This paper describes 3-(3,5-Ditert-butyl-4-hydroxy-phenyl)-propionic acid 2-(4-meth yl-thiazol-5-yl)-ethyl ester (BHMT) as a high-performance multifunctional additive in lithium complex grease (LCG). The tribological properties and antioxidant behaviors of BHMT were evaluated by the tribological test and thermal analysis, respectively, and compared with those of zinc dialkyldithiophosphate (ZDDP). The tribochemical film BHMT generated on the worn surface was analyzed by X-ray photoelectron spectroscopy (XPS). Tribological results indicated that BHMT exhibited better friction-reduction and antiwear properties than ZDDP. The thermal analysis demonstrated that the antioxidation ability of BHMT was superior to that of ZDDP. Moreover, XPS results showed that lubrication film composed of iron oxide, iron sulfate, and nitrogen oxide was formed on the worn surface, which was an explicit explanation of the tribochemical mechanism of BHMT.

•The silica nanoparticles displayed the size-oriented adaptability to the lubricating conditions.•Different sized distribution silica nanoparticles complex additives showed synergistic effects under different lubrication conditions.•The bi-modal size distribution method gives excellent possibilities to design materials with better friction reducing and wear-resistance.The influence of nanoparticle size on the tribological performances of the SiO2/PAG (Polyalkylene glycol) nanofluids under different lubricating condition were investigated. The silica nanoparticles displayed strong size-oriented adaptability to the lubricating conditions. Under lower frequency, the smaller nano-SiO2 could significantly improve the tribological performances, this is due to the formation of tribofilm with stronger intrinsic mechanical properties. However, the lubricating oil containing large nano-SiO2 showed better friction reducing property under higher frequency, it because the flow features of nanofluids has become a dominating factor affecting the tribological performance. What's more, compared with the nano-additives with the uniform size, the mixed nano-additives displayed better anti-wear and friction-reducing properties.

•Nanosized MoS2 on graphene (MoS2/Gr) was used as lubricating oil additive.•The thermal conductivity (TC) of MoS2/Gr suspension in PAG was measured.•The rheological properties of this nanofluid was investigated.•The lubrication mechanism was explored.In this paper, nanosized MoS2 deposited on graphene (MoS2/Gr) were prepared and used as additives in polyalkylene glycol (PAG) for steel/steel contact. Tribological results indicated that MoS2/Gr suspended in PAG exhibited a substantial reduction in friction and wear compared to the neat oil and the oil plus graphene, microsized MoS2 and graphene mixed with microsized MoS2 at elevated temperature. The significantly better tribological behavior of this hybrid lubricant can be explained by the fact that nanosized MoS2 on graphene can enter the contact area of the opposite sliding surfaces and form thin, durable, and stable surface boundary layers that maintain low friction and wear. Additionally, the thermal conductivity (TC) and rheological properties of this nanofluid were also investigated.

•Multi walled carbon nanotubes-polymeric aryl phosphates (MWCNT-PAPs) was successfully synthesised.•MWCNT-PAPs showed exceptional stability in PAG base oil.•The tribological behaviour of MWCNT-PAPs was investigated at elevated temperature.Herein polymeric aryl phosphates (PAPs) were grafted on the surfaces of multi-walled carbon nanotubes (MWCNT) to prepare the nanocomposites of multi-walled carbon nanotubes-polymeric aryl phosphates (MWCNT-PAPs), which is conducive to improve oil dispersibility of MWCNT in the presence of PAPs. The tribological properties of MWCNT-PAPs dispersion in polyalkylene glycol (PAG) base oil were investigated by an oscillating reciprocating tribometer for steel/steel contacts at 150 °C, and the results showed that MWCNT-PAPs could dramatically improve the friction reduction and anti-wear performances of base oil. XPS analysis indicated that a boundary lubrication film was formed on the wear surfaces during friction and wearing process, and the film might contribute to the excellent tribological performances of MWCNT-PAPs in PAG at elevated temperature.

