RU2818207C1 - Obtaining magnetically soft manganese-zinc ferrites by sol-gel method - Google Patents

Abstract

FIELD: chemistry; powder metallurgy.

SUBSTANCE: invention relates to powder metallurgy and chemical engineering and specifically to methods of producing manganese-zinc ferrites. Magnetically soft manganese-zinc ferrites can be used in devices of sensors (memory magnetically operated sealed contacts). Powders of magnetically soft manganese-zinc ferrites are obtained by synthesis from solutions of metal salts by a sol-gel method. Solutions of salts containing Zn²⁺ ions are mixed in the form of Zn(NO₃)₂⋅6H₂O, dissolved in distilled water, or ZnO, previously dissolved in 65 wt.% nitric acid, containing Mn²⁺ ions in the form of Mn(CH₃COO)₂⋅4H₂O and containing Fe³⁺ ions in the form of Fe(NO₃)₃⋅9H₂O. Solutions are stirred with a magnetic mixer at rate of 300–350 rpm until the salts are dissolved, and a citric acid solution is added in amount of 3 mol of acid per 1 mol of the total amount of salts. After stirring, 25 wt.% aqueous ammonia solution is added to the solution to pH=8 and said solution is evaporated in a water bath. Obtained mass is heated in furnace to 200 °C for 5 hours, cooled with furnace to room temperature. Obtained sintered sample is crushed to a powder state, heated in a ceramic crucible in furnace to 500 °C for 2 hours and held at this temperature for 6 hours with subsequent cooling in air to room temperature. Powder in corundum crucible is heated to 1,000 °C for 5 hours, with holding at 1,000 °C for 20 hours with further cooling in air.

EFFECT: obtaining material with high resistance to temperature changes and electromagnetic interference.

1 cl, 3 dwg, 2 tbl, 1 ex

Description

The invention relates to powder metallurgy, in particular to the production of powder with magnetic properties, which can be used in the production of paint and varnish coatings, ceramic glazes, as well as non-ceramic products such as polishing compounds, cosmetics, medicines, fillers, building materials and inks, effective, as a contrast agent in magnetic resonance imaging, it can be used for magnetic powder flaw detection of parts (products, equipment) made of ferromagnetic materials in mechanical engineering, aircraft manufacturing and other industries, as well as in the production of suspensions for wet enrichment of oil shale.

There is a known method for producing magnetite, which includes mixing iron oxide with reduction, heating the mixture, holding it at an elevated temperature and cooling it in a closed volume in an inert environment, while iron powder is used as a reducing agent, heating the mixture is carried out to 740-840°C with holding at at the specified temperature for 2-3 hours and after cooling the product is crushed [RU 2039708, IPC C01G 49/08, 1995].

The disadvantage of this method is the production of powder with a particle size of 5 to 10 microns, the fineness of which depends on the raw materials used, low bulk density values, as well as the need to use a sealed container with a water-cooled lid for annealing in a shaft furnace, which increases the cost of the material.

The technical result of the present invention consists in obtaining magnetite powder, the bulk of particles of which lies in the range from 45 to 160 microns, with a content of the main component FeFe ₂ O ₄ of at least 95% and with a low content of impurities.

The technical result is achieved by the fact that the method for producing magnetite powder includes mixing iron-containing oxide material with the dusty fraction of reduced iron, annealing the resulting mixture in an inert atmosphere, followed by grinding the resulting conglomerate, while mixing the iron-containing oxide material with the dusty fraction of reduced iron is carried out in the following ratio of components , wt.%:

iron-containing oxide material 60 – 80,

powdered fraction of reduced iron 20 – 40,

and annealing of the resulting conglomerate is carried out at a temperature of 730-850°C and an inert atmosphere pressure of 20 - 60 Pa.

An iron-containing oxide material is used with the chemical composition, wt.%:

Fe ₂ O ₃ 93.0-98.0%,

SiO ₂ 1.0-4.0%,

inevitable impurities - the rest.

Use iron-containing oxide material with fractional composition, in mm:

0.20-0.25 no more than 7 wt.%

from 0.16 to 0.20 not more than 7 wt.%

0.045-0.16 rest

Less than 0.045 not more than 15 wt.%.

