Mullite Formation in Al 2 O 3 /SiO 2 /SiC Composites for Processing Porous Radiant Burners
- PDF / 406,631 Bytes
- 7 Pages / 432 x 648 pts Page_size
- 102 Downloads / 232 Views
Mullite Formation in Al2O3/SiO2/SiC Composites for Processing Porous Radiant Burners
Daphiny Pottmaier, Jefferson J. Rosario, Marcio C. Fredel, Amir A.M. Oliveira, Orestes E. Alarcon Mechanical Engineering Department, Federal University of Santa Catarina, Caixa Postal 476 Campus Trindade, 88040-900 Florianopolis, Brazil.
ABSTRACT Use of porous ceramic burners for natural gas combustion is an optimum alternative to enhance energy efficiency and decrease emission of pollutant gases per generated power. Materials requirements for the operation of such porous burners are mainly thermal shock and chemical resistance and those can be reached with cellular ceramics. Mullite was theoretically identified among the best materials for this application; however, its potential was not properly explored yet. Even though mullite can be synthesized from different compounds and processing routes, control of final material characteristics is complicated mainly due to the formation of amorphous phase. In this work, using a technological approach mullite burners were processed by the replication method starting from different mixtures of Al2O3/SiO2/SiC. Rheological study of the slurries has given additives content for the coating of the polyurethane sponges. After varying sintering temperatures up to 1600 °C and isotherm times for 12 h, microstructural aspects and product phases of the final composites were characterized in order to understand the influence of Al2O3/SiO2/SiC ratios in the formation of mullite phase and amorphous content. INTRODUCTION Porous medium combustion using radiant ceramic burners combined with natural gas is and optimum alternative to enhance energy efficiency of the combustion processes as it results in uniform and infrared heating with extension of lean flammability and higher burning rates with lower emission of pollutant gases [1]. That also means economic advantage as it lowers gas consumption per generated power. Combustion inside a porous structure requires specific properties from its constituent materials during operation. Materials for porous burners must resist principally to thermo mechanical stress due to high temperature gradients and corrosion effects depending on the fuel type, ratio and pressure. Additionally, low-priced raw materials are necessary for the fabrication of simple components in many domestic and industrial applications. Cellular ceramics suitably attend the required properties as a function of porosity percentage and morphology, porous distribution and type. Such characteristics may vary depending on the constituent materials (i.e. pure, mixture, composite) and their processing (e.g. replication, foaming, gelation). The most used materials in porous burner systems are: silicon carbide (SiC) due to good thermal transport up to 1350 ºC and other outstanding properties [2], aluminum oxide (Al2O3) for temperatures up to 1900 ºC [3], zircon oxide (ZrO2) for temperatures up to
169
2300 ºC [4], Fe-Cr-Al alloys used for lower temperatures and high thermal shock resistances [5]. They
Data Loading...
