Silica Aerogel Composites (eBook)

Dr. Sunil C. Joshi received his Ph.D. degree from Monash University (Australia) for his work on composites manufacturing processes. Prior to that he worked as Scientist at National Aerospace laboratories, Bangalore, India, where he was part of the composite structures group from 1988 to 1994 after completing his M. Tech in Aeronautical Engineering with aircraft structures specialization.He has been a faculty in the School of Mechanical and Aerospace Engineering, at Nanyang Technological University, Singapore, since 2000, currently serving under Aerospace Engineering cluster with Materials and Structures as the focus area.His research interests encompass aerogel composites, nano-engineered composites, microwave curing, manufacturing of thick composites, damages in braided and filament wound composites, and hygrothermal effects on composites. He looks into applications of composites for impact resistance, thermal insulation, and acoustic damping.He is an area editor for an Elsevier Journal and serves as reviewer for a number of international journals. He has more than 120 international journal and conference papers, 1 book, 1 applied patent and 5 book chapters to his publication list.Mahesh Sachithanadam received his Bachelors’ Degree in Mechanical Engineering from University of Newcastle, Australia, in 2010, with Class 1 Honors. He worked previously as a Military Expert (Engineer) in the Republic of Singapore Armed Forces (RSAF). He is currently pursuing PhD on aerogel composites under the supervision of Assoc. Prof. Sunil Chandrakant Joshi from the School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.Mahesh has been working on aerogel composites for his PhD and has presented his work on “A New Phenomenon of Compressive Strain Recovery in Gelatin-silica Aerogel Composites with SDS”, “Brittle to Ductile Transitions in Silica Aerogel Behaviour with Post Synthesis Binding Treatment” and “High strain recovery with improved mechanical properties of gelatin–silica aerogel composites post-binding treatment” at various forums. Mahesh also coauthored a pending patent titled “Compressibility, Strain Recovery and Hydrophobicity in Silica Aerogel Composites” (TD/181/13) with his supervisor. Currently he is compiling his thesis.

Preface 6
Contents 7
Abbreviations and Symbols 10
1 Introduction 12
1.1 What Is Aerogel??? 12
1.2 How It All Started2026 13
1.3 Uniqueness of the Book 14
References 14
2 Aerogels Today 16
2.1 Introduction 16
2.2 Aerogels Today 16
2.3 Market Outlook 17
2.4 Silica Aerogels 18
2.5 Evolution of Silica Aerogels 19
2.5.1 Formation of Wet Gel 19
2.5.1.1 Precursors, Solvents, and Catalysts 20
2.5.2 Aging and Fluid Exchange of Wet Gel 20
2.5.3 Drying 20
2.5.3.1 Supercritical Drying (SCD) 21
2.5.3.2 Ambient Pressure Drying (APD) 21
2.5.3.3 Freeze Drying (FD) 22
2.6 Concluding Remarks 23
References 23
3 Fabrication Methods 26
3.1 Introduction 26
3.2 Silica Aerogel `Hybrid' Composites---Developments and Limitations 26
3.3 Silica Aerogel Binder Composites 28
3.3.1 Associated Problems 28
3.4 Surface Chemistry of Silica Aerogel Granules 29
3.5 Possible Routes of Binder Composite Fabrication 31
3.5.1 Route 1---Resin Binders 31
3.5.2 Route 2---De-Methylation of Hydrophobic Groups 31
3.5.3 Route 3---Water Soluble Materials 32
3.6 Possible Binder Materials 34
