Advanced Coating Materials
Description
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.
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Liang Li received his PhD from the Institute of Solid State Physics at the Chinese Academy of Sciences and won the Excellent President Scholarship in 2006. He is currently a full Professor at Soochow University, China. His research group (http://ecs.suda.edu.cn) focuses mainly on the energy conversion (solar cells and photodetectors) and storage (Li/Na batteries) devices of low-dimensional nanomaterials. He has published more than 140 papers with 6000 citations with an H-index of 40, as well as 16 patents.
Qing Yang is a Professor in the College of Optical Science and Engineering, Zhejiang University, China. She received her PhD degree from Zhejiang University in 2006. Dr. Yang's research focuses on nanophotonics and piezo-photontronics. She has made original contributions to the fabrication, tuning and applications of nanophotonic devices and has pioneered and systematically investigated nanowire-based lasers. Dr. Yang has published about 55 peer reviewed journal articles with over 1500 citations and an H index of 25, as well as 11 Chinese or U.S. patents.
Content
Preface xvii
Part I: Materials and Methods: Design and Fabrication 1
1 The Science of Molecular Precursor Method 3
Hiroki Nagai and Mitsunobu Sato
1.1 Metal Complex 4
1.2 Molecular Precursor Method 6
1.3 Counter Ion (Stability) 6
1.4 Conversion Process from Precursor Film to Oxide Thin Film 8
1.5 Anatase-Rutile Transformation Controlled by Ligand 8
1.6 Homogeneity 11
1.7 Miscibility 13
1.8 Coatability (Thin Hydroxyapatite Coating of Ti Fiber Web Scaffolds) 13
1.9 Oxygen-Deficient Rutile Thin Films 15
1.10 Cu Thin Film 16
1.11 Applications Using the Molecular Precursor Method 20
1.12 Conclusion 22
References 23
2 Cold Spray-Advanced Coating Process and 3D Modeling 29
Muhammad Faizan-Ur-Rab, Saden H. Zahiri and Syed H. Masood
2.1 Introduction 30
2.1.1 Cold Spray Equipment 31
2.1.1.1 CGT KINETIKS 3000 CS System 31
2.1.1.2 Plasma Giken PCS 1000 System 32
2.1.1.3 Impact Innovations ISS 5/8 and 5/11 CS Systems 33
2.1.2 Applications of Cold Spray Coatings 35
2.2 3D Numerical Modeling of Cold Spray Coating 36
2.2.1 Computational Domain and Boundary Conditions in Numerical Model 37
2.2.2 Three-Dimensional Grid 40
2.2.3 Particle-Fluid Interaction 41
2.3 Experimental Methods of Cold Spray Coatings for Validation of 3D Model 44
2.3.1 Measurement of Substrate's Temperature 44
2.3.2 Particle Image Velocimetry (PIV) 45
2.4 Results and Discussions 48
2.4.1 3D Model Calibration 48
2.4.2 Effect of Propellant Gas 51
2.4.3 Effect of Nozzle Length 53
2.4.4 Particle's Temperature 56
2.5 Conclusion 59
References 60
3 Effects of Laser Process Parameters on Overlapped Multipass/Multitrack Hardened Bead Parameters of Ti-6Al-4V Titanium Alloy Using Continuous-Wave Rectangular Beam 65
D.S. Badkar
3.1 Introduction 66
3.2 Experimental Methodology 70
3.2.1 Principle of Rectangular Beam 70
3.2.2 Materials Used and Experimental Set-Up 70
3.2.3 Fixture Fabrication 73
3.2.3.1 Bottom Plate 74
3.2.3.2 The Top Plate 75
3.2.4 Specimen Preparation 76
