摘要:
A process for stabilizing pyrophoric acicular metal particles consisting essentially of iron, by reaction with oxygen-containing gases in two stages, wherein, in the first stage, up to 1/3 of the passivating layer present in the final state is formed at from 25.degree. to 45.degree. C. and, in a subsequent second stage, the remainder of the passivating layer is formed at from 50.degree. to 70.degree. C.
摘要:
A process for the manufacture of acicular ferrimagnetic iron oxide by reducing heat-treated acicular iron(III) oxide hydroxide with an organic compound which decomposes in the presence of iron oxide at from 450.degree. to 650.degree. C., followed by at least partial oxidation with an oxygen-containing gas at from 200.degree. to 500.degree. C., wherein the iron(III) oxide hydroxide employed is heat-treated at from 450.degree. to 700.degree. C. and has a surface area, measured by the BET method, of from 10 to 23 m.sup.2 /g.
摘要:
A process for the manufacture of acicular ferrimagnetic iron oxide by dehydrating acicular iron(III) oxide hydroxides to give acicular iron(III) oxides, then reducing these iron(III) oxides at from 300.degree. to 650.degree. C. by means of an organic compound which decomposes in this temperature range, and oxidizing the reduced product with an oxygen-containing gas at from 200.degree. to 500.degree. C., wherein the acicular iron(III) oxide hydroxides employed consist of a mixture of goethite and lepidocrocite, containing at least 60% of the latter, and the dehydration is carried out at from 250.degree. to 700.degree. C.
摘要:
Acicular ferromagnetic metal particles consisting essentially of iron are prepared by a process wherein acicular iron(III) oxide hydroxide provided with a shape-stabilizing surface coating, or iron(III) oxide obtained therefrom by dehydration, is reduced by means of a decomposable organic compound and hydrogen.
摘要:
The preparation of acicular ferrimagnetic iron oxides which contain cobalt and phosphate ions and, if desired, further additives, and their use for manufacturing magnetic recording media.
摘要:
A process for the manufacture of acicular ferromagnetic iron particles by reducing acicular iron(III) oxide hydroxides which consist of pure synthetic lepidocrocite or a mixture of synthetic goethite and at least 70% by weight of synthetic lepidocrocite.The iron(III) oxide hydroxides used carry, on their surface, an alkaline earth metal cation and an anion of a monobasic, dibasic or tribasic aliphatic carboxylic acid of up to 6 carbon atoms or an organic compound containing at least two groups capable of chelating the alkaline earth metal cation, and are produced in such a way that they consist of at least 70 percent by weight of lepidocrocite and have a length-to-width ratio of not less than 15:1.Reduction of such iron(III) oxide hydroxides gives iron particles with pronounced shape anisotropy, which exhibit both good magnetic properties and a narrow field strength distribution.
摘要:
A process for the manufacture of an acicular magnetic iron oxide containing from 0.5 to 10 percent by weight of cobalt and up to 24 percent by weight of divalent iron, each based on the amount of iron(III) oxide, wherein an aqueous suspension of gamma-iron(III) oxide, containing cobalt(II) and iron(II) ions, the suspension having a hydroxyl ion concentration of more than 3.6.times.10.sup.-6 moles/liter, is heated at from 50.degree. to 100.degree. C. for at least 15 minutes, and the resulting precipitate is filtered off, washed until neutral, dried at below 100.degree. C. and thereafter heated at from 100.degree. to 200.degree. C.The products thus obtained give, even when their cobalt content is low, a very high coercive force, while the effect of temperature on the coercive force and residual induction is very slight.
摘要:
A process for the manufacture of acicular ferromagnetic metal particles which essentially consist of iron and carry, on their surface, from 0.02 to 0.6% by weight of boron in the form of a borate, by reducing an acicular iron oxide with a gaseous reducing agent at from 250.degree. to 500.degree. C., wherein a compound selected from the group comprising boron oxyacids and their inorganic salts is precipitated on the said iron oxide before reduction.
摘要:
A process for the preparation of cobalt-containing isotropic magnetic iron oxides which are based on gamma-iron(III) oxide, contain from 2 to 7% by weight of cobalt(II) ions and less than 2% by weight of Fe(II) ions, the percentages in each case being based on the iron oxide, and have a particle length of from 0.08 to 0.30 .mu.m, a length/width ratio of from 1.5 to 3.5:1 and a specific remanent magnetization after saturation of not less than 60 nTm.sup.3 /g.
摘要:
Acicular metal particles consisting essentially of iron are prepared by reducing .alpha.-iron(III) oxide obtained--by dehydration--from acicular iron(III) oxide hydroxide prepared in the presence of phosphate ions and having a shape-stabilizing surface coating.