Patent Application
20130296598
Zinc dialkyldithiophosphates (ZDDPs) have been the primary anti-wear and antioxidant additives in engine oil and other industrial lubricant formulations for more than 60 years. Over the past half century, considerable research efforts have been focused on the characterization of ZDDP tribofilm to elucidate its chemical composition and molecular structure, and the mechanism of tribofilm formation. Although the exact pathways leading to the formation of anti-wear film on metal surfaces are not well understood due to the complicated characteristics of reactions in lubricant formulations, it is generally accepted that the thermal, hydrolytic, and oxidative decomposition of ZDDP is involved. In addition it is understood that the degraded intermediates of ZDDP are actively involved with the formation of protective tribofilms on metal surfaces, which prevents the direct contact of metal surfaces in boundary condition, and therefore reduces wear.
During the investigation of the lubrication mechanism of ZDDP, many attempts to simulate combustion engine conditions and the identification of decomposed intermediates have been reported. It is generally accepted now that the rapid decomposition of ZDDP generates both soluble and insoluble organic and inorganic phosphorus intermediate compounds. These soluble products identified by 31P-NMR may include (RO)2P(═S)SSP(═S)(OR)2, (RO)2P(═S)SR, (RO)2P(═S)SH, (RO)3P═S, (RS)3P═O, and (RO)3P═O. The insoluble residue may consist of zinc sulfate, polyphosphate, and/or pyrophosphate compounds.
Over the past two decades, environmental concerns have been the major driving force for replacing ZDDP with zinc-free, lower phosphorus, and lower sulfur anti-wear additives, at least partially, especially in the automobile industry. Ashless lubricant additives are a potential alternative to ZDDP, and provide necessary protection against wear. Earliest research work and application of ashless lubricant additive goes back to the 1940s. In general, based on the elements contained in their chemical structures, ashless lubricant additives can be classified as phosphorus additives, e.g. phosphate esters, phosphites, sulfur additives, e.g. sulfurized olefins, and additives with multiple elements, e.g. alkyldithiophosphates, dithiocarbamates, and amine phosphates. More recently, some novel ashless anti-wear and/or extreme-pressure additives containing other elements, i.e. boron and fluorine, have been reported.
The lubrication mechanism of ashless additives is more complicated than that of ZDDP due to the variety of chemical structures. It is believed that ashless additives function by either promoting physical absorption of additives to metal surfaces, or accelerating chemical reactions with iron to form protective tribofilms. Investigation of chemical composition of tribofilms via modern surface techniques, such as X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES), X-ray photoemission electron microscopy (XPEEM), and Fourier transform infra-red (FT-IR) spectroscopy, shows iron polyphosphates and sulfates are generated by tributyl thiophosphate. Iron sulfide together with iron polyphosphates and sulfates were found in the tribofilm formed by alkyldithiophosphates.
Alkylthioperoxydiphosphates have been identified as the principal decomposed product of ZDDP (Willermet, P. A. and Kandah, S. K. Lubricant degradation and wear v. reaction products of Zinc dialkyldithiophosphate and peroxy radicals. ASLE Trans, 27, 67-72 (1984)). An earlier study reported the synthesis of alkylthioperoxydiphosphates with short alkyl chains (≦C10) by I2 oxidation, and subsequently evaluated their anti-wear properties on four-ball machine (Sarin, R. et al. Synthesis and performance evaluation of O,O-dialkylphosphorodithioic disulphides as potential antiwear, extreme-pressure and antioxidant additives. Tribol Int, 26, 389-94 (1993)).
It would be useful to have better anti-wear lubricant additives, particularly which are zinc-free and contain less phosphorus and sulfur.
It would be useful to have a synthetic method for making alkylthioperoxydiphosphates having various alkyl chain lengths through H2O2 oxidation reactions, rather than using I2 oxidation.
It would be useful to have alkylthioperoxydiphosphates with alkyl chain lengths greater than ten carbons, and a method of making same.
