Factors Affecting the Oxidation of Iron Alloys

Abstract

This paper is about the prevention of the formation of Iron Oxide. For the purpose of this investigation three coatings have been electroplated to the steel electrodes. The electrodes were then placed next to a salt solution approximately the same as that of ocean water .The mass changes in the metal were then measured and placed into a data table. From this data table I made a column graph to clearly show how the effects of each of the coatings had on the rate of oxidation of the steel electrodes. The mass change of the electrodes was shown through the measuring of these electrodes both before and after the two week space of time in which they were allowed to rust.

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The results that were obtained from the investigation have proved to be conclusive with the hypothesis that was suggested. This shows that the best way of protecting metal from corrosion was through the usage of copper as a complete coating of the electrode. This action also showed that current methods of galvanization protected some areas but as soon as there was any disturbance in the surface of the metal the corrosion of the iron took hold and rust was formed where the zinc oxide layer receded from. The overall way that the three coatings worked was that copper was the best followed by zing and finally the nickel coating proved to be worst actually accelerating the decomposition of the steel electrode.

Introduction

The destruction of steel around the ocean’s salty air has been a consistent battle by both fishermen and mariners throughout history. Growing up around the ocean has left me with little doubt about the destructive power of the oceans salty air. The formation of Iron III Oxide and Iron II Oxide more commonly known as rust has always been a problem affecting the local ocean side businesses. The problem of rusting has been around for thousands of years from when man first began to create things made of steel. The first early processes to prevent rusting were to simply cover the metal in animal fat or oil this hydrophobic covering was the main way in which materials were treated to prevent the buildup of iron oxide. The invention of electroplating of metals changed how metals were treated thereafter. Having and interest in maritime transport and seeing how the massive hulls of ships were constructed from steel. Steel has tendency to rust as well as to become highly susceptible to the effects of salt water. Salt water is an aqueous sodium chloride solution acts as an electrolyte solution which allows for rusting to occur at a more significant rate. The prevention of rusting of the hulls of ships is to attach zinc blocks to the hulls of ships. I became aware of this method because one day as I was diving I saw a round block that was attached to the engine of our skiff. When I asked what it was my father told me it was a zinc block. The zinc block reacts with the salt water to create a basic solution which prevents the formation of the iron oxide on the hulls of these tankers. Another method that is commonly used by mariners to combat the ever-present effects of the oxidation on the building materials is a process known as galvanization. Galvanization is the process by which a thin layer of zinc is electrically fused onto the surface of the steel. This fusing of zinc to the surface of the steel is known as electroplating. The electro plating of various metals to the surface of steel has been used as both a way to decorate the steel and as a ways of protecting the surfaces from either corrosion or the buildup of an oxide layer. The usage of copper as a coating was originally used when huge sheets of hammered copper were affixed to the hulls of ships to prevent drill worms from entering the wood as well as to prevent the buildup of bio fouling organic material such as moss or barnacles because copper oxide is mildly poisonous. I wanted to investigate whether metals that experienced similar resistance to oxidation also proved to be beneficial in the coating of steel to prevent the buildup the damaging iron oxides. I have also seen that nickel copper and zinc have each been used in the coating of metals for both the purposes of chemical prevention of degradation of coated metal to decorative uses.

Back ground information

The composition of sea water (sodium chloride solution)

Ocean water is usually around 35 parts per thousand of salt vs water this means that the sodium chloride content in salt water is around 3.5% of the total volume. Therefore in 1 kg of salt water there is 35grams of salt.

(Seawater 01 Apr 2014)

The composition of steel

Steel is an iron alloy which consists of:

• Plain Steel
  • Carbon 1.35%
    • Is used to strengthen the iron in the composition of steel
  • Manganese 1.65%
    • Is to react with the sulphur in the composition of steel and this reaction increases the heat resistance of the steel.
  • Phosphorous .04%
    • Used to reduce the corrosion present on the surface of the steel

• Sulfur .05%
  • May cause steel to become too porous and prone to cracking if the manganese mixture is not correct.
• Silicon .06%
  • Acts as a deoxidizer in the steel making process

(“Steel” January 06 2014)

Rusting chemical equations:

[The rusting of iron is an electrochemical process that begins with the transfer of electrons from iron to oxygen. The iron is the reducing agent (gives up electrons) while the oxygen is the oxidizing agent (gains electrons). The rate of corrosion is affected by water and accelerated by electrolytes, as illustrated by the effects of road salt on the corrosion of automobiles. The key reaction is the reduction of oxygen:

O2 + 4 e− + 2 H2O → 4 OH−

Because it forms hydroxide ions, this process is strongly affected by the presence of acid. Indeed, the corrosion of most metals by oxygen is accelerated at low pH. Providing the electrons for the above reaction is the oxidation of iron that may be described as follows:

Fe → Fe2+ + 2 e−

The following redox reaction also occurs in the presence of water and is crucial to the formation of rust:

4 Fe2+ + O2 → 4 Fe3+ + 2 O2−]………(1)

(Dufour , 01 Mar. 2014)

The reasoning behind why the coatings work

A galvanic anode is the main component of a galvanic cathode protection system. This protection system is usually referred to a (CP) system. The usage of a more reactive metal to be sacrificed instead of the metallic structure is known as sacrificial. The sacrificial anode is usually made from a metal that has a higher electric potential than that of the object being protected. This electrical potential causes the sacrificial anode to be corroded instead of the other ferrous material.

