Исследование особенностей получения методом шликерного литья пленок гексаферритов для подложек сверхминиатюрных микрополосковых ферритовых развязывающих приборов коротковолновой части миллиметрового диапазона длин волн

Using polyelectrolytes, ecologically safe film elements from hexaferrites have been designed for the first time with water slurry casting instead of existing processes with the use of organic solvent binders. The use of polyelectrolyte substances as binders has made it possible to reduce the energy consumption of drying by 20–30% during the process of film casting.

Исследовано влияние лимонной кислоты и изопропилового спирта на процессы мокрого измельчения смеси исходных ферритобразующих компонентов и синтезированной ферритовой шихты. Установлено, что введение добавок при мокром измельчении позволяет заметно снизить температуры синтеза феррита и спекания сырых заготовок, повысить уровень магнитных свойств постоянных магнитов из бариевых ферритов путем формирования плотной мелкозернистой структуры. Увеличение активности порошков объясняется формированием активных гелеобразных прослоек на поверхности частиц в процессе мокрого измельчения.

The effect of citric acid and isopropyl alcohol on the wet grinding of the mixture of initial ferriteforming components and synthesized ferrite charge has been analyzed. It has been established that the introduction of admixtures during wet grinding makes it possible to substantially reduce the ferrite synthesis temperature and the sintering temperature of green billets and to improve the magnetic properties of permanent magnets made of barium ferrites by the formation of a dense, fine-grained structure. The increase in the activity of powders is explained by the formation of active jelly-like interlayers on the surfaces of particles during wet grinding.

Promising absorbing materials include Ni—Zn ferrites, as they quite intensively absorb electromagnetic waves in the frequency range from 50 to 1000 MHz. The electromagnetic properties of Ni—Zn ferrite absorbing materials obtained by different technological methods were studied in this paper. A model making it possible to evaluate the dielectric permeability of the ferrite material, depending on the microstructure parameters and electrophysical properties of grain boundaries, was proposed. The influence of base composition and microstructure on the amount of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials was determined. It was stated that the increase of the content of excess Fe2O3 to 51.0 mol % leads to the shift of the frequency range of the absorption of electromagnetic radiation towards lower frequencies. It can be explained by the increase of the dielectric and magnetic permeability of ferrite. Moreover, the introduction of an excess of Fe2O3 in the grinding stage of the synthesized burden is more efficient. It was revealed that increasing the sintering temperature to 1350°C also shifts the frequency range of absorption of electromagnetic radiation towards lower frequencies. Probably it is caused by the increase of the dielectric and magnetic permeability of ferrite and the shift of the resonance frequency of domain walls as a result of the formation of a coarse-grained structure.

In this work we have studied the influence of ТiO 2 and Bi 2 O 3 doping admixtures and impurities on the microstructure and properties of radio-absorbing Mg-Zn ferrites. The morphological peculiarities of inclusions of these admixtures in a ferrite ceramics are established. It is shown that the use of doping admixtures and impurities of these oxides makes it possible to control the frequency dependences of the magnetic permeability and dielectric permittivity of Mg-Zn ferrite materials. Examples of controlling the absorption spectra in a radio frequency range through variations in the composition of given radio-absorbing materials are presented.

Study the influence of citric acid and isopropyl alcohol on processes of wet grinding mixture of starting ferrite constituting components and synthesized ferrite charge. Found that the introduction of additives during wet grinding allows to significantly reduce the temperature of synthesis and sintering ferrite raw blanks. Increased activity of powders is explained by the formation of active the gelled layers on the surface of particles in the process of wet grinding.

The effects of the base composition and dopants on the saturation magnetization and coercivity of hexaferrites BaAl x Fe 12– x O 19 , SrAl x Fe 12– x O 19 , BaGa x Fe 12– x O 19 , SrGa x Fe 12– x O 19 , BaSc x Fe 12– x O 19 and SrSc x Fe 12– x O 19 have been studied. Isomorphic substitutions of Al 2 O 3 , Ga 2 O 3 , and Sc 2 O 3 for Fe 2 O 3 in barium and strontium ferrites are found to increase coercivity due to increasing crystallographic anisotropy constant and to reduce the saturation magnetization value. Processes controlling microstructure formation, specifically recrystallization processes, are shown to have a noticeable effect on the level of properties of the ferrites under study with the use of dopants. The most efficient dopants are boron, calcium, and silicon oxides, which provide the formation of relatively fine-grained structures. The increased coercivity upon doping with these dopants is also due to the formation of grain-boundary interlayers of a nonmagnetic glassy phase and the associated efficient retardation of moving domain walls.

In this work there have been carried out studies in the radiophysical characteristics of the samples of Ni–Zn ferrite radio-absorbing materials, obtained by the ceramic method under different technological conditions. There has been established the influence of microstructure on the electromagnetic losses of Ni–Zn ferrite radio-absorbing materials. The results indicate that the coarse-grained structure leads to an increase of radio-absorbing capacity at frequencies below 30MHz. It can be explained by the resonance of domain boundaries.

Two−phase influence on microstructure and property of ferrite of different purpose was investigated. It is shown that fine dispersed component doped at the second step (milling) effectively brakes growth of grains, promoting reception of dense, homogeneous, fine−grained ferrite materials. Thus such properties as initial magnetic permeability, mechanical strength essentially raise and magnetic losses decrease. Change of modes of baking allows to receive coarse−grained homogeneous materials.Influence of two−phase synthesis on a microstructure and property nickel−zinc, manganese−zinc, lithium−titanic ferrite spinels is more below considered discussed.

