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.     

The defensive secretion of Carabus lefebvrei Dejean 1826 pupa (Coleoptera,Carabidae): Gland ultrastructure and chemical identification

This study documents the defensive function of flavored humor secreted by the abdominal glands of Carabus lefebvrei pupae. The morphology and the ultrastructure of these glands were described and the volatile compounds of glands secretion were identified by gas chromatography/mass spectrometry. The ultrastructure analysis shows an acinose complex formed by about 50 clusters. Each cluster has 20 glandular units and the unit—composed of one secretory and one canal cell lying along a duct—belongs to the class 3 cell type of Quennedey (1998). In the cytoplasm, the secretory cell contains abundant rough endoplasmatic reticula, glycogen granules, numerous mitochondria, and many well-developed Golgi complexes producing electron-dense secretory granules. Mitochondria are large, elongated, and often adjoining electronlucent vesicles. The kind and the origin of secretory granules varying in size and density were discussed. The chemical analysis of the gland secretion revealed the presence of a mixture of low molecular weight terpenes, ketones, aldehydes, alcohols, esters, and carboxylic acids. Monoterpenes, especially linalool, were the major products. We supposed that ketones, aldehydes, alcohols, esters, and carboxylic acids have a deterrent function against the predators and monoterpenes provide a prophylaxis function against pathogens. Microsc. Res. Tech., 2009. © 2008 Wiley-Liss, Inc.     

New synthetic esters with a complex structure considered as tribological fluids

The paper presents results concerning synthesis and characterisation as lubricant fluids of some esters of different monocarboxylic acids with variable chain length, along with aliphatic‐aromatic complex alcohols and/or with superior alcohols (exclusive of aliphatic). The monocarboxylic acids taken into account were n‐butyric, n‐octanoic and oleic, respectively, while the alcohols considered were isodecyl and isotridecyl as purely aliphatic, and 2‐phenoxy‐ethanol, 2‐[(o‐sec‐butyl)phenoxy]ethanol and 2‐[(p‐nonyl)phenoxy]ethanol, as part of the complex aliphatic‐aromatic alcohols group. Under these circumstances, it became possible to study the influence of the structure on the main physico‐chemical properties of these synthetic oils as well as on their tribological representative features. The results recorded certified the validity of the proposed research programme. Copyright © 2009 John Wiley & Sons, Ltd.     

Proposal of an FTIR Methodology to Monitor Oxidation Level in Used Engine Oils: Effects of Thermal Degradation and Fuel Dilution

This article describes a procedure, based on ASTM standards D7214 and E2412, that has been defined to improve quantification of oil oxidation in used engine oils. Taking into account typical problems that can be found in this type of sample, including thermal oxidation and fuel dilution, Fourier transform infrared (FTIR) spectra were analyzed also considering the effect of the oil formulation. Two zones were considered inside the typical wavenumber range for quantification of oxidation, where those problems can be detected and assessed more easily: zone A between 1725 and 1650 cm^?1, where the main oxidation products, such as aldehydes, carboxylic acids, and ketones, occur due to thermal degradation of the oil; and zone B between 1770 and 1725 cm^?1, where esters due to potential biodiesel dilution problems are detected.     

The Effect of Temperature on Tribological Properties of Chemically Modified Bio-Based Lubricant

Vegetable oil has several characteristics that provide advantages for use as lubricant. This includes a high viscosity index, high flash point, high biodegradability, and friction and wear reduction properties. However, vegetable oil has some disadvantages such as low oxidation stability and low thermal stability. The transesterification process of palm oil using trimethylolpropane (TMP) alcohol has been proven to reduce the oxidation stability of vegetable oil. However, little research has been carried out on the effect of TMP ester as a lubricant in term of friction and wear. Therefore, this study investigated the effect of temperature on the tribological properties of TMP ester using a four-ball machine. The load and speed of the sample were set at 40 kg and 1,200 rpm, respectively. Temperature was varied between 50 and 100°C. It was found that TMP ester improved the friction properties by around 15–20%. At low temperature, TMP esters have a higher coefficient of friction (COF) compared to paraffin oil. However, as the temperature increased higher than 80°C, paraffin oil had a highere COF value. This is because at high temperature, the lubricant filmed formed by fatty acids tends to be less stable and breaks down more easily.     

