Molybdenum disulfide particles and lubricating composition

Abstract

The molybdenum disulfide particles have a 2H crystal structure and a 3R crystal structure of molybdenum disulfide. The presence ratio of the above-mentioned 3R crystal structure in the crystal phase of molybdenum disulfide is 10% or more. The crystallite size of the above-mentioned 3R crystal structure is 1 nm or more and 150 nm or less. The crystallite size of the 3R crystal structure is calculated as follows: Using the spectrum obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, based on the analytical formula L = Kλ / (βcosθ), it is calculated by extended Rietveld analysis. (In the above formula, K is a device constant depending on the XRD optical system (incident side and detector side) and settings, L is the size of the crystallite [m], λ is the measured X-ray wavelength [m], β is the half-value width [rad], and θ is the Bragg angle of the diffracted ray [rad]).

Description

Technical Field

[0001] The present invention relates to molybdenum disulfide particles and a lubricating composition.

[0002] This application claims priority based on Japanese Patent Application No. 2021-050478 filed in Japan on March 24, 2021, the content of which is incorporated herein by reference. Background Art

[0003] Molybdenum disulfide is known as a lubricant for reducing friction and wear, especially in the automotive industry, and is used as a liquid lubricant such as engine oil in various countries. Molybdenum sulfides represented by molybdenum disulfide (MoS2) are known for applications as lubricants contained in, for example, solid sliding members and greases (see Patent Documents 1 to 3).

[0004] Inexpensive powders made by grinding natural molybdenum disulfide minerals are micron-sized and have a very large specific gravity of about 5, so they have the disadvantage of a small effect per unit added weight. Further, molybdenum disulfide commonly used as a lubricant is a hexagonal crystal solid lubricating material and has only 2H (hexagonal crystal) as its crystal structure.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-115920

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2013-144758

[0009] Patent Document 3: Japanese Patent No. 6614471 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] Regarding the molybdenum disulfide particles of nanosize independently developed by the present applicant, their crystal structure has not only 2H but also a rare 3R (rhombohedral) structure. According to this technology, by manufacturing molybdenum disulfide particles using the technology "nanosize molybdenum trioxide fine particles" held by the present applicant as a raw material, it is possible to synthesize "molybdenum disulfide containing a 3R structure, having a nanoscale, and having a light quality advantageous for increasing the surface area", which is difficult to achieve by crushing ore products or synthesizing from general molybdenum trioxide.

[0012] However, the actual full width at half maximum of the nano-sized molybdenum disulfide is significantly greater than that of the XRD peak predicted by the particle size. Therefore, the quantitative determination of the crystal state, i.e., the crystallite size and the ratio of the existence of the 2H crystal structure and the 3R crystal structure, has not been achieved. Therefore, there is a problem that it is difficult to grasp whether the crystallite size and the above-mentioned ratio of existence change depending on the manufacturing conditions, and furthermore, whether it affects the friction characteristics in the application evaluation.

[0013] An object of the present invention is to provide molybdenum disulfide particles and a lubricating composition having appropriate particle sizes and crystallite sizes, which can improve friction characteristics.

[0014] Solutions for Solving the Problems

[0015] Furthermore, the inventors of the present invention further analyzed the heating conditions during the production of the above-mentioned molybdenum disulfide particles, and found that: (1) Since the XRD peak intensity and the full width at half maximum change due to the change in the heating conditions, it is possible to quantify the changes in the crystallite size and crystallinity of the 2H crystal structure and the 3R crystal structure based on this change. In addition, (2) due to this heating condition, the ratio of the 2H crystal structure to the 3R crystal structure changes, and for this ratio, it is possible to use Rietveld analysis software (manufactured by Malvern Panalytical, HighScore Plus, hereinafter referred to as "extended Rietveld analysis") that can consider the crystallite size for quantification. As a result, (3) in the friction test using an oil dispersion system, the friction coefficient changes, so the friction characteristics can be improved by quantifying this friction coefficient.

[0016] In addition, it was found that according to the results of the above-mentioned extended Rietveld analysis and the heating conditions, the 2H crystal structure of the molybdenum disulfide particles has the following cases: a case composed of one crystal phase having a smaller crystallite size; and a case composed of a crystal phase (the first crystal phase) having a larger crystallite size compared to the above-mentioned one crystal phase and a low-crystallinity phase (the second crystal phase) having a smaller crystallite size compared to the above-mentioned one crystal phase.

[0017] That is, the present invention provides the following constitution.

[0018] [1] A molybdenum disulfide particle having a 2H crystal structure and a 3R crystal structure of molybdenum disulfide,

[0019] The ratio of the existence of the above-mentioned 3R crystal structure in the crystal phase of molybdenum disulfide is 10% or more.

[0020] The microcrystalline size of the above-mentioned 3R crystal structure is 1 nm or more and 150 nm or less, and the microcrystalline size of the 3R crystal structure is calculated as follows: using the spectrum obtained by powder X-ray diffraction (XRD) with Cu-Kα ray as the X-ray source, based on the analytical formula L = Kλ / (βcosθ), it is calculated by the extended Rietveld analysis.

[0021] (In the above formula, K is a device constant depending on the XRD optical system (incident side and detector side) and settings, L is the size of the microcrystal [m], λ is the wavelength of the measured X-ray [m], β is the half-value width [rad], and θ is the Bragg angle of the diffraction line [rad].)

[0022] [2] The molybdenum disulfide particles according to the above [1], wherein the above-mentioned 3R crystal structure obtained by the extended Rietveld analysis is composed of the following crystal phases: a crystal phase composed of microcrystals with a microcrystalline size of 5 nm or more and 50 nm or less calculated based on the above analytical formula.

[0023] [3] The molybdenum disulfide particles according to the above [1], wherein the above-mentioned 2H crystal structure obtained by the extended Rietveld analysis is composed of the following crystal phases: a crystal phase composed of microcrystals having a specified microcrystalline size calculated based on the above analytical formula,

[0024] The microcrystalline size of the above-mentioned crystal phase of the 2H crystal structure is 1 nm or more and 20 nm or less.