3.2.5 Phase Transformations of Ti-6Al-4V During Laser Transformation Hardening 78
3.2.5.1 Laser Heating 78
3.2.5.2 Cooling or Self Quenching 78
3.3 Results and Discussion 78
3.3.1 Effect of Laser Process Parameters on Overlapped Multipass/Multitrack Hardened Bead Parameters 78
3.4 Conclusions 82
Acknowledgment 82
References 82
4 Dimensionally Stable Lead Dioxide Anodes Electrodeposited from Methanesulfonate Electrolytes: Physicochemical Properties and Electrocatalytic Reactivity in Oxygen Transfer Reactions 85
Olesia Shmychkova, T. Luk'yanenko and A. Velichenko
4.1 Introduction 86
4.2 Chemical Composition of Coatings 89
4.3 Electrocatalytical Properties of Materials 95
4.3.1 p-Nitroaniline Oxidation 98
4.3.2 p-Nitrophenol Oxidation 100
4.3.3 Oxidation of Salicylic Acid and its Derivatives 101
4.4 Electrode Endurance Tests 108
4.5 Conclusions 116
References 118
5 Polycrystalline Diamond Coating Protects Zr Cladding Surface Against Corrosion in Water-Cooled Nuclear Reactors: Nuclear Fuel Durability Enhancement 123
Irena Kratochvílová, Radek skoda, Andrew Taylor, Jan skarohlíd, Petr Ashcheulov and FrantiSek Fendrych
5.1 Introduction 124
5.2 Zr Alloy Surface Corrosion-General Description 128
5.3 Growth of Polycrystalline Diamond as Anticorrosion Coating on Zr Alloy Surface 131
5.4 Properties of PCD-Coated Zr Alloy Samples Processed in Autoclave 135
5.4.1 Oxidation of Autoclave-Processed PCD-Coated Zr Samples 135
5.4.2 Composition Changes of PCD-Coated Zr Alloy Compared to Autoclaved Zr Alloy and PCD-Coated Zr Alloy 137
5.4.2.1 Capacitance Measurements, NanoESCA, X-Ray-Photoelectron Spectroscopy, Neutron Transmission, and Mass Spectrometry 137
5.4.2.2 Raman, SEM, and SIMS Analysis of the Autoclave-Processed Samples 143
5.4.3 Mechanical and Tribological Properties of Autoclaved PCD Layer-Covered Zr Alloy 145
5.4.4 Radiation Damage Test of Autoclaved PCD-Covered Zr Alloy Sample: Ion Beam Irradiation 147
5.5 PCD Coating Increases Operation Safety and Prolongs the Zr Nuclear Fuel Cladding Lifetime-Overall
Summaries 148
5.6 Conclusion 153
Acknowledgments 154
References 154
6 High-Performance WC-Based Coatings for Narrow and Complex Geometries 157
Satish Tailor, Ankur Modi and S. C.Modi
6.1 Introduction 157
6.2 Experimental 159
6.2.1 Feedstock Powder 159
6.2.2 Substrate Preparation and Coating Deposition 159
6.2.3 Why Choosing 45° and 70° Angles to Design the Connectors 163
6.2.4 Characterizations 163
6.3 Results and Discussion 164
6.3.1 Coating Mechanism Behind the Uniform Coating Properties at Both Spray Angles 45° and 70° 164
6.3.2 Coating Microstructures 164
6.3.3 Microhardness of the "As-Sprayed" Coatings 166
6.3.4 X-Ray Diffraction 167
6.3.5 Residual Stress Analysis 169
6.3.6 Adhesion Strength of the Coatings 171
6.4 Conclusions 172
References 172
Part II: Coating Materials Nanotechnology 175
7 Nanotechnology in Paints and Coatings 177
