Surface Of Zn Research Articles

EIS and XPS investigations on the corrosion mechanism of ternary Zn–Co–Mo alloy coatings in NaCl solution

The changes in composition of the corrosion products of electrodeposited ternary Zn–Co–Mo alloy coatings on AISI 1015 steel during exposure to 0.5moldm−3 NaCl solution were investigated. XPS studies demonstrated that at the initial stage of corrosion on the surface of Zn–Co–Mo coating zinc hydroxide layer is formed. Hydroxyl groups react with chloride and carbonate ions which lead to the formation of zinc hydroxy carbonates and zinc hydroxy chlorides. The share of these compounds in the oxidation products is initially large. However, with time zinc hydroxy compounds slowly changes to zinc oxide, which is more stable corrosion product. It was estimated that after 24h of exposure to NaCl solution nearly 60% of zinc detected on the surface of Zn–Co–Mo coating was present in the ZnO form, 18% in the form of zinc hydroxy chloride, and more than 21% as zinc hydroxy carbonate. XPS analyses revealed that the amount of zinc hydroxy chloride increases as the exposure time lengthens and it is significantly higher than at the surface of binary Zn–Co coating. The presence of crystalline zinc chloride hydroxide as a stable product of corrosion of ternary Zn–Co–Mo alloy coating in a 0.5moldm−3 NaCl solution was confirmed by XRD analysis. According to XRD and FTIR other zinc corrosion products like: ZnO, Zn(OH)2 and Zn5(CO3)2(OH)6 were also present. The results of XPS and EIS measurements allow us to assume that in the presence of Mo in the alloy, on the surface of ternary Zn–Co–Mo alloy (3.4wt.% Co, 2.7wt.% Mo) coating more zinc hydroxy chloride is formed, which favors higher corrosion resistance of this coating.

Magnetism and microwave-absorption properties of Zn particles with magnetic shell

In this work, Zn particles with magnetic shell were synthesised and investigated. Zn particles with different sizes were synthesised by arc-discharge method, and then the Zn particles were put in a suitable concentration of FeSO4 solution with a surface active agent. After some time, the Zn particles with magnetic shell were produced. The particles contain oxygen shell probably in the form of FeO and ZnO, while the core material is Zn. From the saturation magnetisation at room temperature and transmission electron microscopy (TEM) images, it is noticed that the FeO was first formed on the surface of Zn and then ZnO appeared with increasing reaction time. The microwave absorption is not as good as that reported in other materials, because of the weak magnetisation and the faulty core–shell structure formed by metal core and magnetic shell.

Key role of terminal hydroxyl groups and visible light in the reactive adsorption/catalytic conversion of mustard gas surrogate on zinc (hydr)oxides

Rhombic Zn(OH)2 and flower-like ZnO nano-particles were synthesized with a controlled precipitation rate. The materials were characterized by XRD, FTIR, potentiometric titration, nitrogen adsorption, TA-MS, MS-MS, SEM and UV–vis–NIR. A commercial ZnO was used as a reference material. Hydroxyl groups were formed on the surface when a slow addition of NaOH was used. The surface area of Zn(OH)2 was higher (350%) in comparison to that of ZnO. The presence of hydroxyl groups increased the band gap from 3.05eV for ZnO to 3.22eV for Zn(OH)2. The materials were used as reactive adsorbents of mustard gas surrogate, 2-Chloroethyl ethyl sulfide (CEES). On the surface of Zn(OH)2, more CEES was absorbed than of that of ZnO. Moreover, the capacity on Zn(OH)2 significantly increased under a visible light exposure. The results indicated the paramount role of terminal OH groups in the reactive adsorption process. The porosity was also found important since it affects the distribution of these OH active centers. Ethyl vinyl sulfide (EVS) was detected on the surfaces of both samples. At light, hydroxyethyl ethyl sulfide (HEES) was detected only on Zn(OH)2. Thus the absorption of photons led to the formation of the ethyl ethyl sulfide (EES) cations, which were transformed to less toxic EVS by dehydrohalogenation. With water and hydroxyl groups on the surface, the light irradiation promoted the formation of hydroxyl radicals. They reacted with the EES radicals and formed HEES via a hydrolysis pathway. No conversion of CEES was found in the dark.

