Lithium Grease Research Articles

Additive Effect of Carbon Nanohorn on Grease Lubrication Properties

Recently, applications of the carbon nanohorn (CNH) have become of great interest in various industrial fields. The load carrying capacity and wear resistance of lithium soap grease containing CNH and heat-treated CNH (HT-CNH) were studied using a Falex friction tester, and compared with those of grease containing reference carbon materials such as graphite, cluster diamond (CD), and graphite cluster diamond (GCD). The load carrying capacity of the greases with carbon materials was always higher than that of the base grease. The greases with CNH and HT-CNH had the same or higher seizure load than those with CD and GCD. In particular, the grease with HT-CNH exhibited good load carrying capacity even at a low concentration of 1 mass%. The grease with 3 or more mass% graphite had the highest seizure load of all greases in this study. The grease with HT-CNH showed the best wear resistance of all greases in this study. The wear resistance of the grease with other solid lubricants was the same or inferior to that of the base grease.

Preparation of soybean oil-based greases: effect of composition and structure on physical properties.

Vegetable oils have significant potential as a base fluid and a substitute for mineral oil in grease formulation. Preparation of soybean oil-based lithium greases using a variety of fatty acids in the soap structure is discussed in this paper. Soy greases with lithium-fatty acid soap having C12-C18 chain lengths and different metal to fatty acid ratios were synthesized. Grease hardness was determined using a standard test method, and their oxidative stabilities were measured using pressurized differential scanning calorimetry. Results indicate that lithium soap composition, fatty acid types, and base oil content significantly affect grease hardness and oxidative stability. Lithium soaps prepared with short-chain fatty acids resulted in softer grease. Oxidative stability and other performance properties will deteriorate if oil is released from the grease matrix due to overloading of soap with base oil. Performance characteristics are largely dependent on the hardness and oxidative stability of grease used as industrial and automotive lubricant. Therefore, this paper discusses the preparation methods, optimization of soap components, and antioxidant additive for making soy-based grease.

Fatty acids and antioxidant effects on grease microstructures

The search for biobased material as industrial and automotive lubricants has accelerated in recent years. This trend is primarily due to the nontoxic and biodegradable characteristics of seed oils that can substitute mineral oil as base fluid in grease making. The paper discusses the preparation of lithium soap-based soy greases using different fatty acids and the determination of crystallite structure of soap using transmission electron microscopy (TEM). Lithium soaps with palmitic, stearic, oleic, and linoleic acids were synthesized and mixed with soybean oil (SBO) and additives to obtain different grease compositions. TEM measurements have revealed that the soap crystallite structure impact grease consistency. Soap fiber length and their cross-linking mechanism in the matrix control grease consistency (National Lubricating Grease Institute (NLGI) hardness, ASTM D-217 method). Lithium stearate-based soy grease has a relatively more compact fiber structure than Li palmitate. Linoleic acid (C 18,  ) with two sites of CC unsaturation in the chain has a much thinner and more compact fiber network than oleic acid (C 18, ). The presence of additive in grease produces a soap with looser network and larger fiber structure than similar grease containing no additive. A close analysis of grease microstructure will help in the development of better performing grease for industrial applications.

Some aspects of cold upset forming of sintered aluminium preforms using different lubricants

Cold upset forming and densification features in sintered aluminium preforms using different lubricants were investigated. Cylindrical preforms with an initial theoretical density of 91% and 0.75 aspect ratio were prepared using a suitable die, a punch and a die bottom insert on a 1.0 MN capacity universal testing machine. The preforms were well covered with dry fine silica sand and sintered in an electric muffle furnace at 520 ± 10°C for a period of 1 h and then furnace cooled. Cold deformation experiments were carried out in several steps. Dimensions such as height, contact and bulged diameters and densities were measured for each test. In general, each compact was subjected to compressive loading in steps of 0.01 MN until fine cracks appeared on its free surface. Analysis of the experimental data showed an increasing trend in the value of exp(ϵz-ϵθ). Further, it was found that preform lubricated with lithium grease exhibited enhanced densification compared to that for MoS2 or graphite lubricant, provided that the initial preform density and aspect ratio were kept constant. The instantaneous strain hardening exponent ni and strength coefficient ki of the aluminium preforms were calculated and found to reach the peak value when the deformation or packing density was at low value. Further, it was observed that the value of ni and ki decreased and was found to be constant for both the lubricant preforms tested. It was established that the initial geometry of the PM preforms played a predominant role in influencing both ni and ki.

