Ni-Zn Intermetallic Compounds Research Articles

Auto-thermal reforming of acetic acid for hydrogen production by Zn Ni CrO± catalysts: Effect of Cr promoted Ni-Zn intermetallic compound

A series of Zn x Ni y CrO m ± δ catalysts were synthesized via a typical co-precipitation method, in which Zn-Cr layered double hydroxides (LDHs) were found and Ni-Zn intermetallic compound (IMC) was formed after reduction in hydrogen. During auto-thermal reforming (ATR) of acetic acid (HAc), the Ni-Zn IMC was transformed into Ni/(amorphous-ZnO)-ZnCr 2 O 4 species with uniformed distribution and appropriate interaction within these Ni-Zn-Cr-O species; besides, the adsorbed oxygen promoted the activation and transfer of oxygen species; therefore, deactivation by oxidation, sintering and coking was inhibited. And the optimized Zn 2.37 Ni 0.63 CrO 4.5± δ catalyst presented high activity and stability in a 45-h ATR test with HAc conversion near 100% and hydrogen yield at 2.7 mol-H 2 /mol-HAc, showing potential for hydrogen production via ATR of HAc.

Diffusional behaviors and mechanical properties of Ni-Zn system

In this paper, the solid-solid diffusion reaction and growth kinetics of Ni-Zn system were investigated using diffusion couple technique. Three intermetallic compounds (IMCs), β1 (NiZn), γ (Ni2Zn11) and δ (Ni3Zn22) were observed at the diffusion zone with the annealing temperature range between 598 K and 673 K. The results indicate that the growth process of reaction zone was dominated by volume diffusion. And the growth constants, integrated diffusion coefficients, growth activation energies and diffusion activation energies of γ and δ were evaluated based on thickness of the phases, reaction temperatures and annealing times. The Young’s modulus and Vickers hardness of the three phases were evaluated from the displacement-loading curve by nanoindenter testing. The Young's modulus and hardness of the IMCs increased firstly and then decreased with the increasing of Zn concentration, where γ phase has the highest Young's modulus (183.3 GPa) and highest hardness (6.05 GPa) among the three phases. Finally, the bulk modulus (B), shear modulus (G), Young's modulus (E), and Poisson's ratio (v) of the Ni-Zn IMCs were calculated by the first-principles calculations. The tendency of calculated Young's modulus varying with the composition of Zn was consistent with that of experimental results.

Zinc diffusion induced precipitation of σ-phase in austenitic stainless steel

Zinc diffusion-induced degradation of AISI 316LN austenitic stainless steel pot equipment used in 55%Al-Zn and Zn-Al-Mg coating metal baths is described. SEM/EDS analyses results showed that the diffused zinc reacts with nickel from the austenite matrix and results in the formation of Ni-Zn intermetallic compounds. The Ni-Zn intermetallic phase and the nickel depleted zones form a periodic and alternating layered structure and a mechanism for its formation is proposed. The role of cavities and interconnected porosity in zinc vapour diffusion-induced degradation and formation of Ni-Zn intermediate phases is also discussed. The formation of Ni-Zn intermediate phases and the depletion of nickel in the austenite matrix results in the precipitation of σ-phase and α-ferrite in the nickel depleted regions of the matrix. This reaction will lead to increased susceptibility to intergranular cracking and accelerated corrosion of immersed pot equipment in the coating bath. Zinc diffusion induced precipitation of σ-phase in austenitic stainless steels that we are reporting in this work is a new insight with important implications for the performance of austenitic stainless steels in zinc containing metal coating baths and other process industries. This new insight will further lead to improved understanding of the role of substitutional diffusion and the redistribution of alloying elements in the precipitation of σ-phase in austenitic stainless steels.

Deoxygenation of methyl laurate as a model compound on Ni-Zn alloy and intermetallic compound catalysts: Geometric and electronic effects of oxophilic Zn

