[AWK]

Crystallization of boric acid is for patient chemists - close vessel and lowering temperature as slow as possible.

[Siberia]

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.

[AWK]

Try addition of a drop of ammonia (rather diluted) and leave your vessel after cooling to RT for a month or more.

[Siberia]

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?

[AWK]

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.

[Siberia]

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?

[AWK]

You should cool your solution so slowly that the nucleation in the whole solution does not start.

[Siberia]

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?

[AWK]

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.

[Yingtang67]

Did anyone figure out if this worked. Looking into this as well. Thanks