Browse Prior Art Database

Stabilized Silica Coated Ferromagnetic Chromium Dioxide

IP.com Disclosure Number: IPCOM000089372D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Bruce, CA: AUTHOR [+2]

Abstract

A major problem with using chromium dioxide as magnetic particles for a recording media is the instability of the magnetic properties with time. The chromium dioxide particles shown in the figure are protected against reaction with water by encasing each particle in an amorphous silica skin. The silica surface not only protects the chromium dioxide core but also provides a negative surface at high pH values, which is desirable both for keeping the particles dispersed and for providing a surface charge required for attraction to a substrate material.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 68% of the total text.

Page 1 of 2

Stabilized Silica Coated Ferromagnetic Chromium Dioxide

A major problem with using chromium dioxide as magnetic particles for a recording media is the instability of the magnetic properties with time. The chromium dioxide particles shown in the figure are protected against reaction with water by encasing each particle in an amorphous silica skin. The silica surface not only protects the chromium dioxide core but also provides a negative surface at high pH values, which is desirable both for keeping the particles dispersed and for providing a surface charge required for attraction to a substrate material.

As disclosed in the U.S. Patent 2,885,366, a particle core, such as the chromium dioxide particle core 1 of the figure, requires an intermediate coating 2 of a silicate to permit the formation of a tight bond between the skin 3 of amorphous silica and the core 1. The particles are first subjected to a hydrolyzed tetraethyl orthosilicate solution which provides the porous intermediate coating 2. The silicate-coated particles are then treated in a sodium silicate bath solution which completes the dense amorphous silica coating skin 3.

Coating with the sodium silicate alone results in nondiscrete, nonuniform particle coverage. Coating with the orthosilicate solution above produces a porous silica coating which is stable for only a short period of time.

The following is an example of the double silica coating method.

1) Add milled, filtered chromium dioxide particles...