The invention is directed to alkylthioperoxydiphosphates having an alkyl group between about 4 and 18 carbons, or more preferably between about 13 and 18 carbons. The alkylthioperoxydiphosphates have a decomposition temperature between about 150 and 300° C. and a wear volume between about 0.0025 and 0.0015 mm3 in HFRB testing.
The invention further is directed to methods of making alkylthioperoxydiphosphates having an alkyl group between about 4 and 18 carbons by a two step process involving oxidizing an O,O-dialkyl dithiophosphoric acid with H2O2.
In another embodiment, the invention is a lubricant additive that includes an alkylthioperoxydiphosphate. Desirably the alkylthioperoxydiphosphate alkyl groups have between about 4 and 18 carbons, and more preferably about 13 to 18 carbons. The alkylthioperoxydiphosphates have a decomposition temperature between about 150 and 300° C. and a wear volume between about 0.0025 and 0.0015 mm3 in HFRB testing.
The alkylthioperoxydiphosphate is desirably tridecylthioperoxydiphosphate, 1-methyl dodecylthioperoxydiphosphate, tetradecylthioperoxydiphosphate, or octadecylthioperoxydiphosphate.
The present disclosure may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The present disclosure is illustrated in the accompanying drawings, throughout which like reference numerals may indicate corresponding or similar parts in the various figures. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the disclosure. Given the following enabling description, the novel aspects of the present disclosure should become evident to a person of ordinary skill in the art.
The general structure of alkylthioperoxydiphosphates is illustrated below:
Alkylthioperoxydiphosphates having an alkyl chain length between 4 and 18 carbons were synthesized via a two-step reaction, O,O-dialkyl dithiophosphoric acids were obtained by mixing phosphorus pentasulfide with appropriate alcohols at an elevated temperature in toluene; this facile reaction usually gives a quantitative yield.
The oxidation of O,O-dialkyl dithiophosphoric acids was carried out by adding H2O2 solution (37%) into a vigorously stirred O,O-dialkyl dithiophosphoric acid/ice mixture held in an ice bath. The pathway of the reaction is outlined below:
Alkylthioperoxydiphosphates having various alkyl constituents from 4 to 18 carbons were synthesized and characterized. The compounds and their general characteristics are shown in Table 1. All reactions gave fairly good yields.
1H NMR, 31P NMR, Fourier transform infra-red (FT-IR), Electrospray Ionization Time of Flight Analysis (ESI-TOF), and Matrix Assisted Laser Desorption Ionization Mass Spectroscopy (MALDI-MS) were used to confirm the structures of the synthesized compounds. The results are shown in the experimental section.
Volatility and thermal degradation play a critical role in the anti-wear performance of lubricant additives. Accordingly, thermal stability of the synthesized compounds was measured. Alkylthioperoxydiphosphates prepared from primary alcohols demonstrated slightly better thermal stability than those from secondary alcohols, and compounds with long chain length (>13 carbon atoms) are thermally stable under nitrogen beyond 200° C. In a study of thermal decomposition of ZDDP using DSC it was shown that in a flowing nitrogen environment ZDDP decomposes between 170-200° C. depending on the heating rate, with a higher heating rate (5° C./minute) yielding a decomposition endotherm at 200° C. and a slower heating rate (0.1° C./minute) yielding a decomposition endotherm centered around 170° C. The alkylthioperoxydiphosphates can be synthesized with tunable decomposition temperatures, including within the range exhibited by ZDDP, determined by the alkyl chain lengths and whether the alkyl chain has a primary or secondary structure.
High-frequency reciprocating ball (HFRB) tests were carried out to evaluate anti-wear performance of alkylthioperoxydiphosphates, and test conditions are listed in Table 2.
