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Trigger Effects in Spontaneous Electrolysis

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Trigger Effects in Spontaneous Electrolysis TRIGGER EFFECTS IN SPONTANEOUS ELECTROLYSIS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy In the Graduate School of the Ohio State university By RICHARD MAC WILSON, B.S., M.S. The Ohio State University 1959 Approved by Adviser Department of Chemistry Dedicated to m y wife and family 11 PREFACE The research described herein concerning the galvanic cells established between two similar electrodes with the same history suggests a problem In corrosion not previously considered, that is, electrochemical corrosion between two like electrodes. The magnitude of this corrosion is relatively small but It would, under proper conditions, be sufficient to initiate cavitation and lead to serious damage of the corroding object. Ill ACKNOWLEDGMENT The author wishes to express his sincere appreci­ ation to Dr. William M, MacNevin for his encouragement and guidance throughout the course of this research. iv CONTENTS Page INTRODUCTION .................................... 1 Electrochemical Cells ....................... 1 Concentration Cells* ................... 3 Thermogalvanlc Cells ................... 6 Gravity Cells ......................... 8 Centrifugal Cells ..................... 13 Crystallographlc Effect on Potential . 15 Stress Corrosion ....................... IT Motor Electric Potential ............... 23 Effect of a Magnetic Field ............. 25 Effect of Interfaclal Free Energy .... 27 Photovoltaic Cells ..................... 28 Properties of Aluminum ..................... 30 History of the Aluminum-Platinum Electrode Pair 40 Properties of Zirconium ..................... 50 STATEMENT OF PROBLEM ............................. 54 EXPERIMENTAL APPARATUS........................... 56 EXPERIMENTAL PROCEDURE ........................... 65 RESULTS ........................................ 69 Aluminum-Platinum Electrode P a i r ........... 69 Aluminum-Aluminum Electrode P a i r ........... 82 Zirconium-Platinum Electrode P a i r ..............148 Zirconium-Zirconium Electrode P a i r ............ 148 DISCUSSION........................................ 154 SUMMARY .......................................... 168 BIBLIOGRAPHY...................................... 172 AUTOBIOGRAPHY .................................... 178 v LIST OP TABLES Table Page 1. Effect of centrifugal force on the potential of the iodine electrode.................... 15 2• Motor electric potential of the copper e l e c t r o d e ................................ 24 3. Photovoltaic effect on the copper-copper oxide e l e c t r o d e ................................ 29 4. Properties of aluminum..................... 30 5. Partial list of the electromotive series . 31 6 . Comparison of the heat of formation of some sodium, aluminum and iron compounds.......... 32 7. Corrosion resistance of zirconium .......... 51 8 . Analysis of reagent-grade aluminum wire . 61 9. Analysis of zirconium rod................... 62 10. Effect of the size relationship on the response of the aluminum-aluminum electrode pair to 20 micrograms of sodium fluoride............... 94 11. Effect of pH on the response of the aluminum- aluminum electrode pair to 20 micrograms of sodium fluoride............................. 95 12. Response of the same set of 2:1 aluminum electrodes to additions of 20 micrograms of sodium fluoride............................... 105 13. Reproducing conditions on an aluminura-platlnum electrode pair and the response to 20 micro­ grams of fluoride. Pour spirals (4.8 square centimeters) of aluminum wire................. 117 14. Reproducing conditions on an aluminum-platinum electrode pair and the response to 20 micro­ grams of fluoride. A continuation of Runs No. 268-271.................................... 118 vi vii LIST OF TABLES (Contd.) Table Page 15* Response of the aluminum-calomel electrode pair to 20 micrograms of fluoride. All solutions were outgassed with nitrogen and a nitrogen atmosphere maintained above the cell solution............................... 127 16. Effect of outgassing the cell solution on the response of the aluminum electrode to 20 micrograms of fluoride ................. 128 17. Effect of position on the behavior of the 2 :1 aluminum-aluminum electrodepa i r ......... 129 18. Response to 20 micrograms of fluoride of selected combinations of four similar aluminum electrodes................................ 134 19. Effect of shape on the behavior of two aluminum electrodes with relative surface areas of 1 .8 and 2 .8 square centimeters ......... 135 LIST OP FIGURES Figure Page 1. Current-temperature relationship in the aluminum thermogalvanlc c e l l ................. 10 2. Baker type curve ...... ................ 43 3. Holland type curve ........................... 