RU2587456C2 - Method of producing nickel-zinc ferrite with high dielectric loss - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to production of radar absorbent ferrites, which are widely used in anechoic chambers for considerable reduction of reflection of radio waves from walls. Improvement of radar absorbent properties of nickel-zinc ferrite is technical result of proposed invention and is achieved by that synthesised ferrite powder from nickel, zinc and iron oxides is first ground to particle size 1-3 mcm, followed by granulation of mixture with introduction of ligament and pressing workpieces with further sintering thereof in air, cooling of workpieces after sintering is carried out at temperature below 900 °C in a medium with reduced oxygen partial pressure in range from 0.1 to 5.0 kPa.

EFFECT: invention is aimed at production of nickel-zinc ferrites with high radar-absorbing properties in a frequency range from 30 MHz to 1000 MHz.

1 cl, 1 tbl

Description

The invention relates to the technology of radio-absorbing ferrites, which are increasingly used in anechoic chambers, to significantly reduce the reflection of radio waves from the walls.

Known methods for producing radar absorbing Nickel-zinc ferrites [1, 2]. The closest technical solution is the US patent [2] for nickel-zinc ferrite, used as a radar absorbing material, which includes the synthesis of ferrite powder from nickel, zinc and iron oxides, grinding the synthesized charge to particle sizes of 2-5 microns, granulating the charge with the introduction bales, pressing blanks and sintering. The disadvantages of the known nickel-zinc ferrites, when used as radar absorbing materials, include low absorption of radio waves in the frequency range from 30 MHz to 1000 MHz. The absorption of radio waves by radio-absorbing ferrites is due to magnetic losses due to resonance of the magnetic domain walls and ferromagnetic resonance. The low absorption of radio waves by known nickel-zinc ferrites, in our opinion, is due to the fact that the resonance frequencies of the magnetic domain walls and ferromagnetic resonance practically coincide, while the resonance of the domain walls is weakly manifested.

Losses in ferrites can be increased not only due to magnetic, but also due to dielectric losses. The dielectric loss is proportional to the product of the dielectric constant ε and the dielectric loss tangent tanδ for a given frequency of electromagnetic radiation ω. As a rule, nickel-zinc ferrites have relatively low values of ε and tanδ, and, consequently, electrical losses in the dielectric.

The objective of the invention is the development of a new method for the synthesis of nickel-zinc ferrites with high radar absorbing properties in the frequency range from 30 MHz to 1000 MHz.

Improving the radio-absorbing properties is achieved by the fact that a new method for producing radio-absorbing nickel-zinc ferrite is used, including: synthesis of a ferrite powder from nickel, zinc and iron oxides; grinding the synthesized charge to a particle size of 1-3 microns; granulation of the charge with the introduction of ligaments; pressing blanks and sintering in air, which is characterized in that it provides cooling of the blanks after sintering at a temperature below 900 ° C in an environment with a reduced oxygen partial pressure in the range from 0.1 to 5.0 kPa. The proposed synthesis technology for ceramic nickel-zinc ferrite includes the following critical operations: mixing ferrite-forming oxides of nickel, zinc and iron; synthesis of ferrite powder from the resulting mixture in furnaces in air by calcining a mixture of the starting oxides in the temperature range of 890-950 ° C; introducing polyvinyl alcohol as a binder and granulating the resulting mixture; the formation of raw billets in the form of plates of synthesized ferrite powder by pressing and high-temperature sintering of the billets in air at 1290-1350 ° C.

We suggest that the cooling of sintered billets in a medium with a reduced oxygen partial pressure leads to a partial reduction of iron ions in the Fe ³⁺ ferrite material with the transition to Fe ^{2+ ions} . As a result, the electrical resistivity of ferrite decreases and a microstructure is formed of grains with a certain electrical conductivity. At the boundaries, these grains are surrounded by interlayers with low electrical conductivity, which serve as capacitors of electric charges. The resulting structure provides an increase in the dielectric constant of the ferrite material due to an increase in the electric capacitance of the material. High dielectric constant provides an increase in dielectric loss in ferrite crystals. To confirm the effectiveness of the proposed method for the production of radio-absorbing nickel-zinc ferrites, the composition of which corresponds to the composition of nickel-zinc ferrites of the brand 1000НН, we determined the comparative properties of new materials and ferrites obtained by the technology of the known prototype method.

