Structure and Corrosion Resistance Against Intergranular Corrosion of Nickel-based Superalloy VDM ® Alloy C-4

The structure of VDM ® Alloy C-4 (UNS 06455) in “as received” state was studied. The data on the kinetics of secondary phases formation for “sheet” and “tube” samples in the range from 550 to 1100 ∘C after exposure for various period of time (from 30 min to 1000 hours) are presented. The data concerning the resistance against intergranular corrosion of the material under various conditions were analyzed using ASTM G-28 and RD 24.200.15-90 techniques. Keywords: nickel alloy, structure, VDM Alloy C-4, TTP-diagram, intergranular corrosio

Corrosion resistance of alloys of Hastelloy in chloroaluminate melts

The corrosion of Hastelloy S, Hastelloy X, Haynes 230, Hastelloy N, Hastelloy G35 and Hastelloy C2000 alloys was studied in KCl-AlCl3 melts at 550°С. The rates and the mechanisms of corrosion of the studied materials were determined. The processes taking place during the interaction between alloys and chloroaluminate melts were investigated

Spectroelectrochemical study of neptunium in molten LiCl-KCl eutectic

Neptunium behaviour in an LiCl-KCl eutectic melt at 723 K was studied using spectroelectro-chemistry. Cathodic reduction of neptunium(IV)-containing melts led to the formation of Np(III) ions and then neptunium metal. Electronic absorption spectra of Np(IV) and Np(III) chloro species in LiCl-KCl melt were recorded and resolved into individual Gaussian bands. The nature of neptunium complex ions in the melt is discussed. © 2007 Verlag der Zeitschrift für Naturforschung.I. B. P. thanks INTAS (Grant No. 03-55-1453) for financial support

Tungsten chemistry in alkali chloride melts

Speciation of tungsten in alkali chloride melts (based on NaCl-2CsCl, NaCl-KCl and 3LiCl-2KCl mixtures) was studied between 550 and 750æC using electronic absorption spectroscopy. Only W(IV) and W(V) chloro and oxychloro species can be stabilized under the conditions studied. Tungsten(IV) chloride ions are very sensitive to oxide/hydroxide impurities present in the melt. Anodic dissolution of W metal at anodic current densities in the range of 0.005 - 0.1 A/cm2 produces only [WCl6]2- ions that can be electrochemically (on a glassy carbon anode) oxidized to [WCl 6]-. Small amounts of oxide ions present in the melt result in a gradual conversion of W(IV) chloro species into W(IV) oxychloro species. In the presence of O2 in the atmosphere [WCl 6]2- is oxidized into the tungsten(V) species [WOCl 5]2-. Dissolution of tungsten hexachloride, WCl 6, in an NaCl-2CsCl melt initially yields [WCl6] 2- (due to disproportionation). Reaction of metallic tungsten with Pd(II)-containing melts results in the formation of [WCl6] 2- species. The main spectroscopic parameters of [WCl 6]2- and [WCl6]- complex ions were calculated. © 2007 Verlag der Zeitschrift für Naturforschung

Speciation of rhenium in chloride melts: Spectroscopic and electrochemical study

Speciation of rhenium in high-temperature alkali chloride-based melts was studied using electronic absorption and IR spectroscopy of molten salts and diffuse reflectance spectroscopy of quenched melts. Rhenium was added to the melts by anodic dissolution of the metal (at anodic current densities of 0.005-0.05 A/cm2), by reacting Re and ReO2 with Cl 2 and HCl, and by dissolving K2[ReCl6]. The melts included 3LiCl-2KCl and NaCl-2CsCl eutectics, an NaCl-KCl equimolar mixture, and pure NaCl, KCl and CsCl between 450 and 850 °C. Rhenium was present in the melts as Re(IV) hexachloro-ions, [ReCl6]2-; no evidence of species containing rhenium in oxidation states below four was obtained. The kinetics of [ReCl6]2- disproportionation in molten alkali chlorides were investigated, and the IR spectra of [ReO 4]- ions in molten CsCl-CsI and CsI were measured for the first time. © 2008 Verlag der Zeitschrift für Naturforschung, Tübingen

