Sodium pentaborate

Sodium pentaborate, more properly disodium decaborate, is a chemical compound of sodium, boron, and oxygen; a salt with elemental formula NaB5O8, Na2B10O16, or Na2O·5B2O3. It is a colorless crystalline solid, soluble in water.

Not to be confused with Trisodium pentaborate.
Disodium decaborate
Names
Other names
Sodium pentaborate
Identifiers
3D model (JSmol)
ECHA InfoCard 100.031.371
EC Number
  • 234-522-7
UNII
  • InChI=1S/B5O8.Na/c6-1-8-3-11-4-9-2(7)10-5(12-3)13-4;/q-1;+1
    Key: OLBJLOUJSZVXOT-UHFFFAOYSA-N
  • B(=O)OB1OB2OB(OB(O2)O1)[O-].[Na+]
Properties
Na+[B5O6(OH)4]− or Na+[B5O7(OH)2]−·H2O
Molar mass 241.06 g·mol−1
Appearance Colorless crystalline solid
Soluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

The compound is often encountered or traded as hydrates NaB5O8·nH2O, Na2B10O16·2nH2O, or Na2O·5B2O3·2nH2O for n = 2,[1] 4,[2][3] 5,[4][5] or other values. This formula is often misleading as some of the water molecules are actually hydroxyl groups covalently attached to boron atoms.

The compound is used in agriculture as a boron supplement in fertilizer with various trade names such as Solubor[5] and Aquabor.[3] It has also been tested as an additive to improve plasma electrolytic oxidation of magnesium alloys.[4]

The name "sodium pentaborate" has also been used for a distinct compound with formula Na3B5O8·nH2O, better called trisodium pentaborate.[6]

Structure and preparation

Dihydrate

Sodium pentaborate "dihydrate" has the elemental formula NaH4B5O10, which can be parsed as NaB5O8·2H2O or Na2O·5B3O3·4H2O, however the correct formula seems to be either Na+[B5O6(OH)4]− or Na+[B5O7(OH)2]−·H2O. The latter seems more likely, since under thermogravimetric analysis the material starts to decompose at about 130 °C with partial loss of water. [1]

It can be prepared by reacting water solutions of sodium carbonate Na2CO3 and boric acid B(OH)3 in mole ratio 1:10 and evaporating the resulting solution at 40 °C. It belongs to the monoclinic crystal system with symmetry group P21/c (C2h5) and parameters a = 1110.3 pm, b = 1643.7 pm, c = 1356.4 pm, α = 89.960°, β = 112.850° and γ = 89.9°, formulas per cell Z = 4.[1]

References
  1. S. Stella Mary, S. Shahil Kirupavathy, P. Mythili, R. Gopalakrishnan (2008): "Growth and characterization of sodium pentaborate [Na(H4B5O10)] single crystals". Spectrochimica Acta Part A, volume 71, issue 4, 15 pages 1311-1316. doi:10.1016/j.saa.2008.04.021
  2. M. Briggs (2001): "Boron Oxides, Boric Acid, and Borates". Chapter of the Kirk-Othmer Encyclopedia of Chemical Technology. Wiley.
  3. "Aquabor 2 MSR". Product page in the Mineira Santa Rita company website. Accessed on 2022-06-27.
  4. Taha Cagri Senocak, Taha Alper Yilmaz, Hasan Feyzi Budak, Gokhan Gulten, Ahmet Melik Yilmaz, Kadri Vefa Ezirmik, Yasar Totikc (2022): "Influence of sodium pentaborate (B5H10NaO13) additive in plasma electrolytic oxidation process on WE43 magnesium alloys". Materials Today Communications, volume 30, article 103157. doi:10.1016/j.mtcomm.2022.103157
  5. "Solubor DF". Product page in the 20 Mule Team Borax company website. Accessed on 2022-06-27.
  6. Silvio Menchetti and Cesare Sabelli (1977): "The crystal structure of synthetic sodium pentaborate monohydrate". Acta Crystallographica Section B, volume B33, pages 3730-3733. doi:10.1107/S0567740877011959


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