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Topic: What is in my sample?  (Read 2855 times)

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Offline AcesHigh

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What is in my sample?
« on: October 06, 2008, 11:36:37 AM »
I performed an experiment a few months ago and I am currently going trough the results of the experiment. To hastily explain what I did; I compared rust found on a steel screw from my garden shed with Fe2O3 from a labeled jar in my high school's chemistry laboratory. I heated my rust sample to remove all of the H2O I then dissolved both samples in 1M HCl and ran against a sample cuvette in the spectrophotometer after adding 1,5M KSCN. I got two reddish samples, and I had expected them to be quite similar as I assumed that the most abundant ionic compound in my sample would be similarly Fe2O3. Alas this was not the case, the two sample differed ALOT. The rust sample was scewed away from the Fe2O3 (local) maximum at 478nm and was at 492, and strangest of all there was a steep and very tall slope on the far right around 300-380nm. This slope got more distinguised after I heated the sample.

Fe2O3

Rust sample


Heated rust sample


Does anyone know how to explain the variances? I think it might be either Fe3O4 or FeO(OH) =/ but I have no clue to what it might be.

What is clear is that rust does NOT equal Fe2O3 =P

Offline macman104

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Re: What is in my sample?
« Reply #1 on: October 06, 2008, 03:59:23 PM »
If you heat your rust sample to drive off the water, what do you do with it after?  Do you heat it in open air, or under an inert environment?  If you heat it in air, it may oxidize, and if you don't cool it in a desiccator or similarly dry atmosphere, it may reabsorb water while cooling.

Anyway, I do work with Fe3O4 nanoparticles, and when I do UV-Vis measurements, I get a peak that starts absorbing around 350, but it doesn't really take off until 300nm or so.  However, if your sample were oxidized, I would imagine Fe3O4 would be oxidized to Fe2O3, not the other way around...

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