Chromium dioxide
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| Names | |
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IUPAC name
Chromium(IV) oxide, Chromium dioxide
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| Other names
Crolyn
magtrieve |
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| Identifiers | |
12018-01-8 
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| 3D model (Jmol) | Interactive image |
| ChEBI |
CHEBI:48263
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| ChemSpider |
21171202
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| ECHA InfoCard | 100.031.470 |
| PubChem | 176261494 |
| RTECS number | GB6400000 |
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| Properties | |
| CrO2 | |
| Molar mass | 83.9949 g/mol |
| Appearance | black tetrahedral ferromagnetic crystals |
| Density | 4.89 g/cm3 |
| Melting point | 375 °C (707 °F; 648 K) (decomposes) |
| Insoluble | |
| Structure | |
| Rutile (tetragonal), tP6 | |
| P42/mnm, No. 136 | |
| Hazards | |
| Safety data sheet | ICSC 1310 |
| Flash point | Non-flammable |
| US health exposure limits (NIOSH): | |
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PEL (Permissible)
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TWA 1 mg/m3 |
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REL (Recommended)
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TWA 0.5 mg/m3 |
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IDLH (Immediate danger)
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250 mg/m3 |
| Related compounds | |
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Other cations
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Vanadium(IV) oxide Manganese(IV) oxide |
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Related
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Chromium(II) oxide Chromium(II,III) oxide Chromium(III) oxide Chromium trioxide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is  ?) |
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| Infobox references | |
Chromium dioxide or chromium(IV) oxide is an inorganic compound with the formula CrO2. It is a black synthetic magnetic solid. It once was widely used in magnetic tape emulsion. With the increasing popularity of CDs and DVDs, the use of chromium(IV) oxide has declined. However, it is still used in data tape applications for enterprise-class storage systems. It is still considered by many oxide and tape manufacturers to have been one of the best magnetic recording particulates ever invented.
CrO2 was first prepared by Friedrich Wöhler by decomposition of chromyl chloride. Acicular chromium dioxide was first synthesized in 1956 by Norman L. Cox, a chemist at E.I. DuPont, by decomposing chromium trioxide in the presence of water at a temperature of 800 K and a pressure of 200 MPa. The balanced equation for the hydrothermal synthesis is:
The magnetic crystal that forms is a long, slender glass-like rod — perfect as a magnetic pigment for recording tape. When commercialized in the late 1960s as a recording medium, DuPont assigned it the tradename of Magtrieve.
CrO2 adopts the rutile structure (as do many metal dioxides). As such each Cr(IV) center has octahedral coordination geometry and each oxide is trigonal planar.
The crystal's magnetic properties, derived from its ideal shape such as anisotropy which imparted high coercivity and remanent magnetization intensities, resulted in exceptional stability and efficiency for short wavelengths, and it almost immediately appeared in high performance audio tape used in audio cassette for which treble response and hiss were always problems. Unlike the spongy looking ferric oxides used in common tape, the chromium dioxide crystals were perfectly formed and could be evenly and densely dispersed in a magnetic coating; and that led to unparalleled low noise in audio tapes. Chrome tapes did, however, require a new generation of audiocassette recorders equipped with a higher bias current capability (roughly 50% greater) than that used by iron oxide to properly magnetize the tape particles. Also introduced was a new equalization (70 µs) that traded some of the extended high-frequency response for lower noise resulting in a 5–6 dB improvement in signal-to-noise ratio over ferric-oxide audio tapes. These bias and EQ settings were later carried over to "chrome-equivalent" cobalt-modified tapes introduced in the mid 1970s by TDK, Maxell, and others. Later research significantly increased the coercivity of the particle by doping or adsorbing rare elements such as iridium onto the crystal matrix or by improving the axial length-to-deprecated ratios. The resulting product was potentially a competitor to metallic iron pigments but apparently achieved little market penetration.
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Wikipedia