The Determination of Vapor Pressures of Low Viscosity Lubricants from Distillation Data

The vapor pressure of low viscosity aliphatic hydrocarbon lubricants is shown to be determined with good accuracy from data obtained from a modification of the ASTM Distillation Test D86-67. This test gives the initial boiling point of a lubricant from which the vapor pressure at any other temperature can be calculated by use of an empirical equation relating the boiling point to the vapor pressure.

Two other equations were derived, one relating the viscosity of an aliphatic hydrocarbon lubricant to the vapor pressure at any temperature, and the other extending the use of this distillation method to calculation of the vapor pressures of other types of lubricants as, for example, esters, alcohols, and acids.

The data presented indicate that this method is superior to the isoteniscope method in accuracy and ease of operation.     

Formation of adhesive bonds under contact rotaprint lubrication

The mechanism of the formation of adhesive bonds of a friction modifier (a lubricant based on bitumen) with a wheel of railway transport is considered. Calculations performed using quantum chemical methods allow us to draw a conclusion on the existence of the physical adsorption of this lubricant on a wheel surface. The lubrication’s effectiveness can be improved using fatty acids whose introduction into the lubricating material leads to the formation of chemical bonds in the system; this is experimentally confirmed for the contact rotaprint lubrication technology.     

Studies on boundary lubrication properties of oxidised coconut and soy bean oils

Vegetable oils are a potential source of base oils for biodegradable lubricants, with limited oxidative stability. This study focuses on the effect of long‐term ageing and the influence of oxidation products on the boundary lubrication performance of coconut and soy bean oils, by subjecting them to accelerated ageing in a dark oven at elevated temperature. The samples were collected at regular intervals and analysed for the changes in viscosity, percentage of free fatty acid and peroxide number compared to fresh oil samples. The boundary lubrication properties of these samples were evaluated using a four‐ball tester. Increased wear observed with aged oil samples was linked to the destruction of triglyceride structure and formation of peroxides. The difference in the wear properties of soy bean oil to coconut oil was accounted by its high content of unsaturated fatty acids and its susceptibility to undergo oxidation. It was concluded that the coconut oil can perform as a better lubricant and has got a better storage life compared to soy bean oil. Copyright © 2009 John Wiley & Sons, Ltd.     

Oxidative degradation of synthetic ester and its influence on tribological behavior

The oxidative degradation process and oxidation mechanism of di-2-ethylhexyl sebacate (DEHS) were studied in present work. GC–MS results revealed that 2-ethyl-1-hexanol and mono (2-ethylhexyl) sebacate were major degradation products in the liquid phase. Further investigation of degradation mechanism of DEHS showed that oxidation reactions and hydrolysis were main factors degradation of DEHS. The four-ball test results showed that chemical composition changes of DEHS during oxidation could significantly influence its tribological behavior. The formation of hydroperoxides in the initial oxidation period could seriously deteriorate lubrication properties of DEHS. However, as the oxidation proceeded, high polar products (acids, alcohols and monoesters) formed could significantly improve the anti-wear and friction-reducing properties of DEHS.     

The influence of oxidation on the tribological performance of diester lubricant

The oxidative degradation test of di‐2‐ethylhexyl sebacate (DEHS) was carried out by a sealed stainless steel reactor. Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry (GC–MS) were utilised to characterise the chemical composition and molecular structure of the oxidation products. The results revealed that 2‐ethyl‐1‐hexanol and mono(2‐ethylhexyl)sebacate were major degradation products in the liquid phase. Tribological behaviour was measured using a four‐ball tester. Scanning electron microscopy was employed to investigate the morphologies of the worn surface. Tribological results showed that anti‐wear and friction‐reducing performances of DEHS were highly dependent on the chemical composition of the oxidation products generated during the test. The hydroperoxides formed during the initial oxidation process could deteriorate lubrication properties of DEHS. However, certain amount of highly polar degradation products (acids and alcohols) generated could significantly improve the friction‐reducing performance of DEHS by the formation of boundary adsorption films on the rubbing surfaces. Copyright © 2013 John Wiley & Sons, Ltd.     