Electro plating definition/ Apparatus

[Electroplating is a process that uses electrical current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. The term is also used for electrical oxidation of anions onto a solid substrate, as in the formation silver chloride on silver wire to make silver/silver-chloride electrodes. Electroplating is primarily used to change the surface properties of an object (e.g. abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.), but may also be used to build up thickness on undersized parts or to form objects by electroforming.]…… (2)

(Dufour 01 2014)

This apparatus is used in the majority of tanks which is used to be able to coat metals with the ions in the solution. This is done when an electrical charge is applied to the apparatus and causes a flow in the ions of solution. This flow of elections causes the ions dissolved in the solution to coat the surface of the target metal. The usage of the same metal as is dissolved in solution insures that the overall concentration of ions in solution never diminishes and ensures that there is a continuous flow of the ions in the electrolyte solution.

The oxidation processes of copper, nickel, And zinc

• Copper
  • 2 CuSO₄+ 2 Na₂CO₃+ H₂O → Cu₂(OH)₂CO₃+ 2 Na₂SO₄+ CO₂
• Nickel
  • 2Ni(s) + Oâ‚‚(g) → 2NiO(s)
• Zinc
  • 2Zn(s) + O₂(g) → 2ZnO(s)

Both nickel and zinc do not react with water however the constant dissociation of the ions in salt water create a thin layer around the metals which is resistant to corrosion. Copper does the same thing as these other two metals however it does react with air and water to from a (patina) this patina is copper oxide layer. This copper oxide layer turns green and a highly resistant coating that is in susceptible further chemical oxidation.

Research question

How do different metal coatings affect the rate of Iron oxides forming on the surface of iron and iron alloys?

The research question is to determine how through the plating of several different metals onto a steel strip the rate at which these steel strips become oxidized to become Iron oxide. To investigate the rate I am going to take these strips of steel, ensure that they are free of any oxidation, and coat them with exactly the same mass of each of the metals (Copper, Nickel, and Zinc). After measuring the mass of each of these cleaned pieces of metal I am then going to set up an electrolytic cell and plate three steel strips with copper. Then three with nickel ,then three with zinc and finally have three test strips to investigate how much of a difference ,if any, the coatings help the Steel to resist the formation of iron oxide

Hypothesis

I Believe that the copper coating will be the most proficient in saving the steel beneath it from any and all corrosion, The zinc would be second best in the prevention in the buildup of the rust as it would act as a sacrificial anode, finally when the nickel plated metal is to be weighed I believe that it will have seen the greatest increase in mass out of the differently coated metal strips.

• The copper coating would experience the least amount of corrosion. This is because the copper would form a small amount of oxide around the entire steel strip. This protective layer is the main reason that the steel strip would not be affected as much as the other metals. However if there is a piece of the protective coating that may become scratched there would be a significant increase in the rate of rusting by the steel strip. This significant increase in the overall rate of rusting is due to the fact that the iron alloy namely steel would act as a sacrificial anode and this particular trait would cause the formation of iron oxide to increase.

• The zinc coating would experience a very different accumulation of the oxidation. This is because the zinc will act as a Cathode protection system of the overall strip of steel. This protection system would cause an initial gain in mass however the sacrificial nature of the zinc, once all of the zinc has reacted, the iron would begin to rust.

• The nickel would be the least effective because it is even less reactive than the copper. This means that the effectiveness of the nickel would further increase the effectiveness of the steel as becoming a sacrificial anode this sacrificial anode would mean that rather than the iron being protected by the nickel the nickel would be protected by the corrosion of the steel strip.

Variables

Controlled

• The temperature of the solutions being electrolyised
  • This may have increased the rate at which the electrodes were coated with the copper, nickel and zinc
• The salt content of the water the samples were placed next to
  • This may have changed and there would have been an increase in the production of rust on the steel electrodes
• The balance that the masses were measured on
  • Different balances may have changed the readings of the masses of the electrodes
• The molarity/ concentration of the solutions used to electroplate the steel electrodes
  • A difference in the concentration of the solutions used may have caused excess etching of the steel and may have caused certain electrodes to become more or less oxidized.
• The mass of the electrodes that were electrolyised
  • The mass of the electrodes was attempted to be kept the same however they were slightly different but each one was recorded.

Independent

• The amount of time for which the electrodes were left to rust.