[0025] [4] The molybdenum disulfide particles according to the above [3], wherein the ratio of the existence of the above-mentioned 2H crystal structure and the above-mentioned 3R crystal structure in the crystal phase obtained by the extended Rietveld analysis using the spectrum obtained by the above XRD is 10:90 to 90:10.

[0026] [5] The molybdenum disulfide particles according to the above [1], wherein the above-mentioned 2H crystal structure obtained by the extended Rietveld analysis is composed of the following crystal phases: a first crystal phase composed of microcrystals having a specified microcrystalline size calculated based on the above analytical formula, and a second crystal phase having a smaller microcrystalline size than the above first crystal phase,

[0027] The microcrystalline size of the above-mentioned second crystal phase of the 2H crystal structure is 1 nm or more and 20 nm or less.

[0028] [6] The molybdenum disulfide particles according to the above [5], wherein the ratio of the existence of the above-mentioned first crystal phase of the 2H crystal structure, the above-mentioned 3R crystal structure, and the above-mentioned second crystal phase of the 2H crystal structure in the crystal phase obtained by the extended Rietveld analysis using the spectrum obtained by the above XRD is 30 to 10:10 to 70:80 to 15.

[0029] [7] The molybdenum disulfide particles according to any one of [1] to [6] above, wherein the molybdenum disulfide particles contain an amorphous phase, and the presence ratio of the amorphous phase of the molybdenum disulfide particles is 5% or more.

[0030] [8] The molybdenum disulfide particles according to any one of [1] to [7] above, wherein in the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the K absorption edge of molybdenum, the ratio (I / II) of the peak intensity I derived from Mo-S to the peak intensity II derived from Mo-Mo is greater than 1.0.

[0031] [9] The molybdenum disulfide particles according to any one of [1] to [8] above, wherein the median particle size D of the molybdenum disulfide particles obtained by the dynamic light scattering method 50 is 10 nm or more and 1000 nm or less.

[0032]

[10] The molybdenum disulfide particles according to any one of [1] to [9] above, wherein the specific surface area of the molybdenum disulfide particles measured by the BET method is 10 m 2 / g or more.

[0033]

[11] A lubricating composition, which contains: the molybdenum disulfide particles according to any one of [1] to

[10] above; a base oil composed of one or more of mineral oil, synthetic oil, and semi-synthetic oil; and additives such as a dispersant.

[0034]

[12] The lubricating composition according to

[11] above, wherein, based on 100% by mass of the total mass of the lubricating composition, 0.0001% by mass or more and 10% by mass or less of the molybdenum disulfide particles are contained.

[0035]

[13] The lubricating composition according to

[11] or

[12] above, which further contains organometallic complex particles.

[0036]

[14] The lubricating composition according to

[13] above, wherein, based on 100% by mass of the total mass of the lubricating composition, 0.0001% by mass or more and 10% by mass or less of the organometallic complex particles are contained.

[0037] Effects of the Invention

[0038] According to the present invention, molybdenum disulfide particles and a lubricating composition having appropriate particle size, crystallite size, and crystal structure and capable of improving friction characteristics can be provided. Brief Description of the Drawings

[0039] Figure 1Schematic diagram showing an example of an apparatus used in the production of molybdenum trioxide particles that are raw materials for molybdenum disulfide particles according to the present embodiment.

[0040] Figure 2 Graph showing the superposition of the X-ray diffraction (XRD) spectra of the molybdenum disulfide particles obtained in Examples 1 to 3.

[0041] Figure 3 Graph showing the X-ray diffraction (XRD) spectrum of the molybdenum disulfide particles obtained in Example 1.

[0042] Figure 4 Graph showing the X-ray diffraction (XRD) spectrum of the molybdenum disulfide particles obtained in Example 2.

[0043] Figure 5 Graph showing the X-ray diffraction (XRD) spectrum of the molybdenum disulfide particles obtained in Example 3.

[0044] Figure 6 Graph showing the X-ray diffraction (XRD) spectrum of the molybdenum disulfide particles obtained in Comparative Example 1.

[0045] Figure 7 Graph showing the relationship between the calcination temperature and the crystallite size in Examples 1 to 3.

[0046] Figure 8 Graph showing the X-ray diffraction (XRD) spectrum used in calculating the crystallinity of the molybdenum disulfide particles obtained in Example 2.

[0047] Figure 9 Graph showing the X-ray diffraction (XRD) spectrum used in calculating the crystallinity of the molybdenum disulfide particles obtained in Example 3.

[0048] Figure 10 Graph showing the relationship between the calcination temperature and the crystallinity in Examples 1 to 3.

[0049] Figure 11A Graph showing the relationship between the calcination temperature and the ratio of the presence of the 2H crystal structure and the 3R crystal structure in the crystal phase in Examples 1 to 3.

[0050] Figure 11B Graph showing the relationship between the calcination temperature and the ratio of the presence of the first and second crystal phases of the 2H crystal structure, the 3R crystal structure, and the amorphous phase in the particles in Examples 1 to 3 and Comparative Example 1.

[0051] Figure 12 Graph showing the measurement results of the time dependence of the coefficient of friction at 75 °C in Example 4 and Comparative Example 3. Detailed Description

[0052] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0053] <Molybdenum disulfide particles>

[0054] The molybdenum disulfide particles of the present embodiment have a 2H crystal structure and a 3R crystal structure of molybdenum disulfide. The ratio of the presence of the above 3R crystal structure in the crystal phase of molybdenum disulfide is 10% or more, and the crystallite size of the above 3R crystal structure is 1 nm or more and 150 nm or less. The crystallite size of the 3R crystal structure is calculated as follows: Using the spectrum obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, based on the analytical formula L = Kλ / (βcosθ), it is calculated by the extended Rietveld analysis. In the above formula, K is a device constant depending on the XRD optical system (incident side and detector side) and settings, L is the size of the crystallite [m], λ is the wavelength of the measured X-ray [m], K is a constant, β is the half-value width [rad], and θ is the Bragg angle of the diffraction line [rad].

