Looking for etched metal specimens (or possibly conc. nitric acid)

Hi folks,
I'm looking for a few etched specimens of common metals to photograph under a microscope. Preferably including one or two which show a
microstructure which is visually pretty simple. Examples I'd be interested in obtaining include cold rolled low carbon steel, normalised low carbon steel, normalised medium carbon steel, grey and white cast iron, annealed brass, etc. I'm not looking to spend a lot of money. Anyone know where I might obtain some?
Another possibility would be to obtain some concentrated nitric acid in order to make the nitric acid and ethanol mix required for etching most ferrous metals myself, but concentrated nitric acid doesn't seem easy to obtain.
Any suggestions? Thoughts would be appreciated.
Best wishes,
Chris
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Chris,
Where do you live? Contact me off-list (replace "nospam.demon" above with "dlittlewood").
For your DIY solution, if that proves to be the route you choose, you can get nitric acid from jewellers suppliers. It's pretty nasty stuff though, and its vapour will corrode anything within spitting distance.
David
--
David Littlewood

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David Littlewood wrote:
<snip>

Thanks. I've sent you an e-mail.
Best wishes,
Chris
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Christopher Tidy wrote:

You can buy nitric acid from lpchemicals, but they have a minimum 50 order (plus carriage and VAT).
If you are anywhere near Trowbridge, Wiltshire, I can let you have some. But I can't post it :(
-- Peter Fairbrother
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Mixing nitric acid and ethanol os an excellent way of making substantial explosions - I've twice seen the front of a fume cupboard and once the window of a laboratory blown out by accidental mixing of concentrated nitric acid with alcohol. In fact in 40 years of working in chemistry labs this has been the single most common cause of explosions I have encountered.
Have a look at
http://www.ab.ust.hk/sepo/tips/ls/ls005.htm
But don't even attempt it unless you have a great deal of expertise and a safe environment, particularly not with acid and alcohol of unknown purity and provenance - it's about as dangerous as home chemistry can get.
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Norman Billingham wrote:
<snip>

My understanding is as follows:
* That the major hazard is more concentrated mixtures of nitric acid in ethanol (the mixtures used for etching are pretty dilute, 1 or 2 % concentrated nitric acid in ethanol according to a book I have). * That mixtures of nitric acid in ethanol should not be stored. * That the acid should be added to the ethanol, not vice versa.
Obviously there are more general safety precautions that should be taken, but I'd be surprised if there isn't a safe way of making and using this.
Best wishes,
Chris
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Christopher Tidy wrote:

