second objective was to determine the reduction potential of each material given standard electrode of silver chloride Ag/AgCl. The goal of this objective was to demonstrate the differences in reduction potentials between materials, and how that influences the potential of galvanic couple they are in. The third objective was to determine how the oxidized barrier formed during copper corrosion would impede the electron flow, due to it’s greater resistance than that of pure copper. The goal of this objective was demonstrating the how concentration polarization works as mechanisms that motivate it. 2.0 Procedure Section 1: 1) The 400 ml beaker glass was filled with 250 ml of 3wt% Sodium Chloride (NaCl) solution, provided by the Lab TA 2) All residual oxides formed on specimen electrodes’ surfaces were removed using the provided silicon carbide (SiC) paper. The protective coating on the coated copper electrode was not removed.

3) Using the provide chart of anode and cathodes, corresponding electrode specimen were partially submersed in the NaCl solution using clamps. The two electrodes were the then connected using a wire, completing the galvanic couple. 4) The electric potential generated by the galvanic couple was then measured using a voltmeter, with black and red probes, corresponding to the anode and cathode respectively. 5) All galvanic couples were set up and measured identically to the above steps. Section 2 1) Each specimen electrode was partially submerged in the NaCl solution, alongside a reference of electrode of Ag/AgCl solution. 2) Both the specimen and reference electrode were the connected with a wire as to create a galvanic couple. 3) Potential across the galvanic couple was measured using a voltmeter determining the oxidation potential of each material. Section 3 1. The exposed areas of both copper specimens were then sanded using the SiC paper as to remove any surface oxidants. 2. The internal resistance of the exposed copper was then measured to using the voltmeter. 3. The copper specimen was then partially submerged in the electrolytic solution and connected battery for 5 minutes 4. The electrodes were then dry and exposed surfaces were then measured for internal resistance. 3.0 Data Analysis # Anode Cathode ΔE (mV) 1 Copper (Un-sanded) Stainless Steel -121 2 Copper (Sanded) Stainless Steel -228 3 Brass Copper 223 4 Brass Zinc -788 5 Zinc Brass 788 6 Zinc Tin 480 7 Zinc Copper 667 8 Zinc Stainless Steel 687 (Table.1 Full cell potential of each galvanic couple specified in the lab handout) ii) The potential of brass is roughly between that of zinc and copper, based in in the potential of the galvanic couples it is associated with. This likely due to the brass being an alloy of the zinc and copper, thus their material properties combined influence brass’s tendency to corrode [Table 1]. Material Oxidation Potential (mV) Cathodic Un-sanded Copper -100

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Brass -260 ↨ Anodic Un-sanded Copper -330 Stainless Steel -356 Tin -430 Zinc 1046 (Table.2 Galvanic Series of materials submerged in 3wt% NaCl solution) iv) Based on the oxidation potentials determined during the lab, the least likely material to corrode would be Un-sanded copper, as it possesses a potential of -100mv [Table 2]. This means it the cathodic materials and least likely to participate in the electrochemical reaction. The most likely material to corrode would be zinc as it possesses the greatest potential, making it the most anodic material present. Zinc would make for an ideal sacrificial anode as its tendency to lose electrons is greater than any other material [Table 2]. Electrode Resistance Before Resistance After Anode 0.1 Ω 12.3 k Ω Cathode 0.1 Ω 0.6 Ω (Table.3 Measurements of resistance of electrodes before and after undergoing corrosion as a galvanic couple) v) It is observed that when oxidized copper filament developed on surface of the copper electrode due to anodic polarization increases resistance [Table 3]. This represents and important design consideration for any electrical components exposed to corrosive environment, as it they undergo anodic polarization, it may inhibit their ability to faceplate the transport of electrons. Electrical components that may be imperil of this occurring include, any electoral carrier component within a corrosive environment. 4.0 Discussion 4.1 Discussion Questions 1)Why was the corrosion experiment conducted in a chloride containing environment? The electrolytic solution was chosen to be chloride environment as chloride ions can facilitate the follow electrons readily. These overall aids the electrochemical process and spurs on half cell reactions. 2)What is the difference between the Standard emf Series and Galvanic Series? Hint: There is 1 Standard emf Series but there are many Galvanic Series While both the standard EMF and Galvanic series are both electro potential series that determine a material likelihood or tendency to experience corrosion, they differ in some respects. The EMF series is as ranking of different material’s reduction potentials relative to that Hydrogen. This makes determining the potential of a galvanic couple a process that is independent of the environment the reaction is occurring in. So long as the species participating in the reaction are properly identified and the reaction itself is at standard conditions. This compared to the Galvanic series which ranks metals cathodic or anodic tendencies of different materials relative

