Anodization Of Zr Research Articles

In-situ spectroscopic ellipsometry for deeply understanding the interface evolution dynamics of anodic ZrO2 nanotubes

The interface evolution dynamics within the initial anodization of Zr remains ambiguous while it occupies a pivotal role in understanding the growth kinetics and preparing desirable ZrO2 nanotubes. Herein, we conducted an in-situ study on the Zr electrode/electrolyte interface evolution with highly sensitive spectroscopic ellipsometry. Based on the characteristic parameters of the interface layer derived from in-situ ellipsometric spectra, the dynamic evolution of the interface structure was visualized. In addition, the effects of temperature, voltage and F− concentration in the anodic solution on the interface evolution and growth kinetics of ZrO2 nanotubes were revealed. Without F−, ZrO2 grows with a self-limited mode and forms an ultrathin layer. In the presence of F−, the ZrO2 layer dissolves and forms nanotubes under the electric field-assisted dissolution (FAD) effect, and the interface evolution mainly includes three stages of ZrO2 layer formation, void initiation and nanotube generation. The interface parameters derived from in-situ ellipsometric spectra indicate that the preferred F− concentration, voltage and temperature are 0.15 M, 20 V and 293 K, respectively. Under the optimal condition, ZrO2 nanotubes grow linearly (25.4 nm s−1) with a porosity of ∼ 50%. Moreover, the apparent activation energy of ZrO2 formation is approximately 13.5 kJ mol−1 (fitted by the Arrhenius formula). This fundamental work on interface research provides practical guidance for the precise and controllable preparation of ZrO2 nanotubes via anodization.

Unraveling the six stages of the current-time curve and the bilayer nanotubes obtained by one-step anodization of Zr.

The application and growth mechanism of anodic TiO2 nanotubes have been a hot topic in the last ten years, but the formation mechanism of anodic ZrO2 nanotubes has rarely been studied. In one-step constant voltage anodization of Al and Ti, the typical current–time curve has three stages. Moreover, the current–time curves of the three stages can last for 10 min or even 10 hours, resulting in a single layer of nanotubes with the same diameter due to the constant voltage in one-step anodization. However, in this paper, it was found for the first time that the three stages of the current–time curve appeared twice in succession during one-step constant voltage anodization of Zr for only 900 seconds, and bilayer nanotubes with increased diameter were obtained. This six-stage current–time curve cannot be explained by classical field-assisted dissolution and field-assisted flow or stress-driven mechanisms. Here, the formation mechanism and growth kinetics of bilayer ZrO2 nanotubes have been clarified rationally by the theories of ionic current, electronic current and oxygen bubble mold. The interesting results presented in this paper are of great significance for revealing the anodizing process of various metals and the formation mechanism of porous structures.

Comparative study on the anodizing process of Ti and Zr and oxide morphology

Metal anodizations have attracted much attention, but the formation mechanisms of the porous anodic oxides are still unclear. Compared with the Ti anodization, the anodization of Zr is relatively less studied. In order to compare the anodizing processes of Ti and Zr, a comparative study of Ti and Zr was carried out under the different voltages of anodizing process in the same mixed electrolyte of ammonium fluoride and phosphate acid. It was found that the structure and morphology of their nanotubes were very different. The anodizing curve of Ti showed a state of constant current. However, the anodizing curve of Zr did not show the state of constant current and ZrO2 nanotubes were still formed. This indicates that there is no equilibrium between oxide growth and dissolution in the anodization. TiO2 nanotubes show an orderly array of nanotubes, but ZrO2 nanotubes have three kinds of composite structures: nanoflower, nanotube and dense films. By comparing the great difference of current-time curves between the two anodizing processes, the composite structure of ZrO2 nanotubes are interpreted reasonably by combining electronic current theory and oxygen bubble mold.

