INSTRUMENTATION FOR ANODIZATION AND IN-SITU TESTING OF TITANIUM ALLOYS FOR CAPACITOR ANODES by STEVEN JOSEPH EHRET Submitted in partial fulfillment of the requirements For the degree of Master of Science Thesis Advisor: Dr. Frank Merat Department of Electrical Engineering CASE WESTERN RESERVE UNIVERSITY January, 2012 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis of Steven Joseph Ehret_________________ candidate for the Master of Science degree*. Dr. Frank Merat _____________________________________ (chair of the committee) Dr. Christian Zorman _________________________________ Dr.Gerhard Welsch __________________________________ ___________________________________________________ ___________________________________________________ ___________________________________________________ _July, 22 2011___ (date) *We also certify that written approval has been obtained for any proprietary material contained therein. Table of Contents Table of Contents 1 Table of Figures 3 Table of Tables 5 Acknowledgements 6 Abstract 7 1. Introduction 8 1.1 Background 8 1.2 Aims of Work 8 1.3 Capacitors 10 1.3.1 Non-idealities of Capacitors 14 1.4 Titanium Alloy for Anode Material 15 1.4.1 Creation of Anode by Anodization 16 1.5 Instrumentation 19 1.5.1 Analog Control Circuitry 19 1.5.2 Analog to Digital Conversion 20 1.5.3 Microcontrollers 21 1.5.1 Software for User Interface and Data Acquisition 22 2. Experimental Procedure 23 1 2.1 System Level Design 23 2.1.1 Prototype I 26 2.1.2 Prototype II 27 2.1.3 Final Design 29 2.2 Physical Layout 47 2.3 Calibration 48 2.4 Test Setup 51 3. Results and Discussion 53 3.1 Anodization Mode 53 3.2 Testing Mode 65 4. Conclusions 68 5. Future Work 69 5.1 Improvements 69 5.2 High Voltage Version 69 Appendices 71 A. Circuit Schematics 71 B. Board Layout 75 C. Firmware (Pseudo code) 79 Bibliography 84 2 Table of Figures Figure 1 – Structure of a parallel plate capacitor ............................................................ 10 Figure 2 – Representative layout of an electrolytic capacitor .......................................... 12 Figure 3 – Non-ideal capacitor model ............................................................................ 14 Figure 4 - Energy Density vs. Power Density for various types of energy storage devices. Goal 1 and Goal 2 areas represent research goals of ARPA-E funded research by G. Welsch (5) (6)................................................................................................................ 17 Figure 5 – Simplified experimental setup for anodization of sample .............................. 18 Figure 6 - Characteristic curve of anodic oxidation process (20) ................................... 18 Figure 7 – Top-level block diagram of instrumentation .................................................. 25 Figure 8 - Voltage Compliance Circuitry ....................................................................... 31 Figure 9 - Current source and control circuitry ............................................................... 33 Figure 10 - Current sink and control circuitry ................................................................ 35 Figure 11 - Transimpedance amplifier used to measure current through load ................. 37 Figure 12 - Level shift and gain for current measurement signal conditioning ................ 39 Figure 13 - Flowchart of firmware running on microcontroller ...................................... 45 Figure 14 - Anode and cathode suspended in anodizing electrolyte by conducting metal clips ............................................................................................................................... 52 Figure 15 - Test setup to anodize two samples concurrently ........................................... 52 Figure 16 - I V curves for aluminum electrolytic capacitor used as a reference test load. 53 Figure 17 - Current vs. Time for repeated trials of reference capacitor ........................... 54 Figure 18 - Relative standard error for 17 trials of charging reference capacitor ............. 54 3 Figure 19 - Results for 30 minute anodization of ZrTi 80/20 sample on Channel 1......... 56 Figure 20 - Results for 30 minute anodization of ZrTi 80/20 sample on Channel 2......... 57 Figure 21 - TiTa alloy sample showing large amounts of oxide breakdown and repair ... 58 Figure 22 - Results of anodizing titanium lead alloy with a 69/31 ratio of titanium to lead for 15 minutes ............................................................................................................... 59 Figure 23 - Results of attempting to anodize a titanium lead alloy with a 50/50 ratio of titanium to lead .............................................................................................................. 