•Three oil-miscible ionic liquids were synthesized and investigated as potential lubricating additives.•The tribological behaviours of the additives for PETO and TMPTO were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester.•TTP-DDP showed considerably better lubrication properties than commercially available TCP by performing very well at 200 °C.•SEM and XPS results revealed that a protective tribofilm composed of Fe(OH)O, Fe3O4, FePO4 and FeSO4 formed on the worn surfaces, which plays a crucial role in the excellent lubricating behaviours of the ILs-additived lubricants.In this study, three oil-soluble phosphonium-based ionic liquids (ILs) were synthesized and then investigated them as potential lubricating additives. The friction-reduction and antiwear performances of the ILs as lubricant additives in pentaerythritol oleate (PETO) and trimethylolpropane trioleate (TMPTO) were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester. The results indicated that tetradecyltrihexylphosphonium O,O′-diethyldithiophosphate (IL3=TTP−DDP) exhibited considerably better lubrication properties than commercially available tricresyl phosphate (TCP) by performing very well at 200 °C. SEM and XPS were performed to analyze the worn surfaces and revealed the fabrication of tribofilm composed of Fe(OH)O, Fe3O4, FePO4 and FeSO4, which played a crucial role in the excellent lubricating behaviours of the ILs-additived lubricants.

We report the first synthesis of a high-performance lubricant additive by grafting treelike polymeric phosphate esters (PPEs) onto graphene oxide (GO) nanosheets. Characterization of the PPEs modified GO (GO–PPEs) was performed by spectral (FT-IR, Raman, SEM, TEM, XPS), and thermogravimetric analysis (TGA). Performance evaluations of GO–PPEs as a high-temperature friction-reduction and anti-wear additive in polyalkylene glycols (PAG) were conducted by an Optimol SRV-IV oscillating reciprocating friction and wear tester. The results indicated that GO–PPEs possessed excellent tribological properties in PAG compared with pure GO and PPEs under the same conditions, which may be attributed to the good dispersion of GO–PPEs in PAG, and the excellent tribological properties of phosphate at elevated temperature. In addition, the wear mechanism was tentatively discussed according to the surface composition.

An oil-soluble antioxidant, alkylated diphenylamine (ADPA), was prepared by alkylation of diphenylamine. The influence of ADPA on the thermal-oxidative stability of poly-α-olefin (PAO8) was evaluated by thermogravimetry (TG). For comparison, the thermal-oxidative stability of PAO8 with zinc dialkyl dithiophosphate (ZDDP) was also investigated. Activation energy (Ea)of the corresponding thermal-oxidative degradation process was evaluated by the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. To demonstrate the reliability of the kinetic study, the antioxidant performance of ADPA and ZDDP in PAO8 was also studied by the pressure drop (PDT) and accelerated oxidation (AOT) tests. The results indicate that ADPA has better antioxidant ability than ZDDP in increasing the Ea value and enhancing the oxidative stability of PAO8. Good correlation between the applied test methods was established.

This paper describes natural garlic oil (NGO) as a high-performance, environmentally friendly, extreme pressure additive for lubricating oils. The chemical composition of NGO was analyzed by gas chromatography–mass spectrometry (GC-MS). The load-carrying capacities of NGO and sulfurized isobutylene (SIB) in different base fluids were comparatively evaluated by a four-ball tester and an optimol SRV-IV oscillating reciprocating friction and wear tester (SRV tester). The four-ball test results revealed that incorporation of 1 wt % NGO into the base fluids could significantly improve the weld point of the base fluids from approximately 126 to 800 kgf or higher. Moreover, the four-ball test and SRV test results demonstrated that NGO could provide superior load-carrying ability in the selected base fluids than the conventional extreme pressure additive SIB. In addition, X-ray photoelectron spectroscopy (XPS) results showed that NGO and SIB experienced a similar tribochemical process with the generation of tribofilms composed with iron oxides, iron sulfates, iron sulfide, etc. NGO showed great promise for use as an effective, eco-friendly, extreme pressure additive for application in environmentally sensitive areas.Keywords: Environmentally friendly; Extreme pressure additive; Natural garlic oil; Sulfurized isobutylene; Tribological properties;

