A thermogravimetric study of the fluorination of zirconium and hafnium oxides with fluorine gas

A thermogravimetric study of the fluorination of zirconium and hafnium oxides with anhydrous hydrogen fluoride gas

“…Between 300 and 500 8C, increasing mass gains were recorded till the 35% stoichiometric value anticipated for the total conversion of ZrO 2 to ZrF 4 was observed at 525 8C. The 525 8C temperature condition coincides with the optimum conversion temperature reported by both Haendler et al [17] and Monnahela et al [13] on using fluorine as the fluorinating agent. At 300 and 350 8C there was a 1 and 4% mass gain, respectively, and the XRD revealed ZrO 2 as the major phase and phases of Zr 3 O 2 F 8 ( Fig.…”

“…However, these aqueous processes are disadvantageous since they are expensive, ecologically unfriendly and involve intricate processes. Dry routes by which tetrafluorides are prepared from the metal oxides using hydrogen fluoride [9][10][11] or fluorine [12,13] have been proposed. The anhydrous routes present several advantages as they yield the less hygroscopic ZrF 4 as the feed material for pure Zr metal production.…”

Investigation of Zr(IV) in LiF–CaF2: Stability with oxide ions and electroreduction pathway on inert and reactive electrodes

“…ZrF 4 is mainly prepared by chemical reaction between zirconium oxide ZrO 2 and a fluorinating agent, such as fluorine gas [12], hydrogen fluoride [13], ammonium bifluoride [14] or bromium trifluoride [15]. These syntheses evidence the existence of a great number of zirconium oxifluorides solid phases.…”

Fluoridation of HfO2

“…The traditional solid-state approach is to combine precursor oxides and fluorides together and heat them until a reaction occurs. The high reactivity of all but the most stable fluoride materials with SiO 2 and/or water means that this often entails costly setups such as sealed metal tubes. − Alternative methods include exposing the precursor oxide to a reactive fluoride source such as F 2 or HF gas or aqueous hydrofluoric acid, although these must be handled carefully as they are highly toxic. , Safer options include controlled decomposition of stable fluorides and fluoride hydrates or reaction of oxides with solid fluoridation agents such as XeF 2 , CuF 2 , ZnF 2 , NH 4 F (or NH 4 HF 2 ), polytetrafluoroethylene [PTFE; −(CF 2 ) n −], or polyvinylidene difluoride [PVDF; −(CH 2 –CF 2 ) n −], all of which decompose upon heating into more reactive agents. ,,− Of these, the last three are stable under ambient conditions, therefore easy to work with, and conveniently produce volatile products at high temperatures, lowering the risk of secondary phase contamination. As such, these three reagents are commonly used to fluoridate oxides. ,,,, Among the hafnium oxyfluoride studies in the literature, it appears that primarily thermal decomposition of fluorides and reaction of HfO 2 with F 2 or HF have been attempted, whereas a wider variety of synthetic approaches have been used for Zr. − ,− Thus, employing a different fluoridation method for HfO 2 may reveal previously unreported Hf–O–F phases.…”

“…13−16 Alternative methods include exposing the precursor oxide to a reactive fluoride source such as F 2 or HF gas or aqueous hydrofluoric acid, although these must be handled carefully as they are highly toxic. 24,26 Safer options include controlled decomposition of stable fluorides and fluoride hydrates or reaction of oxides with solid fluoridation agents such as XeF 2 , CuF 2 , ZnF 2 , NH 4 F (or…”