Chromium(IV) oxide
Encyclopedia
Chromium dioxide or chromium(IV) oxide is a synthetic
magnetic
substance once widely used in magnetic tape
emulsion
. With the increasing popularity of 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 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 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.
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 audio cassette for which treble response and tape 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 setting (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-width ratios. The resulting product was potentially a competitor to metallic iron pigments but apparently achieved little market penetration.
(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 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 high-speed thermomagnetic duplication of audio and video cassettes for pre-recorded product sales to the consumer and industrial markets.
in Japan and BASF
in Germany in the early 1970s for regional production 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 (Maxell: Epitaxial) "chrome equivalent" Type II audio cassettes and various videotape formats as substitutes. Added to that was 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.
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
magnetic
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
substance once widely used in magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
emulsion
Emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
. With the increasing popularity of CDs
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...
and DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
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
Crystal habit
Crystal habit is an overall description of the visible external shape of a mineral. This description can apply to an individual crystal or an assembly of crystals or aggregates....
chromium dioxide was first synthesized in 1956 by Norman L. Cox, a chemist at E.I. DuPont
DuPont
E. I. du Pont de Nemours and Company , commonly referred to as DuPont, is an American chemical company that was founded in July 1802 as a gunpowder mill by Eleuthère Irénée du Pont. DuPont was the world's third largest chemical company based on market capitalization and ninth based on revenue in 2009...
, by decomposing chromium trioxide
Chromium trioxide
Chromium trioxide is the inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.This compound is a dark-red/orange brown solid, which dissolves in water concomitant with hydrolysis...
in the presence of water at a temperature of 800 K and a pressure of 200 MPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
. 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 anisotropyAnisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
which imparted high coercivity
Coercivity
In materials science, the coercivity, also called the coercive field or coercive force, of a ferromagnetic material is the intensity of the applied magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has been driven to saturation...
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 audio cassette for which treble response and tape 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 setting (70 µs) that traded some of the extended high-frequency response for lower noise resulting in a 5–6 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
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
TDK
, formerly , is a Japanese company which manufactures electronic materials, electronic components, and recording and data-storage media, and markets them globally. Their motto is "Contribute to culture and industry through creativity"...
, Maxell
Maxell
, commonly known as Maxell, is a Japanese company which manufactures consumer electronics. The company's notable products are batteries -- the company's name is a contraction of "maximum capacity dry cell" -- and recording media, including audio cassettes and blank VHS tapes, and recordable optical...
, and others. Later research significantly increased the coercivity of the particle by doping or adsorbing rare elements such as iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
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-throughPrint-through
Print-through is a generally undesirable effect that arises in the use of magnetic tape for storing analogue information, in particular music....
(echo). Output from a tape could drop about 1 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
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
Ferrite (magnet)
Ferrites are chemical compounds consisting of ceramic materials with iron oxide as their principal component. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other applications.Many ferrites are spinels with the...
heads faster than oxide based tapes, it actually wore softer permalloy
Permalloy
Permalloy is a nickel-iron magnetic alloy, with about 20% iron and 80% nickel content. It is notable for its very high magnetic permeability, which makes it useful as a magnetic core material in electrical and electronic equipment, and also in magnetic shielding to block magnetic fields...
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 high-speed thermomagnetic duplication of audio and video cassettes for pre-recorded product sales to the consumer and industrial markets.
Producers
DuPont licensed the product to SonySony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
in Japan and BASF
BASF
BASF SE is the largest chemical company in the world and is headquartered in Germany. BASF originally stood for Badische Anilin- und Soda-Fabrik . Today, the four letters are a registered trademark and the company is listed on the Frankfurt Stock Exchange, London Stock Exchange, and Zurich Stock...
in Germany in the early 1970s for regional production 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 (Maxell: Epitaxial) "chrome equivalent" Type II audio cassettes and various videotape formats as substitutes. Added to that was 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
VHS
The Video Home System is a consumer-level analog recording videocassette standard developed by Victor Company of Japan ....
& S-VHS
S-VHS
S-VHS is an improved version of the VHS standard for consumer-level analog recording videocassettes. It was introduced by JVC in Japan in April 1987 with the HR-S7000 VCR and certain overseas markets soon afterwards...
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
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
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.