borax

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borax
Borax - Kramer Borate deposit, Boron, Kern Co, California, USA.jpg
Borax crystals from the borax open pit mine, Kramer Borate Deposit, Kern County , California
General and classification
other names

Tinkal

chemical formula Na 2 [B 4 O 5 (OH) 4 ] • 8H 2 O
Mineral class
(and possibly department) 		Borates (formerly: carbonates, nitrates and borates)
System no. to Strunz
and to Dana 		6.DA.10 ( 8th edition : Vc / B.05)
04/26/01/01
Similar minerals Kernite , Colemanite , Sassolin , Soda , Trona
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 11.89  Å ; b  = 10.65 Å; c  = 12.21 Å
β  = 106.6 °
Formula units Z  = 4
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) measured: 1.715 (5); calculated: 1.70
Cleavage perfect after {100}, imperfect after {110}
Break ; Tenacity clamshell; brittle
colour colorless, white, gray, light blue to light green, yellowish to brownish
Line color White
transparency transparent to opaque
shine Glass gloss, resin gloss, earthy matt
Crystal optics
Refractive indices n α  = 1.447
n β  = 1.469
n γ  = 1.472
Birefringence δ = 0.025
Optical character biaxial negative
Axis angle 2V = 39 to 40 ° (measured); 32 to 40 ° (calculated)
Pleochroism colorless
Other properties
Chemical behavior soluble in water and glycerine

Borax , out of date and generally uncommon also tinkal , is a rarely occurring mineral from the mineral class of " borates " with the chemical composition Na 2 [B 4 O 5 (OH) 4 ] · 8H 2 O and thus chemically a disodium tetraborate decahydrate ( short sodium borate ).

Borax crystallizes in the monoclinic crystal system and usually develops short, prismatic or tabular crystals with a resin-like to glass-like gloss on the surfaces. But it also occurs in the form of earthy, granular or massive mineral aggregates . In its pure form, borax is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also be translucent white and, due to foreign admixtures, take on a light gray, light blue or light green color. With a Mohs hardness of 2 to 2.5, borax is one of the soft minerals that can be scratched with the fingernail , similar to the reference mineral gypsum (hardness 2).

Borax is an important raw material for the production of various boron compounds , which are used, among other things, in the glass and ceramic industry ( glazes , enamel ) and as a flux for soldering.

Etymology and history

Borax, formerly also called Baurach , referred to various nitrates (saltpeter) as well as the metal solder chrysocolla (malachite or basic copper carbonate) and probably only in the 17th century today's borax ( sodium salt of boric acid). Borax was first scientifically described in 1748 by the Swedish mineralogist Johan Gottschalk Wallerius .

The name is derived from the Persian-Arabic word bauraq / būrak (in Persian būrāh / būraq : potash, saltpeter and other nitrates, borax, possibly also borate of soda) and possibly refers to the Arabic meaning “white”.

Borax was already in the ancient times in China for glazes and in Egypt for embalming used.

In the United States , the mineralogist John Allen Veatch discovered the first occurrence of borax on January 8, 1856. In September of the same year he came to Borax Lake in California .

classification

In the outdated 8th edition of the mineral classification by Strunz of borax was part of the common mineral class of "carbonates, nitrates and borates" and then to the Department of "group borates (Soroborate)" where he collaborated with Tincalconit and in the notes to Halurgit and Hungchaoit the " Tincalconit-Borax-Gruppe “with the system no. Vc / B.05 formed.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. V / H.10-30 . In the “Lapis system” this also corresponds to the section “Group borates” (planar and tetrahedral groups [B 3 O 5 ] 1- to [B 6 O 10 ] 2- ), where borax together with diomignite and tincalconite form an independent, but unnamed group forms.

The 9th edition of Strunz's mineral systematics , valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, assigns borax to the independent class of "borates" and there to the department of "tetraborates". This is also further subdivided according to the type of crystal structure , so that the mineral can be found according to its structure in the sub-section "Island Tetraborate (Neso-Tetraborate)", where it is the only member of the unnamed group 6.DA.10 .

The systematics of minerals according to Dana assigns the borax like the outdated Strunz'sche systematics in the common class of "carbonates, nitrates and borates" and there in the department of "water-containing borates with hydroxyl or halogen ". Here he is to be found as the only member of the unnamed group 04/26/01 within the subdivision of " Hydrogen borates with hydroxyl or halogen ".

Crystal structure

Crystal structure of borax

Borax crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 11.89  Å ; b  = 10.65 Å; c  = 12.21 Å and β = 106.6 ° and 4 formula units per unit cell . Template: room group / 15

Structure of the tetraborate anion in borax

The anions of borax contain tetraborate ions in which each boron atom is connected to two or three (with two atoms) further boron atoms via an oxygen bridge. In addition, each boron atom is saturated to the outside by a hydroxyl group , so that a formula of [B 4 O 5 (OH) 4 ] 2− results for the anion.

characteristics

Tetraborosodium heptaoxide hydrate forms the same compounds as disodium tetraborate decahydrate in aqueous solution.

