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Search Results: 1 - 10 of 707 matches for " alumina-magnesia castables. "
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Agentes ligantes e seus efeitos em concretos refratários alumina-magnésia
Braulio, M. A. L.;Milanez, D. H.;Sako, E. Y.;Bittencourt, L. R. M.;Pandolfelli, V. C.;
Ceramica , 2010, DOI: 10.1590/S0366-69132010000400003
Abstract: the usual binder of alumina-magnesia castables is the calcium aluminate cement. due to in-situ spinel (mgal2o4) formation at high temperatures, these materials present an expansive behavior. when bonded with cement, further reactions (ca2 and ca6 formation) also contribute to the overall expansion. changing the most common cement used (~ 30 wt.% cao) for other containing less calcia (~ 20 wt.% cao) or for hydratable alumina are suitable alternatives for controlling the castables' volumetric stability. nevertheless, the binder replacement may affect castables properties, such as cold mechanical strength, mgo hydration degree and properties during and after sintering. therefore, the objective of the present paper is to analyze the effects of these binders on the alumina-magnesia castables processing. as a result, the binder systems can be used as a tool for designing the alumina-magnesia castables expansion, increasing the flexibility on the selection of steel ladles linings.
Evolution of an alumina-magnesia/self-forming spinel castable. Part I: Microstructural features
Gutiérrez-Campos, D.;Diaz, J. I.;Rodriguez, R. M.;
Ceramica , 1999, DOI: 10.1590/S0366-69131999000200009
Abstract: refractories containing magnesium aluminate spinel (mgal2o4) are materials for emerging technology in several applications like cement and steelmaking processes. in order to deep the understanding of these castables, this work presents the microstructural characteristics of an alumina-magnesia/self-forming spinel castable. several variables such as mgo content, firing temperature and spinel formation are analyzed through xrd and sem analysis. the results showed that the processes of spinel formation and nucleation are not strongly affected by the mgo content, but that the crystal growth is enhanced for samples with 6.0 wt% mgo. hibonite (ca6) bonding in the castable matrix showed a needlelike structure that could increase hot properties of the material. mgo content in the castable seems to affect the hibonite development. the development of a self-forming spinel castable without any synthetic spinel grains appears to be promissory for optimum refractory linings.
Evolution of an alumina-magnesia/self-forming spinel castable. Part II: physico-chemical and mechanical properties
Gutiérrez-Campos, D.;Diaz, J. I.;Rodriguez, R. M.;
Ceramica , 1999, DOI: 10.1590/S0366-69131999000500007
Abstract: this study was carried out in conjunction with the investigation, reported in part i, on the microstructural characteristics of an alumina-spinel castable with several percentages of mgo content. bulk density and cold crushing strength of samples were evaluated dried and at three fired states (1000, 1200, 1400 °c). results indicate little influence of mgo additions on physico-chemical properties of the alumina-magnesia/self-forming spinel castable. characteristics compared with those reported for conventional alumina-spinel castables did not show large difference in values. therefore, the alumina-magnesia/self-forming spinel castable could be a possible material for substitution of the conventional alumina-spinel castable.
Evolution of an alumina-magnesia/self-forming spinel castable. Part II: physico-chemical and mechanical properties
Gutiérrez-Campos D.,Diaz J. I.,Rodriguez R. M.
Ceramica , 1999,
Abstract: This study was carried out in conjunction with the investigation, reported in Part I, on the microstructural characteristics of an alumina-spinel castable with several percentages of MgO content. Bulk density and cold crushing strength of samples were evaluated dried and at three fired states (1000, 1200, 1400 °C). Results indicate little influence of MgO additions on physico-chemical properties of the alumina-magnesia/self-forming spinel castable. Characteristics compared with those reported for conventional alumina-spinel castables did not show large difference in values. Therefore, the alumina-magnesia/self-forming spinel castable could be a possible material for substitution of the conventional alumina-spinel castable.
Evolution of an alumina-magnesia/self-forming spinel castable. Part I: Microstructural features
Gutiérrez-Campos D.,Diaz J. I.,Rodriguez R. M.
Ceramica , 1999,
Abstract: Refractories containing magnesium aluminate spinel (MgAl2O4) are materials for emerging technology in several applications like cement and steelmaking processes. In order to deep the understanding of these castables, this work presents the microstructural characteristics of an alumina-magnesia/self-forming spinel castable. Several variables such as MgO content, firing temperature and spinel formation are analyzed through XRD and SEM analysis. The results showed that the processes of spinel formation and nucleation are not strongly affected by the MgO content, but that the crystal growth is enhanced for samples with 6.0 wt% MgO. Hibonite (CA6) bonding in the castable matrix showed a needlelike structure that could increase hot properties of the material. MgO content in the castable seems to affect the hibonite development. The development of a self-forming spinel castable without any synthetic spinel grains appears to be promissory for optimum refractory linings.
