PUBLICATIONS United States Department of Commerce Technology Admmistration National Institute of Standards and Technology NIST Special Publication 876 Boundary Lubrication of Silicon Nitride Richard S. Gates and Stephen M. Hsu NIST : XlOO »!• : XlOO teal* 6000 CgO-Si-OCg + in CgO-Si-OCg 5250 OCg in CO 4500 tn to/,* ananaToaTsaMaHaaoae »^*>%Jff. iMbo^" 430 49 4ao 4K 440 c 3750 Scan : XIM o .0. ^OCg . o OCg' CgO-Si Si~ + 1 \~OCg 3000 CgO-Si-OCg „ c,o oc» oc. CD 2250 1500 SZSSiBBSOBaBBMMBMaBB BNTM 706 7t0 71S 720 72B 7S0 TSB 740 750 >> i> I 1 r 1 'I 0 I I 100 150 200 250 300 m/z QC 100 .U57 no. 876 1995 yhe National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . and to facilitate rapid commercialization ... of products based on new scientific discoveries." 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NIST Special Publication 876 Boundary Lubrication of Silicon Nitride Richard S. Gates and Stephen M. Hsu Material Science and Engineering Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-0001 February 1995 U.S. Department of Commerce Ronald H. Brown, Secretary Technology Administration Mary L. Good, Under Secretary for Technology National Institute of Standards and Technology Arati Prabhakar, Director National Institute of Standards U.S. Government Printing Office For sale by the Superintendent and Technology Washington: 1995 of Documents Special Publication 876 U.S. Government Printing Office Natl. Inst. Stand. Technol. Washington, DC 20402-9325 Spec. Publ. 876 387 pages (Feb. 1995) CODEN: NSPUE2 PREFACE This report was bom out of a cooperative program between the Chemical Engineering Department of The Pennsylvania State University and the Surface Properties Group in the Ceramics Division, Materials Science and Engineering Laboratory, NIST. The intent of the program is to assist in the education of young scientists and engineers and at the same time fulfill the mission of NIST. The program is also supported by the Department of Energy, Office of Transportation Technologies, Office of Transportation Materials through the Tribology Program. Under the program, young graduate smdents, after they had finished course work, come to NIST to conduct their thesis research under joint University and NIST staff supervision. While at NIST, the smdents are supported through the graduate cooperative program and receive regular salary for their work. At the conclusion of their research, they write the thesis and defend their work in the Department. Either an abridged or an expanded version of the thesis is published as a NIST Special Publication (SP). This is one of the reports. This kind of cooperative program provides additional resources to the University in their training of scientists and engineers, and at the same time, provides a steady stream of high caliber young people who are interested in pursuing research to work at NIST and experience research lives first hand. NIST often not only benefits directly from the results of their labor but also gains an advantage at recruiting the best and the brightest to come to NIST. I would like to acknowledge the efforts of Professors Larry Duda and Erwin Klaus in their tireless assistance and counseling of the students in the program, Mrs. Barbara Bush in the handing of the various administrative details at Penn State, and Carolyn Sladic and Fay Raginski here at NIST. The financial support of DOE is gratefully acknowledged. Stephen M. Hsu Group Leader Surface Properties Group Ceramics Division Materials Sciences and Engineering Laboratory iii ABSTRACT Successful use of advanced ceramics in many tribological applications requires an understanding of the physical, chemical, and mechanical properties of the material. Physical and mechanical data are relatively abundant for most ceramics; however, information on the surface chemical interactions between ceramics and lubricants is lacking. This report describes a systematic study to investigate the effects of selected organic chemical compounds on the friction and wear of silicon nitride under boundary lubrication conditions. A broad range of chemistries were investigated. Results are grouped according to predominant chemical compound class as oxygen, phosphorus, halogen, sulfur, and nitrogen-containing chemistries. A Ball-on-Three-Flat (BTF) wear tester was used to evaluate many different organic compounds under boundary lubrication conditions. Tests were conducted using one weight percent of chemical compounds in paraffin oil, and the test results were compared to a base case of paraffin oil without additive. Results indicated that some compounds could provide significant improvement of friction and wear characteristics. Friction coefficients varied from + 30 % to - 45 % compared with the base case. Wear was measured as the wear increase above the elastic contact diameter (Hertzian diameter). Relative to the base case, wear changes ranged from + 61% to - 96 %. Successful wear reduction was obtained by phosphorus-containing compounds, several glycol compounds, oleic acid, sulfonates, a salicylate, an imidazoline, and a phenate and was generally associated with the formation of a film in the contact region. Additional wear tests conducted using neat compounds indicated that acids and alcohols could provide significantly better friction and wear behavior than neat paraffin oil. In the case of some short chain (Cg-Cio) primary linear alcohols, very low coefficient of friction (/x=0.05) and unique wear scar morphology suggested strong chemical interactions and a possible elastohydrodynamic lubrication contribution. More in-depth study of reaction product films from alcohol-lubricated silicon nitride wear tests showed that organic compounds containing alcohol functional groups can react with the surface of silicon nitride to form high molecular weight silicon-containing organic compound films with lubricating capability. A series of static and dynamic reactions were conducted to elucidate the reaction sequence. Based on these results, a reaction mechanism is proposed in which alcohols react with the silicon nitride surface to form bonded alkoxides. Subsequent reactions in the high temperature, high shear, environment of a wearing contact result in the formation of the high molecular weight silicon alkoxide films which can lubricate. V TABLE OF CONTENTS Page PREFACE iii ABSTRACT v LIST OF TABLES xii LIST OF FIGURES xv Chapter 1. INTRODUCTION 1 Chapter 2.