Bezaleel
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Question: preparation of MnO
Dear all,
I'm looking for a synthesis of MnO, manganese(II)oxide, but I cannot seem to find a synthesis that can be carried out easily in a home lab. The
easiest way I've found is the decomposition of MnCO3 in vacuum, which is cumbersome for the need of a vacuum.
Does anybody happen to know a route to MnO by other means? Redox, for example?
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Xenoid
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Mellor mentions reducing any of the other oxides by heating in a stream of hydrogen.
MnO is also formed by heating manganous oxalate. I guess this could be easily made from manganous carbonate and oxalic acid.
MnO is a greenish powder which oxidises rapidly on exposure to air!
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Bezaleel
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Funny thing is, I prepared it accidentally when I reduced MnO2 with an HCl solution under prolonged refluxing. Upon standing for crystallisation, I
noticed the formation of a very small amount of precipitate. Filtering the solution showed that the precipitate was a light green compound. The colour
resembles that of anhydrous Pr2(SO4)3. The only compound I can think of this could be is MnO.
Heating in a stream of hydrogen! Anyone who ever did that at home?!
I will try the reduction of the oxalate, which will be easy enough for me to do, thanks!
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gsd
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2MnO2 + C -----> 2MnO + CO2
(3n+1)MnO2 + CnH2n+2 -----> (3n+1)MnO + nCO2 + (n+1)H2O
If you decide to follow the 1st equation then take MnO2 mix it thoroughly with carbon and heat it in a good container over a direct flame. After
evolution of fumes and smoke stops quench the whole mass into water. You will have MnO (mixed with some unreacted carbon)
To follow the 2nd reaction, mix MnO2 thoroughly with heavy oil (furnace oil, lubricating oil etc) put it in a closed container but provide for the
vent on the lid. heat it from outside with open flame. After some time the internal reaction will start which will sustain. After a lot of evolution
of fumes, smoke and water vapours, you will have your MnO inside that container. Allow it to cool without contact with air. preserve it under water to
avoid air oxidation.
gsd
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blogfast25
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I've made it by heating Mn(II)CO3, paradoxically perhaps, in a stream of dry CO2. A greenish mass of mostly MnO is obtained.
What do you want the Mn(II)O for?
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kmno4
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I did. It was for CuO and PbO to metal only, but it will work for any Mn oxide (and many organic salts of Mn) to MnO.
Only 300 C is needed to do such a reduction
I would do this for fun but my H2 generator started to leak (25% NaOH... ) and currently I am building a new one.
With electrically heated SS pipe reactor, it is simple and safe..... 
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Bezaleel
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Quote: Originally posted by blogfast25  | I've made it by heating Mn(II)CO3, paradoxically perhaps, in a stream of dry CO2. A greenish mass of mostly MnO is obtained.
What do you want the Mn(II)O for? |
| Quote: Originally posted by gsd |
(...) After a lot of evolution of fumes, smoke and water vapours, you will have your MnO inside that container. Allow it to cool without contact with
air. preserve it under water to avoid air oxidation.
gsd |
Exactly that. The green substance I obtained is very stable under the normal atmosphere and humidity (between 30% and 80% surface moisture, and 10-30
centigrade). It must be some kind of manganese compound, so in order to do a first analysis, I want to compare it to MnO.
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Bezaleel
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kmno4, how did you build your hydrogen generator?
And how do you make sure you avoid explosions? (It's just my scare of explosions that keeps me from using hydrogen as a reductor at elevated
temperatures.)
I suppose you will continue generating hydrogen until everything has been reduced. This means that towards the end of your reduction, most of your
hydrogen will not be oxidised. What do you do with this? Burn on the outlet?
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watson.fawkes
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| Quote: Originally posted by Bezaleel | | I suppose you will continue generating hydrogen until everything has been reduced. This means that towards the end of your reduction, most of your
hydrogen will not be oxidised. What do you do with this? Burn on the outlet? |
Yes, flare it off. Hot hydrogen
is also used for hydrogen brazing, which creates a reducing atmosphere which cleans the metal surfaces to be brazed. You first purge the chamber with
hydrogen, not burning it off at that point but evacuating it with plenty of dilution, then starting up the flare there's no longer any oxygen in the
gas stream.
