For several years, sustainable development and ecological transition are at the center of many concerns. The ceramics industry must follow societal and environmental developments to move towards a “competitive low-carbon economy by 2050”. Environmental issues concerning water, raw materials and waste have to be considered; emissions and energy consumption must be reduced [1].

The production of ceramics includes different steps among which the sintering appears as a determining stage to achieve the targeted final properties of designed products. Two main ceramics families are identified in literature: wide diffusion (mostly silicates) ceramics and advanced ceramics. In most cases, “natural gas” furnaces are used to reach the necessary firing temperatures in the industry. In order to match the “European Green Deal”, whose objective set by the European Commission is to achieve carbon neutrality by 2050, alternatives such as biogas, green hydrogen or electricity furnaces should be considered. These modifications of the sintering environment can influence significantly the kinetics of transformation, namely through the variation of the surrounding atmosphere and the modes of heat transfer. The challenge is therefore to anticipate the impacts of such modifications, particularly on the physical and chemical transformations together with the performance of silicate ceramics.
 
Clays, and more precisely phyllosilicates, generally have a natural origin and are readily available worldwide. This research works focuses on two types of phyllosilicates: kaolinite and illite. Kaolinite is a 1:1: clay mineral where the unit sheet results from the superimposition of an octahedral layer Al(OH)?O and a tetrahedral layer SiO?. Illite clay mineral belongs to the 2:1 phyllosilicates and is characterized by the superimposition of a central octahedral layer Al(OH)?O and two external tetrahedral layers SiO? with potassium ions in the interlayer space [2].

Two model clays were selected for this study: a kaolin noted CR” and n illite denoted “illite ABM” provided respectively by Imerys and Argile du Bassin Méditerranéen companies. A deeply study of biogas allowed identifying some key parameters for sintering: partial dioxygen pressure, impurities, firing mode transformations, etc. From Ellingham diagrams, the impact of some impurities, such as iron or tin oxides, are studied. For this purpose, the sintering behavior of these kaolinitic and illitic compounds is investigated. Controlled additions of fluxes are carried accordingly. Different thermal cycles under controlled stress (atmosphere and mechanical) are applied to simulate the use of biogas. In situ (thermodilatometry, thermogravimetry) and ex situ (X-ray fluorescence, X-ray diffraction) analyses are performed to implement the knowledge in line with these phyllosilicates.

[1] Furszyfer Del Rio D., Sovacool B., Foley A., Griffiths A., Bazilian M., Kim J., Rooney D., Decarbonizing the ceramics industry: A systematic and critical review of policy options, developments and sociotechnical systems, Renewable and Sustainable Energy Reviews, 157, (2022), 112081.
[2] F. Bergaya, F. Teng, G. Lagaly, Handbook of clay science, Elsevier, 2006