Sciencemadness Discussion Board

Sodium on silicagel

Jor - 9-10-2010 at 03:10

Is there anyone who has experience making this material. Acording to some sources it is a great reducing agent, capable of reducing aromatic rings (thus being a possible replacement for alkali metals in liquid ammonia).
http://signachem.com/products/technical-documents/

I have given it a try, but I;m not sure if I had good results. Because I currently have no clamps (I ordered some new ones), as they are all extremely rusted, I did it in a simple setup. In a 100mL beaker, 1,35g of finely powdered silicagel was put in a beaker and quickly 0,40g of sodium metal , wich was cut into about 8-10 pieces were added to this, followed by shaking. The silicagel quickly coated the metal. Next a large stirbar, just fitting in the beaker, was added, the beaker was covered with a watchglass, and put on the hotplate at maximum heat (250-300C). At first nothing happened, but then at once some sodium ignited (I think this is the melting point beig reached), until all oxygen in the beaker was consumed, wich was after 2 seconds. The powder turned from white to grey instantly, with some lumps where the sodium metal was. Stirring/heating were continued for 10 minutes (when lifting the watchglass for a second, the lumps briefly glowed yellow). Then the beaker was cooled down. The lumps were easy to crush with a spatula and were black in color. The lumps gave a slow evolution (I expected faster) of hydrogen, and the grey powder only gave a very slight evolution of gas in contact with water.

This synthesis was not so succesfull, because:
a) a lot of sodium burned in the progress
b) there was no homogenous mix, so some lumps of the material with a high content of sodium were formed, and a lot of powder with a very low loading of metal.

I will try again in 2 weeks, because I have not time anymore, but anyone willing to give this a try, I would greatly appreciate it.

When I succeed in making the nice black homogenous powder, I plan to use this as a very strong reducing agent in inorganic chemistry, similar to the neat metal but much safer! :)

DJF90 - 9-10-2010 at 07:00

Do it under an argon atmosphere next time to prevent oxidation of the sodium metal.

DDTea - 9-10-2010 at 16:57

It's possible that the evolution of H<sub>2</sub> you observed was due to the reaction of Na<sub>2</sub>O with water rather than Na with water.

In the JACS article by Dye et. al. ("Alkali Metals plus Silica Gel"), it is mentioned that the procedure was done under inert atmosphere (as DJF90 mentioned). Also, what about heating the Na to a liquid first and then absorbing it into the silica gel's pores?

It would be worthwhile to clean the surface of your silica gel prior to this procedure, e.g. by washing and heating, so that its pores aren't all gummed up with garbage.

aonomus - 9-10-2010 at 19:52

It would be worthwhile to heat the crap out of your silica gel anyway, because it tends to adsorb water onto the surface. Inert the setup, then perhaps use a 3N flask with a balloon full of silica that you can slowly charge into the reaction, and a valve to vent off excess H2 being evolved. The papers that you linked to on the SiGNa site show that the formation of the SiGNa material is exothermic, so you would be safer off charging the silica in slowly anyway.

Is there any literature on attempted silica gel-lithium reactions?

12AX7 - 9-10-2010 at 21:32

How the heck is sodium supposed to absorb? This is metal we're talking about. I can float rocks on mercury all day without any wetting...

I was at least expecting to hear mention of liquid ammonia in this thread.

Tim

[Edited on 10-10-2010 by 12AX7]

DDTea - 9-10-2010 at 22:44

Quote: Originally posted by 12AX7  
How the heck is sodium supposed to absorb? This is metal we're talking about. I can float rocks on mercury all day without any wetting...

I was at least expecting to hear mention of liquid ammonia in this thread.

Tim

[Edited on 10-10-2010 by 12AX7]


The metal (as a liquid, I presume) is adsorbed into the pores of the silica gel or zeolite.

peach - 10-10-2010 at 00:51

Indeed. Numerous metals are absorbed or deposited onto porous, inert carriers to function as catalysts and increase their surface area.

The zeolites (ZSM-5 etc) are favourites for a number of catalysts.

Have you thought about depositing it on a carrier by precipitation from solution?

I'm not sure how much safer this is going to make the sodium. Finely divided metals tend to react very vigorously. Some metals that are used as building materials, and considered entirely inert as big lumps, will start burning in an explosive manner if atomised.

Coal dust is a prime example of the effect. And blowing flour into a tin with a candle in it. The pneumatic drills smash the coal (which would normally be quite hard to set alight) into dust, then it gets airborne by the huge amounts of air the tools and vehicles all use down there. If it's not knocked out of the air, the mine explodes.

