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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: johnk on February 15, 2012, 11:21:04 PM

Title: Crystallized Boric Acid
Post by: johnk on February 15, 2012, 11:21:04 PM
Hello,

Can someone please help me produce boric acid flakes such as in the image below. I am also putting up a CHNO and PIXE test so maybe it can help identify some elements that may have been used.


Title: Re: Boric Acid Help Please!!
Post by: Arkcon on February 16, 2012, 09:09:31 PM
I really don't know what you're asking.  I'm guessing you want to crystallize flakes of boric acid in a particular way, but I figure those pictured are due to the way they were crystallized, maybe from a solution, not to fast yet not too slow.  I don't know how you figure the trace element profile is very important for the crystalline habit.
Title: Re: Boric Acid Help Please!!
Post by: johnk on February 16, 2012, 10:13:05 PM
Sorry to be exactly clear. Yes I want to recrystallize boric acid. The flakes as seen in photo came into my possession from a client who requires boric acid flakes just like those.

So I am trying to figure out how can I recrystallize boric acid to appear very similar to those flakes?

I have tried just water and they come out granular and greasy.

The sample I have is slippery, will not turn into powder, remains flakes to the smallest bit. And are soft feeling. They are layered. I would say they even resemble mica flakes.

Does anyone know how I can get this result by recrystallizing boric acid?
Title: Re: Boric Acid Help Please!!
Post by: johnk on February 16, 2012, 10:25:35 PM
Also in addition, the trace element profile, I was hoping someone that is very familiar with boric acid could take a look at it and maybe identify any elements that may have been added, for example, sulfuric acid, hcl acid? Or anything else that may cause the result of the crystals.

If someone does have the answer to my problem but charges a fee for help do not hesitate to let me know.
Title: Re: Boric Acid Help Please!!
Post by: AWK on February 17, 2012, 01:50:58 AM
Jusdt add diluted HCl slowly to solution of borax.
Title: Re: Boric Acid Help Please!!
Post by: johnk on March 17, 2012, 09:57:56 PM
thanks I tried this, don't know if I could have done something wrong but it didn't work, it just made simple powder what seems to look like boric acid... any other suggestions? thanks
Title: Re: Boric Acid Help Please!!
Post by: cth on March 17, 2012, 10:54:30 PM
You could try to evaporate off solvent using rotary evaporator. It often gives dry solid with flake shape when you scrub the flask.
Title: Re: Boric Acid Help Please!!
Post by: johnk on March 17, 2012, 11:08:11 PM
Thanks I've actually tried something similar like this already but no luck. I really need them to look as lustrous as the photo above and also have the flakes form. I don't know how nobody seems to know how to achieve this? I've been at it for a while. Thanks!
Title: Re: Boric Acid Help Please!!
Post by: discodermolide on December 20, 2014, 11:01:55 AM
I'm not sure if boric acid has multiple polymorphic forms,you can check this. But if it does see if the flakes correspond to a different form than the granules (which may be amorphous). If that is the case get yourself some flakes and add them as a seed to the re-crystallisation solution and let it crystallise slowly. If you are lucky you may well get flakes out!
Title: Re: Boric Acid Help Please!!
Post by: johnk on December 20, 2014, 11:26:14 PM
I'm not sure if boric acid has multiple polymorphic forms,you can check this.

Good advice but no luck. Comes back granular. I guess it is polymorphic. Just cannot get a clue as to what temperatures or solutions and timings. Any chance I can personally send you a sample? As I said before. Willing to pay for some help on this.

Title: Re: Boric Acid Help Please!!
Post by: MOTOBALL on December 30, 2014, 12:26:29 PM
Suggest you check the following sources.

1.  "The Kirk-Othmer Encyclopedia of Science & Technology" multi-volume set; should be available in large univ. library.  Almost certainly will have section on B(OH)3.

2.  Patent Office for xtlln/prepn. of B(OH)3 as flakes (are they pearlescent ?)

Please let us know if this helps.

Regards,

Motoball
Title: Crystallized Boric Acid
Post by: Siberia on January 03, 2017, 02:37:28 AM
I am trying to crystallize boric acid to obtain flakes as seen in this picture:

https://sc01.alicdn.com/kf/HTB1m0slIFXXXXbRXFXXq6xXFXXXD/boric-acid-flakes-1-3mm-and-3.jpg


I have tried recrystallizing out of water and out of methanol but the crystals I get more resemble sodium chloride crystals than the crystals in the picture. Any idea of how I can obtain the flake like crystals in the picture?
Title: Re: Crystallized Boric Acid
Post by: AWK on January 03, 2017, 04:29:21 AM
Try very, very slow crystallization in closed vessel (eg twist-off jar in pot with hot water)
Title: Re: Boric Acid Help Please!!
Post by: Arkcon on January 03, 2017, 05:23:43 AM
Siberia:, I hope you don't mind that I've merged your question with a much older one.  What you want to achieve is more difficult than you might expect.
Title: Re: Crystallized Boric Acid
Post by: Siberia on January 03, 2017, 11:08:15 AM
Hi Arkcon,

No problem - I had actually seen this thread earlier but didn't find a satisfactory answer in it. I will try the very very slow crystallization as suggested by AWK, but are there any other tips you can give me?


