Effect of Ta on the corrosion performance of Mo<Subscript>3</Subscript>Si intermetallic in NaCl solutions

The effect of Ta contents on the corrosion performance of Mo₃Si intermetallic in 0.5 M NaCl has been evaluated. Materials included Mo₃Si plus 5, 17, 53, 60, and 74 at% Ta. Techniques included potentiodynamic polarization curves and linear polarization resistance curves. Except for 74 at% Ta, additions of Ta induced a passive region, decreasing the anodic current density, the free corrosion potential, the pitting potential, and the corrosion current density.     

The effects of a eutectic modifier on microstructure and surface corrosion behavior of Al-Si hypoeutectic alloys

Hypoeutectic aluminum–silicon alloys can have significant improvements in mechanical properties by inducing structural modification in the normally occurring eutectic. The eutectic modification may affect not only the mechanical properties but also the corrosion resistance of such alloys. It is well known that structural parameters such as grain size and interdendritic spacing can significantly affect corrosion resistance of alloys. However, to date, few researches have been performed to experimentally evaluate the effects of an effective modification of eutectic morphology on surface corrosion behavior of Al–Si alloys. In the present study, modified and unmodified samples of an Al 9 wt.% Si alloy were solidified under similar solidification conditions, and after metallographic procedures, the corrosion resistance was analyzed by both the electrochemical impedance spectroscopy technique and the Tafel extrapolation method carried out in a 0.5 M NaCl test solution at 25 °C. The impedance parameters and corrosion rate were obtained from an equivalent circuit analysis. It was found that the Al-9 wt.% Si alloy casting in the modified condition tends to have its corrosion resistance decreased when compared to the unmodified alloy.     

Thermodynamic properties of transition metals in aqueous solution. 2. The enthalpies of mixing of aqueous solutions of CoCl2, CuCl2, and MnCl2 with NaCl at varying ionic strength at 25°C

Enthalpies of mixing (_m H) aqueous solutions of CoCl₂, CuCl₂, and MnCl₂ with NaCl solutions were measured at constant ionic strengths of 0.5, 1.0, and 3.0 molal at 25°C. The excess enthalpy equations of Pitzer were then fit to the resulting _m H data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system. The heat of mixing data for CoCl₂ and CuCl₂ were in agreement with earlier isomolal results by other workers.     

A SEM/EDXA study on the chemical attack of aqueous NaOH/KOH solutions on the surface of the metal-metalloid glass (Fe, Cr)80 (P, C, Si)20 and Fe75Cr5P8C10Si2, respectively

After a treatment of the metal-metalloid glassy alloy (Fe, Cr)₈₀ (P, C, Si)₂₀ and Fe₇₅Cr₅P₈C₁₀Si₂, respectively, by aqueous alkaline solutions of 1.0M NaOH + 1.0M KOH and 2.5M NaOH + 2.5M KOH, respectively, a SEM/EDXA study of the glass surface was performed.The results of the accelerated ageing procedure demonstrate that the glass treated with the 1.0M NaOH + 1.0M KOH solution at room temperature (20 °C) is characterized by a surface state like that of the initial material.For the glass treatment with the 2.5M NaOH + 2.5M KOH solution at 20 °C the surface layer shows a different morphology and is thicker. It can be supposed that the reinforcing property is reduced.The glass treatment at 80 °C with the aqueous solutions 1.0M and 2.5M (NaOH + KOH), respectively, leads to surface layers of different morphology and such a layer is about 5 m thick. The strength of solid residue of such a treated glass is very low.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Thermal plasma synthesis of transition metal nitrides and alloys

Applications of arc plasma processing to high-temperature chemistry of Group V nitrides and Si and Ge alloys are studied. The transition metal nitrides -VN, -NbN, and -TaN are directly synthesized in a dc argon-nitrogen plasma from powders of the metals. A large excess of N₂ is required to form stoichiometric -VN, while the Nb and Ta can only be synthesized with a substoichiometric N content. In a dc argon plasma the alloys V₃Si, VSi₂, NbSi₂, NbGe₂, Cr₃Si, and Mo₃Si are obtained from powder mixtures of the corresponding elements. The compounds are identified by x-ray diffraction patterns and particle shape and size are studied by electron microscopy.     