Indeed, nitric acid and ethanol can be used as rocket fuel! It might be a good time to go over some rules and safe procedures.
First, nital etchant should be made freshly for each use, and neutralised and discarded immediately afterwards. Never store made-up etchant, especially in a closed container. Never reuse etchant.
Some labs make up a batch every day, but you shouldn't do that, it's unnecessarily dangerous.
Second, mixing and etching is normally done in a fume cupboard. I can't recommend not using one, but it is possible, especially in the quantities mentioned below. if adequate ventilation is available.
Wear gloves and eye protection. Keep a source of water handy for washing off spills. I add about 2% bicarb of soda to the water, but ymmv. Having a second person within earshot, to provide/go for help, is a good idea.
Please note the importance of setting a procedure and sticking to it, following the procedure exactly, every time. Practice the motions before doing it for real - seriously, chemists do that, it's surprising what you find out. You haven't got enough fingers, and that bottle is just out of reach ..
One procedure might be as follows: First, prepare the steel sample. Wear gloves and eye protection. Measure 10 ml of ethanol into an #empty# clean, dry 50 ml polypropylene beaker (eg ebay Item number: 120190765576), then slowly add 0.1 to 0.5 ml of nitric acid with stirring.
The amount of acid used depends on the steel, try 0.2 ml to start. Don't go above 0.5 ml (5%), it starts getting seriously dangerous then.
Carefully place the prepared sample in the container. It takes a few seconds to a few minutes for the sample to etch.
After etching is complete, immediately pour the used etchant over a tablespoonful of soaking wet garden lime in a glass or PP container. If you only do it occasionally, it is safe to dispose of this down the toilet (or in the garden). Do not reuse the etchant.
#Do not refill the beaker until it has been cleaned and dried. Do not top it up.#
The nitric acid bottle in use should contain no more than 25 ml of nitric acid (enough for 50 - 250 etches!). Clean and dry the nitric acid bottle when it is empty, then refill it. #Don't part-refill it.#
#Fresh# disposable 1ml polypropylene pipettes (eg ebay Item number: 350018678030, but not the 40 x 1 ml offerings, which aren't 1 ml!) can be used to measure the nitric acid, but never reuse them - they only cost about 6p each.
Never put the pipette into the nitric acid bottle more than once, use a new pipette instead.
Put half an inch of garden lime in a tall glass full of water, and rinse the used pipettes in it for safety. But do not ever reuse them, it is impossible to clean and dry the insides properly.
Clean equipment with 5% washing soda solution. Dry it before use.
Ethanol: Suitable ethanol isn't easy to get. IMS, industrial methylated spirits, and "denatured alcohol" if you can get either of those, are okay if used as above. Blue meths is not okay. Vodka won't work properly. Clear fuel alcohol, as available in the EU, may be dangerous. Methanol is okay if used as above, except the fumes are dangerous.
Isopropyl alcohol has caused explosions, and many people recommend not using it at all. If you want to use IPA email me offlist.
Nitric acid: The nitric acid lpchemicals sell http://www.lpchemicals.com/product.asp?ProdID 6&CatID1 is LR (laboratory reagent) grade and about 70% - this is what is normally called "nitric acid" or "conc. nitric acid", and is the right stuff to use.
Don't use technical grade, it can be dangerous, use LR or AR grades.
Above 70% nitric acid is usually called white fuming nitric acid. Above about 98% it is called red fuming nitric acid. You don't want to go near either of those!
All this is perhaps a bit more than required, but if you follow it it is about as safe as you need it to be, and it isn't very onerous (except perhaps the bit about never reusing pipettes - but that's seriously important, don't be tempted).
-- Peter Fairbrother
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Peter Fairbrother wrote:

Thanks for all those useful safety tips. If I make any nital I'll follow them, but I might buy some pre-prepared specimens instead.
Just out of interest, what happens (or might happen) if you reuse the pippettes?
Best wishes,
Chris
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Christopher Tidy wrote:

Depends.
Perhaps there is a bit of alcohol in the pipette, and it reacts with the nitric acid, producing gas, which forces the nitric acid in the bottle to splash up over you.
Perhaps there is a bit of alcohol in the pipette, and the mixture gets hot, maybe melting the pipette or igniting the alcohol when you add the nitric acid.
Worst (maybe) case, you add a bit of alcohol to the nitric acid bottle each time, and the concentration of alcohol in the nitric acid rises until it goes bang, and you die. Or if there is already enough nitric acid in the alcohol, perhaps an ignition as above causes it to explode.
There are other possibilities, including partly-reacted old nital acting as a catalyst to make the reaction in the new nital easier, or metal contaminants form used nital doing the same job.
The list goes on ..
-- Peter Fairbrother
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Peter Fairbrother wrote:

I checked their website, but can only find dilute nitric acid. It's my understanding that you need concentrated nitric acid.

I don't unfortunately. But if that's concentrated, I might take you up on the offer if I can't find any locally.
Best wishes,
Chris
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On Sun, 27 Jan 2008 04:38:12 +0000, Christopher Tidy

It's in the section marked Acids/Alkalines (Nitric Acid LR) :-)
I know this because I have a litre bottle that I bought from them.
You want about 10% acid in industrial spirit for etching ferrous materials.
For some website-related reason, you won't see industrial spirit in the list of solvents, but if you search for "industrial" you'll find it.
Mark Rand RTFM
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Finger trouble... 1% for lapped/ground sections. 10% is for macro etching samples and blowing up the workshop...
Mark Rand RTFM
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Mark Rand wrote:

Thanks. That would explain why they don't list the concentration. For some reason I assumed that "Laboratory Reagent" was pre-diluted stuff for giving to students.
Pity about the 50 minimum order charge. That's more that I want to spend. They don't state their carriage charge either. It's seems they're in Cheshire, so maybe I could pick up a bottle from them? That's if they aren't going to be unnecessarily fussy.
My dad said he bought a bottle of concentrated nitric acid from his village chemist when he was a boy.
Best wishes,
Chris
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Christopher Tidy wrote:

It's fairly pure nitric acid of about 70% concentration, ie with 30% water and only a little bit of other substances. It's the right stuff to make nital with.
Chemicals usually come in 3 main grades, Technical, LR and AR. There are other grades though, eg food, ultra-pure, semiconductor and spectroscopic grades.
Technical grade is approximately "mostly the right stuff", and usually will be about 95% pure, though this will depend on the chemical involved.
LR or "laboratory reagent" is a grade of purity, sort of. Usually LR stuff will be 98-99% pure or so. Really however, LR is saying it is suitable for use as a general laboratory reagent.
AR, or "analytical reagent" is usually even purer, maybe 99.9%. Again it varies, and AR is just saying that it's suitable for analytical work.
These can vary a bit, especially AR, when the label may say that there is only a tiny bit of some otherwise common impurity, which would mess up the use of the chemical in (some) analytical situations; but there may be a fair bit of another impurity which doesn't affect the analytical use of the chemical. AR labels usually give lists of maximum levels of impurities, and an assay.
A few chemicals are slightly different, for instance nitric and hydrochloric acids, ammonia solutions etc. They still come in grades, but it assumed that they contain water, which is not counted as an impurity or a diluent - for nitric acid, it's usually about 70% acid, for hydrochloric acid it's about 35% acid, and so on.
The reasons for these differences vary, for nitric acid it's because it fumes and is dangerous to store at concentrations about 70%, for hydrochloric acid it's because only 35% of HCl will dissolve in water (HCl is a gas), and so on.
However, "nitric acid", unless it has something else tacked on, is usually assumed to be 70% in concentration when you buy the chemical. It also comes in grades as above, technical, LR and AR, but these refer to the levels of impurities in the acid, not the concentration of acid, which will always be 70% or so.
Now that's more than you wanted to know, isn't it :)

You could 'phone and ask.
-- Peter Fairbrother
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Peter Fairbrother wrote:
<snip>

I did. Looks like the cheapest thing for me to do is to collect a single bottle from their premises in Cheshire. They said I can do this with no minimum order charge.
Best wishes,
Chris
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Peter Fairbrother wrote: > Christopher Tidy wrote: > >> Hi folks, >> >> I'm looking for a few etched specimens of common metals to photograph >> under a microscope. Preferably including one or two which show a >> microstructure which is visually pretty simple. Examples I'd be >> interested in obtaining include cold rolled low carbon steel, >> normalised low carbon steel, normalised medium carbon steel, grey and >> white cast iron, annealed brass, etc. I'm not looking to spend a lot >> of money. Anyone know where I might obtain some? >> >> Another possibility would be to obtain some concentrated nitric acid >> in order to make the nitric acid and ethanol mix required for etching >> most ferrous metals myself, but concentrated nitric acid doesn't seem >> easy to obtain. >> >> Any suggestions? Thoughts would be appreciated. > > > > You can buy nitric acid from lpchemicals, but they have a minimum 50 > order (plus carriage and VAT).
I checked their website, but can only find dilute nitric acid. It's my understanding that you need concentrated nitric acid.
> If you are anywhere near Trowbridge, Wiltshire, I can let you have some. > But I can't post it :(
I don't unfortunately. But if that's concentrated, I might take you up on the offer if I can't find any locally.
Best wishes,
Chris
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Christopher Tidy wrote:

Whats wrong with using ferric chloride ?It's used for etching pcbs Available at electronic supply shops . Safer than nitric acid . I'm pretty sure it will etch ferrous and non ferrous metals.
--
Kevin (Bluey)
"I'm not young enough to know everything."
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It sure etches stainless steel, as I discovered when I used one of our dessert spoons to mix some. SWMBO wasn't amused.
Jim Hawkins
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Kevin(Bluey) wrote:
<snip>

I don't know. I just know that nitric acid in ethanol is the recommended etch. It's also my understanding that it's possible to over- and under-etch specimens intended for viewing under a microscope. It's not a case where you want to leave it until the reaction ceases.
Best wishes,
Chris
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You realise you need a metallurgical microscope - i.e. one which illuminates from above. The majority of microscopes illuminate from below.
You don't say why you want to do this - are you teaching yourself metallurgy, or hoping to provide a technical service ? Its an interesting area, and a lot of science goes into understanding what you see. I can recommend a good book if you are interested.
Steve
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