微纳跨尺度结构ZnO表面的壁面减阻特性

Micro-nano hierarchical Zn O structures with superhydrophobic surfaces were synthesized by chemical vapor deposition. The contact angle of the water droplet on the sample surface was 150. 7°.The sample structure of micro-column array with nanoneedles on top was confirmed by SEM. By using the AR-G2 Rheometer with step-by-step measurement mode,the relationship between torque and shear rate was obtained by varying the shear rates and spacing. Smooth silicon surface with silane on top and 40% glycerol were used as comparison. The slip length of the surface was 46. 8 μm when the shear rate was 20 s- 1. This indicates that the surface of micro-nano hierarchical Zn O structures is beneficial to increasing the drag properties of the liquid.

Multifractal parameterization of space forms on surfaces of Zn x Cd1 − x Te-Si(111) heterocompositions and its relationship to the conditions of layer synthesis

Multifractal (MF) analysis of space forms on the surfaces of thin layers of Zn x Cd1 − x Te solid solution precipitated onto a Si(111) substrate via the hot wall approach is performed. AFM images of film surfaces are used for MF analysis. The parameters of MF spectra are determined for the film surfaces of the above system. It is shown that the MF functions of system correspond to their canonical forms, and the resulting computational procedure can be applied to describe and analyze the state of spatial fractal structures that form on a layer’s surface. The quantitative relationships between the parameters of the MF spectrum of a film’s surface and its conditions of precipitation are revealed.

A study on corrosion behaviour of magnetron sputtered Zn–Mg coating deposited onto electro-galvanized steel

In this study, a nano-structured Zn–Mg coating was prepared by magnetron co-sputtering on electro-galvanized carbon steel. The microstructure and phase structure of Zn–Mg coating and its behaviour during saltwater immersion test were investigated by means of optical microscopy (OM), environmental scanning electron microscopy (ESEM), X-ray diffractometry (XRD) and electrochemical workstation. Electrochemical impedance spectroscopy (EIS) as a sensitive and reliable method was employed in corrosion mechanism research. The results show the formation process of a passive film on the surface of Zn–Mg coating during the immersion time range. The formation mechanism of this dense corrosion product Zn5(OH)8Cl2·H2O layer was also discussed. An electroplated Zn coating was also investigated for comparison purposes.

The sonochemical approach improves the CuO–ZnO/TiO2 catalyst for WGS reaction

The CuO-ZnO composite was deposited onto two kinds of titania supports, which are synthetic mesoporous TiO2 and commercial TiO2 P25 (Degussa), via the ultrasound assisted precipitation and incipient wetness impregnation (IWI) methods, respectively. The catalysts were tested for WGS reaction in the temperature range of 200-400 °C, and the best catalytic performance was achieved for the sonochemically prepared catalysts supported on the commercial TiO2 P25, which contains well crystallized anatase and rutile phases. Although the synthetic mesoporous TiO2 has a higher surface area, its textural structure is not stable under the reaction conditions, leading to gradual deactivation of the CuO-ZnO/TiO2 catalyst. It is found that the sonochemical preparation offers at least two advantages: (1) generation of mesopores on the catalyst surface and (2) doping of ZnO into the CuO phase. The doping of ZnO, particularly in the case of commercial TiO2 P25, provides high activity and extra stability to the active phase of Cu(0). These new findings provide new insights into the design and development of better heterogeneous catalysts for WGS reaction.

Redox properties of LDH microcrystals coated with a catechol-bearing phosphonate derived from dopamine

The surface of Zn–Al-chloride LDH microcrystals (LDH = Layered Double Hydroxides) was activated by grafting a redox active catechol bearing bis-phosphonate obtained by dopamine derivatization.

Anion-exchange precipitation synthesis of α-Ag2WO4/Zn–Cr layered double hydroxides composite with enhanced visible-light-driven photocatalytic activity

In this paper, we report the obtention of α-Ag2WO4/Zn–Cr Layered Double Hydroxides (LDHs) composite via a facile anion-exchange precipitation reaction method by adding AgNO3 solution into WO42- anions intercalated Zn–Cr LDHs suspensions. X-ray diffraction, field emission scanning electronic microscope, X-ray photoelectron spectroscopy, and Fourier Transform Infrared Spectrum were used to characterize the products. It was found that α-Ag2WO4 crystals were dispersed on the surface of Zn–Cr LDHs materials on a large scale. The photocatalytic degradation studies on Rhodamine B indicate that α-Ag2WO4/Zn–Cr LDHs composite shows a higher visible-light-driven photocatalytic activity for degradation of organic pollutants than α-Ag2WO4 crystals and Zn–Cr LDHs. The possible photocatalytic mechanism is also discussed. Finally, a facile approach to fabricate novel types of visible-light-induced photocatalysts for environment treatment was discovered.

