| 摘要 |
The density of cubic ferrimagnetic ferrites is increased by heating the ferrite in a reducing atmosphere between 1100 DEG C. and 1500 DEG C. and then heating in an oxidising atmosphere between 900 and 1500 DEG C. to restore it to its former state of oxidation. The ferrite may have the formula MFe2O4 where M is Mg, Mn, Zn, Cd, Cu, Ni, Co, or may be solid solutions of two or more of these. During the first heating in a reducing atmosphere which may be CO, CO + CO2, "cracked gas" water gas or mixtures thereof part of the ferrite is reduced to a non-magnetic phase having the formula MO2FeO. The second heating in air or oxygen restores the material to its former state of higher oxidation with an increase in density to more than 99% of the theoretical single crystal density from a previous value of 97%. Magnetic properties are also improved. As an example MgCO3 and Fe2O3 were mixed in 95% ethyl alcohol for 10 minutes in a colloid mill, dried and heated for 10 hours at 1050 DEG C. The resulting material was ground in 95% alcohol, dried, sieved, pressed into bars or rings under 5000 p.s.i. The bodies were fired in CO2 at 1450 DEG C. for 12-15 hours to effect the reduction and subsequently heated for 378 hours at 1250 DEG C. to effect oxidation to MgFe2O4. |