Emmanuel Rotimi Sadiku, Oluranti Agboola, Ibrahim David Ibrahim, Peter Apata Olubambi, BabulReddy Avabaram, Manjula Bandla, Williams Kehinde Kupolati, Jayaramudu Tippabattini, Kokkarachedu Varaprasad, Stephen Chinenyeze Agwuncha, Jonas Mochane, Oluyemi Ojo Daramola, Bilainu Oboirien, Taoreed Adesola Adegbola, Clara Nkuna, Sheshan John Owonubi, Victoria Oluwaseun Fasiku, Blessing Aderibigbe, Vincent Ojijo, Regan Dunne, Koena Selatile, Gertude Makgatho, Caroline Khoathane, Wshington Mhike, Olusesan Frank Biotidara, Mbuso Kingdom Dludlu, AO Adeboje, Oladimeji Adetona Adeyeye, Abongile Ndamase, Samuel Sanni, Gomotsegang Fred Molelekwa, Periyar Selvam, Reshma Nambiar, Anand Babu Perumal, Jarugula Jayaramudu, Nnamdi Iheaturu, Ihuoma Diwe and Betty Chima
7.1 Introduction 178
7.1.1 Paint and Coating 178
7.1.2 Nanopaints and Nanocoatings 180
7.1.2.1 Some Uses of Nanopaints in Different Materials 181
7.1.2.2 Nanomaterials in Paints 183
7.1.3 Types of Nanocoating 189
7.1.3.1 Superhydrophobic Coating 190
7.1.3.2 Oleophobic/Hydrophobic Coating 191
7.1.3.3 Hydrophilic Coatings 191
7.1.3.4 Ceramic, Metal and Glass Coatings 192
7.2 Application of Nanopaints and Nanocoating in the Automotive Industry 195
7.3 Application of Nanopaints and Nanocoating in the Energy Sector 196
7.4 Application of Nanocoating in Catalysis 198
7.5 Application of Nanopaints and Nanocoating in the Marine Industry 200
7.6 Applications of Nanopaints and Nanocoating in the Aerospace Industry 200
7.7 Domestic and Civil Engineering Applications of Nanopaints and Coating 202
7.8 Medical and Biomedical Applications of Nanocoating 205
7.8.1 Antibacterial Applications of Nanocoating 205
7.9 Defense and Military Applications of Nanopaints and Coatings 227
7.10 Conclusion 228
7.11 Future Trend 228
References 229
8 Anodic Oxide Nanostructures: Theories of Anodic Nanostructure Self-Organization 235
Naveen Verma, Jitender Jindal, Krishan Chander Singh and Anuj Mittal
8.1 Introduction 235
8.2 Anodization 237
8.3 Barrier-Type Anodic Metal Oxide Films 237
8.4 Porous-Type Anodic Metal Oxide Films 238
8.5 Theories or Models of Growth Kinetics of Anodic Oxide Films and Fundamental Equations for High-Field Ionic Conductivity 239
8.5.1 Guntherschulze and Betz Model 239
8.5.2 Cabrera and Mott Model 240
8.5.3 Verwey's High Field Model 242
8.5.4 Young Model 243
8.5.5 Dignam Model 244
8.5.6 Dewald Model: (Dual Barrier Control with Space Charge) 244
8.6 Corrosion Characteristics and Related Phenomenon 246
8.7 Electrochemical Impedance Spectroscopy 249
8.8 Characterization Techniques 250
References 251
9 Nanodiamond Reinforced Epoxy Composite: Prospective Material for Coatings 255
Ayesha Kausar
9.1 Introduction 256
9.2 Nanodiamond: A Leading Carbon Nanomaterial 256
9.3 Epoxy: A Multipurpose Thermoset Polymer 258
9.4 Nanodiamond Dispersion in Epoxy: Impediments and Challenges 259
9.5 Epoxy/Nanodiamond Coatings 261
9.6 Coating Formulation 262
9.7 Industrial Relevance of Epoxy/ND Coatings 264
9.7.1 Strength and High Temperature Demanding Engineering Application 264
9.7.2 Thermal Conductivity Relevance 266
9.7.3 Microwave Absorbers 268
9.7.4 In Biomedical 268
9.8 Summary, Challenges, and Outlook 269
References 270
10 Nanostructured Metal-Metal Oxides and Their Electrocatalytic Applications 275
Kemal Volkan Özdokur, Süleyman Koçak and Fatma Nil Ertas
10.1 Brief History of Electrocatalysis 276
10.2 Electrocatalytic Activity 278
10.3 Oxygen Reduction Reaction 280
10.4 Transition Metal Chalcogenides and Their Catalytic Applications 281
