ФОРМИРОВАНИЕ ЭЛЕКТРОПРОВОДЯЩИХ КОМПОЗИТОВ С СЕГРЕГИРОВАННОЙ СТРУКТУРОЙ С ИСПОЛЬЗОВАНИЕМ НАНОРАЗМЕРНЫХ УГЛЕРОДНЫХ ДОБАВОК

УДК 678.7:621.86.064

Abstract

The paper presents the development of a method for producing electrically conductive polymer composites with a segregated structure containing nanoscale carbon fillers. Phenol-formaldehyde resins were used as the matrix, while carbon materials of various morphologies and dispersities-including graphite, carbon black, coke, and carbon nanotubes-served as the conductive phase.

A two-stage method for combining the components is proposed, ensuring the formation of a conductive network primarily along the boundaries of the matrix structural elements during subsequent direct pressing. A morphological analysis of carbon fillers was carried out using scanning electron microscopy, which made it possible to determine the influence of particle shape and size on the mechanism of conductive channel formation.

It is shown that the combination of macrodispersed graphite particles and nanoscale carbon structures promotes the formation of stable conductive “bridges,” reduces contact resistance, and improves the tribological characteristics of the material. The developed experimental composite formulations are recommended for use in current-collecting units and electrical engineering systems operating under dynamic electrical contact conditions.

Аннотация

В работе представлена разработка метода формирования электропроводящих полимерных композитов с сегрегированной структурой, содержащих наноразмерный углеродный наполнитель. В качестве матрицы использованы фенолформальдегидные смолы, а в качестве проводящей фазы — углеродные материалы различной морфологии и дисперсности, включая графиты, технический углерод, кокс и углеродные нанотрубки. Предложен двухстадийный способ совмещения компонентов, обеспечивающий формирование проводящей сети преимущественно по границам структурных элементов матрицы при последующем прямом прессовании.

Проведен морфологический анализ углеродных наполнителей методом растровой электронной микроскопии, позволивший установить влияние формы и размерности частиц на механизм формирования токопроводящих каналов. Показано, что сочетание макродисперсных графитовых частиц и наноразмерных углеродных структур способствует образованию устойчивых проводящих «мостиков», снижению контактного сопротивления и улучшению триботехнических характеристик материала.

Разработанные экспериментальные составы композитов рекомендованы для применения в узлах токосъема и электротехнических системах, работающих в условиях динамического электрического контакта.

Keywords: electrically conductive composites; segregated structure; carbon fillers; graphite; carbon black; coke; carbon nanotubes; contact resistance; volume electrical resistivity; tribological properties; electroerosion wear.

Ключевые слова: электропроводящие композиты; сегрегированная структура; углеродные наполнители; графит; технический углерод; кокс; углеродные нанотрубки; контактное сопротивление; объемное электрическое сопротивление; триботехнические свойства; электроэрозионный износ.

Introduction

Scientific and applied research in the field of electrically conductive contact materials is focused on developing fundamental understanding of the mechanisms and patterns of current flow under dynamic contact conditions. Increased requirements for reliability and service life of current-collecting units in power equipment, railway transport, and urban electric transport necessitate the development of new materials with improved electrophysical and tribological characteristics.

Moving contact interfaces are among the least reliable elements of electrical systems and largely determine their operational reliability and economic efficiency. During operation, the materials of the contact pair are subjected to a complex combination of electrical and mechanical factors. According to [1, 2], a significant proportion of failures in railway current collectors is associated with the wear of contact inserts.

During service, contact pair materials undergo both electroerosion and mechanical wear. Electroerosion damage is caused by sparking and arc discharges that occur when contact stability is disrupted. Mechanical wear results from friction between the contact insert and the contact wire. As shown in [3], mechanical damage to the surface of contact inserts leads to a reduction in the actual contact area, causing a local increase in current density and overheating of the contact zone. This, in turn, intensifies electroerosion processes and accelerates material degradation.

Under modern conditions, the problem of replacing traditional copper-containing contact materials has become particularly relevant due to stricter environmental regulations in the European Union and the United States. Restrictions on the use of heavy metals stimulate the development of alternative materials based on polymer composites with carbon fillers. A promising direction is the development of electrically conductive composites with a segregated structure. In such materials, the conductive phase is predominantly distributed along the boundaries of the structural elements of the polymer matrix, forming a continuous conductive network at relatively low filler concentrations. This approach makes it possible to simultaneously increase electrical conductivity, reduce contact resistance, and improve wear resistance.

Theoretical and technological foundations for producing filled polymer composites are discussed in detail in [4-7], emphasizing the decisive role of the mixing stage in the formation of material structure and properties.

The aim of this work is to develop a method for producing electrically conductive composites with a segregated structure containing nanoscale carbon fillers, as well as to obtain experimental material compositions intended for use in mechanical engineering and current-collecting units.

Materials and Methods

Phenol-formaldehyde resins (PFR) and their compositions were used as the polymer matrix. The choice of this type of binder is обусловлен its high thermal resistance, mechanical strength, and stability under electrical loads.

Carbon fillers of various nature, morphology, and dispersity were used: pencil graphite grade GK-1 (GOST 4404-78); pencil graphite grade GK-3 (GOST 4404-78); crucible graphite grade GT-2 (GOST 4596-75); colloidal graphite preparation S-1 (TU 113-08-48-63-90); crystalline foundry graphite grade GL-1 (GOST 5279-74); carbon black (soot) (GOST 7885-86); graphite for electrocarbon products grade EUT-2 (GOST 10274-79); elemental graphite grade GE-1 (GOST 7478-75); coke (GOST 2669-81); carbon nanotubes OCSiAl (TU 20.13.21-001-91735575-2023).

