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.
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.
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
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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.
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.
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.
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.
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.
Yes I do. I'm thinking of buying one. I'm just researching the practicalities of it before I do.
Two reasons. Firstly for fun and to learn something. Secondly because I'm building a website about engineering design and therefore want a few pictures of the microstructures of common metals.
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.#
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
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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).
I qualified as a metallurgist, but my work has taken me away from that now, but I have a hankering to get the capability back, and have slowly acquired a small furnace, microscope, and hardness tester (its wonderful what you can pick up on ebay). One thing I don't have is the arrangements for mounting and polishing specimens. You might get away without mounting, but you need to be able to get a good flat polish on the surface before etching. Normally successively finer water washed emery papers, then if I remember correctly we used 6micron and then 1 micron diamond paste on a rotating table a bit like a record deck, but with more grunt. Steel etching is a fairly quick affair with 5% nitric in ethanol (referred to as Nital), or maybe 10%. Different etchants could be used for other metals.
The core of metallurgy is understanding how heat treatment changes the microstructure of metals and hence modifies the properties, and understanding this means understanding the phase diagrams which show the solid state transformations, and then understanding how changing the cooling rate changes the microstructure. Much of the rest of metallurgy overlaps with other disciplines, for example fatigue failure, crack growth, overlap with mech eng; corrosion, plating, extraction, refining, overlap with chem eng; and ores and minerals overlaps with geology. For my money the best book I have seen on this 'core' aspect is Metallography of Phase Transformations by Chadwick, it really links the phase diagrams to the microstructure. I still have my copy as well as my notes from the lectures back in the 1970s - so if you want me to look some things up then drop me a line. I may even have some microstructure photos, though generally we drew them by hand
- that way the significant features had to be appreciated by the brain cells. It reminds me of the quote that lecturing is the art of transferring information from the notes of the lecturer to the notes of the student without passing through the minds of either - it is of course not true!
I have a metallurgist's "belt sander" - it has a much superior belt-tracking arrangement than the usual hardware-store version, facilities for keeping the sample and belt wet, and a wash sump.
It's a bit bulky, though - I'd swap it for a more ordinary linisher as long as it had reasonable belt control.
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