10.5 Preparation of Nanostructured Transition Metal Oxide Surfaces 296
10.6 Polyoxometallates (POM) 303
10.7 Future Trends in Electrocatalysis Applications of Metal/metal oxides 305
References 305
Part III: Advanced Coating Technology and Applications 315
11 Solid-Phase Microextraction Coatings Based on Tailored Materials: Metal-Organic Frameworks and Molecularly Imprinted Polymers 317
Priscilla Rocío-Bautista, Adrián Gutiérrez-Serpa and Verónica Pino
11.1 Solid-Phase Microextraction 317
11.2 HS-SPME-GC Applications Using MOF-Based Coatings 320
11.2.1 Metal-Organic Frameworks (MOFs) 320
11.2.2 SPME Coating Fibers Based on MOFs 322
11.3 DI-SPME-LC Applications Using MIP-Based Coatings 331
11.3.1 Molecularly Imprinted Polymers (MIPs) 332
11.3.2 SPME Coating Fibers Based on MIPs 333
11.3.3 MIPs and MOFs Features as SPME Coatings 340
11.4 Conclusions and Trends 341
Acknowledgements 341
References 342
12 Investigations on Laser Surface Modification of Commercially Pure Titanium Using Continuous-Wave Nd:YAG Laser 349
Duradundi Sawant Badkar
12.1 Introduction 350
12.2 Experimental Design 354
12.3 Experimental Methodology 355
12.4 Results and Discussions 358
12.4.1 Analysis of Variance (ANOVA) for Response Surface Full Model 358
12.4.2 Validation of the Models 366
12.4.3 Effect of Process Factors on Hardened Bead Profile Parameters 370
12.4.3.1 Heat Input (HI) 370
12.4.3.2 Hardened Bead Width (HBW) 370
12.4.3.3 Hardened Depth (HD) 374
12.4.3.4 Angle of Entry of Hardened Bead Profile (AEHB) 377
12.4.3.5 Power Density (PD) 381
12.4.4 Microstructural Analysis 384
12.5 Conclusions 387
Acknowledgements 390
References 390
13 Multiscale Engineering and Scalable Fabrication of Super(de)wetting Coatings 393
William S. Y. Wong and Antonio Tricoli
13.1 Introduction 394
13.2 Fundamentals of Wettability and Superwettability 395
13.2.1 Defining Hydrophilicity and Hydrophobicity 397
13.2.2 Defining Superhydrophilicity and Superhydrophobicity 398
13.2.2.1 Wenzel's Model 398
13.2.2.2 Cassie-Baxter's Model 399
13.2.2.3 Contact Angle Hysteresis 400
13.2.2.4 Variants of Superhydrophilicity 402
13.2.2.5 Ideal Superhydrophilicity 402
13.2.2.6 Hemiwicking Superhydrophilicity 402
13.2.2.7 Variants of Superhydrophobicity 403
13.2.2.8 Ideal Lotus Superhydrophobicity 403
13.2.2.9 Petal-Like Adhesive Superhydrophobicity 404
13.2.3 Defining Superoleophobicity, Superamphiphobicity and Superomniphobicity 405
13.2.3.1 Superoleophobicity and Superamphiphobicity 405
13.2.3.2 Superomniphobicity 407
13.2.3.3 Re-Entrant Profiles 407
13.2.3.4 Shades of Grey: Superoleo(amphi) phobicity to Superomniphobicity 408
13.2.4 Characterization Techniques 409
13.2.4.1 Static Contact Angle Analysis 409
13.2.4.2 Dynamic Contact Angle Analysis-Contact Angle Hysteresis 411
13.2.4.3 Dynamic Contact Angle Analysis-Sliding Angle 412
13.2.4.4 Other Modes of Dynamic Analysis-Droplet Bouncing and Fluid Immersion 412
13.3 Nature to Artificial: Bioinspired Engineering 413
13.3.1 Superhydrophilicity 414
13.3.2 "Lotus-Like" Low-Adhesion Superhydrophobicity 416
13.3.3 "Rose Petal-Like" High-Adhesion Superhydrophobicity 416
13.3.4 Anisotropic Low-Adhesion/High-Adhesion Superhydrophobicity 417
