Czeslaw Kajdas

About an anionic-radical concept of the lubrication mechanism of alcohols

Abstract To understand the chemical behaviour of alcohols in sliding contacts, especially in the boundary lubrication of aluminium-steel surfaces, the concept of a negative-ion-radical action mechanism of these compounds has been proposed. The lubrication model is based upon the ionization mechanism of alcohols caused by the action of exoelectrons. It has been shown that alcohols may produce ions and radical anions that react with a metal surface. This fact explains well the formation of a product of waxy appearance during sliding of an aluminium—steel system in the presence of fatty alcohols. The generation of radical and biradical anions elucidates the results that alcohol groups favour the production of an adherent coating composed of many components, including alkynes, dialkynes, alkenes and dialkenes, on sliding surfaces. Furthermore, the proposed action mechanism explains the chemisorption of alcohols on a clean aluminium surface prepared by cutting under high vacuum. Finally, this mechanism makes clear other findings related to pentaerythritol partial ester. The ester, which contains both hydroxyl and ester groups, reacts with the surface aluminium atoms to form amorphous substances such as aluminium complexes.

Triboemission from alumina, single crystal sapphire, and aluminum

Abstract The purpose of this paper is to present experimental research work seeking a better understanding of triboemission and its role in tribochemistry. A new instrument is described for measuring the intensity and retarded-energy spectra of electrons and ions triboemitted from various sliding contacts. This instrument was designed to accommodate a variety of contact geometries and it features a wide range of applied loads and sliding speeds under high vacuum or controlled atmosphere conditions. The particle-measurement technique employs a channel electron multiplier in the pulse-counting mode. Experimental results are reported on triboemission intensity from sliding contact of diamond on three related materials: alumina, single crystal sapphire (Al 2 O 3 ), and aluminum. Significant negatively-charged particle triboemission was observed from diamond-on-alumina and diamond-on-sapphire contacts. The retarded-energy spectrum of the negative-particle triboemission also was measured. Emission of positively-charged particles was found to be of relatively low intensity. Lower levels of negatively-charged triboemission, as compared to those from alumina and sapphire, were found from diamond-on-aluminum. These results are discussed with a focus on the possible role of charged particle emission in tribochemical processes and, in particular, on tribopolymerization as an effective mechanism of ceramic lubrication.

Investigation of tribochemical behavior of Al–Si alloy against itself lubricated by amines

Abstract The friction and wear properties of Al–Si alloy against Al–Si alloy was investigated using an Optimol SRV Tester with the lubrication of pure ethyleneglycol, ethanolamine, ethylenediamine and triethylenetetramine. The tribo-chemical reactions and the compositions of the boundary film formed on the rubbed surface of Al–Si alloy were examined by X-ray Photoelectron Spectrometer (XPS). The wear debris of Al–Si with the lubrication of triethylenetetramine was collected and evaluated with FT-IR, and thermal gravimetric (TG) analysis. Friction and wear tests reveal that triethylenetetramine shows the best antiwear capabilities among the tested compounds. The results of FT-IR, TG and XPS indicate the occurrence of tribo-chemical reactions between Al and amine with the formation of a chemically stable complex of aluminum and amine, as well as the formation of friction polymer.

An exploratory study of vapor-phase lubrication of ceramics by monomers

Abstract Earlier studies on the use of the concept of tribopolymerization as an anti-wear mechanism for ceramics involved liquid carriers such as pure hydrocarbons (e.g. hexadecane) and mineral oils at temperatures ranging from ambient to 150°C. Recent studies have been carried out to determine the effects of potential tribopolymer-forming compounds on ceramic wear in the vapor phase using an inert gas carrier. Three addition-type monomers selected on the basis of the tribopolymerization concept were studied. The liquid additives were heated, vaporized and delivered to an enclosed alumina-on-alumina “pin-on-disk” contact region by a stream of dry nitrogen gas. The results of tests at bulk specimen temperatures up to 145°C showed that indeed significant reductions in ceramic wear were produced by the low vapor concentrations of these compounds in the nitrogen carrier gas. Alumina ball wear reductions of up to 99% were observed, and total wear reductions (ball and disk) of over 70% were also common. Colorful surface films visible to the naked eye were frequently observed. Higher compound delivery temperatures have a significant beneficial effect in reducing wear. Analysis of the worn surfaces using Fourier transform infrared micro-spectroscopy shows clear evidence of chemical reactions with the alumina surface to form soap-like compounds; in addition, evidence of surface polymerization with one of the monomers, diallyl phthalate, was obtained. It is believed that the surface films formed reduce adhesion and therefore decrease both wear and friction. These studies are continuing in an attempt to learn more about the detailed mechanisms involved.

