Sodium tetraborate

Crystal structure
	__ Na + __ B 3+ __ O 2− __ H +
General
Surname	Sodium tetraborate
other names	Disodium tetraborate; borax; E 285 ; Tetraborosodium heptoxide; calcined borax (anhydrate); Orthoboric acid sodium salt;
Ratio formula	Na 2 B 4 O 7
Brief description	colorless odorless solid
External identifiers / databases
PubChem	10219853
ChemSpider	8395345
Wikidata	Q5319
properties
Molar mass	201.22 g mol −1
Physical state	firmly
density	2.37 g cm −3 ; 1.815 g cm −3 (pentahydrate); 1.72 g cm −3 (decahydrate);
Melting point	75 ° C (decahydrate); 742 ° C (anhydrous);
boiling point	1575 ° C (decomposition)
Vapor pressure	7.3 hPa (1200 ° C)
solubility	little in water (25.6 g l −1 at 20 ° C, anhydrous); soluble in water (51.4 g l −1 at 20 ° C, decahydrate);
safety instructions
H and P phrases	H: 360FD-319
	P: 201-305 + 351 + 338-308 + 313
Authorization procedure under REACH	of particular concern : toxic for reproduction ( CMR )
MAK	Switzerland: 0.8 mg m −3 (measured as inhalable dust )
Toxicological data	2660 mg kg −1 ( LD 50 , rat , oral )
Thermodynamic properties
ΔH f 0	−3291.1 kJ / mol
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

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

Occurrence

Sodium tetraborate occurs naturally in the form of the minerals borax (decahydrate), tincalconite (pentahydrate) and kernite (tetrahydrate). It also occurs as a component of brine (e.g. in Searles Lake in California).

Extraction and presentation

Sodium tetraborate anhydrate can be obtained by dehydrating the hydrates in two steps (calcining and subsequent melting). Rapid cooling gives an amorphous product, slow cooling produces the α-shape (rhombic crystals).

properties

Sodium tetraborate is a colorless, odorless solid that is sparingly soluble in water. It decomposes when heated above 1575 ° C, forming boron oxide and sodium oxide . The decahydrate releases crystal water at 75 ° C and dissolves in its own crystal water when heated quickly. When heated slowly, it loses part of its crystal water and forms a pentahydrate. At around 400 ° C, this splits off further water of crystallization and anhydrous sodium tetraborate is obtained. A total of ten mol of water can be split off during dehydration. Eight come from the water of crystallization, two from the [B ₄ O ₅ (OH) ₄ ] ²⁻ anion. This anion has only been known since the crystal structure was clarified in the middle of the 20th century . If this is heated again, it melts from 742 ° C to a glass-like melt.

Numerous metal oxides dissolve in this melt with the formation of characteristic colors and, after cooling, form a glassy bead ( borax bead ). Mineral acids release boric acid from sodium tetraborate. 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 the space group P 1 (space group no.2 ) , the pentahydrate has a trigonal crystal structure with the space group R 3 (space group no.146) and the decahydrate has a monoclinic crystal structure with the space group C 2 / c ( Room group no.15) . Template: room group / 2 Template: room group / 146 Template: room group / 15

Boric acid is formed when it is dissolved in water.

{\ displaystyle \ mathrm {Na_ {2} B_ {4} O_ {7} +7 \ H_ {2} O \ longrightarrow 2 \ NaB (OH) _ {4} +2 \ B (OH) _ {3}} }

{\ displaystyle \ mathrm {Na_ {2} B_ {4} O_ {7} \ cdot 5H_ {2} O + 2 \ H_ {2} O \ longrightarrow 2 \ NaB (OH) _ {4} +2 \ B ( OH) _ {3}}}

use

Sodium tetraborate is used as a flux in brazing and as a wood preservative against fungal and insect attack. It's found in soaps and powders for oily skin, bleaching creams, and various skin care products. It is used to make glasses, fiberglass insulation, fiberglass mats, enamel , boric acid and sodium perborate . It is also used for glazes, for stiffening fabrics and as a flame retardant finish for wood and textiles.

toxicology

Sodium tetraborate has been classified as a Substance of Very High Concern since June 2010 due to its reproductive toxicity .

