Anodic oxides solution composition

It is a valve metal and when made anodic in a chloride-containing solution it forms an anodic oxide film of TiOj (rutile form), that thickens with an increase in voltage up to 8-12 V, when localised film breakdown occurs with subsequent pitting. The TiOj film has a high electrical resistivity, and this coupled with the fact that breakdown can occur at the e.m.f. s produced by the transformer rectifiers used in cathodic protection makes it unsuitable for use as an anode material. Nevertheless, it forms a most valuable substrate for platinum, which may be applied to titanium in the form of a thin coating. The composite anode is characterised by the fact that the titanium exposed at discontinuities is protected by the anodically formed dielectric Ti02 film. Platinised titanium therefore provides an economical method of utilising the inertness and electronic conductivity of platinum on a relatively inexpensive, yet inert substrate. 

Commercial processes Commercial electroless nickel plating stems from an accidental discovery by Brenner and Riddell made in 1944 during the electroplating of a tube, with sodium hypophosphite added to the solution to reduce anodic oxidation of other bath constituents. This led to a process available under licence from the National Bureau of Standards in the USA. Their solutions contain a nickel salt, sodium hypophosphite, a buffer and sometimes accelerators, inhibitors to limit random deposition and brighteners. The solutions are used as acid baths (pH 4-6) or, less commonly, as alkaline baths (pH 8-10). Some compositions and operating conditions are given in Table 13.17 . 

Fig. 3. Current-potential curves for anodic oxidation of H2CO on different metals. Dotted lines current attributable to the anodic dissolution of Cu and Co electrodes. Solution composition 0.1 mol dm-3, 0.175 mol dm 3 EDTA, pH = 12.5, T — 298 °K. Adapted from ref. 38.

A wide variety of electrolyte compositions used for anodic oxidation of silicon can be found in the literature. The electrolytes can be categorized in inorganic or organic solutions. In the latter case electrolytes like ethylene glycol [Ja2, Me6, Ma5, Mel3], methanol [Ma2] or tetrahydrofuryl alcohol [Be3] are used, with salts such as KN03 added in order to improve the conductivity. Studies with pure water [Ga2, Mo3, Hu3] as an electrolyte were performed, as well as with additions... 

Nagayama, M. Cohen, M. (1963) Anodic oxidation of Fe in a neutral solution. 1. Nature and composition of the passive film. J. Elec-trochem. Soc. 109 781-790 Nakai, M. Yoshinaga, N. (1980) Fibrous goethite in some soils from Japan and Scotland. Geoderma 24 143-158 Nakazawa, H. Sato, H. Hasebe, S. (1989) Study of the removal of arsenic from hot waste water by the ferrite formation method. Shigento Sozai 105 239-244 Namjesnik-Dejanovic, K. Maurice, P.A. 

Fabrication of titania nanotube arrays via anodic oxidation of titanium foil in fluoride based solutions was first reported in 2001 by Gong and co-workers [58]. Further studies focused on precise control and extension of the nanotube morphology [21], length and pore size [22], and wall thickness [3]. Electrolyte composition plays a critical role in determining the resultant nanotube array architecture and, potentially, its chemical composition. Electrolyte composition determines both the rate of nanotube array formation, as well as the rate at which the resultant oxide is dissolved. In most cases, a fluoride ion containing electrolyte is needed for nanotube array formation. In an effort to shift the band gap of the titania... 

Martin and coworkers tried to prepare carbon tubes from the carbonization of polyacrylonitrile (PAN) in the channels of anodic oxide film (10). A commercially available film with a pore diameter of 260 nm was immersed in an aqueous acrylonitrile solution. After adding initiators, the polymerization was carried out at acidic conditions under N2 flow at 40°C. The PAN formed during the reaction was deposited both on the pore walls and on both sides of the film. Then the Film was taken from the polymerization bath, followed by polishing both faces of the film to remove the PAN deposited on the faces. The resultant PAN/alumina composite film was heat-treated at 250°C in air, and then it was heat-treated at 600°C under Ar flow for 30 min to carbonize the PAN. Finally, this sample was repeatedly rinsed in I M NaOH solution for the dissolution of the alumina film. The SEM observation of this sample indicated the formation of carbon tubes with about 50 xm long, which corresponds to the thickness of the template film. The inner structure of these tubes was not clear because TEM observation was not done. The authors claim that it is possible to control the wall thickness of the tubes with varying the polymerization period. 

A preliminary knowledge of which reaction steps could be key in determining the overall corrosion rate can be assessed by measurements of Corr as a function of important system parameters, e.g., oxidant concentration, solution composition, temperature. The proximity of ACOrr to either eM/Mn+ or /Red can indicate which of the two half-reactions may be rate determining. This is illustrated in Fig. 3A, which shows an Evans diagram for the combination of a fast anodic reaction coupled to a slow cathodic one. The corrosion of iron or carbon steel in aerated neutral solution would be an example of such a combination. The anodic reaction requires only a small overpotential (1) = /Mn+ - Ecorr) to sustain the corrosion current, /COrr, compared to the much larger overpotential required to sustain the cathodic reaction at this current. The anodic reaction would... 

NiFe species and the less aggressive oxidizing properties of the NiF.x. This finding indicates that an anode coating with composition below NiFs could still be an effective oxidizer and fluorinator. As is seen, the more concentrated solutions of NiFe give a different product distribution. 

Physical development can occur on nuclei with the simultaneous reduction of silver ion and oxidation of the developing agent. The two partial processes can also be separated in a model cell so that the effect of solution composition on the separate anodic and cathodic parts can be seen (Figure 14). Kawashima et al. [59]... 

The channels, which had catalyzed electrodes on the surfaces, were covered with Nafion 112 (thickness 50 pm, equivalent weight 1,100 gmoF, ionic conductivity 0.083 S cm" ) to provide ionic conductivity between the anode and the cathode. The Nafion membrane was pressed with a glass plate to avoid solution leakage (Fig. 3.4a). Voltage-current measurements were performed at room temperature with a mass flow control system of fuel and oxidant as shown in Fig. 3.4b. The fuel and oxidant solutions were supplied to the electrodes with the micro-syringe pumps from the outlet of each channel. The flow rate of both the fuel and oxidant solutions was 80 pL miu". Composition of the fuel solution was 2M methanol solution... 

This change in b can be either due to a change in the surface oxide-layer composition or due to a change in the active site characteristics caused by the surface interactions. Otherwise, the change in b reported for crystalline Ni-Co alloys in alkaline solutions has also been explained by the different nature of the surface oxides [27]. It is also important to say that the nickel and cobalt-spinel voltammetric behavior is attained after potential cycling at a low scan rate, where b = 0.04 V decade-1. However, a pre-anodization at 1.8 V vs. RHE led to a Co304 spinel electrode for which b = 0.06 V decade-1. 

---