43 4. Actual size diagram of Cell I and an electrode holder used with this cell .......... 59 5. Comparison of the response to 20 micrograms of sodium fluoride of the Baker electrode at 27° C., a spiral electrode (99# Al) at 25° C. and a spiral electrode (99# Al) at 50° C ........... 72 6 . Log 1 versus t for the current decay resulting from the addition of 20 micrograms of sodium fluoride to 3 5 .0 mis of 0 .2 M acetic acid at 50.0° C. with the aluminum-platinum electrode p a i r ........................................ 74 7. Fluoride calibration curve with the aluminum- platinum (99.99# Al) electrode pair........... 76 8 . Effect of the preliminary treatment, 3 minutes with 0.01 M HF, on the aluminum anode In combination with a platinum c a t h o d e .......... 79 9. Effect of a soluble aluminum salt on the galvanic current flow between the aluminum- platinum electrode in the presence of 50 micrograms of sodium fluoride................. 8 l 10. Sample current-time curve obtained with a large aluminum electrode in contact with a platinum cathode In 0.2 M acetic acid.......... 85 11. Sample current-time curve obtained with a small aluminum electrode in contact with a platinum cathode in 0 .2 M acetic acid.......... 85 12. Current-time curve for a 10:1 ratio of an aluminum-aluminum electrode pair in the presence of 20 micrograms of sodium fluoride . 87 viii lx LIST OP FIGURES (Contd.) Figure Page 13. Current-time curve with the current values obtained with the Standard Research Instru­ ments Company milliammeter. 20 micrograms of sodium fluoride added. .......... 91 llf. Effect of successive additions of fluoride on the current flow between a 2 :1 aluminum- aluminum electrode p a i r ................... 93 15. Effect of pH on the response of the alumi- num-aluminum electrode pair to added fluoride 98 16. Effect of adding fluoride to the center of the cell solution, to the vicinity of the anode and to the vicinity of the cathode. 101 17. Variation of the response of a 2:1 aluminum- aluminum electrode pair to changes In added f l u o r i d e ................. 104 18. Effect of use on the response of the aluminum-aluminum electrode pair to added f l u o r i d e ................................... 107 19. Current response of the aluminum-aluminum electrode pair to a constant fluoride concentration ............................. 114 20. Current response of the aluminum-platinum electrode pair to a constant fluoride concentration ............................. 116 21. Current flow between a platinum end saturated calomel electrode in 0.2 M acetic acid. The platinum was either rinsed with water or Immersed In hot concentrated nitric acid. • . 122 22. Reproducible current flow between a platinum and saturated calomel electrode in 0.2 M acetic acid. The platinum was stored in the electrolyte before use and the solution out- gassed...................................... 125 X LIST OP FIGURES (Contd.) Figure Page 2 3. Effect of differential stirring on the current flow between two similar aluminum electrodes. 132 24. Change of potential with time of a large and small aluminum electrode In 0.2 M acetic acid • 137 25. Diagrams of the spiral and disk-shaped elec­ trodes and the apparatus used for measurements with the Luggin capillary..................... 141 26. Change of resistance with time of a 0.2 M acetic acid solution containing 2 .0 grams of aluminum metal •••••.............................. 145 27. Effect of ultrasonics on the current flow between two aluminum electrodes In 0.2 M acetic acid......................................... 147 2 8 . Fluoride calibration curve with the zirconlum- platinum electrode pair In 0.1 M perchloric acid......................................... 150 29. Current-time curve for two zirconium electrodes in 0.1 M perchloric acid.......................153 30. Polarization diagram for a process under anodic c o n t r o l ...................................... 162 INTRODUCTION Electrochemical Cells The tern electrolysis means in general terms "a chemical change due to the passage of electricity." A common example of this Is the battery-operated electroly­ sis cell In which chemical reactions are initiated and maintained by the passage of current from an external current source. The electricity referred to is direct current or Ohm*B Law electricity, and Faraday!s Laws re­ late the quantity of electricity flowing through the cell to the amount of chemical change. In contrast, cells are known that do not require an outside current source. These cells are known by several names: galvanic cells, voltaic cells, spontaneous electrolysis cells and Internal electrolysis cells. In such a cell the current flow does not cause the chemical reactions to occur but Is the result of chemical energy or a related form of potential energy,
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