Year Eleven Chemistry

Rust prevention in coating.

Introduction/Abstract.
The context of ships rusting at sea.
Steel has many properties that make it a useful and essential building material in boats. Its strength and durability make it a great choice for structures exposed to high amounts of stress, such as weather, heat, large amounts of applied force and constant usage and is also a viable option for the sea although it can still be bettered. Steel is better protected by; galvanisation, waterproof paint or a sacrificial anode to better the corrosion protection for boats in the water compared to just bare steel framework (Corrosion methods, Corrosion-doctors.com;) these methods in theory protect the steel from the chlorides and salts to further the durability and life of the framework of a boat and hence allow them to endure more, and with corrosion costing $2.7 billion to just ships alone it’s easy to see why corrosion must be prevented.
(The cost to the world because of corrosion with ships at $2.7 billion.)
The chemistry of rust.
Rust is caused by a few factors; moisture is the leading cause of rust along with water and salt, all making boats the most common victims of rust. (4 Fe+ 3O2 + 6 H2O= 4 Fe(OH)3,) Both water and oxygen must be present for rust to start and with water and oxygen on its own enough for rust to start destroying the structure of a boat, but along with salt to the water, it’ll become evident quickly that rust can be a big problem for many boat owners but also industries that revolve around boats. Not only can water do damage, but the moisture in the sea air can wreak havoc on boats and also its components. Rust is also a problem with iron components and can make parts break. Steel has the same problem, but there are some of those elements that are added during the steel production that can help stabilise and prevent rust. For example, stainless-steel is designed so that it will not rust, but it is more expensive that other types of steel this is because it has been made an alloy.
Protection methods
There are many ship treatments designed to prevent rusting usually intended for steel based ships, methods varying from paint to basic principle coatings with the intent of creating alloys that resist or prevent rust (Alloys are a mixture of metals, for example stainless steel forms a passivation layer of chromium(III) oxide, and zinc can protect steel by catholically onto it because it’s more electrochemically active, zinc being -1.1 and mild steel being -0.5.) While these methods all have widespread industrial applications--and are tested and refined in large research facilities, the basic principles behind them can be demonstrated in a simple and single high school chemistry class. With some simple equipment and some nails to experiment on, students can quickly observe the effectiveness of various methods of rust prevention.
How it helps.
Testing the various methods against each other in equal environments to show the better protectant against salt and chlorides to help further the life of future boats to show evidently which one should be used because it’s not just the better protectant, but also cost effective, for example coating steel with zinc to galvanize it requires a lot more manpower and also suitable electronic equipment to sustain its electrical conductivity of about 1.4 million Siemens per meter to galvanize it, compared to the needed equipment used to simply paint a boat, although the now alloyed steel might be a titan of a protector against the salt and chlorides. This all goes to show the hypothesis of how steel can be better protected to prevent or slow down the creation of rust.

Experiment Procedure: Testing Corrosion on Steel

Materials list: * 3 x pieces of steel 35mm x 5mm x 150mm * 70 grams of Salt (NaCl) * 50 grams of Zinc Sulphate * 2 litres of Distilled water * 4 x 500 ml beaker * 1 x Power Pack * 2 x Alligator clips * 1 x 10 cm Zinc strip * 1 x Can of Spray on metal paint * Scales (0.001grams) * 1 x beaker holder
Procedure
Method 1: Galvanising steel

1. The materials Zinc strip, 1 steel piece, 1 power pack, 50 grams of zinc sulphate, 500 ml of distilled water and 2 alligator clips. 2. 50 grams of Zinc sulphate was added to 500 ml of distilled water. 3. Solution was then stirred until all the zinc sulphate was dissolved into the solution. 4. One piece of steel was attached to the positive terminal using an alligator clip. 5. The Zinc strip was attached to the negative terminal using an alligator clip. 6. The two pieces of metals were added to the solution and the voltage was put on 8 volts. 7. It was then left for 1 day then taken out and dried.
Method 2: Painting steel 1. One piece of steel, a can of spray paint for metal and paper towel was gathered. 2. All materials were taken outside and the steel was placed on the paper towl. 3. One side of the steel was painted and dried. 4. The steel was then flipped and dried again.

