To improve further the designs and ensure the stable operation of vacuum electronic devices that function in the ultra-high frequency (UHF) range at 1–100 GHz, the characteristics of microwave radiation absorption have been enhanced. We addressed the highly complex task of producing bulk absorbers made from AlN–Mo composites with a high attenuation level of 10–12.3 dB, which corresponds to a microwave radiation absorption coefficient of 37–56 dB/cm. They achieved a good low voltage standing wave ratio (VSWR) value of 1.5–1.6 in the frequency range of 9.3–10 GHz. The study found that chemical treatment of the absorber’s surface, which involves removing molybdenum particles using an acid mixture, improves matching by reducing microwave radiation reflection values, consequently decreasing the VSWR peak by 26–30

Dielectric matrix ceramic composites based on high thermal conductivity AlN are important for engineering of new electronic devices with lower operation temperature. Composites of AlN dielectric matrix with electroconductive inclusions of TiB2 have been prepared and investigated with the aim to establish their electrical resistivity for possible applications. The ceramic composites AlN–hBN–TiB2 have been prepared by hot pressing (T=1950 °С, P=30 MPa) with TiB2 content from 45 to 66 wt.%. The four-probe electrical resistivity measurements of as-obtained specimen at room temperature showed correspondingly values between 1.0•10–5 and 0.2•10–5 Ohm•m. The observed relatively small decrease of electrical resistivity of the hot-pressed AlN–hBN–TiB2 system composite for increasing conductive phase content by 21 wt.%, and when conductive phase content is higher than a percolation threshold may testify in favor of a tunnel character of charge transfer, discussed in [1]. Addition of hBN under mixing of the starting powder system may form an additional dielectric layer at the surface of the conductive particles (TiB2). Thus a tunnel mechanism of charge transfer in the hot-pressedAlN–hBN–TiB2 ceramic composites may dominate in a wide region of concentrations including the percolation threshold.

Epoxy resin polymer composites with improved mechanical and thermophysical properties have been developed. To improve the material characteristics, an ultradisperse diamond and a multifunctional discrete fibrous (polyester–viscose–elastane) filler are added to the epoxy oligomer. The following properties of the composites are studied: hardness, residual stress, and thermal coefficients of linear expansion. It is established that the optimal concentration is in the range of q = 0.02–0.03 wt

The results of studying the thermal conductivity of hot-pressed AlB12–AlN ceramic composites with different AlN concentrations were presented. The thermal conductivity coefficient was measured for composite specimens at room temperature and approximated for AlB12.

The article presents the results of a study on the thermal conductivity of ceramic cutting materials produced from exothermic mixtures of Cr2O3 with AlN and ZrO2(M)–Al–C via hot pressing. The characteristics of the resulting materials were compared with those of commercial cutting ceramics Al2O3–TiC grade CC650 (Sandvik Coromant, Sweden).

We determined the thermal conductivity of the dense structure of reaction-sintered silicon carbide, a ceramic material obtained by impregnating the SiC framework with silicon, followed by liquid-phase carbidization. The resulting SiC material has a thermal conductivity of 177 W/(m K), which is 36% of the theoretical value.

Different additives' influence on electric conductivity of 'dielectric/conductor'-type composites (namely, polycrystalline c BN-based composites contained c BN as a dielectric phase and NbN as a conductor phase) is investigated. Investigated samples are obtained by the application of HPHT (high pressure-high temperature) sintering ( P = 7.7 GPa, T = 2000 degrees C). Electrical-resistance dependences on the temperature and applied voltage are measured for all samples. Obtained results' analysis shows that all sintered samples have a semiconductor nature of conductivity. It is interesting that addition dielectrics (Al 2 O 3 , Si 3 N 4 ) as well as semiconductor (SiC) leads to the electric-conductivity improve (drop in electrical resistance) for c BN-NbN composites in some degree (despite the lower electrical conductivity of these substances). Alumina whiskers' addition to c BN-NbN composites leads to a more significant drop in electrical resistance compared to powder particles' addition (from 1.85 to 0.72 Ohm center dot cm for samples with whiskers (Al 2 O 3 w) and from 1.35 to 0.17 Ohm center dot cm for samples with Al 2 O 3 powder). Hence, as con cluded, the sample electrical conductivity is affected by both the additive particles' morphology and the grain boundaries' state of the sintered poly- crystalline ceramics.

