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Material Synthesis and Methodologies
Published in It-Meng Low, Hani Manssor Albetran, Victor Manuel de la Prida Pidal, Fong Kwong Yam, Nanostructured Titanium Dioxide in Photocatalysis, 2021
It-Meng Low, Hani Manssor Albetran, Victor Manuel de la Prida Pidal, Fong Kwong Yam
The electrochemical anodization method is simple and straightforward, and it is reported as the most studied technique for the synthesis of 1D TiO2 nanotubes in the last 15 years [29]. A typical electrochemical setup is illustrated in Fig. 2.1. In the classical electrochemical oxidation of a valve metal, a barrier oxide layer is formed on the metal surface [30]. In 1984, Assefpour-Dezfuly et al. discovered that anodization in chromic acid electrolyte resulted in TiO2 porous layers [31]. Later in 1999, Zwilling et al. added HF in the chromic acid electrolyte and produced very thin nanotube layers [32]. These early works suggest that F− is the prime component for the formation of tubular morphology.
Mass Transport and Current Distribution
Published in Madhav Datta, Electrodissolution Processes, 2020
The shape evolution of a cavity in isotropic electrochemical micromachining through a photoresist mask has been studied theoretically by West et al. [36] for the limiting cases of primary current distribution and uniform dissolution rate, respectively. With progressing dissolution, a given cavity evolves from an initially flat shape into a hemispherical shape. The simulation yielded the variation of the etch factor which is a measure of the undercutting as a function of the dimensionless charge of dissolution. The shape evolution in two-sided through foil electroetching was also considered by these authors. During electroetching of photoresist patterned metal films/sheets, the slope of the cavity wall increases with increasing dissolution time resulting in an increased extent of undercutting of the photoresist. The numerical results permit the estimation of the undercutting required to achieve a given wall steepness. Shenoy and Datta [38] theoretically modeled the shape evolution of relatively large cavities which can lead to island formation. They proposed to protect the center of a feature with a dummy mask which eventually is eliminated by undercutting. Shenoy and Datta also investigated the effect of the resist wall angle [37]. Madore et al. [41] presented a numerical simulation of the shape evolution of cavities in titanium, a valve metal, and found good correspondence with measured cavity shapes produced in a methanol-based electrolyte. Some of the aspects of shape evolution in through-mask electrochemical micromachining will be discussed in detail in another chapter.
Leaching with Acids
Published in C. K. Gupta, T. K. Mukherjee, Hydrometallurgy in Extraction Processes, 2019
The dissolution of stainless steel, in the case of stainless steel-clad fuel, in nitric acid requires addition to either H2SO4 or HCl. According to Rhode and Bomar,92 the steel-clad fuel can be subjected to electrodissolution in HNO3 alone with great advantage. The clad fuel is placed in a perforated valve metal (Nb, Ta, Ti, etc.) basket connected to the anode, and the basket itself is placed in a cathode container filled with nitric acid.
Relationship between the inductive response observed during electrochemical impedance measurements on aluminium and local corrosion processes
Published in Corrosion Engineering, Science and Technology, 2019
Y. Yang, F. Scenini, N. Stevens, M. Curioni
The spectra obtained for aluminium in 1 M H2SO4 during constant cathodic polarisation (–100 mV and –200 mV vs OCP) in the absence of chlorides are shown in Figure 6(a and d). Overall, the impedance modulus values decreased with increasing immersion time. The spectra mainly displayed a capacitive behaviour, with the phase approaching 0 degrees for frequencies below 1 Hz. A slight decrease in the impedance modulus with decreasing frequency was observed for the first spectrum, but this is likely to be a residual artefact due to the approximation introduced during the correction procedure described in ‘Correction of EIS spectra due to non-stationarity’ section. As expected for a valve metal such as aluminium, hydrogen evolution was readily observed during cathodic polarisation and shown in Figure 7(a,b).
EUROCORR 2017 in combination with the 20th International Corrosion Congress and the Process Safety Congress 2017: Corrosion Control for Safer Living. Part 2
Published in Corrosion Engineering, Science and Technology, 2018
The paper abstract ‘In-situ monitoring of the dissolution and passivity of valve metals’ was presented by Achim Hassel of the Johannes Kepler Universität Linz, Austria (Figure 4). In this study, an electrochemical flow cell was directly coupled to an inductively coupled plasma mass spectrometer in order determine the actual metal dissolution rate. In the case of titanium, it was found that only a few per cent of the total current was used for metal dissolution while the majority was probably used for oxide formation. During long-term transient experiments, no clear correlation between the measured current and the dissolution rate was observed. For tantalum, which is typically considered the most corrosion-resistant valve metal, the spontaneous dissolution rate in concentrated sulphuric acid was about 0.3 pg s−1 cm−2. During the electrochemical experiments up to 3 V SHE, less than 0.2% of the total current was used for metal dissolution, reflecting its extremely high passivity.
Pretreatment on Ti substrate for Ti/Pt anode by electrolytic plasma processing
Published in Transactions of the IMF, 2018
L. Yang, P. Zhang, Y. Liu, J. Liang, W. B. Tian, Y. M. Zhang, Z. M. Sun
Dimensionally stable anodes (DSA) consist of a valve-metal substrate and a noble metal (oxide) coating. The Ti/Pt anode is one of such DSAs and it is extensively used for industrial electrochemical applications due to its good catalytic effect.1–4 In Ti/Pt electrodes, the platinum film not only acts as electrical conductor but also as protector for the base metal, allowing the electrodes to be used in highly corrosive or harsh environments.5–9