Individual evidence

↑ Entry on E 285: Sodium tetraborate (borax) in the European database for food additives, accessed on June 27, 2020.
^ ^A ^b ^c Franz v Bruchhausen, Siegfried Ebel, Eberhard Hackenthal, Ulrike Holzgrabe: Hager's Handbook of Pharmaceutical Practice: Volume 5: Substances LZ . Springer-Verlag, 2013, ISBN 978-3-642-58388-9 , pp. 299 ( limited preview in Google Book search).
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Entry on sodium tetraborate in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
↑ ^a ^b Jean de Ans, Ellen Lax: Pocket book for chemists and physicists: Volume 3: Elements, Inorganic ... Springer DE, 1998, ISBN 3-540-60035-3 , p. 602 ( limited preview in Google Book search).
↑ ^a ^b ^c data sheet di-sodium tetraborate decahydrate (PDF) from Merck , accessed on November 27, 2012.
↑ ^a ^b Data sheet di-sodium tetraborate (PDF) from Merck , accessed on November 27, 2012.
↑ Entry on Disodium tetraborate, anhydrous in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
↑ ^a ^b Entry in the SVHC list of the European Chemicals Agency , accessed on October 18, 2015.
↑ Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 7440-42-8 ), accessed on December 21, 2019.
↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-6.
↑ mindat.org: Search Minerals By Chemistry
↑ ^a ^b Seilnacht: Borax
↑ N. Morimoto, Mineral J. (Sapporo) 2 (1956) 1. Chem. Abstr. 52 (1958) 12687
↑ Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume II, Ferdinand Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 809.
↑ europa.eu: Annex XV dossier of disodium tetraborate, anhydrous (PDF; 363 kB)

[E-Nummer285-1] Entry on E 285: Sodium tetraborate (borax) in the European database for food additives, accessed on June 27, 2020.

[Hagers-2] A ^b ^c Franz v Bruchhausen, Siegfried Ebel, Eberhard Hackenthal, Ulrike Holzgrabe: Hager's Handbook of Pharmaceutical Practice: Volume 5: Substances LZ . Springer-Verlag, 2013, ISBN 978-3-642-58388-9 , pp. 299 ( limited preview in Google Book search).

[GESTIS-3] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Entry on sodium tetraborate in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .

[Jean_“d&”_Ans,_Ellen_Lax-4] Jean de Ans, Ellen Lax: Pocket book for chemists and physicists: Volume 3: Elements, Inorganic ... Springer DE, 1998, ISBN 3-540-60035-3 , p. 602 ( limited preview in Google Book search).

[MerckD-5] ta sheet di-sodium tetraborate decahydrate (PDF) from Merck , accessed on November 27, 2012.

[Merck-6] Data sheet di-sodium tetraborate (PDF) from Merck , accessed on November 27, 2012.

[CLP_100.014.129-7] Entry on Disodium tetraborate, anhydrous in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .

[SVHC-8] Entry in the SVHC list of the European Chemicals Agency , accessed on October 18, 2015.

[9] Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 7440-42-8 ), accessed on December 21, 2019.

[CRC90_5_6-10] David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-6.

[mindat.org-11] t.org: Search Minerals By Chemistry

[Seilnacht-12] Seilnacht: Borax

[13] N. Morimoto, Mineral J. (Sapporo) 2 (1956) 1. Chem. Abstr. 52 (1958) 12687

[14] Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume II, Ferdinand Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 809.

[europa.eu-15] uropa.eu: Annex XV dossier of disodium tetraborate, anhydrous (PDF; 363 kB)