Maybe it'll help if I am more specific about what I did: So I crystallized out of water. I brought 100 mL of water to a boil and made a saturated solution of the boric acid. I poured that boiling water into another beaker and let it cool to room temperature, which took about a half hour or so. I then put it in the fridge for 10 minutes, followed by an ice bath for 15 minutes. I filtered out the crystals. The crystals that were floating on top of the solution were flat and flake-like. They were also pearlescent, just like the ones in the picture above - though they were quite small . The crystals that settled on the bottom and that were stuck to the side were more granular, like salt.

So what I did partially worked. Based on what I just described, any more advice?
Title: Re: Crystallized Boric Acid
Post by: AWK on January 03, 2017, 01:02:30 PM
Crystallization of boric acid is for patient chemists - close vessel and lowering temperature as slow as possible.
Title: Re: Crystallized Boric Acid
Post by: Siberia on January 03, 2017, 01:17:21 PM
Crystallization of boric acid is for patient chemists - close vessel and lowering temperature as slow as possible.

I just repeated the recrystallization but did it very, very slowly in a closed vessel. Once the saturated solution was created, it was poured into a closed mason jar, which was then placed into a pot of near-boiling water. I let it cool to room temperature, which took over an hour, but I got the exact same type of crystals.
Title: Re: Crystallized Boric Acid
Post by: AWK on January 03, 2017, 01:28:14 PM
Try addition of a drop of ammonia (rather diluted) and leave your vessel after cooling to RT for a month or more.
Title: Re: Crystallized Boric Acid
Post by: Siberia on January 03, 2017, 06:41:14 PM
Try addition of a drop of ammonia (rather diluted) and leave your vessel after cooling to RT for a month or more.

Hi AWK,

Upon making a saturated solution, it almost immediately forms a thin layer of crystals on the surface of the solution. These crystals are good enough for me. The only problem is that only these desirable crystals only grow on the surface. On the bottom and along the sides, there is a different type of crystal growth. I have two questions.

1) Why do the surface crystals grow differently than the others?

2) What can I do to force all of the crystals to grow the same way that the surface crystals grow?
Title: Re: Crystallized Boric Acid
Post by: AWK on January 03, 2017, 07:26:39 PM
Too fast cooling since solubility of boric acid is very small. First you observe nucleation at surface. Later, since solution become oversaturated  the nucleation starts at the whole volume.
Title: Re: Crystallized Boric Acid
Post by: Siberia on January 03, 2017, 07:28:13 PM
Too fast cooling since solubility of boric acid is very small. First you observe nucleation at surface. Later, since solution become oversaturated  the nucleation starts at the whole volume.

So to obtain the same crystals as the surface crystals, I should cool the solution faster than I was before?
Title: Re: Crystallized Boric Acid
Post by: AWK on January 03, 2017, 07:38:50 PM
You should cool your solution so slowly that the nucleation in the whole solution does not start.
Title: Re: Crystallized Boric Acid
Post by: Siberia on January 03, 2017, 09:55:42 PM
Too fast cooling since solubility of boric acid is very small. First you observe nucleation at surface. Later, since solution become oversaturated  the nucleation starts at the whole volume.

So to make sure that I understand what you're saying - you're saying that the initial cooling of the solution was rapid and hence there were many nucleation sites on the surface, but there was less nucleation throughout the rest of the solution, and that's why those crystals are different than the surface ones?
Title: Re: Crystallized Boric Acid
Post by: AWK on January 04, 2017, 12:38:20 AM
Small crystals are because of too fast cooling. You cannot obtain an industrial conditions of crystallization at home (eg 10 cubic meters of volume solutions) where crystals grow falling in solution for a few hours.
You can only be patient for a few month (at least). In lab this is possible using programmed temperature change less than 1 degree per day.
Change your reagent to sodium carbonate, copper sulfate or alum - then you can obtain nice crystals by slow evaporation of saturated solutions at RT for a week or more.
Title: Re: Crystallized Boric Acid
Post by: Yingtang67 on May 26, 2019, 07:00:49 PM
Did anyone figure out if this worked. Looking into this as well. Thanks