Papers by Keyword: Magnesia

Abstract: The paper presents the results of investigations on the influence of the starting mass grain size distribution on microstructure of sintered magnesia-spinel products. The model investigation was conducted using magnesia clinkers and fused spinel. The grain size distribution of starting mixes were selected according to Dinger and Funk's theoretical curves with different values of n coefficient. The results clearly indicate that the best properties were achieved when n value changed in the range of 0.22 - 0.30 and forming pressure was contained in the range of 160 - 200 MPa.

Abstract: Rheological test results on alumina-magnesia castables, containing extruded flake graphite pellets, as well as steel fibers are considered at first. After being fired at different temperatures, thermomechanical properties of such castables containing either carbon steel or stainless steel fibers have been determined, at room temperature, as well as at temperatures up to 1100°C. Those results indicate that the use of fibers improves the performances of carbon containing castables at intermediate temperatures (800 º - 1100 °C), increasing the work of fracture by 50% at 1100 °C and by 10 fold at room temperature.

Abstract: Carbon-containing refractory bricks are used extensively in the steel industry worldwide. Since the first generation became commercially available in the 1970’s, 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 carboncontaining 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 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 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.

Abstract: A novel phosphate bonded magnesia cement was developed recently, which sets quickly and develops high strength in the early ages. In the present research, the physical and mechanical properties, hydration products, and microstructure of the new cement were investigated. The new cement was mainly consists of dead burned magnesia, phosphate and fly ash. The results showed that it not only has high early strength, but also has high long-term strength. Interestingly, the strength of the cement increase with the content of fly ash, from 10 % - 40 % by weight. The hardened cement paste has a dense microstructure, low open porosity and water sorptivity due to the low water to binder ratio. The reaction products after hydration of the cement includes struvite mineral and amorphous species.

Abstract: The magnesium phosphosilicate cement (MPSC) is a novel inorganic binder, it sets quickly and has very high strength. Also, it is a promising material for the sustainable development. In the present study, the durability of MPSC were investigated, including deicer scaling resistance under freezing-thawing cycles, chemical corrosion resistance in sodium sulfate and magnesium sulfate solutions, and wet-dry resistance in fresh and natural sea water. For comparison, Portland cement samples were also prepared for parallel tests. Test results showed that the chemical durability of MPSC is superior that of Portland cement. The causes of the high performance may be attributed to the low water demand and a reasonable microstructure of hardened paste matrix.