Behaviour of rare earth elements in molten salts in relation to pyrochemical reprocessing of spent nuclear fuels

The kinetics of chlorination of lanthanide oxides (by Cl2 and HCl) and precipitation of lanthanide phosphates was studied by in situ electronic absorption spectroscopy in 3LiC1-2KC1 and NaCl-KCl melts at 400-750°C Products of the chlorination are the corresponding hexachlorospecies, LnCl63-, and the rate of chlorination increases with increasing temperature. Composition of the precipitated phosphates depends on the melt composition and 1.5-5 fold excess of phosphate, depending on the nature of lanthanide, is needed for the complete removal of the lanthanides from the melt. Over three hours are required for completing the reaction of phosphate precipitation. copyright The Electrochemical Society.Electrochemical Society, Phys. Anal. Electrochem. Div.;Electrochemical Society, Electrodeposition Division;Electrochemical Society, High Temperature Materials Division;Electrochemical Society, Battery Division;Electrochemical Society, Energy Technology Divisio

Processing of vanadium and niobium electrodeposited from alkali chloride melts

The methods of hydrometallurgical treatment of cathodic deposits obtained by electrorefining vanadium and niobium metals in chloride melts were studied. The effectiveness of employing nitric acid was demonstrated. The optimal conditions of leaching trapped salt were determined: HNO3 concentration of 2.5 wt. % for vanadium and 5 wt. % for niobium; solid-to-liquid ratio 1:10 for both metals. The effect of increasing duration of a washing cycle on number of process stages was investigated. The methods of final washing and drying metallic powders were considered. ©The Electrochemical Society.Physical and Analytical Electrochemistry;Electrodeposition;Energy Technolog

Spectroelectrochemical study of stainless steel corrosion in NaCl-KCl melt

High-temperature spectroelectrochemestry was applied to study corrosion of various types of stainless steel in molten salts. The electronic absorption spectra of products of anodic dissolution of stainless steel major components (iron, chromium, nickel, molybdenum, manganese, titanium) were measured in NaCl-KCl melt at 750 °C The effectiveness and limitations of applying spectroscopic method for studying alloys corrosion was demonstrated on example of anodic dissolution of AISI 316L, 316Ti and 321 austenitic steels. The major corrosion products of steels are iron, manganese and chromium species. Prolongation of anodic dissolution leads to increasing chromium-to-iron ratio in the melt. Titanium in steels forms very stable carbonitride species that aren't dissolved during anodic oxidation. © The Electrochemical Society.Physical and Analytical Electrochemistry;Electrodeposition;Energy Technolog

Study of causes of film formation on the electrolyte surface during niobium electrorefining

Formation of a conducting film on the surface of fused electrolyte during electrorefining of niobium in chloride melts was investigated. It was found that this film has metallic nature and is formed as a result of disproportionation of niobium(III) ions at a liquid-gas interface. Decreasing temperature gradient along the heated part of the electrolyser can be used to limit the influence of the disproportionation onto film formation. The metal film formation on solid ceramics can be used for creation of conducting layers on various oxide materials. copyright The Electrochemical Society.Electrochemical Society, Phys. Anal. Electrochem. Div.;Electrochemical Society, Electrodeposition Division;Electrochemical Society, High Temperature Materials Division;Electrochemical Society, Battery Division;Electrochemical Society, Energy Technology Divisio

Effect of melt composition on the reaction of uranium dioxide with hydrogen chloride in molten alkali chlorides

The reaction of uranium dioxide with excess hydrogen chloride in alkali chloride melts (LiCl, 3LiCl-2KCl, NaCl-KCl and NaCl-2CsCl) has been studied between 450 and 750°C, and the reaction products were characterized by electronic absorption and X-ray absorption spectroscopy. Uranium(V), [UO 2Cl4]3-, and uranium(IV), [UCl 6]2-, species were formed. They depended upon the temperature and the radius of the alkali cations present. Uranium(V) ions predominated in melts with small cations (LiCl and 3LiCl-2KCl). © 2007 Verlag der Zeitschrift für Naturforschung