Method 3: Testing Corrosion 1. An identical scratch was made on each piece of steel 3cm long in the centre of the metal 1cm from the bottom. 2. The mass each piece of metal was measured using electronic scales and recorded. 3. 70 grams of Salt (NaCl) was measured with scales and added to 2 litres of distilled water and stirred until all salt was dissolved. 4. 3 x 500ml beakers were filled with the solution of salt water. 5. Each piece of metal was placed in a different beaker. 6. The galvanised steel was pegged into a beaker holder and suspended above the line of galvanisation. 7. The three metals were left in the beakers for 7 days with any observations recorded and photographed. 8. Each piece of metal was then taken out of the beaker and dried. 9. Each metal had the rust removed with a steel wool and paper towel.. 10. The end amount of metal was weighed and the percentage of mass difference was calculated and recorded. 11. Any visible changes were also recorded and photographed.

Safety(measures taken, any risk?)
Attached

Results (Table One) | Steel | Painted Steel | Galvanised steel | Day One | Turned yellow.Orange colloids throughout beaker. | Turned pale yellow.Colloids throughout beaker. | No colloids noted.White substance | Day Seven | Solution turned orange with colloids suspended in the water. Black coating seen on surrounding metal. Rust seen on scratch | Solution turned dark orange with orange colloids suspended in the water. Rust seen evident on the scratch. Paint peeling. | Solution turned cloudy with white precipitate taking place. | | | | |
(Table Two below) | Painted Steel | Galvanised Steel | Plain Steel | Weight before (g) | 103.342 | 101.284 | 101.273 | Weight day 7 (g) | 103.281 | 101.737 | 101.192 | Weight difference (g) | 0.61 | 0.453 | 0.081 | Difference % | 0.06% | 0.45% | 0.08% |

Discussion
The corrosion testing was carried out over a seven day elapse of which in that time a few factors indicated that chemical reaction had taken place. By examining the tables above it can be seen that corrosion took place in both the beakers where painted steel and bare steel were placed, thus making them lose electrons and oxidising. However in the third beaker that was holding the galvanised steel it is seen that it gained weight of the elapse from 101.284 to 101.737 (See table two,) making it reducing agent. Following the rules of rust in which rust causes oxidisation it is evident that both the painted steel and plain steel rusted whereas the galvanised steel reducing agent, this is because zinc (The anode,) plated the steel (The cathode,) and caused it to gain it’s electrons and the zinc then protects the scratch that was made, forming a layer over it to prevent rust, making it an effective rust prevention method. These results are seen in just the room temperature and with 75 gram salt added to all beakers to speed up the reaction for the seven day period. These results support the hypothesis that corrosion can be better managed via various corrosion prevention methods and halt or slow down the rate of corrosion. The reason for the galvanization of the steel from the zinc is due to the chemical properties of zinc and steel. Zinc is lower than steel on the electrochemical series and therefore has a greater tendency to corrode in the presence of water and oxygen.
Looking at the galvanized metal it is evident that Zinc protects the steel in two ways; the first is it’s high resistant to rust and also iron which is a major component of steel, reacts exponentially with oxygen and moisture and will eventually at a rapid rate disintegrate. The layer of zinc on the surface prevents those elements from reaching the steel so quickly. It also develops a patina which is a layer of zinc oxides, salts, and other compounds. This offers further protection to further the prevention of rust and keeping the steel in good condition. Zinc is also extremely durable and scratch resistant. The outer layer protects the steel by acting as a sacrificial layer (In a similar sense to a sacrificial anode.) if rust does start to happen upon the surface of galvanized steel, the zinc will get corroded first hence the sacrificial in its term. Even in areas where the surface is scratched or damaged, the surrounding zinc will still corrode before the steel does, tis was evident in the test where the galvanized steel didn’t rust at all and a white layer was formed around the scratch.
When Zn catholically protects steel, the electrons generated in the anodic reaction: Zn→Zn2++2e−
Reversing the initial step of the corrosion reaction of iron, Fe→Fe2++2e−
The iron being poised now at the potential of the zinc anode, where it could, instead, be plated:
Fe2++2e−→Fe.
The necessary electrochemical half-cell reaction: Zn→Zn2++2e− Because oxygen reacts with the zinc, it reduces the utilization efficiency of the zinc that cathodically protects the steel in galvanized steel.
Also Metal, being a malleable substance, due to its atomic structure (seen in diagram one), is susceptible to scratching and abrasion. It is likely that the increased thickness of the zinc is delaying the rusting of the steel by providing more zinc to sacrificially oxidize and producing more of the protective zinc hydroxide.

