[TheForge] Re: Sodium filled valves

[Mike Spencer]

Bruce wrote:

> As you are aware, sodium is so reactive that it will "burn" with
> water, instead of air, as the oxidant, and this reaction will start
> at room temperature.  The flames you see from this are not the
> sodium, but rather the hydrogen gas released from the water.

Metallic sodium can be handled reasonably safely, using routine eye
and other protection, at room temperature.  You store it as chunks
submerged in kerosene or similar liquid that is totally immiscible
with water.

When exposed to the air at room temperature, it gradually changes from
silvery to murky brown and begins to develop a surface coating of ugly
scum as the sodium reacts with moisture in even low-humidity air.  The
scum is soggy sodium hydroxide -- lye -- so you need to handle sodium
with tongs if you don't want to get alkali burns.  As Bruce says, the
reaction that produces the alkali scum also produces hydrogen.

Now if you actually drop a chunk of room-temp sodium into water or
drench it somehow, you get a whole nother deal.  The reaction forming
the hydrogen and the sodium hydroxide progresses with furious
rapidity, evolving a cloud of hydrogen.  It's exothermic, i.e. it also
evolves a lot of heat, enough heat that (a) the solid sodium melts and
(b) the cloud of hydrogen ignites explosively.  The explosion blasts
gobbets of liquid sodium all over the place.  Bits that hit skin burn
you instantly and then continue to react with body fluids in the now
open wound, eating into your flesh and producing more alkali.  Gobbets
that hit more water evolve more hydrogen which explodes again,
repeating the above scenario.

Cutting open sodium-filled valves in a *completely dry place* at *room
temp* using a method that doesn't heat the valve (drill or hacksaw but
not grinder or cutoff wheel) should be relatively safe.  See, for example,

   http://www.ms-motor-service.com/ximages/PDF_Kataloge/x1_ventil_en_web.pdf 

(That PDF has one glaring error [1] but it seems, in general to be
reasonably authoritative.)

Simply sticking a random exhaust valve of unknown provenance into the
forge would be Russian roulette.  The boiling point of sodium is
880C/1616F, so when completely sealed in the valve, any temp around
there would be building up lotsa pressure inside the valve from
boiling liquid sodium trying to get out.  Cutting one open with a
power saw that uses water-based coolant, equally deprecated, similar
reason.

All that said, I've made tools from a couple of car valve stems and
they weren't very good.  I'd go with Don's advice and use something
else.  I have a whole box of new old stock BMC/British Leyland valves
that I've never found a use for because other bits of tool steel have
always offered more promise and less scary uncertainty.


- Mike


[1] In one place it says that the sodium/water reaction produces
    oxygen.  BZZZT! The reaction produces hydrogen. In another
    paragraph, they get it right.

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^