Topography of the wear scars was measured using the Veeco Wyko NT9100 Optical Profiler. The results indicate that formulations with alkylthioperoxydiphosphates of long alkyl chain length produce significantly lower wear volume in comparison to ZDDP at the same phosphorus level. The topographical image derived from optical profilometry for ZDDP in base oil shown a wear scar with a maximum depth of 10 μm which remains more or less uniformly deep along the length of the wear scar. However the wear scar from tridecylthioperoxydiphosphate has a maximum depth of 3.5 μm with many regions much shallower than that. 1-methyl dodecylthioperoxydiphosphate exhibits the best wear performance with a maximum depth of only 2 μm for similar test conditions. The differentiation in extent of wear is also reflected by the amount of debris build up on the sides of the wear track with ZDDP exhibiting the largest build up and the 1-methyl dodecylthioperoxydiphosphate exhibiting the smallest build up. Calculated wear volume for all the formulations and ZDDP is shown in
Scanning electron microscopy using secondary electrons was used to examine local morphology of the wear scar in all compositions. The morphology and characteristics of the wear track provides insight to explain the wear behavior of the different chemistries. Under the test conditions used, it is evident that the ZDDP exhibits a higher level of abrasive wear and tribofilm pullout that is likely responsible for its relatively poor performance in comparison to the different alkylthioperoxydiphosphates. All of the alkylthioperoxydiphosphates exhibit a small pad like morphology, which is discontinuous on the wear surface. In some cases such as octylthioperoxydiphosphate and 1-methyl dodecylthioperoxydiphosphate the pads grow to become more continuous across the wear surface. The wear test with octylthioperoxydiphosphate had the best wear performance, but cannot be directly correlated to the tribo pad size as the 1-methyl dodecylthioperoxydiphosphate had larger pad sizes but a slightly higher wear volume. However, none of the alkylthioperoxydiphosphates exhibited the kind of abrasive wear seen in ZDDP resulting in significantly improved wear performance.
XANES has been used extensively in the past to examine the chemical structure of tribofilms formed when ZDDP and ashless thiophosphates are used as an anti-wear agent. Accordingly, XANES was used to examine the tribofilms of the present compounds as well as thermal films. Both P and S L-edge and P and S K-edge XANES were examined for thermal films. The P K-edge provides insight into the formation of phosphates while the S K-edge provides information on the sulfates and sulfides that form. The TEY at the P and S K-edge typically provides information from the top 50-100 nm of the thermal films which is deeper than what is acquired from the L-edge. The K-edge has been used extensively in the past to study tribofilms and is well suited to study thermal films as well. Results of XANES are thoroughly discussed in the experimental section.
In brief, XANES analysis of thermal films suggests the formation of phosphates of Zn when ZDDP is used and of Fe when alkylthioperoxydiphosphates are used. However, the severe oxidative conditions of the test result in sulfur being oxidized into sulfates in the thermal films. The K-edge spectra indicate small presence of sulfides in the thermal films as well.
XANES analysis of tribofilms suggests the formation of polyphosphates of iron near the surface of tribofilms from alkylthioperoxydiphosphates while Zn3(PO4)2 is present when ZDDP is used. In addition in the near surface region both ZDDP and alkylthioperoxydiphosphates have a mixture of sulfides with ZDDP having ZnS and alkylthioperoxydiphosphates having FeS.
The examples serve to further illustrate the invention, to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices, and/or methods claimed herein are made and evaluated, and are not intended to limit the scope of the invention. In the examples, unless expressly stated otherwise, amounts and percentages are by weight, temperature is in degrees Celsius or is at ambient temperature, and pressure is at or near atmospheric.
All reagents were purchased from commercial suppliers and were used without purification unless otherwise specified. Reactions involving air- or water-sensitive compounds were conducted in oven-dried (overnight) glassware under an atmosphere of dry argon. Neutral-100 base oil and zinc dialkyldithiophosphates (ZDDP) were obtained from Chevron Oronite (Richmond, Calif., USA).
Nuclear Magnetic Resonance (NMR) spectra (1H, 13C, and 31P) were recorded on JEOL eclipse instrument at 500, 125, and 202 MHz respectively using CDCl3 as solvent and TMS as reference.
