While steel is often used for infrastructure, appliances, buildings, and more, it is very susceptible to corrosion. Zinc, however, has high corrosion resistance, though it lacks many desirable properties that steel has. By electroplating steel with zinc, the resulting sample can retain the positive qualities of steel - strength, toughness, ductility, weldability, durability - while having an additional layer of corrosion protection. There are many reasons for why it is relevant to study the corrosion of steel and find ways to limit the extent of it. Large boats and ships, for example, are made from steel or steel alloys. As the steel corrodes from the salt water and sulfides present in polluted harbors, the material is weakened, and the excessive amount of metal ions released into the water can be harmful to the existing flora and fauna.
For our senior research project, we are studying how the electroplating process of plating zinc onto steel affects the corrosion resistance of plated steel to salts. To accomplish this, we will be using a two-factor Design of Experiment. Therefore, we will be changing two factors in the electroplating process: voltage and the duration of time the steel is electroplated for. Zinc and Steel samples will be attached to the positive and negative terminals of a power source and then placed into a Zinc Nitrate solution. The power source will be turned and the Zinc will plate the steel. Electroplating will continue for the duration of time and with the voltage indicated in the Design of Experiment (DOE) depending on the combination of factors and levels being tested in that specific trial. After the steel samples are plated, their masses will be recorded and a controlled portion of each plated sample will be exposed and immersed in salt water to corrode for two days. After this, the masses of the plated samples will be recorded again to find the change in mass from before corrosion testing to after. The change in mass per unit area will be the response variable used for statistical analysis. In our partnership with an international automotive supplier, DENSO, we will be examining our steel samples before plating, after plating, and after corrosion with a Scanning Electron Microscope (SEM). The SEM will allow us to capture detailed images of the surface of our metal samples to observe the quality of the plating layer as well as quantitatively measure their chemical composition. Devices such as a micrometer will also be used to take additional descriptive statistics. Ultimately, the purpose of this experiment is to find a method for electroplating steel that will yield the highest corrosion resistance of steel when it is exposed to common corrosives. At the conclusion of experimental testing and analyzation, the researchers were able to make valuable observations and arrive at conclusions pertaining to the hypothesis. The method for electroplating and analysis mentioned in the research plan was carried out. From the response variable measured (change in mass per surface area), the descriptive statistics recorded using the Scanning Electron Microscope, and the observations made throughout the duration of the research trials, it was evident that using a high voltage significantly decreases the plating quality. The samples plated under the condition of a high voltage, despite different plating times, suffered from significant mass loss after corrosion testing compared to the samples that were plated at a low or standard voltage. The conclusions are helpful for industry as they prove that the quality of the electroplating layer hits a tipping point as the voltage increases. The time of duration for electroplating does has a small effect on the electroplating quality.
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We realized this week that there is not an infinite supply of Zinc Nitrate! It's all fun and games until you run out of the most important chemical in your experiment and there isn't enough time to order more...RIP. With that luck, we also ran out of steel and zinc sheet metal. You would have thought we would be better at planning ahead. Johanna took a trip to Home Depot to look for steel and zinc. She was only able to find steel, but it was at the cost of her beautifully even skin. Turns out, steel is more dangerous than Zinc Nitrate!
Pre-Trials are over, and now we have a much better sense of what will and will not work in this experiment. We have found that a power source with a controllable voltage and current is completely necessary, and we now have one. We have found that with a higher controlled voltage (approximately 3 V) it only takes a few seconds for zinc to electroplate onto steel. In accordance with our pre-experimentaion, and with Faraday's Law, we will be using time and current as the factors in our experiment.
We have also found that plated steel in distilled water, rather than saltwater or acetic acid, actually yields the quickest measurable results. While this will be helpful for experimentation, we are disappointed that this eliminates both the idea of galvanic corrosion and acid corrosion. However, we have found that the experiment has been more complex than we originally believed that it was, so it is for the better that we change the experiment in this way. Metals have many properties, one common property being strength. Consequently, metals are used to accomplish many purposes. Scientists and engineers continue to study metals and their potential properties with hopes to find better used or solution to various projects that are more economical without robbing quality. Though metals are strong and powerful, they are not perfect. Metals can corrode. Metals corrode through a process called oxidation, where a metal's atoms are robbed of their electrons. When metals because oxidized, they lose strength and malleability; many properties of the metal change at this point. There are many processes that induce the corrosion of metals, such as galvanic corrosion and sulfide corrosion. For this research project, we decided to focus on sulfide corrosion because it a huge problem in places where the sulfide concentration is high in the air or water. Metal panels on ships corrode within the presence of sulfide polluted water or acid rain. The researchers wanted to know if factors controlled during the electroplating process of a metal have a significant affect on the corrosion resistance of the plated metal.
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