[0055] The molybdenum disulfide (MoS2) particles of the present embodiment contain a 2H crystal structure and a 3R crystal structure. Molybdenum disulfide, which is usually used as a lubricant, is a hexagonal crystal solid lubricant material and basically has a 2H crystal structure (refer to Figure 6 ). When molybdenum disulfide particles with a ratio of the presence of the 3R crystal structure in the crystal phase of 10% or more are used as a lubricant, they have the following excellent friction characteristics: sintering is not easily generated even when a high load is applied, and moreover, the friction coefficient is reduced by 20 to 30%. The ratio of the presence of the above 3R crystal structure in the crystal phase of molybdenum disulfide can be 5% or more and 60% or less, can be 20% or more and 60% or less, preferably 20% or more and 60% or less, and can be 20% or more and 45% or less.

[0056] The fact that the molybdenum disulfide particles have a 2H crystal structure and a 3R crystal structure can be confirmed, for example, using extended Rietveld analysis software (manufactured by Malvern Panalytical, HighScore Plus) that can take into account the crystallite size. This Rietveld analysis software can use a crystal structure model including the crystallite size to simulate the entire XRD diffraction pattern, and compare it with the XRD diffraction pattern obtained through experiments, so as to optimize the lattice constants, atomic coordinates, etc. of the crystal structure factors, weight percentages (existence ratios), etc. of the crystal structure model by the least squares method in such a way that the residual between the diffraction pattern obtained through experiments and the diffraction pattern obtained through calculations is minimized, and perform high-precision identification and quantification of each phase of the 2H crystal structure and the 3R crystal structure. Thus, based on the crystal structure type and its ratio calculated by the usual Rietveld analysis, the crystallite size can also be calculated. In this patent, the analysis method using the above-mentioned HighScore Plus will be hereinafter referred to as "extended Rietveld analysis".

[0057] The median particle size D of the molybdenum disulfide particles of this embodiment 50 is preferably 10 nm or more and 1000 nm or less.

[0058] Commercially available MoS2 is a crushed product of ore, contains many particles with a particle size exceeding 1 μm, and has a small effect of lubricant per unit weight, which causes sedimentation in a lubricating composition containing a base oil with low viscosity. On the other hand, by making the above-mentioned median particle size D 50 be 1000 nm or less, when the molybdenum disulfide particles are used as a lubricant, they are not easily sintered even under high loads. This is because, under high loads, when the friction surfaces of the sliding materials approach each other to a distance less than 1 μm (i.e., 1000 nm), the lubricant does not escape from this gap but remains, and the lubricating performance can be continuously maintained. In addition, by making the above-mentioned median particle size D 50 be 1000 nm or less, when used in a lubricating composition containing a base oil, it is not easily sedimented and has excellent storage stability.

[0059] In addition, by making the median particle size D of the molybdenum disulfide particles 50is below 1000 nm, so that the above molybdenum disulfide particles become floating components and are not easily sedimented. Therefore, even when arranged in a state perpendicular or nearly perpendicular to each other between the friction surfaces of the sliding material and easily affected by gravity, they can exist in a state where they have already entered the gap between the friction surfaces of the sliding material at the moment before sliding. In addition, there is also the following effect: when molybdenum disulfide enters the gap and is subjected to the shear force peculiar to layered compounds, slipperiness is generated between the crystal planes, reducing the friction coefficient between the contact surfaces. Therefore, compared with the conventional molybdenum disulfide particles that are easily sedimented, it is possible to prevent grinding, wear, etc. of the sliding member at the start of sliding. As a result, it is considered that it can contribute to improving the life of the friction surface of the sliding material.

[0060] In addition, the molybdenum disulfide particles of the present embodiment can be supplied as a lubricant to, for example, the sliding portions of a plurality of metal balls. In this case, when they are squeezed against each other under high load and the distance between the metal balls reaches a distance less than 1 μm (= 1000 nm), due to the above median particle size D 50 is as small as below 1000 nm, it will not be excluded due to the clearance between the above metal balls and can remain in the gap. In this state, when subjected to the shear force peculiar to layered compounds, slipperiness is generated between the crystal planes, showing the effect of reducing the friction coefficient between the contact surfaces, forming a state where the contact probability (or contact area × time) between the friction surfaces of the metal balls is low, and it is considered that sintering is not easily caused by friction.

[0061] From the viewpoint of the above effects, the median particle size D of the above molybdenum disulfide particles 50 is preferably 600 nm or less, more preferably 500 nm or less, and further preferably 400 nm or less. The median particle size D of the above molybdenum disulfide particles 50 can be 20 nm or more and can be 40 nm or more. The median particle size D of the molybdenum disulfide particles 50 can be measured, for example, using a dynamic light scattering type particle size distribution measuring device (manufactured by MicrotracBEL Corporation, Nanotrac WaveII), a laser diffraction type particle size distribution measuring device (SALD-7000 manufactured by Shimadzu Corporation), etc.

[0062] In addition, in the molybdenum disulfide particles of the present embodiment, the crystallite size of the above-mentioned 3R crystal structure is 1 nm or more and 150 nm or less. When the crystallite size of the above-mentioned 3R crystal structure is 1 nm or more and 150 nm or less, when used as a dispersant contained in a base oil such as lubricating oil, the smaller the crystallite size when entering the gap, the easier it is to generate slip between layers when subjected to shear force, the friction coefficient of the dispersion system can be reduced, and the friction characteristics can be improved. The crystallite size of the above-mentioned 3R crystal structure is preferably the value obtained by extended Rietveld analysis. The friction coefficient can be measured, for example, by the Stribeck curve using a ball-on-disk tester or a four-ball tester.

[0063] From the viewpoint of the above effects, the above-mentioned 3R crystal structure obtained by the above extended Rietveld analysis preferably consists of the following crystal phases: a crystal phase composed of crystallites with a crystallite size of 1 nm or more and 50 nm or less calculated based on the above analytical formula, and the crystallite size is more preferably 5 nm or more and 50 nm or less, and further preferably 10 nm or more and 40 nm or less.

[0064] In addition, the crystallite size of the above-mentioned 2H crystal structure of the molybdenum disulfide particles of the present embodiment is preferably 1 nm or more and 150 nm or less. When the crystallite size of the above-mentioned 2H crystal structure is 1 nm or more and 15 nm or less, when used as a dispersant contained in a base oil such as lubricating oil, the friction coefficient of the dispersion system can be reduced, and the friction characteristics can be improved.