In this study, two kinds of calcite calcium carbonate nanoparticle additives (CN), with a grain size of ca. 30 nm and 80 nm, respectively, were synthesized via the carbonation method. Then, a series of additives were prepared through tuning the grain size distribution, and the corresponding tribological performances were also carefully investigated. Compared to the uniform size additives, the performance of the additives with a bimodal grain size distribution was obviously improved and the application range was further extended. Moreover, it can be observed that CN with a large grain size could improve tribological behavior under high frequency conditions, whereas the CN with a small grain size determined the load bearing capacity. The corresponding lubrication mechanisms were also investigated according to the characterization results of the wear scar surface, such as the morphology, composition and microstructure. The results indicated that a continuous protective film was formed on the contact surface and the corresponding mechanical properties determined the final lubricity. The enhancement of the tribological performance can be attributed to the improved toughness of the protective film, due to the reinforcing effect of the bimodal grain size distribution.

•Influence of antioxidants on the thermal–oxidative degradation of DEHS was studied.•Oxidative stability of antioxidants in DEHS was also evaluated.•Antioxidants could increase the E values of thermal–oxidative degradation of DEHS.•Good corresponding relationship was observed between these analytical techniques.The influence of pentaerythritol tetrakys 3-(3,5-ditert-butyl-4-hydroxyphenyl) propionate (1010) and octylated/butylated diphenylamine (L57) on the thermal–oxidative degradation of di-2-ethylhexyl sebacate (DEHS) was studied by using model-free thermo analysis under air atmosphere. Activation energies about the thermal–oxidative degradation of lubricants were evaluated by Kissinger–Akahira–Sunose (KAS) method. Pressure drop test (PDT) and pressurized differential scanning calorimetry (PDSC) tests were also employed to study their antioxidant performance in DEHS. The results showed that the addition of 1010 and L57 could enhance the oxidation stability of DEHS and increase the activation energy of thermal–oxidative degradation especially at the initial stage of thermal–oxidative decomposition. Meanwhile, a good corresponding relationship was found between model-free method and traditional test methods.

•Oxidative stability of antioxidants in TMPTO was evaluated by RBOT, PDSC and OOST.•Good correlation between these analytical techniques was observed.•The optimal primary antioxidant for TMPTO was determined.•Synergistic effect of antioxidants in TMPTO was also carefully investigated.•Good antioxidant synergism was due to their complementary anti-oxidation mechanisms.The aim of this study was to determine the optimum formulation for vegetable oils-based synthetic ester lubricant (trimethylolpropane trioleate, TMPTO) by searching for suitable antioxidants to extend its service life. The oxidative stability was evaluated by rotary bomb oxidation test (RBOT), pressurized differential scanning calorimetry (PDSC) and oven oxidation stability test (OOST). The results indicated that N-phenyl-alpha-naphthylamine (Am2) exhibited superior antioxidant activity compared to other selected antioxidants and thus could be used as the optimal primary antioxidant for TMPTO. Synergistic antioxidant effect between Am2 and a sulfur-containing auxiliary antioxidant (DLTDP) was also carefully investigated. The results suggested that the combination of Am2 and DLTDP revealed a good antioxidant synergism and could effectively improve the anti-oxidation ability of TMPTO. The best anti-oxidation result was achieved by the combination of 0.9 wt.%/0.1 wt.% Am2/DLTDP. Good antioxidant synergism between Am2 and DLTDP could be attributed to their complementary anti-oxidation mechanisms (Am2: radical scavenger and DLTDP: peroxide decomposer).

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.Highlights► The detailed degradation mechanism of di-2-ethylhexyl sebacate (DEHS) is proposed. ► Oxidation reactions and hydrolysis were main factors of degradation of DEHS. ► We first report the influence of oxidation on the tribological performance of DEHS. ► The tribological performance depends on the chemical composition change in oil.

