RU2764763C1 - Method for obtaining titanium-substituted barium hexaferrite - Google Patents

Abstract

FIELD: chemical industry.SUBSTANCE: invention relates to the production of magnetic oxide materials by solid-phase synthesis and can be used in microwave devices and electronics. To obtain a sintered powder of titanium-substituted barium hexaferrite BaFe12-XTiXO19, where x = 0.25÷2.0, powders of Fe2O3and TiO2oxides and BaCO3carbonate, taken in a stoichiometric ratio, are subjected to homogenizing grinding in dry form for 3 hours. The powder mixture is pressed at a pressure of 60-80 kg / mm2, subjected to synthesizing baking in air before sintering in two stages with intermediate grinding for 1 hour, and then slowly cooled. Baking at the first stage is carried out at a temperature of 1200°C for 5 hours, and at the second stage at 1350°C for 5 hours.EFFECT: invention makes it possible to obtain barium hexaferrite with adjustable electrophysical properties of the material, such as dielectric and magnetic permeability, susceptibility, and to regulate the frequency range of ferromagnetic resonance by varying the composition of the initial mixture.1 cl, 4 dwg, 3 ex

Description

The invention relates to the field of obtaining magnetic oxide materials, and can be used in microwave devices and electronics to expand the scope of their application (ferrite absorbers of electromagnetic waves, antennas, cores, memory elements, permanent magnets, etc.).

A known method of obtaining hexagonal ferrites by chemical coprecipitation, which consists in the deposition of insoluble compounds (iron hydroxides and alloying elements, barium carbonate) from salt solutions, followed by washing and sintering the resulting precipitates using ceramic technology [Mattei, J.-L. A simple process to obtain anisotropic self-biased magnets constituted of stacked barium ferrite single domain particles / J.-L. Mattei, CN Le, A. Chevalier et al. // Journal of Magnetism and Magnetic Materials. - 2018. - V. 451. - P. 208-213]. The essence of the method is to obtain anisotropic dense products of hexagonal barium ferrites, using different deposition rates and types of precipitating agents (NaOH and Na ₂ CO ₃ ). It is shown that with a large excess of Na ₂ CO ₃ after pressing and firing at 1140°C, a high-density packing of hexagonal BaFe ₁₂ O ₁₉ plates is obtained without additional crushing and firing processes.

The main problems of this technique are the difficulty of obtaining the same stoichiometry both in the precipitate and in the initial solution, since the solubility products of individual salts often differ by orders of magnitude; adsorption of foreign ions from the solution by the dispersed precipitate.

A known method of obtaining hexagonal ferrites by the sol-gel method [Li, Q. Preparation, characterization and microwave absorption properties of barium-ferrite-coated fly-ash cenospheres / Q. Li, J. Pang, B. Wang et al. // Advanced Powder Technology. - 2013. - V. 24, is. 1. - P. 288-294]. The essence of the method is as follows. First, the starting materials are mixed and a sol is formed. A sol is a dispersed system in which the dispersion medium is a liquid, and dispersed phases are distributed in it: liquid droplets, gas bubbles or solid nanoparticles (1-100 nm). Next, the sol is converted into a gel by increasing the concentration of the dispersed phase or by changing the technological parameters (temperature, pressure). By carrying out one or more successive processes, such as condensation, hydrolysis, ultrafiltration, drying, aging or heat treatment, the formation of contacts between particles is achieved, which leads to the creation of a monolithic polymer gel in which a three-dimensional ordered network is formed. At the end, barium hexaferrite powder is obtained by accelerated heating to a temperature of 600-1200°C. Particle sizes, depending on the chosen precursor and synthesis conditions, can range from several tens to hundreds of nm.

The disadvantages of this method include the duration of the solvent removal stage, drying and firing of coatings and monolithic products can lead to significant shrinkage (up to 70%); polydispersity of particles; the impossibility of obtaining anisotropic particles and spatially ordered systems; interaction of particles with a solvent.