A series of Ni-Zn bimetallic catalysts with different Ni/Zn atomic ratios were prepared from layered double hydroxides (LDHs) with an atomic ratio of 3 between divalent (Ni2+ and Zn2+) and trivalent ions (Al3+). After the mixed oxides derived from calcined LDHs were reduced with H2 at 650°C, Ni-rich alloy with a fcc structure was synthesized at Ni/Zn ratios≥2, while an Ni-Zn intermetallic compound (IMC) with a tetragonal L10 structure was generated at Ni/Zn atomic ratios of 1 and 1/2, and an Ni-Zn IMC was generated with a cubic structure at Ni/Zn ratio of 1/8. HAADF-STEM-EDS, H2 chemisorption and magnetic measurements showed that Ni and Zn atoms were uniformly distributed in catalysts, and the ensembles of Ni atoms decreased with decreasing Ni/Zn ratios. XPS and CO-TPD characterizations revealed a charge transfer from Ni to Zn. In the deoxygenation of methyl laurate as a model compound to diesel-like hydrocarbons, although the addition of Zn reduced the conversion of methyl laurate, mostly due to the decrease in Ni content, a synergetic effect between Ni and Zn was suggested to enhance turnover frequency (TOF), and higher TOFs were obtained on the catalysts with Ni/Zn ratios of 1/1 and 1/2. Because of the high oxophilicity of Zn, this synergetic effect also promoted the hydrodeoxygenation pathway. With decreasing Ni/Zn ratios, the molar ratio between C11 hydrocarbons and both C12 hydrocarbons and oxygenates decreased. Particularly, it was smaller than 0.2 on Ni-Zn IMC when the reaction temperature was 330°C, and much lower than that of 60.5 on the metallic Ni catalyst. Compared with metallic Ni, Ni-rich alloys and IMCs (especially IMCs) showed lower reactivity for CC bond hydrogenolysis and CO/CO2 methanation, which was more remarkable with decreasing Ni/Zn atomic ratios and increasing reaction temperatures. Particularly, when the conversion of methyl laurate was close to 100% at 400°C, the metallic Ni catalyst dominatingly gave methane, which was derived from CC bond hydrogenolysis as well as complete methanation of CO/CO2, and the total selectivity to C11 and C12 (i.e., SC11+C12) was only 1.1%. However, when the Ni/Zn atomic ratio was≤2/1, SC11+C12 reached as high as 96.2%, and the molar ratio between (CO+CO2) and C11 hydrocarbons was still larger than 1.0, i.e., CC bond hydrogenolysis and methanation were remarkably suppressed on Ni-Zn IMC catalysts. We suggest that the role of Zn is ascribed to its geometric and electronic modification of Ni in the alloy and IMC.

Effects of 0.1 wt% Ni addition and rapid solidification process on Sn–9Zn solder

Effects of 0.1 wt% Ni addition and rapid solidification process on Sn–9Zn solder alloy were investigated. Characteristics of Sn–9Zn–0.1Ni alloy were analyzed compared with those of as-solidified Sn–9Zn alloy. Mechanical properties and interfacial microstructure of solder/Cu joints obtained using these solders were comparatively studied. By comparison with as-solidified Sn–9Zn alloy, the wettability of solder was obviously improved with 0.1 wt% Ni addition, and the melting behavior of the solder was promoted due to the rapid solidification process. The corrosion resistance of as-solidified and rapidly solidified Sn–9Zn–0.1Ni alloys was improved due to the formation of Ni–Zn intermetallic compound (IMC) and the refining of Zn-rich phases. Formation and growth of IMCs at the interface of Sn–9Zn–0.1Ni/Cu joints was significantly depressed. Rapid solidification process promoted the interfacial reaction during soldering and improved the bonding strength of joints.

Diffusion Behavior of Zn During Reflow of Sn-9Zn Solder on Ni/Cu Substrate

Reflow behavior of Sn-Zn solder on Ni/Cu substrate was investigated in an infrared (IR) reflow furnace using different heating rates from 180 °C/min to 36 °C/min. Energy dispersive spectroscopy (EDX) studies of the reflowed samples showed increased diffusion of Zn from the solder to the intermetallic compound (IMC) layer with a decrease in heating rate. Higher interfacial activity and affinity of the Zn in the formation of the IMC with the lowering of the heating rate were further demonstrated by electron probe microanalyzer (EPMA) results. The Zn diffusion behavior was related to its higher reactivity and smaller size in comparison with Sn, phase separation during heating, and affinity of Zn to form Ni-Sn-Zn and Ni-Zn intermetallic compounds.

The 450 °C Isothermal Section of the Zn-Fe-Ti System

The isothermal section of the Zn-Bi-Ni ternary system at 450 °C was determined experimentally using the equilibrated alloys approach. The specimens were investigated by means of optical microscopy, scanning electron microscopic/energy-dispersive spectrometric analysis and x-ray diffraction. Six three-phase regions exist in this isothermal section. The L-Bi phase is in equilibrium with all phases of Ni-Zn binary system except the α-Ni phase. Experimental results indicate that the third element, Zn or Bi, is almost insoluble in the Bi-Ni or Ni-Zn intermetallic compounds.

Influence of Ni-electrodeposited pretreatment on galvanized coatings of reactive steels

Four types of steel sheets containing 0.04%, 0.09%, 0.14% and 0.36% Si, respectively, were electrodeposited with a nickel layer of 3 μm in thickness and then galvanized in molten Zn at 450°C for various periods of time. The formation and growth of intermetallic compound layers on the surface of the samples were investigated by SEM and EDS. The experimental results show that the method of Ni-electrodeposited pretreatment can distinctively restrain the over-growth of the galvanized coatings of reactive steels and get eligible coatings with a proper thickness, bright appearance and strong adherence. EDS results indicate that a series of Ni-Zn intermetallic compounds γ′, γ and δ2 are first formed on the surface of the samples. With a prolonged immersion time, the Γ2-Fe-Zn-Ni and δ-Fe-Zn are formed accompanied by the gradual disappearance of γ′, γ and δ2 layer. After a longer immersion time, the lumpy ζ-Fe-Zn occurs between δ and liquid Zn and the Γ-Fe-Zn does between steel substrate and δ. Subsequently, ζ is in the form of a continuous and compact layer. The method of Ni-electrodeposited pretreatment changes the formation of Fe-Zn intermetallic compounds, which delay the growth of lumpy ζ and promote the growth of compact δ. Consequently, the abnormal growth of reactive steels is eliminated.

