![]() | |
Names | |
---|---|
IUPAC name Chromium(IV) oxide, Chromium dioxide | |
Other names
| |
Identifiers | |
3D model (JSmol) | |
ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.031.470 |
PubChem CID | |
RTECS number |
|
UNII | |
CompTox Dashboard (EPA) | |
| |
| |
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 | |
Flash point | Non-flammable |
NIOSH (US health exposure limits): | |
PEL (Permissible) | TWA 1 mg/m3 [2] |
REL (Recommended) | TWA 0.5 mg/m3 [2] |
IDLH (Immediate danger) | 250 mg/m3 [2] |
Safety data sheet (SDS) | ICSC 1310 |
Related compounds | |
Other cations | |
Related | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Chromium dioxide or chromium(IV) oxide is an inorganic compound with the formula CrO2. It is a black synthetic magnetic solid. [3] It once was widely used in magnetic tape emulsion. [4] 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 (527 °C; 980 °F) 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. [3]
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 cassettes for which treble response and hiss were always problems. Unlike the imperfectly formed ferric oxide coating commonly used, the chromium dioxide crystals were perfectly formed and could be evenly and densely dispersed in a magnetic coating leading to higher signal-to-noise ratios in audio recordings. Chrome tapes did, however, require audio cassette recorders to be equipped with a higher-bias current capability (roughly 50% greater) than that used by ferric 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[ clarification needed ] ratios. The resulting product was potentially a competitor to metallic iron pigments but apparently achieved little market penetration.
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]
DuPont licensed the product to Sony in Japan and BASF in Germany in the early 1970s for regional production and distribution. Japanese competitors 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.
Chromium is a chemical element; it has symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnetic tape could with relative ease record and playback audio, visual, and binary computer data.
The Compact Cassette, also commonly called a cassette tape, audio cassette, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. Invented by Lou Ottens and his team at the Dutch company Philips, the Compact Cassette was released in August 1963. Compact Cassettes come in two forms, either containing content as a prerecorded cassette (Musicassette), or as a fully recordable "blank" cassette. Both forms have two sides and are reversible by the user. Although other tape cassette formats have also existed—for example the Microcassette—the generic term cassette tape is normally used to refer to the Compact Cassette because of its ubiquity.
A cassette deck is a type of tape machine for playing and recording audio cassettes that does not have a built-in power amplifier or speakers, and serves primarily as a transport. It can be a part of an automotive entertainment system, a part of a portable mini system or a part of a home component system. In the latter case it is also called a component cassette deck or just a component deck.
Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of iron for the steel industry. Fe2O3 is readily attacked by acids. Iron(III) oxide is often called rust, since rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as hydrous ferric oxide.
Titanium dioxide, also known as titanium(IV) oxide or titania, is the inorganic compound with the chemical formula TiO
2. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insoluble in water, although mineral forms can appear black. As a pigment, it has a wide range of applications, including paint, sunscreen, and food coloring. When used as a food coloring, it has E number E171. World production in 2014 exceeded 9 million tonnes. It has been estimated that titanium dioxide is used in two-thirds of all pigments, and pigments based on the oxide have been valued at a price of $13.2 billion.
Print-through is a generally undesirable effect that arises in the use of magnetic tape for storing analog information, in particular music, caused by contact transfer of signal patterns from one layer of tape to another as it sits wound concentrically on a reel.
Video Cassette Recording (VCR) is an early domestic analog recording format designed by Philips. It was the first successful consumer-level home videocassette recorder (VCR) system. Later variants included the VCR-LP and Super Video (SVR) formats.
Chromate salts contain the chromate anion, CrO2−
4. Dichromate salts contain the dichromate anion, Cr
2O2−
7. They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.
Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.
A recording head is the physical interface between a recording apparatus and a moving recording medium. Recording heads are generally classified according to the physical principle that allows them to impress their data upon their medium. A recording head is often mechanically paired with a playback head, which, though proximal to, is often discrete from the record head.
Maxell, Ltd., commonly known as Maxell, is a Japanese company that manufactures consumer electronics.
A ferrite is a ceramic material made by mixing and firing iron(III) oxide with one or more additional metallic elements, such as strontium, barium, manganese, nickel, and zinc. They are ferrimagnetic, meaning they are attracted by magnetic fields and can be magnetized to become permanent magnets. Unlike other ferromagnetic materials, most ferrites are not electrically conductive, making them useful in applications like magnetic cores for transformers to suppress eddy currents. Ferrites can be divided into two families based on their resistance to being demagnetized.
Chromium(III) oxide is an inorganic compound with the formula Cr
2O
3. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.
Barium ferrite, abbreviated BaFe, BaM, is the chemical compound with the formula BaFe
12O
19. This and related ferrite materials are components in magnetic stripe cards and loudspeaker magnets.
EMTEC is part of the Dexxon Group headquartered in Gennevilliers, France, and markets consumer computer data storage products and other computer related consumables. Dexxon Group's North American subsidiary, Dexxon Digital Storage Inc. is located in Lewis Center, Ohio. EMTEC evolved from BASF Magnetics producing magnetic tapes. Between 1998 and 2002 all of BASF's cassette lineup were rebranded EMTEC. While cassette manufacture has since ceased in 2005, and reel-to-reel tape operations were sold to RMGI, EMTEC continues to manufacture other recordable media such as optical discs, memory cards, USB flash drives. Distribution channels have decreased and EMTEC presence in the market is a shadow of its former BASF self. Since its sale by BASF, EMTEC has undergone several transformations.
Preservation of magnetic audiotape comprises techniques for handling, cleaning and storage of magnetic audiotapes in an archival repository. Multiple types of magnetic media exist but are mainly in the form of open reels or enclosed cassettes. Although digitization of materials on fragile magnetic media in library and information science is a common practice, there remains a need for conserving the actual physical magnetic tape and playback equipment as artifacts.
Sticky-shed syndrome is a condition created by the deterioration of the binders in a magnetic tape, which hold the ferric oxide magnetizable coating to its plastic carrier, or which hold the thinner back-coating on the outside of the tape. This deterioration renders the tape unusable. Some kinds of binder are known to break down over time, due to the absorption of moisture (hydrolysis).
Audio compact cassettes use magnetic tape of three major types which differ in fundamental magnetic properties, the level of bias applied during recording, and the optimal time constant of replay equalization. Specifications of each type were set in 1979 by the International Electrotechnical Commission (IEC): Type I, Type II, Type III, and Type IV. 'Type 0' was a non-standard designation for early compact cassettes that did not conform to IEC specification.
{{cite encyclopedia}}
: CS1 maint: multiple names: authors list (link)