Thermoinductive Decomposition of Hydrated Iron Trifluoride in a Stream of Argon

Abstract

Спільна науково-дослідна лабораторія фізики магнітних плівок Інституту металофізики ім. Г. В. Курдюмова НАН України та ДВНЗ Прикарпатський національний університет ім. Василя Стефаника, вул. Шевченка, 57, 76025 Івано-Франківськ, Україна Роботу присвячено встановленню умов одержання безводного фториду заліза методою термічного розкладу тригідрату трифториду заліза. Уточ-нено базис кристалічної структури -FeF 3 3H 2 O. Встановлено температур-ні границі розкладу фази -FeF 3 3H 2 O та продуктів її дегідратації. Одер-жано нанокристалічний трифторид заліза ромбоедричної модифікації.Работа посвящена установлению условий получения безводного фторида железа методом термического разложения тригидрата трифторида желе-за. Уточнён базис кристаллической структуры -FeF 3 3H 2 O. Установлены температурные пределы разложения фазы -FeF 3 3H 2 O и продуктов её де-гидратации. Получен нанокристаллический трифторид железа ромбоэд-рической модификации.The article deals with the conditions for anhydrous iron fluoride obtaining by thermal decomposition of iron trifluoride trihydrate. The basis of the -FeF 3 3H 2 O crystal structure is outlined. Temperature limits of the -FeF 3 3H 2 O phase decomposition as well as products of its dehydration are established. Nanocrystalline iron trifluoride of rhombic modification is obtained.Ключові слова: FeF 3 , кристалічна структура, термічний розклад, Мессба-уерівська спектроскопія, термогравіметричний аналіз. Металлофиз. новейшие технол. / Metallofiz. Noveishie Tekhnol. 2015, т. 37, № 3, сс. 355-365 Оттиски доступны непосредственно от издателя Фотокопирование разрешено только в соответствии с лицензией 2015 ИМФ (Институт металлофизики им. Г. В. Курдюмова НАН Украины) Напечатано в Украине.

Morphological Characteristics of Hydrothermally Synthesized Iron Trifluorides with Various Hydration Degrees

“…It is worth noting that the magnitude of quadrupole splitting for the dominant doublet component ( = 0.64 mm/s) differs from the result of work [11], where the value = 0.12 mm/s was registered. The value of quadrupole splitting close to zero agrees well with the crystallographic model, in which the near environment of every Fe 3+ ion -it is formed by F − anions -is spherically symmetric.…”

“…To prevent the pyrohydrolysis [9], we applied the annealing in the argon atmosphere. In comparison with thermogravimetric researches of commercial crystalline hydrate -FeF 3 3H 2 O [11], the dehydration process began, in our case, at a temperature of 100 ∘ C. More specifically, a shift of the temperature interval, in which the main mass fraction was lost (in our case, this was an interval from 100 to 215 ∘ C) toward low temperatures by about 15 ∘ C was detected (see the TG-curve in Fig. 4).…”

“…At the first stage, OH − groups are desorbed in a temperature interval of 100-162 ∘ C, which is verified by the presence of an endo peak in the DTA curve at 159 ∘ C and a change of the TG-curve slope in a vicinity of 162 ∘ C. The corresponding mass loss amounts to 8.6%. The next stage includes the phase transition -FeF 3 3H 2 O → HTB-FeF 3 3H 2 O with the removal of hydrated water (2.67 H 2 O molecules per FeF 3 3H 2 O formula unit) in a temperature interval of 162-215 ∘ C, which is verified by the presence of the main endo peak in the DTA curve in a vicinity of 175 ∘ C [11] and the correspondence of the measured mass loss of the specimen to a theoretically calculated value of 28.8% (crystalline hydrate HTB-FeF 3 0.33H 2 O has Cmcm space group symmetry [17]). The third stage includes the phase transition HTB-FeF 3 0.33H 2 O → HTB-FeF 3 followed by the removal of hydrated water in a temperature interval of 215-460 ∘ C. At this stage, no variations in the crystal structure and its parameters take place [18].…”

“…According to the results of X-ray phase analysis (XPA) and Mössbauer spectroscopy ( Fig. 1), the produced material was the -form of the crystalline hydrate of iron trifluoride ( -FeF 3 3H 2 O, PDF: 32-0464 [10]) with a modified crystallographic basis proposed by us in work [11] (see Table). In particular, the coordinates for F − and O 2− ions in (8g)-positions were changed from (0.2754, 0.1025, 0.1394) (coordinates were given in work [12], PDF: 85-0404, ICSD 14134) to (0.2754, 0.1025, 0.8794).…”

“…The results of thermogravimetric analysis obtained for the development of the dehydration process of -FeF 3 3H 3 O formed a basis for the selection of a strategy for producing FeF 3 0.33H 2 O and FeF 3 . The former was obtained by applying the thermal annealing in the argon atmosphere at a temperature of 180 ∘ C for 4 h. For producing the latter, the initial crystalline hydrate was thermally annealed in the argon flux (a rate of gas supply of 42 × 10 −9 m 3 /s) at a temperature of 400 ∘ C for 4 h. In our case, the holding time was increased to 4 h in comparison with the dehydration procedure applied in work [11] in order to provide the monophase character of the decomposition end-products. As a result, according to the XPA data ( Fig.…”