ERRATA SHEET PAGE NO LINE NO SHOULD READ 78 11 One Of
Total Page：16
File Type：pdf, Size：1020Kb
ERRATA SHEET PAGE NO LINE NO SHOULD READ 78 11 one of which functions as an .... 141 28 the chlorides of iron, vanadium and copper ... 110 34 radiation polarised parallel to the plane of incidence is absorbed by surface species. Installation of a polariser ...... 151 21 a) ZDDPs at room temperature ... 202 18 3) ZDDP and parent phosphorodithioic acid ... 129 7 attributed to the symmetric and antisymmetric .. Imperial College London -LUB-R-I CANT—ADD ITIVES a im n wi= a r LU6RKANT A$VlTi\/£S COwr/BNiNp- p H0SPHORU3 by Philippa Mary Cann A Thesis Submitted for the Degree of DOCTOR OF PHILOSOPHY of the University of London and also for the DIPLOMA OF IMPERIAL COLLEGE June 1982 Lubrication Laboratory Department of Mechanical Engineering Imperial College London SW7 I ABSTRACT Organophosphorus additives have been used for many years as load-carrying and anti-oxidant agents for lubri- cating oils. This thesis describes an investigation into the load-carrying properties of a series of zinc dialkyl- dithiophosphates (ZDDP) and related compounds. A short literature review is presented which concludes that despite extensive research into ZDDPs the mechanism of their anti-wear action is still not fully understood. A basis of this study therefore was an investigation into the AW mechanism of ZDDPs. The problem was studied in two ways. Firstly, the friction-temperature properties of the additives were evaluated on a High Frequency Reciprocating test device. The second approach was to investigate chemical films formed on steel surfaces during immersion in additive solutions. Analysis of these films was by infrared reflection-absorption spectroscopy. This study concludes that the load-carrying properties ofZDDPs are not due simply to their thermal degradation products and that the anti-oxidation reactions of ZDDPs play an important role in determining L-C properties. Also ZDDPs operate by forming thick non-conducting (boundary) films especially at high temperatures, which reduce friction. II ACKNOWLEDGEMENTS I would like to. thank the following: Professor A Cameron and Dr H Spikes for their encouragement and supervision throughout this project. Reg, Tony and Paul for their technical support and assistance. All members of the Lubrication Laboratory, both past and present, for their forbearance and help with the engineering aspects of this project. Jane for the excellent typing, and endless patience with this thesis. Cinderhill Pharmacy for the photographs. Rolfe and Nolan Computer Services PLC for the photocopying. Graham, my mother and Elf (Aquataine) Ltd for financial support and encouragement. Ill CONTENTS Title Page Abstract i Acknowledgements II Contents III List of Figures and Tables VIII Nomenclature XIII CHAPTER ONE GENERAL INTRODUCTION AND OUTLINE OF PROJECT 1.1 Introduct ion 1.2 Frict ion 1.3 Wear 1.4 Type and Role of Additives in Boundary Lubrication 1.5 Introduction to Project 1.6 Outline of Project