Fluorinating Reagents and Method of Fluorination

In the sol-gel processing of fluoride glasses, the fluorination treatment is a more important process to obtain chemically and optically pure materials. Therefore, fluorinating reagents such as BrF3, HF, NF3 and SF3 are used for direct fluorination of oxide precursors. It should be noted that BrFa is a toxic material and an extremely reactive fluorinating reagent with the potential to cause fire. 

Konishi et al. [15] prepared amorphous 60ZrO2-30BaO-10LnOi 5 gels (Ln = La, Ce, Pr, Nd or Eu) and fluorinated them by NF3. In the fluorination process, the reaction rates were found to be substantially different with the Ln species, becoming slower in the order of La, Ce, 

Nd and Eu. Saad and Poulain [5] carried out fluorination of a wet oxide gel containing Zr, Ba, La, A1 and Na using anhydrous HE as a fluorinating reagent. Eigure 10.1 shows a typical experimental setup for fluorination. The reaction time was approximately 1 h for a 10 g batch at 200 °C. In this process, fluorination is implemented on an oxide gel, which still contains a significant amount of water and alcohol. At 200 °C, the chemical equilibrium 

Metal fluoride nanomaterials can also be prepared by fluorination of oxide gels. The reaction of magnesium and aluminum alkoxides with HE in nonaqueous solvents led to the formation of amorphous or crystalline nanosized MgE2 and AIF3, respectively, with high specific surface areas [16, 17]. 

Using this chemical phenomenon, heavy-metal fluoride glasses were prepared using trifluoroacetates of zirconium, barium, lanthanum, aluminum and sodium [21]. Eigure 10.2 shows thermal gravimetric analysis of the ZBLAN powder in this process. A drastic decrease in weight (47.4%) was observed in the range of 220-300 °C, which was attributed to the decomposition from the trifluoroacetate to the sohd ZBLAN fluoride. 

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