The European Ceramic Society

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Oct 13, 2022

YCN Newsletter 14 : Article by Isabela Reis Lavagnini

Conventional sintering is a slow process that involves heating a ceramic body from the outside to the inside using extremely high furnace temperatures.

During this process, a considerable amount of energy is wasted due to low-efficiency heating. However, the conventional sintering method is still widely used in the majority of ceramic industries today, being the stage in ceramic manufacturing that uses the most energy. Optimizing sintering is an opportunity to reduce the carbon footprint of the ceramic industries and also lower the costs and prices of the final products. In this way, an effort is being focused on creating more efficient ways to sinter materials. That is why I am working with a non-conventional sintering technique called Flash Sintering (FS), a new technique proposed in 2010. In essence, FS uses Joule heating to heat the sample from the inside, densifying ceramic materials in a matter of seconds. In a typical FS experiment, a ceramic body is directly exposed to an electric field while also being heated in a furnace. At a critical temperature (substantially lower than the sintering temperature), if the applied electric field is high enough, the electric current flowing through the sample will suddenly increase (triggered by thermal runaway). At this stage, which is frequently referred to as the "flash event", the sample releases light and rapidly shrinks, densifying in a matter of seconds.

As this technique is relatively new, several researchers are studying its application in different materials. It has been discovered that each material presents different behaviors during the flash event, as well as different final properties when compared to those obtained by conventional sintering. Therefore, the main goal of my study was to evaluate the potential of FS in the production of composite materials based on zirconia and hydroxyapatite.

My choice for this material relays on the fact that hydroxyapatite zirconia-based composites are of great commercial interest in the biomaterials industry. Biomaterials produced by this composite have potential in bone tissue replacements, as it allows the combination of two important properties: bioactivity (from hydroxyapatite) with high mechanical strength (from zirconia). However, these composites are difficult to sinter because each material presents different shrinkage rates, which could result in microcracks that will affect the final product. That is why I decided to test FS as a possible production route for this composite as the almost instantaneous shrinkage promoted by FS could prevent the formation of microcracks.

Currently, I am still carrying out several FS experiments on the hydroxyapatite zirconia-based composites, but the preliminary study was enough to show that the results obtained were unique: a dandelion-shaped crystalline structure was observed for the first time in flash-sintered specimens. This crystal structure exhibits special surface characteristics and has a high surface area. Thus, this morphology may open a new window for potential applications to this material.

 

Isabela Reis Lavagnini ( isabela.lavagnini@usp.br )

Department of Biosystem Engineering, Faculty of Animal Science and Food Engineering (FZEA), University of São Paulo (USP), Pirassununga, SP, Brazil.

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