Chromium(IV) oxide

Chromium dioxide or chromium(IV) oxide is a 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 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 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 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 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 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 aluminum 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.

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