[Edited on 10-10-2010 by peach]

12AX7 - 10-10-2010 at 14:22

Yes, metals can be finely divided, but that simply doesn't occur spontaneously from a blobby liquid state. Pd-C is made by reducing the metal from solution, a process which goes from (nothing) to "small" particle size. Thermo is against you if you want to do the opposite (like atomizing aluminum). You can't make Pd-C by soaking charcoal in molten palladium. The only other way to absorb a metal is by capillary action, which only works on clean metals. Have you tried soldering to glass today?

(Ceramics are often soldered and brazed, but this requires a metallization step. And if the metallization goes away, it's impossible to fix with more solder. Tektronix infamously used silvered ceramic terminal strips in many of their instruments, which can only be soldered with silver-bearing solder. They even included a spool of such solder inside their machines, so technicians wouldn't need any. But when it ran out, and they used regular tin-lead solder, they quickly discovered what a bad idea that was!)

Seems to me, this process could only work with a solvent (fortunately, a solvent for this metal does exist!), or a ridiculous amount of heat (enough to vaporize the sodium). I don't see how something like silica gel could be "sticky" enough for any metal to adsorb onto it.

Tim

bahamuth - 10-10-2010 at 14:37

http://pubs.acs.org/doi/abs/10.1021/ja051786%2B

DDTea - 11-10-2010 at 05:46

Quote: Originally posted by 12AX7  

Seems to me, this process could only work with a solvent (fortunately, a solvent for this metal does exist!), or a ridiculous amount of heat (enough to vaporize the sodium). I don't see how something like silica gel could be "sticky" enough for any metal to adsorb onto it.


I think the first paper on the page linked by Jor mentioned adsorption of sodium vapors. That makes sense now.

peach - 11-10-2010 at 06:05

Indeed, indeed. It is highly unlikely it's going to work by just melting the sodium with the silica around.

I've seen quite a few pictures of wonky SMD components and explanations of what's causing it, like the leaching effect of the solder. The funniest are all the resistors standing up on one end.

If you're feeling brave, you could try boiling the sodium and depositing it that way. But I mean, damn... that's even further in the opposite direction to safe. And may not even yield something that nice (e.g. a big blob of sodium mixed with the carrier).

I think the safest and easiest way to finely divide it on the carrier will be doing it from solution. Again, I'm not sure this is going to make it easier to handle or safer.

Nickel is usually pretty easy to handle as strips. Raney Nickel, on the other hand, is pretty darn active.

bahamuth - 11-10-2010 at 06:34

The article states that:

"Alkali metals absorbed into silica gel yield three types of loose black powders (M-SG) that are strong reducing agents. All react nearly quantitatively with water to form hydrogen. Liquid NaK alloys form air-sensitive powders at room temperature that can be converted at 150 °C to a form that is sensitive to moisture but not to dry air. Slowly heating sodium and silica gel to 400 °C yields a third type that can be handled in ambient air with only slow degradation by atmospheric moisture."

Then it mentions the vapor phase method:

"Alkali metals, at concentrations up to 12 mol %, can be absorbed
from the vapor phase into aluminosilicate3 or pure silica zeolites."

Then it mentions the method this paper is about and the way Jor attempted:

"This report describes the incorporation of up to 60 mol % alkali metals from the liquid metal phase into amorphous silica gel(porous SiO2)."

It also mentions that;

"Preliminary atomic pair distribution function measurements
similar to those applied to “inorganic electrides” suggest that stage
I samples retain mostly SiO2 character and that stage II Na-SG
contains nanoparticles of Na4Si4.6 The fate of the released electrons
in stage I M-SG remains a mystery. Are they delocalized in a
high energy band of silica, or have they partially reduced the silica,
or are they present in the void spaces along with partially ionized
cations, as with “inorganic electrides”?"


Heat the pre dried silica gel with ~60 mol% sodium metal treated in such a way that there would be no oxide coating under argon or nitrogen, to ~400 C to make the "Stage 3" M-SG, or adjust temp. accordingly to make the other types (Type 0-1): "Uniform black powders of stage I Na-SG can be made by
heating Na with SG to 165 °C with continual agitation."


If one read the article thoroughly, I wouldn't need to list the main points here.


Ref.

Dye, James L., Kevin D. Cram, Stephanie A. Urbin, Mikhail Y. Redko, James E. Jackson, and Michael Lefenfeld. "Alkali Metals Plus Silica Gel: Powerful Reducing Agents and Convenient Hydrogen Sources." Journal of the American Chemical Society. July 2005; 127(26); 9338-9339.

questions - 1-5-2011 at 22:43

I have found a site that aims to make sodium silicate gel by mixing caudistic soda with silica gel and periodicaly heating it;

http://www.indyarocks.com/videos/Make-Sodium-Silicate-199088...

Is this what you need, let me know?