Investigation of the Effect of LiCl and LiF Additives on the Kinetics of Spark Plasma Sintering of Fine-Grained Alumina

• Published in: Inorganic materials : applied research 2023-12, Vol.14 (5-6), p.1361-1370
• Main Authors: Boldin, M. S., Popov, A. A., Shcherbak, G. V., Smetanina, K. E., Permin, D. A., Koshkin, V. A., Nokhrin, A. V., Chuvil’deev, V. N., Moskvichev, A. A., Murashov, A. A.
• Format: Article
• Language: English
• Subjects: Additives; Aluminum oxide; Aqueous solutions; Ceramics; Chemistry; Chemistry and Materials Science; Fluorides; Grain boundary diffusion; Heating rate; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Kinetics; Lithium; Lithium chloride; Lithium fluoride; Low temperature; Materials Science; New Technologies for Obtaining and Processing Materials; Planetary mills; Plasma sintering; Shrinkage; Sintering (powder metallurgy); Spark plasma sintering; Specific gravity; Temperature
• ISSN: 2075-1133; 2075-115X
• DOI: 10.1134/S2075113323050064

— The effect of the lithium chloride and lithium fluoride additives (2 wt %) on the kinetics of spark plasma sintering of industrial fine alumina powder was investigated. The Al 2 O 3 + 2% LiF powder was obtained by mixing the α-Al 2 O 3 fine powders with the aqueous solution of LiF. The Al 2 O 3 + 2% LiCl fine powder was obtained by joint grinding of the components in a planetary mill. The sintering of the powders was performed with the heating rates of 10 and 50°C/min up to the temperature corresponding to the end of the shrinkage. The ceramics sintered with the heating rate of 10°C/min had the relative density of 97.4‒98.7%. The addition of lithium fluoride into the alumina powder was found to allow reducing the temperature of the beginning of the intense powder shrinkage from 1400–1500 to 1255–1335°C. LiCl was shown to evaporate at low heating temperatures and not to affect the compaction intensity of the Al 2 O 3 powder. The presence of the overheated LiF melt (not having enough time to evaporate from the specimen volume completely) in the ceramic leads to the appearance of the residual porosity and to the reduction of the hardness of the ceramic. Using the Young–Cutler equation, the powder compaction mechanisms were determined for pure alumina α-Al 2 O 3 and for the powder compositions with the LiCl and LiF additives in the rapid heating conditions. The sintering activation energy was shown to be close to the energy of the grain boundary diffusion. The LiF melt was found to promote the sliding of the Al 2 O 3 fine particles during the low-temperature compaction stage.