Double Decomposition Reactions for the Production of Alkaline and Alkaline-Earth Oleic Soaps under Salting-Out Conditions

Double decomposition reactions are studied through the screening of crude oleic soaps and inorganic compounds. Our study agrees with the exchange theory formulated for pure soaps: reactions proceed in the direction of the formation of the most insoluble compound under salting-out conditions. By studies on exchange reactions between lithium soap and calcium chloride, we define a domain of LiOOCR/CaCl2/H2O mixtures in which conversion of the lithium soap into the calcium one is highest: under stoichiometric conditions (LiOOCR/CaCl2 = 2/1), calcium chloride should be dilute ([CaCl2] = 11−19 g/L), and under conditions of excess calcium chloride (LiOOCR/CaCl2 = 2/4.9), it can be less dilute ([CaCl2] = 53 g/L). Kinetic studies indicate that the yield of the LiOOCR/CaCl2 exchange reaction is highest for reactions carried at 90 °C for 3 h. These reactions kinetics can be enhanced by adding ethanol to the aqueous medium (50 wt % at 50 °C and 25 wt % at 90 °C).

Fourier‐transform infrared spectra of fatty acid salts—Kinetics of high‐oleic sunflower oil saponification

AbstractSodium, lithium, and calcium soaps obtained by saponification of high‐oleic sunflower oil were studied by Fourier‐transform infrared spectroscopy. Spectra of crude mixtures containing soap, glycerin, residual alkali, and triacylglycerols were compared to those of pure soaps obtained from fatty acids. The infrared spectra of crude soaps showed the same characteristic bands as pure ones. The absorption bands of asymmetric (ω2) and symmetric (ω1) stretching vibrations of the carboxylate group indicated that the metal‐oxygen bonds of these soaps had an ionic character whose strength differed from one cationic counterion to another. Once the characteristic absorption bands of the soaps were assigned, a kinetics study of saponification was performed. Saponification by sodium, anhydrous lithium, and calcium hydroxides was an autocatalytic reaction, characterized by an S‐shaped kinetics curve, whereas saponification by aqueous lithium hydroxide was stoichiometric. The structure of the metal‐oxygen bond played a role in the kinetic mechanisms.

The Effect of Metal 8-Hydroxyquinolinates as Lubricant Additives on the Friction Process

This paper presents an investigation of tribological properties of lithium grease with 8-hydroxyquinoline complexes with copper, zinc, cobalt, cadmium, lead and manganese. The tribological tests were performed on a T-02 four-ball machine produced at the Institute for Terotechnology (ITeE) in Radom. The influence of the applied additive on the friction coefficient and wear was discussed. Compositions containing complexes of copper, cadmium and lead show the most significant effect on the reduction of motion resistance and wear, especially at high loads. The results of seizure tests performed according to the procedure of M. Szczerek [1,2] are also presented. The highest seizure load was obtained for lubricants containing copper and cadmium, while the highest limiting pressure of seizure—for the copper complex. The observed changes in antiseizure properties can be interpreted as a result of destruction of complexes and formation of protective metallic layers. The presence of deposited metal from the complexes was confirmed by X-ray microanalysis surface tests.