CHAPTER TWO GENERAL REVIEW OF ZINC PIALKYLDITHIO- PHOSPHATE LITERATURE 2.1 General Introduction 8 2.2 Solution Chemistry of ZDDPs 9 2.2 Thermal Decomposition of ZDDPs 9 2.2 Discussion 21 2.3 Anti-oxidant Action in Solution 24 2.3.1 Literature Review 24 2.3.2 Discussion 31 2.4 Relationship Between AW and AO Action 34 2.5 Nature of ZDDP Films on Metal Surfaces 34 2.6 Load-Carrying Properties of MDDPs 39 2.7 Mechanism of ZDDP L-C Action 42 CHAPTER THREE PREPARATION OF ORGANOPHOSPHORUS ADDITIVES 3.1 Introduction 46 3.2 Preparation of 0,0 Dialkyldithiophosphoric Acids 46 3.2.1 Experimental 46 3.2.2 Purification of Dithiophosphoric Acids 47 IV 3.2.3 Analysis of Dithiophosphoric Acids 48 3.3 Preparation of ZDDP Salts 48 3.3.1 Purification of Basic and Neutral Zinc Salts 50 3.3.2 Characterisation of ZDDPs 52 3.4 Analysis of Commercial Additives 52 3.4.1 Analysis of Commercial ZDDPs 53 3.5 Discussion 53 CHAPTER FOUR INFRARED SPECTRA AND MOLECULAR STRUCTURE OF ZINC DIALKYLDITHIQPHOSPHATES AND RELATED COMPOUNDS 4.1 Introduction 55 4.2 Infrared Spectroscopy 55 4.3 Literature 57 4.4 IR Spectra of Dialkyldithiophosphoric Acids 58 4.4.1 Experimental and Introduction to Results 58 4.4.2 -S-H Bond 58 4.4.3 -P-O-C Bond 60 4.4.4 P=S Thiophosphoryl Bond 62 4.4.5 P-S Bond 73 4.5 IR Spectra ZDDPs 73 4.5.1 Literature Survey Crystal and Molecular Structure -of MDDPs 7 3 4.5.2 IR Spectra ZDDPs - Experimental 81 4.5.3 Results and Discussion 81 4.5.3.1 P-O-C Bond 81 4.5.3.2 P-S Bond 91 4.5.3.3 Zn-S Bond 91 4.5.3.4 Discussion of ZDDP Results 95 4.6 IR Spectroscopic Analysis of Lubrizol 1395 96 V CHAPTER FIVE INFRARED SPECTROSCOPIC ANALYSIS OF THIN FILMS ON METAL SURFACES 5.1 General Introduction 100 5.2 Analysis of Thin Films on Metal Surfaces 100 5.3 Infrared Reflection-Absorption Spectroscopy 102 5.3.1 Introduction 102 5.3.2 Applications of Infrared Reflection- Absorption Spectroscopy 103 5.3.3 Theory and Development of Infrared Reflection-Absorption Spectroscopy 105 5.3.4 Optimisation of Experimental Conditions 110 5.4 Experimental 113 5.4.2 Equipment - IR Spectrometer 113 5.4.3 Sample Optics 115 5.5 Preliminary Experiments 118 5.6 Experimental Procedure 120 5.6.1 Room Temperature Tests 120 5.6.2 High Temperature Tests 120 5.6.3 Scanning Procedure 122 5.6.4 Reference Spectra 122 5.7 Results 123 5.7.1 Di-ethylphosphorodithioic Acid 123 5.7.1.1 Room Temperature 124 5.7.1.2 100°-150°C 127 5.7.1.3 160°-200°C 133 5.7.2 Zinc Diethyldithiophosphate 134 5.7.2.1 Room Temperature Tests 134 5.7.2.2 100°-150°C Tests 137 5.7.2.3 160°-200°C Tests 137 5.7.3 Commercial Additive - Lubrizol 1395 142 5.7.3.1 Room Temperature Tests 142 5.7.3.2 100°-150°C Tests 144 5.7.3.3 160°-200°C Tests 144 5.8 General Discussion 148 5.9 Conclusions 151 VI CHAPTER SIX LUBRICATION OF STEEL BY ZINC DIALKYL- DITHIOPHOSPHATE S 6.1 Introduction 153 6.2 Methods of Studying Load-Carrying Additives 153 6.3 Test Apparatus and Procedures 157 6.3.1 HFR Rig 157 6.3.2 Description of HFR Device 157 6.3.3 Test Procedure 160 6.3.4 Cleaning Procedure 161 6.3.5 