Trevor,
Borax is not alcohol soluble, boric acid is somewhat soluble in it
and is what is normally used to make the typical goldsmiths
firecoat. Borax will just try to pull all the water out of the
alcohol.
Jim Binnion
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
@James_Binnion
Member of the Better Business Bureau
Borax is not alcohol soluble, boric acid is somewhat soluble in it and is what is normally used to make the typical goldsmiths firecoat. Borax will just try to pull all the water out of the alcohol.
Hello James,
I did know that Borax was not soluble in alcohol but it does make a
respectable medium to deliver the borax to it’s destination via brush
or pick. The classic 3:1 ratio of Borax and Boric Acid in alcohol is
what I normally use as my soldering flux. Of course it’s not perfect
–clumping, puffing, etc-- but it is easy to make and use and of
course it is quite effective in it’s intended purpose.
My thoughts on the “baked” Borax --that home spun approach to
anhydrous Borax-- was that it might help reduce the puffing of the
Borax/Boric Acid mix. What I didn’t know was that there was enough
water in alcohol to rehydrate the Borax. Having tried this I now know
a great way to make extremely puffy Borax flux. As educational as
that may have been I have not as yet found an application that will
benefit from this particular behavior. Lesson learned nonetheless.
For firescale protection I use one of Brepohl’s formulas (The Theory
and Practice of Goldsmithing, p.300) and find that quite satisfactory
although it does have to be heated before use in order to re-dissolve
the large crystals that come out of solution when it cools to room
temperature.
Cheers,
Trevor F.
James, I am sure the following is of no surprise to you but I wish
to reiterate it for our audience.
Borax is comprised of a group of the borates including:
Sodium tetraborate - an anhydrous sodium borate (Na2 B4 O7) contains
little or no water that melts at 741 deg C (1366 deg F)
Sodium Tetraborate decahydrate - a hydrous sodium borate (Na2 B4 O7
*10H2O) contains water and melts at 75 deg C (167 deg F).
Tetraborate decahydrate can be dehydrated by heating to 120 deg C
(248 deg F). It will lose all water when heated above 320 deg and
fuses at 740 deg C,
Knowing that, I find it difficult to understand the results of your
experiments when there are finite conclusions re the melting points
of specific varieties of Borax. True, there is a wide range of Borax
products available but generally speaking, commercially sold borax
is usually the dehydrated variety, i.e., the anhydrous type which
has a high melting and fusing temperature. At high temperatures,
borax has a strong solvent effect on metal oxides and related
materials. Believe it or not, I do hot have a copy of Dr Bephrol’s
book in my 200 or so book library. Perhaps Charles and/or Tim could
provide some further or maybe John can chime in from
down under?
Boric acid is yet another question mark. Boric Acid (H3 BO3) aka
orthoboric acid, is refined borax that dehydrates above 170 deg C,
melting at 171 deg C to form metaboric acid. Metaboric acid, in
turn, melts at 236 deg C and further dehydrates into tetraboric acid
above 300 deg c. Each providing its level of protection to the metal
surface. So its decomposition is well below the more common
tetraborate variety of borax.
Comments? Cheers from Don at The Charles Belle Studio in SOFL where
simple elegance IS fine jewelry! @coralnut2
Gday; Somebody rattled my cage.
In the dead distant days of long ago when there weren’t many more
than 92 chemical elements, youngsters like I was learned chemistry
at a bench doing ‘wet chemistry’ - analysis. We were given a
mix of two or more chemicals and told to provide evidence proving
what we thought the mix might be. So the first thing was to get
the stuff into water solution. If a part or none would dissolve, we
had to try various acids. If is still wouldn’t dissolve we has to
heat it on a charcoal block (using a mouth blowpipe) and note the
results. Then we had to heat the insoluble mix strongly in a
crucible with borax powder. We finally ground the solid and treated
it with water and acids, and it was then usually soluble in
something. Another test was to strongly heat a little of the solid
mix with borax, in a little loop of platinum wire (six pence an
inch!) The molten borax and mix formed a little bead and one had
to note the colour and appearance of the bead. (The Borax Bead
test, would you believe!) Blue for cupric salts, green for cuprous,
purple for manganese, etc etc. Then the mix was subjected to a whole
series of tests using solutions of various chemicals in a certain
sequence… Quite a laborious business, but doing all this certainly
taught us some elementary chemistry!! Of course we had lectures as
well, and when it came to exam time, we found we could answer most
of the questions. I used to get 80 - 90% !!! (And came bottom in
arithmetic) Thus we learnt that borax strongly heated dissolves
almost all metal oxides And now you know why borax is used as a
flux to dissolve metal oxides when soldering. by converting metal
oxides to soluble borates. Everyone hates chemistry these days I am
told, because they have to learn the theory, mainly. And it’s
boring boring boring. Messing with chemicals was interesting and
could occasionally get exciting!