Modification of contact surfaces by fullerene-like solid lubricant nanoparticles

Recently, it has been established that WS2 and MoS2 nanoparticles (IF) mixed in oil, and impregnated into porous matrix of powdered materials appear to enhance the tribological properties in definite loading range in comparison to typical metal dichalcogenides particles. Modification of the contact surface by IF-WS2 nanoparticles from oil, grease and from pores of densified powdered samples is considered in this work. The role of the IF solid lubricants as a part of a third body is discussed also in this work. The effect of the IF in oil was studied using a pin-on-disk tester. The study of IF in greases and impregnated into the pores of densified matrices was performed using a ring-block tester. The state of the mating surfaces and the nanoparticles before and after the friction test has been studied by TEM, SEM and XPS. It was established that the IF nanoparticles form a protective film allowing an increase in the load capacity of rubbed pairs. The tribological behavior of lithium grease with IF was found to be appreciably better than that of a commercially available grease incorporating MoS2 platelets (2H). It is found that the IF nanoparticles lead to improved tribological behavior of greases with the IF nanoparticles under very high loads. Impregnation of the IF-WS2 into the pores of densified powdered materials provides a reduced friction coefficient and wear rate over a wide load range in comparison to 2H solid lubricant. The main advantages of the IF nanoparticles is ascribed to the release and furnishing of the nanoparticles from the open pores onto the metal surface and their confinement at the interface, which is not possible with dense flat surfaces. It is expected that the spherical shape of IF nanoparticles facilitate their sliding/rolling between the rubbed surfaces.

Total vegetable‐oil based greases prepared from castor oil

AbstractTotal vegetable oil greases are those in which both the lubricant and gellant are formed from vegetable oil. Vegetable oil may be used as a lubricant as such or, with appropriate structural modification, as an ester or alkylated ester. Total vegetable oil greases have the advantage of good biodegradability and conform to the requirements for high performance.Total vegetable‐oil based greases can be formed by mixing preformed soap and lubricant in the required proportions to form a grease with the desired properties. Alternatively, a grease can be formed from the same vegetable oil by simultaneous alcoholysis and saponification of the oil to form the lubricant and soap. The alkali used as a catalyst for the alcoholysis reaction serves as a reactant for the saponification reaction. The use of the appropriate proportion of oil, alcohol, and alkali will thus form a grease of the desired composition.A simultaneous reaction scheme to form sodium and lithium grease using castor oil has been studied. The alcoholysis reaction is separately studied for its kinetics, and the kinetics of the alcoholysis and saponification reaction are reported. Greases with 20% soap have been formed and their properties evaluated.

Tribological Performance of Some Pennzane®-Based Greases for Vacuum Applications

Commercial greases for space applications usually fulfill the requirements imposed by the severe conditions of use (load, ultrahigh vacuum, speed, etc.). The main requirement is their ability to create an elastohydrodynamic lubrication film, boundary film, or both, for the speed, load, and temperature conditions under which the mechanisms will operate. Three greases, all based on a multiply alkylated cyclopentane (Pennzane®) base oil, were studied. The thickeners were an n-octadecylterephthalamate soap, a lithium soap, and a urea derivative. A four-ball tribometer and a spiral-orbit tribometer were employed to evaluate the greases under ultrahigh vacuum. The results indicated that all three greases yielded very low wear rates and extended lifetimes. In addition, routine physical property data are reported for each grease.

Technical note: Extreme‐pressure activity assessment of certain nitrogen and sulphur compounds in lithium‐based grease

AbstractIn this paper we report on the preparation and extreme‐pressure (EP) activity assessment of certain substituted 1‐amino‐3‐aryl‐2,3‐dihydro‐2‐thioxo‐4,6‐(1H,5H)‐pyrimidinediones as additives in a lithium‐based grease. These additives significantly decreased the wear and friction and possessed the ability to increase load‐carrying capacities and weld loads. Two greases were prepared with the above additives, and both greases exhibited lower values of wear‐scar diameter at higher loads and higher values of weld load in the four‐ball test than the lithium‐based grease alone. The prepared greases also passed rust and corrosion, and oxidation tests.