13.3.5 Superhydrophobic-Hydrophilic Patterning 418
13.3.6 Superoleo(amphi)phobicity 418
13.4 Top-Down and Bottom-Up Nanotexturing Approaches 419
13.4.1 Templating 419
13.4.2 (Photo)-Lithography 420
13.4.3 Scalable Bottom-Up Texturing Approaches 421
13.5 Superhydrophilicity 421
13.5.1 The State of Superhydrophilicity 421
13.5.1.1 Plasma and Ozone Surface Hydroxylation 421
13.5.1.2 Aerosol Deposition 422
13.5.1.3 Electrospinning 423
13.5.1.4 Chemical Etching Hydroxylation 424
13.5.1.5 Wet-Deposition 424
13.5.1.6 Sol-Gel and Photoactivation 424
13.5.1.7 Thiol-Functionalization 425
13.6 Superhydrophobicity 426
13.6.1 Ideal Lotus Slippery Superhydrophobicity 426
13.6.1.1 Plasma 426
13.6.1.2 Chemical Vapor Deposition 427
13.6.1.3 Spraying (Wet-Spray, Liquid-Fed Flame Spray, Sputtering) 428
13.6.1.4 Wet-Deposition 433
13.6.1.5 Sol-Gel 434
13.6.1.6 Electrodeposition 435
13.6.1.7 Chemical Etching 436
13.6.2 Petal-Like Adhesive Superhydrophobicity 437
13.6.2.1 Templating 437
13.6.2.2 Liquid-Fed Flame Spray Pyrolysis 438
13.6.2.3 Sol-Gel and Hydrothermal Synthesis 438
13.6.2.4 Electrospinning 440
13.6.2.5 Electrodeposition 441
13.6.2.6 Micro- and Nanostructural Self-Assembly 441
13.6.2.7 Mechanical Methods 442
13.7 Superoleophobicity and Superamphiphobicity 443
13.7.1 Nanofilaments, Fabric Fibers, Meshes, and Tubes 443
13.7.2 Aerosol-Coating (Wet-Spray, Candle Soot / Liquid-Fed Flame Spray) 445
13.7.2.1 Wet-Spray Deposition 445
13.7.2.2 Flame Soot Deposition 445
13.7.2.3 Flame Spray Pyrolysis 447
13.7.3 Sol-Gel 448
13.7.4 Wet-Coating (Dip- and Spin-Coating) 448
13.7.4.1 Dip-Coating 448
13.7.4.2 Spin-Coating 449
13.7.5 Micro- and Nanostructural Self-Assembly 449
13.7.6 Electrospinning 450
13.7.7 Electrodeposition and Electrochemical Etching 450
13.7.7.1 Electrochemical Etching 450
13.7.7.2 Electrodeposition 451
13.7.8 Perfluoro-Acid Etching 452
13.7.9 Physical Etching 452
13.8 Superomniphobicity 452
13.8.1 Electrospun Beads on Mesh-Like Profiles 453
13.8.2 Controlled Sol-Gel Growth 455
13.8.3 Etched Aluminum Meshes 455
13.8.4 Hybridized Lithography 455
13.9 Conclusions 456
References 457
14 Polymeric Materials in Coatings for Biomedical Applications 481
Victoria Oluwaseun Fasiku, Shesan John Owonubi, Emmanuel Mukwevho, Blessing Aderibigbe, Emmanuel Rotimi Sadiku, Yolandy Lemmer, Idowu David Ibrahim, Jonas Mochane, Oluyemi Ojo Daramola, Koena Selatile, Abongile Ndamase and Oluranti Agboola
14.1 Introduction 482
14.1.1 Coating Materials 483
14.2 Polymeric Coating Materials 484
14.2.1 Structure, Synthesis, and Properties 485
14.2.1.1 Polyvinyl Alcohol (PVA) 485
14.2.1.2 Parylene 486
14.2.1.3 Polyurethane (PU) 487
14.2.2 Coating Methods 489
14.2.3 Biomedical Coating Applications 492
14.2.3.1 Antifouling Coating 492
14.2.3.2 Nanoparticle Coating for Drug Delivery 493
14.2.3.3 Implants Coating 495
14.2.3.4 Cardiovascular Stents 497
14.2.3.5 Antimicrobial Surface Coating 498
14.2.3.6 Drug Delivery Coating 499
14.2.3.7 Tissue Engineering Coating 500
14.2.3.8 Sensor Coating 501
14.3 Conclusion 502
References 503
Index 519
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: lccsato@cc.kogakuin.ac.jp
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.
