Porous thermal insulators for microwave sintering of ceramic materials at ultra-high temperatures

• Grant number: 23/06154-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): July 01, 2023
• Effective date (End): June 30, 2024
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Rodolfo Foster Klein-Gunnewiek
• Grantee: Iago Cordeiro Santa Bárbara
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil

Abstract

Reduction of energy costs and increased energy efficiency in industrial processes are among the main topics of today. Similarly, the ceramic industry, especially the refractory industry, also follows this call for obvious reasons: in the case of high-performance refractories, the processing temperatures of the parts exceed 1500 °C, often reaching temperatures above 1700 °C. This process takes many hours or even days to complete. Technologically, processes are being sought to obtain refractory parts that can be processed in reduced times and/or at lower temperatures while presenting equal or superior performance to those obtained conventionally. The application of microwaves in this segment is a viable option. However, there are few studies focused on this technique at high and ultra-high temperatures. Due to the volumetric interaction between microwaves and ceramic materials, sintering times are significantly reduced, resulting in savings of up to 90% and shorter times. There are several factors that justify the lack of works: selection of insulating and inert materials that are transparent to microwaves, resistant to thermal shock damage, and capable of withstanding many cycles. Insulating materials with pores between 0.5 to 3µm are ideal. However, the electromagnetic field, in addition to accelerating diffusion processes, enables the opening of microplasma in the pores, making usage conditions even more severe. Considering this, the present project aims to obtain insulating materials based on transparent alumina and alumina-mullite materials for use in high and ultra-high temperature microwave applications. Porosity will be controlled via direct foaming. The parts will be properly characterized (physically, structurally, and microstructurally) and tested for their performance. From a scientific standpoint, it is hoped to clarify how microwaves interact with porous materials and what damage they can cause. From a technological perspective, it is hoped to obtain simple insulating materials that can withstand severe operating conditions, opening many possibilities for microwave processing at very high temperatures.