Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
 Pages:  1  2
Author: Subject: Potassium oxide decomposition
Endimion17
International Hazard
*****




Posts: 1468
Registered: 17-7-2011
Location: shores of a solar sea
Member Is Offline

Mood: speeding through time at the rate of 1 second per second

[*] posted on 5-5-2013 at 13:16


Quote: Originally posted by KonkreteRocketry  
hehe yes, but here it is only nitrogen gas, magnesium oxides out there, no CO2 or SO2 or any O2 or anything else, so the K2O is alone, what will happen then ? become a gas ?

Also, what will happen to K2CO3 at 1900 degree ? I see that it decomposes to K2O and CO2 ... ummm ? so if at 1900 degree, K2O will be alone ?

[Edited on 5-5-2013 by KonkreteRocketry]


As usual, Wikipedia is wrong on potassium oxide. It won't decompose above 350 °C. Simple ionic compounds like sodium chloride have a melting and boiling point and above that their constituents lose electrons and become a mix of ions and electrons, therefore plasma.

Potassium metabisulphite bought at the store won't decompose neatly. It won't give pure potassium oxide. That would be too easy, now wouldn't it? ;)
The stuff is ~95% pure, so you get a mixture. I don't know what you get, but it isn't a simple compound.

Potassium carbonate decomposes to potassium oxide and carbon(IV) oxide at very high temperatures. Every carbonate does that.




View user's profile Visit user's homepage View All Posts By User
woelen
Super Administrator
*********




Posts: 7722
Registered: 20-8-2005
Location: Netherlands
Member Is Offline

Mood: interested

[*] posted on 6-5-2013 at 01:37


As I wrote before, the K2O only exists fleetingly. It may be at 1900 C when it leaves the rocket, but it very soon cools down and then it combines with other chemicals in the smoke and with constituents of air.

What kind of propellant mix are you takling about which only gives N2 and MgO besides K2O? That seems like a very special propellant to me. If there is only N2, MgO and K2O, then no further reactions occur, but I can hardly believe that you have such a system and then you still have the daunting task of collecting the K2O and MgO and separating these.




The art of wondering makes life worth living...
Want to wonder? Look at https://woelen.homescience.net
View user's profile Visit user's homepage View All Posts By User
KonkreteRocketry
Hazard to Others
***




Posts: 165
Registered: 12-11-2012
Location: Dubai
Member Is Offline

Mood: No Mood

[*] posted on 6-5-2013 at 04:14


Quote: Originally posted by woelen  
As I wrote before, the K2O only exists fleetingly. It may be at 1900 C when it leaves the rocket, but it very soon cools down and then it combines with other chemicals in the smoke and with constituents of air.

What kind of propellant mix are you takling about which only gives N2 and MgO besides K2O? That seems like a very special propellant to me. If there is only N2, MgO and K2O, then no further reactions occur, but I can hardly believe that you have such a system and then you still have the daunting task of collecting the K2O and MgO and separating these.


alright nvm about that thing, i was just confused a bit...

can you tell me what happenes to K2CO3 at 1900 degree ? does it become a gas ? i saw that it decomposes at 1500 to form K2O which already will decompose at 350 degree, umm what ? so potassium end up being alone ?

and if k2o does not further decompose is it a gas or a solid or what ? cus i need to know the % of gas mass being expelled to get further calculations.
View user's profile View All Posts By User
woelen
Super Administrator
*********




Posts: 7722
Registered: 20-8-2005
Location: Netherlands
Member Is Offline

Mood: interested

[*] posted on 6-5-2013 at 04:47


K2O does not decompose at 350 C, whoever writes that makes a mistake. K2O may absorb oxygen at 350 C to form K2O2, but that is something different than decomposition. I expect true decomposition of K2O not to occur at all, unless you get VERY high temperatures (thousands of C) at which it will fall apart in ions and electrons (i.e. a plasma). I expect that at 1900 C K2O simply escapes as solid and that CO2 escapes as gas. I'm not sure though whether you can simply assume that the exit-temperature is 1900 C as well. In the mix (the front of burning) you might have 1900 C, but near the exit the temperature may have fallen considerably already, due to expansion of gasses and due to loss of heat through the mantle of the rocket.

