Vol 64, No 13 (2019)

Selection of wasteform materials for higher activity nuclear waste containment is considered. Utilization of materials such as glasses, ceramics, glass composite materials and cements is discussed as practiced in different countries. Emphasis is on multiple parameter approach on selecting the wasteform where the durability is not solely the most important characteristic.

The paper is a review of the recent developments in the field of creation and application of new promising composites of ionic liquids with inorganic oxide nanomaterials. The combination of properties of inorganic materials—high thermal stability, chemical inertness, different combinations of dielectric properties and low-temperature melts of organic electrolytes that are characterized, in addition to high ionic conductivity, by low vapor pressure, high thermal stability, solvation ability—is the basis for developing new types of functional materials. The paper considers two types of nanocomposites: physical mixtures—ionic liquids thickened with inorganic oxide fillers and systems formed by porous oxide materials and ionic liquids, in which the ionic liquids can be included into the nanocavities of the inorganic materials. It also describes the methods of synthesizing composite materials of different types. They include methods of direct mixing, sol-gel synthesis of hybrid organo-inorganic mesostructures and inclusion into the inter-layer spaces of natural layered alumosilicates. The paper also discusses mutual effects of ionic liquids and inorganic oxides as well as the role of confinement of an organic electrolyte in the pores of inorganic materials on the formation of new structures, thermal and transport properties of the composites. Possible application areas of the new types of nanocomposites are electrochemical devices (lithium chemical sources of electrical energy, supercapacitors, sensors), environment protection (ion-exchangers, adsorbents of organic pollutants), biomedicine (antibacterial coatings, surface modifiers, gels), functionalized polymer films, plastics.

Graphite, the most stable carbon allotrope, is widely used for various applications due to its interesting properties. In the present work, graphite surface has been partially oxidized by concentrated hydrochloric acid (37%); then, the graphite oxide surface has been modified by a low-temperature method using sulfur and cobalt atoms to obtain a Co–S–GC catalyst. The current density passing through Co–S–GC catalyst has been higher than that passing through graphite. The novel cobalt-based catalyst has been demonstrated good performance for oxygen reduction reaction (ORR) due to the unique bio-inspired structure. The number of electrons transferred for ORR vary from 2.17 to 2.41 in a wide range of over-potentials indicating an effective 2-electron pathway form O₂ to H₂O₂. The Tafel slope (≈30 mV dec^–1) indicates significant amount of cobalt oxide on the surface of the catalyst. The catalyst durability test displays a negative shift of only 11.7 mV after 10 000 cycles for its half-wave potential (E_1/2).

Samples of an ultra-high-temperature HfB₂–30 vol % SiC ceramic material with an SiC crystallite size of ~50 nm have been fabricated by hot pressing of an HfB₂–(SiO₂–C) composite powder synthesized through a sol–gel route. It has been found that the selected hot-pressing conditions (1800°C, 15 min, 30 MPa) ensure complete conversion of silica to silicon carbide and afford a material with a relative density of 96.9%. The effect of a relief applied to the sample surface in the form of ring grooves with a depth of <0.5 mm on the oxidation of the material exposed to a subsonic dissociated air flow—temperature distribution over the surface, elemental and phase composition, and microstructure—has been studied using a high-frequency induction plasmatron.