Characterisation of oxide films on Zn and Zn alloy coatings

The processes of oxide film formation on the surfaces of Zn, Zn–Co (0·6 wt-%), Zn–Fe (0·5 wt-%) and Zn–Ni (12%) coatings during anodic polarisation in bicarbonate media have been investigated. The composition, thickness, porosity and protective ability of these films were studied by applying X-ray photoelectron spectroscopy, voltammetric and electrochemical impedance spectroscopy measurements with the aim of establishing the influence of Zn alloying on the properties of the oxide layer and the nature of a higher corrosion resistance of some Zn alloys. The oxide films formed on Zn–Ni surface were found to possess a lower thickness, with respect to that of other investigated samples, but at the same time, they exhibited a higher passivating capacity. No significant difference in the composition of the inner layer of the oxide film between different samples was detected, and only the porosity of the oxide film on Zn–Ni was lower, with respect to that of other investigated coatings. It can be assumed that thinner, and at the same time, more compact (less porous), films on a Zn–Ni surface make these oxide layers more resistant.

Investigation of native oxide growth on zinc in different atmospheres by spectroscopic ellipsometry

AbstractThe native oxide layer formed spontaneously on the surface of metallic Zn was investigated by in situ spectroscopic ellipsometry (SE) and ex situ X‐ray photoelectron spectroscopy (XPS). XPS analysis shows the coexistence of hydroxide and oxide in the oxide film. The growth kinetics of the oxide films in different atmospheres was measured in a specially designed optical cell. The growth in O2, Ar and air at high (>95%) and low (<10%) relative humidity was monitored for up to 72 h. Differences in the growth kinetics of the films are observed in different atmospheres. In argon, growth in layer thickness is limited. In oxygen, one obtains a growth with a fast initial phase followed by a linear second phase with a growth rate of ≈0.01 nm h−1. The electronic structure of the layer changes rapidly at the beginning of exposure of the surface to the respective atmosphere, with no further changes observed during the experiment. magnified image

A novel biosensor for reduced l-glutathione based on cobalt phthalocyaninetetrasulfonate-intercalated layered double hydroxide modified glassy carbon electrodes

A cobalt phthalocyaninetetrasulfonate (CoTsPc) intercalated Zn–Al layered double hydroxide (ZnAl–CoTsPc–LDH) has been prepared and used as a modified electrode material for electrocatalytic oxidation and detection of an important biological molecule, reduced l-glutathione (GSH). As the intercalated structure can efficiently immobilize the CoTsPc and inhibit its aggregation, a ZnAl–CoTsPc–LDH modified glassy carbon (GC) electrode exhibited significantly enhanced electrocatalytic activity and stability towards GSH compared with GC electrodes modified with pure CoTsPc or CoTsPc adsorbed on the outer surfaces of Zn–Al layered double hydroxide (CoTsPc/ZnAl–LDH). At physiological pH, the ZnAl–CoTsPc–LDH modified GC electrode showed a wide linear range from 1 to 818 μM and low detection limit of 0.2 μM for GSH determination. Our results show that intercalation of cobalt phthalocyanine complexes into the interlayer galleries of a LDH host is an effective way to improve the electrocatalytic activity and stability of cobalt phthalocyanine modified electrodes, and may have potential applications in fields such as biosensors, biofuel cells, and bioelectronic devices.

Degradation of methyl orange by Zn(0) assisted with silica gel

The degradation of methyl orange (MO) by Zn(0) assisted with silica gel was investigated under different conditions. The results show that the degradation of MO by Zn(0) alone was slow and incomplete due to the rapid corrosion of Zn(0) particles on surface. However, the degradation of MO can be markedly enhanced when Zn(0) and silica gel coexist, even under neutral and alkaline conditions. MO removal was improved with a pH decrease, an increase of the initial amount of silica gel and Zn(0), and specific surface area of silica gel. The degradation of MO by Zn(0) assisted with silica gel can be described by a pseudo-first-order kinetic. And the surface of Zn(0) before and after the reaction was characterized by the microscopic analysis of morphology, revealing the potential mechanism responsible for the enhanced reactivity of silica gel.

