Composite polymer-containing protective layers on titanium

Abstract

The method of plasma electrolytic oxidation (PEO) allows for significantly enlarging the sphere of practical application of metals and alloys by modifying their surface properties. PEO coatings, characterized by their good adhesion to substrate and by their developed surfaces, may be an appropriate base for obtaining of composite layers containing polymer materials. In this connection, the application of polytetrafluoroethylene (PTFE) is of considerable interest due to the practical importance of the properties of this fluoropolymer. The method of polytetrafluoroethylene residue utilization developed in the Institute of Chemistry of the FEB RAS allows us to obtain superdispersed polytetrafluoroethylene (SPTFE of the Forum grade) with particle dimensions less than 1 µ m by gas-dynamic thermodispersion. This material is promising for obtaining thin composite coatings (CC).At the same time, when subjecting SPTFE to repeated pyrolysis, one can obtain its different oligomeric fractions, which, in turn, may be applied to the structure of composite layers oriented toward specific operating conditions. Since the products of SPTFE pyrolysis differ in fractional composition, morphology, and thermodynamic properties [1], it seems necessary to study the properties of both the fractions themselves and the heterostructures obtained on their basis in detail so the conditions of layer formation characterized by optimum consumer demand qualities can be selected.The present paper is a continuation of previous studies [2][3][4][5] on revealing the influence of different fractions of polytetrafluoroethylene, which is a constituent of composite coatings, on the charge transfer processes at the oxide heterostructure/electrolyte interface in order to develop a high-performance method of heatexchange surface protection from the deleterious effect of an aggressive medium, including scale formation. It was established in [3,5] that the fractional composition of PTFE and modes of heat treatment (HT), particularly its duration, render the determining influence on protective properties of composite layers. The following fractions of polytetrafluoroethylene were applied in [5]: low-temperature fraction (ltf) educed from PTFE when heated at 70 ° C; high-temperature fraction (htf), which is a residue obtained after heating the initial PTFE to 300 ° C; and PTFE fraction of averaged composition (afc).In the present paper, there was an attempt to study samples with composite coatings containing two intermediate PTFE fractions educed at 90 ° C and in the temperature range 300-314 ° C. Since the most homogeneous and intact CC on PEO structures are formed as a result of heat treatment, optimum modes of HT with differing fractional compositions of applied fluoropolymer were additionally sought.As was been shown earlier [2][3][4][5], composite coatings have complex structures and they consist of a nonporous underlayer and a porous layer which is partially or completely filled with polymer. It is efficient to study this complex object by electrochemical...

Quantum chemistry studies of unbranched fluoropolymers

“…EðC 5 F 12 Þ; DE ¼ 78 kcal=mol (8) (c -intra-chain radical, t -terminal radical) demonstrated that addition of the CF 3 -group to a radical formed, for example, as a result of irradiation yielded the system stabilization. Here the system stabilization occurs independently of whether the trifluoromethyl group is added inside the chain or at the terminal position.…”

“…For example, the basic fluoropolymer -polytetrafluoroethylene (PTFE) -belongs to the class of high-molecular systems of a molecular weight up to one million, whereas accurate calculations are possible only for fragments whose size is limited by a few dozens of atoms. Nevertheless, a number of parameters characterizing the molecular structure of small macromolecules would be also valid for polymers built from the above fragments and, moreover, lowmolecular forms (telomers, fluoro paraffins) themselves have been recently in high practical demand as coatings, nanofilms and composites [7,8]. In the latter case the problem of unambiguous and reliable interpretation of empirical data can be solved by performing quantum chemistry calculations of geometric parameters, conformation, IR-, Raman and NMR-spectra of small macromolecules comprising the polymer forming units [6,[9][10][11].…”

Thermal properties and degradation of polytetrafluoroethylene low‐molecular fractions

“…Systematic studies of this powder by the set of physical methods revealed that it contains fractions of different molecular weights, has more complex (in comparison with PTFE) molecular, phase and morphological structure, and radically different thermal parameters . The revealed possibilities for the separation of powder into fractions enabled to isolate low‐, middle‐, and high‐molecular fractions, each of which have its specific features and, as a result, different fields of practical application . The obtained results served as a basis for finer material separation into fractions and their subsequent study.…”

Change in the properties of composite coatings during climatic tests in a salt spray chamber

“…В связи с этим ПЭОслой позволяет внедрить полимерный материал для модификации покрытия с целью улучшить его защитные характеристики. Наиболее перспективен для этой роли ультрадисперсный политетрафторэтилен, обладающий высокой стойкостью, низкой поверхностной энергией и широким диапазоном температур [8][9][10][11].…”

“…Однако в основном исследуются покрытия, не прошедшие какого-либо срока службы или хранения и находящиеся полностью в условиях лабораторного эксперимента. Указанные в работах [8][9][10][11] показатели защитных свойств покрытий находятся на своих пиковых значениях. Это не дает возможности в полной мере проследить процессы коррозии и разрушения в течение длительного срока эксплуатации или в условиях интенсивного воздействия на них агрессивной среды, чтобы оценить устойчивость сформированных слоев.…”