Closest to the proposed method is a method of obtaining an absorbent material based on substituted barium hexaferrite [US Pat. 2651343 Russian Federation, IPC C09D 5/32, H01Q 17/00]. The used method of obtaining aluminum-substituted barium hexaferrite with the addition of boron oxide improves the absorbing characteristics of the synthesized materials. In accordance with the prototype method, to obtain an absorbing material based on substituted barium hexaferrite, a substituted barium hexaferrite BaFe _12-x Al _x O ₁₉ is synthesized, where 0.5≤x≤2, from oxides of Fe ₂ O ₃ , Al ₂ O ₃ and BaCO _{3 carbonate} , taken in a strictly stoichiometric ratio, while before mixing in the initial charge from a mixture of oxides and carbonate add fusible eutectic - In ₂ About ₃ 1-2 wt. %, the mixed powders are subjected to wet grinding, after which the mixture of powders is pressed and subjected to synthesizing firing in air at 1150-1250°C until sintering, and then slowly cooled.

The disadvantages of the prototype method include its inapplicability to materials where other alloying elements are used, where there is a high probability of a negative impact on the final product when adding B ₂ O ₃ , as well as additional costs for alcohol.

The technical objective of the proposed method is to obtain titanium-substituted barium hexaferrite by solid-phase synthesis, which has anisotropy of properties, high chemical stability, corrosion resistance for industrial use as materials absorbing electromagnetic radiation of a certain frequency, and also as a material for microwave electronics elements.

The technical problem is achieved due to the fact that the method of obtaining titanium-substituted barium hexaferrite in the form of a sintered powder by solid-phase synthesis from powders of two oxides, including Fe ₂ O ₃ oxide and BaCO ₃ carbonate, taken in a stoichiometric ratio, in which the mixed powders are subjected to a homogenizing grinding, after which the mixture of powders is pressed and subjected to synthesizing roasting in air before sintering in two stages with intermediate grinding, and then slowly cooled, characterized in that substituted barium hexaferrite is synthesized: BaFe _12-x Ti _x O ₁₉ , where x=0, _{25 ÷ 2.0, TiO 2 is} used as the second oxide, grinding is carried out in dry form for three hours, pressed under a pressure of 60-80 kg / mm ² , firing at the second stage is carried out at a temperature of 1350 ° for 5 hours, with intermediate grinding for 1 hour.

EFFECT: obtaining barium hexaferrite with controlled electrical properties of the material, for example, dielectric and magnetic permeability, susceptibility, regulation of the frequency range of ferromagnetic resonance by varying the composition of the initial mixture, controlled changes in anisotropy.

Unlike the prototype method, substituted barium hexaferrite BaFe _12-x Ti _x O ₁₉ , 0.25≤x≤2, is synthesized from oxides Fe ₂ O ₃ , TiO ₂ and carbonate ВаСО ₃ taken in a strictly stoichiometric ratio, do not add to the initial charge boron oxide B ₂ O ₃ , then mixed powders, are subjected to grinding, but in dry form, after which the mixture of powders is pressed at a pressure of 60-80 kg / mm ² and subjected to synthesizing firing in air in two stages at a temperature of 1200 ° for 5 hours with intermediate grinding for 1 hour, with repeated pressing and sintering at 1350 ° for 5 hours. After each sintering, the samples must be slowly cooled at a rate of ~100°C/h.

The method is illustrated by the graphs shown in Fig. 1-4.

In FIG. 1 shows a graph of the modulus of the complex reflection coefficient of a layer substituted with titanium barium hexaferrite - BaFe _11.5 Ti _0.5 O ₁₉ on the frequency of electromagnetic radiation.

In FIG. 2 shows a plot of the modulus of the complex reflectance of the BaFe ₁₁ TiO ₁₉ layer as a function of the electromagnetic radiation frequency.

In FIG. 3 shows a plot of the modulus of the complex reflection coefficient of the BaFe ₁₀ Ti ₂ O ₁₉ layer as a function of the electromagnetic radiation frequency.

On FIG. Figure 4 shows the dependence of the real part of the permittivity on the frequency of the electric field radiation for titanium-substituted barium hexaferrites BaFe _11.5 Ti _0.5 O ₁₉ , BaFe ₁₁ TiO ₁₉ , BaFe ₁₀ Ti ₂ O ₁₉ compared with pure BaFe ₁₂ O ₁₉ hexaferrite.

The essence of the invention is as follows.

Substitution of a part of the iron ions with such an alloying element as titanium makes it possible to modify the properties - to vary the values of the dielectric constant and magnetic susceptibility, and makes it possible to control the frequency range of the ferromagnetic resonance. In addition, due to its crystalline structure, barium hexaferrite has anisotropy of properties, high chemical stability, corrosion resistance, which makes it possible to use this material in industry, for example, as hard magnetic materials for permanent magnets and magnetic composites, information storage devices, magneto-optical devices, etc. .d.

