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Rate of corrosion via electrolysis help please

June 27, 2008

Hi guys,
well so far I'm lost and this is my assessment

(I) to compare the corrosion rate, in a suitable electrolyte, of a variety of metals, including named modern alloys to identify those best suited for use in marine vessels, and
(II) to compare the effectiveness of different protections used to coat a metal such as iron and prevent corrosion.

so far alloys I'm going to use are stainless steel and brass
metals used are aluminium, iron, zinc, copper

is that too many? or should I use iron (wrought and/or cast), mild steel (e.g., bolts) and stainless steel

in salt water electrolytes ; how much salt should I put in. or should I use distilled water, salt water and acidic water

I actually have no idea what I'm doing please help me
thanks guys

Jas W.
student - Sydney, NSW, Australia

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Hi, Jas. Flash forward a few years. You've graduated and have a job with a company that makes boat parts; the boss is paying you by the hour to do your job. She calls you in and gives you this assignment: "Compare the corrosion rate, in a suitable electrolyte, of a variety of metals, including named modern alloys to identify those best suited for use in marine vessels, and compare the effectiveness of different protections used to coat a metal such as iron and prevent corrosion."

Would you leave the room at that point, saying to yourself "I actually have no idea what I'm doing"? Or would you insist: "I'll be happy to do the project, boss, once I am clear on what you are saying. So let me ask you this . . ."

We can help you with technique and will be very happy to do so. But the biggest single problem in industry if not in life is failing to understand what the other person is trying to say. Please come back after you've talked to your teacher and can say "I clearly understand what my teacher wants me to do." Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2, 2008

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July 3, 2008

I am a substitute teacher in science and math and your assignment is rather well stated. Read it again.
"marine" means ocean or sea water. In your area it will run around 30 PPT or 3 parts per hundred or 3% salt. Now because there is more in sea water than sodium chloride, go to your tropical fish store and buy or beg a pound of salt for a saltwater aquarium makeup.
Better yet, Sydney is on the water, get a couple of gals of real saltwater (a mile or two off shore) in some clean plastic bottles. Fill them completely full and cap them securely to keep air out until you use it.
Remember that corrosion is temperature dependent so all of the samples need to be the same temp. IE: you have to do all of them at the same time. Absolutely positively--no dissimilar metals in the same dish and preferably only one to a dish. 8" test tubes work well. Another variable--Totally submerged or only partially submerged? Oxygen makes a huge difference. Sunlight affects algal growth which can have an effect, so you need to specify light or dark environment. Regular light bulbs have a different affect than fluorescent, so I would look at a glass covered "dog house" where each sample got the exact same amount of light- i.e., a big box.
Next is metals. Bolts introduce a number of variables, so avoid them! Use bar stock as much as possible. As many as you can find. Remember junk yards as a possible source. Wet sand everything with FRESH fine sandpaper (wet/dry silicon carbide or emery cloth) NO cross contamination!
Use your imagination on what you might use for protection-paint-what kindS, oilS, waxeS. I would avoid plating as it introduces too many more variables.
The name of the game is to control your variables and identify them, all of them.
So, see, your problem was well stated and still allowed you some room for research and execution of the experiment.
I am positive that some class that you have had has covered the Scientific Methods. Find that and read it first.

Now, we have been kind, so let us know what your results were.

James Watts
- Navarre, Florida

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July 7, 2008

James,

Couldn't disagree with you more. That is a very poorly structured question. There are libraries on this very subject. How is a student supposed to define the test parameters when there is such a wide variety of a) Materials, b) Coatings, c) Test solutions.

If this was for an MSc or a PhD then one could expect the post graduate student to define the exact parameters. If this is a High School question, it is well beyond their remit to define those sort of parameters.

This sort of question is so open to opinion there can be no right answer, or at least none in a reasonable timescale.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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Hi Brian,
We can easily disagree, but I have seen middle school projects of a complexity that would put this to gross shame. With the internet and students that want to do well, they have all of the assets that they need.
Most teachers are not looking for a dissertation, but for a student that used a scientific investigation. Most teachers are looking for how did you go about it rather than finite answers.
If, as a teacher, I lay out a complete experiment, down to the last nut and bolt, what did the student learn other than a result and the ability to follow instructions.
Thinking is still a requirement, although a dying one, in school.
For really far out, 2 years ago a local student won SECOND place in the national science fair and had received two patents for medicines that he had developed for his senior project.

James Watts
- Navarre, Florida
July 7, 2008

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July 8, 2008 Regardless of whether the question is well formed or is poorly formed in the opinion of we readers, the pertinent issue in this case is that student Jas has no clue what he is expected to do: "I'm lost" ... "Is that too many, or should I ..." and "I actually have no idea what I'm doing" very clearly indicate that if he proceeds he will neither please the teacher nor will he learn much :-) It's not a question of whether we should blame the teacher vs. blame the student for the lack of understanding; it's a matter that the student must come to understand that, regardless of whether the teacher is busy or not, the student should not guess what the teacher wants but must find out what the teacher wants ... and not by asking a third party, but by asking the teacher. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey Hi James, I have this problem with my own children coming back with questions that cover a whole branch of the sciences. Forgive me, but there need to be some guidelines, especially as the tutor is asking for named modern alloys, without guidance as to the material type. Imagine how many steels are currently available, let alone adding in nickel alloys, titanium alloys, brass alloys, aluminium alloys etc, etc. We obviously do not know the age of the child asking the question, but the breadth of the question is still huge and some rationalisation by the tutor should have been considered. I am not expecting children to be given such a structured question that all they had to do is pump in the question into the internet and up pops the answer, but be fair on the child, give them some guidance, cut down the breadth, or maybe change the focus. Sorry, dealing with these sort of generalised questions on a daily basis. Brian Terry Aerospace - Yeovil, Somerset, UK July 9, 2008

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Ted,

You are, of course, right. The student does need to get clarification if he doesn't understand what is being asked of him. An open forum is not the best solution and by the time an answer is forthcoming it will probably be too late for the student anyway.

Brian Terry
Aerospace - Yeovil, Somerset, UK
July 10, 2008

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I agree that the student must understand the "question" to be able to answer it.

I find that about a third of the students do not pay ANY attention to instructions until they find out that they can not do the problem.
Example: the teacher put the assignment on the board for each of two classes. I wrote the class name again in 6" red letters and circled each class assignment. I read the assignment and pointed to each item for each class and later got questions like Mr Watts, the book does not go to page 723. Solution: do the assignment for your class, not the other one.

I wear out the saying- read the question and answer THE question that is asked, not something else.
Teaching is a struggle. I just wish that once in a while we could hear from the teacher what was given.
Yes, there are bad teachers out there, at least in this country.

James Watts
- Navarre, Florida
July 10, 2008