Artem P. Malakho

The paper examines the issues dealing with making and evaluating the properties of synthetic thermal insulation materials based on polymer matrices and glass microspheres. The aim of this study is to clarify the effect of the volume content of spherical single-shell particles on the thermophysical properties of composite materials. The thermophysical properties of a two-component system consisting of epoxy resin and glass microspheres are investigated. The volume fraction of hollow glass microspheres varies from 0 to 70%. The thermal conductivity of the composite is determined experimentally using the hot plate method. The results suggest that the thermal conductivity decreases with increasing microsphere content from 0.53 W/(m K) for pure resin to 0.4 W/(m K) for a composite with 70% volume filling. The thermal conductivity is determined and compared with theoretical predictions based on an anisotropic material model compiled using the effective medium theory approximation. The values of the thermal conductivity of microspheres and epoxy resin are calculated using the experimental graph of the change in the thermal conductivity plotted against the particle content. The results obtained can be used to design composite materials taking into account the specificity of distributed particles.

Graphite foil is widely used as a sealing material in flange joints in the form of gaskets or gasket components. Predicting gasket permeability during stress relaxation remains challenging because both the compression state and the gas pressure affect leakage. No unified semi-empirical model based on the Darcy–Klinkenberg framework with compression pressure as a direct input has been available for use in flange-joint numerical simulations. Graphite foil gaskets with a density of about 1.0 g/cm³ and a thickness of ~1.5 mm were tested under compression pressures from 5 to 100 MPa. Helium leakage was measured at helium pressures from 0.5 to 8 MPa. Leakage and deformation during loading and unloading were recorded using EN 13555-based procedures. The results were analyzed using a Darcy–Klinkenberg formulation and equivalent slit- and capillary-based representations of the leakage channels. The second-order model reproduced the pressure-dependent leakage more accurately than the first-order Darcy approximation (R² ≥ 0.9985 vs. 0.916–0.992), particularly where slip-flow effects were significant. Exponential dependences of the intrinsic permeability and the Klinkenberg coefficient on deformation and power-law relations with compression pressure are proposed to model leakage during unloading. The proposed semi-empirical model allows estimation of graphite-foil permeability under stress relaxation with the use of EN 13555 test procedures and its subsequent implementation in numerical simulations of flange joints. Limits of the model’s applicability, including loading regime, ranges of compression pressure, gas pressure and anisotropic nature of permeability, are discussed.

The application of additive technologies to the manufacture of polymer and composite products is now actively expanding. The FDM printing process is popular because of its ability to adapt to specific tasks and to bring products with complex geometries into production quickly and at minimal cost, and is seen as a technology that can compete with injection molding. However, due to the nature of the process, FDM printed parts are significantly inferior in quality to injection molded parts. Much attention is now being paid to research into supplementary treatment methods to improve the properties of FDM printing parts. However, there is no complete and clear description of such methods, nor are there any recommendations on the choice of treatment methods aimed at improving the specific parts properties. The aim of this review is to analyse the research in the field of post-treatment of parts in order to systematise their advantages and limitations, which will allow a more reasoned choice of a post-treatment method to improve specific properties of FDM printing parts. The bibliography includes 120 references.

Graphite foil (GF) compressed from exfoliated graphite (EG) is a sealing material, which is used in nuclear energy and the chemical industry. The preparation of graphite foil is a complex process, which includes the intercalation of graphite, water washing, thermal exfoliation and pressing of intermediate products. The preparation conditions significantly influence the structure of the material and its physicochemical properties. Thus, the aim of work was to reveal the correlation between GF processing conditions, its crystalline structure, porosity and gas permeability as well as thermal stability. Sealability of the material is connected with low value of gas permeability, while thermal stability allows use of the material in high-temperature processes. Optimization of these parameters allow for the obtaining of a reliable material and expanding of the areas of its application. Exfoliated graphite for GF was prepared at different temperatures of 600, 800 and 1000 °C from the H₂SO₄–graphite intercalation compound (GIC) of II, III, IV stages. The influence of the GF processing conditions (the GIC stage number and the EG preparation temperature) on the main properties (gas permeability and thermal oxidation stability) of the sealing materials was investigated. A decrease in GIC stage number leads to the formation of GF with lower macroporosity and lower nitrogen and hydrogen permeability. However, an increase in GF surface area leads to an increase in the rate of GF oxidation by air oxygen. An increase in the EG preparation temperature from 800 to 1000 ^oC results in the formation of EG with a developed micro- and mesoporosity and increasing GF gas permeability. A decrease in EG preparation temperature down to 600 °C promotes the formation of new transport macropores in GF. The change of the EG preparation temperature has little effect on GF oxidation stability.

The iron-containing graphite foil, micropore graphite material modified by α‑iron (III) oxide, was obtained. The composition of iron-containing phase was investigated by XRD analysis, the morphology of structure of the iron-containing graphite foil was investigated by scanning electron microscopy. The values of hydrogen and nitrogen permeabilities of the modified graphite foil with different content of iron (III) oxide were measured.