•The final tribological performances depend on both the mechanical properties of tribofilm and the perfection of grease fiber network structure.•It is interesting to observe a selectivity of nanoparticles with different size for the various test conditions.•Larger CCNP exhibited optimal performance under higher frequency, while for smaller CCNP, it happened under higher load and lower frequency.In this study, three kinds of calcite calcium carbonate nanoparticles (CCNP) with different average diameters as eco-friendly grease additives were successfully fabricated via the carbonation method. The morphologies and phase compositions of the CCNP were determined via XRD, FTIR and TEM. The effects of the concentration and size of synthesized products on the tribological properties of grease have been investigated via an Optimol-SRV IV oscillating friction and wear tester (SRV) and MicroXAM 3D non-contact surface mapping profiler. The results show that the tribological properties of grease can be improved significantly by addition of CCNP. There exists an optimum CCNP concentration, where the grease can exhibit simultaneously optimal anti-wear and friction-reducing properties. Meanwhile, the final tribological performances of the grease not only depend on the mechanical properties of tribofilm formed with CCNP, but also lie on the perfection of grease fiber structure. More importantly, it is interesting to observe a selectivity of nanoparticles with different size for the test conditions. That is, the larger CCNP exhibits optimal performance under higher frequency, while for the smaller CCNP, it happens under higher load and lower frequency.

The effect of nanoparticle size (4∼44 nm) on the thermal conductivities of heat transfer oils has been systematically examined using iron oxide nanoparticles. Such Fe3O4 nanoparticles were synthesized by a simple one-pot pyrolysis method. The size (16∼44 nm), shape and assembly patterns of monodisperse Fe3O4 nanoparticles were modulated by only controlling the amount of Fe(acac)3. After the as-prepared Fe3O4 NPs were dispersed in heat transfer oils, the prepared magnetic nanofluids exhibit higher thermal conductivity than heat transfer oils, and the enhanced values increase with a decrease in particle size. In addition, the viscosities of all nanofliuids are remarkably lower than that of the base fluid, which has been found for the first time in the nanofluid field. The promising features offer potential application in thermal energy engineering.

Three kinds of protic ionic liquids with ammonium salts, dodecylamine salt of S-(1-carboxyl)-propyl-N, N-diethyldithiocarbamate (coded as DDED), dodecylamine salt of S-(1-carboxyl)-propyl-N, N-dibutyldithiocarbamate (coded as DDBD), dodecylamine salt of S-(1-carboxyl)-propyl-N, N-dioctyldithiocarbamate (coded as DDOD) were synthesized, characterized, and their tribological behaviors as additives in lithium complex grease were studied for steel/steel contact. The tribological properties were evaluated on an Optimol SRV-I oscillating reciprocating friction and wear tester and a MRS-10A lever-type fourball tester in details. The results of tests demonstrated that the novel additives were able to remarkably improve the extreme pressure, friction-reducing, and anti-wear properties of the base lithium complex grease when added at a low adding concentration (<3 %). Based on the performance comparison of three novel additives with different chain lengths in DTCs groups and a commercial additive with similar DTCs groups but no PILs groups, methylene bis dibutyldithiocarbamate (T323), a number of primary conclusions were drawn. The carboxylic acid ammonium salts, the typical function groups of the PILs existing in the molecule structures of three additives, could not only greatly enhance the physical and/or chemical adsorption on the metal surface to reduce friction of the base grease, and also have better synergism with DTCs groups in improving anti-wear performance of base grease. Based on the characterization and analysis of the worn surface by a PHI-5702 multifunctional X-ray photoelectron spectrometer (XPS) and a JSM-5600LV scanning electron microscope (SEM), a protective film consisting of FeS, organic compound was formed on the surface. The ordered adsorbed film and chemical reactive film on the sliding steels contributed to the main factor in improving the tribological properties of base lithium complex grease.

In this article, we synthesized the calcium sulphonate grease (CSG) based on the calcite using the bright stock (150BS) as the base oil. In order to investigate the tribological performance of lubricating grease containing different calcium carbonate polymorphs under boundary lubrication condition, a calcium sulphonate complex grease (CSCG) based on the vaterite was used as a reference. An oscillating reciprocating friction and wear tester set at a series of applied loads and frequencies was adopted to evaluate the tribological performance under boundary condition. Results showed that the lubricating grease that was composed of crystalline calcite as the partial thickener had excellent friction-reducing and antiwear (AW) properties, regardless of the applied loads and frequencies. The vaterite in CSCG easily experienced a polymorph transformation into calcite or aragonite characterized by Raman spectroscopy. This polymorph transformation was attributed to the highly local friction temperature and activated hydrogen from water or acids oxidated in the rubbing process at high load or frequency. The physical polymorph transformation corresponded to the fluctuations of the friction coefficients, then contributed to the severe wear. XPS analysis indicated that two calcium sulphonate lubricating greases occurred a tribochemical reaction and boundary tribofilms consisted of CaCO3, CaO, iron oxide and FeSO4 were formed on the rubbing surfaces. The tribofilm formed by the introduction of the CSG that mainly depended upon the thickeners of calcite structure contributed to an excellent AW protection. The possible boundary friction mechanism for greases based on various calcium carbonate polymorphs was also proposed. Effect of calcium carbonate polymorphs on the tribological performance was discussed.