[0065] The crystallite size of the above-mentioned 2H crystal structure is preferably the value obtained by extended Rietveld analysis. The above-mentioned 2H crystal structure obtained by the above Rietveld analysis preferably consists of a crystal phase composed of crystallites with a crystallite size of 1 nm or more and 150 nm or less calculated based on the above analytical formula, and the crystallite size is more preferably 5 nm or more and 150 nm or less.

[0066] The above-mentioned 2H crystal structure obtained by extended Rietveld analysis preferably consists of the following crystal phases: a single crystal phase composed of crystallites with a specified crystallite size. By setting the heating temperature in the heat treatment to a lower temperature in the manufacturing method described later, a 2H crystal structure composed of a single crystal phase can be obtained. In this case, the crystallite size of the above-mentioned 2H crystal structure is more preferably 1 nm or more and 20 nm or less, and preferably 5 nm or more and 15 nm or less.

[0067] The crystallite size of the above-mentioned 2H crystal structure and the crystallite size of the above-mentioned 3R crystal structure can also be calculated, for example, using the peak half-width of the XRD diffraction pattern.

[0068] The ratio of the presence of the above-mentioned 2H crystal structure to the above-mentioned 3R crystal structure in the crystal phase (2H:3R) obtained by extended Rietveld analysis using the spectrum obtained by the above-mentioned XRD is preferably 10:90 to 90:10. When the ratio of the presence of the 3R crystal structure in the crystal phase is 10% or more and 90% or less, when molybdenum disulfide particles are used as a lubricant, sintering is not likely to occur even under high loads, and the coefficient of friction can be reduced by 20 to 30%.

[0069] From the viewpoint of the above-mentioned effects, the ratio of the presence of the above-mentioned 2H crystal structure to the above-mentioned 3R crystal structure in the crystal phase (2H:3R) obtained by extended Rietveld analysis using the spectrum obtained by the above-mentioned XRD is more preferably 10:90 to 80:20, and further preferably 40:60 to 80:20.

[0070] In addition, the above-mentioned 2H crystal structure obtained by the above-mentioned extended Rietveld analysis may be composed of the following crystal phases: a first crystal phase which is a crystal phase composed of microcrystals having a specified microcrystal size, and a second crystal phase having a smaller microcrystal size than the above-mentioned first crystal phase. By further heating the molybdenum disulfide particles as a post-treatment in the manufacturing method described below, a 2H crystal structure composed of the first crystal phase and the second crystal phase can be obtained. The microcrystal size of the first crystal phase of the above-mentioned 2H crystal structure is, for example, greater than 20 nm and 150 nm or less, may be 50 nm or more and 150 nm or less, and may be 100 nm or more and 150 nm or less. Among them, in order to reduce the coefficient of friction, it is preferable that the first crystal phase does not exist or its ratio of presence is small in the crystal phase of the above-mentioned 2H crystal structure. In addition, the microcrystal size of the second crystal phase of the above-mentioned 2H crystal structure is preferably 1 nm or more and 20 nm or less, may be 1 nm or more and 10 nm or less, and may be 5 nm or more and 15 nm or less.

[0071] The microcrystal size of the first crystal phase of the above-mentioned 2H crystal structure, the microcrystal size of the above-mentioned 3R crystal structure, and the microcrystal size of the second crystal phase of the above-mentioned 2H crystal structure can be calculated in the same manner as above, for example, using the half-value width of the peak of the XRD diffraction spectrum.

[0072] The ratio of the presence of the first crystal phase of the above-mentioned 2H crystal structure, the above-mentioned 3R crystal structure, and the second crystal phase of the above-mentioned 2H crystal structure in the crystal phase (2H (first crystal phase): 3R: 2H (second crystal phase)) obtained by extended Rietveld analysis using the spectrum obtained by the above-mentioned XRD is preferably 30 to 0:10 to 70:80 to 15. When the ratio of the presence of the first crystal phase of the 2H crystal structure, the 3R crystal structure, and the second crystal phase of the 2H crystal structure in the crystal phase is 30 to 10:10 to 70:80 to 15, when molybdenum disulfide particles are used as a lubricant, sintering is not likely to occur even under high loads, and the coefficient of friction can be reduced by 20 to 30%.

[0073] From the viewpoint of the above effects, the abundance ratios of the first crystal phase of the above 2H crystal structure, the above 3R crystal structure, and the second crystal phase of the above 2H crystal structure obtained by the extended Rietveld analysis using the spectrum obtained by the above XRD are more preferably 30 to 0:10 to 70:80 to 15, and further preferably 25 to 0:20 to 60:75 to 20.

[0074] In the spectrum of the above molybdenum disulfide particles obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, the peaks around 39.5° and around 49.5° originate from the 2H crystal structure, and the peaks around 32.5°, around 39.5°, and around 49.5° originate from the 3R crystal structure. The half-value widths of the peaks around 39.5° and around 49.5° are preferably 1° or more. Furthermore, the above molybdenum disulfide particles may contain crystal structures other than the 2H crystal structure and 3R crystal structure of molybdenum disulfide, such as the 1H crystal structure.

[0075] The fact that the above molybdenum disulfide particles contain the metastable 3R crystal structure can be distinguished as follows: in the spectrum obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, the peaks around 39.5° and around 49.5° are both composed of the composite peaks of the 2H crystal structure and the 3R crystal structure.

[0076] In fact, using the spectrum obtained by the above powder X-ray diffraction (XRD), the abundance ratio of the 2H crystal structure is determined by the peaks around 39.5° and the broad peaks around 49.5°. In addition, the difference between the peaks around 39.5° and the broad peaks around 49.5° is optimized by the two peaks around 32.5° and the two peaks around 39.5°, thereby determining the abundance ratio of the 3R crystal structure. That is, the peaks around 39.5° and around 49.5° are both composite waves from the 2H crystal structure and the 3R crystal structure, and the abundance ratios of the 2H crystal structure and the 3R crystal structure in the molybdenum disulfide particles can be calculated from these composite waves.