60 Figure 24 - Anodization results of a zirconium lead alloy with a ratio of Zi to Pb of 50/50 ...................................................................................................................................... 61 Figure 25 - Results for two samples of ZrTi 40/60 alloy showing possible contamination of the sample anodized on channel 2 of the instrument................................................... 62 Figure 26 - Results of anodizing ZrTi 50/50 for 24 hours. .............................................. 63 Figure 27 - ZrTi - 50/50 leakage current testing at 2.5V for 2 minutes ........................... 64 Figure 28 - Energy required to form oxide during anodization, 1 second intervals.......... 65 Figure 29 - Voltage across 1000 µF load with device in test mode ................................. 66 Figure 30 - Voltage across 1 µF load with device in test mode ....................................... 66 4 Table of Tables Table 1 – Dielectric constant (εr) and dielectric strength for various materials (2) .......... 13 Table 2 - Final technical specifications .......................................................................... 24 5 Acknowledgements I would like to thank the following: Dr. Frank Merat for his insight and guidance as my advisor throughout the process of performing the work contained within and writing this thesis, Dr. C. C. Liu and Laurie Dudik for providing me with materials, lab space, and training to be able test the instrumentation designed for this thesis, Dr. Gerhard Welsch and Donald McGervey for providing insight into the electrochemical processes and materials science behind anodization of capacitor anodes, Friend and fellow student Morgan McClure for the use of his personal equipment and previous experience during assembly and debugging of the instrumentation designed for this thesis And the United States’ Department of Energy’s ARPA-E Directorate for providing the funding to make this work possible. 6 Abstract INSTRUMENTATION FOR ANODIZATION AND IN-SITU TESTING OF TITANIUM ALLOYS FOR CAPACITOR ANODES by STEVEN JOSEPH EHRET The development of smaller, more efficient energy storage devices is needed in industries ranging from consumer electronics to the automobile industry. One such device is the capacitor, which stores electrical energy in the form of an electric field. This electric field is established by the separation of charge between two conductors with an insulating dielectric between them. In electrolytic capacitors, this dielectric is an anodic oxide that is grown directly on the anode of the capacitor in an electrochemical process known as anodization. Research to develop electrolytic capacitors with increased power and energy densities using new materials and processes to create the capacitor anodes require the ability to record voltage and current data during the anodization process. This thesis presents the design of custom instrumentation that provides researchers with a platform to control the anodization parameters via a computer interface and record the current and voltage data necessary to aid in the development of advanced materials for capacitor anodes to a computer hard drive for later viewing and analysis. Initial results and performance analysis are also included. 7 1. Introduction 1.1 Background In the electronics industry, the need for devices that have higher levels of performance is ever increasing. In particular, energy storage devices require greater energy and power densities, smaller physical size, and elimination of parasitic losses to allow the development of smaller, lighter, and more efficient technologies to be applied in areas ranging from portable consumer electronics to hybrid electric vehicles. One such energy storage device is a fundamental circuit element known as a capacitor. When a potential difference is applied to the conductors of a capacitor, energy is stored in the resulting electric field. An attractive feature of the capacitor is its ability to store and supply energy very quickly, resulting in capacitors being used in a multitude of applications where high power is needed for short periods of time. To achieve better performance in these areas, new materials and processes are being developed to manufacture capacitors. These processes would enable capacitors to achieve higher energy and power densities and have fewer parasitic losses (1). To facilitate the rapid development of these new materials, it is necessary to efficiently measure the pertinent electrical parameters to reject or further the development of samples. 1.2 Aims of Work Research is being funded by ARPA-E to develop both materials and processes to create anodes for capacitors based on regular and surface enhanced