Surface properties and dye loading behavior of Zn2SnO4 nanoparticles hydrothermally synthesized using different mineralizers

We present for the first time the influence of different mineralizers on the isoelectric point (IEP) of zinc stannate (Zn{sub 2}SnO{sub 4}) nanoparticles hydrothermally prepared using three different mineralizers, viz., Na{sub 2}CO{sub 3}, KOH and tert-butyl amine, and the effect of the IEPs on the dye loading behavior of Zn{sub 2}SnO{sub 4} based photoelectrodes in dye sensitized solar cells (DSSCs). To produce highly crystalline, uniform sized Zn{sub 2}SnO{sub 4} nanoparticles, hydrothermal processing parameters, such as reaction temperature, time, and the mineralizers used have been critically adjusted. The structural and morphological features of the as-synthesized Zn{sub 2}SnO{sub 4} nanoparticles have been observed using both scanning and transmission electron microscopy. For the surface state characterization of shape- and size-controlled Zn{sub 2}SnO{sub 4} nanoparticles, the IEPs of Zn{sub 2}SnO{sub 4} surfaces were determined through zeta potential measurements. The IEPs were found to be 5.7, 7.4 and 8.1 for Zn{sub 2}SnO{sub 4} nanoparticles formed using Na{sub 2}CO{sub 3}, KOH and tert-butyl amine, respectively, suggesting that the surface properties of Zn{sub 2}SnO{sub 4} nanoparticles can be manipulated through the choice of the mineralizers used during the hydrothermal reaction. The amount of N719 dye loading on the surfaces of Zn{sub 2}SnO{sub 4} electrodes having different IEPsmore » was also evaluated. It was revealed that the higher the IEP, the higher the dye loading amount, which means that the IEP mainly affects the dye loading at the dye-metal oxide interface. - Highlights: {yields} The effect of various mineralizers on the isoelectric point of Zn{sub 2}SnO{sub 4} was discussed. {yields} The IEP of Zn{sub 2}SnO{sub 4} can be modified by the choice of mineralizer. {yields} Change in IEP affects the surface properties and the morphology of Zn{sub 2}SnO{sub 4} particles. {yields} Modified surface affects the N719 dye loading behaviour of the Zn{sub 2}SnO{sub 4} based DSSCs.« less

Vibrational Characteristics of Outer-Sphere Surface Complexes: Example of Sulfate Ions Adsorbed onto Metal (Hydr)oxides

The vibrational characteristics of outer-sphere complexes of sulfate at several mineral oxide-water interfaces were investigated by in situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. In the IR spectra obtained from surface outer-sphere complexes, only one peak of the asymmetric stretching vibrational mode υ(3) similar to that of free sulfate ion SO(4)(2-) in aqueous solution is observed. However, on the investigated (hydr)oxide surfaces of Al(3+), Ti(4+), Fe(2+/3+), Cr(3+), Ce(4+), Cu(2+), Y(3+), Zn(2+), and Nd(3+), a shift of up to 14 cm(-1) was found, which was correlated to the polarizing power of the metal cations. A high polarizing power was found to result in a stronger shift of υ(3) compared to that of the aqueous SO(4)(2-) ion. Furthermore, the impact of the metal oxide structure on the characteristics of the formed outer-sphere complex was negligible because different Al and Fe (hydr)oxides did not show any changes in the respective IR spectra. Finally, the ionic strength (1-10(-4) M) and pH (6.8-3.1) have been modified to change the surface potential, showing no direct influence on the spectra (i.e., on the geometry of the outer-sphere complex).

Morphology and properties of hot dip Zn–Mg and Zn–Mg–Al alloy coatings on steel sheet

Hot dip coating on low carbon steel sheet samples by binary Zn–Mg alloy with low and high Mg and a ternary Zn–Mg–Al alloy, and their characterization and property evaluation have been described in this article. A good quality coating with respect to surface quality, coating structure and anti-corrosion properties was achieved at a lower bath temperature than in conventional galvanizing. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction studies have revealed the presence of eutectic phase mixtures in these coatings. Formation of MgZn2 has been observed on the top surface and through the cross-section of coating made from higher Mg bath. The hardness of the top surface of Zn–Mg and Zn–Mg–Al coating layers was found to be higher than Zn coating layer due to the presence of MgZn2 and other intermetallics. Steel samples coated in Zn–Mg–Al bath show better corrosion resistance properties than the ones coated in pure zinc and Zn–Mg binary baths. The correlation of these improved properties with the coating morphology has been discussed.

