Porous ceramics produced from Al2O3-Mg(OH)2

• Grant number: 13/07306-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2013
• End date: June 30, 2015
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Rafael Salomão
• Grantee: Pedro Henrique Lopes Cardoso
• Host Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil
• Associated research grant: 10/19274-5 - Novel methodology for hydrotalcite (Mg6Al2(OH)16CO3.4H2O) synthesis from aqueous suspensions of magnesium oxide (MgO) and aluminum hydroxide (Al(OH)3) and its application in porous ceramics for high temperature thermal insulation, AP.JP

Abstract

Porous ceramics have large field of application as thermal insulation in industrial processes involving generation, replacement or maintenance of heat. This good performance is explained by the fact that these materials combine the low thermal conductivity of porous materials with the high refractoriness and chemical inertia of ceramics. One point that still needs improvement regarding their performance is the ability to maintain thermal insulation at elevated temperatures (above 1300ºC). In such cases, the densification promoted by sintering reduces the amount of pores, thus compromising its performance. Recent studies indicate that porous structures based on spinel (MgAl2O4) have good resistance to densification due to the inherent difficulty of sintering this compound displays. This is due to two effects: 1) the volumetric expansion that follows spinel formation and ii) the fact that it forms a stable solid solution in a wide range of composition and temperature (thus favoring grain growth at the expense of sintering). Although these effects are deleterious in dense ceramics (refractory bricks, for instance), they can have great technological applications in porous structures. In this Project, porous structures will be formed by raw materials that can behave as porogenic additives (magnesium and aluminum hydroxides) and generate spinel after their decomposition, in high temperatures. Different ratios of these compounds will be combined, pressed and sintered at different temperatures. By means of measurements of mechanical strength, porosity and pore size is expected to find a sweet spot between generate large fraction of pores (for good thermal insulation capacity) and sintering (to ensure thermomechanical strength during use). X-ray diffraction and scanning electronic microscopy analysis will be carried out to evaluate the composition and microstructure attained. (AU)