Salman
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Cromate
I like to make black color used as body stain in ceramic tile from chromate ore what is the simplest way for this please if any body know help me
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crystalXclear
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Sorry old bean, I'm a little confussed by your question, do you wish to make the chrome oxide, dioxide or pentoxide salt's directly from the chromite
ore (FeCr2O4)?
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Salman
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Thank for your kind reply.
I just need that there is iron and chromium i need to get chromium oxide green from it
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ScienceSquirrel
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If you need chromium oxide the easiet way is to buy it.
It is widely used as a pigment and an abrasive.
It is stable, insoluble and as far as I know completely nontoxic if used sensibly.
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redox
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I'll give it a try. How about acidification to get chromic acid followed by neutralization with ammonia? The ammonium (di?)chromate could then be
subject to self-propagated thermal decomposition leaving you with Chromium (III) Oxide.
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crystalXclear
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SALMAN, What cone temp are you useing? It maks quite a differance to the colour variations you will get.
But to answer your question, Yes. Chrome oxide (green) & Iron oxide (brown).= Black
Iron oxide is a must have realy, so it's just your temp that will depend on what to mix with it & on your desired finish (streaked, speckled, etc.
Tell me, Are you a HOT MATURE PINK SALMON? Mr S Bisqueware 
That should have come from a woman realy, but not one woman took the bait.
Wrong track redox, I was walking that verry same path when salmon contacted me about the two mixed together to create the colour black .seems a waste
of chrome oxide to me.
[Edited on 19-4-2011 by crystalXclear]
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woelen
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Quote: Originally posted by redox  | | I'll give it a try. How about acidification to get chromic acid followed by neutralization with ammonia? The ammonium (di?)chromate could then be
subject to self-propagated thermal decomposition leaving you with Chromium (III) Oxide. |
The ferrochrome oxide, mentioned by Salman, does not contain any chromate. It is very inert and only dissolves in acids with great difficulty. I see
no practical method of converting this to Cr2O3 without the use of molten solutions of the mixed oxide in sodium hydroxide.
As ScienceSquirrel said, it is best to buy Cr2O3. It is cheap, can be purchased at any pottery supplier, and is non-toxic. No need to hassle with
toxic and highly corrosive chemicals.
If Salman wants a black pigment, then it is easier to buy Fe3O4, also from pottery suppliers. This comes as a very inert, non-toxic black powder.
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crystalXclear
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recieved via u2u from salmon.
thanks for your kind reply. I am just asking that i make black color by mixing iron oxide and chromium oxide with a same ratio and fire it at 1200
degree centigrade to get a black color. In chromate we have both the think binding with each other if we use it as it is in ore it does not give black
color. I just want to know how to make both iron and chromium react each other to get black color.
It would seem he want's to use chromates to make black. But any usefull glazeing from Chromite ore would only produce grey.
And only after extensive refining, I don't think you can. sorry an all that salmon
Read the posts above mine, there's more then one way to skin a cat.... well make black in this case.. Xtal
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Salman
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this is not the answer of my question. I need the reply that if you dont tell the answer then give me the detail how to make chromium oxide green from
chromate
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woelen
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You are talking about chromate, but what kind of chromate? Is it really chromate, in the sense that it contains CrO4(2-) ions, i.e. hexavalent
chromium? Or is it some mixed oxide of chromium(III) and iron(II)? The latter sometimes is called ferrous chromite.
If you really have chromate(VI), then you could try to dissolve the material in a strongly acidic solution and then add erhanol or sulfite in order to
reduce all chromium(VI) to chromium(III). Next you add a large excess of sodium hydroxide to precipitate all iron as ferric hydroxide and redissolve
the chromium(III) as green chromite. Filter the liquid and keep the green liquid. This green chromite then can be acidified again such that all of it
dissolves as chromium(III) and then by adding ammonia you precipitate most of it as Cr(OH)3, which can be filtered out and heated to obtain Cr2O3.
If you have ferrous chromite, which seems more plausible to me, then you need to heat the material in a nickel crucible with molten NaOH. It dissolves
in this. Use an excess amount of NaOH. Next, let the melt cool down and add this to water. The chromium(III) and excess NaOH leach out, the iron
remains as a solid and does not go in solution. Filtering and further treatment with acid and ammonia then is as above. Beware though that this
treatment with molten NaOH is very risky and requires very good protection of your body and especially the face. This is not something for the faint
of heart!
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Salman
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ferrous chromite
Yes you are right i have ferrous chromite can you u please tell me all the process with its quantity so that it could be easy for me to process it
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woelen
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You need to dissolve the stuff in molten NaOH. I would start off with a certain weight of NaOH and add half that weight of ferrous chromite. It is not
easy to tell which ratios are needed. There is a reaction in which chromite is formed, but more NaOH is needed, because the material needs to dissolve
as well. I think that a 2 : 1 ratio of NaOH and ferrous chromite by weight will be a fair guess to start with. You can always add more NaOH or ferrous
chromite if necessary.
But do you really want to do this? Molten NaOH is extremely corrosive and very dangerous. You need a metal can (preferrably nickel, but iron will also
do for single use) in which to melt the NaOH. You need to heat above a roaring flame, the heat of a simple alcohol burner or the heat of a hot plate
is not sufficient. Any splashes on the skin will lead to very bad wounds!!
Also from a cost point of view this is not recommended. You probably will have more cost in the required NaOH than in buying Cr2O3.
So, the only reason why one would do this is as an intellectual and experimental challenge, from an economical and safety point of view I strongly
recommend against this.
