Process for the preparation of ferromagnetic chromium dioxide
AssigneeE. I. Du Pont de Nemours and Company
InventorsDavid Wyckoff Williston, Lewis Clinton Bancroft, Dale Murray Hiller
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Abstract
CrO.sub.2 synthesized by the known hydrothermal reaction of CrO.sub.3 /Cr.sub.2 O.sub.3 /H.sub.2 O mixtures (including minor dopants) by the use of a reaction vessel having a hollow longitudinal core open at both ends. The core may have a cross section of convenient size and shape. This process results in shortened heating and cool/vent/dry cycles resulting in increased overall productivity despite the apparent reduced volume of the reaction vessel.
Claims8
In a process for the preparation of ferromagnetic chromium dioxide which comprises heating a reaction mixture comprising one or more chromium oxides wherein the chromium has an average valence other than +4 in the presence of water to a temperature greater than 250.degree. C. and under a pressure of at least 200 atmospheres, and cooling and drying the resulting ferromagnetic chromium dioxide, the improvement comprising:
- heating said reaction mixture to form a rigid mass of chromium dioxide, in an annulus closed at one end and defined by inner and outer walls coaxially aligned each having a thermal coefficient of expansion different from that of said rigid mass of chromium dioxide, said inner wall defining a hollow column open at both ends, and
- cooling both said chromium dioxide and said annulus to cause one of said walls to separate partially from contact with said rigid mass of chromium dioxide forming a ring-like escape path for water vapor.
Dependencies are inferred from the claim text.