The effect of Nb and Ni addition on crystallization behavior of amorphous–nanocrystalline Fe–Cr–B–Si alloys

The crystallization behavior of amorphous Fe–Cr–B–Si alloys in the presence of Ni and Nb elements was the goal of this study. In this regard, four different amorphous–nanocrystalline Fe₄₀Cr₂₀Si₁₅B₁₅M₁₀ (M=Fe, Nb, Ni, Ni_0.5Nb_0.5) alloys were prepared using mechanical alloying technique up to 20 h. Based on the achieved results, in contrast to Fe₅₀Cr₂₀Si₁₅B₁₅ alloy, the amorphous phase can be successfully prepared in the presence of Ni and Nb in composition. Although the crystallization mechanism of prepared amorphous phase in different alloys was the same, the Fe₄₀Cr₂₀Si₁₅B₁₅Nb₁₀ alloy showed higher thermal stability in comparison with other samples. The crystallization activation energy of this amorphous alloy was estimated about 410 kJ mol^?1 which was much higher than Fe₄₀Cr₂₀Si₁₅B₁₅Ni₁₀ (195.5 kJ mol^?1) and Fe₄₀Cr₂₀Si₁₅B₁₅Ni₅Nb₅ (360 kJ mol^?1) samples. The calculated values of Avrami exponent (1.5 < n < 2.2) indicated that the crystallization process in different alloying systems is the same and to be governed by a three-dimensional diffusion-controlled growth.     

Electrochemical behaviour of Ni-Co amorphous alloys in alkaline solutions

The dissolution processes of amorphous G15 (Ni₅₈Co₂₀B₁₂Si₁₀) and G16 (Ni₂₅Co₅₀B₁₀Si₁₅) alloys in carbonate-bicarbonate buffers (8.9≤pH≤10.5) have been studied using voltammetry and stationary polarization techniques combined with electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Results indicate that the electrochemical processes are dependent on the applied potential, the alloy composition, and the pH and ionic strength of the electrolyte. An enhancement of the corrosion processes is observed when the pH and the ionic strength are increased and when the Co content of the alloy diminishes. Furthermore, XPS provided information about the composition of the surface layer. Electronic Publication     

Catalytically active electrodes in the redox processes of oligomeric peroxides

The catalytic activity of different electrodes (Pt, glassy carbon, and amorphous metal alloys Al_87.0Y_5.0Ni_8.0, Fe_78.5Ni_1.0Mo_0.5Si_6.0B_14.0, and Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4) in the redox processes of polyfunctional oligomeric peroxides based on vinylacetate, 3-tert-butylperoxy-3-phenylbutylmethylmethacrylate and maleic anhydride and vinylacetate, 3-tert-butylperoxy-3-methylbutylmethacrylate and maleic anhydride was evaluated by potentiometry and cyclic voltammetry. It was established that amorphous metal iron-based Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4 and Fe_78.5Ni_1.0Mo_0.5Si_6.0B_14.0 electrodes manifested a high electrocatalytic activity comparable with that of a platinum electrode in the redox processes of polyfunctional oligomeric peroxides.     

Corrosion performances of a Nickel-free Fe-based bulk metallic glass in simulated body fluids

The corrosion performance of a Nickel-free Fe-based bulk metallic glass (BMG), Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ alloy, in Hank’s solution with pH value 7.4 and artificial saliva solution with pH value 6.3, was investigated by electrochemical techniques, aiming to assess the feasibility of Fe-based BMG as potential biomaterial. It was found that Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ BMG shows superior corrosion resistance in both simulated body fluids (SBF). The EIS analysis and cyclic polarization measurements indicated that the Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ BMG has larger polarization resistance value than that of 316L SS. The pitting corrosion potentials of Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ BMG are much higher than that of the 316L SS, resulting in very few ions releasing into the SBFs while a significant amount of Ni and Fe ions release was found for 316L SS under the same condition.     

