chromium dioxide Property

Melting point:

>375 °C (dec.)(lit.)

Boiling point:

decomposes to Cr2O3℃ [KIR78]

Density 

4.85 g/mL at 25 °C(lit.)

solubility 

insoluble in H2O; soluble in acid solutions

form 

brown-black tetragonal powder

color 

brown-black tetragonal powder

Water Solubility 

insoluble H2O, soluble acids giving Cr+++and dichromate [KIR78]

Merck 

13,2254

CAS DataBase Reference

12018-01-8

EPA Substance Registry System

Chromium oxide (CrO2) (12018-01-8)

Safety

Hazard Codes 

Xi

Risk Statements 

36

Safety Statements 

26-36

WGK Germany 

3

RTECS 

GB6400000

Hazardous Substances Data

12018-01-8(Hazardous Substances Data)

Hazard and Precautionary Statements (GHS)

Symbol(GHS)

Signal word

Warning

Hazard statements

H319Causes serious eye irritation

Precautionary statements

P305+P351+P338IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continuerinsing.

chromium dioxide Chemical Properties,Usage,Production

Chemical Properties

dark brown or black powder(s); tetr; used in magnetic tapes [KIR78]; ferromagnetic; rutile structure [MER06]

Physical properties

Chromium dioxide [12018-01-8], chromium(IV)oxide, CrO2, is a ferromagnetic material with a specific saturation magnetization Ms/? of 132 A m2 kg?1 at 0 K, corresponding to the spin of two unpaired electrons per Cr4+ ion. TheMs/n value of CrO2 at room temperature is ca. 100 A m2 kg?1; CrO2 magnetic pigments reach values of 77–92 A m2 kg?1. The material crystallizes with a tetragonal rutile lattice in the form of small needles, which have the desired magnetic shape anisotropy. The morphology of the particles can be varied with several dopants, particularly antimony and tellurium. The coercive field strength can be controlled between ca. 30 and 75 kA m?1 (in addition to shape) by doping with transition metal ions, which modify the magneto-crystalline anisotropy of the material; the Fe3+ ion being industrially important.

Uses

Chromium dioxide is used exclusively for magnetic recording media. It may also be used in combination with cobalt-modified iron oxides in the production of magnetic recording media. The world consumption of CrO2 is decreasing continuously as compact disc and digital videodisc are taking over the audio and video market. The sole producer is DuPont.
In the course of the development of pigments for magnetic information storage, CrO2 was the first widely used pigment material that gave a higher recording density than ã-Fe2O3. In the field of audio recording this led to the IEC II standard or “chrome position”.

Uses

Facilitates high yield aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines.

Uses

In magnetic recording tapes; as catalyst.

Production Methods

The conversion of an intimate mixture of Cr(III) and Cr(VI) compounds into CrO2 under hydrothermal conditions has been developed into an industrial process in autoclaves at ca. 350 °C and 300 bar.
Pure CrO2 slowly disproportionates in the presence of water. The CrO2 crystal surface of commercial pigments is therefore topotactically converted to â-CrOOH, which serves as a protection layer. In the absence of moisture, CrO2 is stable up to ca. 400 °C, above this temperature it decomposes to form Cr2O3 and oxygen.