The study of electromagnetic parameters in the frequency range 8-12 GHz (Fig. 1) revealed that an increase in the titanium content causes an increase in the dielectric constant up to 6.2 at x=0.5-1 and up to 10.5 at x=2. This effect is due to an increase in the polarizability of the crystal due to the introduction of Ti ⁴⁺ ions with a high ionic polarizability. A similar effect is well known in the optical spectral range, where the introduction of Ti ⁴⁺ ions with high electronic polarizability into the oxide crystal lattice leads to a significant increase in the refractive index. From which it follows that the proposed compositions of the absorbing material from barium hexaferrite: BaFe _12-x Ti _x O ₁₉ , where x=0.25÷2, have sufficient electromagnetic properties to be used as absorption elements in such microwave devices as phase shifters, dividers power and attenuators.

_{Boron oxide B 2} O _{3 is} not added to the initial mixture due to the fact that this will adversely affect the final properties of the material using the proposed method. In combination with alloying with titanium, which conducts electric current, the addition of boron oxide, although it will reduce the conductivity of the material to improve the final properties of the material, it will require the development of another production technology, since both the prototype and the proposed method are not suitable for material synthesis, because there is a high probability of obtaining several phases in addition to barium hexaferrite BaFe ₁₂ O ₁₉ , which will significantly affect the final characteristics of the resulting material.

With dry grinding for 3 hours, optimal homogenization of the mixture is achieved, with a decrease in grinding time, an uneven distribution of elements and their large inclusions are observed, which will negatively affect the final synthesis product. Increasing the grinding time will not lead to a significant improvement in homogenization, so grinding for 3 hours is necessary and sufficient to homogenize the mixture.

Due to the fact that the addition of alcohol helps to increase the intensity of mixing, but is not economically viable due to the complexity of the technology and the increase in the cost of production, it is possible to carry out grinding without it or another liquid.

Pressing powders is carried out in metal molds at a pressure of 60-80 kg/mm ² . At a higher pressing pressure, the wear of mold parts increases significantly. At lower pressures, there is a possibility of sample cracking. This can be avoided by adding a binder to the material, for example, 5 wt. % paraffin. Both options are economically disadvantageous, and therefore the pressing pressure of 60-80 kg/mm ² was chosen.

It has been empirically proven that if the sintering of titanium-substituted barium hexaferrites BaFe _12- Ti _x O _{19 is} carried out for less than 5 hours, then there is a high probability that the required phase of barium hexaferrite BaFe ₁₂ O ₁₉ will not be obtained, but if the material is sintered for more than 5 hours, there will be no significant changes . Thus, sintering titanium-substituted barium hexaferrite should be carried out for at least 5 hours. The choice of time and temperature of sintering is due to the fact that in this mode the final ferritization of the material occurs. At a lower sintering temperature and the same holding time, incomplete ferritization takes place in the material and the Fe ₂ O ₃ phase is present. If the temperature is increased, for example, to 1400°C, there are signs of melting in the material, which negatively affects the performance.

The temperature of 1200°C of the first stage is chosen for pre-sintering, which allows the removal of volatile compounds from the sample, as well as the initial stage of ferritization. If the temperature is chosen below 1200°, ferritization for titanium-substituted barium hexaferrite will not proceed, which may further affect the homogeneity of the material. A temperature above 1200°C will make it possible to carry out ferritization faster, but due to the uneven distribution of components at the first stage, foci of the reacted mixture and depleted areas may appear, in which the initial components of iron oxides, titanium and barium carbonate will be present.

Since the solid phase reaction is slow, a sintering time of 5 hours was chosen. An increase in time increases the wear of the heaters, but does not entail a visible change in the characteristics in the samples. Reducing the sintering time will not allow the initial components to react sufficiently to start ferritization.

After the first stage of sintering, intermediate grinding follows, which maximizes the homogeneity of the material, minimizes porosity, which entails an increase in density and an improvement in the structure of the final material after pressing and the completion of the second stage of sintering. Grinding for 1 hour allows you to get the optimal particle size suitable for further pressing. Reducing the time entails the coarsening of the particles and the difficulty of the transition to the stage of pressing, where cracking of the pressed sample is possible. Increasing the grinding time leads to the production of finer powder particles, which has a beneficial effect on further pressing, but increases the time of its production.

