Sciencemadness Discussion Board

Will dilution of a powdered solid in an inert solid reduce a violent reaction with water?

AJKOER - 28-4-2014 at 05:30

There are apparently many elements/compounds that react voilently and even explosively with water. My hypothesis is that by diluting such solid powders in an inert solid, one may be able to reduce the problematic exothermic reaction with water.

The logic is that by reducing the amount of the exothermic material reacting locally, more water may be available to absorb some of the heat of reaction.

Has anyone tried this technique in practice?

Bert - 28-4-2014 at 05:49



Dilution works. Heat sinking into an inert mass works. Slowing rate of reaction via slowing contact with a liquid reactant works. Do you have a specific application in mind?

Adding Cesium to water without a large "BANG!"? Or something a little less demanding...

Zyklon-A - 28-4-2014 at 06:20

Yes, I do that with things other than water too. I generally dilute my calcium hypochlorite with sand before I add it to hydrochloric acid. (To isolate chlorine.)

AJKOER - 28-4-2014 at 08:08

Given the potential safety advantages of diluting a solid with a solid, in addition to extending the range of applications of the otherwise dangerous reaction, I am a little surprised on its lack of discussion.

There may also be examples among those who experiment with thermites.

I recently came across an example of the more common dilution of mixing an inert gas to a gas with the reaction:

2 NH3 + Cl2 ----) NH2Cl + NH4Cl

as absence gaseous dilution, the formed chloramine is likely to explode. Related is the laboratory preparation of aqueous chloramine by mixing dilute aqueous NaClO with ammonia at zero degrees Centigrade. As such, in general, the cooling of the water prior to mixing is also advised.

[Edited on 28-4-2014 by AJKOER]

blogfast25 - 29-4-2014 at 12:14

Yes, of course. Dilution, either with extra solvent or by means of some inert material added to the mix, works and helps keeping end temperature down.

Water and sand (among other things) can be used in aqueous media. In thermite CaF2/CaO have similar effects of 'cooling' the reaction mix (besides other functions).
Quote: Originally posted by AJKOER  
The logic is that by reducing the amount of the exothermic material reacting locally, more water may be available to absorb some of the heat of reaction.



… is a rather clumsy formulation. Look at it mathematically, with a simplified model.

Let ΔH be the total exotherm released by whatever reaction, assume in solution (e.g.) In the absence of external cooling (or other heat losses) this heat is absorbed by the reaction products and other components in the post reaction mix, so that:

ΔH = [ ∑(m<sub>i</sub> Cp<sub>i</sub>;) ] x ΔT

With ΔT the overall temperature increase of the mix and m<sub>i</sub> Cp<sub>i</sub> the product of mass and heat capacity of each component i and ∑ the sum of these terms from 1 to n (for n components). Adding one or more ‘heat sinks’ to the sum can only lead to ∑ increasing and thus at constant ΔH, ΔT must decrease.


[Edited on 29-4-2014 by blogfast25]

aga - 29-4-2014 at 12:48

If the objective were to add the explosive reactants and avoid the Damage that the explosion would cause, how about just putting them together slower ?

E.g. powdered caesium to water.
Add it grain by grain and produce much smaller BOOM reactions that can be handled.
Or vice-versa.
A fine mist of water sprayed thru a pinhole, after which it passes thru a fan to add the water to the caesium slower.

No, i have not tried adding non-reacting solid stuff to solid explosives to see if it explodes slower.

woelen - 29-4-2014 at 22:37

I used the same principle for experiments of making impure Mg3P2. A mix of powdered Mg and red P reacts very violently when ignited, when a mix of MgO, Mg and red P is used, the reaction is less violent. The more MgO is used, the more tame the reaction. Of course, the reaction product becomes impure in the latter case (MgO does not react or maybe a tiny fraction of it may lead to formation of phosphorus-oxygen compounds or magnesium phosphate(*) compounds).

[Edited on 30-4-14 by woelen]

blogfast25 - 1-5-2014 at 12:10

Quote: Originally posted by aga  
If the objective were to add the explosive reactants and avoid the Damage that the explosion would cause, how about just putting them together slower ?

E.g. powdered caesium to water.
Add it grain by grain and produce much smaller BOOM reactions that can be handled.


Cs can't be powdered but you're on the right track: adding much smaller quantities per addition keeps the released energy per addition low. Note that the TOTAL released energy only depends on the TOTAL amount of Cs added, over the entire run.

aga - 1-5-2014 at 12:19

Quote:
Cs can't be powdered


Cs in liquid nitrogen for a few seconds, add a hammer ?

I'd bet a fiver that it'd be in smaller pieces.
Need a powder ? Bash faster (and colder) !

blogfast25 - 2-5-2014 at 09:49

Quote: Originally posted by aga  
Quote:
Cs can't be powdered


Cs in liquid nitrogen for a few seconds, add a hammer ?

I'd bet a fiver that it'd be in smaller pieces.
Need a powder ? Bash faster (and colder) !


You have a vivid imagination! Assuming the liquid nitrogen is inert towards the caesium after powdering the powder would quickly clump together again, on reaching room temperature because its MP is only 28 C.

But it's not impossible to envisage such a technology for extreme niche applications. Cs is incredibly reactive though, thus difficult to handle. Surface area is always beneficial to reaction speed, so powdered Cs would be even more reactive!

[Edited on 2-5-2014 by blogfast25]