Melting points were obtained in capillary tubes on a Mel-Temp II apparatus, and the thermometer was uncorrected.
Fourier transform infrared (FT-IR) spectra were obtained on a Bruker Vector 22 FT-IR spectrometer, using KBr pressed pellets for solids or neat films between KBr plates for liquids and oils, and are reported in cm−1 with a resolution of 4 cm−1.
High-resolution electrospray ionization time-of-flight (ESI-TOF) experiments were performed on an Agilent ESI-TOF mass spectrometer at Scripps Center for Mass Spectrometry (La Jolla, Calif. 92037). Sample was electrosprayed into the TOF reflectron analyzer at an ESI voltage of 4000V and a flow rate of 200 micro liters/minutes.
MALDI-TOF spectra were obtained on Applied Biosystems Voyager-STR Mass spectrometer.
The thermo gravimetric analysis (TGA) measurements were performed using a TA 2050 thermo gravimetric analyzer (TA Instruments) at a heating rate of 5° C./min under nitrogen.
All column chromatography separations were performed on Sorbent Technologies silica gel (standard grade, 60A, 32-63 μm).
HFRB (High Frequency Reciprocating Ball) tests were performed on a home-built HFRB machine with test condition: 1.0 Kg Load, 100° C., 50 Hz, 1 hour and travel distance of 5 mm and a ball diameter of 6.25 mm. Both the moving ball and stationary disc were made of 52100 steel with the ball having a hardness of 55 HRc and the stationary disc having a hardness of 40 HRc.
Wear volume was measured by Veeco Wyko NT9100 Optical Profiler System equipped with Vision® software.
Scanning electron microscopy (SEM) images were obtained with Hitachi S-3000N Variable Pressure SEM.
X-ray absorption near-edge structure (XANES) spectra were obtained at VLS-PGM beamline at the Canadian Light Source (Saskatoon, SK, Canada). A 100 μm slit size was used with a 0.1 eV step size, the energy sweep for the absorption spectra was between 160-190 eV for sulfur L-edge and 130-155 eV for phosphorous L-edge. The PGM entry slit size was 200 μm by 200 μm.
The P and S K-edge spectra were acquired at the double crystal monochromator (DCM) beamline at Synchrotron Radiation Center, Madison Wis. The P K-edge spectra were acquired between 2110-2200 eV with an energy increment of 0.15 eV and the S K-edge spectra was acquired between 2460-2510 eV with an energy increment of 0.15 eV. All measurements were normalized to the incident flux I0 and the background subtracted.
Preparation of alkylthioperoxydiphosphates was achieved via a two-step reaction. O,O-dialkyl dithiophosphoric acid was obtained by mixing phosphorus pentasulfide with alcohol at an elevated temperature in toluene. The oxidation of O,O-dialkyl dithiophosphoric acid was carried out by adding H2O2 solution (37%) into a vigorously stirred O,O-dialkyl dithiophosphoric acid/ice mixture held in an ice bath.
The synthesis of octylthioperoxydiphosphate was performed as follows. 1.75 mL hydrogen peroxide solution (37% in H2O) was added slowly into a vigorously stirred 3.6 g (7.3 mmol) O,O-dioctyldithiophosphoric acid/50 g ice mixture in an ice bath. After addition of H2O2, the mixture was kept in an ice bath for another 4 hours, then allowed to naturally warm up to room temperature overnight. The reaction mixture was extracted with chloroform (50 ml×3), and combined organic layers were washed with water and brine, then dried over magnesium sulfate. Removing solvent under vacuum affords crude product as a pale yellow oil. The crude product was further purified by column chromatography (silica gel, hexane) to yield 3.5 g octylthioperoxydiphosphate as colorless oil.