Example 1

Oxides Fe ₂ O ₃ (OSCh) and TiO ₂ (OSCh) of high purity and carbonate BaCO ₃ (OSCh) are used to prepare doped BaFe _11.5 Ti _0.5 O ₁₉ samples by the solid-phase synthesis method.

Calculations of the masses of the constituent components of the samples and the formation of weights should be carried out in accordance with the stoichiometric ratio of the general reaction equation:

Stoichiometrically mixed powders 0.1708 wt. % BaCO ₃ , 0.7947 wt. % Fe ₂ O ₃ , 0.0346 wt. % TiO ₂ , subjected to dry grinding in a ball mill for 3 hours. After grinding, the initial powder mixtures were pressed on a hydraulic press in a cylindrical shape (diameter 12 mm, height 10 mm). Compositions pressed under a pressure of 60–80 kg/mm ² were subjected to synthesizing firing in air in 2 stages: at the 1st stage, heating was carried out to 1200° in a tubular furnace with silicon carbide heaters for 5 hours and cooled at a rate of ~100°C /h, then the material was crushed for 1 hour using a ball mill, re-pressed under a pressure of 60-80kg/mm ² and fired in a tube furnace with silicon carbide heaters at 1350° for 5 hours and cooled at a rate of ~100°C/h .

In FIG. 1 shows a graph of the modulus of the complex reflection coefficient of a layer substituted with titanium barium hexaferrite - BaFe _11.5 Ti _0.5 O ₁₉ on the frequency of electromagnetic radiation.

Example 2

High purity Fe ₂ O ₃ (OSCh) and TiO ₂ (OSCh) oxides and BaCO ₃ carbonate (OSCh) are used to prepare a doped BaFe ₁₁ TiO ₁₉ sample by solid phase synthesis. Calculations of the masses of the constituent components of the samples and the formation of weights should be carried out in accordance with the stoichiometric ratio of the general reaction equation:

Stoichiometrically mixed powders 0.1708 wt. % BaCO ₃ , 0.7601 wt. % Fe ₂ O ₃ , 0.0691 wt. % TiO ₂ , subjected to dry grinding in a ball mill for 3 hours. After grinding, the initial powder mixtures were pressed on a hydraulic press in a cylindrical shape (diameter 12 mm, height 10 mm). Compositions pressed under a pressure of 60–80 kg/mm ² were subjected to synthesizing firing in air in 2 stages: at the 1st stage, heating was carried out to 1200° in a tubular furnace with silicon carbide heaters for 5 hours and cooled at a rate of ~100°C /h, then the material was crushed for 1 hour using a ball mill, re-pressed under a pressure of 60-80 kg/mm ² and fired in a tubular furnace with silicon carbide heaters at 1350° for 5 hours and cooled at a rate of ~100°C/ h.

In FIG. 2 shows a plot of the modulus of the complex reflectance of the BaFe ₁₁ TiO ₁₉ layer as a function of the electromagnetic radiation frequency.

Example 3

High-purity Fe ₂ O ₃ (OSCh) and TiO ₂ (OSCh) oxides and BaCO ₃ carbonate (OSCh) are used to prepare doped BaFe ₁₀ Ti ₂ O ₁₉ samples by the solid-phase synthesis method. Calculations of the masses of the constituent components of the samples and the formation of weights should be carried out in accordance with the stoichiometric ratio of the general reaction equation:

Stoichiometrically mixed powders 0.1708 wt. % BaCO ₃ , 0.6910 wt. % Fe ₂ O ₃ , 0.1382 wt. % TiO ₂ , subjected to dry grinding in a ball mill for 3 hours. After grinding, the initial powder mixtures were pressed on a hydraulic press in a cylindrical shape (diameter 12 mm, height 10 mm). Compositions pressed under a pressure of 60–80 kg/mm ² were subjected to synthesizing firing in air in 2 stages: at the 1st stage, heating was carried out to 1200° in a tubular furnace with silicon carbide heaters for 5 hours and cooled at a rate of ~100°C /h, then the material was crushed for 1 hour using a ball mill, re-pressed under a pressure of 60-80 kg/mm ² and fired in a tubular furnace with silicon carbide heaters at 1350° for 5 hours and cooled at a rate of ~100°C/ h.

In FIG. 3 shows a plot of the modulus of the complex reflection coefficient of the BaFe ₁₀ Ti ₂ O ₁₉ layer as a function of the electromagnetic radiation frequency.

