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In this paper, the latest R & D towards new generation carboncontaining refractory bricks as well as carbon-containing refractory castables have been highlighted. In the first part, current techniques used to improve mechanical properties of carbon-containing refractory bricks are summarised. A new concept using a catalytic-growth technique to create insitu oxide nanofibres and/or carbon nanotubes in carbon-containing refractory bricks is introduced. The second part addresses some important technical issues of low carbon carboncontaining refractory bricks. Besides the concern about thermal shock resistance, other new problems arising from the use of nanosized carbon, such as the accelerated MgO-C reaction and carbon oxidation, are discussed. In the final part of the paper, technical difficulties hindering the development of carboncontaining castables as well as measures to overcome them are discussed. A novel molten salt synthesis technique developed recently at Sheffield to prepare high quality carbide coatings on graphite is introduced.
Refractory bodies based on magnesia with different amounts of zircon and lime were sintered through two firing stages. The bodies were characterized for their mineralogy composition by XRD and microstructure by SEM. Periclase, calcium zirconate, zirconia, and merwinite were detected. The densification and mechanical properties were correlated with their minerology and microstructure. An improvement of refractoriness under-load was recorded with increasing zircon content. The fracture mode in the thermally loaded bodies was both intergranular and transgranular. The parepared bodies showed a good corrosion resistance to attack by Portland cement clinker.
A new technology has been developed for making refractory products based on the naturally occurring wollastonite (calcium metasilicate) intended for the aluminum industry. The articles were made by using steel-mold pressing, slip casting and vacuum forming methods. The thermal shock resistance has been improved by the introduction of coarse-grained fillers and inorganic fibers. The study has been made into ceramics structure comprising inorganic fibers. The developed materials are chemically inert to aluminum melt. They show no sticking, no mechanical erosion and they are thermal-resistant. With the above methods, the following products are being made on the basis of the naturally occurring wollastonite: spouts, lining plates, heat nozzles, stopper-rod devices, pipes and other articles that have been operating successfully in the aluminum industry of Russia.
Relations between technological factors such as grain size distribution of mixes, forming pressure and firing temperature and properties of magnesia spinel refractories have been investigated. The model investigation was based on magnesia clinker with low Fe2O3 content and different content of fused spinel. Grain composition of mixtures was calculated according to Dinger and Funk model. Apparent density, open porosity, compression strength, permeability and pore size distribution of products were determined. The results clearly showed that higher amount of fine grains fraction in mixes of magnesia spinel products led to the increase of open porosity and crushing strength but simultaneously led to the decrease of bulk density and permeability. The increase of forming pressure for mixes with constant grain size distribution led to the increase of crushing strength and bulk density with simultaneous open porosity and permeability decrease. Higher forming pressure of samples led to the increase of the share of the pores below 10 mm. Generally, the higher was the amount of pores below 10 mm, the lower was the permeability of the material.
The present research is concerned with the production and characterization of ceramic materials obtained using demolition debris alone or in mixtures with bottom ash from an incinerator of municipal solid waste, incinerated sewage sludge and steelmaking slag. Blending of the different components was performed by attrition milling. Milled and dried powders were uniaxially pressed into specimens which were sintered and characterized by shrinkage on firing, density, water absorption, hardness, strength, fracture toughness measurements as well as by XRD and SEM investigations. The fired samples were also tested in acid environment (HCl) in order to evaluate their leaching behaviour. All materials produced have low water absorption, fine microstructures, good mechanical properties and the release of most of the hazardous metals contained in the starting powders is low. On the contrary, shrinkage on firing is high for most of the compositions studied.
Population balances are the most useful tool in solving many engineering problems including comminution process modeling. Studying batch grinding in terms of material balances inevitably demands for determining two basic functions: breakage rate function, also known as selection function and breakage distribution function. They depend on many factors such as initial fraction size or distribution of sizes, material characteristics, comminution machine characteristics etc. This paper investigates the influence of process parameters (grinding ball material and diameter, mill speed, relative ball filling ratio) on dry batch grinding behavior of single size fraction (3.36+2.25 mm) dolomite ground by using two different planetary ball mills. Effects are expressed in terms of breakage rate (selection) function and breakage distribution function.
Alumina-zirconia fibres (Al2O3-10 wt.% ZrO2) were prepared by the sol-gel method with organic additives viz. hydroxy ethyl cellulose (HEC) and polyvinyl alcohol (PVA). As the organic content is increased, the phase transition to a-Al2O3 is retarded in the presence of hydroxy ethyl cellulose and enhanced in the presence of polyvinyl alcohol. The phases present in the sintered fibres are a-Al2O3, t-ZrO2 and m-ZrO2. Infra red spectra of the sintered fibres show bands corresponding to a-Al2O3. The surface morphology of fibres prepared with higher amount of organics shows equiaxed grains with relatively dense microstructure for fibre prepared with hydroxy ethyl cellulose, whereas the structure is porous with polyvinyl alcohol. Tensile strength decreases with the increase in organic content.
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