Papers by Keyword: Castable

Abstract: The present study aims to analyze the corrosion mechanism of Al₂O₃-SiC-C castables for blast furnace main trough. The anti-oxidation and corrosion properties of the castable caused by slag were studied with residual lining investigation and microstructure analysis. A rapid recognition of grain distribution, ingredients, and mineral phases was achieved by using cathodoluminescence (CL) in conjunction with stereo microscopy. Different materials such as brown fused alumina, spinel, and low-melting CaO containing phases etc. can be detected due to their distinct fluorescence. The result indicated that when carbon in the matrix of castables was oxidized, its non-wetting property to slag was reduced, which causes slag penetrate into the castable and formed low-melting CaO containing phases. On the contrary, when the anti-oxidation property of castable was improved, the carbon in the matrix was not easily oxidized and corroded by slag. Furthermore, MgO of slag reacted with Al₂O₃ in the matrix to form a continuous spinel layer, which retarded slag to penetrate and corrode the castable.

Abstract: In this experiment, preparation of samples were based on original ratio of bauxite matrix Al₂O₃-SiC-C castable for iron runner, and partial bauxites of size 8-5 mm, 5-3 mm, 3-1 mm and 2O₃-MgO-C materials from spent ladle bricks, respectively. Effects of particle size and content of the recycled materials on sintering performance of the castable were investigated. The sintering performance was analyzed by measuring apparent porosity, room temperature flexural strength, room temperature pressure strength and high temperature flexural strength. The results showed that the apparent porosity of the samples overall tended to increase with content of the recycling materials increasing, while room temperature flexural strength, room temperature pressure strength and high temperature flexural strength of the samples reduced gradually. 8-5mm and 5-3 mm particle of 5%-15% the recycling Al₂O₃-MgO-C materials was more suitable for the preservation of high temperature flexural strength and room temperature strength of the samples than 3-1 mm and < 0.074 mm particle.

Abstract: The effects of B₄C addition on the room temperature physical properties and hot mechanical properties of MgO-SiC based refractory castables were investigated using magnesia and SiC fines as starting materials and silica fume as a binder. The microstructure was characterized by scanning electron microscopy (SEM). The results showed that drying strength of MgO-SiC based castables decreased with the increase in B4C addition, the immediate temperature strength and hot temperature strength increased. The HMOR at 1400°C for 0.5h decreased. This is because B4C oxidized and produced a liquid phase during heating, contributing to sintering and making the material denser. So the cold strength increased. On the other hand, due to the formation of liquids, direct binding reduced and the HMOR decreased

Abstract: Refractory castables containing calcium aluminate cement (CAC) are widely used in a range of furnace lining applications in the iron and steel, cement, glass, ceramic, and petrochemical industries. However, magnesia-phosphate cement (MPC) based material could be a new types of cement material, with many advantages such as rapid hydration, high early strength and circumstance suitability, which has very important value and wide application. In this study, MPC was used at Chromia/Alumina castable as binder addition instead of conventional calcium aluminate cement. Meanwhile, it also explains the relationship between the micro-mechanism and performance by micro methods such as SEM. The results shows that MPC based castables have good corrosion resistance, interface adhesiveness and abrasion resistance.

Abstract: The effects of SiC addition on physical properties and slag resistance of MgO-based castables were investigated using magnesia as the main raw and silica micropowder as binder. The result revealed that with increasing SiC addition, dried strength decreased, medium and high temperature strength first increased and then decreased and reached a maximum at 3% SiC addition. The hot modulus of rupture (HMOR) of the materials maximized at 3% SiC addition. The slag penetration resistance of the castables was improved while resistance to slag attack was deteriorated with the increase in SiC addition. The materials exhibited optimum slag resistance at 3% SiC additions.

