Richard S. Gates

Tribochemical Mechanism of Alumina With Water

Water has been found to exhibit significant effects on the tribological behavior of alumina. A film-like substance was found on the surfaces of water lubricated alumina wear surfaces, suggesting the possibility of tribochemical reaction between water and alumina in the contact junction. This paper describes an investigation of the alumina/water tribosystem to determine the chemical interaction between these two materials under rubbing conditions. A combination of x-ray powder diffraction and thermogravimetric analysis (TGA) has been used to investigate the kinetics of alumina/water reactions. These experiments have determined that transition (gamma) alumina reacts with water to form hydroxides of aluminum. At high temperature (≊ 200°C) aluminum oxide hydroxide (boehmite—AlO(OH)) is formed, while at lower temperature (≊ 100°C) the formation of aluminum trihydroxide (bayerite—Al(OH)3) is favored. Aluminum trihydroxide (bayerite) was found in the wear debris from water lubricated wear tests. A mechanism for ...

Effect of selected chemical compounds on the lubrication of silicon nitride

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 chemical interactions of ceramics is scarce. This is especially true for chemical interactions with regard to lubrication of these materials. This paper investigates the influence of selected chemical compounds on the friction and wear of silicon nitride under boundary lubrication conditions. A ball-on-three-flat modification of the four-ball wear tester was utilized to evaluate the tribological characteristics of a hot pressed silicon nitride lubricated with a paraffinic base oil containing 1 weight percent additives. Friction, wear, and. film formation tendencies were observed for a range of oil soluble chemical compounds containing oxygen, sulfur, nitrogen, chlorine, and phosphorous. A wide range of additive response was observed. Friction c...

Precise atomic force microscope cantilever spring constant calibration using a reference cantilever array

A method for calibrating the stiffness of atomic force microscope (AFM) cantilevers is demonstrated using an array of uniform microfabricated reference cantilevers. A series of force-displacement curves was obtained using a commercial AFM test cantilever on the reference cantilever array, and the data were analyzed using an implied Euler-Bernoulli model to extract the test cantilever spring constant from linear regression fitting. The method offers a factor of 5 improvement over the precision of the usual reference cantilever calibration method and, when combined with the Systeme International traceability potential of the cantilever array, can provide very accurate spring constant calibrations.

Tribochemistry Between Water and Si3N4 and SiC: Induction Time Analysis

Under certain conditions, silicon nitride and silicon carbide ceramics can be lubricated by water; however, silicon carbide generally takes 5-6 times longer to enter the effective tribochemical regime than silicon nitride. Despite this, the operating range for silicon carbide is much larger once it enters into this regime. This paper examines the various explanations for why these two ceramics should exhibit different time constants for tribochemistry to occur. Using a ball-on-three-flat bench wear test in water, a preworn-in procedure was used to control surface roughness and tribochemical induction times were measured. It was found that wear-particle-induced third body effect prevented the successful entrance into the tribochemical regime for silicon carbide. It was postulated that the films formed are very susceptible to third body effect and require smooth surfaces for the tribochemical reaction films to be effective.

A study on the nature of boundary lubricating film: analytical method development

The nature of the boundary lubricating film and its formation mechanism has been the subject of research in the last several decades. This study describes the development of a novel analytical technique designed specifically for the analysis of small amounts of lubricating film using an integrated size exclusion chromatography-refractive index-ultraviolet-graphite furnace atomic absorption (SECRI-UV-GFAA) system. Experiments under static simulation conditions as well as under dynamic rubbing conditions were conducted. Analysis of the reaction products in each case indicates the formation of high molecular weight organometallic compounds with molecular weights range from 1,000 to 100,000. This paper describes the methodology, equipment, and the procedures developed to measure nanogram quantities of the organometallic compounds generated by tribochemical reactions under boundary lubrication conditions. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conferen...

Accurate and precise calibration of AFM cantilever spring constants using laser Doppler vibrometry

Accurate cantilever spring constants are important in atomic force microscopy both in control of sensitive imaging and to provide correct nanomechanical property measurements. Conventional atomic force microscope (AFM) spring constant calibration techniques are usually performed in an AFM. They rely on significant handling and often require touching the cantilever probe tip to a surface to calibrate the optical lever sensitivity of the configuration. This can damage the tip. The thermal calibration technique developed for laser Doppler vibrometry (LDV) can be used to calibrate cantilevers without handling or touching the tip to a surface. Both flexural and torsional spring constants can be measured. Using both Euler-Bernoulli modeling and an SI traceable electrostatic force balance technique as a comparison we demonstrate that the LDV thermal technique is capable of providing rapid calibrations with a combination of ease, accuracy and precision beyond anything previously available.

