Advanced Coating Materials

Liang Li, Qing Yang, Liang Li, Qing Yang

• Publisher: Wiley-Scrivener
• Year: 2018
• Print ISBN: 9781119407560
• eBook ISBN: 9781119407645
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Provides a comprehensive, yet practical source of reference, and excellent foundation for comparing the properties and performance of coatings and selecting the most suitable materials based on specific service needs and environmental factors.

Coating technology has developed significant techniques for protecting existing infrastructure from corrosion and erosion, maintaining and enhancing the performance of equipment, and provided novel functions such as smart coatings greatly benefiting the medical device, energy, automotive and construction industries.

The mechanisms, usage, and manipulation of cutting-edge coating methods are the focus of this book. Not only are the working mechanisms of coating materials explored in great detail, but also craft designs for further optimization of more uniform, safe, stable, and scalable coatings.

A group of leading experts in different coating technologies demonstrate their main applications, identify the key bottlenecks, and outline future prospects. Advanced Coating Materials broadly covers the coating techniques, including cold spray, plasma vapor deposition, chemical vapor deposition, sol–gel method, etc., and their significant applications in microreactor technology, super(de)wetting, joint implants, electrocatalyst, etc. Numerous kinds of coating structures are addressed, including nanosize particles, biomimicry structures, metals and complexed materials, along with the environmental and human compatible biopolymers resulting from microbial activities. This state-of-the-art book is divided into three parts: (1) Materials and Methods: Design and Fabrication, (2) Coating Materials: Nanotechnology, and (3) Advanced Coating Technology and Applications.

Part I
MATERIALS AND METHODS: DESIGN AND FABRICATION

Chapter 1
The Science of Molecular Precursor Method

Hiroki Nagai and Mitsunobu Sato*

Department of Applied Physics, School of Advanced Engineering, Kogakuin University, Tokyo, Japan

*Corresponding author: [email protected]

Abstracts

The metal complexes are used in various applications such as catalysts, luminescent materials, and medicines. In 1996, one of the authors, M.S., focused on the thin-film fabrication of various metal oxides and phosphate compounds, using coating solutions involving stable metal complexes of industrially available multidentate ligands. This is the molecular precursor method (MPM). The method is based on the facile preparation of coating solutions involving the metal complex anions and alkylammonium cations. The stability, homogeneity, miscibility, coatability, and other characteristics of the coating solutions are practical advantages, as compared to the conventional sol–gel method. This is because metal complex anions with high stability can be dissolved in volatile solvents by combining with appropriate alkylamines. Furthermore, the resultant solutions can form excellent precursor films through various coating procedures including spin-coating. The precursor films obtained by the coating process on various substrates should be amorphous, just as with the metal/organic polymers in the sol–gel processes; otherwise, it would not be possible to obtain the resulting metal-oxide or metal-phosphate thin films spread homogeneously on substrates by heat treatment. The advantages of the molecular precursor solutions will be also explained through detailed results of thin film fabrication in this chapter.

Keywords: Molecular precursor method, stability, homogeneity, miscibility, coatability, functional thin films

1.1 Metal Complex

Metal complexes (coordination compounds) are one of the most important chemical compounds and form the basis of coordination chemistry. Coordination chemistry is being considered a science only after the formulation of the coordination theory proposed by A. Werner [1, 2]. After Werner, enormous metal complexes were obtained, characterized, and widely applied. Especially, their syntheses, structures, and properties have been investigated.

Metal complexes consisted of a central metal atom (ion) and ligands connected to the metal atom. The combination of metal atom and ligand produces the coordination sphere, which is formed by coordination bonds having donor–acceptor interactions. A coordination bond is mostly formed as a result of the overlapping of atomic orbitals (AO) of ligands, filled with electrons and/or vacant AO of the central metal atom. Lewis acid can form a new covalent bond by accepting a pair of electrons, and Lewis base can form a new covalent bond by donating a pair of electrons. The fundamental Lewis acid–base theory is described by a direct equilibrium, leading to the complex formation as follows.

