L. N. Ignat’eva

Oxyfluoride Glasses (A Review)

The influence of oxygen on the glass formation and the structure of oxyfluoride glasses has been considered using different glass systems containing fluorine and oxygen.

X-ray powder diffraction study of polytetrafluoroethylene

Samples of polytetrafluoroethylene were studied by X-ray diffraction. A quantitative X-ray powder diffraction analysis of three components of the polymer was performed for the first time. All samples of polytetrafluoroethylene were found to be three-phase and consist of one crystalline and two amorphous phases. One of the amorphous phases is composed of low-molecular-weight products. The structure of the latter phase was established for the first time by X-ray diffraction methods and computer simulation.

IR-spectroscopic examination of polytetrafluoroethylene and its modified forms

The results of IR-spectroscopic examinations of the molecular and supramolecular structure of polytetrafluoroethylene and polymer materials thereof were summarized. It was shown that, upon heat, mechanical, and other treatment, as well as under radiation exposure, polytetrafluoroethylene preserves its chain-helical conformation, and the resulting modified forms consist of crystalline and amorphous phases in a ratio depending on the history of the sample. The degree of the structural ordering in the polymer decreases with increasing temperature and pressure. The formation of branched moieties and short macromolecules with double bonds (−CF=CF2) in the terminal groups is specific for the process caused by thermal and radiation-induced degradation. The oxidation of the polymer macromolecules requires applying high irradiation doses and heating samples in an oxygen or air atmosphere.

Quantum-chemical calculations of the IR absorption spectra of modified polytetrafluoroethylene forms

DFT(B3LYP) (basis set 6–31 + G(d)) and HF (basis set 6–31G) calculations were performed to determine the geometric structure and vibrational spectra of the CnF2n and CnF2nO molecules (n = 3–13). The IR spectra of chain CnF2nO molecules with the terminal carbonyl group (-COF) were found to contain a band at 1885 cm−1. The C=C and C=O stretching vibrations of the-CF=CF2 and COF terminal groups were independent, and there was no mutual influence of their frequencies starting with the seven-fragment molecule. In the presence of chain branching, the sensitivity of the ν(C=C) and ν(C=O) frequencies in the olefin and carbonyl groups depended on where branching occurred. The chain configuration was found to be energetically favorable compared with branched structures.

Radiation-chemical synthesis of tetrafluoroethylene telomers and their use for preparation of thin protective fluoropolymer coatings

The specific features and possibilities of preparation of protective coatings and composite materials based on fluoromonomers using high-energy rays (60Co γ-rays, fast electrons) were analyzed. The emphasis was placed on synthesis and application of tetrafluoroethylene telomers in acetone. The structure and properties of telomers were examined by IR and NMR spectroscopy, as well as by X-ray diffraction analysis and diathermy. The radiation initiation allows preparation of new products with a broad spectrum of functional properties and opens wider prospects for technological application of fluoromonomers.

Ionic conduction in glasses in the MnNbOF5-BaF2-BiF3 system

The electrical conductivity of oxyfluoride glasses in the MnNbOF5-BaF2-BiF3 system in the temperature range 299–550 K was studied by impedance spectroscopy. It was shown that the conductivity is mainly caused by fluoride ions forming fluorobismuth polyhedra in the glass structure, being as high as 7.46 × 10−3 S/cm (533 K) in the 20MnNbOF5-30BaF2-50BiF3 system reaches, which is at the level of the best values for fluoride glasses.

Synthesis and characterization of bismuth-containing oxyfluoroniobate glasses

New glasses are prepared in the MnNbOF5-BaF2-BiF3 system. The thermal parameters of these glasses are analyzed as influenced by bismuth trifluoride. IR and Raman spectroscopy shows that the glass structures are built of Nb(O, F)6 polyhedra, which are linked by oxygen bridges to form glass nets via. A medium-order order region in the glass includes fluoroniobate polyhedra not linked directly to bismuth trifluoride polyhedra. A Ba0.55Bi0.45F2.45 crystalline phase is discovered at 320°C in a glass of composition 20MnNbOF5-40BaF2-40BiF3.

Effect of bismuth trifluoride on the characteristics of fluoroindate glasses : The InF3-BiF3-BaF2 system

Glass formation in the InF3-BiF3-BaF2 system is studied. Partial substitutions of BiF3 for InF3 in the InF3-BaF2 system reduce the glass-transition and glass-crystallization temperatures and increase the thermal stability range and refractive index. The glass structure is studied using IR and Raman spectroscopy. InF6 and BiFn polyhedra are identified in the system. Doping the glass with bismuth trifluoride changes the degree and linkage character of the InF6 polyhedra in the glass network. The medium-range order length is not affected by the bismuth trifluoride concentration in the glass. The modifier cation (Ba2+) substantially determines the correlation length in the glasses.

The structural features of fluorinated paraffins

A systematic study of the molecular and supramolecular structural features of fluorinated paraffins has been conducted with the use of a set of physical methods and quantum-chemical calculations of the parameters of the IR and NMR spectra. The presence of nonuniformity in the morphological structures of samples obtained from different initial products has been shown. Incomplete substitution of fluorine for hydrogen during synthesis has been revealed, and the types of structural groups in which the substitution occurs have been determined. Fluoroparaffins have been found to effectively dissolve in supercritical carbon dioxide, a phenomenon that opens new fields of application for these materials.

New zirconium fluoride complexes (NH4)6MZr4F23 (M = K, Rb, and Cs): Synthesis and physicochemical properties

Ammonium-containing zirconium fluoride complexes of the formula (NH4)6MZr4F23 (M = K, Rb, and Cs) were obtained and studied. The complexes crystallize in the orthorhombic system. Their unit cell parameters were determined. The IR absorption spectra of the complexes in the 350–4000 cm−1 range were recorded and examined.