Crystallization kinetics of metallic glasses

In this study, the temperature-heating rate diagram of the main crystallization process of two metallic glasses, Fe₇₄Ni_3.5Mo₃B₁₆Si_3.5 and Fe₄₁Ni₃₈Mo₃B_18, was obtained from one experimental differential scanning calorimetry (DSC) scan and the knowledge of their activation energy as determined by an isoconversional method. A good concordance was observed between the diagram curves obtained by calculation (isoconversional approach) and the experimental data, which verifies the reliability of the method and the validity of the kinetic approach in these alloys.     

Characterization of the passive films on electrodeposited Fe-Ni-Cr alloys in borate solution at pH 8.4

The corrosion properties of the passive layers formed on iron-nickel-chromium electrodeposits of Fe₂₉Ni₅₁Cr₂₀ were investigated in 0.3 M borate solution at a‘ pH of 8.4. On the basis of measurements by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy, a low passive dissolution/corrosion rate was identified for the electrodeposited Fe-Ni-Cr alloys due to the nature of the established corrosion layer. The stability of this passive layer was further enhanced after corrosion under oxidizing conditions. Mössbauer spectroscopic measurements confirmed the existence of a thin passive layer on the amorphous electrodeposits.      

Influence of Ni content on Fe–Nb–B alloy formation

In this work three alloys, Fe₇₄Nb₆B₂₀, Fe₆₄Ni₁₀Nb₆B₂₀ and Fe₅₄Ni₂₀Nb₆B₂₀, were obtained by mechanical alloying to analyze the influence of Ni content on Fe–Nb–B alloy formation. Structural analysis by X-ray diffraction (XRD) confirms that partial substitution of Fe by Ni favours the formation during milling of a more disordered structure. Furthermore, thermal stability study was performed by differential scanning calorimetry (DSC) because thermally induced structural changes can affect soft magnetic behaviour. After 40 h of milling time, all DSC curves show several exothermic effects on heating associated to structural relaxation and crystallization. All alloys present a crystallization process with associated activation energy values ranged between 238 and 265 kJ mol^–1 related to the crystalline growth of the bcc-Fe rich phase. In alloys with Ni, a second crystallization process appears at temperatures over 500°C with activation energies 397 (10% Ni alloy) and 385 kJ mol^–1 (20% Ni alloy) probably associated to the nucleation and crystalline growth of a new phase.     

An effect of low temperature processing on stability of physical and chemical properties of amorphous alloy Fe78.5Ni1.0Mo0.5Si6.0B14.0

As a result of detailed investigation of physico-chemical properties of the amorphous alloy ribbon Fe_78.5Ni_1.0Mo_0.5Si_6.0B_14.0 it was found that its high-speed cooling (1–3 s) with a temperature gradient ΔT = (298–77) K affects chemical reactivity of surface at constant volume parameters: microhardness, magnetic properties. This feature can be used for special applications of metal-doped amorphous alloy based on Fe in extreme conditions.     

Thermodynamic parameters of liquid ternary Fe1−x(Ni5/6Cr1/6)x alloys

Summary Computer-aidedKnudsen cell mass spectrometry is used for thermodynamic investigations on liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys. The thermodynamic excess properties have been determined by means of the Digital Intensity-Ratio (DIR) method. Liquid ternary Fe_1–x(Ni_5/6Cr_1/6)_x alloys are characterized by exothermic molar heats of mixingH ^E, negative molar excessGibbs energiesG ^E, and negative molar excess entropiesS ^E. At 1850 K, the minimumH ^E value is –3120 J/mol (42.3 at.% Fe), the minimumG ^E value is –2540 J/mol (30 at.% Fe), and the minimumS ^E value is –0.44 J/(mol K) (60 at.% Fe). At 1850 K, the thermodynamic activities of Fe show slight negative deviations from the ideal behaviour for alloys with a Fe-content of less than 75 at.%, and ideal behaviour for the Fe-rich alloys (x _Fe>0.75).

