Influence of Surface Area on the Flowability Behaviour of Self-Flow Refractory Castables

Alumina, with high melting point (2050°C), high hardness and mechanical strength, and excellent abrasion resistance, is one of the most common raw materials used in self-flow refractory castables (SFRC) for monolithic linings and is commercially available in various fine to coarse size classes. However, the performance of the refractory lining depends not only on the properties of its ingredients but also on its easy installation (good flowability). The aim of this work was to evaluate the relationship between the flowability index (FI) of fresh castable and the specific surface area (SSA) of its particles, which is mostly determined by the finer particles content. The results obtained showed that, by controlling the proportion between matrix and aggregate, it is possible to control the SSA of the refractory castable and find a mathematical relationship between the specific surface area and the minimum flowability index required to obtain a self-flow refractory castable. It is, thus, possible to optimize the refractory castable size composition and obtain an estimate for FI as a function of SSA. Using a minimum 45 wt.% matrix content in the castable mixture, a SSA value above 2.215 m2/g is obtained, which leads to FI ≥ 80%, the recommended value for self-flow.</jats:p

Characterisation of Refractory Ceramic Pressed Body Containing Industrial Waste

This study investigates the use of an industrial refractory brick waste in the refractory based silica and alumina ceramic body. From the characterization of the waste, a mixture containing a clay, silica, alumina and waste was processed via wet route and sintered at 1400 °C. The specimens were evaluated in dry (density) and after sintering (linear shrinkage, density and modulus of rupture).Microstructural characterization by scanning electron microscopy (secondary electron) revealed a microstructure unevenly and a presence of big porous which shows also small amounts of vitreous phase, which can be related to sintering process not fully finished. The results for the linear shrinkage (about 6 %) and modulus of rupture at three points (about 63 MPa) showed that the mixture containing the refractory brick waste and the processing conditions were satisfactory for obtaining a suitable refractory material for the manufacture of bricks for melting furnaces.</jats:p

Caracterização de materiais cerâmicos à base de CuCr 2 O 4 preparados pelo método da reação de combustão em solução para uso como pigmentos

CuCr2O4-based ceramic pigments were prepared by the method of solution combustion synthesis starting at calcination in the range of 500 to 1100 °C, aiming to the application as ceramic pigment. The structural, morphological, chemical and optical properties of the material were studied using the techniques of X-ray diffraction, Rietveld refinement, field emission gun scanning electron microscopy, X-ray fluorescence, diffuse reflectance and L*, a*, b* colorimetric coordinates based on the CIE-L*a*b* method. The synthesized powders were mixed with matte and transparent glazes and applied in ceramic matrices. The results indicated that an increase in temperature led to the conversion of the chromite phase, in which regular polyhedra were observed, to delafossite, presenting a hexagonal platelike morphology. Diffuse reflectance revealed the formation of dark colored powders, confirmed by the colorimetric data. The synthesized powders exhibited green pigmenting ability when mixed into the ceramic glazes.PPGEMPPGQDAQ IFMA, Av. Getúlio Vargas 4, S. LuísPPGEA UFMA, Av. dos Portugueses 1966, S. LuísCMDMC LIEC Instituto de Química UNESP, C.P. 355CMDMC LIEC Instituto de Química UNESP, C.P. 35