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kmno4
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| Quote: Originally posted by Bezaleel | kmno4, how did you build your hydrogen generator?
And how do you make sure you avoid explosions? (It's just my scare of explosions that keeps me from using hydrogen as a reductor at elevated
temperatures.)
I suppose you will continue generating hydrogen until everything has been reduced. This means that towards the end of your reduction, most of your
hydrogen will not be oxidised. What do you do with this? Burn on the outlet? |
It is electrolytically generated H2 (1,5 dm3 of 25% NaOH as electrolyte, electrodes from SS gauze - construction is up to you). It could work with
current maximum 5 A (corresponds to ~2 dm3 H2 per hour).
First, I pass stream of H2 to remove air from all parts of a set.
Pipe reactor is placed alomst horizontally (made as self draining) the part after heat region of this pipe acts as air cooler and outlet is immersed
in water (via set of joints and pipes). Then I can control amount of absorbed H2 by counting bubbles of gas. At the beginning it is usually 1 bub./s
and as reaction strarts (increased heating) this amout decreases.
At this moment I try to get 1 bubble for minimum 10 seconds (but can be reduced to zero = complete H2 absorption) by regulation of heating.
At the end of reaction H2 passes without absorption - amount of bubbles increases and product is cooled in H2 stream.
At home laboratory scale there is no need to burn H2 from outlet - its amount is too smal to be dangerous (in my opinion)
Any hood or just good ventilation is enough.
With small amounts of reagents to be reduced (CuO.....) there is no need to introduce carrier gas , usually N2.
In industry such reductions are done by recylculation of N2 with small and monitored amount of H2 (for example 2% v/v) to prevent sudden and
exothermic reaction. We have done this recently at my work 
[Edited on 8-7-2010 by kmno4]
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kmno4
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To test new H2 generator I made experiment with MnO2 reduction.
Starting material: MnO2 prepared from KMnO4 and MnSO4. It means that it is rather MnO(OH)2 than MnO2. Brown powder, on the right side.
(After treatment with HNO3 (some heat was given off) it gave darker product . Probably my starting oxide was impure (some basic substances I think)
but I suspected it earlier. After this treatment and drying, the oxide was finally taken for reduction).
Left side - MnO prepared at higher temperature (~400 C). Grey powder, when introduced to acid it gives a lot of heat. When heated in air it quickly
turns to brown Mn3O4.
Down - the same oxide but prepared at lower temperature (~300 C). Colour is grey-green (but much more grey than green).
MnO prepared in higher temp. seems to be much more paramagnetic than the rest of substances. Among substrates and products only it reacts on neodymium
magnet from 2 mm distance (small movements of grains).
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Bezaleel
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Hi kmno4, I'm very surprised to see the colour of the substances you obtain. My eyes identify them as black (very dark brown, right), greyisch (top
left) and beige-brown (left bottom). By comparison, the substance I obtained tends towards emerald
The green substance above is completely stable, is seems. It's no more than 0.2 gram (estimate), on a piece of filter paper. Can it be that it has a
crystal structure that passivates it?
So far, I haven't been in the position to do any experiments. I'm cleaning/re-organising my home and all glassware will be moved into a closet I'm
trying to construct (takes time...)
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kmno4
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Nice colour
According to "Chemistry of the Elements (2nd Edition)" by Greenwood, N.N.; Earnshaw, MnO colour is "green to grey"
( http://home.postech.ac.kr/~chey/Fund-metal/chap24-Mn-Tc-Re.p... ). Brauer says that colour depends on temperature of reduction and time of
reaction (green->light gray).
http://dx.doi.org/10.1021/ja01394a007 says :
Manganous oxide was prepared by reduction of amorphous manganous-manganic oxide by hydrogen and crystallization by gaseous hydrochloric acid. A
finely crystalline, bright green product resulted..
Another funny article says in the end: "......aligned. Further work is now desirable on manganous oxide of both stoichiometric and known
non-stoichiometric composition, which is free from particles of second phase. Unfortunately, good quality MnO is currently very difficult
to obtain. "
I realize that my picture is bad quality. Substance on the left side has colour rather bright than dark grey .
Just out of curiosity - I will try to additionaly purify my Mn salt and repeat experiment.
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