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Thermodynamische Parameter flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen

Zusammenfassung Die Thermodynamik flüssiger ternärer Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen wurde mit Hilfe der computerunterstützten Knudsenzellen-Massenspektrometrie studiert. Die thermodynamische Auswertung der experimentellen Untersuchungen erfolgte nach der digitalen Intensitätsverhältnismethode (DIR). Flüssige ternäre Fe_1–x(Ni_5/6Cr_1/6)_x-Legierungen zeigen exotherme molare MischungswärmenH ^E, negative molareGibbssche ZusatzenergienG ^E, und negative molare ZusatzentropienS ^E. Bei 1850 K sind die Minimumswerte fürH ^E –3120 J/mol (42.3 At.% Fe), fürG ^E –2540 J/mol (30 At.% Fe) und fürS ^E –0.44 J/(mol K) (60 At.% Fe). Bei 1850 K zeigen die thermodynamischen Aktivitäten von Fe bei Legierungen mit einem Fe-Gehalt von höchstens 75 At.% leichte negative Abweichungen vom idealen Verhalten, die Fe-reichsten Legierungen (x _Fe>0.75) verhalten sich hingegen nahezu ideal.

     

Investigation of the influence of nickel content on the correlation between the hydrogen equilibrium pressure for hydrogen absorbing alloys and the capacity of MH electrodes in open and closed cells

Two series of overstoichiometric AB_2.4 alloys [(Zr_0.35Ti_0.65)(V_1.33Cr_0.4Fe_0.27)_{2– x} Ni_{0.4+ x} and (Zr_0.5Ti_0.5)(V_0.8Mn_0.8Cr_0.4)_{2– x} Ni_{0.4+ x} ], differing in the Zr to Ti ratios in group A and the presence of Mn or Fe in group B, were examined to consider the influence of various amounts of nickel on the structural parameters following the sorption of hydrogen. To predict the electrochemical behaviour of the prepared alloys as negative electrodes for Ni-MH cells, the pressure-composition isotherms (PCT) determined for the gas/solid phase system were correlated with the electrochemical pressure-composition (EPC) isotherms estimated from the rest potential of the alloy electrode. For preliminary assessment of the practical usefulness of the prepared samples, the electrodes made of all the alloys were subjected to charge/discharge measurements in a half-cell in 6 M KOH solution and the discharge capacities were estimated. Of the alloys with Fe and Mn components, the samples (Zr_0.35Ti_0.65)(V_0.93Cr_0.28Fe_0.19Ni_1.0) and (Zr_0.5Ti_0.5)(V_0.68Mn_0.68Cr_0.34Ni_0.7) provided the highest capacities. These alloys were chosen for testing the charge/discharge cycleability in closed Ni-MH cells. The reversibility of the cell with the former sample decreased significantly around the 25th cycle, whereas the discharge capacity of the cell with the latter sample remained almost unchanged during 100 cycles of testing. Electronic Publication     

Surface characteristics of high corrosion resistant Ni–Nb–Zr–Ti–Ta glassy alloys for nuclear fuel reprocessing applications

This work firstly discovered that the Ni₆₀Nb₁₅Zr₅Ti₁₅Ta₅ metallic glass exhibits high corrosion resistance in boiling 6 N HNO₃ solutions with and without Cr⁶⁺ ions, which may be of great potential for nuclear fuel reprocessing applications. The high corrosion resistance of the alloy is due to the formation of the passive film composed exclusively of Nb⁵⁺ and Ta⁵⁺ cations after immersion in the solution without Cr⁶⁺ ions, and Nb⁵⁺, Ta⁵⁺ and Cr³⁺ cations after immersion in the solution with Cr⁶⁺ ions.     