We present the results of the study of the microstructure of a ceramic composite based on aluminum nitride with different concentrations of yttrium oxide, synthesized by pressureless sintering. The thermal conductivity of the obtained materials was investigated, and the optimal amount of yttrium oxide in the composition for sintering large-sized parts used in electrotechnical devices was determined.

The application of ceramic dielectrics in various microwave electronic instruments and devices is determined by their properties such as dielectric constant, dielectric loss factor, thermal conductivity, and absorptance. Alumina nitride composites with dielectric losses (high dielectric loss tangent tgδ varying from 0.1 to 0.6) are promising functional materials, but there are few publications with detailed dielectric characteristics including thermal conductivity, which is especially important for devices with high output power. To determine the dielectric characteristics (ε′ and tgδ), the resonance measurement method with a cylindrical resonator was employed. The electromagnetic energy absorptance L (attenuation in a bulk absorber with respect to absorber length) was used to compare absorbers of different sizes. Microwave attenuation in the absorber ring located in a resonator of the delay line of the traveling-wave tube model was measured employing a P2-61 panoramic meter for voltage standing wave ratio and attenuation. Experimental values of the real and imaginary ε′′ parts of the complex dielectric constant in pressureless-sintered AlN–SiC composites with different contents and sizes of semiconducting silicon carbide particles are presented. When SiC increases from 20 to 50% in the AlN-based composite, ε′ becomes 1.7–2.1 times higher and ε′′ 5.4–6.8 times higher. The smaller the SiC particles, the greater the increase in ε′ and ε′′, silicon carbide content being the same. The relationship between the thermal conductivity and electromagnetic energy absorptance in the AlN–SiC composites was studied. The range of compromise values was found: they combine relatively high thermal conductivity, 45–55 W/(m · K), and significant absorptance, L = 2.8–3.5 dB/mm, corresponding to the highest silicon carbide content (40–50%) and microsized SiC particles (2.3–4.4 μm). A relationship was established between the imaginarabsorptance L(dB/mm) $$ =\sqrt[2]{2.8{\upvarepsilon}^{\prime \prime }} $$ , allowing the absorptance to be determined from known ε′′ at a frequency of 3.3 GHz.

High-power microwave electrovacuum devices require bulk absorbers with a high absorption rate of microwave radiation. The absorption of microwave radiation by AlN–SiC composites is studied for their possible application, and it is found that high absorption rates can be achieved in the AlN–50 wt % SiC composite owing to the presence of micrometer and submicrometer SiC particles that provide complex and repeated absorption of microwave radiation. Absorption rate L is 4.6 dB/mm for disks with dimesions of ∅4.2 × 1.0 mm and 6.6 dB/mm for rings with sizes of ∅4.2 (external) × ∅1.9 (internal) × 1.0 mm. It is proposed to compare dielectric losses of the composites through the directly measured absorption rate of microwave radiation in real operating conditions of the bulk absorber in the microwave device, rather than through the value of dielectric losses ɛ'' or tan δ. The relationship between the quality factor, attenuation, and absorption of radiation is determined. It is shown that ɛ' and ɛ'' are frequency-dependent values in the frequency range of 1–40 GHz, but their ratio ɛ''/ɛ' = tan δ is a constant frequency-independent value at frequencies greater than 8 GHz. In the studied composite, the measured values of the real and imaginary parts of the complex permittivity are ɛ' = 32 and ɛ'' = 7 at a frequency of 3.3 GHz, and the calculated values are ɛ' = 19.3 and ɛ'' = 6.2 at a frequency of 34 GHz.

Electrophysical characteristics (electrical resistance and activation energy) of the aluminum nitride–titanium nitride ceramic composite are determined in the temperature range of 27–215°C.

The electrophysical properties of an islet gold film on the surface of cubic boron nitride are considered. The calculated electrical resistance values are compared with the resistance of similar films on dielectrics with different heat conductivities (glass, sapphire, aluminum nitride).

In a system of dielectric matrix–conducting particles, the dielectric characteristics are analyzed over a wide frequency range (3–37 GHz). Experimental values of the dielectric constant ε ′ and dielectric loss tangent tan δ are presented for pressureless sintered AlN-based composites with different contents of the conducting particles (Mo, W, and TiN) within the interval from 0% to the percolation threshold. Both the real ε ′ and imaginary ε ″ parts of the dielectric constant of the investigated composites monotonically increased, reaching maximum values ( ε ′ = 15 – 26.5, ε ″ = 0.14–0.28) when the content of the conductive particles approached the percolation threshold. The dielectric loss tangent of the composites, depending on the conducting particle content, reached values of 0.0085 for AlN–16.6%Mo, 0.0095 for AlN–16%W, and 0.0105 for AlN–20.4%TiN. The dielectric losses ε ″ in the AlN-based composites, as long as they remain nonconductive for the direct current, are low compared to losses of ε ″ = 0.04 in polycrystalline AlN ceramics and exceed them by only 4–7 times. A relationship between the dielectric losses and the level of microwave absorption has been established. The dielectric characteristics, electrical resistance, and thermal conductivity of the produced AlN-based composites and their achievement of a high absorption of the microwave radiation ( L  = 23–32 dB/cm) make these materials promising bulk absorbers in microwave devices (TWTs, klystrons).

