Behavior of ZrO2 / Al2O3 composites using flash and conventional sintering processes

Author(s)

Christiane Lago Ojaimi

• Document type: Doctoral Thesis
• Press: Pirassununga.
• Institution: Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT)
• Defense date: 2019-10-10

Examining board members

Eliria Maria de Jesus Agnolon Pallone; Osmar Roberto Bagnato; Julieta Adriana Ferreira; Maria Virginia Gelfuso; João Adriano Rossignolo; Alfredo Jose Zara

• Advisor: Eliria Maria de Jesus Agnolon Pallone; Adriana Scoton Antonio Chinelatto

Abstract

One of the challenges faced by researchers regarding the sintering of ceramic material is to achieve high densification with reduced grain size. Thus, several unconventional techniques have been standing out. Flash sintering is one of those techniques, in which an electric field is applied until the electric current flows, while the material is heated in a conventional furnace. The electric current flow causes linear shrinkage accompanied by instant densification (flash event). In this context, this study aimed to compare flash sintering with conventional techniques already established to understand the influence of flash sintering parameters on the ZrO2/Al2O3 system. For this purpose, ZrO2, Al2O3, and ZrO2 ceramic powders containing 5, 25, 50, 75, 95 vol% of Al2O3 were processed and sintered by different techniques: conventional (one and two-step) sintering, and flash sintering. The parameters involved in flash sintering were electric field and electric current using dynamic sintering. The parameters were changed according to the composition, and the permanence of the electric current was 60 seconds. In the conventional one-step process, the temperature of 1550 °C / 2h was used. In two-step sintering, sintering curves were evaluated to obtain the best density/grain size ratio. Therefore, the physical (apparent density and X-ray diffraction), microstructural (grain size measurement) and electrical (activation energy, grain and grain boundary conductivity) characterizations from the different compositions were evaluated and compared between the sintering techniques used. In general, flash sintering was influenced by the ZrO2 phase and the flash event occurred in compositions containing up to 25 %vol ZrO2. The conductivity of the specimens after flash sintering was different from that found in the literature. In all three sintering techniques, relative densities greater than 95% were achieved. Two-step sintering led to a more than 40% reduction in grain size over one-step sintering. On the other hand, sintering time was reduced by 95% in flash sintering compared to conventional sintering. (AU)

• FAPESP's process: 16/13256-1 - Study of the behavior of zirconia /alumina composites using flash sintering process and two-step sintering
• Grantee: Christiane Lago Ojaimi
• Support Opportunities: Scholarships in Brazil - Doctorate