Kinetics and Thermal Decomposition of Lithium Soaps

Kinetics and Thermal Decomposition of Lithium Soaps

Study on Fiber Length Control for Ester-Based Lithium Soap Grease

The soap fiber structure of ester-based lithium soap grease influences its tribological performance such as friction and wear, so that the effect of the producing conditions of ester-based lithium soap grease on the fiber length was investigated. Decreasing the soap concentration or increasing the cooling rate could produce long fiber grease. In contrast, short fiber grease could be produced by increasing the soap concentration or raising the cooling rate, since the growth of soap fiber in cooling process was restricted in very short time for high concentration or high cooling greases. In addition, keeping grease at a temperature fluctuating near the dissolution temperature of soap or heat retention process was effective in promoting the growth of soap fiber. Especially the addition of soap powder to grease in the heat retention process brought about the generation of gigantic fibers. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001

Grease Life Prediction for Sealed Ball Bearings

Sealed ball bearings are used widely for electric motors and automotive components. Appropriate grease is selected for the each application, considering grease life, bearing torque, sound characteristics, etc. Recently, as these components have become progressively more compact, the sealed ball bearings are required to operate at higher temperatures and rotational speeds. In such cases, grease life has become more critical in determining the bearing's overall life. Therefore, it is important to estimate grease life in order to select the appropriate grease and predict the life of the final product. In this paper, the grease life formulas for both urea and lithium soap greases were generated. The formulas were derived from grease life data generated on 6204 bearings with inner ring rotation. The formulas were composed of temperature, rotational speed and applied load terms. These terms were obtained, based on the test results, the temperatures from 100 °-180 °C, the rotational speeds from 10,000–20,000 revolutions per minute (rpm) and the axial loads from 67-670 N, respectively. The grease life formulas were further improved to be applicable to outer ring rotation bearings. It was found that the grease life in bearings with outer ring rotation was shorter than for bearings with inner ring rotation. The difference in cage rotational speed was found to affect the grease life. By adding a correction factor for outer ring rotation to the rotational speed term, the same grease life formula, independent of rotational type, can be utilized. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

Conductance behavior of lithium soaps in aqueous methanol

AbstractConductance behavior of lithium soaps (abietate, oleate, and myristate) has been used to evaluate the true dissociation constant, limiting molar conductance, and thermodynamic parameters (viz., enthalpy, free energy, and entropy changes) for dissociation. The soaps behave as week electrolytes in mixtures, and the Debye‐Huckel‐Onsagar equation is not applicable for these soap solutions.

Mechanical Contact Frequency Response Measurements

This paper presents friction frequency response measurements taken from a planar steel contact subjected to controlled random broadband normal vibration. Data are included from both dry and various lubricated contact conditions under different vibration input levels and different sliding velocities. Frequency response data for dry contacts are found to have nearly steady magnitude and negligible phase lag over a relatively wide range of frequencies. This suggests a coefficient of friction, independent of frequency but dependent on levels of normal acceleration and sliding velocity, may adequately define the dry contact frequency response. The frequency response data for lubricated contacts are mixed. For example, with MoS2 grease the frequency response may adequately be defined by a constant, as with dry conditions. However, frequency response data for contacts with pure mineral oils, mineral oils with additives, and lithium grease are found to be dependent on frequency. [S0742-4787(11)00101-9]

Oleochemicals I: Studies on the preparation and the structure of lithium soaps.

Lithium stearate, palmitate, myristate, laurate, caprate and caprylate were prepared by means of fusion method. Elementary analysis and the infrared absorptions spectra of the prepared lithium soaps as well as their X-ray diffractions and the thermogravimetric analyses were carried out. The anhydrous lithium salts of fatty acids with 12 carbon atoms or less showed thermal stability up to ca. 300 ± 78 °C depending on the chain length. On other hand the salts with 14 carbon atoms or more were decomposed at 126 ± 4 °C leading to formation of lithium carbonate. The homologous lithium soaps had very similar crystal structure among them and their metal -to- oxygen bonds were similar for the acyl chains between 8 and 18 carbons. However the angle of inclination of the molecular axes to the basal plane increased with the decreasing of the number of carbon atoms of the fatty acid chain, as determined by X-ray diffraction. In addition, the ionic character of the metal -to- oxygen bond was enhanced with the decrease of the number of carbon atoms as shown by infrared spectroscopy.