Electrochemical and surface science investigations of PtCr alloy electrodes

Electrodes of supported Pt, modified with Cr, have shown an increase in electrochemical activity for oxygen reduction in phosphoric acid fuel cells over supported Pt only electrodes. To clarify the role of chromium and its chemical nature at the electrode surface, we have characterized a series of Pt_xCr(_1-x) bulk alloys (x = 0.9, 0.65, 0.5, 0.2) by electrochemical and ex-situ surface science methods. In this paper we report the surface characterization of native and post-electrochemical electrodes by XPS, cyclic voltammetry in 0.05 M H₂SO₄ and 85% H₃PO₄, and analysis of 0.05 M H₂SO₄ electrolyte following electrochemical treatment. The surface Cr(1 to 2 nm) was oxidized to Cr³⁺ oxide for surfaces at open circuit and those exposed to potentials < + 1.3 V vs DHE in 0.05 M H₂SO₄ and < + 1.55 V vs. DHE in 85% H₂PO₄. In 0.05 M H₂SO₄ the Cr component was electrooxidized to solube Cr⁶⁺ species at potentials > +1.3 V with the extent of Cr dissolution dependent on initial alloy stoichiometry. Alloys with Cr content 0.5 are capable of producing (dependent on time spent at potentials above +1.3 V in 0.05 M H₂SO₄) very porous Pt-rich surfaces. Loss of Cr was also observed in 85% H₃PO₄ for the alloys with Cr content 0.5, although at the more positive potential limit of +1.55 V. For the Pt_0.2Cr_0.8, treatment in 85% H₃PO₄ at +1.4 V and above led to the appearance of Pt⁴⁺ and Cr⁶⁺ species, apparently stabilized in a porous phosphate overlayer up to 5 nm thick (dependent on time spent at potentials above this limit). The enhancement reported for supported Pt+Cr oxygen cathodes is discussed in the light of these results.     

Alloying effect on K to L shell vacancy transfer probabilities in 3d transition metals

The alloying effects on K to L shell vacancy transfer probabilities (η_KL) in 3d transition metals have been carried out by X-ray fluorescence studies of various alloy compositions. K X-ray intensity ratios of Ti, Cr, Fe, Co, Ni, and Cu elements in the Fe_xNi_1?x, Fe_xCr_1?x, Ni_xCr_1?x, Fe_xCr_yNi_1?(x+y), Ti_xNi_1?x, Ti_xCo_1?x, and Co_xCu_1?x alloys have been measured following excitation by 22.69 keV X-rays from a 10 mCi ¹⁰⁹Cd radioactive point source and η_KL values for alloying elements have been determined from these ratios. The spectrum of characteristic K-X-ray photons from samples were detected with a high resolution Si(Li) detector coupled to a 4 K multichannel analyzer. The present investigation makes it possible to perform reliable interpretation of experimental K to L shell vacancy transfer probabilities for various 3d transition metals in alloys and can also provide quantitative information about the changes of K to L shell vacancy transfer probabilities of these metals with alloy composition.     

Determination of hydrogen peroxide in pickling baths for copper alloys by linear sweep voltammetry

Hydrogen peroxide in pickling baths for copper and copper alloys can be determined by linear sweep voltammetry with a glassy carbon electrode. The oxidation mechanism changes around 0.15 M H₂O₂. Catalytic decomposition was found to be much smaller at glassy carbon electrodes than at platinum electrodes. An almost linear calibration curve was obtained up to 60 mM H₂O₂. Interferences from Cu²⁺, Zn²⁺, Ni²⁺, Al³⁺, Fe³⁺ and Pb²⁺ as well as from the stabilizers were small. All measurements were made in sulphuric acid solutions.     

乙酸自热重整制氢用类水滑石衍生Zn-Ni-Al-Fe-O催化剂研究

采用共沉淀法制备了Zn_(2.4)Ni_(0.6)Al_xFe_(1-x)O_(4.5±δ)(x=1/0.5/0)系列类水滑石型镍基催化剂,用于乙酸自热重整制氢,并利用XRD、H_2-TPR、BET、XPS等表征手段对催化剂进行了表征。结果表明,Zn_(2.4)Ni_(0.6)Al_(0.5)Fe_(0.5)O_(4.5±δ)催化剂在乙酸自热重整中乙酸转化率维持在100%,氢气产率为2.39 mol-H_2/mol-HAc。Zn-Al水滑石前驱体经焙烧后形成了ZnO为骨架的复合氧化物,铁的适量添加增大了催化剂的比表面积,经还原后形成Fe NiZn合金,Fe以及Zn的给电子作用提高了Ni的抗氧化能力,催化剂的抗氧化烧结和抗积炭能力得到提高。     

Magnetic Properties of Ball-Milled Nanocrystalline Alloys Fe78B13Si9

 Magnetic properties of nanocrystalline Fe₇₈B₁₃Si₉ alloys are studied for three series prepared by ball milling starting from amorphous ribbons, crystallized ribbons, and elemental powders. Temperature variation of static magnetization results in strong ferromagnetic interaction which is weakly dependent on the initial material. Magnetic hysteresis loops show that saturation magnetization, magnetic remanence, and coercive field increase with frequency for both series of ribbon samples, whereas they decrease for alloys prepared from elemental powders. Power losses raise faster for the alloys prepared from elemental powders than for the two other alloys.     