脂肪酶Novozym435改性大豆油的摩擦学性能研究

为提高食用大豆油作为润滑剂的抗磨性能,在超声振动条件下采用脂肪酶Novozym435作为催化剂使食用大豆油中的不饱和脂肪酸与甲醇进行环氧化反应,在温和反应环境下合成一种改性大豆油.利用红外、拉曼光谱仪对其结构进行表征,使用同步热分析仪TG-DSC考察其热氧化稳定性,在四球机上考察其摩擦磨损性能,用扫描电子显微镜、三维表...     

A mechanism of thermo-oxidative degradation of polyol ester lubricants

Polyol ester lubricants are used in a wide range of temperature conditions, normally from −54 up to +220 °C, and their application can be limited by high temperature oxidation leading to viscosity increase, sludge, and/or formation of deposits. This paper is concerned with the chemical processes which take place during the oxidation of esters, particularly polyol esters, and discusses the selectivity of oxygen attack on ester molecules, and the formation and decomposition of hydroperoxides as well as other products formed as a result of ester oxidation. Proposed mechanisms of polyol ester lubricant oxidation are discussed, and unresolved problems which require additional research efforts are revealed.     

Hydrogen's interaction with hardened surface layers in lubricated frictional couples

The obtained results confirmed the influence of surface layer structure on the boundary layer durability of oil in concentrated contact. The advantageous effect of increased concentration of hydrogen in surface layer on the quality of lubrication as well as its significant contribution to tribological process was validated. The results of boundary friction for different structures of surface layer will be presented taking into consideration or not the influence of hydrogen on their durability. The experimental methods were based on the measurements of relative time when the short circuit was present in lubricated frictional nodes, chromatography and low-temperature diffraction measurements. The physico-chemical model of interaction between lubricant (oil base and motor oil) and hardened elements varied from chemical and structural point of view has been proposed. The model is based on the specific interactions of protons with aliphatic chains of lubricant.     

Thermal oxidative ageing of neopentylpolyol ester oils: Evaluation of thermal-oxidative stability by quantitative determination of volatile ageing products

During thermal-oxidative ageing of pentaerythritol ester-based oils a variety of volatile degradation products, eg acids, aldehydes, ketones, esters and O-heterocyclic compounds are produced. It is shown that quantitative determination of individual acids and carbonyls using GC-MS and/or HPLC can be used to assess the ageing behaviour of fully formulated aviation turbine oils. Of special importance is the Tenax-GC method which allows a simultaneous determination of all volatile degradation products by GC-MS. This is the third of a series of papers on thermal-oxidative ageing of neopentylpolyol ester oils.^1,3     

Effect of chemical structure of aramide and polyoxadiazole fibers on friction of organoplastics

Unlike aliphatic polyamides, the friction coefficient of polyaramides depends not only on the relative concentration of hydrogen bonds in a macromolecule unit, but also on the structural factor, which is related to various positions of the hydrogen bonds in a phenylene nucleus, in this case, the para- and metapositions. During dry friction, aramide organoplastics are characterized by a high coefficient of friction, while for materials based on polyoxadiazole fibers, a low and stable coefficient of friction is retained.     

Tribochemistry of n‐hexadecane in different material systems

Hexadecane is widely used as the model base oil to investigate both tribological effectiveness and tribochemical reaction mechanisms of various antiwear and extreme pressure additives. On the other hand, it is well known from existing references that hexadecane, similarly to hydrocarbon oils, oxidizes during the lubrication process of tribological systems. It has frequently been pointed out that carboxylic acids are formed which — reacting with rubbing surfaces — generate soaps. Most recent studies, however, demonstrate that the oxidation process under friction conditions is very complex and the major oxidation compounds from hexadecane under boundary friction conditions relate to other oxygenates than carboxylic acids. This paper aims to examine what types of surface compound are generated from the hexadecane lubricant in the friction contact zone. Tribological tests were performed on a ball‐on‐disc tribometer. The discs used were made from several materials (steel, aluminium, brass, bronze). Fourier transform infrared (FTIR) microspectrophotometry and techniques involving a scanning electron microscope equipped with an energy‐dispersive spectrometer were used to analyse tribochemical reaction products formed on different substrates. Analytical results obtained clearly demonstrate a similar tribochemical reaction process operating on all the metals tested. The FTIR results obtained allowed new absorption bands to be discovered and accounted for. These absorption bands have been assigned to specific complex compounds. Copyright © 2006 John Wiley & Sons, Ltd.     