Effect of materials on tribochemical reactions between hydrocarbons and surfaces

Tribochemistry can be defined as the chemical reactions between the surface and the lubricant molecules inside a sliding contact under boundary lubrication conditions. These reactions are important because they control the lubrication processes, and therefore they determine the reliability and durability of moving parts in machineries. In spite of its practical significance, our understanding of the nature of tribochemistry is limited, and to a large extent, empirical in nature, and mainly restricted to the steel?hydrocarbon system. As new materials emerge and are being applied to various applications, users are often hampered by the lack of knowledge of how these new materials can be effectively lubricated via tribochemical reactions, resulting in occasional premature failure and product recall.There are many tribochemical reactions which occur in a sliding system, such as tribocorrosion, electro-chemistry, hydrolysis of ceramics and anti-wear additive film formation. However, the fundamental basis of lubrication in most of the practical systems starts with the reactions between materials surfaces and hydrocarbon base oils. Without this reaction, for example, an anti-wear additive such as zinc dithiophosphate would not be effective. Therefore, in this paper, we will focus on the effect of materials on the basic tribochemical reactions between hydrocarbons and surfaces.This paper integrates existing information in the literature on the lubrication chemistry of various materials and provides a consistent framework in the context of tribochemistry. For discussion purposes, we will examine metals, semiconductors, and insulators. The preponderance of data in the metals?hydrocarbon systems suggests that thermochemistry and organometallic chemistry dominate the interfacial chemical reactions. For semiconductors and insulators, there is evidence that electrostatic charge induced electron emission plays an important role in the tribochemistry of these materials. Various measurement methods used to characterize tribochemical behaviours are introduced and discussed in terms of reactivity analysis and tribochemical mechanisms.

Silicon Nitride Boundary Lubrication: Lubrication Mechanism of Alcohols

This paper describes the lubrication mechanism of alcohols with silicon nitride under boundary lubrication conditions. Dynamic wear tests and static chemical reaction studies were conducted to study the chemical interaction between alcohols and silicon nitride. Direct evidence of chemical reactions occurring between alcohols and silicon nitride was collected. Gel-permeation-chromatography-graphite-furnace-atomic-absorption (GPC-GFAA) analysis detected the presence of high molecular weight (HMW), silicon-containing, metallo-organic compounds in the wearing contact. Secondary ion mass spectrometry (SIMS) analysis of the reaction products from wear tests revealed the formation of silicon alkoxides. These alkoxides subsequently reacted to form HMW products which had been independently verified as capable of lubricating silicon nitride surfaces. A two-ball collision test was used to verify the lubricating quality of the film generated from the wear test. A lubrication mechanism is proposed in which alcohols ad...

Etching Process Effects on Surface Structure, Fracture Strength, and Reliability of Single-Crystal Silicon Theta-Like Specimens

The etching processes used to produce microelectromechanical systems (MEMS) leave residual surface features that typically limit device strength and, consequently, device lifetime and reliability. In order to optimize MEMS device reliability, it is therefore necessary to determine the effects that these etching processes have on MEMS component strength. The microscale theta specimen, which is shaped like the Greek letter Θ, acts as a tensile test specimen when loaded in compression by generating a uniform tensile stress in the central web region of the specimen. Three sets of single-crystal silicon theta specimens are fabricated using two deep reactive ion etching recipes and a temperature-controlled cryogenic plasma etching recipe, each set resulting in a different specimen surface structure. The resulting strength distributions are analyzed in two ways. First, the strength data are fit to a three-parameter Weibull distribution function to determine the lower bound, or threshold strength, of each distribution. Second, the strength data are used in conjunction with various loading schemes to assess their effect on the lifetime spectrum of the device. In both approaches, the theta specimen is used to great effect to gain quantitative insight into the role of etching-induced surface features on the manufacturing yield and operational reliability of MEMS components.

Direct measurement of cantilever spring constants and correction for cantilever irregularities using an instrumented indenter

A method is presented that allows direct measurement of a wide range of spring constants of cantilevers using an indentation instrument with an integrated optical microscope. An uncertainty of less than 10% can be achieved for spring constants from 0.1 to 10(2) Nm. The technique makes it possible to measure the spring constant at any desired location on a cantilever of any shape, particularly at the tip location of an atomic force microscopy cantilever. The article also demonstrates a technique to detect and correct apparent length anomalies of cantilevers by analyzing spring constants at multiple positions.