FINAL REPORT Morphology and Mechanism of Benign Inhibitors SERDP Project WP-1619 JULY 2012 Dale W. Schaefer University of Cincinnati ii Table of Contents List of Tables..………………………………………….………………………………….…………………..……………….v List of Figures ……………………………………………...…………………………….…………………..……………….vi List of Acronyms ......................................................................................................................... xiv List of Keywords……………………………………………………………………….…………….……..……………….xv Acknowledgements ...................................................................................................................... xvi 1. Abstract .................................................................................................................................... 1 2. Objective .................................................................................................................................. 3 3. Background .............................................................................................................................. 4 4. Materials and Methods ............................................................................................................. 6 4.1 Silicon wafer cleaning ........................................................................................................ 6 4.2 e-beam evaporation ............................................................................................................. 6 4.3 Metal-wafer systems ........................................................................................................... 6 4.3.1 Aluminum alloy (AA 2024) coated silicon wafers ...................................................... 6 4.3.2 Al-coated silicon wafers. .............................................................................................. 7 4.3.3 Noble metal coated silicon substrates. ......................................................................... 7 4.3.4 Optimization of the metal layer.................................................................................... 7 4.4 Metal coupons..................................................................................................................... 7 4.5 Characterization Methods ................................................................................................... 8 4.5.1 Neutron reflectivity (NR) and x-ray reflectivity (XRR) .............................................. 8 4.5.2 X-ray diffraction ........................................................................................................... 9 4.5.3 Ultra small angle x-ray scattering and small-angle neutron scattering ........................ 9 4.5.4 Time-of-flight secondary ion mass spectrometry ...................................................... 10 4.5.5 Inductively coupled plasma (ICP) atomic emission spectroscopy ............................. 10 4.5.6 Scanning electron microscopy ................................................................................... 11 4.6 Vanadate inhibition system .............................................................................................. 11 4.6.1 Formulation ................................................................................................................ 11 4.6.2 Film growth procedure ............................................................................................... 11 4.7 The Trivalent Chromium Process (METALAST® TCP-HF) system .............................. 11 4.7.1 Formulation ................................................................................................................ 11 i 4.7.2 Film growth procedure ............................................................................................... 11 4.8 Electro-assisted (EA) and simplified trivalent chromium processes ................................ 12 4.8.1 Formulation ................................................................................................................ 12 4.8.2 Film growth procedure ............................................................................................... 12 4.9 Step-by-step anodic hardening for TCP-passivated AA2024-T3 substrates .................... 13 4.9.1 Substrate cleaning ...................................................................................................... 13 4.9.2 TCP formulation and EA deposition .......................................................................... 13 4.9.3 Step-by-step anodic hardening by Ce(III) .................................................................. 13 4.10 In situ liquid NR split cell ............................................................................................... 13 4.11 Aluminum Anodizing ..................................................................................................... 15 4.11.1 Voltage-controlled anodizing ................................................................................... 15 4.11.2 Simultaneous current-limited and voltage-controlled anodizing ............................. 15 4.11.3 Sealing of Anodic Aluminum Oxide ........................................................................ 15 5. Results and Discussion .......................................................................................................... 16 5.1 Wafer-based metal substrates ........................................................................................... 16 5.1.1 Morphology of AA2024 substrate ............................................................................. 16 5.1.2 Morphology of pure copper substrate ........................................................................ 17 5.1.3 Annealing of layered Al-Cu alloy films ..................................................................... 17 5.1.4 Metal substrate thickness optimization ...................................................................... 18 5.2 Vanadate inhibitor films (V films) ................................................................................... 18 5.2.1 Precursor exposure optimization ................................................................................ 18 5.2.2 Structure of as-prepared vanadate conversion coatings (VCC) ................................. 19 5.2.3 Hydrophobicity and porosity of VCC film ................................................................ 22 5.2.4 Speciation of VCC film .............................................................................................. 23 5.2.5 Response to water immersion and high temperature baking ..................................... 24 5.2.6 Vanadate films under an epoxy top coating ............................................................... 25 5.2.7 Effect of K3Fe[CN]6 ................................................................................................... 26 5.2.8 Summary on VCC coating ......................................................................................... 26 5.3 Trivalent chromium process (METALAST® TCP-HF) system ....................................... 27 5.3.1 H2SO4 activation ........................................................................................................ 27 5.3.2 Film structure of TCP immersion films ..................................................................... 28 ii 5.4 Electro-assisted (EA) and the simplified trivalent chromium process system ................. 29 5.4.1 Structure of as-prepared EA- TCP film ..................................................................... 29 5.4.2 RT drying and vacuum baking ................................................................................... 31 5.4.3 Speciation of EA-TCP film by XRR and NR ............................................................ 31 5.4.4 EA deposition process ................................................................................................ 35 5.4.5 Transition from hydroxide to crystal.......................................................................... 36 5.4.6 EA-TCP film structure after vacuum baking ............................................................. 37 5.4.7 SIMS of EA-TCP film ............................................................................................... 37 5.4.8 Summary of EA deposition ........................................................................................ 37 5.5 In situ NR study of TCP passivity .................................................................................... 38 5.5.1 In situ NR of bare Al .................................................................................................. 38 5.5.2 In situ NR study of TCP passivity.............................................................................. 40 5.5.3 Summary of in situ TCP passivity ............................................................................. 45 5.6 Step-by-step anodic hardening by Ce(III) ........................................................................ 46 5.6.1 Anodic hardening process .......................................................................................... 46 5.6.2 Effect of pH ................................................................................................................ 48 5.7 In situ evolution of TCP film on Al under Ce(III) anodic hardening ............................... 48 5.7.1 In situ NR of Ce(III) anodic hardening ...................................................................... 49 5.7.2 The content of Ce(III) in TCP film ...........................................................................