The aim of this study was to examine the tribological behavior of amorphous overbased calcium sulfonate (AOBCS) and crystalline overbased calcium sulfonate (COBCS, transformed from the AOBCS) as additives in lithium complex grease. The transformation product of the calcium carbonate polymorph from AOBCS was calcite, as determined by Fourier transform infrared spectroscopy. Tribological properties were evaluated by an oscillating reciprocating friction and wear tester and a four-ball tester. The results showed that the addition of COBCS can dramatically improve both the antiwear performance and the friction-reducing and load-carrying properties of the base grease. However, improvement of the tribological properties of the base grease by AOBCS was highly dependent on the concentrations added and the loads applied. The tribological properties of the base grease were improved more by the addition of COBCS than by the addition of AOBCS. X-ray photoelectron energy spectrometry and thermogravimetric analysis revealed that both AOBCS and COBCS underwent complicated tribochemical reactions in the base grease and that chemically reactive films consisting of CaCO3, CaO, iron oxide and organic compounds were formed on the worn surfaces. Taken together with the results of the tribo-tests, we suggest that transformation of the calcium carbonate polymorphs was the main factor in improving the tribological properties of lithium complex grease. The transformation of calcium carbonate polymorphs can broaden the application of AOBCS as an extreme pressure/antiwear additive in greases under boundary lubrication conditions.

Environmentally friendly boron-containing soybean lecithin (BSL) was synthesised. Constant temperature and humidity box was applied to evaluate the hydrolytic stability of the novel lubricant additive. The friction-reducing, anti-wear, and extreme pressure performance of BSL in synthetic base fluids were studied by an optimol SRV-I oscillating reciprocating friction and wear tester and four-ball tester. The hydrolytic resistance test results reveal that BSL possesses good hydrolytic stability. Tribological tests show that the friction-reducing performance of BSL in A51 is inferior to PAO10. The incorporation of BSL in synthetic basestock can dramatically reduce the wear volume of the lower steel disc under different test conditions. BSL can also enhance the load-carrying capacities of the synthetic base fluids. Morphology and chemical composition of the wear surface were characterized by scanning electron microscope and X-ray photoelectron spectroscopy. The results indicated that excellent tribological performance of the BSL can be attribute to the formation of chemisorption and chemical reaction protecting films composed of Fe2O3, iron polyphosphates, organic amines, and BN, etc.

Sulphate-functionalized multi-walled carbon nanotubes (S-CNTs) were synthesized by an efficient and convenient method and characterized by FT-IR and TEM methods. Catalytic activities of the S-CNTs were evaluated in the esterification of glycerol with acetic acid at low temperature under atmospheric pressure. The CNTs grafted with sulphate groups show activity and stability in this reaction. The catalyst can be recycled and reused for several times without any significant loss of its catalytic activity.

A water-soluble boron (B)-containing thiophosphite derivative (BTP) was synthesized, and its tribological, anticorrosion, and antirust properties as an additive for the base liquid of water–glycol hydraulic fluid were evaluated in detail. The results of tests demonstrated that BTP is indeed a high-performance and multifunctional water-soluble lubricant additive that was able to remarkably improve the extreme pressure, friction-reducing, antiwear, anticorrosion, and rust-inhibiting properties of the base liquid when added at a low adding concentration (<3 wt%). Based on a performance comparison of BTP and thiophosphite (TP), whose chemical structure is similar to that of BTP but without B, a number of primary conclusions were drawn. The B element existing as alkanolamine borate group could greatly improve the extreme pressure, antiwear, and antirust performance of BTP, especially the antirust performance, but had only a small effect on the friction-reducing and anticorrosion properties. Based on characterizations and analyses of the worn surfaces, we propose that the antiwear mechanism consists of the prepared compound BTP reacting with the steel surface during the friction process to generate a protective film mainly composed of phosphate, sulfide, sulfate, organic amine, and B2O3.