If you really want to do computations on your rockets, then try to find literature about that. I am no expert on this at all. Maybe someone else can help you with this. I am inclined to think that good rocket design is not easy at all and should be considered a science and an art on its own.




The art of wondering makes life worth living...
Want to wonder? Look at https://woelen.homescience.net
View user's profile Visit user's homepage View All Posts By User
AJKOER
Radically Dubious
*****




Posts: 2999
Registered: 7-5-2011
Member Is Offline

Mood: No Mood

[*] posted on 6-5-2013 at 06:32


More science (or junk) from Wikipedia (https://en.wikipedia.org/wiki/Alkoxide ) with possible implications for the stability/formation of K2O:

"Thermal stability
Many metal alkoxides thermally decompose in the range ~100–300 °C. Depending on process conditions, this thermolysis can afford nanosized powders of oxide or metallic phases. This approach is a basis of processes of fabrication of functional materials intended for aircraft, space, electronic fields, and chemical industry: individual oxides, their solid solutions, complex oxides, powders of metals and alloys active towards sintering. Decomposition of mixtures of mono- and heterometallic alkoxide derivatives has also been examined. This method represents a prospective approach possessing an advantage of capability of obtaining functional materials with increased phase and chemical homogeneity and controllable grain size (including the preparation of nanosized materials) at relatively low temperature (less than 500−900 °C) as compared with the conventional techniques."

The apparent existing commercial significance of the above statement, however, appears to lend to its credibility, although I make no such assertion.

If however accurate, the implications for the possible thermal decomposition of a compound like Potassium tert-butoxide would be interesting (K2O or even K (?!) under the right 'process conditons'), but, of course, this is only as reliable/accurate as the references supplied by Wikipedia (cited below, and note the recent years 2001, 2002, 2004, 2005 and 2012):

" References
1. Bradley, D. C.; Mehrotra, R.; Rothwell, I.; Singh, A. "Alkoxo and Aryloxo Derivatives of Metals" Academic Press, San Diego, 2001. ISBN 0-12-124140-8.
2. Turova, N.Y.; Turevskaya, E.P.; Kessler, V.G.; Yanovskaya, M.I. "The Chemistry of Metal Alkoxides" Kluwer AP, Dordrecht, 2002. ISBN 0-7923-7521-1.
3."Single and mixed phase TiO2 powders by excess hydrolysis of titanium isopropoxide". Advances in Applied Ceramics 111 (3). 2012.
4. P.A. Shcheglov, D.V. Drobot. Rhenium Alkoxides (Review). Russian Chemical Bulletin. 2005. V. 54, No. 10. P. 2247-2258. doi: 10.1007/s11172-006-0106-5

Further reading
N.Ya. Turova. Metal oxoalkoxides. Synthesis, properties and structures (Review). Russian Chemical Reviews. 2004. V. 73, No. 11. P. 1041-1064. doi:10.1070/RC2004v073n11ABEH000855 "


[Edited on 6-5-2013 by AJKOER]
View user's profile View All Posts By User
AJKOER
Radically Dubious
*****




Posts: 2999
Registered: 7-5-2011
Member Is Offline

Mood: No Mood

[*] posted on 6-5-2013 at 07:32


More on K2O from one of my favorite sources:

"The Potassium monoxide, K2O, is formed by incomplete oxidation of potassium by dry oxygen at reduced pressure, and removal of the excess of metal by distillation in vacuum. The product forms microscopic octahedra, which become pale-yellow at 200° C., and have a density of 2.32 at 0° C. Above 400° C. in vacuum it is decomposed into the metal and the peroxide. The heat of formation of the monoxide from its elements is 86.80 Cal. It is reduced by hydrogen to the hydride and hydroxide. With water it reacts energetically to form the hydroxide, the heat of solution being 75.0 Cal. It also combines with fluorine, chlorine, and iodine. The heat of formation from the elements is 86.8 Cal."

Source: http://potassium.atomistry.com/potassium_monoxide.html
View user's profile View All Posts By User
 Pages:  1  2

  Go To Top