Formation of ideally ordered porous anodic zirconia by anodization of vacuum deposited Zr on molds

We studied the formation of ideally ordered nanoporous zirconia by anodizing Zr having a texturing pattern. A texturing pattern was formed on a Zr surface by peeling off a sputtered zirconium film from a metal (Ni) mold having an ordered array of convexes. In contrast to texturing by nanoimprinting, the present texturing process never requires the pressing of a mold onto the Zr surface. During the anodization of Zr that has a texturing pattern on its surface, which is an ideally ordered array of concaves, each concave acted as a starting point of the formation of nanoholes. By the present process, porous anodic zirconia having an ideally ordered array of nanoholes was obtained. The interval between nanoholes in the porous anodic zirconia agreed with the texturing pattern.

Comparison of ZrO2, TiO2, and α-Fe2O3 nanotube arrays on Cr(VI) photoreduction fabricated by anodization of Zr, Ti, and Fe foils

This paper presents the fabrication of self-organized ZrO2, TiO2, and α-Fe2O3 nanotube arrays by anodization of Zr, Ti, and Fe foils, respectively in fluoride-containing EG electrolyte at 40 V for 20 min. The as-anodized nanotubes were annealed in a tube furnace at 400 °C for 3 h to induce the crystallization of the oxide film. Morphology, crystal structure, surface properties, and optical properties of the anodic ZrO2 nanotubes (ZNTs), TiO2 nanotubes (TNTs), and α-Fe2O3 nanotubes (FNTs) were characterized by Field-Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), x-ray Diffraction (XRD), Fourier-Transform Infrared (FTIR) spectroscopy, Photoluminescence (PL) spectroscopy, and UV–visible Near-Infrared Diffuse Reflectance Spectra (UV–vis NIR DRS) spectroscopy, respectively. Based on the FESEM and TEM micrographs, ZNTs possessed the longest nanotubes (i.e. 9.6 μm) compared with TNTs and FNTs under the same anodization condition. The aspect ratio of the nanotubes can be arranged in the order of ZNTs > FNTs > TNTs. The surface of the annealed ZNTs, FNTs, and TNTs was enriched with –OH groups to facilitate the Cr(VI) adsorption. According to the UV–vis NIR DRS spectra, strong visible light absorption was observed on the FNTs due to their low band gap. Whereas, the TNTs predominantly absorbs the UV light at λmax = 360 nm. Rapid Cr(VI) removal was observed on FNTs, i.e. 100% after 2 h activated by sunlight with negligible Cr(VI) removal for ZNTs and TNTs. When exposed to UVC (λ = 254 nm), only 39% versus 37% Cr(VI) removal efficiencies were obtained on TNTs and ZNTs after 3 h suggesting sluggish electron transfer due to rapid charge carriers recombination as evident in the PL spectra.

A humidity-sensitive nanocomposite solid ion conductor: sulfonated poly-ether-ether-ketone in nanotubular TiO2 or ZrO2 matrix

A nanocomposite solid ion conductor was prepared by infiltrating zirconia or titania nanotube arrays, made by electrochemical anodization of Zr or Ti metal, with proton-conducting sulfonated poly(ether-ether-ketone) (SPEEK) ionomer. The resulting material was characterized using scanning electron microscopy, X-ray diffraction, and infrared spectroscopy showing the successful filling of the nanotubular matrix with the ionomer. Impedance spectroscopy revealed a conductivity increase by several orders of magnitude after infiltration; furthermore, the impedance of the TiO2nt-SPEEK nanocomposite is very sensitive to the relative humidity. Possible applications of these ionic conducting nanocomposites include solid-state humidity sensors or heterogeneous catalytic materials.

Electrolyte Influence on the Morphologies of Anodic ZrO<sub>2</sub> Nanotube Arrays Formed by Anodization

Self-aligned ZrO2 nanotube (ZNT) arrays were produced by anodization of Zr in aqueous sulphate/fluoride and ethylene glycol (EG)/fluoride electrolytes. The morphologies of the oxide produced were compared. It appears that the nanotubes formed in EG/fluoride are clearer showing smoother walls indicating better cell boundaries separation in this electrolyte. They are also longer with length > 10 µm after 1 hour of anodization. The x-ray diffraction pattern of the ZNTs revealed that ZNTs are cubic oxide.

