This site makes use of cookies necessary for the operation and useful for the purposes described in the cookie policy. If you want to learn more, see the cookie policy. By closing this banner, scrolling this page, clicking on a link or continuing navigation in any other way, you consent to the use of cookies.
The influence of the correlation between the drying constant and the diffusion coefficient of the liquid on the behavior of two raw materials for brick manufacturing during their drying process was examined. The test was performed in a laboratory dryer with air recirculation. It has been observed that the behavior of some raw materials during fast drying process regimes does not depend only on external drying conditions, but also depend on internal controlling mechanisms, in this case moisture diffusion in the slab.
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.
Carbon-containing refractory bricks are used extensively in the steel industry worldwide. Since the first generation became commercially available in the 1970s, their processing, microstructures and properties have been improved dramatically, and the service lives of industrial furnaces have thus been extended substantially. In addition to the work on carbon-containing refractory bricks, much effort has been, and is being, made worldwide towards the development of carbon-containing refractory castables. In this paper, the latest R & D towards new generation carbon-containing 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 in-situ oxide nanofibres and/or carbon nanotubes in carbon-containing refractory bricks is introduced. The second part addresses some important technical issues of low carbon carbon-containing 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 carbon-containing 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.
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.
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 α-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 α-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.
Up to now most of the efforts for developing HTS technology have been directed to devices for grid applications. However, HTS synchronous machines as motors and generators become more and more interesting within the world-wide development programs. Replacing the copper winding of the rotor by an HTS one and introducing an iron-less air-core stator winding the very compact HTS machine has less than half the weight and volume, higher efficiency and an excellent operational behavior when compared to the conventional devices. These features make HTS rotating machines very attractive for e.g. ship drives and industrial applications for the processing industry and power generation in power plants and wind parks. World-wide, HTS machines have already demonstrated their advantages and technical feasibility. The prototypes are ranging from the 5 MW low-speed high-torque propulsion motor to the highspeed 3600 rpm 4 MVA HTS generator. Feasibility studies clearly show the financial benefits when introducing high-efficient HTS wire based rotors into a large scale power generator systems. At present, most of the industry driven activities take place in the United States, Germany, Japan and Korea and are mainly directed towards applications aboard ships. Further potential applications as well as the technical and economic benefits will be discussed.
Address
Links
Information