Electrochemical influence of the nature and composition of halides on Al-12Si

The aluminium alloy Al-12Si has been polarized by potentiodynamic method at 25 °C under magnetic stirring and in an aerated solution. Its electrochemical behaviour was tested first by varying the concentration of NaI or NaCl (10⁻⁴, 10⁻³, 10⁻²) added respectively to NaCl or NaI (10⁻³ M), and the pH of NaCl 10⁻³ M (pH = 2.3, 7.3, 10) when adding HCl or NaOH (i.e. the composition of the solution), then by incorporating different ions familiar to an industrial atmosphere (Cu²⁺, Zn²⁺, , , ) at 10⁻⁶ M to NaCl 10⁻³ M (i.e. the electrolyte nature). The use of the electrokinetic curves obtained allowed the access to the passivation (i _pass , E _rup and E _rep ) and to the electrokinetic parameters (i _corr , R _p and P). They prove the behaviour dependence of the above alloy on the composition and nature of the electrolyte.     

Thermodynamic properties of transition metals in aqueous solution: 3. The heats of mixing aqueous solutions of CdCl2, NiCl2 and ZnCl2 with NaCl at varying ionic strength at 25°C

The heat of dilution of aqueous solutions of ZnCl₂ and the heats of mixing H _m of aqueous solutions of CdCl₂, NiCl₂, and ZnCl₂ with NaCl solutions were measured at 25°C. The heats of mixing were made at constant ionic strengths of 0.5, 1.0, and 3.0 molal. The excess enthalpy equations of Pitzer were then fitted to the resulting heats of dilution and heats of mixing data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system.     

Corrosion behavior of PEO-treated AZ31 Mg alloy in chloride solution

Corrosion behavior and resistance of plasma electrolyte oxidation (PEO)-treated AZ31 Mg alloy were investigated by immersion and potentiodynamic polarization tests in 0.5 M NaCl solution in view of the PEO film thickness and sealing treatment of the PEO films in boiling water. The PEO films were formed using pulse current for various durations in 1 M NaOH?+?0.5 M NaF solution. Filiform corrosion was observed during the immersion test while pitting corrosion occurred during the potentiodynamic polarization test, irrespective of sealing treatment of the PEO films. Corrosion resistance of AZ31 Mg alloy was improved remarkably by the formation of thicker PEO films and their sealing treatments.     

Isotopic analysis of243Cm and244Cm by internal conversion electron spectrometry

The electrodeposition of uranium and trace quantities of²³⁹Pu,²³⁴Th,¹⁴⁴Ce on a stainless steel disk has been investigated from 0.5–2.0M NaOH and the two-phase system: extract of actinides in TBP-aqueous solution of NaOH. The electrodeposition yield of the above elements reaches 98–100% in 40 min of electrolysis with current density 0.4–0.5 A/cm². The presence of 0.5M Na₂CO₃, 2.0M NaNO₃, 2.0M NaNO₂, 0.2M NaF in alkaline solutions does not decrease the electrodeposition yield. The electrodeposited films meet all the requirements of -spectrometry. The uranium oxidation states (V) and (IV) have been determined in the electrodeposited films.     

Position sensitive atom probe study of segregation in molybdenum alloys

Three dimensional atom-probe measurements have been carried out to study the segregation behaviour of Mo_xW_(1–x) alloys (x = 0.9; 0.75; 0.5; 0.25). As predicted from alloy thermodynamics, on in situ annealed specimens a significant surface enrichment of molybdenum has been observed. For alloys with tungsten contents above 25% the composition profiles measured are in a good agreement with the theoretical predictions. The positive regular solution parameter of this binary system gives reason for a random distribution of alloy components. In the three-dimensional reconstructions local agglomerations and combined features of tungsten atoms are to observe in alloys with Mo as major component.     

The effect of pressure on the ionization of water at various temperatures from molal-volume data1

The apparent molal volumes of dilute (0.002 to 1.0m) aqueous HCl and NaOH solutions have been determined at 0, 25, and 50°C and NaCl solutions at 50°C. The partial molal volumes ( ) of HCl, NaOH, and NaCl solutions have been determined from these apparent molal volumes and other reliable data from the literature. The partial-molal-volume changes ( ) for the ionization of water, H₂OH⁺+OH^–, have been determined from 0 to 50°C and 0 to 1m ionic strength from the partial molal volumes of HCl, NaOH, NaCl, and H₂O. The partial molal compressibilities ( for HCl, NaOH, NaCl, and H₂O have been estimated from data in the literature and used to determine the partial molal compressibility changes ( ) for the ionization of water from 0 to 50°C and 0 to 1m ionic strength. The effect of pressure on the ionization constant of water has been estimated from partial-molal-volume and compressibility changes using the relation from 0 to 50°C and 0 to 2000 bars. The results agree very well with the directly measured values.Contribution Number 1548 from the University of Miami.     

