Chromium nitride

Crystal structure
__ Cr      __ N
General
Surname	Chromium nitride
other names	Chromium (III) nitride
Ratio formula	CrN
Brief description	dark odorless solid
External identifiers / databases
CAS number 24094-93-7 EC number 246-016-3 ECHA InfoCard 100,041,819 PubChem 90362 ChemSpider 81581 Wikidata Q424741
properties
Molar mass	66.00 g mol −1
Physical state	firmly
density	5.9 g cm −3
Melting point	1500 ° C (decomposes to Cr and N 2 )
solubility	almost insoluble in water
safety instructions
GHS labeling of hazardous substances Mixture of CrN and Cr 2 N danger H and P phrases H: 334-302-317 P: 285-261-280-302 + 352-321-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Chromium nitride is an inorganic chemical compound of the two elements chromium and nitrogen , which is counted among the intermetallic compounds . It is characterized by its very high hardness and extreme resistance to corrosion , from which a number of technical applications such as B. Passivation and finishing of chrome materials or coating of cutting tools result.

Occurrence

Chromium nitride occurs naturally as the mineral carlsbergite and has been detected in various iron meteorites .

Extraction and presentation

Chromium nitride is usually produced in the form of extremely thin coatings, less often as a ceramic body or as a powder.

A production from the elements is possible at temperatures above 800 ° C. In this process, the workpiece or the chrome powder is heated to the required temperature for several hours under a pure nitrogen atmosphere. This is done according to the following equation:

${\displaystyle \mathrm {2\ Cr+N_{2}\longrightarrow 2\ CrN} }$

It is also possible to display it by reacting chromium (III) chloride with ammonia .

${\displaystyle \mathrm {CrCl_{3}+4\ NH_{3}\longrightarrow CrN+3\ NH_{4}Cl} }$

properties

Chromium nitride is an embedded nitride with metallic properties. An ionic formulation in the sense of Cr ³⁺ and N ³⁻ is misleading, while an assignment of corresponding oxidation numbers is correct.

It is in the form of a black, magnetic powder that is insoluble in acids and alkalis. It has a crystal structure of the sodium chloride type (a = 415 pm). At higher temperatures, chromium nitride (γ-chromium nitride phase) increasingly decomposes and changes to chromium heminitride Cr ₂ N (β-chromium nitride phase, CAS number: 12053-27-9). Depending on the temperature and the nitrogen pressure, an equilibrium is formed between these two phases, for example at 1100 ° C. and a nitrogen pressure of 1.7 Torr. Chrome heminitride has a trigonal crystal structure, which has the space group P 3 1 m (space group no. 162) .

Individual evidence

1. ↑ ^{a b c d} Datasheet Chromium nitride at AlfaAesar, accessed on June 30, 2013 ( PDF )(JavaScript required) .
2. ^ ^{A b} Jean d'Ans, Ellen Lax, Roger Blachnik: Pocket book for chemists and physicists . Springer DE, 1998, ISBN 3-642-58842-5 , pp. 400 ( limited preview in Google Book Search).
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Properties of the Elements and Inorganic Compounds, pp. 4-58.
4. ↑ ^{a b c d} Georg Brauer (Ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 , p. 1494.
5. ↑ by Eckart Doege, Bernd-Arno Behrens: Handbook of forming technology: Basics, technologies, machines - Eckart Doege, Bernd-Arno Behrens . Springer DE, 2010, ISBN 3-642-04249-X , p. 435 ( limited preview in Google Book search).
6. ↑ Webmineral: Carlsbergite
7. ↑ John Williams Anthony: Mineralogy of Arizona . University of Arizona Press, 1995, ISBN 0-8165-1555-7 , pp. 154 ( limited preview in Google Book search).
8. ↑ TH Lee, S.-J. Kim, E. Shin, S. Takaki: On the crystal structure of Cr ₂ N precipitates in high-nitrogen austenitic stainless steel. III. Neutron diffraction study on the ordered Cr ₂ N superstructure. In: Acta Crystallographica , 2006, B62, pp. 979-986, doi : 10.1107 / S0108768106034173 .