A magnetite powder is obtained containing, wt.%:

FeFe ₂ O ₄ 95.0-97.0%,

FeO 1.0-4.0%,

SiO ₂ no more than 2%,

inevitable impurities - the rest.

Magnetite powder is obtained with a fractional composition, microns:

100-160 2.0-5.0 wt.%

from 71 to 100 45.0-52.0 wt.%

from 45 to 71 30.0-37.0 wt.%

less than 45 12.0-17.0 wt.%.

The essence of the invention

A method for producing magnetite powder includes mixing an iron-containing oxide material with a dusted fraction of reduced iron, annealing the resulting agglomerate in an inert atmosphere, followed by grinding the resulting conglomerate, while mixing the iron-containing oxide material with a dusted fraction of reduced iron is carried out at the ratio of components, wt.%: iron-containing oxide material 60 – 80, dusty fraction of reduced iron 20 – 40. This ratio is optimal for obtaining a powder with a FeFe ₂ O ₄ content of at least 95.0%.

After mixing, annealing is carried out in a continuous furnace in an inert atmosphere at a temperature of 730-850°C and an inert atmosphere pressure of 20-60 Pa. These conditions ensure the reduction of hematite to magnetite, without excessive caking of the powder particles to each other, which allows grinding the reduced material to a powder of the required fractional composition.

The powdered fraction of reduced iron used is a production waste and has the following characteristics: the particle size does not exceed 5 microns, and the required volume of up to 10% excess against the stoichiometrically required amount ensures the production of a powder containing more than 95.0% magnetite, with magnetic permeability of at least 3.5 rel. units.

For mixing, an iron-containing oxide material is used with the chemical composition, wt.%: Fe ₂ O ₃ 93.0-98.0%, SiO ₂ 1.0-4.0%, inevitable impurities - the rest. The use of this material in production with the necessary technological parameters ensures the production of magnetite powder that meets the requirements for its use in various fields of industry. Oxide material is obtained from metallurgical waste, in particular oxide materials extracted from waste pickling solutions.

Before mixing, the iron-containing oxide material is ground in a ball mill to a fractional composition, mm: 0.20-0.25 not more than 7 wt.%, from 0.16 to 0.20 not more than 7 wt.%, 0.045 to 0.16 rest , less than 0.045 not more than 15 wt.%. This is necessary to obtain powder of the required size with high magnetic characteristics.

After annealing, the resulting conglomerate is ground to obtain magnetite powder of the following fractional composition, microns: 100.0-160.0 2.0-5.0 wt.%, from 71.0 to 100.0 45.0-52.0 wt. .%, from 45.0 to 71.0 30.0-37.0 wt.%, less than 45.0 12.0-17.0 wt.%. Grinding is carried out in a hammer crusher, which ensures the production of magnetite powder of the required fractional composition.

The resulting magnetite powder contains, wt.%: FeFe ₂ O ₄ 95.0-97.0%, FeO 1.0-4.0%, SiO ₂ no more than 2% and inevitable impurities - the rest.

Implementation examples

Under the conditions of PJSC Severstal, several variants of iron-containing oxide material were obtained from metallurgical production waste, the characteristics of which are presented in Table 1. Subsequently, the resulting iron-containing oxide material was mixed with a dusty fraction of reduced iron with a particle size of no more than 5 microns and the required volume of up to 10% excess against the stoichiometrically required amount, the resulting conglomerate was annealed in a continuous furnace in an inert atmosphere at a temperature of 730-850 ° C and an inert atmosphere pressure of 20 - 60 Pa, after which it was crushed to obtain magnetite powder. The characteristics of the resulting magnetite powder are presented in Table 2.

In the first example, iron-containing oxide material and reduced iron powder were mixed in a ratio of 65% and 35%, respectively, after which the resulting conglomerate was annealed in a continuous furnace in an inert atmosphere at a temperature of 800°C and an inert atmosphere pressure of 40 MPa; in the second example, iron-containing material was mixed oxide material and reduced iron powder in a ratio of 75% and 25%, respectively, after which the resulting conglomerate was annealed in a continuous furnace in an inert atmosphere at a temperature of 740°C and an inert atmosphere pressure of 55 MPa; in the third example, the iron-containing oxide material and reduced iron powder were mixed in a ratio of 68% and 32%, respectively, after which the resulting conglomerate was annealed in a continuous furnace in an inert atmosphere at a temperature of 830°C and an inert atmosphere pressure of 34 MPa, in the fourth example, the iron-containing oxide material and reduced iron powder were mixed in a ratio of 60% and 40 %, respectively, after which the resulting conglomerate was annealed in a continuous furnace in an inert atmosphere at a temperature of 765°C and an inert atmosphere pressure of 30 MPa.