Abstract: Slagging coal gasifiers operate at temperatures as high as 1650°C in a reducing environment so that combustion chambers are lined with high chromia refractories. The quality of these refractories applied on IGCC should be a key factor that affects the entire cost of electric power production. In this study, low cost chromia-alumina castables were chosen as candidate refractories for IGCC. To enhance the workability of chromia-alumina castables, ultrafine alumina powder was added to improve the workability. It’s proved that the specific surface area and particles size distribution of ultrafine powders in matrix part greatly affect the flow values and microstructures.

Abstract: Monolithic refractories are now well established as linings for a range of holding and melting applications for the processing of aluminium. The refractory lining in an aluminium furnace has to withstand a wide variety of physical and chemical environments. Each of the different furnace zones presents a different set of operating conditions, in terms of peak temperature, temperature fluctuation, metal contact, flux contact, impact from ingot loading, etc. Therefore, in order for a monolithic material to successfully perform in a particular area of the furnace, it needs to be able to cope with the specific environmental conditions in that region of the furnace. Aluminium producers continue to increase productivity through their Melt-Hold furnaces to maintain competitiveness. The use of more powerful burners to increase heat input to the furnace is therefore becoming increasingly common practice. But faster melting leads to increased metal losses from surface oxidation and to segregation from large heat gradients. These effects are countered by increased use of fluxes and increased stirring. Given the increasingly challenging environment within which the refractory lining has to work, traditional lining solutions can no longer be relied upon to provide the service lives that were previously achieved. Therefore, a new generation of furnace lining materials is required to cope with today’s aluminium furnace. This paper describes one such newly developed monolithic material, designed specifically to improve performance in the superstructure zone of Aluminium furnaces. The non-metal contact, superstructure regions of aluminium furnaces present their own unique set of challenges for the refractory lining. Refractories in these regions – roof, upper walls and flue – have to cope with excessively high levels of alkali vapour and thermal shock. This paper reviews the operating conditions found in the superstructure areas of a typical melting and holding furnace and the implications these have on monolithic lining material design and performance. The improved behaviour of the newly developed monolithic material against the critical performance criteria in these furnace regions is demonstrated in the laboratory, compared to existing industry leading materials, using industry standard test methods.

Abstract: In terms of this work formulations of carbon bonded castables based on new binder approaches and nanoadditions will be demonstrated. The new binder system allows the manufacturing of water based magnesia carbon castables with the same properties and chemistry of pressed magnesia carbon bricks. This binder can be also applied in oxide castables offering them high refractoriness and workability during processing. According to the workability nano-additions improve significantly the spreading diameter of carbon castables and as a result their flowability.

Abstract: Refractories cover a wide range of products. With the aim to precisely describe the key product properties, end-users and refractory producers have progressively developed a common language: refractory standards. After a brief description of refractory standards history, and a synoptic overview of the present status, future prospects are illustrated by an example. The Belgian Ceramic Research Centre (BCRC) has recently launched a pre-normative research in the field of unshaped refractories. It focuses on robust methods to assess the workability and setting of hydraulically bonded unshaped products. Among the investigated methods, the so-called “exothermic profile” appears to have a high potential to become a standard for refractory producers or end-users.

Abstract: To prevent the shrinkages by the densification during the application of unfired Al2O3-C refractories or Al2O3 castables in steel making conditions, MgO was added as aggregate or matrix powder and the expansion caused by spinel formation was studied. Because the spinel was formed at the contacting areas between Al2O3 and MgO particles and the volume of in-situ formed spinel increased more abnormally at the side of Al2O3 particles than MgO, the addition of MgO aggregates was not recommendable due to the formation of large voids around the MgO aggregates. Nevertheless, corrosion resistance was increased with the amount of fine MgO added, and the finer MgO powder added, the better residual expansion and minute structure formation was observed. In the contrary, in case of castables volume expansion due to spinel formation was not obvious because the degree of densification was less than high-pressure formed refractories. But CA6 phase would not form around alumina aggregates during corrosion so the corrosion resistance was much more enhanced.