**Author details**

optimal anodizing parameters, independent of the electrolyte used. The porous oxide layer thickness and hence pore height can grow to many times the height of the barrier layer. It is usually during this oxide growth that electrolyte anions can integrate into the forming porous structure near the oxide/electrolyte interface, while pure alumina is predominantly found in layers close to the metal/oxide interface. It is also possible for voids to form in the pore walls during the growth of the oxide layer. Possible causes of these voids range from oxygen evolution during oxide formation to localized defects in the barrier layer. These defects produce a condensation effect that involves cations and/or metal vacancies at the metal/oxide

Diggle et al. [86].discussed the contradictory research results of the period. For example, the non- porous barrier layer was regarded as amorphous and anhydrous, while the porous layer had been found to be both amorphous and crystalline. In the case of the barrier layer, under normal anodization conditions the layer will be amorphous. However, studies by Uchi et al. [87] have shown that with the right growth conditions it was possible to have amorphous or crystalline Al oxide being produced during anodization. To form a crystalline oxide structure; an Al substrate was first immersed in boiling water to form a hydrous oxide layer [oxyhydroxide with excess water (AlOOH.H2O)]. The substrate was then anodized in a neutral borate solution at high temperatures, during which Al3+ ions move from the metal substrate to the hydrous oxide interface, where they combine and transform the hydrous oxide to crystalline Al2O3. Some of the contradictory evidence of the earlier works discussed by Diggle et al. [86] of the porous layer could be explained by the work of De Azevedo et al. [88]. In this study the structural characteristics of doped and un-doped porous Al oxide, anodized in oxalic acid was investigated using X-ray diffraction (XRD). The XRD patterns for the un-doped samples revealed several peaks associated with Al and Al2O3 crystalline phases on top of a broad peak that was approximately centered on the 2θ angle of 25°. This broad peak indicated that the synthesized layer was a highly disordered and/or amorphous Al oxide compound.

**•** One of the most important aspects of self-assembly lies in the capability of producing uniform structures over a large area using conventional electrodepsotion and anodizing

**•** Nanostructured Ni-Fe alloys, produced by electro-deposition technique provide material with significant improved strength and good magnetic properties, without compromising

**•** Due to better anticorrosive in several aggressive environments, mechanical and thermal stability characteristics of Ni-Mo alloys, the electro deposition of these alloys plays an important role. Broad application of nickel-based composite coatings in electrochemistry is due to the highly catalytic activity in electrocatalytic hydrogen evolution (HER) and electrocatalytic oxygen evolution (OER) as well as good corrosion resistance of nickel in

interface, which subsequently become detached, and form the void.

**6. Conclusions**

150 Modern Surface Engineering Treatments

processes.

the coefficient of thermal expansion.

aggressive environments.


### **References**


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**Chapter 7**

**Coating Technology of Nuclear Fuel Kernels:**

The coating technology of nuclear fuel kernels (NFKs) is an important part of the nuclear safety research. Now there are many new designs of nuclear reactor which based on the coated fuel particles. Among them, high temperature gas-cooled reactor (HTGR) is one of the Gen-IV reactors and has a bright future in the electricity and hydrogen production because of its

The inherent safety characteristics of HTGR have been paid more attention among many nuclear reactors in the nuclear renaissance, even more adequately after the Fukushima nuclear accident. The first security assurance is the HTGR nuclear fuel element based on the coated fuel particles, so the coating process of nuclear fuel particles is one of the most important key technologies in the research on HTGR. The tristructural-isotropic (TRISO) type coated fuel particle, which has been commonly used in the current HTGR consists of a microspheric UO2 fuel kernel surrounded by four coated layers: a porous buffer pyrolysis carbon layer (buffer PyC), an inner dense pyrolysis carbon layer (IPyC), a silicon carbide layer (SiC) and an outer dense pyrolysis carbon layer (OPyC), as shown in Fig.1. All coating layers are prepared in the spouted fluidized bed by chemical vapour deposition (CVD) method in different

Now, HTR-PM (high-temperature-reactor pebble-bed module), a Chinese 2×250 MWth HTR demonstration plant, is under construction in Weihai City, Shandong Province, PRC. A pilot fuel production line will be built to fabricate 300,000 pebble fuel elements per year, and each pebble fuel element contains about 15000 coated fuel particles, so the higher requirements for mass production of coated fuel particles for fuel elements are put forward. In order to optimize and scale up the coating process of fuel kernels from the lab to the factory, the multiscale study

> © 2013 Liu; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 Liu; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

research groups in Germany, USA, South Korea, Japan and China [1-5].

Additional information is available at the end of the chapter

**A Multiscale View**

http://dx.doi.org/10.5772/55651

**1. Introduction**

superior characteristics.

Malin Liu
