Viliam Pavlík

High-Temperature Corrosion Behavior of Superalloys in Molten Salts - A Review

ABSTRACT The use of molten salts based on fluorides/chlorides/nitrates/sulfates or carbonates is now an accepted practice in energy conversion technologies and many other industrial processes. However, compatibility of molten salts with the structural alloys and materials corrosion has been of real concern at such temperatures (600–900°C). Hence, the material development and corrosion studies turn out to be an essential part of research. The results of recent studies are reviewed to understand the developments that have occurred in the latter part of the last decade. The corrosion kinetics of modern materials in variety of molten salts with focus on reaction mechanisms and corrosion products is investigated by scientists around the globe. Emphasis has also been given on the composition of the oxide films/corrosion products on alloys of interest in wide a range of melts. By and large, molten salt corrosion has been predominantly studied by gravimetric, electrochemical techniques and, morphology and chemical analysis of corrosion products by means of XRD, SEM/EDX, ICP/AAS, etc. This article gives in-depth insight into the composition of materials, the molten salt mixtures, and various aggressive environments mainly high temperatures and long exposures.

Corrosion of titanium diboride in molten FLiNaK(eut)

Pure and enriched titanium dibromide (TiB2) samples (prepared by hot isostatic pressing) with different mole ratios of Ni and Ta were investigated in contact with molten eutectic salt (FLiNaK(eut); LiF/NaF/KF 42.5 mole %: 11.5 mole %: 42.0 mole %) at 600°C. Corrosion resistance of the materials was studied, the mass losses and depths of corrosion were calculated, and sample surfaces were investigated by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). Nickel addition decreased the corrosion resistance of TiB2. Simultaneous additions of both elements, Ni and Ta, as well as the addition of Ta only showed reducing effect on grain formation and they increased the corrosion resistance which is highest in the last case.

Formation of coordination compounds with aniline in the interlayer space of Ca2+-, Cu2+- and Fe3+-exchanged montmorillonite

The influence of Ca2+-, Cu2+- and Fe3+-exchanged montmorillonite (MMT) on the type of interaction with aniline in the interlayer space of MMT has been studied by means of X-ray powder diffraction and infrared spectra. Results of X-ray diffraction showed that aniline was successfully intercalated into the interlayer space of MMT. Based on IR spectra evaluation, aniline was indirectly coordinated through a water-bridge in Ca2+- and Fe3+-MMT and it was indirectly coordinated through a water-bridge as well as protonated in Cu2+-MMT (the spectrum of protonated aniline showed deformation and changes in the NH3+ absorption at approximately 1521 cm−1). It is important to point out that Cu2+-MMT indirect coordination and protonation occur simultaneously.

Thermal, spectral and diffraction properties of Hg(II)-exchanged montmorillonite with alkylamines

Many papers have been published concerning the influence of different steric properties of metylamine, dimethylamine and trimethylamine on the type of interactions with different exchanged montmorillonite and their properties. The most effective active sites in montmorillonite are placed between two silicate layers, where the naturally occurring cations can easily be replaced by heavy metals and organic groups. Mercury is one of the most serious contaminants in environment. All forms of mercury are poisonous; however, organic mercury species are the most dangerous. It is harmful even in very small amount and presents a significant environmental threat. The results of thermogravimetry, differential thermogravimetry, X-ray powder diffraction and IR spectroscopy analysis show that methyl, dimethyl and trimethylamines are intercalated into the interlayer space of Hg-MMT. The effect of different steric properties of studied alkylamines is evident.

Interaction of metallic zirconium and its alloys Zry-2 and E110 with molten eutectic salt of LiF—NaF—KF containing zirconium fluoride components

The interactions of selected zirconium alloys used as special construction materials (Zr-pure, Zry-2, E-110) with the molten system of (LiF—NaF—KF)(eut.) with additions of K2ZrF6 or Na7Zr6F31 were studied. Corrosion losses of pure zirconium decrease sharply with 5 mole% addition of K2ZrF6 to (LiF—NaF—KF)(eut.). The presence of alloying additives (Sn, Nb) has a positive influence on corrosion resistance in the eutectic mixture — up to 60% increase in corrosion resistance in comparison with pure zirconium. The mass losses of pure zirconium indicate an increasing corrosion attack with increasing Na7Zr6F31 content in (LiF—NaF—KF)(eut.) mixtures.

Thermal Stability vs. Crystallization of the Lithiumsilicate Glasses with Addition Zirconium Dioxide and Titanium Dioxide

The glasses with composition of Li2O . 2 SiO2 . n ZrO2 . n TiO2 (where n = 0; 0.015; 0.031; 0.050; 0.075; 0.1; 0.15; 0.2) were prepared and the relationship between structural and selected parameters of thermal stability vs. crystallization has been studied by differential thermal analysis. Structural analysis was provided by X–ray diffraction. The order of thermal stability vs. crystallization representing of activation energy of studied glass systems which increase with higher addition both oxides. The same order was obtained from the values of XRD. On the comparison the glasses with zero addition titanium dioxide their activation energy was much higher.