- 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.
- All acids and bases can be divided into hard, soft, and/or intermediate.
- 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+, Be2+, Mg2+, Ca2+, Sr2+, Mn2+, Al3+, N3+, As3+, Cr3+, Co3+, Fe3+, Si4+, Sn4+, BF3, AlCl3, CO2 H2O, OH-, F-, SO42-, PO43-, CH3CO2-, RO-, Cl-, ClO4-, NO3-, ROH, NH3, RNH2 Borderline Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Sn2+, Sb3+, Bi3+, Rh3+, Ir3+, SO2, NO+, Ru2+, Os2+, R3C+, C6H5+ C6H5NH2, C5H5N, N3-, Br-, NO2-, SO32-, N2 Soft Ag+, Cu+, Au+, Tl+, Hg+, Pd2+, Cd2+, Pt2+, Hg2+, Pt4+, Tl3+, 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 localized in the place of primary attack on the donor atoms by the electrophilic reagent, without further change of coordination mode in the reaction of complex formation.
1.2 Molecular Precursor Method
In 1996, one of the authors, M.S., focused on the thin-film fabrication of various metal oxides and phosphate compounds using the stable metal complexes [4-54]. This is the Molecular Precursor Method (MPM), which is one of the chemical processes used for thin-film fabrication. In those days, most of the researchers in the field of thin-film formation by chemical processes preferred to use rather unstable metal complexes. It is easy to imagine the capability of polymers to form "films" because we use polymer films every day. In fact, well-adhered precursor films involving metal ions can be formed on various substrates by coating the solution dispersing the produced oligomers and polymers including metallic species provided by hydrolyzing the unstable metal complexes. These results led us to believe for a long time that only the oligomers and polymers can form precursor films, but the stable metal complexes having a discrete molecular weight would not be useful in the fabrication of such thin films. The MPM was a challenge to this central belief.
The MPM, pertinent to coordination chemistry and materials science including nanoscience and nanotechnology, has been used to fabricate various high-quality thin films with appropriate film thicknesses. As a result, the MPM represents a facile procedure for thin-film fabrication of various metal oxides or phosphates, which are useful as electron and/or ion conductors, semiconductors, dielectric materials such as In2O3, ZnO, LiCoO2, Li3Fe2(PO4)3, TiO2, Cu2O, Co3O4, SrTiO3, ZrO2, SiO2, BaTiO3, and Ca10(PO4)6(OH)2. The MPM aims to develop many functional materials by surface modification of various substrates including glasses, metals, and ceramics, through chemical fabrication of thin films. One of the features related to this method is the low-cost manufacture involving the chemical process, which can save both resource and production energy.
1.3 Counter Ion (Stability)
The appropriate alkyl groups in the used amines play an essential role. This principle of the MPM is absolutely different from that of the conventional sol-gel method, which needs and uses the mixture of oligomers and polymers for the identical purpose. Amino group itself is usually very reactive, forming simple salts with metal complex anions. The stability of these salts is dependent on the basicity of amine and pH in the used solvent. Most of these salts are rather soluble in both water and aprotic organic solvents. Additionally, the presence of the ligands in metal complex anions and alkylammonium cations in the precursor films generally affects the properties of resultant thin films, as expected. It is very interesting that the thermal reactions between them and...