(Diagram One, Cschaller Univeristy, 2004.)

Conclusion/recommendations.
With it being evident that steel can be better protected via various methods such as painting steel, galvanizing the steel, compared to just bare steel framework it should be considered that although painted steel is better than bare steel, painted steel showed that the paint peeled after just seven days, making it ineffective for boats as it would be just bare steel in just a week because the chlorides and salts rub away the paint rapidly. However galvanized steel requires more effort than that of just bare steel it is shown that it’s an extremely effective corrosion method as no rust was shown after the seven days. However there is another way of preventing rust, cathodic protection, this is used to control the corrosion of a metal surface by making a more electronegative metal connect to the protected metal making it a more easily corroded sacrificial metal to which it will act as an anode.

Bibliography

What is the loss and gain of electrons to form ions. 2013. What is the loss and gain of electrons to form ions. [ONLINE] Available at: http://wiki.answers.com/Q/What_is_the_loss_and_gain_of_electrons_to_form_ions#slide3. [Accessed 16 November 2013].
Corrosion cost. 2013. Corrosion cost. [ONLINE] Available at: http://www.corrosion-doctors.org/Principles/Cost.htm. [Accessed 16 November 2013].

Corrosion of Iron | Tutorvista.com. 2013. Corrosion of Iron | Tutorvista.com. [ONLINE] Available at: http://www.tutorvista.com/content/chemistry/chemistry-ii/metals/iron-corrosion.php. [Accessed 17 November 2013].
Reduction of the loss of zinc by its reaction with oxygen in galvanized steel and batteries - Board Of Regents, The University Of Texas System. 2013. Reduction of the loss of zinc by its reaction with oxygen in galvanized steel and batteries - Board Of Regents, The University Of Texas System. [ONLINE] Available at: http://www.freepatentsonline.com/y2007/0125644.html. [Accessed 17 November 2013].

Definitions:

Rusting
The corrosion of iron and readily occurs in the alloy steel. The formation of a reddish brown flake which adheres to iron is called rust.
Steel
An alloy made of iron and carbon. The carbon atoms in steel greatly increase the strength of the metal. They prevent the iron atoms in the crystal lattice from slipping over one another.

Anode.
In an electrochemical cell, the anode is the site where electrons are produced through the chemical activity of the metal. The anode is the area where metal loss occurs, the reaction is called oxidation. The metal loses electrons and migrates from the metal surface through the environment. The electrons remain in the metal but are free to move about in response to voltage

Electrolyte.
Electrolytes are solutions that can conduct electrical currents through the movement of charged chemical constituents called ions. Positive and negative ions are present in equal amounts. Positive ions tend to migrate away from anodic areas and toward cathodic areas. Negative ions tend to migrate away from cathodic areas and towards anodic areas.

Components.
In order for electrochemical reactions to occur, four components must be present and active. These components are the anode, cathode, electron path, and electrolyte. gradients. Cathode.
The cathode in an electrochemical cell is the site where electrons are consumed. For each electron that is produced at an anodic site, an electron must be consumed at a cathodic site. No metal loss occurs at sites that are totally cathodic.

Anodic Reactions.
Metal loss at anodic sites in an electrochemical cell occurs when the metal atoms give up one or more electrons and move into the electrolyte as positively charged ions.

Typical Reactions.
The generic chemical formula for this metal loss at an anodic site is:

M ---> M+ + e-

M = uncharged metal atom at the metal surface
M+ = positively charged metal ion in the electrolyte e- = electron that remains in the metal