摘要:
Acicular cobalt-containing magnetic iron oxides having a high coercive force and a core/shell structure and hence low temperature dependence of the coercive force are prepared by a process in which, in a first stage, surface activation is effected by means of iron(II) and cobalt ions under alkaline conditions on the iron oxide core under an inert gas atmosphere and thereafter, in a second stage, an epitactic coating of cobalt ferrite is applied, which coating is formed oxidatively from iron (II) and cobalt (II) hydroxide, likewise under alkaline reaction conditions. The total amount of cobalt ions used for doping remains unchanged compared with the known doped iron oxides or is even smaller. In the second process stage, the achievable coercive force can be controlled by the proportion of air in the gas mixture during the formation of the epitactic coating.
摘要:
A finely divided acicular CrO.sub.2 modified with iron, tellurium and/or antimony and having a high coercive force possesses improved heat stability of the residual induction and a relatively narrow distribution of the particle size and of the coercive force. This CrO.sub.2 pigment is obtained by a method in which the iron compound used for the modification is iron oxalate, which is employed in an amount of 1-10% by weight, based on the theoretical CrO.sub.2 yield.
摘要:
A magnetic recording medium comprising a nonmagnetic substrate and at least one magnetic layer applied thereon and containing an acicular chromium dioxide uniformly distributed in a polymeric binder and additives and having a coercive force of at least 60 kA/m, a mean particle length of the chromium dioxide of less than 300 nm, whose factor HD according to the formula ##EQU1## where KT is the coercive force of the magnetic layer in [kA/m], measured in an external field of 380 kA/m, L is the mean particle length and .DELTA.L is the range of the particle size distribution, determined from the numerical distribution of the particle length, both measured in [nm], is greater than 1.85, and a process for the preparation of this chromium dioxide.
摘要:
Acicular, cobalt-modified iron oxides consisting of a core of an iron oxide of the formula FeO.sub.x where x is from 1.33 to 1.5 and a ferrite shell which contains a total amount of from 0.4 to 12% by weight of cobalt ions and not more than 5% by weight of iron(II) ions, the percentages being based on the total amount of the material, which iron oxides have improved aging resistance, particularly with regard to the coercive forces, and a process for their preparation.
摘要:
The present invention relates to phosphorus-containing ferromagnetic pigments comprising, in particular, from 30 to 70% by volume of a core, said core comprising essentially iron and cobalt, and from 30 to 70% of a shell, said shell comprising essentially aluminum, phosporus, silicon, oxygen, and optionally magnesium and sodium; the invention further relates to a process for preparation of said pigments, their use in magnetic recording materials and magnetic recording materials which contain such pigments.
摘要:
The invention provides a process for preparing aromatic amines by catalytically hydrogenating the corresponding nitro compounds, especially for preparing tolylenediamine by hydrogenating dinitrotoluene, which comprises using hydrogenation catalysts in which the active component present is a mixture of platinum, nickel and an additional metal on a support.
摘要:
The invention relates to a catalyst for fuel cells which comprises a support, at least one catalytically active metal from the platinum group or an alloy comprising at least one metal of the platinum group and also at least one oxide of at least one metal selected from among Ti, Sn, Si, W, Mo, Zn, Ta, Nb, V, Cr and Zr. The invention further relates to a process for producing such a catalyst and its use.
摘要:
The present invention relates to a process for the preparation of cis-2-(2-methylprop-1-enyl)-4-methyltetrahydropyran comprising the catalytic hydrogenation of 2-(2-methylprop-1-enyl)-4-methylenetetrahydropyran in the presence of hydrogen and a heterogeneous catalyst comprising ruthenium on a support and subsequently bringing the compounds obtained in this way into contact with a strongly acidic cation exchanger.
摘要:
Process for preparing olefins, which comprises the following steps: a) preparation of a synthesis gas comprising carbon monoxide and hydrogen, b) introduction of carbon dioxide recirculated from step d) into the synthesis gas during or after the preparation of synthesis gas as per step a), c) conversion of the synthesis gas having a hydrogen to carbon monoxide ratio of ≦1.2:1 which is obtained in step b) into olefins in the presence of a Fischer-Tropsch catalyst, d) removal of the carbon dioxide comprised in the reaction product from step c), where the ratio of hydrogen to carbon monoxide in step c) is set via step b).
摘要:
A process for removing sulfur compounds from a hydrocarbonaceous gas mixture, which comprises contacting the hydrocarbonaceous gas mixture with an adsorber material comprising copper oxide on magnesium silicate as support material.