Papers by Keyword: Magnesia

Abstract: The structure and composition of carbon materials affect obviously the result of carbothermic reduction of magnesia. Coke, charcoal and graphite were used in reduction experiments under the same conditions. The reactivity ratio of magnesia and XRD pattern of residues were analyzed and compared. The reactivity ratio of magnesia by coke was similar to the one by charcoal. The amorphous carbon in coke graphitized partly in reduction experiments of 1673K. The results show that the effective composition in coke is the amorphous carbon. It also suggests that the temperature of reaction should be control less than 1700K to avoid the amorphous carbon’s graphitization.

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: BR/MgO composites were prepared with seven kinds of particle sizes of MgO filled respectively. Effects of particle sizes on dynamic mechanical properties, vulcanization characteristics and physical properties of BR/MgO composites were studied. The results showed that the tensile strength of composites filled nanoscale of MgO was nine times of pure BR, and the vulcanization time was significantly shorter than that of composites filled with micron grade filler. The RPA experiments proved that the composites filled with MgO of 20nm and 50nm have greatly higher G＇, and that the G＇of the composites increase markedly while the value of tanδ decrease sharply with given temperature above 90 °C increasing. the higher value of tanδ at the frequency mode, and the obvious Payne effect compared with the composites filled micron grade of MgO

Abstract: Magnesia (MgO) is a fundamental component of many minerals found in nature and is used widely in our life, especially in refractory industry. However, the antihydration of MgO is a key concern in refractory suspension processing, MgO additions only in form of coarse particles(≥ 50 μm) or its contents of up to 10 wt.% are as a result of their high possibility to take place hydration reaction in water and the reaction can lead to volumetric expansion obviously. In the present work, citric acid (CA) can complex with Mg²⁺ in the MgO suspension under the condition of 4h and 25°C, and the deposit of magnesium ion-CA complexes become protective coating to inhibit magnesia react with water to form Mg(OH)₂.The test results of RSV of different additives shows CA is the best antihydration compound to inhibit MgO hydration comparing with EDTA-2Na，sodium pyrophosphate(SP)，trimeric sodium phosphate(TSP), which RSV is only 5.3ml when its dosage is 0.3%wt.

Abstract: The present paper focuses on the experimental investigation of the aluminothermic reduction of magnesia under vacuum condition with the fixed magnesia to aluminum molar ratio of 11:6. The influences of reaction temperature and time on the reduction ratio of magnesia were studied. The chemical composition, phase constitution and morphology of the condensed magnesium and the briquettes after thermal reduction were investigated by X-ray diffraction, scanning electron microscopy equipped with energy dispersive spectrometry. The reduction ratio of magnesia increases with the increase in the reaction temperature and time. The briquettes after thermal reduction at 1050°C-1150°C are mainly composed of the spinel, unreacted magnesia and aluminum. The briquette after 1 hrs thermal reduction at 1200°C contains corundum, magnesium aluminium oxide, trace amount of spinel, unreacted MgO and aluminium.

Abstract: In order to reduce energy costs, light-weight alumina-spinel refractories with tri-modal pores were prepared by foaming process. The influence of foaming agent and magnesia on the properties of light-weight alumina-spinel refractory was investigated. The rheology of the original slurry and the density, mechanical properties and microstructure of samples were evaluated. The results showed that light-weight alumina-spinel refractory contained a highly interconnected network of spherical cells, consisting of the large-sized cells (larger than 40 um), moderate-sized pores( averaging about 20 um) and small-sized voids, which mainly attributed to the foaming agent and in-situ formation of spinel. The cold compressive strength of the samples varied within the range of 2-12MPa, corresponding to densities of 0.8~1.2g/cm3,and the thermal conductivity changed from 0.273W/(m•K) to 0.315 W/(m•K) at the 500 °C. It was found that the density of the sintered samples was dependent both on the content of foaming agent and magnesia. With the help of magnesia, light-weight alumina-spinel refractories with good volume stability were prepared by foam method.

Abstract: A patching material for converter was investigated by using sintered magnesia as the main starting material, a certain carbohydrate as binder and graphite flake and Al metal as additives. The effects of the additions of binder, graphite and aluminium metal on the performances of patching materials were studied respectively. The results revealed that the carbohydrate binder melted during heating, making the patching materials spread out and flow; graphite flake could improve the flow ability, but decrease the bulk density; aluminium metal could partially be oxidized or nitrided, and hence fill the gap and increase the strength.

Abstract: Magnesia is a widely used inorganic chemical product. magnesite is an advantageous resource in China, and also an important source of magnesia. There are tree methods to making magnesia from magnesite using heat treatment. They are light burning, dead burning and melt. In recent years, domestic researches have been done on processes, product performance and process mechanism of these methods.

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: The MgO-Al₂O₃ system materials were prepared at 1600°C for 3h with magnesia powder and alumina powder as raw materials and with ferric oxide powder as additive. The effect of the ferric oxide additive on the sintering and thermal shock resistance of the composite materials was studied. The results showed that increasing the ferric oxide dosage could improve the densification of the MgO-Al₂O₃ system materials. In sample MAF-0, crystal phases all are spinel phase. With the ferric oxide dosage increased from 2% to 6% in MAF-2, MAF-4 and MAF-6, the MgAl2O4 (spinel) became the primary crystal phases, and less amount of sosoloid 20MgO•19Al2O3•Fe2O3. In comparison with samples MAF-0, MAF-2, MAF-6, sample MAF-4 has better structure compactness and thermal shock resistance, the optimum ferric oxide dosage was added in MgO-Al₂O₃ system material is equal to 4%. The MgO-Al₂O₃ system material is acceptable for application in cement rotary kiln linings and high temperature gas filter support.