[0077] In addition, the molybdenum disulfide particles may contain an amorphous phase. The abundance ratio of the amorphous phase of the molybdenum disulfide particles is expressed as 100 (%) - (crystallinity (%)), and is preferably 5% or more, more preferably 15% or more, and further preferably 20% or more. When the abundance ratio of the amorphous phase of the molybdenum disulfide particles is 5% or more, the coefficient of friction further decreases, and the friction characteristics can be improved.

[0078] In a two-dimensional image taken with a transmission electron microscope (TEM), the shape of the primary particles of the molybdenum disulfide particles described above can be granular, spherical, plate-like, needle-like, rope-like, ribbon-like, or flake-like, and these shapes can be combined and included. The shape of the molybdenum sulfide is preferably disc-shaped, ribbon-like, or flake-like. On average, the shape of 50 primary particles of the molybdenum sulfide preferably has a size in the range of length (longitudinal) × width (transverse) × thickness (height) = 50 to 1000 nm × 50 to 1000 nm × 3 to 100 nm, more preferably has a size in the range of 100 to 500 nm × 100 to 500 nm × 5 to 50 nm, and particularly preferably has a size in the range of 50 to 200 nm × 50 to 200 nm × 5 to 20 nm. By being disc-shaped, ribbon-like, or flake-like, the specific surface area of the molybdenum disulfide particles can be increased. Here, being disc-shaped, ribbon-like, or flake-like means being in a thin layer shape. The aspect ratio of the primary particles of the molybdenum sulfide, that is, the value of (length (size in the longitudinal and transverse directions)) / thickness (height)) is preferably 1.2 to 1200 on average for 50 particles, more preferably 2 to 800, further preferably 5 to 400, and particularly preferably 10 to 200.

[0079] By making the shape of the primary particles of the molybdenum disulfide particles not a simple sphere but a disc shape, ribbon shape, or flake shape with a large aspect ratio, it is possible to expect more efficiently covering between the friction surfaces of the sliding materials in contact, and reducing the contact probability (or contact area × time) between the friction surfaces of the sliding materials through the interphase sliding of the crystal structure, and it is considered that wear and sintering are not easily caused by friction.

[0080] The specific surface area of the molybdenum disulfide particles measured by the BET method is preferably 10 m 2 / g or more, more preferably 30 m 2 / g or more, and particularly preferably 40 m 2 / g or more. The specific surface area of the molybdenum disulfide particles measured by the BET method can be 300 m 2 / g or less, and can be 200 m 2 / g or less.

[0081] For the primary particles of the molybdenum disulfide particles described above, the layers constituting the primary particles are close to each other due to weak interactions and are easily displaced from each other by external forces such as friction. Therefore, when the primary particles of the molybdenum disulfide particles are sandwiched between metals as sliding materials, the layers constituting the primary particles are displaced due to this frictional force, which can reduce the apparent friction coefficient and also prevent contact between the metals as sliding materials.

[0082] The specific surface area of the molybdenum disulfide particles measured by the BET method is 10 m 2When it is above / g, when the above-mentioned primary particles exist between metals as the materials to be slid, the contact area between the metals as the materials to be slid can be further reduced, so it is considered to be helpful for both improving the performance of the lubricant and preventing sintering.

[0083] In the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the K absorption edge of molybdenum of the above-mentioned molybdenum disulfide particles, the ratio (I / II) of the peak intensity I derived from Mo-S to the peak intensity II derived from Mo-Mo is preferably greater than 1.0, more preferably 1.1 or more, and particularly preferably 1.2 or more.

[0084] Whether the crystal structure of molybdenum disulfide is the 2H crystal structure or the 3R crystal structure, the distance between Mo-S is basically the same due to covalent bonds. Therefore, in the extended X-ray absorption fine structure (EXAFS) spectrum of the K absorption edge of molybdenum, the peak intensity derived from Mo-S is the same. On the other hand, the 2H crystal structure of molybdenum disulfide is hexagonal, so the same hexagon is directly below the hexagon of Mo atoms at 90°, so the distance between Mo-Mo becomes closer and the peak intensity II derived from Mo-Mo becomes stronger.

[0085] On the contrary, the 3R crystal structure of molybdenum disulfide is rhombohedral, and the hexagon is not directly below the hexagon at 90°, but is offset by half, so the distance between Mo-Mo becomes farther and the peak intensity II derived from Mo-Mo becomes weaker.

[0086] In the pure 2H crystal structure of molybdenum disulfide, the above ratio (I / II) becomes smaller, but as the 3R crystal structure is included, the above ratio (I / II) becomes larger.

[0087] In the 3R crystal structure, the hexagons of each Mo atom in the three layers are only offset by half of the hexagon from each other. Therefore, compared with the 2H crystal structure in which the hexagons of Mo atoms in the two layers are regularly arranged perpendicular to each other, it can be expected that the interaction between the layers is small and it becomes easier to slide.

[0088] For the 2H crystal structure, it can also be expected that the smaller the crystallite size, the easier the sliding property of the contact surface is generated.

[0089] It is considered that the presence of molybdenum trioxide will have an adverse effect on the lubrication performance. Therefore, the conversion rate R of the above-mentioned molybdenum trioxide particles to MoS2 C is preferably 70% or more, more preferably 80% or more, and further preferably 90% or more.

[0090] For the above-mentioned molybdenum disulfide particles, by making the conversion rate R to MoS2 CNumbers close to 100% are shown, and lubricating performance is exhibited by heating generated by friction. However, compared with other molybdenum disulfide raw materials and their precursors that may by-produce or contain molybdenum trioxide, the lubricating characteristics can be made excellent.

[0091] The conversion rate R of molybdenum trioxide particles to MoS2 can be obtained from the spectral data obtained by X-ray diffraction (XRD) measurement of molybdenum disulfide particles according to the RIR (reference intensity ratio) method. C . The RIR value K of molybdenum disulfide (MoS2) can be used. A and the integrated intensity I of the peak near 2θ = 14.4° ± 0.5° attributed to the (002) plane or (003) plane of molybdenum disulfide (MoS2). A and the RIR value K of each molybdenum oxide (MoO3 as the raw material and Mo9O as the reaction intermediate 25 , Mo4O 11 , MoO2, etc.) B and the integrated intensity I of the strongest radiation peak of each molybdenum oxide (MoO3 as the raw material and Mo9O as the reaction intermediate 25 , Mo4O 11 , MoO2, etc.), the conversion rate R to MoS2 is obtained from the following formula (1). B . C .

