Vladimir A. Shulyak

An automatic technological line to produce a three-layer composite material based on a steel base and multigraphene tapes as fillers in spiral-wound gaskets was developed. It has been experimentally shown that multigraphene materials have a pronounced anisotropy of gas permeability due to a layered-porous microstructure. The longitudinal gas permeability of multigraphene materials obtained from intercalated graphite compounds is 20.3·10⁻³ mg/(m·s) for stage II and 22.9·10⁻³ mg/(m·s) for stage IV, while the transverse permeability is significantly lower and amounts to 0.75·10⁻³ mg/(m·s) for stage II and 0.85·10⁻³ mg/(m·s) for stage IV, respectively. The in-plane gas permeability of the composite based on stage II multigraphene is reduced to 5.8·10⁻³ mg/(m·s) due to the barrier effect of the metal tape. The recoverability of the composite increases to 19% with compressibility of 34%. To achieve the tightness class L0.0000001, it is proposed to manufacture spiral-wound gaskets from a three-layer composite based on stage II multigraphene with a fluoropolymer sealing coating. This made it possible to significantly reduce fugitive emissions through the composite gaskets.

This study investigates the influence of the thermal expansion parameters during the production of a multigraphene-based composite gasket on its performance properties. Under laboratory conditions (near-laminar flow), compared with 700 °C, expansion at 1000 °C increased recovery from 7.5 to 9.2% and tensile strength from 3.8 to 5.6 MPa. For continuous industrial-scale production, MGS was pneumatically transported to increase process productivity. At the expansion temperature of 1000 °C, the material obtained under these conditions exhibited lower mechanical performance than that produced in the laboratory-scale process. The transport parameters themselves also had a measurable effect on the resulting properties. At pressures of 0.2 and 0.6 MPa, recovery increased from 8.6 to 9.1%, while tensile strength increased from 3.4 to 3.7 MPa. The highest recovery (10.0%) was obtained at a feed pipe insertion depth of 100 mm within the investigated range of 50–200 mm. Increasing the feed pipe diameter from 8 to 16 mm also improved the mechanical performance, with recovery increasing from 9.0 to 10.4% and tensile strength from 3.7 to 5.4 MPa. The experimental results, supported by thermal and gas-dynamic simulations, show that processing conditions alter the length, tortuosity, and fragmentation of multigraphene structures before compaction, which in turn affects the mechanical performance of the final material. These results establish a link between thermal and gas-dynamic processing conditions and the mechanical properties of CMGMs, providing a basis for optimizing their continuous production for sealing applications.

A measurement setup was developed for leakage determination in flanged joints with diameters up to 654 mm at temperatures ranging from −196 °C to +500 °C and pressures up to 200 bar. The operating principle is based on the differential pressure method, enabling the utilization of both helium and gaseous hydrocarbons as working media. The setup was validated through specific leak rate measurements on standard DN40/PN40 multigraphene gaskets in accordance with EN 13555, showing close agreement with data obtained from the reference Amtec TEMES fl.ai1 test rig. An intrinsically safe architecture combined with strain-gauge monitoring of tightening loads enabled the transition from bench-scale characterization to in situ testing of large-scale gaskets.

We report natural graphite-based multigraphene materials with thermal conductivity enhanced by 20% compared to our previously reported results. The influence of density on the thermal conductivity of these materials was examined. Increasing the density from 1.0 to 1.8 g cm−3 leads to a more than twofold enhancement in thermal conductivity, surpassing the 600 W m−1 K−1 threshold. This result is attributed to a reduction in crystallite misorientation angles to below 15° and a two-order-of-magnitude decrease in defect density from 2 × 10−2 % to 4 × 10−4 %. A multiscale thermal conductivity model for such multigraphene materials was developed, calibrated, and assessed using experimental x-ray diffraction data and electrical conductivity measurements.

The approach and the setup for high thermal conductivity material λ > 300 W × m−1 × K−1 measurement were developed. The method is based on the measurement of established temperature gradients and thermal flows, followed by hardware and software processing. The setup was tested on copper, aluminum, isotropic graphite, and multigraphene materials with different thermal conductivities. Heat distribution and loss computer modeling was done to improve the measurement accuracy. Raw experimental data of multigraphene material with λ ∼ 500 W × m−1 × K−1 thermal conductivity were established to be 2% overestimated due to heat losses. The designed device is shown to provide high thermal conductivity and reliable measurements, complementing the instrumental capabilities of the laser flash assay and HotDisc.