3.6.1 Gelatin 34
3.6.1.1 Properties of Gelatin 36
3.6.2 Additives 37
3.6.2.1 Sodium Dodecyl Sulfate (SDS) 37
3.6.2.2 Carbon Nanotubes (CNTs) 37
3.6.2.3 Functionalized CNTs 38
3.7 Materials' Property and Data 39
3.8 Fabrication Methodologies of GSA Composites 40
3.8.1 FM Method 40
3.8.2 FD Method 42
3.9 Concluding Remarks 43
References 44
4 Microstructural Analysis 47
4.1 Introduction 47
4.2 Hypothesis on Binder Concept 47
4.3 Chemical Analysis of Gelatin Films 48
4.4 Microstructural Examination of Silica Aerogels and Their Composites 53
4.4.1 SEM/EDX Characterization 53
4.4.2 XPS/ESCA Surface Characterization 56
4.5 Concluding Remarks 59
References 59
5 A New Phenomenon---Brittle to Ductile Transition 61
5.1 Introduction 61
5.1.1 Parametric Model 62
5.1.2 Direct Experimental Measurements 65
5.2 Experimental Setup 65
5.3 GSA and GSA--SDS Composites (FM Method) 67
5.3.1 Compressive Stress--Strain Behavior (FM Composites) 67
5.3.2 Unusual Phenomenon---Brittle to Ductile Behavior 69
5.3.3 Influence of SDS on Composite Properties from ANOVA 70
5.3.3.1 Statistical Analysis of Measured Data 70
5.3.3.2 General Trend of Density 73
5.3.4 Strain Recovery Optimization via Empirical Models 74
5.4 Validation of Optimal Properties with GSA--SDS Composites 77
5.4.1 Influence of Silica Aerogel Granules on Mechanical Properties of GSA--SDS Composites 79
5.5 FMWNT-Doped GSA and GSA--SDS Composites (FM) 82
5.5.1 Influence of FMWNT on Composites 82
5.5.2 Experimental Result---General Trend of Stress--Strain Curves 83
5.5.3 Empirical Analysis of Various Properties 85
5.5.3.1 Strain Recovery 85
5.5.3.2 Compressive Strength and Modulus 87
5.6 Concluding Remarks 88
Appendix 5A---Failed Specimen Analysis (FM Method) 89
References 89
6 Superhydrophobic and Ultralow Thermal Insulation 91
6.1 Introduction 91
6.1.1 Hydrophobicity 92
6.2 Thermal Conductivity Measurements 94
6.3 Operating Temperature of GSA--SDS Composites 97
6.4 Silica Aerogel Granule Size Distribution 98
6.5 Thermal Conductivity of Silica Aerogel Granules 99
6.6 Thermal Conductivity of GSA--SDS Composites 101
6.6.1 Influence of Silica Aerogel Granules on the Thermal Conductivity of GSA--SDS (FD) Composites 103
6.7 Thermal Conductivity of GSA--SDS/FMWNT Composites 104
6.7.1 Optimization and Validation 107
6.8 Thermal Transport Phenomenon in GSA--SDS/FMWNT Composites 108
6.9 Superhydrophobicity of FMWNT doped GSA--SDS Composites 111
6.10 Concluding Remarks 114
Appendix 6A---Granule Size Distribution 115
Appendix 6B---Optimization of Coupled Function 116
Derivation of Optimal Values for Coupled Function of SDS and FMWNT 116
1st Derivation Test 116
2nd Derivation Test 116
References 117
7 Acoustic Performance of Silica Aerogel Composites 119
7.1 Introduction 119
7.2 Experimental Procedure 121
7.2.1 Transfer Function Method (2-microphone) 121
7.2.2 Inferential Transmission Loss (InTLM) 123
7.2.3 Sound Meter Measurements 125
7.3 Silica Aerogel Granules Optimization 125
7.3.1 Transmission Loss of Silica Aerogel Granules 128
7.4 Acoustic Performance GSA--SDS Composites and Other Materials 129
7.4.1 GSA--SDS 130
7.4.2 GSA--SDS/FMWNT Composites 135
7.4.3 `InTLM' and Sound Meter 137
7.5 Comparative Analysis with Other Traditional Materials 138
7.5.1 Acoustic Activity 139
7.6 Concluding Remarks 140
References 141
Appendix: Useful MATLAB Codes 143
Index 145