Chromium (III) oxide

Crystal structure
__ Cr 3+      __ O 2−
General
Surname	Chromium (III) oxide
other names	Chromium oxide Chromium sesquioxide Dichromium trioxide
Ratio formula	Cr 2 O 3
Brief description	green, odorless powder
External identifiers / databases
CAS number 1308-38-9 EC number 215-160-9 ECHA InfoCard 100,013,783 PubChem 517277 ChemSpider 451305 Wikidata Q407905
properties
Molar mass	151.99 g mol −1
Physical state	firmly
density	5.21 g cm −3
Melting point	2435 ° C
boiling point	~ 3000 ° C
solubility	practically insoluble in water
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
Toxicological data	> 5,000 mg kg −1 ( LD 50 ,  rat ,  oral ) >> 5.41 mg l −1 ( LC 50 ,  rat , 4 h )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Chromium (III) oxide , Cr ₂ O ₃ , is a chemical compound made of chromium and oxygen . It is often called just chromium oxide , although this name can lead to confusion with the three other chromium oxides chromium (II) oxide , chromium (IV) oxide and chromium (VI) oxide .

Bayer AG brought it onto the market in 1929 as a synthetically produced pigment chromium oxide green .

properties

Depending on the production method, chromium (III) oxide is available as a green powder or as brightly colored, shiny, metal-like, very hard, hexagonal rhombohedral crystals . Chromium (III) oxide is (in contrast to the dangerous chromium (VI) oxide ) non-toxic .

use

Chromium (III) oxide

Chromium oxide green pigment

Chromium (III) oxide is used in abrasives because of its hardness . It serves as a catalyst in many organic reactions .

It is available as an olive green pigment under the name chrome oxide green . Among other things, it serves as an enamel paint and for coloring glass .

The passenger coaches of the Deutsche Bundesbahn and the Deutsche Reichsbahn were painted with paints that contained chrome oxide green (see also Cologne Bridge Green ).

The pigment chrome oxide green should not be confused with the toxic chrome green , a mixture of chrome yellow and Berlin blue .

proof

Chromium oxide can be detected by oxidation to yellow chromate . For this purpose, the sample is z. B. melted down together with potassium nitrate and sodium hydroxide ( oxidation melt ):

${\displaystyle {\ce {Cr2O3 + 4NaOH + 3KNO3 -> 2Na2CrO4 + 2H2O + 3KNO2}}}$

Risk assessment

Chromium (III) oxide was included in 2018 by the EU in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation in the Community's ongoing action plan ( CoRAP ). The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. The reason for the uptake of chromium (III) oxide were concerns regarding high (aggregated) tonnage and the possible dangers of reproductive toxicity and sensitizing properties. The re-evaluation has been running since 2019 and is carried out by France .

Individual evidence

1. ↑ ^{a b c d e f} Entry on chromium (III) oxide in the GESTIS substance database of the IFA , accessed on December 21, 2019(JavaScript required) .
2. ↑ ^{a b c} Entry on chromium oxides. In: Römpp Online . Georg Thieme Verlag, accessed on June 13, 2014.
3. ↑ ^{a b} Chromoxid 24. (pdf) Carl Jäger, September 13, 2016, accessed on December 21, 2019 . 
4. ↑ K. Dohnke: The paint story: 100 years of color between protection, beauty and the environment . Dölling and Galitz, Hamburg 2000, ISBN 3-933374-64-2 , p. 143 .
5. ↑ M. Binnewies et alii : Allgemeine und Anorganische Chemie . 2nd Edition. Spectrum, 2010, ISBN 3-8274-2533-6 , pp. 677 .
6. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): Chromium (III) oxide , accessed on March 26, 2019.