On FIG. 1-3 show the reflectance spectra of the layers for BaFe _11.5 Ti _0.5 O ₁₉ , BaFe ₁₁ TiO ₁₉ and BaFe ₁₀ Ti ₂ O _{19 ,} respectively, calculated for normal incidence and several thicknesses of deposited powders. As can be seen from FIG. 1, for the BaFe _11.5 Ti _0.5 O ₁₉ composition, the absorption is very sensitive to the thickness of the powder layer of titanium-substituted barium hexaferrite (meaning the thickness of the powder layer in the measurement cell). Indeed, for layer thicknesses of 8 and 10 mm, a broad absorption of >15 dB in magnitude was found. Relative to a thickness of 9 mm, two sharp and strong absorption peaks of ~40 and ~28 dB in magnitude are observed at 9.25 and 10.25 GHz, respectively. The absorption maximum appeared at a frequency of 9.25 GHz, since in this case the layer thickness is well related to a quarter wavelength. The second minimum at 10.25 GHz is caused by the interaction of input and secondary reflected waves. For BaFe ₁₁ TiO ₁₉ , as shown in FIG. 2 for the same thicknesses, the reflection spectra are obviously different, and in the considered frequency range they contain only one shallow band at the level of -(12-14) dB. For absorption bands, the position of the maximum strongly depends on the layer thickness. For comparison, in the case of BaFe ₁₀ Ti ₂ O ₁₉ , Fig. 3, the calculations were carried out for relatively thin layers. It can be seen that a reflection below 15 dB can be achieved in a wide frequency range of 8.25–9 GHz in a 2 mm thick layer. The strong minimum at 8.35 GHz appears due to a thickness equal to a quarter wavelength. The other two sharp minima are determined by the interaction of the input wave with the second and third reflected waves. Thus, the absorption properties of the BaFe _12-x Ti _x O ₁₉ layers can be greatly modified by appropriate selection of the ferrite composition and layer thickness.

Substitution of a part of the iron ions with such an alloying element as titanium, in contrast to the prototype method (sintering in 2 stages at different temperatures without adding boron oxide), makes it possible to obtain a single-phase material (i.e., the material contains a phase of barium hexaferrite BaFe ₁₂ O ₁₉ , but there is titanium in the elemental composition, which affects the final properties.) and to modify the properties - to vary the values of the permittivity and magnetic susceptibility, which is proved by Fig. 1-4, as well as reduce the time and cost of obtaining the final material.

On FIG. Figure 4 shows the dependence of the real part of the permittivity on the frequency of the electric field radiation for titanium-substituted barium hexaferrites BaFe _11.5 Ti _0.5 O ₁₉ , BaFe ₁₁ TiO ₁₉ , BaFe ₁₀ Ti ₂ O ₁₉ compared with pure BaFe ₁₂ O ₁₉ hexaferrite. Studies have shown that an increase in the content of Ti causes an increase in the dielectric constant up to 6.2 at x=0.5-1 and up to 10.5 at x=2.

As a rule, alloying BaFe ₁₂ O ₁₉ with titanium greatly increases the dielectric loss tangent, and, accordingly, barium hexaferrite BaFe _12-x Ti _x O ₁₉ substituted with titanium can be used to create effective absorbing layers that absorb electromagnetic waves in the microwave range. The absorbing properties of said material layers can be optimized for a selected frequency range by varying its composition and thickness. In addition, BaFe _12-x Ti _x O ₁₉ ferrites can be used as absorption elements in microwave devices such as phase shifters, power dividers and attenuators.

Claims (1)

A method of obtaining titanium-substituted barium hexaferrite in the form of a sintered powder by solid-phase synthesis from powders of two oxides, including Fe ₂ O ₃ oxide, and BaCO ₃ carbonate, taken in a stoichiometric ratio, in which the mixed powders are subjected to homogenizing grinding, after which the mixture of powders is pressed and subjected to synthesizing roasting in air before sintering in two stages with intermediate grinding, and then slowly cooled, characterized in that substituted barium hexaferrite BaFe _12-x Ti _x O _{19 is} synthesized, where x=0.25÷2.0, as _{TiO 2 is} used for the second oxide, grinding is carried out in dry form for three hours, pressed under a pressure of 60-80 kg / mm ² , firing at the first stage is carried out at a temperature of 1200 ° C for 5 hours, firing at the second stage is carried out at a temperature of 1350 °C for 5 hours with intermediate grinding for 1 hour.

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