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Disodium decaborate

Names
Other names Sodium pentaborate
Identifiers
CAS Number	12007-92-0 trihydrate: 12631-71-9
3D model (JSmol)	Interactive image
ECHA InfoCard	100.031.371
EC Number	234-522-7
PubChem CID	131634859
UNII	XQG9Q75WDN
CompTox Dashboard (EPA)	DTXSID50894254
InChI InChI=1S/B5O8.Na/c6-1-8-3-11-4-9-2(7)10-5(12-3)13-4;/q-1;+1Key: OLBJLOUJSZVXOT-UHFFFAOYSA-N
SMILES B(=O)OB1OB2OB(OB(O2)O1).
Properties
Chemical formula	Na[B5O6(OH)4] or Na[B5O7(OH)2]·H2O
Molar mass	241.06 g·mol
Appearance	Colorless crystalline solid
Solubility in water	Soluble
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references

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.

The compound is often encountered or traded as hydrates NaB₅O₈·nH₂O, Na₂B₁₀O₁₆·2nH₂O, or Na₂O·5B₂O₃·2nH₂O for n = 2, 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 and Aquabor. It has also been tested as an additive to improve plasma electrolytic oxidation of magnesium alloys. It is also used in nuclear reactors as a neutron absorber/poison .

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

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.

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 (C_2h) 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.

References

1. ^ S. Stella Mary, S. Shahil Kirupavathy, P. Mythili, R. Gopalakrishnan (2008): "Growth and characterization of sodium pentaborate 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. AmerGen Energy Company. "LICENSE RENEWAL APPLICATION OYSTER CREEK GENERATING STATION" (PDF): 2.3-207. {{cite journal}}: Cite journal requires |journal= (help)
7. 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

• Borates