The effects of heat treatment temperature (HTT) of polyacrylonitrile-based carbon fiber (CF) on the mechanical, thermal, and tribological properties of C/C composites were investigated. It was found that HTT (graphitization) of CF affects the thermal conductivity and mechanical and tribological characteristics of C/C composites. Thermal treatment of fibers at temperatures up to 2800°C led to a decrease of the wear rate and the friction coefficient of C/C composite-based discs from 7.0 to 1.1 μm/stop and from 0.356 to 0.269, respectively. The friction surface morphology and friction mechanism strongly depended on the mechanical properties of the CFs. The relief of the friction surface of composites based on CFs with final graphitization was also modified, compared to that of composites based on initial fibers. This phenomenon could be explained by modification of the abrasive wear resistance of reinforcement fibers and consequently modification of the friction and wearing properties of composites. Correlation of the graphitization temperature with the increased flexural and compressive strength, apparent density, and thermal conductivity of the composites was also demonstrated.

The morphology of the quenched and slowly crystallized samples in the ZrO 2 -Al 2 O 3 system is investigated in the composition range 25-70 wt % ZrO 2 . It is revealed that, irrespective of the cooling rate, the samples contain large baddeleyite (or corundum) crystals, eutectic mixtures, and characteristic regions of intergrown elongated baddeleyite and corundum grains with micron sizes. These regions have the same phase composition at any initial ratio between zirconium and aluminum oxides and at any cooling rates of the melt. A hypothesis is put forward that these regions are products of the decomposition of ZrO 2 · 2Al 2 O 3 associates.

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The wettability of carbon fibers from different manufacturers with finish, rinsed of finish, and heat treated at 2000°C by the model liquids water and octane was studied comprehensively. The polar and dispersion components of the carbon-fiber surface free energy were calculated. It was shown that finished fiber had a polar nature whereas removal of the finish could increase or decrease the surface polarity. This could be related to the fiber preparation method. The surface tension of pitch melts was measured and factored into its components. It was shown that the contribution of the polar component to the pitch surface tension was always at least 50% for the studied pitches. The surface tension correlated well with the pitch viscosity but was not related to the softening temperature. Edge wetting angles of the carbon fibers by pitch were calculated based on the experimental results. Fibers for which the contribution of the surface-energy polar component was greater demonstrated better wettability.Carbon fibers (CF) exhibit a unique combination of physicomechanical and chemical properties that comprises high strength and chemical inertness. This enables them to be used for the formulation of composites not only for general purposes but also for aviation and space applications [1,2]. The strength and reliability of such materials in addition to the simple processing procedure for preparing them depend on the nature of the CF-matrix interface interaction. Functionalization of CF, modification of the binder, and other changes can increase the adhesion of the fiber to the matrix and improve the mechanical properties of the composite [3][4][5].Recent investigations established that the affinity of CF for the polymer matrix could be described quantitatively in terms of wetting theory [4][5][6]. Many works on this topic address polymer composites. However, the strength of carbon-carbon composites, including those intended for friction, will obviously also be determined by the CF-matrix interface because penetration of the CF by the polymeric binder, in this instance coal-tar pitch, is a key step in their preparation [1]. Therefore, the goal of the present work was to study the wetting of CF by a coal-tar-pitch melt.We studied CF Panex ® 35 (50K) (Zoltek Inc.) and UK (320K) (Argon Ltd., Balakovo, Russian Federation) with finish, after removal of finish by a solvent, and also after annealing at 2000°C (Table 1).Three types of coal-tar pitch were selected as the binders (Table 2). These were Bx95KS high-temperature pitch and Carbores F112M (Rutgers Basic Aromatics GmbH, Germany) and medium-temperature coal-tar pitch (GOST 10200-83, OAO Enakiev Coke Chemical Plant, Ukraine).The model substances were de-ionized distilled water (γ = 72.8 mN/m, γ D = 21.8 mN/m, γ P = 51.0 mN/m), octane (γ = 21.6 mN/m, γ D = 21.6 mN/m), and Teflon plates (5.0×0.5×0.3 cm 3 , γ = γ D = 19.6 mN/m), where γ is the surface free energy (surface tension) of the substances and γ D and and γ P are its dispersion and polar components.Wetting processes wer...