Chromium(IV) oxide
Names | |
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IUPAC name
Chromium(IV) oxide, Chromium dioxide
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Other names
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Identifiers | |
3D model (
JSmol ) |
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ChEBI | |
ChemSpider | |
ECHA InfoCard
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100.031.470 |
PubChem CID
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RTECS number
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
CrO2 | |
Molar mass | 83.9949 g/mol |
Appearance | black tetrahedral ferromagnetic crystals
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Density | 4.89 g/cm3 |
Melting point | 375 °C (707 °F; 648 K) (decomposes) |
Insoluble | |
Structure | |
Rutile (tetragonal), tP6 | |
P42/mnm, No. 136 | |
Hazards | |
Flash point | Non-flammable |
NIOSH (US health exposure limits): | |
PEL (Permissible)
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TWA 1 mg/m3[2] |
REL (Recommended)
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TWA 0.5 mg/m3[2] |
IDLH (Immediate danger) |
250 mg/m3[2] |
Safety data sheet (SDS) | ICSC 1310 |
Related compounds | |
Other cations
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Related
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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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Chromium dioxide or chromium(IV) oxide is an
Preparation and basic properties
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 (527 °C; 980 °F) and a pressure of 200 MPa. The balanced equation for the hydrothermal synthesis is:
- 3 O2
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
Uses
The crystal's magnetic properties, derived from its ideal shape such as
Problems
Until manufacturers developed new ways to mill the oxide, the crystals could easily be broken in the manufacturing process, and this led to excessive print-through (echo). Output from a tape could drop about 1 dB or so in a year's time. Although the decrease was uniform across the frequency range and noise also dropped the same amount, preserving the dynamic range, the decrease misaligned Dolby noise reduction decoders that were sensitive to level settings. The chrome coating was harder than competitive coatings, and that led to accusations of excessive head wear. Although the tape initially wore hard ferrite heads faster than oxide-based tapes, it actually wore softer permalloy heads at a slower rate; and head wear was more a problem for permalloy heads than for ferrite heads. After 500 hours of running across ferrite heads, chrome tape had polished the granular surface enough that there was no more detectable wear, and the gap edges remained sharp and distinct. The head wear scare and licensing issues with DuPont kept blank consumer chrome tapes at a great disadvantage versus the eventually more popular Type II tapes that used cobalt-modified iron oxide, but chrome was the tape of choice for the music industry's cassette releases. Because of its low Curie temperature of approximately 386 K (113 °C; 235 °F), chrome tape lent itself to high-speed thermomagnetic duplication of audio and video cassettes for pre-recorded product sales to the consumer and industrial markets.[5]
Producers
DuPont licensed the product to
References
- ISBN 0-8493-0594-2.
- ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0141". National Institute for Occupational Safety and Health (NIOSH).
- ^ ISBN 978-0-08-037941-8.
- ISBN 978-3527306732.)
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: CS1 maint: multiple names: authors list (link - ISSN 1941-0069.
Further reading
- Jaleel, V. Abdul; Kannan T. S. (1983). "Hydrothermal synthesis of chromium dioxide powders and their characterisation". Bulletin of Materials Science. 5 (3–4): 231–246. S2CID 93216540.
- Bate, G. (1978). "A survey of recent advances in magnetic recording materials". IEEE Transactions on Magnetics. 14 (4): 136–142. .
- O'Kelly, Terence (1981). "The Technical Argument for Chromium Dioxide." The BASF Inventor's Notebook Number 6; http://www.ant-audio.co.uk/Tape_Recording/Library/Chrome.pdf