Vol 57, No 2 (2016)

The working layer of a ladle furnace unit (LFU) lining made from periclase-graphite refractory is most strongly subjected to the effect of corrosion factors that concern thermal, mechanical, and chemical action. The strongest destructive effect on a lining is the chemical factor. This article provides results of studying the effect slag phase composition on chemical breakdown of a LFU periclase-graphite lining.

Results are presented from a study of the service conditions of the lining of electric-arc furnaces and the character of fracture of their lining. New compositions of refractory mortars and mixes were developed along with new lining systems. Extensive factory tests were conducted of new systems that employ high-quality refractory mortars and protective refractory mixes in the lining of the furnace roof. Implementation of the measures that were proposed have made it possible to increase the durability of the lining by a factor in the range 1.4 – 1.6.

Stages of multilayer carbon nanotube formation are studied during mechanical activation of amorphous carbon prepared by pyrolysis from plant raw material. It is shown that prolonged mechanical activation of a carbon composite in a vario-planetary mill (>36 h) leads to formation of aggregates and loss of nanotube thermal stability.

The effect of a fiber filler on properties and phase composition of a ceramic based on a corundum-mullite matrix is studied. It is established that use of a steel fiber for reinforcement during preparation of cordierite ceramic is impossible. It is shown that with use of a mullite-silica fiber within the mix composition for cordierite ceramic preparation it is possible to achieve an increase in material mechanical strength by a factor of 1.2 – 2.0; ceramic LTEC at 800°C is 4.1 × 10–^{6 –} 5.0 × 10^–6 K^–1. It is shown that with introduction of mullite-silica fiber into the ceramic composition the relative amounts of cordierite and mullite increase insignificantly.

Results are presented from tests of the corrosion resistance of fused-cast zircon-bearing and high-chromium refractories in melts of borosilicate and phosphate glasses used to immobilize radioactive waste products (RWP). It is shown that high-chromium refractories Kh-99 and KhPL-85 can be recommended for use in lining the most important sections of the melters employed in RWP vitrification.

Ways of improving the refractoriness of carbon-carbon composite materials due to increasing their density and reducing oxidation rate, and in turn due to reducing the combustion surface, are studied. Oxidation heterogeneous reaction surface in an Arrhenius equation expression is considered as the sum of object outer surface and the reaction surface within pores. It is shown that with an apparent density of 1.93 g/cm³ or more surface oxidation at normal pressure and ~500 °C almost corresponds to the nominal object surface. Processing measures are suggested for improving carbon material refractoriness due to an increase in density and changing surface structure by special high-temperature treatment regimes.

A clinker-less binder that is based on refractory waste products and includes silica, alumina, calcium oxide, and calcium sulfate is obtained. The addition of sulfates to the composition, based on filter cakes and grinding powder, increases the reactivity of the powder’s aluminate component and helps form hydrate compounds. The chemical relationship between the components of the complex binder is explained and the effects of each ingredient and the heat-treatment temperature on the properties of the silicate stone are individually examined.

A technique for the investigation of the stressed state of the boundary between ceramic and a coating is developed. The basic laws governing the development of stresses in the boundary layers of nitride ceramic and a coating made of titanium nitride under the effect of concentrated and distributed forces are found with the use of the technique. The need to take into account the stressed state of a ceramic — coating boundary in the course of analyzing the wear and degradation of ceramic parts in the course of design, manufacture, and service is noted.

The main approaches are formulated for improving the ballistic efficiency of ceramic composite armor protection based on improving the structure of shock-resistant ceramic materials and ceramic armor elements at nano-, micro-, and macro-levels. The contemporary state and development trends are reviewed and analyzed for ways of improving ballistic properties that are based on forming a fine-grained monolithic ceramic structure, creation of composite (dispersion-strengthened and fiber-reinforced) ceramic materials, creation of materials with properties varied throughout the volume (layered and graded), and creation of a discrete (mosaic) ceramic layer structure.

A thermomechanical method is examined for its potential use in concentrating magnesia-bearing raw materials from the Satka deposit by removing the impure components. It is shown that roasting magnesite within the range 680 – 750°C and its subsequent break-up (abrasion) under certain mechanical loads can increase MgO content in the <0.5 mm fraction of the roasted product nearly 10%. It is established that dust entrainment is minimal and does not exceed 1.5% when the magnesite is roasted in a fixed bed. This result can be obtained with a tenfold change in the thickness of the bed (from 20 to 200 mm).

The main conditions and criteria are considered for forecasting a range of refractory materials and objects of the future. Materials science, raw material geochemistry, processing efficiency, ecology, and production economics, are suggested as development criteria for ceramics. An important factor governing substance composition and range of future ceramics is an optimum combination of maximum values of thermal energy content (with respect to wear resistance) and minimum manufacturing cost.

The effect of alkali-containing additive of water soluble lump silicate on the degree of cristobalitization and thermal expansion of specimens based on fuzed quartz HCBS is studied. The additive content (for Na₂0) is varied within the limits of 0.1 – 2.0% or from 0.025 to 0.50%. In specimens given prior nonisothermal heating to 1500°C the cristobalite content is from 32 – 34% (specimens without additive) to 88 and 96% (specimens with 1 and 2% additive). Specimen maximum thermal expansion corresponding to transition of low-temperature into high-temperature cristobalite occurs within a limited range of 150 – 300°C.