Retardation of spalling by the addition of Ag in Sn–Zn–Bi solder with the Au/Ni metallization

The work presented in this paper focuses on the role of Ag addition in the Sn–8%Zn–3%Bi solder on the shear strengths and the interfacial reactions with Au/Ni/Cu pad metallization in ball grid array (BGA) applications. Sn–Zn–Bi(–Ag) solder alloys were kept in molten condition (240 °C) on the Au/electrolytic Ni/Cu bond pads for different time periods ranging from 1 to 60 min. After the shear test, fracture surfaces were investigated by scanning electron microscopy. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The results indicated that the spalling of the Au–Zn intermetallic compound (IMC) layer was regulated by the addition of 0.3%Ag in Sn–Zn–Bi solder. The retardation of spalling of the initial IMC, limited the formation of Ni–Zn compound in the Ag doped Sn–Zn–Bi solder. The formation of thick Ni–Zn IMC layer in Sn–Zn–Bi alloy deteriorated the mechanical strength of the joints after extended reflow.

Effect of substrate metallization on interfacial reactions and reliability of Sn–Zn–Bi solder joints

The scope of this paper covers a comprehensive study of the lead-free Sn–Zn–Bi solder system, on Cu, electrolytic Ni/Au and electroless Ni(P)/Au surface finishes. This includes a study of the shear properties, intermetallic compounds at the substrate–ball interface and dissolution of the under bump metallization. The Sn–8Zn–3Bi (wt.%) solder/Cu system exhibited a low shear load with thick IMCs formation at the interface. The dissolution of the Cu layer in the Sn–Zn–3Bi solder is higher than that of the other two Ni metallizations. It was found that the formation of a thick Ni–Zn intermetallic compound (IMC) layer at the solder interface of the electrolytic Ni bond pad reduced the mechanical strength of the joints during high temperature long time liquid state annealing. The solder ball shear-load for the Ni(P) system during extended reflow increased with an increase of reflow time. No spalling was noticed at the interface of the Sn–Zn–3Bi solder/Ni(P) system. Sn–8Zn–3Bi solder with electroless Ni(P) metallization appeared as a good combination in soldering technology.

Effect of reaction time on mechanical strength of the interface formed between the Sn-Zn(-Bi) solder and the Au/Ni/Cu bond pad

In this work, the shear strengths and the interfacial reactions of Sn-9Zn, Sn-8Zn-1Bi, and Sn-8Zn-3Bi (wt.%) solders with Au/Ni/Cu ball grid array (BGA) pad metallization were systematically investigated after extended reflows. Zn-containing Pb-free solder alloys were kept in molten condition (240°C) on the Au/electrolytic Ni/Cu bond pads for different time periods ranging from 1 min. to 60 min. to render the ultimate interfacial reaction and to observe the consecutive shear strength. After the shear test, fracture surfaces were investigated by scanning electron microscopy equipped with an energy dispersive x-ray spectrometer. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The solder ball shear load for all the solders during extended reflow increased with the increase of reflow time up to a certain stage and then decreased. It was found that the formation of thick Ni-Zn intermetallic compound (IMC) layers at the solder interface of the Au/electrolytic Ni/Cu bond pad with Sn-Zn(-Bi) alloys deteriorated the mechanical strength of the joints. It was also noticed that the Ni-Zn IMC layer was larger in the Sn-Zn solder system than that in the other two Bi-containing solder systems.

Anodic Dissolution of Nickel from the Individual and NiZn Intermetallic Phases in Acidic Sulfate Solutions. II. NiZn Intermetallic Compound

Comparative investigation of the anodic behavior of nickel in its own phase and in NiZn intermetallic compound in acidic sulfate solutions showed that the kinetics of anodic process is the same in both cases, but the partial anodic curve and the passivation potentials of nickel in NiZn phase are shifted in the negative direction by 140 mV. The passivation current is larger, and the dissolution rate of nickel from NiZn phase at the cathodic polarization is higher. The peculiarity of the behavior of nickel in NiZn phase is related to the activity of surface nickel atoms and the increase in the number of active sites of anodic dissolution. It is shown that introducing an electrochemically negative metal into an alloy can, under certain conditions, facilitate the passivation of the latter irrespective of the passivability of the former.

Anodic Dissolution of Nickel from the Inherent and NiZn Intermetallic Phases in Acidic Sulfate Solutions. I. Nickel

For comparative investigation of the anodic dissolution kinetics of nickel from its own phase and NiZn intermetallic compound, the literature data are generalized and supplemented with new results concerning the anodic behavior of individual nickel in acidic sulfate environments. During the anodic dissolution of nickel at all the stages either in its passive or active state, the main role is shown to be played by the adsorption of water. HSO– 4, Cl–, and I– anions decelerate the active dissolution of nickel in a potential range from 0.0 to 0.2 V and accelerate it in a range from 0.2 to 0.3 V.