• Disodium tetraborate
  • Borax
  • E 285

Colorless odorless solid


  • 2.37 g · cm -3
  • 0.7 g · cm -3 ( bulk density )
  • 1.815 g · cm -3 ( pentahydrate )
  • 1.72 g · cm -3 ( decahydrate )

75 ° C

  • 742 ° C
  • 1575 ° C ( decomposition)

7.3 hPa ( 1200 ° C)

  • Slightly soluble in water ( 25.6 g · l-1 at 20 ° C)
  • Soluble in water ( decahydrate 51.4 g · l-1 at 20 ° C)


2660 mg · kg -1 ( LD50, rat, oral)

-3291.1 KJ / mol

Template: Infobox chemical / molecular formula search available

Sodium tetraborate is a chemical compound of sodium from the group of borates.


Sodium tetraborate occurs naturally in the form of the minerals borax ( decahydrate ), Tincalconit ( pentahydrate ) and kernite (tetrahydrate ) ago.


Sodium tetraborate is a colorless odorless solid which is slightly soluble in water. It decomposes when heated above 1575 ° C, forming boron oxide and sodium oxide. The decahydrate is at 75 ° C from crystal water and dissolves in rapid heating in its own water of crystallization. With slow heating, it loses part of its water of crystallization and is a pentahydrate. At about 400 ° C, these further crystal water splits off and is obtained anhydrous sodium tetraborate. For draining a total of ten moles of water can be removed. Eight are from the crystal water, two from the [ B4O5 (OH ) 4] 2 - anion. This anion is known only after the crystal structure determination. Heats turn this on, it will melt from 742 ° C to form a vitreous melt. In this melt, numerous metal oxides dissolve with the formation of characteristic coloration and form, after cooling, a glassy bead ( " borax bead "). With acids Sodium tetraborate is decomposed into boric acid. The tetrahydrate can be obtained by heating a mixture of equal parts of sodium tetraborate pentahydrate and sodium tetraborate decahydrate to 120 ° C. The anhydrate has a triclinic crystal structure with space group P1, the pentahydrate a trigonal crystal structure with space group R3, and decahydrate a monoclinic crystal structure with space group C2 / c.

When dissolved in water to form boric acid, respectively.


Sodium tetraborate is used as a flux when brazing and wood preservatives against fungal and insect infestation, and is included in soaps and powders for oily skin bleaching creams and various skin care products. It is for the production of glasses, glass fiber insulation, glass fiber mats, enamel, boric acid and sodium and used for glazes used for strips of tissues and as a flame retardant treatment of wood, and textiles.