Solvents, Additives, Metals Employed 161 6.4 Preliminary Results 164 6.4.2 Other Preliminary Tests 164 6.5 Main Results 168 6.5.1 Testing Programme 168 6.5.2 No Additives 195 6.5.3 Organophosphorus Additive Tests 195 6.5.3.1 Zinc Dialkyldithiophosphates 195 6.5.3.2 Dialkylphosphorodithioic Acids 201 6.6 Mixed Additive Tests 201 6.6.1 Introduction 201 6.6.2 Results 203 6.6.2.1 Di-ethyl Additives 203 6.6.2.2 Di-iso-propyl Additives 204 6.6.2.3 Organophosphorus/Preoxidised Hexadecane Additive Mixtures 205 6.6.2.4 ZDDP and Anti-oxidant 205 6.7 Discussion 206 6.7.1 Effect of Initial Concentration 213 6.7.2 Effect of Alkyl Chain Length 214 6.7.3 Presence of Acid Impurities 215 6.7.4 Addition of Polar Oxidised Species 215 6.7.5 General Discussion 216 6.7.6 Nature of the Boundary Film 220 6.7.7 Comparison of HFR Test Results with Previous Work 221 6.8 IR Spectroscopic Analysis of Bulk Oil Changes 223 6.9 General Conclusions 224 VII CHAPTER SEVEN GENERAL CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK 7.1 Introduction 226 7.2 Chapter 4. IR Spectroscopy of ZDDPs 226 7.3 Chapter 5. IR Reflection-Absorption Studies of Surface Films 227 7.3.1 Conclusions 227 7.3.2 Future Work 2 28 7.4 Chapter 6. Lubrication of Steel by ZDDPs. 228 7.4.1 Conclusion 228 7.4.2 Future Work 229 7.5 Mechanism of ZDDP AW Action 229 APPENDIX 1 Analysis of Organophosphosphorus Additives by Thin Layer Chromatography 231 REFERENCES 234 VIII LIST OF FIGURES Page No 1.1 Typical Load-Carrying Additives 4 2.1 Metal Dialkyldithiophosphates 8 2.2 ZDDP Thermal Decomposition Mechanism from Ashford et al (23) 12 2.3 Mechanism of ZDDP Thermal Degradation from Luther et al (24) 13 2.4 Mechanism of ZDDP Thermal Degradation from Dickert and Rowe (27) 15 2.5 Mechanism of ZDDP Thermal Degradation from Brazier and Elliott (28) 17 2.6 Mechanism of ZDDP Thermal Degradation from Jones and Coy (30) 20 2.7 Reaction Mechanism of Hydrocarbon Auto- oxidation in the Liquid Phase (33) 24 2.8 Mechanisms of ZDDP Chain Breaking from Burns et al (35) 26 2.9 Reaction Profiles for the Decomposition of Cumene Hydroperoxide in the Presence of ZDDP from Burns et al (38) 28 2.10 Ionic Versus Free Radical Hydroperoxide Decomposition (40) 30 2.11 Summary of ZDDP Anti-oxidant Reaction Mechanisms 33 4.1 Infrared Spectrum of n-Hexadecane 56 4.2 Rotational Isomers of (RO) P(S)SH (68) 59 2 4.3 IR Spectrum of Di-ethylphosphorodithioic Acid 63 4.4 IR Spectrum of Di-n-propylphosphorodithioic Acid 64 4.5 IR Spectrum of Di-iso-propylphosphorodithioic Acid 65 4.6 IR Spectrum of Di-n-butylphosphorodithioic Acid 66 4.7 IR Spectrum of Di-n-hexylphosphorodithioic Acid 67 4.8 IR Spectrum of Di-n-octylphosphorodithioic Acid 68 4.9 Tetramethyldiphosphorus Disulphide (TMPDS) 70 4.10 Proposed Molecular Structures of ZDDPs 75 IX 4.11 Resonance Structures of MDDPs from Gallopoulos (66) 76 4.12 Equilibrium Chelate Structures of ZDDPs in Solution from Heilwell (81) 77 4.13 Molecular Structure of the Zinc Di-iso-propyl- dithiophosphate Dimer from Lawton and Kototailo (86 ) 79 4.