Chemical Interaction Between LiF and MgAl₂O₄Spinel During Sintering

Abstract

Reactions between LiF and MgAl2O4 at temperatures up to 1500°C are examined with a variety of tools, including differential scanning calorimetry, thermo‐gravimetric analysis, X‐ray diffraction, and scanning electron microscopy. LiAlO2 and MgF2 are found to be the active reaction products at these temperatures. A transient liquid phase comprising MgF2 and LiF forms at intermediate temperatures, but then is consumed at higher temperatures during the reformation of MgAl2O4. If processed as an uncompacted powder mixture, all of the initial LiF in the system eventually vaporizes at temperatures exceeding 1300°C. A new reaction sequence relevant to the densification of LiF‐doped MgAl2O4 spinel is proposed.

Densification of transparent yttrium aluminum garnet (YAG) by SPS processing

“…The high transparency level was associated with the presence of 1 vol.% of LiF additive, which accelerates the rate of synthesis of spinel from elemental oxide powders, its consolidation to full density and provides a cleansing effect that allows eliminating the carbon impurities. The results of this study also support the findings of by Rozenburg et al, 17 namely that the presence of the LiF additive promotes the consolidation of the samples.…”

Effect of 1wt% LiF additive on the densification of nanocrystalline Y2O3 ceramics by spark plasma sintering

“…In this respect, chemical reaction between LiF and the carbonic species such as sputtered carbon at the particle surfaces and CO gas present within the die atmosphere, may be responsible for the formation of gaseous graphite fluoride, (CF) n , and Li ions, as suggested by Reimanis and Kleebe, 18 Meir et al 19 and Nakajima. 34 The solubility of Li + ions in oxides such as spinel, 21,35 MgO, 14,36 and BaTiO 3 37 was reported. Adsorption of the very active Li + ions in the Y 2 O 3 nanoparticle surfaces may enhance their surface activity, improve the surface diffusivity, and the wetting ability by forming point defects.…”

A thermodynamic approach to obtaining transparent spinel (MgAl2O4) by hot pressing

“…30 LiAlO 2 formation becomes endergonic in the presence of carbon, and for temperature below 1300 • C, while the reaction becomes exergonic again if the temperature is raised above 1300 • C.…”

“…30 Reaction (5) can thus be simplified, taking only the interaction between LiF and Al 2 O 3 into account.…”