[0092] R C (%) = (I A / K A ) / (Σ(I B / K B )) × 100…(1)

[0093] Here, the RIR values can be the values described in the Inorganic Crystal Structure Database (ICSD) (manufactured by the Chemical Information Association of Japan, Inc.), and the integrated powder X-ray analysis software (manufactured by Rigaku Corporation, PDXL2) can be used in the analysis.

[0094] Note that the lubricating composition of this embodiment preferably contains molybdenum disulfide particles (MoS2), but is not limited thereto, and may also contain molybdenum sulfide particles represented by MoS x (X = 1 to 3), and may contain one or more of the molybdenum sulfide particles represented by MoS x (X = 1 to 3).

[0095] <Manufacturing method of molybdenum disulfide particles>

[0096] The above-mentioned molybdenum disulfide particles can be manufactured, for example, by heating molybdenum trioxide particles with an average particle size of 2 nm or more and 1000 nm or less at a temperature of 200 to 1000 °C in the presence of a sulfur source.

[0097] The average primary particle diameter of molybdenum trioxide particles refers to: photographing molybdenum trioxide particles with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and measuring the major axis (Feret diameter of the longest part observed) and the minor axis (short Feret diameter in the direction perpendicular to the Feret diameter of the longest part) of the particles (i.e., primary particles) that are the smallest units constituting the aggregates on the two-dimensional image, and taking the average value of the primary particle diameters of 50 randomly selected primary particles as the primary particle diameter.

[0098] In the method for manufacturing the molybdenum disulfide particles described above, the average primary particle diameter of the molybdenum trioxide particles is preferably 1 μm or less. From the viewpoint of reactivity with sulfur, it is more preferably 600 nm or less, further preferably 400 nm or less, and particularly preferably 200 nm or less. The average primary particle diameter of the molybdenum trioxide particles can be 2 nm or more, can be 5 nm or more, and can be 10 nm or more.

[0099] The molybdenum trioxide particles used in the manufacture of the molybdenum disulfide particles described above preferably contain an aggregate of primary particles having a β crystal structure containing molybdenum trioxide. Compared with the existing molybdenum trioxide particles composed only of α crystals as the crystal structure, the molybdenum trioxide particles have good reactivity with sulfur, and since they contain the β crystal structure of molybdenum trioxide, the conversion rate R to MoS2 can be increased in the reaction with a sulfur source. C 。

[0100] The β crystal structure of molybdenum trioxide can be confirmed by the presence of a peak belonging to the (011) plane of the β crystal of MoO3 (2θ: near 23.01°, No. 86426 (Inorganic Crystal Structure Database (ICSD))) in the spectrum obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source. The α crystal structure of molybdenum trioxide can be confirmed by the presence of a peak of the (021) plane of the α crystal of MoO3 (2θ: near 27.32°, No. 166363 (Inorganic Crystal Structure Database (ICSD))).

[0101] The ratio of the peak intensity of the (011) plane of the β crystal of MoO3 to the peak intensity of the (021) plane of the α crystal of MoO3 (β(011) / α(021)) in the spectrum obtained by powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source for the molybdenum trioxide particles described above is preferably 0.1 or more.

[0102] For the peak intensity of the (011) plane attributed to the β crystal of MoO3 and the peak intensity of the (021) plane attributed to the α crystal of MoO3, the maximum intensity of the peak is read respectively, and the above ratio (β(011) / α(021)) is obtained.

[0103] In the above molybdenum trioxide particles, the above ratio (β(011) / α(021)) is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and particularly preferably 0.4 to 10.0.

[0104] The β crystal structure of molybdenum trioxide can also be confirmed by the presence of peaks at wavenumbers 773, 848 cm -1 and 905 cm -1 in the Raman spectrum obtained by Raman spectroscopy. The α crystal structure of molybdenum trioxide The α crystal structure of molybdenum trioxide can also be confirmed by the presence of peaks at wavenumbers 663, 816 cm -1 and 991 cm -1 in the Raman spectrum.

[0105] The average particle size of the primary particles of the above molybdenum trioxide powder is preferably 5 nm or more and 2000 nm or less.

[0106] Examples of the sulfur source include sulfur, hydrogen sulfide, etc. They can be used alone or in combination of two.

[0107] The method for manufacturing the above molybdenum disulfide particles may include the following steps: heating molybdenum trioxide particles containing an aggregate of primary particles of the β crystal structure of molybdenum trioxide at a temperature of 100 to 800 °C in the absence of a sulfur source, and then heating at a temperature of 200 to 1000 °C in the presence of a sulfur source.

[0108] The heating time in the presence of the sulfur source only needs to be the time for the sulfidation reaction to proceed sufficiently, and can be 1 to 20 hours, can be 2 to 15 hours, and can be 3 to 10 hours.

[0109] In the method for manufacturing the above molybdenum disulfide particles, the input ratio of the S amount of the above sulfur source to the MoO3 amount of the above molybdenum trioxide particles is preferably the condition for the sulfidation reaction to proceed sufficiently. Relative to 100 mol% of the MoO3 amount of the above molybdenum trioxide particles, the S amount of the above sulfur source is preferably 450 mol% or more, more preferably 600 mol% or more, and still more preferably 700 mol% or more. Relative to 100 mol% of the MoO3 amount of the above molybdenum trioxide particles, the S amount of the above sulfur source can be 3000 mol% or less, can be 2000 mol% or less, and can be 1500 mol% or less.

[0110] In the method for manufacturing the molybdenum disulfide particles described above, the heating temperature in the presence of the sulfur source only needs to be a temperature at which the sulfidation reaction proceeds sufficiently, preferably 320 °C or higher, more preferably 340 °C or higher, and further preferably 360 °C or higher. Additionally, the heating temperature can be 320 to 1000 °C, can be 340 to 1000 °C, or can be 360 to 500 °C. By setting the heating temperature to a low temperature, the crystallinity of the molybdenum disulfide particles becomes smaller, and the ratio of the amorphous phase can be increased.

