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Unexpected result (Borax in an oven)

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So, I've been using borax for flux and I'm finding it a bit obnoxious how it fluffs up when it gets up to heat. I've read from the internets that if you bake it and "dehydrate" it beforehand, it won't fluff up as much. I'm not exactly sure what I was expecting but it definitely wasn't this. Thought I'd share for a laugh.

This was a layer of borax spread out on a cookie sheet

20200726_214103.thumb.jpg.69af8d72fef183b8eb15aa1a2dd3fedc.jpg

 

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So Borax fluffs up when you heat it in the forge; but you were not expecting it to fluff up when heating it in the oven???

Freebie: water gets you wet when it's raining and also when you take a shower!

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It was the surprise that got me; I thought it was a great pic to warn folks about how much it can expand when dehydrating it.

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Uh HUH. Maybe not so thick a layer next time? How hot was the oven set? At least you didn't melt it, that is completely unnecessary. 

Spread it thin next time and I highly recommend using a silicone baking pan it's much easier to get the anhydrous borax out, you can flip it over and crumple the pan. 

Next time set the oven to 170-180f. for an hour per 1/8" thickness in the pan, then increase it to 200f. for an hour per 1/8" then his as close to 212f as you can, use an oven thermometer don't rely on the oven control. Again for an hour per 1/8". Lastly set it for 230f. for an hour per 1/8" and this is where you CAN exceed the procedure but only time. Do NOT exceed 230f. you do NOT want to melt it all you want is to drive off the hygroscopic moisture. That's moisture that is molecularly bound to the borax and is a step deeper than "hydration". 

It'll still be plenty stuck together and require crushing but it won't be a glassy vitrified mass that takes extreme effort and time to crush. The time needed to crush a cup of vitrified borax will take you longer than making and selling plenty of bottle openers to just buy a can of welding flux at a welding supply. 

I haven't made my own flux in years and I have a small rock tumbler and steel bearings to do my crushing and mixing for me, ball mill fashion. A 1lb. can of Peterson's blue #1 works as well as any "forge welding flux" I've tried and in Alaska cost $26 per can. It's anhydrous borax, boric acid and something to make it blue. There is no moisture in it so it doesn't foam up as it boils off.

Frosty The Lucky.

 

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1 hour ago, ThomasPowers said:

Freebie: water gets you wet when it's raining and also when you take a shower!

Shucks, is that what keeps happening when I jump in the pool? :blink: I need to be more careful...

Definitely one of those "duh" moments. Used too thick a layer and too high heat. It adhered to itself and expanded outside the cookie sheet. No damage done to the oven or the sheet. The shape was pretty interesting, though.

Thank you AGAIN Frosty for the detailed instructions. One day (once I get out of my ignorance, as Glenn would say) I hope to be able to repay in kind.

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I'm just glad to find something useful to do with some of what I learned in the materials  lab! 

It was an amusing pic.

Frosty The Lucky.

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There's a BIG difference between dry borax and anhydrous borax. Drying borax in the oven only removes any water that happens to be on or between the surfaces of the borax crystals. Think of it like sand: when it's wet, it sticks together, but when it's dry, it crumbles. 

However, borax crystals themselves are hydrates; that is, they have water molecules trapped within their crystal lattice. When borax crystals melt, the water escapes, evaporates, and causes bubbling.

Therefore, to make true anhydrous borax, we need to heat the borax not only until the free moisture evaporates from the surface of the crystals, but until the crystals themselves melt and release the moisture bound inside. When the resulting goo cools, it hardens into a solid moisture-free mass. When this is ground up into fine particles, those particles have no moisture bound in the crystals -- that is, it is truly anhydrous.

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Does the anhydrous borax need to be kept in a tightly sealed container so that it won't re-hydrate?  I know that some guys just leave their borax out in the open in a can or jar, so that would be a bad idea if you go to the trouble to dehydrate it.

 

 

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That's incorrect John. What you're describing is "hygroscopic" moisture and driving off hygroscopic moisture was literally a 24/7 operation in the soils lab. We did the same to all sorts of things, road salt to fertilizers and 230f. was the temp. American Standard Test Methods was pretty specific.

If you have specific information to the contrary please post the cites, I can be convinced.

Just keep it covered Arkie, a mason jar is overkill but works a treat.

Frosty The Lucky.

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Luckily no damage to the oven. That would have given you a week or so sleeping in the forge.

Steve

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Frosty, borax is basically one of three compounds:

  1. anhydrous sodium tetraborate, Na2B4O7

  2. sodium tetraborate pentahydrate, Na2B4O7·5H2O

  3. sodium tetraborate decahydrate, Na2B4O7·10H2O

These three are all hygroscopic (absorbing moisture from the surrounding environment) to some degree, and heating to 230F does indeed get rid of that absorbed moisture. However, that doesn't get dehydrate the crystals themselves in the pentahydrate and decahydrate forms.

2 hours ago, Frosty said:

If you have specific information to the contrary please post the cites, I can be convinced.

Your wish is my command:

Quote

Anhydrous borax is made by fusing hydrated borax into a glass and regrinding it. It thus contains little or no water of crystallization. The powder does not rehydrate under normal dry storage conditions. It is somewhat water soluble, but considerably less so than raw borax (in aqueous solution it can thus provide slow release of boron).

This material does not puff or swell during melting (minimizing loss of powder in kilns with strong drafts), and melts easier (the swelling in other forms can create a porous state with an insulation factor that slows melting).

 (From Digital Fire Reference Library article on Anhydrous Borax)

Furthermore, 

Quote

Most of the water of hydration is removed from the decahydrate (see below) by evacuation at 25ºC for three days, followed by heating to 100ºC and evacuation with a high-speed diffusion pump. The dried sample is then heated gradually to fusion (above 966ºC), allowed to cool gradually to 200ºC, then transferred to a desiccator containing P2O5 [Grenier & Westrum J Am Chem Soc 78 6226 1956]. [Becher in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 794-795 1963.]

Quoted on the Chemical Book website; note that phosphorus pentoxide is a powerful dehydrator.

Additionally, the company that makes 20 Mule Team also makes an anhydrous product called "Dehybor", regarding which their website notes:

Quote

Dehybor® results from the dehydration and fusion of borax. 

and

Quote

In glass manufacturing, Dehybor has no water of crystallization to dispel in the furnace. 

(I won't give a link to the commercial site, but you can find it at borax[dot]com[forward slash]products[forward slash]dehybor.)

Hope this helps.

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Thanks John, right you are. Good sites. I'd rather know I'm wrong than think I'm right.  

Frosty The Lucky.

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Χαίρετε, νικῶμεν!

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I thought it was "Hail we are battered and dimpled!"   must not have any good sized hail in those parts.  The hail storm Socorro had in 2004 destroyed every roof and every car not under cover.

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18 hours ago, ThomasPowers said:

Pity their sample request form is only for companies.

Since I retired, and when I request info from companies that won't give info or sell to anyone other than companies, I just enter "Consulting xxxx" (related to whatever it is I am requesting).  It works a surprising number of times!

********************

Frosty and JHCC, thanks for the info on how to keep the anhydrous borax.

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“You’re such a cynic!” said John doggedly. 

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I guess that is one advantage to my forge being an LLC

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We'll just be friends said Tom platonically.... 

You're looking for an honest man Tom said finally enlightened.

Been a while since Tom Swifties and ancient greeks collided Tom said philosophically...

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