Personal Protective Equipment (PPE)

P2 - Corrosion

Safety:

Personal Protective Equipment (PPE):

· Safety Glasses.

· Closed toed Shoes.

· Lab coat or equivalent protective clothing.

· Gloves (supplied in laboratory)

Rules of Lab:

1. No food or drink allowed.

2. You must wear PPE at all times within laboratory as instructed or leave the laboratory.

3. Wash you hands thoroughly with soap upon finishing prac.

4. If in doubt about any part of the prac ask your prac supervisor.

Equipment / materials – Caution:

RISK RATING TABLE:

Equipment /Material / Personal risk / Protection / Risk
NaCl solution / May cause eye irritation / wear eye protection / low
10% H2SO4 solution / very corrosive, causes severe burns; avoid contact with skin/eyes. Do not ingest or inhale / wear gloves and eye protection / Medium

Evacuation / Emergency Process:

· Calmly turn off equipment on first alarm, prepare to evacuate.

· On second alarm calmly evacuate area and go to assembly area (grassed area near the liquid nitrogen vessel just to the north of Chemistry Building 23N)

· Supervisor is to close doors on exiting room/s.

· If an emergency exists and no alarm is activated then activate break glass alarm or contact 333 on any internal phone or red phone

· Leave the building via the closest exit or as directed by warden’s instructions and assemble at the evacuation assembly areas.

· Do not leave assembly area until all clear is given by building warden.

First Aid:

If you feel as if something unsafe has or could occur in the area please inform the prac supervisor. If you are injured inform the supervisor of the Prac immediately, always seek assistance of First Aid officers for any injury sustained in laboratories.

Name / Contact # / Location
Steven Lin / x20326 / Bld 23S Rm 249
Usman Ali Rana / x20326 / Bld 23S Rm 249

· First aid kit is located in corridor outside room 249

P2 – Corrosion

This practical session aims to introduce the topic of metallic corrosion by means of exploring the Galvanic (EMF) series, bi-metallic corrosion, and crevice corrosion. Preliminary reading for this session is found in Principles and prevention of corrosion, Denny A. Jones. 2nd ed., Prentice Hall, 1996, chapters 2.1, 2.3 and 7.1 (these sections are also attached).

The preliminary reading will provide in-depth background on the topics covered in this session. The chapters outlined above will need to be read prior to the practical session to ensure appropriate understanding of the topics covered in order to effectively complete the session.

Part 1: Galvanic Series

Materials needed: Epoxy mounted Cu, Mg, Zn, Steel with electrical connections; 3.5% NaCl, 10% H2SO4, beakers x8, reference electrode, multimeter.

Q: Write down the EMF of each metal (inc. appropriate units)

Cu Mg Zn Fe

The metals listed above are to be immersed in a 3.5% NaCl solution and a 10% H2SO4 solution.

Q: List the half cell reactions for each metal in each of the electrolytes

In 3.5% NaCl

Cu: Anodic Cathodic

Mg: Anodic Cathodic

Zn: Anodic Cathodic

Steel: Anodic Cathodic

In 10% H2SO4

Cu: Anodic Cathodic

Mg: Anodic Cathodic

Zn: Anodic Cathodic

Steel: Anodic Cathodic

Q: Predict which metal will corrode slowest and fastest in 3.5% NaCl.

Slowest Fastest

Now immerse the epoxy mounted samples into the beakers containing the electrolytes (1 sample per beaker). Ensure that the electrical connection wire is not fully immersed in the solution.

**Take care in handling sulphuric acid solution. Ensure appropriate PPE is used**

In this next part we will measure the potential of the corroding metals in the electrolyte with respect to a reference electrode. The voltage measured is with respect to the reference electrode used, and to be able to compare these values measured against the galvanic series (measured with respect to the Standard Hydrogen Electrode (SHE)) the measurements should be converted to a value with respect to the SHE.

Q: What is a reference electrode?

Q: Using the electrical connection on each sample, the multimeter and reference electrode, measure the potential of each sample in each electrolyte.

Reference electrode used: @ V vs. SHE

In 3.5% NaCl

Cu: Measured Potential (V) vs. Standard Hydrogen Electrode (SHE) (V)

Mg: Measured Potential (V) vs. SHE (V)

Zn: Measured Potential (V) vs. SHE (V)

Steel: Measured Potential (V) vs. SHE (V)

In 10% H2SO4

Cu: Measured Potential (V) vs. Standard Hydrogen Electrode (SHE) (V)

Mg: Measured Potential (V) vs. SHE (V)

Zn: Measured Potential (V) vs. SHE (V)

Steel: Measured Potential (V) vs. SHE (V)

Part 2: Galvanic couples (Bi-metallic corrosion)

Materials needed: Al, Cu, steel, Zn, 3.5% NaCl, beakers x4

Galvanic couples are produced by the joining of two dissimilar metals. The couples produced here are couples of aluminium with copper, and steel with zinc. There are duplicates of each couple: 1 with a small piece of Al with a large piece of Cu, 1 with a small piece of Zn with a large piece of steel, and 2 couples with the same size of each metal. The EMF of Al is –1.662V

The couples are to be placed in beakers containing 3.5% NaCl solution.

Q: Upon immersion in 3.5% NaCl, predict which metals will corrode?

Al/Cu couple:

Why?

Steel/Zn couple:

Why?

Q: Which metals will act anodic and which will act cathodic?

Al/Cu couple:

Steel/Zn couple:

Notice the difference in size of the different metals in the galvanic couples.

Q: Do you think that the difference in size of the metals will have an effect?

Immerse the galvanic couples into the beakers containing the solution and observe the results. Does what you see match up with what you predicted?

The galvanic couples produced in this section are representative of some real life galvanic couples found in industrial applications.

Q: Where do these galvanic couples exist in real world applications?

Al/Cu couple:

Steel/Zn couple:

Part 3: Crevice corrosion

Materials needed: Stainless steel sheets x2, 3.5% NaCl, beaker, elastic band.

Crevice corrosion occurs in small crevices produced by joints or rivets etc. In this section we will produce a joint with a strip of stainless steel and a plastic cap. Crevice corrosion occurs when the corrosive medium can penetrate the small space of the crevice but due to the size of the crevice remains stagnant and does not get replenished.

The stainless steel lap joint is produced by joining the stainless steel sheet and plastic cap and holding together with an elastic band. Inspect the lap joint to identify any possible crevice corrosion sites.

Immerse the stainless steel lap joint into a beaker containing 3.5% NaCl solution. After a period of exposure, remove the lap joint from the solution and separate the joint.

Inspect visually and under the microscope.

Sketch what you observe:

Q: Stainless steel is usually considered to be corrosion resistant, but what we see here could suggest otherwise. Why has this occurred? Explain.

Please hand in completed worksheets at the end of the laboratory session for marking by your demonstrator. Marked sheets will be returned to you in class. No report is needed for this laboratory class. Participation during the session will contribute 50% of the marks for this practical, the remaining 50% will be based on assessment of your worksheet.