Abstract
Typical boron compounds are sodium tetraborate decahydrate (borax) and orthoboric acid (boric acid). These boron compounds are broadly used as medical supplies, fireproof material, the raw material of special glass, photographic developing agent, etc. It is well known that boric acid is obtained by acidification of borax, however, it is unclear whether the reverse reaction from boric acid to borax takes place or not. In this experimental study, sodium hydroxide was added to boric acid solution to make basic, and the formation or crystallization of borax from boric acid solution was examined, especially from pH point of view.
The experimental results showed that borax crystals were formed from the solution of boric acid by adjustment of pH to 8-11 and by addition of seed crystals of borax. The maximum formation amount of borax and the maximum formation rate were observed when the pH of boric acid solution was adjusted to 9.85. The adjustment of pH to 4-7 yielded boric acid, while in the pH range of 7-8 and higher than 11 there appeared no precipitates without evaporating the water from boric acid solution. pH adjustment is important to crystallize boric acid and borax. And it was recognized that borax was obtained by basification of boric acid solution.
