Anodic electrodeposition

Paints are specially formulated for one of two processes. In the first, anodic electrodeposition, the article to be painted is made the anode in a d.c. circuit. Cathodic electrodeposition is the reverse operation. The process takes place under carefully controlled conditions in a tank. Current passes through the paint causing it to deposit uniformly over the article in a uniform film whose thickness can be accurately controlled. The paint film is insoluble in water and exhibits remarkable adhesion after stoving. Electrodeposition is widely used to apply primers, e.g. by car manufacturers, and one coat finishes. 

A. Bezbaruah and T. Zhang, Fabrication of anodically electrodeposited iridium oxide film pH microelectrodes for microenvironmental studies. Anal. Chem. 74, 5726-5733 (2002). 

Anodic electrodeposition (AED), 10 448 Anodic electrodeposition coatings, 10 381 Anodic inhibitors, 7 815 Anodic oxidation, on tantalum, 24 327—330 Anodic oxidation waste treatment, 9 643 Anodic oxide films... 

Fujishima and coworkers reported a method to electrochemically deposit IrO,. NPs at BDD electrodes [87]. The deposition process was based on preparation of a solution containing hydrolysis products of IrClg and oxalate, followed by anodic electrodeposition of IrO from this solution onto an anodically pretreated BDD electrode. 

Ir Ir02 electrodes (commercially available from Cypress Systems, Lawrence, KS) can measure pH in harsh environments or microscopic spaces [S. A. M. Marzouk, Improved Electrodeposited Iridium Oxide pH Sensor Fabricated on Etched Titanium Substrates, Anal. Chem. 2003, 75, 1258 A. N. Bezbaruah and T. C. Zhang, Fabrication of Anodically Electrodeposited Iridium Oxide Film pH Microelectrodes for Microenvironmental Studies, Anal. Chem. 2002, 74. 5726 D. O. Wipf. F. Ge, T. W. Spaine, and J. E. Baur, Microscopic Measurement of pH with Ir02 Microelectrodes, Anal. Chem. 2000, 72, 4921]. For pH measurement in nanoscopic spaces, see X. Zhang,... 

Iridium dioxide — Iridium oxide crystallizes in the rutile structure and is the best conductor among the transition metal oxides, exhibiting metallic conductivity at room temperature. This material has established itself as a well-known - pH sensing [i] and electrochromic [ii] material (- electrochromism) as well as a catalytic electrode in the production of chlorine and caustic [iii]. The oxide may be prepared thermally [iv] (e.g., by thermal decomposition of suitable precursors at temperatures between 300 and 500 °C to form a film on a substrate such as titanium) or by anodic electrodeposition [v]. 

These materials, the original galena, the refined lead metal, lead oxide, glass, and pigment were put into solution. The lead was purified by anodic electrodeposition and was analyzed by a mass spectrometer using previously published procedures (6). The results of the measurements of the isotopic ratios of the above samples are shown in Table II. 

The anodic oxidation of phenol (dissolved in sodium sulfate) was studied by De Sucre and Watkinson using two types of lead dioxide anodes [26]. The first was made of 2 mm lead shot that was oxidized for 12 h at 526mA/cm in 20% sulfuric acid while the second anode, electrodeposited lead dioxide flakes, was supplied by a commercial manufacturer. The phenol oxidized faster on the electrodeposited Pb02, which also turned out to be more corrosion-resistant than the oxidized lead shot. While all of the phenol oxidized rapidly (1.5 h) on the electrodeposited anode, not all of it formed CO2. It was found that 80% of the total organic carbon remained in solution after the phenol was completely oxidized. Phenol destruction increased with an increase in current density, and decreased as electrolyte flowrate, pH, and anode particle size were increased. 

Fujishima and coworkers reported a method to electrochemically deposit IrOx NPs at BDD electrodes [87]. The deposition process was based on preparation of a solution containing hydrolysis products of IrCl63 and oxalate, followed by anodic electrodeposition of IrO% from this solution onto an anodically pretreated BDD electrode. They showed that for conditions under which only limited deposition was allowed to occur it was possible to deposit about 30 nm diameter IrO% N Ps that were relatively homogeneously distributed across the surface. They examined these deposits for hydrogen-peroxide oxidation and observed significant oxidative current at potentials as low as + 0.35 V at pH 7. 