The resulting powder was characterized by the content, wt.%: FeFe ₂ O ₄ 95.0-97.0%, FeO 1.0-4.0%, SiO ₂ no more than 2%, inevitable impurities - the rest, and fractional composition, microns: 100.0-160.0 2.0-5.0 wt.%, from 71.0 to 100.0 45.0-52.0 wt.%, from 45.0 to 71.0 30.0-37 ,0 wt.%, less than 45.0 12.0-17.0 wt.%.

Using the proposed method makes it possible to obtain magnetite powder with a FeFe ₂ O ₄ content of at least 95%, with a magnetic susceptibility of at least 3.5 rel. units, with a particle size from 0 to 160 microns, suitable for use in the production of paint and varnish coatings, suspensions for wet enrichment of oil shale, as well as suitable for magnetic particle flaw detection of parts (products, equipment) made of ferromagnetic materials in mechanical engineering, aircraft manufacturing and others industries.

Table 1

Characteristics of iron oxide material

Example No. Chemical composition, wt.% Grading, % _{Fe2O3 ​ SiO2} inevitable impurities 0.20-0.25, mm from 0.16 to 0.20, mm 0.045 to 0.16, mm less than 0.045, mm 1 94.0 2.0 4.0 6.0 5.0 77.0 13.0 2 97.0 2.8 0.2 5.0 5.0 80.0 10.0 3 95.5 1.5 3.0 6.5 2.0 80.5 11.0 4 96.0 2.0 2.0 4.0 3.5 84.0 8.5

table 2

Characteristics of magnetite powder

Example No. Chemical composition, wt.% Granulometric composition, microns _{FeFe2O4 ​} FeO _SiO2 Inevitable impurities 100.0-160.0 from 71.0 to 100.0 from 45.0 to 71.0 less than 45.0 1 96.0 2.6 1.35 0.05 2.5 47.3 33.8 16.4 2 95.0 2.2 2.0 0.8 3.2 48.7 32.5 15.6 3 97.0 1.4 1.0 0.6 4.0 50.9 32.6 12.5 4 95.4 2.2 1.2 1.2 3.5 45.7 34.4 16.4

Claims (1)

A method for producing magnetically soft manganese-zinc ferrite powder, including the synthesis of components from solutions of metal salts by the sol-gel method, characterized in that the following salt solutions are mixed: containing Zn ²⁺ ions - Zn(NO ₃ ) ₂ ⋅6H ₂ O, dissolved in distilled water, or ZnO, previously dissolved in 65 wt.% nitric acid, containing Mn ²⁺ ions - Mn(CH ₃ COO) ₂ ⋅4H ₂ O and containing Fe ³⁺ ions - Fe(NO ₃ ) ₃ ⋅9H ₂ O, in this case, the amounts of salts containing the indicated ions are calculated in the ratio, respectively, x: 1-x: 2x, where x is the content of zinc ions, 1-x is the content of manganese ions, 2x is the content of iron ions, these solutions are stirred with a magnetic stirrer at speed 300-350 rpm until the salts dissolve, add the previously obtained solution of citric acid at the rate of 3 mol of acid per 1 mol of the total amount of salts, after stirring, add a 25 wt.% aqueous ammonia solution to the solution to pH = 8 and evaporate the specified solution in water bath to a honey-like mass, the resulting mass is heated in a furnace to 200°C for 5 hours, cooled with the furnace to room temperature, the resulting sintered sample is ground to a powder state, heated in a ceramic crucible in an oven to 500°C for 2 hours and kept at this temperature for 6 hours, followed by cooling in air to room temperature, and then the powder in a corundum crucible is heated to 1000°C for 5 hours, kept at 1000°C for 20 hours, followed by further cooling in air.