amitkkamble
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Boron extraction from Borax via Aluminum melt
This is industrial experiment trial:[]
In pit furnace Aluminum melt was heated to 900C and further spectrometric Borax (fine) powder was added slowly, to gain AlB12 alloy.
initially the reaction was found to be exothermic with addition of sodium nitrate on top of melt.
We are getting unreacted glassy cake type slag of borax+Al2O3.
This retards the reaction of formation of AlB and temperature drops down.
As we need to extract nearly 8% boron in Aluminum melt. But through this method we are able to achieve only 1% boron in Al.
Help me out in reaching a suitable method for using same reactants.
I even tried the same with Boric Oxide and Aluminum Melt; results are same
[Edited on 5-7-2010 by amitkkamble]
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blogfast25
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There is a procedure in Brauer's handbook of preparative inorganic chemistry (see this forum's library) for the synthesis of AlB12, starting from Al
powder, B2O3 powder and sulfur in a thermite-like batch reaction. Makes more sense than what you're trying to do...
Even at 900 C I would expect the reduction of borax with molten aluminium to be very slow indeed, because B2O3 has a very high Heat of Formation too.
[Edited on 5-7-2010 by blogfast25]
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amitkkamble
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Yesterday I tried the experiment with Borax and Aluminum Melt. Initially the reaction was quite exothermic.
But eventually the addition powder caused excess dross formation, which includes which is undissolved borax with covered Al2O3. The final temp. of
liquid reached to 1012C. The extraction of Boron is nearly 2% in Aluminum. yield of alloy is also very low;
Expt. procedure was, first Aluminum melt is kept at 900C. while addition of borax powder in melt; dross of undissolved Borax+B2O3+Al2O3 was generated,
which was removed in 5 min. after reaction;
then again remaining powder is added for further reaction, again dross removed with in 5 min. Now the final melt is Aluminum liquid with little boron.
Is I'm doing something wrong. I even tried to added energizer for instantaneous temperature rise ; which is even not reducing the Al2O3.
Help me out in reaching a good quantity of Boron in Al? Has any body have personal experimental Experience!!
[Edited on 7-7-2010 by amitkkamble]
[Edited on 7-7-2010 by amitkkamble]
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not_important
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Consider that borax is Na2B4O7, or Na2O + 2 B2O3, so you as much mass in sodium as boron. Under the reaction conditions some sodium may be reduced
and vapourise, taking both heat energy and using up Al.
Also plus water of crystallisation if you didn't dehydrate it, water that soaks up heat at first and reacts with Al if hot enough.
| Quote: | | ....while addition of borax powder in melt; dross of undissolved Borax+B2O3+Al2O3... |
If you are just adding borax, where is the B2O3 coming from? How do you thee is B2O3 in the slag? And how do you know that thee is 2% B in the Al?
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amitkkamble
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Sorry for mentioning B2O3 in the same reactions. It is Borax powder which is kept at 200C for half hr to remove retained moisture. Then it is charged
in the Al melt.
We analyzed the melt in spectroscope. Does Sulfur has any role in reaction with Na in borax? As Brauer's handbook of preparative inorganic chemistry
suggested addition of S in powder form..
pls suggest!!
[Edited on 7-7-2010 by amitkkamble]
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watson.fawkes
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Quote: Originally posted by not_important  | | Also plus water of crystallisation if you didn't dehydrate it, water that soaks up heat at first and reacts with Al if hot enough.
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Water like this pretty much all reacts with molten aluminum. The oxygen goes into making alumina. The
hydrogen dissolves. The solubility of hydrogen in molten aluminum is astonishingly large; it's the major source of porosity in aluminum casting. Two
major sources are adsorbed water on the charge and atmospheric moisture. In the present case, I have to imagine that water of crystallization is the
source of the oxygen in the alumina coating around the unreacted borax, exactly because the borax inside is unreacted and still has its oxygen bound
in borate. So at the very least you'll want to work with anhydrous borax. I doubt that half an hour of 200°C treatment is enough to get to
anhydrous.
My suggestion is to convert anhydrous borax into a molten form with additions of other materials, then cool it off to solidify, and break it up for
addition to your melt. In this way you're excluding the bulk of entrained atmosphere and getting the borax more quickly dispersed into the melt. If
the additions aren't reducing, though, you'll get a rather low reaction rate. One way of thinking about this is that you're smelting borax into boron
in a reactive, reducing molten aluminum flux, but that you need additional help with reducing. You may have a problem with the reduced boron
partitioning into the flux, though.
The first material I'd try is carbon, as lampblack. An excess of carbon in the mixture provides a path for the oxygen to leave the reaction zone as
CO2 gas. I'm not sure how much boron carbide you'd generate, though. You might also try magnesium powder as a reducer. Another additive to try is a
carbonate mineral to lower the melting point of your charge, presumably also decreasing its viscosity when liquid.
Since you're not trying to cast the aluminum, however, you probably don't care about dissolved hydrogen, and free hydrogen is good reducer. In that
case, you could use a hydride, but that's a little pricey. You might try a hydrocarbon, but use one with a very low vapor pressure such as petroleum
jelly or wax. There are also any number of organic compounds to look at, such as oxalates and citrates.
If you're willing to consider a rather more energetic reaction, you could cast your borax into molten sulfur, and then grind for addition. You'll be
evolving rather large quantities of SO2, which for an industrial process creates a whole new class of cost to deal with the emissions. I'd guess it's
not economical for that reason. Also in that class of whole-new-problems is using a cyanide salt as an additive.
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blogfast25
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| Quote: Originally posted by amitkkamble |
We analyzed the melt in spectroscope. Does Sulfur has any role in reaction with Na in borax? As Brauer's handbook of preparative inorganic chemistry
suggested addition of S in powder form..
pls suggest!!
[Edited on 7-7-2010 by amitkkamble] |
The sulfur in Brauer's method plays the same part as it does in the Goldschmit reaction of SiO2 with Al and sulfur: to provide extra heat of reaction.
The reduction of SiO2 with Al isn't very exothermic at all and neither is the reduction of B2O3 with Al. The Al - S oxidation provides the extra heat.
Heat booster reactions are very common in aluminothermy.
Similarly, the Brauer method for AlB12 really relies on a 'mixture of two mixtures':
1. B2O3 and Al powder (B2O3 + 2 Al --> 2 B + Al2O3), which on reaction yields the AlB12
2. S powder and Al powder (2 Al + 3 S ---> Al2S3). The latter reaction provides much needed heat to keep the first one going and to ensure the slag
forms in the liquid state.
After cooling one obtains a solid heterogeneous mixture of Al2O3, Al2S3 (the slag) and blackish AlB12 crystals. The slag (Al2O3 + Al2S3) is removed by
treatment with HCl (caution! This is a H2S factory!)
[Edited on 7-7-2010 by blogfast25]
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saqib.microbiologist
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its still undiscovered completely
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