Tribochemistry of Fluorinated Fluids Hydroxyl Groups on Steel and Aluminum Surfaces

This paper describes products of tribochemical reactions of Z-Dol 2500 and 1H,1H,2H,2H-tetra-fluorooctanol, produced on steel and aluminum surfaces. The fluorooctanol was used as a model compound to study the reactions of hydroxyl groups. Tribochemical reactions were initiated by friction in the steel/steel and steel/Al contacts, using an Optimol SRV (Schwingung Reibung Verschleiβ) reciprocating sliding tester. The products of these reactions, deposited in the wear scars on steel and Al discs, were studied using reflective FTIR spectrometry (microscopy and grazing angle) and X-Ray photoelectron spectroscopy (XPS). Under boundary lubrication conditions on metal surfaces, fluorinated compounds containing hydroxyl groups formed carboxylic and alkoxyl salts. FTIR spectra indicate that Fe and Al carboxylic salts occur mainly in bidentate configuration. Presented at the STLE Annual Meeting in Las Vegas, Nevada May 15-19, 2005 Review led by Tom Karis

Lubrication studies of head-disk interfaces in a controlled environment Part 2: Degradation mechanisms of perfluoropolyether lubricants

Abstract The decomposition mechanisms of the perfluoropolyether (PFPE) lubricants were studied in this paper using several experimental approaches. The PFPE lubricant film can be bonded to disk surface by illuminating the lubricant film with ultraviolet (UV) light; then the durability of the head-disk interface can be improved. However, during the sliding process, the illumination with UV light can accelerate the decomposition of the lubricant, reducing the head-disk interface durability and causing more gaseous fragments because low-energy electrons created by the illumination interact with the lubricant molecules, activating and breaking up the molecules. A decomposition mechanism of the lubricant with the effect of low-energy electrons was proposed. Mechanical shear is also found to have an important effect on the decomposition of the lubricant. The partial pressures of the gaseous fragments of the lubricant increase rapidly with increase in the sliding velocity. No obvious effect of ambient temperature up to 70 °C on the decomposition of the PFPE lubricant was observed, although higher temperatures are expected to be detrimental.

About a negative-ion concept of the antiwear and antiseizure action of hydrocarbons during friction

Abstract A new negative-ion concept of the mechanism of lubrication of hydrocarbons has been derived. The thesis of the concept is based on the mechanism of ionization of saturated and aromatic hydrocarbons caused by the action of exoelectrons. The following stages have been considered in the model: (a) the low energy electron (2–3 eV) emission process and creation of positively charged spots; (b) the reaction of the emitted electrons with hydrocarbon molecules adsorbed on the rubbing surface, leading to the formation of negative ions and radicals; (c) the reaction of the negative ions with the metal surface. The proposed model explains the untypical behaviour of these hydrocarbons under different atmospheres in the friction process.

Tribological performance of PFPE and X-1P lubricants at head–disk interface. Part II. Mechanisms

This paper, with the concepts of hydrogen bonding interaction and tribo-emission, develops a new approach of the mechanism of perfluoropolyether (PFPE) lubricant degradation at the head–disk interface. The role of lubricant X-1P in tribological performance is also described. The mechanism is as follows: (1) at the interface, there exist hydrogen atoms with partial positive charge and oxygen atoms with partial negative charge; (2) hydrogen bonding interactions at the sliding interface result in high friction which depletes the lubricant film at some sites; (3) low energy electrons are emitted from the sites with solid–solid asperity contact, inducing C–O bond scission through the interaction of low-energy electrons with PFPE lubricant molecules. Carbon overcoat on Al2O3–TiC surface passivates the interaction between water and PFPE lubricant molecules. Hydrogen bonding interactions are minimized during the presence of lubricant X-1P. The new approach well explains experimental results in part I of the paper.

Tribo-catalysis in the synthesis reaction of carbon dioxide

Palladium was rubbed against aluminum oxide in an atmosphere of carbon monoxide and oxygen. The synthesis of carbon dioxide was enhanced during the rubbing. The activation energy of this reaction was 2.49 kJ/mol. As the sliding commenced, the desorption of carbon dioxide overshot its equilibrium value before stabilizing. The overshoot correlated with the time interval between the friction tests. The desorption mechanism of carbon dioxide is discussed in terms of the NIRAM (negative-ion-radical action mechanism) approach; exoelectron emission was enhanced by the friction of palladium. The electrons reacted with the adsorbed species to make negative-ion-radicals. These radicals further reacted on the surface to form carbon dioxide, which then desorbed.

Interactions of n-Hexadecane with 52100 Steel Surface Under Friction Conditions

Straight-chain aliphatic hydrocarbons, particularly n-hexadecane, are used as reference fluids in research concerning the AW/EP effectiveness of triboactive additives. It is assumed, however, that under boundary lubrication conditions these apparently non-reactive hydrocarbons might influence the tribochemistry of the additives because aliphatic compounds also undergo chemical reactions. Both the thermochemical and tribochemical oxidation of aliphatic hydrocarbons lead to the formation of triboactive products (e.g. alcohols, aldehydes and carboxylic acids). Interactions of these compounds with rubbing surfaces were examined using GC/MS, XPS and EDS techniques. It has been found that carboxylic acids react with the iron surface generating salts or complex compounds.