Cheers for now,
JohnB of Mapua, Nelson NZ
Lest the newcomer become confused by the scientific rhetoric being
bandied about, I’ll just point out that I am happy to use, and have
for many years, 20 Mule Team Borax. It sits beneath my sink and has
picked up a little extra moisture over the years and continues to
work fine.
Charles,
With regards to Boric Acid (H3BO3) Brephol states that the water is
driven out at 70C which decomposes to Metaboric Acid (HBO2) and he
does mention that Metaboric Acid has a melting point of 160 C and
upon further heating to 500 C it decomposes to boron trioxide (B2O3)
which at 577 C it forms a “fibrous cloak”. However melting does not
mean a low viscosity fluid. If you will take a couple of
tablespoons of boric acid and place them in a copper crucible and
begin to heat the crucible in a kiln you will observe that contents
of the crucible are a bubbling lumpy granular mass with large
amounts of water vapor being released from it even at temperatures
much higher than 160 C and it will not flow at all or cover a
surface until reaching the 500-600 C range (even at this point it
has the consistency of taffy) and it is not until much higher
temperatures (900 C) are reached that it becomes so fluid that it
can freely move on the surface of the metal. It is at this higher
temperature of 900 C where the fluxing action (boron trioxide
dissolving metallic oxides to form metaborates) begins.
Borax because it contains sodium decomposes upon heating to sodium
metaborate and boron trioxide (Na2B4O7 to 2 NaBO2 + B2O3) The
presence of the sodium metaborate makes the liquid much more fluid
at a lower temperature 700 C this presence also provides an
advantage over boric acid in that it mixes with the newly formed
metaborates and transports them away from the metal surface where
the pure boron trioxide from the decomposition of the boric acid is
much more viscous and tends to hold the metaborates formed by
dissolving oxides against the surface of the piece and not allow
fresh boron trioxide to contact the surface of the metal so is not
as good a flux.
So while at lower temperatures boric acid can be used as a glassy
barrier to keep oxygen away from the metal as in pripps flux (if
properly applied) it provides no reduction of oxides or fluxing
action until much higher temperatures are reached.
Jim Binnion
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
@James_Binnion
Member of the Better Business Bureau
It sits beneath my sink and has picked up a little extra moisture over the years and continues to work fine.
Goldwerx. You may think it continues to work fine but it probably
is not. Research has shown that anhydrous borax does its job much
better than hydrous. If you want it to work effectively, put it in
an oven and heat it at around 250 deg for an hour. I too have used
20 Mule Team for years but I keep it in a dry cool environment and
keep it tightly closed.
Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! @coralnut2
Goldwerx. You may think it continues to work fine but it probably is not. Research has shown that anhydrous borax does its job much better than hydrous. If you want it to work effectively, put it in an oven and heat it at around 250 deg for an hour. I too have used 20 Mule Team for years but I keep it in a dry cool environment and keep it tightly closed.
As I was saying, I drive the water off with a torch, Doesn’t require
an hour. More like 12 seconds. I did 2 perfectly fine castings today
… plus an ingot. I guess that that qualifies as three.
Bruce
I left something out of this.
With regards to Boric Acid (H3BO3) Brephol states that the water is driven out at 70C which decomposes to Metaboric Acid (HBO2) and he does mention that Metaboric Acid has a melting point of 160 C and upon further heating to 500 C it decomposes to boron trioxide (B2O3) which at 577 C it forms a "fibrous cloak". However melting does not mean a low viscosity fluid.
sorry it should read
With regards to Boric Acid (H3BO3) Brephol states that the water is
driven out at 70C which decomposes to Metaboric Acid (HBO2) and he
does mention that Metaboric Acid has a melting point of 160 C .
Metaboric acid loses water when heated above its melting point and
solidifies into boron trioxide (B2O3) which begins to melt at 450 C
and at 577 C it forms a “fibrous cloak” as described by Brephol.
However melting does not mean a low viscosity fluid.
Jim Binnion
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
@James_Binnion
Member of the Better Business Bureau
So while at lower temperatures boric acid can be used as a glassy barrier to keep oxygen away from the metal as in pripps flux (if properly applied) it provides no reduction of oxides or fluxing action until much higher temperatures are reached.
Jim,
Thanks for the much more detail explanation than I could ever have
provided. It does appear then that my original premis is correct?
Boric Acid does in fact provide protection of the mteal’s surface
from oxygen at ‘lower’ temperatures, even if it is not working as a
flux at those temperatures? That is what I was really looking for.
Thanks and cheers from Don at The Charles Belle Studio in SOFL where
simple elegance IS fine jewelry! @coralnut2
Many hardware stores will carry a variety of brands of boric acid
powder marketed as a cockroach killer. VERRRRRRY cheap!!! And the
same stuff that you’d pay a fortune for at pharmacies. You can get
a large plastic bottle for a few bucks.
Many restaurants will mix boric acid into their floor washes as a
roach control measure–the fine powder residue can infiltrate the
cracks in many floors and help eliminate their roach problems.