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ScienceSquirrel
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I have done this reaction with potassium hydroxide and potassium nitrate and either manganese dioxide or chromium III oxide on a few gram scale in a
porcelain crucible.
It will produce either the green potassium manganate or the yellowish potassium chromate as a solution on cooling, lixivation and filtering.
The addition of a few drops of sulphuric acid and cooling produces a few small crystals of potassium permanganate or potassium dichromate.
Wearing appropriate protection; stout clothing, gloves and eye shielding it is quite safe on a small scale and it illustrates some interesting
chemistry but I would not do it in a bucket!
Edit: Oops, I put chromium trioxide instead of chromium III oxide, luckily everyone was sleeping! 
[Edited on 20-4-2011 by ScienceSquirrel]
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blogfast25
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ScienceSquirrel is right: this isn’t particularly dangerous to do and you don’t really need to ‘dissolve’ the chromate ore into molten NaOH
either. I’ve done this, like SS with KOH (textbooks recommend it over NaOH). After firing the mix of chromate ore and KOH (allow plenty of air or
add an oxidiser), grind the frit and lixiviate with hot water: you get potassium chromate (filter off the hydrated Fe2O3 and other insolubles).
Acidifying the chromate solution causes the dichromate to form. This can be crystallised (it’s poorly soluble in cold water) or reduced back to Cr3+
with alcohol, methanol, etc. Neutralise carefully to precipitate the hydrated Cr2O3…
But shop bought Cr2O3 will be cheaper, safer and easier all around!
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woelen
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It depends on what you call dangerous. For me, this type of reactions crosses a line, but of course, for each person the line is at a different
position. But I definitely do not recommend this process to a person who has no experience with home chemistry at all. It is the experience with
handling potentially dangerous situations in an adequate way which counts and I am not sure about that with Salman. Don't overestimate your own
experience and own capabilities!
Another thing is what you expect to gain with the reaction. I can imagine that I might do such a potentially dangerous reaction on a small scale if it
gives me a very special chemical, which I cannot obtain otherwise (e.g. I have done a small scale hot-melt reaction for making Mg2Si and silane and
consider doing a similar thing for making Mg3P2 and phosphine), but if your goal is just Cr2O3, then I simply would say: don't do it.
[Edited on 21-4-11 by woelen]
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Salman
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chromate
thanks for your kind reply. I have a lot of chromate ore and the cost of chromium is too much higher. Regarding dangerous the most dangerous thing is
the world is human and if we could handle them then every other things are simple just only seem difficult to start. I will start this process very
soon and i will be in touch with u guys just hope for my success and if any help i need i will contact you all Thanks once again for your help.
Secondly suggest KOH or Noah both are cheaper here in my country.
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ScienceSquirrel
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I said that I would do it on a few gram scale as it is an interesting reaction. I would not do it with a couple of hundred grams to make chromium III
oxide, that is lunacy.
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blogfast25
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Hmmm… larger scale, larger problems of course but the dangers of ‘alkali fusions’ tend to be exaggerated, IMHO. For one, the term ‘fusion’
is a bit of a misnomer, as usually you add something like twice the amount of alkali needed and no real melting takes place, at least not
macroscopically: it’s not like creating a bath of molten NaOH or KOH (for electrolysis, see that would really scare me!). I’ve used it on zircon,
on cassiterite and on Fe2O3/Cr2O3 co-precipitates.
One way of making it even safer is so-called ‘wet fusion’ (even more of a misnomer!), using a 50 % watery solution of the alkali. This is then
mixed with the target oxide into a paste. The mixture is first oven dried at about 200 C until almost or completely dry (needless to say this greatly
improved contact between the alkali and the ore) and then fire to whatever’s needed. Even something fairly stubborn like zircon cracks at about 600
C.
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ScienceSquirrel
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But Salman does not seem to have a clue.
He seems to be thinking of heating a large quantity of chromite ore with a lot of alkali but does not know if he should use potassium or sodium
hydroxide.
I would not want to try and extract litres of alkaline chromate solution from the fused ore mass and then concentrate and acidify it to form and
crystallise the dichromate.
I have years of experience, a good grasp of the chemistry, a lot of kit and I think it is verging on barmy, in my opinion he is in the running for a
Darwin Award!
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blogfast25
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You mean the Ignoble prize?
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ScienceSquirrel
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No, a Darwin Award;
http://www.darwinawards.com/
I think Salman with his chromate fusion and kuro96inlaila with his platinum arsenic extraction are both good candidates
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blogfast25
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Ah, yes, the people who want to volunteer themselves out of the gene pool w/o resorting to a piece of rope of the right length and strength...
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Salman
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chromate
I m getting confused i had not got the results
I have chromate of black color and i thing it is chromium silicate. Please guide me again for the reaction and also with the exact ratio so that it
could be easy for me to do secondarily if you have any video of this please show me to become easy
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Neil
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Out of curiosity, if human is the most dangerous thing and molten NaOH turns humans into puddles of goo, then what does that make NaOH?
Have you tried firing the ore you have to see what color it produces?
Edit: adding this stuff.... I'm not vouching for any of this information or suggesting you try it. I'm posting it for the gents who have posting
above...
The first one details making black ceramic pigments with manganese oxides and chromite ore - seems trial and error friendly
“Synthesis of coloured ceramic pigments by using chromite and manganese ores mixtures”
http://www.scielo.br/pdf/ce/v56n338/v56n338a10.pdf
The second details a route to Cr2O3 without a molten NaOH bath, middle of page 222.
http://books.google.ca/books?id=Owuv-c9L_IMC&pg=PA222&am...
Are these possible routes that might not end with him dissolving himself?
[Edited on 27-4-2011 by Neil]
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