У роботі досліджено вплив вмісту поліефірної смоли Norsodyne O 12335 AL у епоксидному олігомері ЕД-20 за показниками теплофізичних властивостей. Проаналізовано динаміку показника термостійкості (за Мартенсом) композиту при збільшенні вмісту поліефірної смоли у епоксидному олігомері до q = 120 мас.ч. та встановлено оптимальний вміст поліефірного зв’язувача. Досліджено зміну показників термічного коефіцієнту лінійного розширення (ТКЛР) епоксиполіефірного композиту у різних температурних діапазонах та лінійну усадку від вмісту поліефірної смоли. Експериментально доведено, що при введенні Norsodyne O 12335 AL у кількості q = 10–20 мас.ч. формується композитний матеріал, який характеризу-ється мінімальними показниками ТКЛР у діапазонах: у області ΔТ = 303–323 К – α =1.610-5 К-1, у області ΔТ = 303–373 К – α =(2.0–2.5)10-5 К-1, у області ΔТ = 303–423 К – α =(3.8–3.9)10-5 К-1, у області ΔТ = 303–473 К – α =(8.8–8.9)10-5 К-1. При цьому показники лінійної усадки зменшуються порівняно з епоксидною матрицею від Δl = 0,32 % до Δl = 0,13–0,14 %. Проаналізовано, що отримані значення ТКЛР, лінійної усадки корелюють із показниками термостійкості (за Мартенсом) та із попередньо дослідженими значеннями фізико-механічних властивостей. Встановлено склад епоксиполіефірної матриці, який у комплексі відрізняється підвищеними показниками теплофізичних властивостей. На основі отриманих результатів розроблено епоксиполіефірну матрицю, яку запропоновано використовувати при формуванні захисних покриттів для елементів засобів транспорту, що експлуатуються в умовах впливу змінних та підвищених температур.

We studied the peculiarities of obtaining the structural organization of a single-layer diamond-galvanic coating for the ruling tool, considering the orientation and anisotropy of diamond grains in the structure of the coating layer and the introduction of fine filler into the coating together with large diamond grains, the particle size of which is two orders of magnitude smaller. Comparison of galvanic nickel bonding, applied by different methods, in terms of orientation and anisotropy of the surface layer confirmed a significant difference in the structure. The peculiarities of diamond-galvanic coating with the introduction of micropowders of silicon carbide and boron are discussed. Using a technological approach, we can affect the structural organization in the working layer of such a single-layer diamond tool and change its properties.

The structure of island gold films on the surface of cubic boron nitride is reported. The average size of islands, the nature of their distribution on the surface, and the average number per surface unit are given.

The significance of application of the polymer composite materials in current technologies has been proven, since they have been demonstrating high performance parameters, offering improved adhesion failure resistance, enhanced mechanical and thermophysical properties which as a consequence enables their application under both ambient and elevated temperatures. The purpose of the current work is to investigate the influence of the phthalimide modifier on the adhesive and physico-mechanical properties of epoxy composite materials and protective coatings based on them. The ED-20 epoxy diane oligomer has been taken as the main component for the binder in the formation of epoxy materials. Polyethylene polyamine hardener has been used for the crosslinking of epoxy compositions. Phthalimide has been taken as a modifier. The molecular formula of the modifier is: C8H5NO2. The molar mass of phthalimide is 147.13 g/mol. It has been proven that with the introduction of the phthalimide modifier in the amount of 2.0 pts.wt. into 100 pts.wt. of ED-20 epoxy oligomer, the material which offers the following properties is being built up: adhesive failure resistance at breaking off - 47.7 MPa, residual stresses - 1.1 MPa. Compared to the parent epoxy matrix, these properties demonstrate an improvement of the adhesive failure resistance at breaking off by 1.9 times, and in addition to the above, the residual stresses are being reduced by 1.3 times. The composite obtained may be reasonably taken in the form of a matrix when building up an adhesive layer for protective coatings. It has been experimentally proven that in order to build up the materials which would offer improved cohesive properties, it is necessary to use a composition of the following makeup: ED-20 epoxy oligomer (100 pts.wt.), polyethylene polyamine hardener (10 pts.wt.), phthalimide modifier (0.25 pts.wt.). Compared to the parent epoxy matrix, the formation of that kind of a material provides an improvement of the following indicators of physical and mechanical properties of composites: bending critical stresses - from 48.0 MPa to 62.1 MPa; impact value - from 7.4 kJ/m2 to 14.7 kJ/m2. Note that the elasticity coefficient of this material is being reduced compared to the parent epoxy matrix from 2.8 GPa to 2.2 GPa. The composite obtained may be reasonably taken in the form of a matrix when building up the surface layer for protective coatings.