1H and 31P NMR spectra were obtained on a JEOL eclipse+ NMR spectrometer at operating frequency of 500 and 202 MHz, respectively. The sweep width of 1H was 7508 Hz (−2.5-12.5 ppm), and chemical shifts were calibrated by tetramethylsilane (TMS). The sweep width of 31P was 50760 Hz (−75-175 ppm), and chemical shifts were externally calibrated by phosphoric acid. All NMR experiments were performed at room temperature of 21° C.
1H and 31P NMR spectra for tridecylthioperoxydiphosphate and 1-methyldodecylthioperoxydiphosphate are shown in
The 31P NMR spectrum of tridecylthioperoxydiphosphate (
1H NMR spectrum of 1-methyldodecylthioperoxydiphosphate (
31P NMR spectrum of 1-methyldodecylthioperoxydiphosphate (
FT-IR has been used extensively to examine the oxidative stability and structure of lubricant additives. FT-IR spectra of tridecylthioperoxydiphosphate and 1-methyldodeeylthioperoxydiphosphate are illustrated in
Time-of-flight (TOF) mass analysis coupled with two “soft” ionization techniques, electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) have been widely used in mass spectrometry owing to their excellent sensitivity and broad mass range. Compared with other traditional ionization methods, ESI and MALDI generate few fragments, which is ideal for molecular peaks detection in mass spectrometry. In ESI, an analyte solution is forced through a capillary surrounded by nebulizing gas in the presence of an electric field. As the solution exits the capillary, an aerosol of charged droplets forms. Droplets in the aerosol shrink as the solvent evaporates, and undergo “Columbic explosion” to generate analyte ions into vapor phase at various charge states. The MALDI method employs a chromophoric matrix in which the analyte is dissolved. The analyte-matrix mixtures are subject to pulsed laser irradiation, and energy absorbed by matrix causes the analyte molecules to be ionized and ejected from the matrix into the mass spectrometer.
Listed below is the spectral data from NMR and FT-IR for all the compounds synthesized as well as ESI-TOF and MALDSI-MS spectral data for select compounds.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.20-4.26 (m, 4H), 4.08-4.15 (m, 4H), 1.70-1.76 (m, 8H), 1.39-1.47 (m, 8H), 0.96 (t, J=6.87 Hz, 12H). 13C-NMR (125 MHz, CDCl3): 68.7, 68.6, 32.02, 31.96, 18.8, 13.7. 31P-NMR (202 MHz, CDCl3): 86.1. FT-IR (KBr): 2961, 2934, 2874, 1464, 1382, 1148, 1015, 979, 902, 855, 803, 737, 646, 520 cm−1.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.64-4.73 (m, 4H), 1.71-1.81 (m, 4H), 1.61-1.69 (m, 4H), 1.394 (d, J=6.0 Hz, 3H), 1.390 (d, J=6.0 Hz, 3H), 1.37 (d, J=6.0 Hz, 6H), 0.97 (t, J=7.3 Hz, 6H), 0.96 (t, J=7.3 Hz, 6H). 13C-NMR (125 MHz, CDCl3): 79.42, 79.37, 79.31, 79.27, 30.40, 30.36, 30.10-30.18 (m), 20.9, 20.8, 9.6, 9.54, 9.51. 