Abstract This invention relates to a process for stabilizing ferromagnetic chromium dioxide in respect of water and oxidizable organic compounds which it may contact in magnetic tapes. The process is applicable to a starting CrO2 having good magnetic properties, i.e. a coercive force not lower than about 400 Oersted, a maximum magnetic induction Bm not lower than about 2500 gauss, and a magnetic induction Br not lower than about 1600 gauss. The CrO2 is subjected to a heat treatment at a temperature ranging from 300 DEG to 390 DEG C. in the presence of a gas stream not exerting any oxidizing or reducing action on the compounds of trivalent, tetravalent and hexavalent chromium. Suitable gases are, for example, nitrogen, helium and argon.
A process for stabilizing ferromagnetic chromium dioxide having before said stabilization: (a) a coercive force H c ≧about 400 Oersted; (b) a maximum magnetic induction B m ≧about 2500 gauss; and (c) a residual magnetic induction B r ≧about 1600 gauss the process comprising subjecting said CrO 2 to a heat treatment at a temperature ranging between 300° and 390° C. in the presence of a stream of gas not exerting any oxidizing or reducing action on compounds of trivalent, tetravalent and hexavalent chromium, and selected from the group consisting of nitrogen and noble gases at a flow rate at least equal to 2.5 liters/hour/kg of CrO 2 and for a period of time ranging between 20 minutes and 15 hours.
Claim 2
Dependent Claim
121 words
A process for stabilizing ferromagnetic chromium dioxide having before said stabilization: (a) a coercive force H c ≧about 400 Oersted; (b) a maximum magnetic induction B m ≧about 2500 gauss; and (c) a residual magnetic induction B r ≧about 1600 gauss the process comprising subjecting said CrO 2 to a heat treatment at a temperature ranging between 300° and 390° C. in the presence of a stream of gas not exerting any oxidizing or reducing action on compounds of trivalent, tetravalent and hexavalent chromium, and selected from the group consisting of nitrogen and noble gases at a flow rate at least equal to 2.5 liters/hour/kg of CrO 2 and for a period of time ranging between 20 minutes and 15 hours.
Claim 3
Dependent Claim
18 words
The process of claim 1 wherein said flow rate ranges between 2.5 and 100 liters/hr/kg CrO 2 .
Claim 4
Dependent Claim
10 words
The process of claim 1 wherein said gas is nitrogen.
Claim 5
Dependent Claim
15 words
The process of claim 1 wherein said temperature ranges between 340° C. and 390° C.
Claim 6
Dependent Claim
22 words
The process of any one of claims 1 through 3 wherein the stabilized CrO 2 is washed with water after the treatment.