[0111] In the method for manufacturing the molybdenum disulfide particles described above, as a post-treatment, the obtained molybdenum disulfide particles can be heated after cooling as needed. In this heat treatment, it is preferable to calcine the molybdenum disulfide particles in an inert atmosphere, for example. By heating and calcining the obtained molybdenum disulfide particles, the crystallization of the amorphous phase can be promoted, and the crystallinity can be improved. Additionally, as the crystallinity increases, a 2H crystal structure and a 3R crystal structure are newly formed respectively, and the ratio of the 2H crystal structure and the 3R crystal structure changes. If reheating is performed as described above as a post-treatment, the crystallinity of the molybdenum disulfide particles becomes high. Although the easy peelability due to lubrication of each layer is somewhat reduced, the ratio of the 3R crystal structure that contributes to improving the friction characteristics increases. Therefore, the friction characteristics can be improved compared to when only the 2H crystal structure is present. Additionally, by changing the temperature when heating the obtained molybdenum disulfide particles, the ratio of the 2H crystal structure and the 3R crystal structure can be adjusted.

[0112] When the obtained molybdenum disulfide particles are heated and calcined at a specified temperature or higher to transform the amorphous phase into a 2H crystal structure, a second crystal phase composed of microcrystals with a microcrystal size of 20 nm or less, preferably 10 nm or less, is newly formed. At this time, when there are microcrystals with a microcrystal size of 10 nm or less in the 2H crystal structure before heating the molybdenum disulfide particles, after heating the molybdenum disulfide particles, the microcrystals grow to a microcrystal size of 100 nm or more, and a first crystal phase composed of the grown microcrystals is formed.

[0113] As described above, it is speculated that in the crystal structure of the molybdenum disulfide particles, the crystal phase constituting the 3R crystal structure contributes to improving the friction characteristics, and the first crystal phase constituting the 2H crystal structure is not helpful for the friction characteristics or may be a factor that reduces the friction characteristics. Therefore, from the viewpoint of increasing the ratio of the crystal phase of the 3R crystal structure and minimizing the ratio of the first crystal phase of the 2H crystal structure, the heating temperature of the molybdenum disulfide particles in the post-treatment is preferably 500 to 900 °C, more preferably 500 to 800 °C.

[0114] Additionally, the heating rate of the molybdenum disulfide particles in the post-treatment is preferably 1 °C / minute or more and 50 °C / minute or less, more preferably 2 °C / minute or more and 10 °C / minute or less.

[0115] In the method for manufacturing the molybdenum disulfide particles described above, the content ratio of MoO3 in the molybdenum trioxide particles measured by fluorescent X-ray (XRF) is preferably 99.5% or more. Thereby, the conversion rate R to MoS2 can be increased. C , and molybdenum disulfide with high purity, without worrying about the formation of disulfide derived from impurities and having good storage stability can be obtained.

[0116] The specific surface area of the molybdenum trioxide particles measured by the BET method is preferably 10 m 2 / g to 100 m 2 / g.

[0117] From the viewpoint of good reactivity with sulfur, the specific surface area of the molybdenum trioxide particles is preferably 10 m 2 / g or more, more preferably 20 m 2 / g or more, and further preferably 30 m 2 / g or more. From the viewpoint of easy manufacturing, the specific surface area of the molybdenum trioxide particles is preferably 100 m 2 / g or less, may be 90 m 2 / g or less, and may be 80 m 2 / g or less.

[0118] For the molybdenum trioxide particles, it is preferable that the ratio (I / II) of the peak intensity I derived from Mo-O to the peak intensity II derived from Mo-Mo in the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum of the K absorption edge of molybdenum is greater than 1.1.

[0119] For the peak intensity I derived from Mo-O and the peak intensity II derived from Mo-Mo, the maximum intensity of the peak is read respectively, and the above ratio (I / II) is obtained. It is considered that the above ratio (I / II) is a standard for obtaining the β crystal structure of MoO3 in the molybdenum trioxide particles, and the larger the above ratio (I / II), the more excellent the reactivity with sulfur.

[0120] In the molybdenum trioxide particles, the ratio (I / II) is preferably 1.1 to 5.0, may be 1.2 to 4.0, and may be 1.2 to 3.0.

[0121] (Method for manufacturing molybdenum trioxide particles)

[0122] The molybdenum trioxide particles can be manufactured as follows: vaporize the molybdenum oxide precursor compound to form molybdenum trioxide vapor, and cool the molybdenum trioxide vapor, whereby they can be manufactured.

[0123] The method for manufacturing the molybdenum trioxide particles described above includes the following steps: roasting a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound to vaporize the molybdenum oxide precursor compound to form molybdenum trioxide vapor. With respect to 100% by mass of the raw material mixture, the ratio of the metal compound in terms of oxide conversion is preferably 70% by mass or less.

[0124] The method for manufacturing the molybdenum trioxide particles described above can be suitably implemented using Figure 1 the manufacturing apparatus 1 shown.

[0125] Figure 1 FIG. is a schematic diagram showing an example of an apparatus used when manufacturing molybdenum trioxide particles as a raw material for molybdenum disulfide particles of the present embodiment.

[0126] As Figure 1 shown, the manufacturing apparatus 1 has: a roasting furnace 2 that roasts the molybdenum oxide precursor compound or the raw material mixture to vaporize the molybdenum oxide precursor compound; a cross-shaped cooling pipe 3 connected to the roasting furnace 2 that granulates the molybdenum trioxide vapor vaporized by the roasting; and a recovery mechanism, i.e., a recovery machine 4, that recovers the granulated molybdenum trioxide particles in the cooling pipe 3. At this time, the roasting furnace 2 and the cooling pipe 3 are connected via an exhaust port 5. In addition, an opening degree adjustment damper 6 is disposed at the left end of the cooling pipe 3 at an external gas suction port (not shown), and an observation window 7 is disposed at the upper end. The recovery machine 4 is connected to an exhaust device 8 that serves as a first air supply mechanism. The exhaust device 8 exhausts air, whereby the internal gas of the recovery machine 4 and the cooling pipe 3 is sucked, and external gas is supplied to the cooling pipe 3 from the opening degree adjustment damper 6 provided in the cooling pipe 3. That is, the exhaust device 8 functions as a suction function, thereby passively generating air supply in the cooling pipe 3. It should be noted that the manufacturing apparatus 1 may have an external cooling device 9, whereby the cooling conditions of the molybdenum trioxide vapor generated from the roasting furnace 2 can be arbitrarily controlled.