Ligantes hidráulicos e a hidrata??o de óxido de magnésio em concretos refratários
Salom?o, R.;Bittencourt, L. R. M.;Pandolfelli, V. C.;
Ceramica , 2010, DOI: 10.1590/S0366-69132010000300008
Abstract: the presence of calcium aluminate cement and hydratable alumina can significantly modify the magnesia sinter hydration behavior in aqueous suspensions. as a consequence of these studies, the present paper investigates how these binders content could affect magnesia hydration in refractory castables using hydration-dehydration tests, ph, ave, mechanical strength and porosity measurements. besides this, because for these materials the aspects related to mechanical strength, porosity and refractoriness also must be taken into account, binder-free, magnesia-free and magnesia-and-binder-free samples were also tested as references. it was found out that the deleterious effects of magnesia hydration can be greatly minimized by the binder content.
Efeito da adi??o de microssílica na hidrata??o de óxido de magnésio em concretos refratários
Salom?o, R.;Pandolfelli, V. C.;
Ceramica , 2008, DOI: 10.1590/S0366-69132008000100007
Abstract: magnesia hydration is an important concern when it is added to refractory castables. the volumetric expansion that follows this reaction can cause the material?s breakdown. recent reports in literature suggest that if this reaction could be halted or slowed down, significant benefits in castables properties would be attained. in this work, microsilica addition was employed as a magnesia anti-hydration technique (maht). using apparent volumetric expansion (ave) and mechanical strength measurements, the drying behavior and x-ray diffraction, an anti-hydration mechanism based on the generation of protective magnesium silicate coating is proposed. its limitations and effects upon castables processing were also evaluated.
Aspectos da hidrata??o de óxido de magnésio em formula??es de concretos refratários
Salom?o, R.;Bittencourt, L. R. M.;Pandolfelli, V. C.;
Ceramica , 2006, DOI: 10.1590/S0366-69132006000200005
Abstract: magnesium oxide (mgo) or magnesia is one of the most important raw materials for the refractories industry. because of high refractoriness (melting point of 2800 oc), corrosion resistance in basic environments and relatively low costs, its use in bricks has allowed a significant increase in the performance and service life of these materials. however, its use in refractory castables did not attain the same impact in industrial applications because of its great tendency in react with water and the consequent volumetric expansion generated. therefore, magnesia additions in castables has been kept in small amounts (bellow 10 wt%) and restricted to large particles (> 100 μm). in the present work, several reports on magnesia hydration in refractory castables, its effects on the castables processing and the anti-hydration techniques were critically reviewed.
Mulitiza??o em refratários utilizando diferentes fontes precursoras: revis?o
Magliano, M. V. M.;Pandolfelli, V. C.;
Ceramica , 2010, DOI: 10.1590/S0366-69132010000400009
Abstract: mullite is a ceramic phase currently applied in the refractory industries due to its excellent properties, high refractoriness and it is formed by the reaction of silica and alumina at elevated temperatures. in the literature, many works analyze its synthesis and reactions, as well as the in-situ formation or addition as pre-reacted powder. this review gathers the main works involving mullite synthesis, focusing on the mullitization kinetics, such as the formation of a metastable liquid phase. it also brings about a general view of the many different sources of silica and alumina, analyzing their characteristics and the properties of the resulting mullite. the study suggests that the use of high reactive alumina and silica favors the mullitization by reducing its formation temperature and the amount of residual liquid phase on the final product.
Espinelas Sintetizadas en Laboratorio Aplicadas en la Adsorción de Cromo
Flores,M.I.; Maldonado,M; Martínez,J.M.; Guzmán,J.J.;
Información tecnológica , 2004, DOI: 10.4067/S0718-07642004000300014
Abstract: in this study three adsorbents including magnesium aluminate of spinel type (mgal2o4), magnesia (mgo) and g -alumina (g -al2o3), were obtained and characterized. these materials were evaluated for their capacity to adsorb chromium from 50 ppm solutions of k2cr2o7 in a low stirring vessel and a packed bed adsorption column. the activated magnesia showed the greatest capacity for adsorption reaching 91.66% (11 m mol of cr/gr) in the stirred batch system over 1.5 h, while the packed bed column adsorbed only 36.67% (4.4 m mol cr/gr). with the magnesium aluminate and the g -alumina the adsorption of chromium was lower compared with the magnesia when varying conditions of mass, ph, and temperature in the stirred batch system. it is concluded that the temperature and turbulence promoted by stirring in the batch system favored the adsorption of chromium especially in magnesia
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