Determination of corrosion rate of molybdenum,rhenium and their alloys in sodium chloride solution by the method of Tafel extrapolation

Based on the measured voltammograms, the corrosion potentials and corrosion current densities of Mo, Re, and several their alloys in the NaCl solutions were determined by the method of Tafel extrapolation. The dependences of E _corr and i _corr on the alloy composition, including the corresponding values for the metals (alloy components), were plotted. The obtained values of i _corr and the corrosion rates in the linear units were compared with the literature data.     

Interdiffusion without a common ion in aqueous NaCl−MgSO4 and LiCl−NaOH mixed electrolytes

When a solution of electrolyte MX interdiffuses with a solution of electrolyte NY, the transport of four different ions (M, X, N, and Y) is constrained only by electroneutrality. Because three degrees of freedom remain, the interdiffusion of two electrolytes without a common ion can produce an independent flow of a third electrolyte. This behavior is demonstrated by using Taylor dispersion to measure interdiffusion coefficients, including cross-coefficients, for NaCl–MgSO₄-water and LiCl–NaOH-water mixed electrolytes at 25°C. The measurements are made for electrolyte mole ratios of 01, 13, 11, 31, and 10 at a total electrolyte concentration of 0.100 mol L^–1. The results are used to calculate concentration profiles across NaCl(aq)/MgSO₄(aq) and LiCl(aq)/NaOH(aq) liquid junctions. The interdiffusion of NaCl and MgSO₄ produces relatively small flows of Na₂SO₄. As a result of large differences in ionic mobilities for the aqueous LiCl–NaOH system, substantial flows of NaCl develop during the interdiffusion of LiCl and NaOH.     

Development of very high strength Mo2NiB2 complex boride base hard alloy

A previous investigation revealed that additions of Cr and V to the Mo₂NiB₂ complex boride base hard alloy changed the boride phase crystal structure from orthorhombic to tetragonal and resulted in a remarkable improvement of mechanical properties associated with microstructural refinement. Moreover, an addition of Mn turned out to be effective in further improvement of the mechanical properties in the V-containing alloy. In this investigation, Ni-5B-xMo-12.5V-2.5Mn (mass%) model alloys with four levels of Mo contents corresponding to Mo/B atomic ratio ranging from 1.0 to 1.3 were prepared to study the effect of the Mo/B atomic ratio on the mechanical properties and microstructure. The results indicated that transverses rupture strength (TRS) increased with increasing Mo/B atomic ratio and showed a maximum value of 3.2 GPa at Mo/B=1.2 and then decreased with increasing atomic ratio. Hardness increased linearly from 86.8 HRA to 90.8 HRA with increasing Mo/B atomic ratio.     

Electrolessly Plated Ni-Zn（Fe）-P Alloy and Its Corrosion Resistance Properties

The autocatalytic deposition of Ni-Zn(Fe)-P alloys has been carried out on substrate of carbon steel from a bath containing nickel sulfate, zinc sulfate, sodium hypophosphite, sodium citrate and boric acid. The effects of pH and the molar ratio of NiSO4/ZnSO4 on the deposition rate and the composition of deposits have been studied. It was found that the presence of zinc sulfate in the bath has an inhibitory effect on the alloy deposition. The structure and the surface morphology of Ni-Zn(Fe)-P coatings were characterized with XRD and SEM, respectively. The alloys plated under the experimental conditions consisted of an amorphous phase coexisting with a crystalline cubic Ni phase (poly-crystalline). The surface morphology of the coating is dependent on the deposition parameters. The corrosion resistance of the Ni-Zn(Fe)-P deposits was examined via mass loss tests and anodic polarization measurements, respectively. The results show that the surface morphologies of the deposits and the corrosion resistance of the deposits have been improved. The results of mass loss tests almost accord with those of anodic polarization measurements. The corrosion mechanisms of Ni-Zn(Fe)-P alloys in NaCl and NaOH solutions were investigated by means of EDX. The deposit immersed in an NaCI or an NaOH solution contains more content of oxygen and less contents of the metals(except Fe) than that placed in air, which shows that the NaCl or NaOH solution can accelerate the oxidation of the deposit.     