Preparation of Fe-doped ZrO2 nanotube arrays by anodization of Zr–Fe alloy and their magnetic properties

Zr–Fe (Fe: 16.95wt%) alloy was prepared through the vacuum melting method. Fe-doped ZrO2 nanotube arrays have been achieved directly by anodizing the Zr–Fe alloy. Morphologies and structures of the samples were characterized by a scanning electron microscope, a transmission electron microscope and X-ray diffraction. The effects of electrolyte and temperature on the morphologies were studied. Magnetic properties of the samples were studied as well. Results show that the as-prepared sample was amorphous. Pure monoclinic phase was obtained when annealed at 400°C, monoclinic and tetragonal phase coexisted at 500°C and 600°C. Higher value of coercivity (627Oe) was achieved when annealed at 500°C.

The photoluminescence properties of Er3+-doped ZrO2 nanotube arrays prepared by anodization

Er3+-doped ZrO2 nanotube arrays were prepared by anodization of Zr–Er alloy which was obtained by melting zirconium with 1.0wt% erbium. The morphology, structure and photoluminescence properties were studied through scanning electron microscope, transmission electron microscope, X-ray diffraction and photoluminescence analyzer. X-ray diffraction results indicate that doping of Er3+ affects the crystal structure and grain size obviously and the Er3+-doped samples tend to form small tetragonal grains. Photoluminescence analyses show that when Er3+-doped zirconia nanotube arrays are excited at 317nm, there are two strong photoluminescence emission peaks at 373nm and 415nm. When the excitation wavelength is 257nm, a photoluminescence emission peak appears at 363nm. Under same measurement conditions, emission peaks of the undoped ZrO2 nanotube arrays are very weak.

Synthesis and growth mechanism of zirconia nanotubes by anodization in electrolyte containing Cl−

The formation and growth of a self-organized zirconia porous layer can be achieved directly by anodization of Zr in chloride containing electrolytes. The morphology of the porous layers is affected by electrochemical conditions such as Cl− concentration. Zirconia nanotubes with diameters ranging from 250 to 300 nm and a length of 33 μm were formed under proper conditions. The nanotubes have smooth and straight walls. The composition of the nanotubes was characterized by using an energy dispersive spectrometer. Selected area electron diffraction investigation reveals that the as-anodized zirconia nanotubes have an amorphous structure. Crystal phase transition and structural stability of the ZrO2 nanotubes after heat treatment were characterized. A possible growth mechanism is presented.

Preparation of Thin-Film Capacitor with High Reliability by Anodization of Zr–Al Alloy Film

We have prepared Zr–Al thin-film capacitors by anodizing a sputter-deposited Zr–Al alloy film with 46 at. % Al, and examined their properties before and after heat treatment and their leakage current mechanism. In addition, anodized Zr–Al films were characterized by X-ray diffraction (XRD) analysis and Auger electron spectroscopy (AES). It is revealed that the reliability of an anodized pure-Zr capacitor is markedly improved by substituting the anodized Zr–Al film for anodized pure-Zr, because the crystallization of anodized Zr–Al amorphous films hardly occurs. In addition, it is clarified that the leakage current mechanism of the anodized Zr–Al capacitor is due to Schottky emission and that the thermal degradation observed after heat treatment above 350 °C is triggered by the diffusion of Zr atoms from the underlying unoxidized alloy layer into the anodized Zr–Al layer.

