| Pages:
1
2 |
woelen
Super Administrator
Posts: 7977
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
I do not use any heating in these reactions.
I think that the MnO2 is full of iron impurity. Magnetite, Fe3O4 is black and on heating that may form Fe2O3 (orange/brown), with uptake of oxygen
from the MnO2, surrounding it.
I get the impression that your MnO2 is not the chemically pure compound, but some finely powdered ore. I know of an ore (called "mangaanknollen" in
dutch, I don't know the english word for it), which is mostly MnO2, but also contains a considerable amount of ironoxides and manganese in its +3
oxidation state.
|
|
|
YT2095
International Hazard
Posts: 1091
Registered: 31-5-2003
Location: Just left of Europe and down a bit.
Member Is Offline
Mood: within Nominal Parameters
|
|
Im beginning to think you`re exactly right, here we call it Pyrolusite.
an ore would make Perfect sense!
in the PM I sent you, I said that of this 250g, probably 100g is actualy good material.
an interesting note though, when roasted with the carbon, the resulting material will react directly with 50% sulphuric acid, giving off a little heat
and leaving a pinkish soln with brown mud at the bottom.
it also Hisses when you add it to dil HNO3 but there`s little color change except to a yellow tinge and it becomes quite turbid and a little thicker
(viscous).
I can personaly vouch for the Carbon purity (I did it myself with ABA treatment TWICE)
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
|
|
|
manimal
Hazard to Others
Posts: 180
Registered: 15-1-2008
Member Is Offline
Mood: ain't even mad
|
|
Does anyone know if MnO2 reacts with dilute acetic acid? I have about 350 grams of MnO2 that I extracted from alkaline batteries, and I washed the
crude material in vinegar to remove residual Zn and ZnO, and it immediately evolved gas. Is it just H2 from the residual zinc, or is it MnO2 reacting
to form MnAc2?
|
|
|
The_Davster
A pnictogen
Posts: 2861
Registered: 18-11-2003
Member Is Offline
Mood: .
|
|
I am not sure if MnO2 will react quickly with acetic acid, but if it did, it would not produce any gases. You are likely right in that it is just
fizzing with the residual zinc.
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Alkalines? Could be CO2 from atmospheric exposure.
Tim
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
MnO2 thermite problems
Another problem with Mn thermites, especially MnO2 based, and often overlooked is the following. To produce decent metal, the slag and newly formed
metal have to separate out from each other. For this to stand a chance, both slag and metal have to be liquid at the end of the reduction reaction. In
the case of a thermite reaction, the slag is mainly alumina, with a melting point of 2,054 C. Unfortunately the boiling point of
Mn is only scarcely higher: 2,061 C and as a result a successful MnO2 reduction can only lead to part of the metal being boiled off... The
end-temperature of such a thermite reaction (in adiabatic conditions) can be estimated quite accurately. My own calculations show clearly that the
end-temperature of a fast MnO2 aluminothermic reduction is well above 2,061 C.
An example of such a calculation can be found on this page, here applied to a Titanium thermite reaction.
I've used various grades of MnO2, with fairly high amounts of flux (CaF2 - a slag fluidiser) and have rarely obtained good quality metal and always
with quite low yields (< 20 % of theoretical yield).
I believe the key points to obtaining good Mn metal are:
• use the lower oxides or a blend of MnO and MnO2
• use fairly coarse Al to reduce reaction speed and suppress thermite end-temperature: too high and your metal will simply distil off
• use adequate amounts of CaF2 to improve slag fluidity
In one particular reaction, using homemade (from battery crud) but quite pure MnO2, I found much of the metal back in the form hundreds of sub-mm Mn
globules around the crucible: frozen Mn rain (I kid you not)!
Industrially, Mn metal is made by thermite reduction but in a semi-continuous way, rather than by batch method. This allows to keep the
temperature as low as possible, while still melting the alumina, necessary to allow the Al2O3 and Mn metal to separate out.
I've not found any Internet accounts of successful Mn thermites that mentioned good metal obtained. Batch-wise the heat balance may be too
precarious...
[Edited on 15-6-2008 by blogfast25]
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Probably fine in a bomb. Got to be careful it doesn't melt though, hahah. Probably a large steel pipe nipple lined with refractory (sand or etc.)
and the thermite charge would suffice. A good way to make sodium, too!
Tim
|
|
|
nodrog19
Harmless
Posts: 38
Registered: 29-5-2008
Member Is Offline
Mood: No Mood
|
|
my friend was messing around in hos lab, had a MnO2 related accident.
MnO2+2HCl-->Mn(OH)2+Cl2
Mn(OH)2+2HCl-->MnCl2+2HOH
he got a mouth full clorine, but then he (i dont know why)
decides to add H2SO4
MnCl2+H2SO4-->MnSO4+2HCl
squirted in to his eyes and burned his bench.
good thing he had a wash bottle laying around
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
Regarding possible explosions with MnO2 thermites:
in my notebooks I found the following adiabatic heat balance for MnO2:
MnO2 + 4/3 Al ---> Mn + 2/3 Al2O3
Heat of reaction ΔHr = - 597 kJ (per mol of MnO2)
The enthalpies to heat 1 mol of Mn and 2/3 mol of Al2O3 to 2,740 K are respectively 110.5 kJ and 300.1 kJ or a total of 411 kJ. Since as ΔHr is
-597 kJ, there is about 186 kJ to spare. Simply put, in adiabatic conditions a pure MnO2 thermite is energetic enough to heat both the
formed metal and the alumina slag to well above 2,740 K (2,470 C) and thus well above the boiling point of Manganese metal. In an enclosed
space, pressure build up would be inevitable and an explosion becomes a possibility.
For MnO + 2/3 Al ---> Mn + 1/3 Al2O3 the situation is very different because ΔHr = -176 kJ (per mol of MnO) and this reaction would not reach
2,740 K because:
176 < 110.5 + 150 or 176 < 260 (all kJ)
A blend of MnO and MnO2 at carefully chosen molar ratio of the oxides, might allow the right temperature to be reached without boiling off the metal
on the one hand or obtaining very poor slag/metal separation (too low temperature) on the other hand.
|
|
|
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