Examples

As the starting components in the proposed method used high-purity oxides of Nickel (GOST 17607-72 "analytical grade"), zinc (GOST 10262-72 "analytical grade"), copper (GOST 16539-79 "h .da. "), iron (TU 6-09-4783-83" MM-1 "). The starting components were mixed during co-grinding in a vibratory mill M-50 for 5 hours. The ferrite mixture was synthesized by calcining the mixture at 920 ° С in a tunnel furnace with air. The synthesized powders were ground by wet grinding in an attritor for 10 hours to a specific surface of 6000 cm ² / g, corresponding to an average particle size of 2 μm. A binder in the form of an aqueous solution of polyvinyl alcohol was introduced into the powder dried after grinding to prepare a granular powder. From granular powders, plates 60 × 60 × 6 mm were made by compression under a pressure of 100 MPa, which were then sintered in a tunnel furnace at 1300 ° C with a controlled oxygen atmosphere while cooling below 900 ° C. For comparison, plates were made from a mixture obtained by a known method [2]. The averaged data on the measurement of permittivity and the frequency dependence of the reflection coefficient of radio waves from the surface of the plates are shown in the table.

Table No. p / p Relative permittivity ε _r Reflection coefficient, dB P (O ₂ ), kPa at a field frequency ω at a field frequency ω Note 30 MHz 200 MHz 1000 MHz 30 MHz 200 MHz 1000 MHz one 20.8 12 eleven 10 -23 -24 -fifteen Prototype 2 0.05 212 142 83 -29 -27 -16 Going beyond 3 0.1 229 168 125 -31 -38 -21 According to the formula four 2.5 223 151 124 -32 -42 -24 According to the formula 5 5,0 112 105 95 -26 -41 -25 According to the formula 6 5.5 95 91 68 -twenty -26 -19 Going beyond

As can be seen from the table, the manufacture of radio-absorbing nickel-zinc ferrites by the proposed method can significantly reduce the reflection of radio waves from the surface of the plates. The deterioration of parameters beyond the scope of the invention can be explained either by an insufficient amount of Fe ^{2+ ions} formed upon cooling of ferrites after sintering (at a partial oxygen pressure of more than 5.0 kPa), or an excess of Fe ^{2+ ions} (at a partial oxygen pressure of less than 0, 1 kPa). An excess of Fe ^{2+ ions} leads to a marked increase in the electrical conductivity of ferrites, thereby increasing the reflection of electromagnetic waves from the surface.

1. US patent US No. 5,711,893 Ni-Cu-Zn ferrite U.S. Class: 252 / 62.62; 252 / 62.59; 252 / 62.6 International Class: C04B 35/26 (20060101); H01F 1/34 (20060101); H01F 1/12 (20060101); C04B 035/28 Inventor Park Jonghak (Seoul, KR) Assignee: Samsung Corning Co., Ltd. (Suwon, KR) Filed: October 23, 1995.

2. US Patent US No. 6146545 Radio wave absorbent U.S. Class: 252 / 62.56 International Class: H01Q 17/00 (20060101); C04B 035/01 Inventor: Murase; Taku (Tokyo, JP) ssignee: TDK Corporation (Tokyo, JP) Filed: December 2, 1999.

Claims (1)

A method for producing nickel-zinc ferrite with high dielectric losses, including the synthesis of ferrite powder from nickel, zinc and iron oxides, grinding the synthesized charge to particle sizes of 1-3 μm, granulating the mixture with the introduction of a binder, pressing the blanks and sintering, characterized in that it provides cooling the preforms after sintering at a temperature below 900 ° C in an environment with a reduced partial oxygen pressure in the range from 0.1 to 5.0 kPa.