The synthesis of sucrose ester and selection of its catalyst

Sucrose fatty acid ester (called sucrose ester for short) is a kind of non-ionic surface active agent with excellent performance and many uses. This paper describes the process of synthesis and selection of its catalyst. The results show that neutral lithium soap oil acid is the best catalyst for the synthesis of sucrose ester. Using mixed alkali metal soap with proper ingredient ratio as catalyst can improve the yield of sucrose ester.

Biogenic sedimentary structures produced by worms in soupy, soft muds; observations from the Chattanooga Shale (Upper Devonian) and experiments

Abundant trace fossils occur within rhythmically interbedded black and gray shales of the Chattanooga Shale (Upper Devonian) in central Tennessee. Burrows cross the boundaries between layers and tend to obscure the contacts between alternate layers. Infills of individual burrows often display an array of complex, convoluted features, apparently due to mixing of soft to soupy black and gray muds. Assuming that the burrowers were elongate worm-like organisms, experiments were made to study the relationships between the general morphology of burrowers (simple worms, worms with appendages, etc.), sediment viscosity, and textural features. Rubber bait worms were pulled through superimposed layers of plaster in a first set of experiments. Comparable experiments were then conducted with earthworms. The resulting textures were studied by sawing the hardened plaster blocks perpendicular and horizontal to bedding. The explored viscosities ranged from that of heavy motor oil to that of lithium grease (at 258 degrees C). The study shows that (1) convolute textures observed in plaster experiments closely resemble those seen in Chattanooga Shale burrows; (2) the degree of convolution increases as the viscosity of the substrate decreases; (3) the length of the worm determines the extent of mixing between layers; (4) mixing patterns produced by smooth worms and worms with appendages, although similar, contrast in detail; (5) earthworms and bait worms produce generally similar structures but show certain differences due to contrasting styles of locomotion (peristalsis vs. unidirectional pull). Virtual compaction and decompaction of digital images shows close resemblance between experimentally produced structures and burrow textures from the Chattanooga Shale, suggesting that the latter were indeed produced by worm-like animals that moved through semi-fluid muds.

The deterioration of lithium greases under the influence of electric current—an investigation

AbstractIn the present work, we report on the analysis of the deterioration of lithium greases used in rolling‐element bearings by X‐ray diffractometry (XRD), X‐ray fluorescence spectrometry (XRFS), and atomic absorption spectrometry (AAS). These techniques give reproducible, reliable data with which to establish the severity of deterioration of greases recovered from the active zone of bearings. XRD appears more suitable for diagnosing quickly the chemical changes that have occurred in the soap residue of greases, even in small quantity, than other analytical and performance evaluation techniques.Fresh lithium greases, their chemical composition, and the formation of new compounds in the greases have been investigated after use in rolling‐element bearings run in the presence of electric fields, and also under pure rolling friction conditions without electric fields on a roller‐bearing test rig. The deteriorated greases recovered from various motor bearings have also been analysed and the results are compared with those for the greases from the test bearings.X‐ray diffraction analysis shows that the chemical composition of the soap residue of the fresh lithium grease, lithium stearate (C18H35LiO2), does not change in bearings operated without the effect of electric fields, under pure rolling friction. However, lithium iron oxide (Li5FeO2) peaks were detected after prolonged operation of the bearings. On the other hand, under the influence of electric fields, the chemical composition of the grease changed to lithium palmitate (C16H31LiO2), and peaks of gamma lithium iron oxide (Γ‐LiFeO2) and lithium zinc silicate (Li3.6Zn0.2SiO2) were detected. The surface of the bearings was found to be corroded after operation under electric fields. AAS showed a considerable increase in the lithium percentage, and lithium carbonate and lithium hydroxide in the used greases in aqueous solution, compared to the fresh greaseThe investigations reported in this paper, together with study of damaged/corrugated bearing surfaces, offer potential in diagnosing the cause of bearing failure in teh presence of electric fields, and in establishing the severity of deterioration of the lithium greases used in the bearings.