Dehydration

When heated, it loses part of its water of crystallization at around 100 ° C and forms a pentahydrate. Anhydrous sodium tetraborate is obtained above 400 ° C.

safety instructions

Borax (sodium tetraborate decahydrate) has CAS number 1303-96-4. It is classified as a hazardous substance, the fertility impaired and as a teratogenic applies. For further safety instructions and labeling of hazardous substances, see sodium tetraborate and borates .

The mean lethal dose (LD 50 value) for borax is given as 2 to over 6 grams per kilogram of body weight.

Education and Locations

Borax tuber from Death Valley
Borax, half converted in pseudomorphoses from tincalconite to borax

Borax occurs naturally in crystalline or massive form, similar to anhydrite or gypsum, as evaporite , so it is formed when salt lakes dry out , which are then also referred to as borax lakes . The mineral can also be found as efflorescence in arid areas or as sintering at thermal springs . As Begleitminerale occur among other calcite , gypsum, halite , soda and other borates, carbonates and sulfates.

As a rare mineral formation, borax could only be detected in a few places worldwide, whereby around 80 sites have been documented (as of 2018).

Well-known sites include the “Loma Blanca Borat deposit” (Coranzuli, Jujuy ) and the “ Tincalayu Mine ” (Salta) in Argentina , the Salar de Surire in Chile , the Salar de Challviri in the Bolivian province of Sur Lípez , the Chabyêr Caka salt lake (Tibet) in China , the Indian region of Ladakh , Larderello in the Italian province of Pisa , Pachuca de Soto in Mexico , the Sankaya borate deposit near Kırka in Turkey , the Kerch peninsula in Ukraine and Boron , the Borax Lake, of Searles Lake , the Death Valley and Calico in California (USA).

use

As a raw material

Borax is produced annually worldwide in the megaton range and is an important raw material for the production of boric acid , for the extraction of borates and perborates as well as other boron compounds. Today it is extracted almost exclusively from the borax mineral kernite, which has less water of crystallization .

In industry and in the construction sector

Anhydrous borax is used as an additive for easy-melting glazes (mostly in frits ) on low-fired ceramics (e.g. raku , earthenware and other earthenware ), for the production of borosilicate glass and in enamel production.

Its use as a flux during brazing of metals and the forge welding is based on its oxidlösenden effect.

Borax is occasionally a component of fertilizers and is used as an additive in cement and insulation materials.

Borax also acts as a preventive wood preservative against mold and insects and is used in around 5 to 20 percent by weight of the total amount as a flame retardant , here primarily for cellulose- based insulation . In the latter application, its properties are seen as problematic in some cases and a reduction is considered sensible. A study carried out on behalf of the Federal Environment Agency comments: "In summary, it is stated that the use of borax as a flame retardant is acceptable. However, since the background exposure via food is already so high that the daily tolerable intake is exhausted, it must be ensured that the use of borate as a flame retardant does not result in any significant additional exposure to humans. " Up to an amount of 8.5% by mass borax equivalent or 5.5% by mass boric acid equivalent, the addition does not have to be declared.

In chemistry

Numerous metal oxides dissolve in the borax melt , forming characteristic colors and, after cooling, form a glass- like bead, the borax bead . These colorations are used as evidence of cations in the cation separation process and are of the rank of a preliminary sample .

Whereas the combustion of methanol occurs with Borax green flame coloration caused by trimethyl borate is caused, is a simple test for methanol.

In addition, borax is used for buffer solutions (borate and borate-phosphate buffers) and in the borax-carmine solution ( Grenacher's solution ) as a dye in microscopy .

In household and business

In households and laundries, borax is used in soap , water softeners and as a raw material for the extraction of perborates in detergents . Borax is used in disinfectants , cleaning agents and bleaching agents , cosmetic products and as an insecticide (for ant traps ). The sale of borax to private end users has been prohibited in Germany since June 1, 2009 by the Chemicals Prohibition Ordinance . Products with “borax” in their brand names have therefore been prepared without borax ever since.

As a food additive , it has the designation E 285, but is only approved in the EU for real caviar and is completely banned in the USA.

Along with polyvinyl alcohol , distilled water and food coloring, borax has been a basic ingredient in the manufacture of the popular toy slime .

See also

literature

  • Georgius Agricola: De Re Metallica. Borax . 1st edition. Dover Publications, New York 1950, pp. 560 ( rruff.info [PDF; 221 kB ; Retrieved October 21, 2019] Latin: De Re Metallica . 1556. Translated by Herbert Clark Hoover, Lou Henry Hoover).
  • Johan Gottschalk Wallerius , Johann Daniel Denso : Mineralogy or mineral kingdom. Borax . Bergts Christoph Gottlieb Nicolai, Berlin 1750, p. 246–250 ( rruff.info [PDF; 1.8 MB ; accessed on October 21, 2019]).
  • Graeme J. Gainford, Tim Kemmitt, Caleb David Higham: Redetermination of the borax structure from laboratory X-ray data at 145 K . In: Acta Crystallographica . E64, May 2008, p. i24 – i25 , doi : 10.1107 / S1600536808010441 (English, authors and abstract at researchgate.net ).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 133 .

