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Grinding Magnetic Alloy Particles

IP.com Disclosure Number: IPCOM000083835D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Marsh, TJ: AUTHOR

Abstract

It is not unusual to grind or mill magnetic particles which are to be utilized in a dispersion, such as in a magnetic recording media coating composition. Unfortunately, during such grinding operations magnetic alloy particles sometimes experience a loss in coercivity. For example, materials such as cobalt-phosphorus particles produced by chemical reduction from a cobalt cation hypophosphite anion bath, in which the pH is controlled with ammonium hydroxide, have been found to lose 30-50% of their coercivity during dry grinding or during grinding in the presence of a low-viscosity fluid.

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Grinding Magnetic Alloy Particles

It is not unusual to grind or mill magnetic particles which are to be utilized in a dispersion, such as in a magnetic recording media coating composition. Unfortunately, during such grinding operations magnetic alloy particles sometimes experience a loss in coercivity. For example, materials such as cobalt-phosphorus particles produced by chemical reduction from a cobalt cation hypophosphite anion bath, in which the pH is controlled with ammonium hydroxide, have been found to lose 30-50% of their coercivity during dry grinding or during grinding in the presence of a low-viscosity fluid.

It has now been discovered that if grinding is carried out in the presence of a high-viscosity fluid, the loss of coercivity which cobalt-phosphorus particles exhibit can be limited. With increasing viscosity the amount of coercivity lost decreases inversely. For example, in a mixture having a viscosity of 37 cps, the coercivity lost is on the order of about 20% after 42 hours of attrition. When the same particles are ground in a mixture having a viscosity of about 1100 cps, the loss of coercivity is limited to about 5%.

Viscosity during grinding can be increased by a number of means. One simple method is to include polymers and suitable solvents for the polymers in the particle grinding mixture.

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