31P-NMR (202 MHz, CDCl3): 83.9, 83.8, 83.7, 83.3, 83.1, 83.1, 82.6, 82.5, 82.4. FT-IR (KBr): 2974, 2936, 2880, 1462, 1381, 1173, 1013, 975, 856, 814, 761, 646, 522 cm−1.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.76-4.84 (m, 4H), 1.69-1.80 (m, 8H), 1.41 (d, J=6.4 Hz, 6H), 1.36-1.39 (m, 6H), 1.29-1.35 (m, 4H), 0.91-0.97 (m, 24H). 13C-NMR (125 MHz, CDCl3): 76.7-76.9 (m), 46.9, 46.8, 46.63, 46.59, 24.6, 24.47, 24.45, 22.90, 22.85, 22.80, 22.77, 22.55, 22.14, 21.84. 31P-NMR (202 MHz, CDCl3): 84.1, 84.0, 83.8, 83.2, 83.1, 83.0, 82.9, 82.3, 82.1, 82.0. FT-IR (KBr): 2960, 2932, 2871, 1467, 1382, 1121, 976, 790, 640, 541 cm−1.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.10-4.16 (m, 4H), 3.98-4.04 (m, 4H), 1.64-1.69 (m, 4H), 1.27-1.47 (m, 32H), 0.89-0.93 (m, 24H). 13C-NMR (125 MHz, CDCl3): 71.2, 40.0, 39.9, 39.8, 30.1, 30.0, 29.0, 28.9, 23.44, 23.40, 23.0, 14.1, 11.0, 10.9. 31P-NMR (202 MHz, CDCl3): 86.7-86.9 (m). FT-IR (KBr): 2960, 2930, 2862, 1462, 1380, 1003, 870, 661, 512 cm−1.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.18-4.25 (m, 4H), 4.07-4.13 (m, 4H), 1.71-1.77 (m, 8H), 1.28-1.40 (m, 40H), 0.89 (t, J=6.4 Hz, 12H). 13C-NMR (125 MHz, CDCl3): 69.0, 68.9, 31.9, 30.1, 30.0, 29.3, 29.2, 25.6, 22.7, 14.2. 31P-NMR (202 MHz, CDCl3): 86.0. FT-IR (KBr): 2955, 2926, 2856, 1464, 1380, 989, 856, 647, 510, 499 cm−1.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.69-4.77 (m, 4H), 1.71-1.77 (m, 4H), 1.53-1.61 (m, 4H), 1.29-1.40 (m, 44H), 0.87-0.90 (m, 12H). 13C-NMR (125 MHz, CDCl3): 78.4, 78.3, 78.2, 37.60, 37.55, 37.50, 37.29, 31.8, 29.23, 29.16, 25.19, 25.16, 22.7, 21.6, 21.4, 14.2. 31P-NMR (202 MHz, CDCl3): 84.2, 84.0, 83.9, 83.4, 83.3, 83.2, 83.1, 82.8, 82.5, 82.4. FT-IR (KBr): 2930, 2858, 1462, 1380, 1121, 973, 803, 643, 519 cm−1.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.18-4.24 (m, 4H), 4.06-4.13 (m, 4H), 1.71-1.76 (m, 8H), 1.23-1.39 (m, 80H), 0.88 (t, J=6.87 Hz, 12H). 13C-NMR (125 MHz, CDCl3): 68.91, 68.87,32.0, 30.0, 29.9, 29.73, 29.70, 29.64, 29.57, 29.4, 29.2, 25.6, 22.7, 14.1. 31P-NMR (202 MHz, CDCl3): 86.0. FT-IR (KBr): 2954, 2925, 2855, 1463, 1378, 989, 858, 723, 648, 514 cm−1. ESI-TOF (High accuracy) calculated for C52H108O4P2S4 as 987.6678 (MH+), found 987.6632.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.69-4.72 (m, 4H), 1.70-1.76 (m, 4H), 1.53-1.61 (m, 4H), 1.23-1.40 (m, 84H), 0.88 (t, J=6.87 Hz, 12H). 13C-NMR (125 MHz, CDCl3): 78.3, 78.2, 37.60, 37.56, 37.5, 37.3, 32.0, 29.4-29.8 (m), 25.3, 25.2, 22.8, 21.6, 21.4, 14.2. 31P-NMR (202 MHz, CDCl3): 84.1, 83.9, 83.8, 83.4, 83.3, 83.2, 83.1, 82.8, 82.6, 82.4. FT-IR (KBr): 2925, 2854, 1465, 1380, 972, 800, 644, 524 cm−1. ESI-TOF (High accuracy) calculated for C52H108O4P2S4 as 987.6678 (MH+), found 987.6663.