Formation of Self-Organized Zirconia Nanostructure

The present work investigates the anodic formation of a self- organized high-aspect-ratio zirconia nanotube layer on Zr. Under specific electrochemical conditions anodization of Zr in (NH4)2SO4/NH4F electrolyte results in arrays of individual nanotubes with a diameter of 50 nm and a length of 17 μm - the aspect ratio is estimated as more than 300. The tube walls where extremely straight and smooth - this morphology is significantly different from a nanotubular zirconia shapes formed in acidic electrolytes. SAD pattern reveals that the nanotubes have a crystalline structure already after anodization, that is, without any further annealing. The nanotube growth features are similar to that of HfO2 nanotubes, but is different from that of TiO2.

Anodic Porous Zirconium Oxide Prepared in Sulfuric Acid Electrolytes

We report the formation of self-organized porous ZrO2 layers by anodization of Zr in H2SO4 electrolytes. Anodization at 20 V after a potential sweep from open-circuit potential with a defined sweep rate results in tube-like porous ZrO2. In particular, under optimized electrolyte condition and polarization, a highly ordered porous structure is obtained. Furthermore, sponge-like porous ZrO2 is also fabricated under a specific electrochemical condition.

Self‐Organized High‐Aspect‐Ratio Nanoporous Zirconium Oxides Prepared by Electrochemical Anodization

The electrochemical formation of self-organized porous structures has recently attracted much attention due to the broad range of nanoscale applications that become accessible through nanopore arrays made of materials such as Al2O3, [1–12] Si, and InP. Particularly, the anodic oxidation of Al has been studied in detail and a variety of highly ordered porous oxide structures with a high-aspectratio pore geometry have been successfully prepared. In addition to direct applications, the nanostructures have also been employed as a template for the deposition and fabrication of secondary nanostructures. Applications include magnetic recording media, optical devices, functional electrodes, and waveguides. 7, 8] Recently we reported that under optimized electrochemical conditions, self-organized pore formation on Ti can be achieved to grow TiO2 nanotubes with aspect ratios of more than 20. Herein, we report the electrochemical fabrication of highly ordered porous zirconium oxide layers of nanotubular shape with very high aspect ratios (>100) by anodization of Zr. This is a clear improvement in comparison with other ongoing attempts. Key to achieving the high aspect ratio is an adjustment of the electrochemical parameters to an optimized competition between dissolution and formation of the oxide. Zirconium oxide is an important functional material that plays a key role as an industrial catalyst and catalyst support with particular acid catalysis properties. 22] Furthermore, zirconium oxide is known to have excellent ion-exchange properties that are exploited in various applications. Highsurface-area structures are often required to provide an enhanced performance. These structures are typically synthesized by sol–gel methods or colloid electrodeposition. A well-established fact in the literature is that when Zr or other so-called “valve metals” are anodized in most electrolytes, a compact oxide layer of up to several hundred nanometers thickness is formed. A unique feature in comparison to other valve metals is that the growth of these compact ZrO2 layers at room temperature in most electrolytes leads to a crystalline film. However, in electrolytes containing fluoride ions, the oxide formation process is fundamentally changed. Figure 1 shows SEM images of porous zirconium oxide layers observed after anodization in fluoride-containing electrolytes. Figure 1a shows the surface morphology, and

Electrical characteristics of ZrO2 prepared by electrochemical anodization of Zr in an ammonium tartrate electrolyte

An investigation of the electrical characteristics of ultrathin ZrO2 formed by anodization in an ammonium tartrate electrolyte is reported. Compared with low temperature thermal oxidation, the formation of zirconium oxide by anodization shows self-limiting oxidation behavior with an increase in time, and, thus, provides superior control of the oxide thickness. The growth of anodized oxide inhibits aggressive oxidation by blocking the flow of current through a dielectric since the location at which the oxide forms would become a region of high resistance. The equivalent oxide thickness of ultrathin zirconium oxide by anodization within an acceptable dispersion was scaled down to 11.4 Å with leakage current density of less than 1.5×10−3 A/cm2 at Vfb of −1 V. The density of the interface state and fixed charge density of zirconium oxide using the anodization process are also discussed.