Preparation of High-Quality Porous Calcium Hexa-Aluminate Ceramics using Salt as Both Reaction Medium and Pore-Former
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Porous calcium hexa-aluminate (CA6) ceramics were synthesized by a molten salt-mediated technique using CaCO3 and α-Al2O3 powders as the main raw materials. The effects of salt type and content, along with firing temperature on phase formation, microstructural evolution, pore generation and size distribution, and mechanical strength of fired samples were investigated and compared. Among the three tested salts (KCl, NaCl, and CaCl2), KCl showed the best whereas CaCl2 showed the worst accelerating effect on CA6 formation. In the case of the former, phase-pure CA6 was formed after 3 h at 1500 °C, whereas in the case of the latter, CA2 was formed instead as a main phase. The salt not only acted as a reaction medium, accelerating CA6 formation, but also acted as a pore former, creating high levels of porosity in the fired samples. The apparent porosity of the fired samples clearly increased with an increase in KCl content. But the majority of pores were still micron sized and the pore size distribution was relatively narrow. This, along with the possible toughening effect from the well-developed plate-like CA6, conferred relatively high mechanical strength on the final highly porous CA6 ceramics.
Keywordscalcium hexa-aluminate porous ceramics molten salt pore size distribution
This work was financially supported by the National Natural Science Foundation of China (Grant no. 51032007), the Fundamental Research Funds for the Central Universities (Grant no. 2012067), and the Doctoral Scientific Research Foundation of Quzhou University (Grant no. BSYJ201707).
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