We have developed a technological process for obtaining compacted multi-graphene structures (CMGSs) with the thermal conductivity of 500 W/(m×K). We propose the “Soft” regime of graphite intercalation procedure, which yields conglomerates with alternating stacks of five graphene layers, while the “Standard” regime is characterized by the formation of alternating stacks of three graphene layers. X-ray diffraction analysis and transmission electron microscopy studies of Soft and Standard CMGS have shown that the thermal conductivity of these materials is limited by defect density, size distribution, and misorientation of nanocrystallites. The effect of micro-deformations and residual macro-stresses on thermal conductivity of CMGS is discussed. The Soft method facilitated the formation of CMGSs with a less disrupted internal structure, characterized by increased nanocrystallites and reduced misorientation angles relative to the Standard approach, resulting in a 38% enhancement in thermal conductivity. A refined model is proposed that incorporates these key structural factors governing heat transport in CMGSs. The proposed method made possible the preparation of CMGS-based material with a thermal conductivity 25% higher and with a density five times lower than those of copper. Our findings demonstrate that precise regulation of the intermolecular explosion parameters enables the design of lightweight, flexible carbon-based materials with engineered thermal conductivity characteristics for advanced thermal-management applications.

In this work, the possibilities of introducing nitric acid molecules with a solution concentration of 75–98% into graphite matrices in the form of synthetic quasi-monocrystal graphite and natural graphite of four different farcical compositions were determined in order to identify factors of the acid concentration and graphite size on the production process and properties of graphite foil. The actual stage of graphite intercalation in the resulting compound was determined by X-ray diffraction analysis (XRD). The differences in the temporal patterns of the intercalation process for different intercalation stages (from 2 to 5) are demonstrated. The obtained acid solutions were used in the manufacturing of flexible graphite foil from natural graphite of four different particle size distributions. The mass characteristics of the intermediate and final products were determined as the graphite was treated with these solutions. The actual difference in the characteristics of the raw materials and intermediate synthetic products was recorded by measuring the electrical conductivity of the final material, graphite foil. Analysis of the results has shown that a decrease in the acid concentration of a solution leads to an increase in the intercalation stage. Weight gains due to the formation of oxygen-containing groups and the introduction of water and acid were reduced by this effect, whereas the yield of the final product (thermally expanded graphite) increased. Foil made of thermally expanded graphite obtained from intercalated compounds of high stages had greater electrical conductivity. An improvement in the conductive properties of the material implies that there should be fewer defects in its structure.

In this research paper, the factors impacting electrical conductivity of the flexible graphite foils (GFs) produced by different forming processes, namely, either by rolling or pressing, were studied. The relationship between electrical conductivity and texture and structure that formed when producing the material was examined. Correlation was determined between the texture sharpness and anisotropy of electrical conductivity, as well as the extent of impact from the substructural characteristics on the properties’ values. Besides, it was demonstrated that the higher values of micro-strains, as well as the secondary phase substructure, reduced conductivity in foils. Electrical conductivity calculation was optimized for different directions in foils using the Kearns texture parameters and taking into consideration the foil structural characteristics.

This study investigates the tribological properties of graphite foils (GF) with densities of 1.0, 1.3, and 1.6 g/cm³, produced from purified natural graphite of different particle sizes (40–80 μm, 160–200 μm, >500 μm). Surface roughness was measured after cold rolling and friction testing at static (0.001 mm/s) and dynamic conditions (0.1 Hz and 1 Hz). Results showed that static friction tests yielded similar roughness values (S_a ≈ 0.5–0.7 μm, S_q ≈ 0.5–1.0 μm) across all densities and particle sizes. Dynamic friction tests revealed increased roughness (S_a from 0.7 to 3.5 μm, S_q from 1.0 to 6.0–7.0 μm). Friction coefficients (µ) decreased with higher sliding speeds, ranging from 0.22 to 0.13. GF with 40–80 μm particles had the lowest friction coefficient (µ = 0.13–0.15), while 160–200 μm particles had the highest (µ = 0.15–0.22). Density changes had minimal impact on friction for the 40–80 μm fraction but reduced friction for the 160–200 μm fraction. Young’s modulus increased with density and decreased with particle size, showing values from 127–274 MPa for 40–80 μm, 104–212 MPa for 160–200 μm, and 82–184 MPa for >500 μm. The stress–strain state in the graphite foil samples was simulated under normal and tangential loads. This makes it possible to investigate the effect of the anisotropy of the material on the stress concentration inside the sample, as well as to estimate the elasticity modulus under normal compression. Structural analyses indicated greater plastic deformation in GF with 40–80 μm particles, reducing coherent-scattering region size from 28 nm to 24 nm. GF samples from 160–200 μm and >500 μm fractions showed similar changes, expanding with density increase from 18 nm to 22 nm. Misorientation angles of GF nanocrystallites decreased from 30° to 27° along the rolling direction (RD). The coherent scattering regions of GF with 40–80 μm particles increased, but no significant changes in the coherent scattering regions were observed for the 160–200 μm and >500 μm fractions during dynamic friction tests. Microstrains and residual macrostresses in GF increased with density for all fractions, expanding under higher friction-induced loads. Higher values of both stresses indicate a higher level of accumulated deformation, which appears to be an additional factor affecting the samples during friction testing. This is reflected in the correlation of the results with the roughness and friction coefficient data of the tested samples.