Thus, the coordination (donor–acceptor) bond between the central metal (M) and each joining group (ligand, L) is formed by the electron pair. The conventional theory by Lewis made a considerable contribution in understanding the reaction with participation of Lewis acids and bases.

The HSAB (Hard and Soft Acids and Bases) principle is one of the important theories for coordination chemistry, formulated by Pearson in 1963 [3]. The following three statements are the basis of HSAB.

1. Chemical reactions, in particular complex formation, can be classified as acid–base ones; the resulting products can be examined as complexes of the type Lewis acids and bases.
2. All acids and bases can be divided into hard, soft, and/or intermediate.
3. The HSAB principle itself is the following: the acid–base reactions take place in such a way that hard acids prefer to be connected with hard bases, meanwhile soft acids react with soft bases.

The classification of HSAB is summarized in Table 1.1.

Table 1.1 HSAB classification of metal and ligand.

	Metal	Ligand
Hard	H^+, Li^+, Na^+, K^+, Be^2+, Mg^2+, Ca^2+, Sr^2+, Mn^2+, Al^3+, N^3+, As^3+, Cr^3+, Co^3+, Fe^3+, Si^4+, Sn^4+, BF3, AlCl3, CO2	H2O, OH^–, F^–, SO4^2–, PO4^3–, CH3CO2^–, RO^–, Cl^–, ClO4^–, NO3^–, ROH, NH3, RNH2
Borderline	Fe^2+, Co^2+, Ni^2+, Cu^2+, Zn^2+, Pb^2+, Sn^2+, Sb^3+, Bi^3+, Rh^3+, Ir^3+, SO2, NO^+, Ru^2+, Os^2+, R3C^+, C6H5^+	C6H5NH2, C5H5N, N3^–, Br^–, NO2^–, SO3^2–, N2
Soft	Ag^+, Cu^+, Au^+, Tl^+, Hg^+, Pd^2+, Cd^2+, Pt^2+, Hg^2+, Pt^4+, Tl^3+, RS^+, I^+, HO^+, I2, Br2, ICN,	R2S, RSH, RS^–, I^–, SCN^–, R3P, CN^–, RCN, CO, C2H4, C6H6, H^–

The HSAB principle emphasizes the preference for hard–hard and soft–soft interactions, and the highest thermodynamic stability of complexes formed as a result is achieved.

The rows shown below indicate that the hardness of the elements (donor atoms in ligands) decreases from left to right:

Ligands with N, O, F, Cl donor atoms containing a combination of these elements are hard bases according to Pearson. On the contrary, containing elements further to the right are soft bases. The hardness and softness of acids depend considerably on the oxidation number of the metal center.

The HSAB conception has been widely used to explain various coordination modes in the complexes of di-and polydentate ligands. The solvent nature can be also an important factor. The most favorable conditions to control the localization mode of a coordination bond with participation of ligands containing hard and soft donor atoms are created when complex-formation reactions are carried out in aprotic nonaqueous solvents.

Ligands, as the main part of metal complexes, are the object of a great deal of attention in coordination and organometallic chemistry. The reaction control should be emphasized among the reaction conditions of competitive complex formation. It is necessary to take into account that it is possible to determine, and frequently predict, the direction of the electrophilic attack to the donor atom of di- and polyfunctional donors (ligands) only in the case when the thermodynamically stable products are formed under conditions of kinetic control.

Thus, the thermodynamic stability of complexes is discussed, when the bond between the metal and di- and polydentate ligands is...

Table of contents

• Cover
• Title page
• Copyright page
• Preface
• Part I: Materials and Methods: Design and Fabrication
• Part II: Coating Materials Nanotechnology
• Part III: Advanced Coating Technology and Applications
• Index
• End User License Agreement