Measuring degradation/decomposition

dsfranca

Hi guys,
I would like to know if any of you knows a method to determine the time it takes for a given substance to decompose. I would really like to perform such experiment, but I was not able to find anything, and I am sure this method exists, as everyone has already seen a table like this one: http://www.qldlitter.com/pdfs/wastea3.pdf .
I would need to perform the experiment for Alimunium, wood and iron.
It would already help if you could tell me if I am using the right terminology (degradation/decomposition) or the name of this field of study, as in this way I could refine my search.
Thank you in advance!

kldickson

Aluminum and iron are pure elements; they do not decompose. Wood is an organic and heterogeneous solution, in chemical terms; decomposition only applies insofar as bacterial decomposition.

Dissolution for aluminum and iron can occur in a variety of solvents, each with different powers of dissolution.

dsfranca

Thanks for the answer!
But I am still not sure about the wood. I mean, I could just leave the wood in a environment that is ideal for bacterial growth and then measure the mass (or should I measure something else, such as volume?) of the piece of wood as time passes and then infer when the wood will be totally decomposed. As I am only interested in one specific piece of wood, it only matters how much time it takes for this piece to decompose, so this eliminates lots of variables.
But my problem is that, as there is varnish on this specific piece, it will not normally decompose. How could I measure how much time it would take for the varnish to loose its effect?
By the way, I am sorry for my poor chemistry knowledge, so thanks for helping me out!

Lok

There are methods but they rarely involve any chemistry, usually research about old stuff and how it degrades. Finding old trash and determining it's state and age. Testing would involve setting the object on your lawn and forgetting it for a couple of years. The 1950's waste that we still find today is best.

There are tables about corrosion, and you should look it up. Corrosion depends on a lot of factors like material, humidity, temperature difference, wind, sun exposure, pH of medium, bacteria etc.

dsfranca

Thanks for the answer Lok.
I found this corrosion table: http://www.srcoils.com/resources-and...n-table2.php#S
But I am not sure how to interpret it, neither if it is the right table. Most importantly, how can I calculate the time it takes for the varnish to loose its effect from this source of data? The varnish has shellaq as its main component, so for what exact property of shellaq am I looking for and how should I use it?
Thks

Lok

That table seems to be for steel copper and aluminium.

I've no ideea how to calculate a time till loosing effect, the practical experiments in fixed conditions seem the only solution. There are way to many variables and chemical reactions taking place.

dsfranca

Yes, I agree that only practical experiments could tell me the answer, but unfortunately I am not sure if I have the time to perform them, afterall, it could take months. I would therefore like to know if there is a way of using some sort of catalyst and then infering the time it would normaly take, or another way of speeding up the process...
Besides that, do you believe that my method to determine how much time it would take for the piece of wood already without the varnish to decompose would produce a decent result?
Thks for your help

Lok

For wood ... it can me acomplished. Be careful with the conditions as a little miosture in the air will significantly alter the weight of wood.

dsfranca

I believe that I will try to call the company that produces the varnish and see if they have any information on how long it lasts (I would really rather do it myself, but I dont believe I have enough time to collect enough data.). I will start doing the experiment with the wood tommorow, I hope it works out. Lets see if someone comes up with a magical idea in the meantime!
Thks for the warning about the moisture and everything else Lok, you have been really helpful!