Mechanical evaluation at high temperatures of hot gunning refractory mixtures
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he mechanical behavior at high temperatures of three hot gunning refractory mixtures used for coke oven repair was studied. The materials were characterized by chemical, mineralogical, granulometric, and microscopic analyses, exhibiting differences in composition and particle size distributions of both aggregates and bonding phases. The hot adhesion of the mixtures to silica bricks was determined using torsional forces, and the interphase between them was analyzed by scanning electron microscopy. Thermal expansion up to 1200 °C and creep under compressive load (172 kPa at 1200 °C, 3 h) were carried out on prisms prepared by ramming and sintering (1200 °C, 1 h). The creep strain–time data are well fitted using constitutive equations. The mixtures showed differences in both hot adhesion and thermal expansion–creep tests: the material based on calcium aluminates exhibited poorer properties than those based on calcium silicate. The results are explained taking into consideration the characteristics of both aggregates and bonding phases.
I. INTRODUCTION
Monolithic refractories are progressively extended into more uses due to their remarkable performance advantages under severe service conditions (high temperature, thermal cycling, corrosive environments) and the possibility of allowing automated installation. The steelmaking industry is a major consumer for this class of refractories.1,2 The thermomechanical wear imposed on refractories demands careful material selection on behalf of the consumers. As a consequence, an evaluation of their properties in conditions close to those in service is essential. In addition, an interpretation of data on the basis of operative mechanisms and material microstructures is useful for refractory materials design. For monolothic refractories used in coke oven repair and applied by hot gunning, the adhesion to the bricks and the dimensional changes under load determine the material performance acceptance at high temperature. The short-time behavior of the repair will mainly depend on the hot adhesion, while the creep response will especially influence the long-time performance of the hot gunning mixture. The measurement of the adhesion of gunning materials to bricks under operating conditions that involve high temperatures and torsional forces is rather difficult and
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J. Mater. Res., Vol. 18, No. 2, Feb 2003 Downloaded: 13 Mar 2015
therefore uncommon. However, laboratory-scale methods have been proposed3,4 that surmount the experimental drawbacks. The measurement of dimensional changes during heating and at high temperature and compressive load is routine for refractories, and there are several standards according to the type of material and its use.5,6 Even though the interpretation of creep is very complex for refractory materials since they usually have heterogeneous microstructures and simultaneous creep mechanisms occur, the strain–time behavior can be modeled using equ
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