Dependent

• The mass of rusting / oxidation present after two weeks

Apparatus

Methodology-Experimentation

1. Placement of the steel cathode and the metal solutions source metal as an anode.
2. Make sure both the steel strip and the copper anode as free of any corrosion/ oxidation before the submersion of the electrodes
3. Make a 1 molar solution of copper sulphate /zinc chloride/Nickel chloride
4. Fill a 100 cm³ beaker with the .5 molar solution of the metal salt solution.
5. Place a 2 volt charge onto the system
6. Electrolyize till there is a thorough coating around the entire steel strip
7. The coating will add around .5 grams of weight to the steel strip.
8. Then take the electrode and gently place it on a piece of paper towel.
9. Wait until the coated steel strip has dried thoroughly
10. If necessary use steel wool to clean away any scum/ produce a shiny surface on the electro plated surfaces.
11. Place the metal strips where they are exposed to both moisture and sodium chloride solution approximately the same as sea water.(22ppt)
12. Measure the mass change of the metal after 2 weeks make any other observations such as color change.

Raw data

Copper

Zinc

Nickel

Steel untreated (Control)

Analyised Data-Graph

Analysis of the graph

This graph shows that the copper was the best at preventing the overall gain in the mass of the steel electrode. This prevention in the gaining of mass was mainly due to the fact that the copper made a complete coating around the entire steel electrode. This coating proved to create a thin film of copper oxide shown to be present on the surface of the electrode because of a slight green color that was beginning to form around the corners of the electrode. The zinc proved to be worse than even the control this was due to the fact that the zinc oxide formed also had mass and then the steel also started to become oxidized by the time the two weeks had passed. Although the areas of the electrode which were covered in the zinc oxide there was no iron oxide. The surface of the electrode was spotted with dark brownish red patches this means that there were small rust patches along with the zinc oxide which accounts for the slightly higher mass than that of the control. The reasoning behind why the nickel plated steel electrode had a high mass increase is because of the tendency of the sacrificial anode to be the most reactive metal. The nickel was a lot less reactive than the steel electrode. The fact that the steel electrode was higher along the reactivity series than that of the nickel used caused the steel to become “sacrificed” in the place of the nickel. This reason is why the steel was most affected in the coating containing the nickel.

Conclusion

After my testing the hypothesis was proven to be correct. This proving of the hypothesis allowed for me to be able to ascertain that the best way in which to treat steel was with a complete copper covering and secondly with a zinc coating . These two ways in which the metals may be treated are feasible in the fact that zinc bars are usually attached to underwater structures this prevention is known as CP system. This CP prevention is highly affective however it requires a lot of up keep and it does not completely protect the entire surface of the steel as was seen by my testing results. The only one of the results that seemed to have completely worked was the copper coating. The coating of the steel by copper created a hydrophobic coating of copper oxide. The copper oxide had a slight increase in the mass measured by the balance. This slight increase in the mass was due to the fact that the salty air was not able to reach the steel electrode. This prevention ultimately allowed for the electrode to become protected from the oxidation. The overall way in which the metals were protected is going to allow for me to take my findings and apply them to the everyday usage in which I have begun to realize that we use both electrolysis and oxidation prevention on a daily basis.

Possible improvements

The amounts of retests as well as the length of testing may be increased this increase in length of testing can allow to see the amount of time taken for the complete disintegration of the metal. The increase of testing of the metals will allow for the in accurate nature for these results as well as the nature by which the metals have been protected from the corrosion. The accuracy of the testing may have been increased through the usage of metal which may have been free of corrosion unlike the metal which I have used. The metal that I used for my expirement had already been heavily corroded and I had to clean it with strong acid as well as to use some sand paper to clean the surface of the metal. After the cleaning of the metal I was only able to remove some of the corrosion. This major limitation of my expirement was that I wasn’t able to clean the corrosion which might have caused the copper coating not to adhere to the surface of the electrode. Finally the most major limitation of my expirement was the time I had in which to complete the experiments. Firstly I had to wait for the materials to arrive for which to be able begin my expirement, my chemicals as well to get the metal strips cut from a long sheet.

Bibliography

Jim, Dufour. “Electroplating.”Wikipedia. Wikimedia Foundation, 01 Mar. 2014. Web. 06 Jan. 2014. <http://en.wikipedia.org/wiki/Electroplating>.

“Rust.”Wikipedia. Wikimedia Foundation, 01 Aug. 2014. Web. 09 Jan. 2014. <http://en.wikipedia.org/wiki/Rust>.

“Seawater.”Wikipedia. Wikimedia Foundation, 01 Apr. 2014. Web. 06 Jan. 2014. http://en.wikipedia.org/wiki/Seawater

“American Experience: TV’s Most-watched History Series.”PBS. PBS, n.d. Web. 06 Jan. 2014. <http://www.pbs.org/wgbh/americanexperience/features/general-article/streamliners-steel/>.