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ArticleName Understanding the effect of lithium fluoride additive on the properties of pressureless sintered magnesium aluminate spinel ceramics
DOI 10.17580/tsm.2022.09.02
ArticleAuthor Senina M. O., Lemeshev D. O., Protasov A. S., Zhukov D. Yu.

D. Mendeleev University of Chemical Technology of Russia, Moscow, Russia:

M. O. Senina, Associate Professor at the Department of Chemical Technology of Ceramics and Refractories, Candidate of Technical Sciences, e-mail:
D. O. Lemeshev, Dean of the Faculty of Technology of Inorganic Substances and High-Temperature Materials, Candidate of Technical Sciences
A. S. Protasov, Engineer at the Department of Chemical Technology of Ceramics and Refractories
D. Yu. Zhukov, Director of Ekokhimproekt Technology Centre, Candidate of Technical Sciences


This paper looks at the problem of obtaining high-density transparent ceramics. The paper considers a method for producing such material from magnesium aluminate spinel (AMS) using sintering additives, as well as its potential application. The paper gives an overview of possible additives that are most commonly used by researchers for magnesium aluminate spinel ceramics synthesis. Based on the reviewed literature, lithium fluoride (LiF) was selected by the authors as a sintering additive for the purposes of this research. The paper describes the results of a study that looked at obtaining transparent ceramics by pressureless vacuum sintering at 1,750 оC. By means of thermal synthesis, powders with a single magnesium aluminate spinel phase and bimodal particle size distribution were obtained. Different mechanisms were considered of how LiF densifier acts to create a pore-free ceramic structure. Lithium fluoride was found to form a solid solution with magnesium aluminate spinel, which changes the crystal lattice parameter resulting in a high-density material. Ceramic samples with zero open porosity and relative density of 99% were obtained. The average density was 3.51 g/cm3 at the lithium fluoride concentration of 2.6 wt. %, and 3.55 g/cm3 when the lithium fluoride concentration was 2.7 wt. %. The obtained ceramics can transmit light in the visible region of the electromagnetic spectrum. The residual light diffusion in the obtained ceramic samples can be attributed to the residual closed porosity, which is equal to 1%. The paper describes possible solutions to the problem in order to achieve better light transmission.
The researches were conducted using the equipment of the Research sharing center named after D. I. Mendeleev within the framework of the project No. 075-15-2021-688.

keywords Magnesium aluminate spinel, high-density ceramics, sintering additives, lithium fluoride, vacuum sintering, defect formation, porosity

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