Colorless oil. 1H-NMR (500 MHz, CDCl3): 4.18-4.24 (m, 4H), 4.06-4.13 (m, 4H), 1.70-1.76 (m, 8H), 1.26-1.40 (m, 92H), 0.88 (t, J=6.9Hz, 12H). 13C-NMR (125 MHz, CDCl3): 68.9, 68.8, 32.0, 30.1, 30.0, 29.81, 29.80, 29.78, 29.7, 29.6, 29.5, 29.3, 25.6, 22.9, 14.2. 31P-NMR (202 MHz, CDCl3): 86.0. FT-IR (KBr): 2955, 2922, 2854, 1463, 1380, 989, 852, 722, 648, 512 cm−1.
White solid. Melting point: 37-38° C. 1H-NMR (500 MHz, CDCl3): 4.18-4.25 (m, 4H), 4.06-4.13 (m, 4H), 1.71-1.76 (m, 8H), 1.22-1.40 (m, 124H), 0.88 (t, J=6.9 Hz, 12H). 13C-NMR (125 MHz, CDCl3): 69.0, 68.9, 32.0, 30.05, 29.99, 29.7-29.8 (m), 29.7, 29.6, 29.4, 29.3, 25.6, 22.8, 142 31P-NMR (202 MHz, CDCl3): 86.0. FT-IR (KBr): 2919, 2850, 1466, 1381, 989, 852, 722, 647, 537, 508 cm−1. MS (MALDI-TOF): m/z 1267.84 (MH+).
Volatility and thermal degradation play a critical role in the anti-wear performance of lubricant additives. Thermal stability of alkylthioperoxydiphosphates was studied by thermo gravimetric analysis (TGA) under nitrogen atmosphere at a heating rate of 5° C./minute. The results are shown in
High-frequency reciprocating ball (HFRB) tests were carried out to evaluate anti-wear performance of alkylthioperoxydiphosphates, and test conditions are listed in Table 2 above. All formulations were tested at 0.1 wt % P level in base oil. 52100 steel disks were ground with 100, 240, 400 and 600 grit sandpapers, followed by polishing with 25, 5, and 0.5 μm Al2O3 aqueous solutions to achieve reproducible surface condition. Each lubricant formulation was consecutively tested three times on HFRB to obtain wear results.
Topography of the wear scars were measured using the Veeco Wyko NT9100 Optical Profiler. Calculated wear volume for all the formulations is shown in
Thermal films were deposited at a temperature of 160° C. with air being bubbled into the oil mixture to ensure the harsh oxidizing environments seen in combustion engines. Thermal films were grown for periods of 30 minutes under these conditions. In order to ensure that the observed XANES spectra were indeed from films formed on the surface, reference spectra of the pure compounds used in this study were acquired at the P and S L-edge.
The P K-edge provides insight into the formation of phosphates while the S K-edge provides information on the sulfates and sulfides that form. The TEY at the P and S K-edge typically provides information from the top 50-100 nm of the thermal film which is deeper than what is acquired from the L-edge. The K-edge has been used extensively in the past to study tribofilms and is well suited to study thermal films as well.
Subsequent to the HFRB test the tribological specimens were preserved with a layer of base oil (sulfur free) on the surface until they were examined at the Canadian Light Source. Total electron yield (TEY) and fluorescent yield (FLY) spectra were acquired. The L-edge spectra are much more sensitive to the surface in comparison to the K-edge spectra and TEY spectra for the L-edge of P and S provide information from the top about 5 nm of the tribofilm while FLY spectra provides information from the top about 50 nm of the tribofilm. As tribofilms are generally less than 100 nm in thickness, these two edges provide useful information on the distribution of P and S in the tribofilm.
Modifications and variations of the present invention will be apparent to those skilled in the art from the forgoing detailed description. All modifications and variations are intended to be encompassed by the following claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety.
This application claims priority to provisional application Ser. No. 61/642,921 filed on May 4, 2012.
| Number | Date | Country | |
|---|---|---|---|
| 61642921 | May 2012 | US |