Synthesis and Characterization of α‐Titanium Phosphate/Propylamine Intercalation Compounds Containing Transition‐Metal Ions

Polycrystalline intercalated TiM_xH_2−nx(PO₄)₂· yC₃H₇NH₂·wH₂O compounds with transition metal (TM) ions (Mⁿ⁺ = Co²⁺, Ni²⁺, Fe³⁺ or Cr³⁺) have been prepared by means of an indirect route and characterised using X-ray diffraction, scanning electron microscopy, chemical and thermal analysis, X-ray absorption and magnetic measurements. These novel pillared layered materials, which were obtained from the monoclinic (P2₁/c space group) α-Ti(HPO₄)₂·H₂O phase, lose its crystallinity after intercalation. However all the TM ions are octahedrally surrounded by 6 oxygen atoms, although the X-ray absorption spectra evidence a clear dependence on the temperature. Surprisingly, all the materials behave as paramagnetic down to 1.5 K, but they exhibit different colours, what means that they are optically active (Co²⁺: violet; Ni²⁺: pale green; Fe³⁺: yellow; Cr³⁺: dark green).     

Das Dreistoffsystem Nickel—Chrom—Bor

The ternary system Ni?Cr?B was established at 1000°C by X-ray diffraction and metallographic examinations. Binary chromium resp. nickel borides and two ternary borides Cr₃NiB₆ and Cr₂Ni₃B₆ were confirmed. Differential thermoanalysis of binary Ni?B-alloys showed the possibility of a metastable solidification according the partial system Ni?Ni₂B up to 19 at % B. The melting temperatures of ternary alloys were established.     

Thermal Stability Study of Fe-Ni-Based Alloys Determination of T-HR-T and T-T-T diagrams

The low-temperature parts of the temperature-heating rate-transformation (T-HR-T) and temperature-time transformation (T-T-T) diagrams were obtained for crystallization processes. A knowledge of the kinetic model governing crystallization is not needed because both transformation curves can be obtained from non-isothermal calorimetric experiments. The calorimetric study was performed by means of differential scanning calorimetry. The method was applied to analyse crystallization processes of Fe-Ni-based amorphous alloys prepared by melt spinning. The compositions studied were Fe₄₀Ni₄₀P₁₄Si₆, Fe₄₀Ni₄₀P₁₀Si₁₀ and Fe₄₀Ni₄₀P₆Si₁₄. A good concordance was observed between the experimental T-HR-T curves obtained by calculation and the experimental data, which verifies the reliability of the method. In the T-T-T diagrams, the agreement was good in process B1, while in processes A1 and C1 there are small differences that could be related to different crystallization products obtained in isothermal/non-isothermal experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-Voltage Polyanion Positive Electrode Materials

High-voltage generation (over 4 V versus Li⁺/Li) of polyanion-positive electrode materials is usually achieved by Ni³⁺/Ni²⁺, Co³⁺/Co²⁺, or V⁴⁺/V³⁺ redox couples, all of which, however, encounter cost and toxicity issues. In this short review, our recent efforts to utilize alternative abundant and less toxic Fe³⁺/Fe²⁺ and Cr⁴⁺/Cr³⁺ redox couples are summarized. Most successful examples are alluaudite Na₂Fe₂(SO₄)₃ (3.8 V versus sodium and hence 4.1 V versus lithium) and β₁-Na₃Al₂(PO₄)₂F₃-type Na₃Cr₂(PO₄)₂F₃ (4.7 V versus sodium and hence 5.0 V versus lithium), where maximizing ΔG by edge-sharing Fe³⁺-Fe³⁺ Coulombic repulsion and the use of the 3d²/3d³ configuration of Cr⁴⁺/Cr³⁺ are essential for each case. Possible exploration of new high-voltage cathode materials is also discussed.