The key stage in composite fabrication is the mixing of components. The formation of a segregated structure was carried out in two stages. At the first stage, the surface of macroscopic filler particles was saturated with nanoscale and highly dispersed additives using a vertical high-speed mixer under high shear rates. This ensured the adsorption of nanosized particles onto the surface of larger fractions and created the prerequisites for the formation of conductive “bridges.”

At the second stage, the composite material was further processed in a twin-blade mixer at low shear rates, which made it possible to preserve the formed spatial organization of the conductive phase. Sample molding was performed by direct pressing. This method is effective for producing segregated-type composites, as it minimizes the redistribution of the filler within the material during processing.

The morphology of carbon filler particles was studied using scanning electron microscopy (SEM) on a VEGA II LSH scanning electron microscope.

Results and Discussion

To study the influence of particle shape and size on the performance characteristics of polymer composites, SEM images of the selected carbon fillers were obtained using electron microscopy methods. The study of carbon filler particles was carried out using a VEGA II LSH scanning electron microscope.

Figure 1 shows SEM images of various types of carbon fillers at a magnification corresponding to 200 μm.

Figure 1. SEM images of carbon fillers of various types at a magnification of 200 μm: (a) graphite grade GK-1; (b) graphite grade GK-3; (c) graphite grade GT-2; (d) colloidal graphite preparation S-1; (e) graphite grade GL-1; (f) carbon black (soot); (g) graphite grade EUT-2; (h) graphite grade GE-1; (i) coke; (j) carbon nanotubes OCSiAl.

The microstructural analysis (Figure 1) showed that the studied carbon fillers differ significantly in particle shape and size. Graphite materials are characterized by a lamellar structure with pronounced anisotropy. The colloidal graphite preparation and carbon black exhibit a highly developed aggregated structure with a large specific surface area. Coke is represented by larger and more irregular particles. Carbon nanotubes possess a fibrous nanoscale morphology with a high aspect ratio.

The identified differences have a significant impact on the formation of a conductive network within the polymer matrix. Plate-like particles contribute to the formation of planar conductive contacts, whereas nanoscale fibrous structures provide spatial reinforcement and the formation of a branched conductive network.

The use of nanoscale carbon fillers makes it possible to implement a segregated distribution mechanism of the conductive phase. As a result, conductive elements are concentrated mainly along the boundaries of polymer particles, forming stable conductive channels at a lower overall filler content.

The proposed approach is also aimed at reducing the difference between the coefficients of static and dynamic friction. Minimizing this difference reduces the stick-slip behavior during friction, lowers the likelihood of sparking, and contributes to the stabilization of contact resistance.

Thus, the results of the morphological analysis confirm the feasibility of using complex carbon systems that include both macrodispersed graphite fillers and nanoscale carbon structures.

Conclusion

A method for producing electrically conductive polymer composites with a segregated structure has been developed, based on a two-stage combination of macro- and nanoscale carbon fillers followed by direct pressing. The conducted studies have shown that the morphology and dispersity of carbon fillers have a decisive influence on the formation of the conductive network and, consequently, on the electrophysical properties of the composite. The use of nanoscale carbon structures enables the formation of stable conductive “bridges” along the boundaries of matrix structural elements, which ensures increased electrical conductivity, reduced contact resistance, and improved tribological properties of the material.

The developed experimental formulations of electrically conductive composites can be recommended for use in current-collecting units, electric transport systems, and other mechanical engineering components operating under dynamic electrical contact conditions. Further research will focus on the quantitative evaluation of volume electrical resistivity, analysis of friction films after tribological testing, and optimization of composite compositions taking into account operational requirements.

References:

1. Characteristics of the Sliding Electric Contact of Pantograph/Contact Wire Systems in Electric Railways / Guangning Wu, Jie Wu, Wenfu Wei, Gao Guoqiang // Energies. – 2017. -  11(1):17, DOI: 10.3390/en11010017
2. Tokosemnye vstavki dlya tokopriemnikov zheleznodorozhnogo transporta / I. S. Gershman, N. V. Mironos, M. A. Melnik, E. I. Gershman // Vestnik Nauchno-issledovatelskogo instituta zheleznodorozhnogo transporta. – 2012. – № 4. – S. 3–10.
3. Li V. N. Opredelenie kachestva izgotovleniya ugolnyh vstavok tokopriemnikov / V. N. Li, E. V. Matycyn // Elektrifikaciya transporta. – 2012. – № 3. – S. 71–73.
4. Metallopolimernye materialy i izdeliya / Belyj V. A., Egorenkov N. I., Koreckaya L. S. i dr. / pod red. V.A. Belogo. – M.: Himiya. – 1979. – 312 s.
5. Tehnicheskie svojstva polimernyh materialov: Ucheb.-sprav. posobie / V.K. Kryzhanovskij, V.V. Burlov, A.D. Panimatchenko, Yu.V. Kryzhanovskaya. – SPb.: Professiya. – 2007. – 240 s.
6. Abed Nodira, Malohat Tukhtasheva, Sayibjan Negmatov, Tulyaganova Vasila, Komila Negmatova, Shuhrat Bozorboyev, & Djabarov Bekzod (2025). Study on the impact of mineral, fibrous, and carbon-graphite fillers on the physical and mechanical properties of composite friction resistant polymer materials. Universum: технические науки, 9 (6 (135)), 33-39. doi: 10.32743/UniTech.2025.135.6.20461
7. Negmatov Sayibjan, Abed Nodira, Djabarov Bekzod, & Bozorboyev Shuxrat (2024). Influence of organomineral fillers content on electrical-physical properties of developed composite polymer materials. Universum: технические науки, 12 (11 (128)), 41-45. doi: 10.32743/UniTech.2024.128.11.18494.