We analyze the effect of duration of dry crushing of strontium hexaferrite powders (manufactured at joint-stock corporation Olkon) in a vibratory mill on the degree of disaggregation of powders and on the properties of articles on their basis. It is shown that an increase in the vibrational frequency of the vibromill from 25 to 50 Hz with the amplitude of vibrations maintained in the limits 3–4 mm makes it possible to reduce by 5 times the crushing time ensuring complete disaggregation of powders. An increase in the impact energy of balls with increasing vibrational frequency activates the powders due to microdistortions appearing in the crystal lattice. An increase in the degree of disaggregation of powders leads to sintering and formation of a dense fine-grain microstructure ensuring an increase in the maximal energy product (BH)max of magnets by 15–20%.

The possibility of obtaining Mn—Zn-ferrite 2000 NM on the short process flow, which differs from the usual lack of diffusion operations roasting and grinding. It is shown that the use of the basic composition in sintering processes develop secondary recrystallization and zonal isolation, leading to the formation of highly inhomogeneous microstructure obtained with low values of the magnetic permeability. A homogeneous microstructure characteristic recrystallization, managed by doping copper oxide and zinc. By doping CuO permeability far from the desired value, but its temperature coefficient is small. By doping ZnO reached the desired value of magnetic permeability, but dramatically increases its temperature coefficient.The optimum combination of the magnetic parameters obtained in complex copper oxides doped ferrite and zinc.

We have examined the feasibility of obtaining polycrystalline barium hexaferrite with multiferroic properties. It has been shown that doping with boron trioxide ensures the formation of a fine-grained structure with high-resistivity nonmagnetic layers between the grains. Such a structure, in combination with texture, ensures pronounced multiferroic properties after exposure of the barium hexaferrite to an external magnetic field.

The possibility of increasing the coercive force of barium hexaferrite by the isomorphous substitution of iron oxide with alumina, gallium and scandium oxides, and by impurity doping is shown. The results of the synthesis and study of new a ( Me +2 Me +4 ) x Me y + 3 Fe 12– x – y O 19 hexagonal ferrites with thermally stable anisotropy field and coercive force are presented. It is shown that doping with metal vapors of Me +2 Me +4 = Ni +2 Ti +4 , Ni +2 Ge +4 , Ni +2 Cu +2 Ge +4 , Me +3 = Al +3 , Cr +3 allows improvement in the reproducibility of the properties and the thermal stability of barium hexaferrite.

Currently, the global production of permanent magnets is about 150000 tons per annum, in which the share of ceramic magnets made of barium and strontium hexaferrites is more than 90%. Anisotropic hexaferrites have outstanding magnetic properties; in these materials, the texture is formed by pressing in the magnetic field, i.e., the hexagonal axes of flaky powder particles are oriented in the direction of the magnetic field; thus, the magnetic properties in this direction increase and decrease in the other directions. However, in a great number of applications, cheaper isotropic magnets, which have inferior magnetic properties, are successfully used; in these magnets, the magnetic axes of the particles are distributed uniformly in all directions, so magnetic properties are the same in all directions. The well-known technologies for fabricating isotropic magnets do not provide sufficient isotropy of magnetic properties, since the texture, which is due to the orientation of flaky hexaferrite particles, is formed in the process of pressing, which, in turn, reduces the magnetic energy of ring magnets in the radial direction. In this paper, we investigate the possibility of obtaining barium hexaferrite with isotropic properties by using a short manufacturing scheme, which includes no operations of diffusion annealing and grinding. It is shown that such a manufacturing scheme, which involves pressing the mixture (granulated with a binder) of the initial components with the near-spherical shape of particles, makes it possible to improve the isotropic properties of the magnet.

Promising absorbing materials along with Ni−Zn−ferrites are Mg—Zn−ferrites, as they are also intensively absorb electromagnetic waves in the frequency range from 50 MHz to 1000 MHz. The main advantage of the Mg−Zn−ferrite is that it is an inexpensive raw material magnesium oxide. The aim of this work was to study the effect of alloying elements — TiO2 and Bi2O3, — as well as impurities on the microstructure and properties of radar Mg—Zn−ferrite. The influence of alloying elements and impurities on the magnetic and dielectric constant of Mg—Zn−ferrite absorbing materials has been revealed. The addition of bismuth oxide causes a reduction of the permittivity and permeability Mg—Zn−ferrite in the range of up to 1000 MHz. Addition of titanium oxide increases the dielectric constant in the range of up to 1000 MHz, which is important to reduce the wavelength of radar ferrite materials. Addition of titanium oxide leads to a frequency shift of the absorption Mg—Zn−polycrystalline ferrite material towards lower frequencies, and bismuth — towards high frequencies. Thus, the dopant can be regarded as a tool to regulate the wavelength range of the absorption of radar and ferrite materials.

The influence of the modes of wet grinding of the original ferrite-forming components on their activity and the temperature of the synthesis powders of hexaferrites. It is shown that grinding of the initial components in the acidic environment can reduce the synthesis temperature of hexaferrites. The increased activity of the powders during milling in acidic medium due to the formation on the surface of particles of gellike layers of hydroxides of barium or strontium. The activity formed gelled layers to a significant extent can be controlled by introducing surfactants in the wet grinding.