CaCO3 nanoparticles with an average size of 45 nm were synthesized via the carbonation method. The tribological properties of the CaCO3 nanoparticles as an additive in lithium grease were evaluated with a four-ball tester. The results show that these CaCO3 nanoparticles exhibit good performance in anti-wear and friction-reduction, load-carrying capacity, and extreme pressure properties. The action mechanism was estimated through analysis of the worn surface with X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The results indicate that a boundary film mainly composed of CaCO3, CaO, iron oxide, and other organic compounds was formed on the worn surface during the friction process.

Hydrophobic spike-like vaterite CaCO3 composed of nanoparticles with an average size of 100 nm has been successfully synthesized via a simple synthetic method. The crystallization of vaterite CaCO3 was fabricated by the reaction of CaCl2 with Na2CO3 in ethanol–water solvents in the presence of oleic acid. The as-prepared products were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and contact angle analysis. The characterization results revealed that oleic acid played an important role in determining the phase and morphology of the sample. In addition, the surface properties of the vaterite CaCO3 changed from hydrophilic to hydrophobic. The contact angle of the modified CaCO3 reached 95.8°.

The high-temperature tribological performance of lithium grease is enhanced by addition of Lewis acid borate ester, which could interact with Lewis base RCO2− of lithium 12-hydroxystearate (LHS, constitute the thickener fiber network of lithium grease) to form a Lewis acid–base complex. Important details about the Lewis acid–base complex and its reinforcing effect on the tribological performance are elucidated by means of SRV oscillating friction and wear tester (SRV), Fourier transformation infrared spectroscopy (FTIR), TGA–DSC, and rheological methods. The experimental results strongly suggest that there is a Lewis base–acid interaction between the boron atom of borate ester or boric acid and the oxygen atom of RCO2−. Lewis acid centers can serve as second-level linking points to reinforce the strength of the thickener fiber network and further improve the colloidal stability of lubricating grease. Compared with pure LHS, the Lewis acid–base complex displays higher thermal stability, allowing lithium grease to be applied to higher temperature. Because of the enhancement of thermal stability and colloidal stability, film-forming property under high temperature can be greatly improved, resulting in >15% friction and >95% wear reductions.The high-temperature tribological performance of lithium grease was enhanced via a Lewis acid–base interaction.Download high-res image (99KB)Download full-size image

Spheroidal vaterite CaCO3 composed of irregular nanoparticals have been synthesized by a fast microwave-assisted method. The structures are fabricated by the reaction of Ca(CH3COO)2 with (NH4)2CO3 at 90 °C in ethylene glycol–water mixed solvents without any surfactants. The diameters of the spheroidal vaterite CaCO3 range from 1 to 2 μm, and the average size of the nanoparticals is about 70 nm. Bundle-shaped aragonite and rhombohedral calcite are also obtained by adjusting the experimental parameters. Our experiments show that the ratio of ethylene glycol to water, microwave power, reaction time, and two sources of ammonium ions and acetate anions are key parameters for the fabrication of spheroidal vaterite CaCO3. A possible growth mechanism for the spheroidal structures has been proposed, which suggests that the spheroidal vaterite CaCO3 is formed by an aggregation mechanism.

The effect of nanoparticle size (4∼44 nm) on the thermal conductivities of heat transfer oils has been systematically examined using iron oxide nanoparticles. Such Fe3O4 nanoparticles were synthesized by a simple one-pot pyrolysis method. The size (16∼44 nm), shape and assembly patterns of monodisperse Fe3O4 nanoparticles were modulated by only controlling the amount of Fe(acac)3. After the as-prepared Fe3O4 NPs were dispersed in heat transfer oils, the prepared magnetic nanofluids exhibit higher thermal conductivity than heat transfer oils, and the enhanced values increase with a decrease in particle size. In addition, the viscosities of all nanofliuids are remarkably lower than that of the base fluid, which has been found for the first time in the nanofluid field. The promising features offer potential application in thermal energy engineering.