to a specified electrolytic solution. Thus, when determining the potential of galvanic couple, the environment that electrochemical reaction is taking place in must be accounted for. In response there exists a variety of galvanic series that describe differ anodic and cathodic tendencies of materials in different electrolytic environments 3) Answer the following questions: a. Suppose you have two joined metals (Gold and Copper (II)) immersed in 1M HCl acid, based on the reactants present write possible half cell (anode/cathode) and full cell reaction(s). Oxidation: Cu 2+ + 2e - → Cu Reduction: H 2 → 2H + + 2e - Anode: Copper (II), Cathode: Copper (II) b. Would corrosion happen in part (a) on its own? Why or why not The above-described reaction would not occur spontaneously as both gold and copper are more cathodic than hydrogen and are listed higher on the emf series. There is also a lack of copper ions within the solution to drive a spontaneous reaction, as without these ions the reduction reaction indicated cannot occur. c. Would actual corrosion occur if we start bubbling air into the solution? Why or why not? The action of bubbling air into the solution would initiate corrosion as air molecules would react with the copper electrode to form copper oxide. This would represent the oxidation portion of the electrochemical reaction of the reaction. The copper oxide product would then react with HCL molecules within the surrounding solution, representing the reduction portion of the electrochemical reaction. d. How fast is the corrosion occurring? Do we have enough information to answer this question? If not, what additional information is needed? Not enough information is provided to calculate the rate of corrosion as this would require the corrosion potential of the reaction and the potential of each electrode in the reaction. These steps constitute and are determined by the Tafel extrapolation technique. However, pre-requite information, such as each reactants specified emf values and the concentration if the electrolytic solution, is precluded, making ush calculation impossible.

4.2 Sources of Error Possible sources of error that may influence the data attained during the experiment include the incorrect measuring of galvanic couples’ potential using the voltmeter. Ideally the measuring of galvanic within the lab were to be conducted identically, however inconsistencies the pressure applied to voltmeter probes or degree of contact between the probe and electrode may cause deviation for it’s true potential. Discrepancies the electrolytic solutions concentration may be considered a possible source of error, as they would influence the rate both the reduction and oxidation reaction are occurring, directly effecting the galvanic couple’s potential. 5.0 Conclusion In conclusion based on the data obtained while conducting the lab 5 procedure, various observations can be made about a materials influence on the corrosion process. These observations include, the stainless steel and un-sanded copper galvanic couple possessing the least potential. This can be interpreted as due to them possessing material properties that reduce the corrosion, such as their protective layering. Furthermore, the effect concentration polarization had on the corrosion process was also demonstrated with the measuring of copper resistance after developing an oxidised layer. The increase in resistance will present a barrier for electrons to penetrate through and become part of the electrochemical reaction. These observations and data can be used in the future to inform material selection pertaining to corrosive environments. 6.0 Design Question Observing the galvanic series of seawater, it is shown that stainless steel would act as the cathode and carbon steel would act as the anode, in a bimetallic structure. Due these metals’ vicinity the bimetallic corrosion may have occurred, in which carbon steel oxidize and stainless steel would reduce. If this corrosion is continually and un-checked, then it is reasonable to assume the galvanic attack would occur to carbon steel, the anode, creating this pinhole corrosion above the welded area. This corrosion would only be accelerated due the high anode to cathode surface area ratio, as it is assumed the stainless steel and carbon steel are welled the entirety around the cylindrical tank. Thus, the observed pinoles were caused by the bimetallic corrosion of the carbon steel and stainless steel, causing the tank to fail. To solve this issue this, issue the tank may be constructed out of a singular material to avoid bimetallic corrosion. This may be constructing the entirety of stainless steel, or carbon steel with baked phenolic paint coating. 7.0 References [1] G. Koch, “1 - Cost of corrosion,” ScienceDirect , Jan. 01, 2017. https://www.sciencedirect.com/science/article/pii/B9780081011058000012#:~:text=Using%20di fferent%20approaches%2C%20the%20studies (accessed Nov. 15, 2023). [2] “An Introduction to the Galvanic Series: Galvanic Compatibility and Corrosion,” Corrosionpedia , Nov. 12, 2020. https://www.corrosionpedia.com/an-introduction-to- the-galvanic-series-galvanic-compatibility-and-corrosion/2/1403 [3] W. D. Callister and D. G. Rethwisch, Fundamentals of Materials Science and Engineering: An Integrated Approach . Hoboken, NJ: Wiley, 2012.

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