Compositions of AlN–Y2O3–Mo and AlN–Y2O3–TiN composite materials with high thermal conductivity have been selected for bulk absorbers of microwave energy in delay systems. The thermal conductivity, electrical resistivity, and electromagnetic absorption of pressureless sintered AlN-based composites with different volume concentrations of conducting Mo and TiN particles are determined.

It was proved, that in order to increase the operational characteristics of parts of river and sea transport, including their physical and mechanical properties, it is advisable to use protective polymer composite coatings. It was shown, that in order to increase the performance of the physical and mechanical properties of the epoxy binder, it is necessary to introduce additives: dispersed and fibrous fillers. It is important to use them in complex. The effect of the modifier and the filler on the adhesive strength and impact strength of the epoxy composite coating has been preliminary analyzed. The critical content of the components in the epoxy oligomer was determined by the method of mathematical planning of the experiment: the modifier is 2, 4-diaminoazobenzene-4’-carboxylic acid (DAABCA) and the synthesized powdery titanium-aluminum charge (PTAC). The introduction of such ingredients into the epoxy binder in the complex allows to increase the adhesion strength and impact strength of a two-layer epoxy composite coating. The results obtained make it possible to create a protective coating with improved adhesion and physical-mechanical properties.

Показано, що полімерні композитні матеріали мають важливе значення в сучасній техніці, позаяк характеризуються високими показниками експлуатаційних параметрів, у тому числі поліпшеною адгезійною міцністю, покращеними механічними і теплофізичними властивостями, що забезпечує можливість їх використання за звичайних та підвищених температур. Як основний компонент для зв’язувача при формуванні епоксидних матеріалів вибрано епоксидний діановий оліґомер марки ЕД-20. Для зшивання епоксидних композицій використано твердник поліетиленполіамін. Як модифікатор використано фталімід. Молекулярна формула модифікатора: C8H5NO2. Молярна маса фталіміду – 147,13 г/моль. Густина – 1,47 г/cм3. Модифікатор розчинний у воді та полярних органічних розчинниках. Доведено, що при введенні модифікатора фталіміду у кількості q = 2,0 мас.ч. на 100 мас.ч. епоксидного олігомера ЕД-20 формується матеріал з наступними властивостями: адгезійна міцність при відриві – sа = 47,7 МПа, залишкові напруження – sз = 1,1 МПа. Це забезпечує підвищення, порівняно з вихідною епоксидною матрицею, показників адгезійної міцності при відриві у 1,9 разів, а залишкові напруження водночас зменшуються у 1,3 рази. Отриманий композит доцільно використовувати у вигляді матриці при формуванні адгезійного шару для захисних покриттів. Експериментально доведено, що для формування матеріалів з поліпшеними когезійними властивостями необхідно використовувати композицію наступного складу: епоксидний олігомер марки ЕД-20 (q = 100 мас.ч.), твердник поліетиленполіамін ПЕПА (q = 10 мас.ч.), модифікатор фталімід (q = 0,25 мас.ч.). Формування такого матеріалу забезпечує порівняно з вихідною епоксидною матрицею підвищення наступних показників фізико-механічних властивостей композитів: руйнівних напружень при згинанні – від σзг = 48,0 МПа до σзг = 62,1 МПа; ударної в’язкості – від W = 7,4 кДж/м2 до W = 14,7 кДж/м2. Зазначимо, що модуль пружності такого матеріалу зменшується порівняно з вихідною епоксидною матрицею від Е = 2,8 ГПа до Е = 2,2 ГПа. Отриманий композит доцільно використовувати у вигляді матриці при формуванні поверхневого шару для захисних покриттів.