Tribological properties of AlCoCrFeNiCu high-entropy alloy in hydrogen peroxide solution and in oil lubricant

Pin-on-disc tests to investigate the tribological behavior of AlCoCrFeNiCu high-entropy alloy under lubrication conditions with 90% hydrogen peroxide solution and lubricant oil, respectively, were performed. The study demonstrates that the AlCoCrFeNiCu high-entropy alloy lubricated correspondingly with lubricant of 90% hydrogen peroxide solution (hereafter termed hydrogen peroxide lubricant) and lubricant oil significantly improves its friction and wear-resistance properties. Results showed that the friction coefficient, after a grinding stage, of the rubbing pair was lower than that with normal lubricant oil. The AlCoCrFeNiCu alloy in the lubricant with 90% hydrogen peroxide solution and lubricant oil exhibits a high resistance to wear. Analysis of the worn surface revealed that the AlCoCrFeNiCu high-entropy alloy lubricated with the hydrogen peroxide lubricant exhibited signs of inhomogeneous polishing oxidation and abrasive wear, with the wear mechanism changing with sliding distance, while the rubbing pair in normal lubricant oil is mainly dominated by abrasive wear.     

New unsymmetrical complex diesters of adipic acid considered as tribological fluids

The paper presents results concerning the synthesis and characterisation of some unsymmetrical diesters of adipic acid with a mixed, complex structure in order to produce synthetic ester oils with specific tribological properties. These complex diesters have been synthesised by taking into account medium and superior aliphatic alcohols, such as n‐butanol, n‐hexanol, 2‐ethyl‐hexanol, isodecanol and isotridecanol along with special alcohols of a complex alkyl–aryl nature, namely 2‐phenoxy‐ethanol, 2‐([o‐sec butyl] phenoxy) ethanol and 2‐([p‐nonyl] phenoxy) ethanol, respectively. By varying the length of the aliphatic alcohols and also by modifying the length and position of the alkyl pendant group on the aromatic ring of the complex alkyl–aryl alcohols, three series of products have been realised. On the basis of this programme, it has been possible to obtain fluid products that show valuable tribological features with adequate and versatile characteristics. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthetic lubricants based on sebacic complex esters

This paper presents the results of a study carried out in order to produce synthetic ester oils of a mixed structure based on sebacic acid with beneficial tribological properties. These series of unsymmetrical diesters were synthesized using superior aliphatic alcohols such as 2‐ethyl‐hexanol, isodecanol and isotridecanol, along with special alcohols of a complex alkyl‐aryl structure, namely 2‐phenoxy‐ethanol, 2‐[(o‐sec butyl) phenoxy] ethanol and 2‐[(p‐nonyl) phenoxy] ethanol. Also synthesized were symmetric esters based on the complex aliphatic‐aromatic alcohols with pendant aliphatic chain. The variation in the principal properties as a function of both the length of the aliphatic chain introduced by the aliphatic alcohol, and the length and position of the aliphatic pendant chain on the aromatic nucleus of the complex alkyl‐aryl alcohol was assessed. Based on this, it has been possible to obtain fluid products with variable properties. The introduction of the aromatic function in the structure of these diesters led to interesting features, and the superior values recorded for the main tribological characteristics demonstrated their versatility. Copyright © 2006 John Wiley & Sons, Ltd.     

Sxynthesis and properties of adamantane synthetic lubricants

Adamantane hydrocarbons and esters have already been described in the literature. This paper examines the properties of two types of adamantane oils, tri- and tetrabutyladamantanes, and esters prepared from adamantyl methanols and aliphatic acids, and alkyladamantane carboxylic acids and aliphatic alcohols. The preparation, properties and in particular the electrical properties are presented.