For exploring SECM features of the electrochemical robotic system, two electrodes were controlled by the robotic system to electrochemically deposit spots of an anodic electrodeposition paint82 on a surface. The deposition of the negatively charged polymer is realized by anodic water oxidation under generating of protons. The process is schematically illustrated in Fig. 14.28. The pH shift in the vicinity... 

Fig. 9 Electrode reaction for (A) the cathodic electrodeposition of Cu and (B) the anodic electrodeposition of AI oxide.

The current that flows at the working electrode may be divided into two kinds faradaic and non-faradaic. The faradaic processes are the ones where charges are transferred across the liquid-solid interface. These processes are called faradaic because they follow Faraday s law, which says the amount of substance that undergoes oxidation or reduction at each electrode is directly proportional to the amount of electricity that passes through the cell. Two faradaic processes that are directly related to electrodeposition are shown in Fig. 9, where Fig. 9A represents simply the deposition of Cu by reduction of Cu " and Fig. 9B the growth of A1 anodic oxide by oxidation of metallic aluminum, this being an example of anodic electrodeposition. Non-faradaic processes are... 

The compositions of cathodic and anodic electrodeposition baths are given in Table 3.11. The main components are resins, pigments, extenders, some solvent, and neutralization agents. The latter are used to neutralize the charge on the resins so that they become water dispersible. The application data affect the plant and equipment technology (e.g., choice of construction materials, energy consumption, and rectifier design) [3.109], [3.117]. 

In anodic electrodeposition the workpiece acts as the anode. This method is only used to a small extent. Disadvantages compared with cathodic electrodeposition are its poorer handling and corrosion protection. Advantages include the lower paint price and lower expenditure on plant technology. 

In cathodic electrodeposition the workpiece acts as the cathode this method is more important than anodic electrodeposition. The binders consist largely of non-water-soluble epoxy resins, and to a lesser extent of acrylic resins (one-layer coatings). These resins are converted into a water-soluble (i.e., ionized) state by neutralization with organic acids (e.g., acetic acid) ... 

Anticorrosive Primers. Anticorrosive primers are applied in dip tanks so that they reach all parts of the car body dipping is a fast method of application. The standard method for application of primers is electrodeposition. Anodic electrodeposition paints were used when the electrocoating technique was first applied, but cathodic electrodeposition is now predominant because it provides better corrosion protection. 

The drying oil fatty acid chains can be partially maleinized to permit emulsification when the carboxyls have been partially neutralized and the resin dispersed in water/solvent mixtures. These waterborne epoxyesters can be used as binders for anodic electrodeposition primers (see p. 109). 

Gu, L., Y. W. Wang, R. Lu, L. Guan, X. S. Peng, and J. Sha. 2014. Anodic electrodeposition of a porous nickel oxide-hydroxide film on passivated nickel foam for supercapacitors. Journal of Materials Chemistry A 2 7161-7164. 

Spray, R.L., Choi, K.-S. Photoactivity of transparent nanocrystalline Fc203 electrodes prepared via anodic electrodeposition. Chem. Mater. 21, 3701 (2009)... 

The binder properties are useful in other pigmented coatings such as clay-based paints (119). The zinc-lithium silicate coatings can be applied by anodic electrodeposition on steel (120). In another-typc of use, lithium polysilicate provides an intermediate bond between the fluorocarbon polymer coating and metal on antisticking cook ware (121). 

The solubility of phosphate films varies with pH, the type of phosphate, and its morphology. In the alkaline range of pH >10 the solubility of phosphate film is directly related to the adhesion of paint film. Formation of corrosion cells under the paint film causes an increase in pH at the cathodic area since the cathodic reactions produce OH ions and pH at the interface between the steel and paint film reaches 13.5. During the cathodic electrodeposition process for primers, pH at the surfaces reaches a value of 10-12, whereas in the anodic electrodeposition process pH at the surface is 3-4. 

Petit MA, Plichon V (1997) Anodic electrodeposition of iridium oxide films. J Electroanal Chem 444 247-252... 

---