Web links

Commons : Borax  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 192 .
  2. ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  346 .
  3. ^ A b c David Barthelmy: Borax Mineral Data. In: webmineral.com. Retrieved January 9, 2019 .
  4. ↑ a b c d Borax . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 69  kB ; accessed on October 21, 2019]).
  5. ↑ a b c d e Borax. In: mindat.org. Hudson Institute of Mineralogy, accessed October 21, 2019 .
  6. ↑ a b Entry on sodium tetraborate in the GESTIS substance database of the IFA , accessed on September 25, 2007 (JavaScript required)
  7. ↑ Dietlinde Goltz: Studies on the history of mineral names in pharmacy, chemistry and medicine from the beginnings to Paracelsus. (Mathematical and natural science dissertation, Marburg an der Lahn 1966) Wiesbaden 1972 (= Sudhoffs Archive. Supplement 14), pp. 248-252.
  8. ↑ John Randolph Spears: Illustrated Sketches of Death Valley and Other Borax Deserts of the Pacific Coast . BiblioBazaar, 2008, ISBN 978-0-554-70751-8 , pp. 172 .
  9. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  10. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed October 21, 2019 .
  11. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1108.
  12. ↑ Information on tetraborosodium heptaoxide, hydrate in the database of the "helpdesk reach-clp-biocide"; accessed in September 2016.
  13. ↑ Bernd Glassl: REACH event "Effects of the candidate list - effort and benefit". In: reach-clp-biozid-helpdesk.de. Federal Institute for Occupational Safety and Health (BAuA), April 11, 2011, archived from the original on September 22, 2018 ; accessed on October 21, 2019 .
  14. ↑ borate Sodium, decahydrate. In: chemcas.com. ChemCAS, accessed October 21, 2019 .
  15. ↑ a b c Study on the handling of boron in the assessment of contaminated sites on behalf of the Canton of Aargau, Switzerland. (PDF 430 kB) In: ag.ch. BMG Engineering AG, January 22, 2013, accessed on October 21, 2019 .
  16. ↑ Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p.  724 .
  17. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  563-564 .
  18. ↑ Number of borax sites. In: mindat.org. Hudson Institute of Mineralogy, accessed October 21, 2019 .
  19. ↑ List of locations for borax in the Mineralienatlas and Mindat , accessed on October 21, 2019.
  20. ↑ a b 64000 Borax, Tinkal. (PDF 34 kB) In: naturfarben-leipzig.de. Kremer pigments, accessed October 21, 2019 .
  21. ↑ Lars Nierobis: Comparison of the most important insulation materials. In: waermedaemmstoffe.com. August 17, 2007, accessed October 21, 2019 .
  22. ↑ Pollutant Advice Tübingen: What are the advantages and disadvantages of different insulation materials? ( Memento of March 4, 2010 in the Internet Archive ), accessed on February 23, 2010.
  23. ↑ André Leisewitz, Hermann Kruse, Engelbert Schramm: Results and summary overview on the substitution of environmentally relevant flame retardants . In: Development of evaluation bases for the substitution of environmentally relevant flame retardants . tape 1 , December 2000, pp. 121 ff . ( Umweltbundesamt.de [PDF; 1.7 MB ; accessed on October 21, 2019]).
  24. ^ André Leisewitz, Hermann Kruse, Engelbert Schramm : Results and summary overview . In: Development of evaluation bases for the substitution of environmentally relevant flame retardants . tape 1 , December 2000, pp. 1–2 ( Umweltbundesamt.de [PDF; 13 kB ; accessed on October 21, 2019] Research report 20408542 (old) 29744542 (new), environmental research plan of the Federal Minister for the Environment, Nature Conservation and Nuclear Safety, on behalf of the Federal Environment Agency).
  25. ↑ Product group information cellulose insulation materials. In: wecobis.de. WECOBIS, accessed on October 21, 2019 (30th ATP of Council Directive 67/548 / EEC on the classification, labeling of dangerous substances, Chapter 2.3.2.4).
  26. ↑ Entry on Sodium borate decahydrate (borax) in the Consumer Product Information Database , accessed on December 19, 2019.
  27. ↑ No supply of borax in pharmacies. PTA News, November 17, 2008, archived from the original on April 27, 2015 ; accessed on April 2, 2018 .
  28. ↑ "Kaiser Borax" does not contain borax. In: orf.at , September 8, 2012, accessed on October 27, 2020.
  29. ↑ Information on Food Additives - E285 Borax. In: zuatzstoffe-online.de. Retrieved October 21, 2019 .
  30. ↑ University of Bayreuth - effect experiments: Slime ( Memento of 27 September 2007 at the Internet Archive )