Near infrared study of aqueous lanthanide perchlorates

The near infrared spectra of water in aqueous solutions of La(ClO₄)₃, Pr(ClO₄)₃, Nd(ClO₄)₃, Gd(ClO₄)₃, Er(ClO₄)₃, Yb(ClO₄)₃, Lu(ClO₄)₃, and NaClO₄ have been measured in the concentration range from 0.3 to 2.5 mol-dm^–3, at 25°C. The relative contents of free OH groups in the 1.0, 1.6, and 2.2M solutions have been calculated from extinction coefficients for water at 1160 nm. They increase with increasing salt concentration and are greater in solutions of the lighter lanthanide perchlorates at any fixed molarity. The results are discussed in terms of the stoichiometry and structure of hydrated cations of trivalent lanthanides.     

Corrosion properties of nickel coatings obtained from aqueous and nonaqueous electrolytes

Nickel was deposited on a copper substrate from aqueous and nonaqueous ethanol electrolytes. X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and chronovoltametry, scanning electron microscopy, and atomic force microscopy were used to study the effect of the solvent on the surface and corrosion properties of the Ni coatings formed. Unifom and relatively smooth Ni films were obtained as measured with microscopy techniques. The formation of a passive film in acidic, alkaline, and neutral chloride-containing media was confirmed with X-ray photoelectron spectroscopy. The water-based nickel-plating electrolyte makes it possible to deposit coatings with higher corrosion resistance as compared with coatings deposited from ethanol electrolyte in NaOH and NaCl media. The proposed mechanism of corrosion in a 0.5 M H₂SO₄ solution involves cycles of active-passive surface behavior due to its passivation by corrosion products.     

Effects of Ca and Ag addition and heat treatment on the corrosion behavior of Mg-7Sn alloys in 3.5 wt.% NaCl solution

The effects of 1 wt.% Ca or 1 wt.% Ca + 1 wt.% Ag addition and heat treatment on the corrosion behavior of Mg-7Sn (wt.%) alloy in 3.5 wt.% NaCl solution were investigated by electrochemical measurements and immersion tests. The alloys were characterized by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that all alloys were corroded by pitting corrosion and grain boundary corrosion and further corroded with time going. Loose layers of compounds, including Mg (OH)₂, MgO, SnO₂, and other compounds containing Ca and Ag elements, were calibrated on the surface of corroded Mg-7Sn-1Ca-1Ag alloy. The Ca addition improved the corrosion resistance of Mg-7Sn alloy due to the formation of relatively stable compounds containing calcium element and grains refinement. Furthermore, the solid solutioned alloys obtained a superior corrosion resistance due to the dissolve of eutectic Mg₂Sn phase and homogenization treatment. However, the aging treatment is slightly detrimental to the corrosion resistance of Mg-7Sn alloys with the formation of Mg₂Sn precipitates. In conclusion, the aged Mg-7Sn-1Ca-1Ag alloy exhibited a better corrosion resistance and a noticeable micro-hardness property compared with those of as-cast Mg-7Sn alloy. And this study provides an important idea for the research on the comprehensive properties of Mg-Sn alloys.     

Refinement of the cation distribution in Nb-Mo double oxide

The structure of Nb₂Mo₃O₁₄ double oxide is refined from powder data using synchrotron radiation and the anomalous scattering effect; space group P $ \bar 4 The structure of Nb₂Mo₃O₁₄ double oxide is refined from powder data using synchrotron radiation and the anomalous scattering effect; space group P 2₁ m is found for the material. It is demonstrated that in the tetragonal unit cell with parameters a = 23.173 ?, c = 4.0027 ? Nb⁵⁺ and Mo⁶⁺ ions are stochastically distributed in MO₆ octahedra and MO₇ pentagonal bipyramids of the polygonal network structure of the Mo₅O₁₄ type. Original Russian Text Copyright ? 2008 by T. Yu. Kardash, L. M. Plyasova, V. M. Bondareva, and A. N. Shmakov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 4, pp. 729–735, May–June, 2008.     

Aggregation of Rhodamine B in Water

Protolytic and associative equilibria in aqueous solutions of rhodamine B were studied. The curves of potentiometric titration with NaOH solution of the dye hydrochloride within the 5 ×10^-4-3 ×10^-2 M range and at an ionic strength of 0.1 M (NaCl or KCl) were treated by chemometric methods of successive modification of the equilibrium system models with regard to spectrophotometric data. The most probable value of the equilibrium constants of the reaction iH⁺ + jR H _i R _j ⁱ⁺ were determined.