Surface of Zn–Mn–O and its role in room temperature ferromagnetism: An XPS analysis

The existence of ferromagnetism in Zn–Mn–O semiconductor samples and dependence on the preparation condition were investigated. We systematically examined the samples with manganese concentration ranging from 0 to 10 at.%, prepared by a solid state reaction route using (ZnC 2O 4·2H 2O) 1− x and (MnC 2O 4·2H 2O) x as precursors. Thermal treatment was carried out in air at temperatures ranging from 400 to 900 °C. The samples were investigated by X-ray diffraction, transmission electron microscopy, magnetization measurements and XPS spectroscopy. XPS surface composition, chemical analysis and depth profiling were successfully employed on powder revealing the chemical composition at the surface of the grains and underneath. The present investigation suggests that physical properties and observed room temperature ferromagnetism might be due to grain surface effects. It seems that the ferromagnetic phase is correlated with oxygen build up at the surface.

Template Route to Chemically Engineering Cavities at Nanoscale: A Case Study of Zn(OH)(2) Template.

A size-controlled Zn(OH)2 template is used as a case study to explain the chemical strategy that can be executed to chemically engineering various nanoscale cavities. Zn(OH)2 octahedron with 8 vertices and 14 edges is fabricated via a low temperature solution route. The size can be tuned from 1 to 30 μm by changing the reaction conditions. Two methods can be selected for the hollow process without loss of the original shape of Zn(OH)2 template. Ion-replacement reaction is suitable for fabrication of hollow sulfides based on the solubility difference between Zn(OH)2 and products. Controlled chemical deposition is utilized to coat an oxide layer on the surface of Zn(OH)2 template. The abundant hydroxyl groups on Zn(OH)2 afford strong coordination ability with cations and help to the coating of a shell layer. The rudimental Zn(OH)2 core is eliminated with ammonia solution. In addition, ZnO-based heterostructures possessing better chemical or physical properties can also be prepared via this unique templating process. Room-temperature photoluminescence spectra of the heterostructures and hollow structures are also shown to study their optical properties.

高温高圧 O2-CO2 下における NaCl 水溶液中の Fe-Zn ガルバニ腐食

Electrochemical characteristics of a Fe-Zn galvanic couple were studied under O2-CO2 mixtures of 2 MPa in a 3 mass% NaCl solution at 423 K for 14.4 ks. In 100% O2 and in 10% CO2+90% O2, both the galvanic corrosion current and corrosion potential of the couple remarkably changed after a certain period. Then, the polarities of the galvanic corrosion currents of the couple were reversed, indicating that Fe was not protected any more and rather corroded at an accelerated rate. On the other hand, the polarities of the current of the couple in 20% CO2+80% O2 and in 100% CO2 were not changed during the immersion time, indicating that Fe was still protected, although the galvanic currents were very low in 100% CO2. The galvanic corrosion potentials were always close to the corresponding cathodic potentials, indicating that the corrosion is governed by cathodic control. In 10% CO2+90% O2 and in 100% O2, the polarization characteristics of Zn specimen before and after the immersion test drastically changed, indicating that the galvanic couple of Zn anode and Fe cathode before the test changed to the couple of Fe anode and Zn cathode after the test. But, in 20% CO2+80% O2 and in 100% CO2, the galvanic couple of Zn anode and Fe cathode was hold during the immersion time. As CO2 ratio decreased, the corrosion products on the surface of Zn changed in the sequence: ZnCO3→Zn5(CO3)2(OH)6→Zn5Cl2(OH)8→ZnO. Above results show that Zn specimen in a Fe-Zn couple acts as a cathode due to the formation of ZnO on Zn. Therefore, whether Zn acts as a sacrificial anode or not, depends on the possibility of the formation of ZnO on Zn.

HR-TEM observation of laser pressure weld of galvannealed steel and pure aluminium

Laser pressure welding was conducted by changing the laser power and the roller pressure in the previous experiment. It was revealed that dissimilar metal welding of galvannealed steel and pure aluminium was feasible in a wide range of welding conditions. When the roller pressure was more than 1.96 kN at the laser powers equal to or less than 1400 W, the joint strengths were so high that the specimens in the tensile shear and the peel tests fractured in the A1050 parent metal. In order to know the reason for such high strengths of joints with thick compound layers and the joining mechanism, the compound layer was observed by HR-transmission electron microscopy (TEM). The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al + Zn. Moreover, the intermetallic compound was identified as FeAl, Fe2Al5, Fe4Al13 and Fe2Al5Zn0.4 phase by electron diffraction. The Fe3Zn10 (Γ phase) of Fe–Zn intermetallic compound was confirmed on a Fe base material. It is guessed that the joining areas were heated at a range of 782°C more than 665°C, a melting point of Al, by laser irradiation because the δlk phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10 μm thicker. The reason for the production of high-strength joints with a relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.