Chromium(IV) oxide
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2008-05-29T01:58:47Z
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[[WP:UNDO|Undid]] revision 213790975 by [[Special:Contributions/67.175.104.68|67.175.104.68]] ([[User talk:67.175.104.68|talk]])
{{Chembox new
| Name = Chromium(IV) oxide
| ImageFile = Chromium(IV) oxide.jpg
<!-- | ImageSize = 200px -->
| ImageName = Chromium(IV) oxide
| IUPACName = Chromium(IV) oxide<!-- e.g. Iron(II) chloride -->
| OtherNames = Chromium dioxide, Chromium oxide<!-- e.g. Ferrous chloride etc, + linked mineral names -->
| Section1 = {{Chembox Identifiers
| CASNo = 12018-01-8
| RTECS =
}}
| Section2 = {{Chembox Properties
| Formula = CrO<sub>2</sub>
| MolarMass = 83.9948 g/mol<br />
| MolarMass_notes = ''Cr=61.90%, O=38.10%''
| Appearance = black ferromagnetic Crystals
| Density = 4.9 g/cm³
| Solubility = Insoluble
| MeltingPt = 400°C (decomposes)
}}
| Section3 = {{Chembox Structure
| MolShape =
| Coordination =
| CrystalStruct =
| Dipole =
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = carcinogenic, toxic
| RPhrases =
| SPhrases =
}}
| Section8 = {{Chembox Related
| OtherAnions = CrO<sub>3</sub>, Cr<sub>2</sub>O<sub>3</sub>, Cr<sub>3</sub>O<sub>4</sub>, MnO<sub>2</sub>
}}
}}
'''Chromium dioxide''' or '''chromium(IV) oxide''' is a [[chemical synthesis|synthetic]] [[magnetism|magnetic]] substance once widely used in [[magnetic tape]] [[emulsion]]. With the increasing popularity of [[compact disc|CDs]] and [[DVD]]s, 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 today by many oxide and tape manufacturers to have been the most perfect magnetic recording particulate ever invented.
[[Acicular]] chromium dioxide was first synthesized in 1956 by Norman L. Cox, a chemist at [[DuPont|E.I. DuPont]], by decomposing [[chromium trioxide]] in the presence of water at a temperature of 900 °[[Fahrenheit|F]]. and a pressure of 30,000 lbf/in². 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 ''Crolyn''.
==Uses==
The crystal's magnetic properties, derived from its ideal shape [[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 the standard [[compact audio cassette|audio cassette]] for which treble response and tape hiss were always problems. Unlike the spongy looking [[ferric oxide]]s 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 playback equalization setting (70 microseconds) that traded some of the extended high-frequency response for lower noise resulting in a 4–5 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-width ratios. The resulting product was potentially a competitor to metallic iron pigments but apparently achieved little market penetration.
==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. Output from a tape could drop about 1 [[decibel|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 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. The head wear scare and licensing issues with DuPont kept chrome 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]], chrome tape lent itself to thermomagnetic high speed duplication of audio and video cassettes for pre-recorded product sales to the consumer and industrial markets.
==Producers==
DuPont licensed the product to [[Sony]] in Japan and [[BASF]] in Germany in the early 1970s for regional producion and distribution. Because Japanese competitors of Sony resented payment of licensing fees to it for use of the pigment, they developed cobalt-adsorbed (TDK: ''Avilyn'') and cobalt ferrite (''[[Epitaxial]]'') "chrome equivalent" Type II audio cassettes and various videotape formats as substitutes. Add to that the problem that the production of CrO2 yielded toxic by-products of which Japanese manufacturers had great difficulty properly disposing. BASF eventually became the largest producer of both the chromium dioxide pigment and chrome tapes, basing its [[VHS]] & [[S-VHS]] video tape, audio cassettes, and 3480 data cartridges on this formulation. Dupont and BASF had also introduced chrome-cobalt "blended" oxide pigments which combined about 70% cobalt-modified iron oxide with 30% chrome oxide into a single coating, presumably to offer improved performance at lower costs than pure chrome. Many high grade VHS tapes also used much smaller amounts of chrome in their formulations because its magnetic properties combined with its cleaning effects on heads made it a better choice than [[aluminium oxide]] or other non-magnetic materials added to VHS tape to keep heads clean. Dupont discontinued its production of chromium dioxide particles in the 1990s. In addition to BASF, which no longer owns a tape manufacturing division, Bayer AG of Germany, Toda Kogyo and Sakai Chemical of Japan also do or can produce the magnetic particles for commercial applications.
==References==
{{Unreferenced|date =September 2007}}
<references/>
[[Category:Chromium compounds]]
[[Category:Oxides]]
[[ar:أكسيد كروم رباعي]]
[[de:Chrom(IV)-oxid]]
[[ja:酸化クロム]]