[0127] By setting the opening degree adjustment valve 6 to open, taking in air from the external gas suction port, and cooling the molybdenum trioxide vapor vaporized in the roasting furnace 2 in an air atmosphere to form molybdenum trioxide particles, the ratio (I / II) can be made greater than 1.1. In the molybdenum trioxide particles, it is easy to obtain the β crystal structure of MoOO3. When cooling the molybdenum trioxide vapor using liquid nitrogen or the like, cooling the molybdenum trioxide vapor in a state where the oxygen concentration in the nitrogen atmosphere is low easily increases the oxygen defect density and reduces the ratio (I / II).

[0128] As the above molybdenum oxide precursor compound, as long as it is a compound that forms molybdenum trioxide vapor by calcining it, there is no particular limitation. Examples include metallic molybdenum, molybdenum trioxide, molybdenum dioxide, molybdenum sulfide, ammonium molybdate, phosphomolybdic acid (H3PMo 12 O 40 ), silicomolybdic acid (H4SiMo 12 O 40 ), aluminum molybdate, silicon molybdate, magnesium molybdate (MgMo n O 3n+1 (n = 1 - 3)), sodium molybdate (Na2Mo n O 3n+1 (n = 1 - 3)), titanium molybdate, iron molybdate, potassium molybdate (K2Mo n O 3n+1 (n = 1 - 3)), zinc molybdate, boron molybdate, lithium molybdate (Li2Mo n O 3n+1 (n = 1 - 3)), cobalt molybdate, nickel molybdate, manganese molybdate, chromium molybdate, cesium molybdate, barium molybdate, strontium molybdate, yttrium molybdate, zirconium molybdate, copper molybdate, etc. These molybdenum oxide precursor compounds can be used alone or in combination of two or more. The form of the molybdenum oxide precursor compound is not particularly limited. For example, it can be in the form of powder such as molybdenum trioxide, or in the form of liquid such as aqueous ammonium molybdate solution. Powder form with good processability and energy efficiency is preferred.

[0129] As the molybdenum trioxide precursor compound, commercially available α - crystal molybdenum trioxide is particularly preferably used. In addition, when ammonium molybdate is used as the molybdenum oxide precursor compound, it is converted to thermodynamically stable molybdenum trioxide by calcination, so the vaporized molybdenum oxide precursor compound becomes the above - mentioned molybdenum trioxide.

[0130] Molybdenum trioxide vapor can also be formed by calcining a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the above molybdenum oxide precursor compound.

[0131] Among these, from the viewpoint of easily controlling the purity, average particle size of primary particles, and crystal structure of the obtained molybdenum trioxide powder, the molybdenum oxide precursor compound preferably contains molybdenum trioxide.

[0132] An intermediate may be formed between the molybdenum oxide precursor compound and a metal compound other than the above molybdenum oxide precursor compound. However, even in this case, the intermediate can be decomposed by calcination to vaporize molybdenum trioxide in a thermodynamically stable form.

[0133] Among these, as the metal compound other than the above molybdenum oxide precursor compound, an aluminum compound is preferably used to prevent damage to the calcination furnace, and in order to improve the purity of molybdenum trioxide particles, a metal compound other than the above molybdenum oxide precursor compound may not be used.

[0134] The metal compound other than the above molybdenum oxide precursor compound is not particularly limited, and examples thereof include aluminum compounds, silicon compounds, titanium compounds, magnesium compounds, sodium compounds, potassium compounds, zirconium compounds, yttrium compounds, zinc compounds, copper compounds, iron compounds, etc. Among these, as the above metal compound, it is preferable to use the above aluminum compound, silicon compound, titanium compound or magnesium compound.

[0135] An intermediate may be formed between the molybdenum oxide precursor compound and the metal compound other than the above molybdenum oxide precursor compound. However, even in such a case, the intermediate can be decomposed by calcination, and molybdenum trioxide can be vaporized in a thermodynamically stable form.

[0136] As the metal compound other than the above molybdenum oxide precursor compound, an aluminum compound is preferably used to prevent damage to the calcination furnace. In the above manufacturing method, in order to improve the purity of the molybdenum trioxide powder, it is also possible not to use the metal compound other than the above molybdenum oxide precursor compound.

[0137] Examples of the aluminum compound include aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum hydroxide, boehmite, pseudo-boehmite, transition alumina (γ-alumina, δ-alumina, θ-alumina, etc.), α-alumina, and mixed alumina having two or more crystal phases.

[0138] When calcining the raw material mixture containing the molybdenum oxide precursor compound and the metal compound other than the above molybdenum oxide precursor compound, the content ratio of the above molybdenum oxide precursor compound relative to 100% by mass of the raw material mixture is preferably 40% by mass or more and 100% by mass or less, may be 45% by mass or more and 100% by mass or less, and may be 50% by mass or more and 100% by mass or less.

[0139] The calcination temperature varies depending on the molybdenum oxide precursor compound, metal compound, and desired molybdenum trioxide particles used, etc. Usually, it is preferably set to a temperature at which the intermediate can be decomposed. For example, when using a molybdenum compound as the molybdenum oxide precursor compound and an aluminum compound as the metal compound, aluminum molybdate may be formed as an intermediate. Therefore, the calcination temperature is preferably 500 to 1500 °C, more preferably 600 to 1550 °C, and further preferably 700 to 1600 °C.

[0140] There is no particular limitation on the calcination time. For example, it can be set to 1 minute to 30 hours, can be set to 10 minutes to 25 hours, and can be set to 100 minutes to 20 hours.

[0141] The heating rate varies depending on the molybdenum oxide precursor compound used, the above-mentioned metal compound, and the characteristics of the desired molybdenum trioxide particles, etc. From the viewpoint of manufacturing efficiency, it is preferably 0.1 °C / minute to 100 °C / minute, more preferably 1 °C / minute to 50 °C / minute, and further preferably 2 °C / minute to 10 °C / minute.

[0142] The internal pressure in the roasting furnace is not particularly limited and can be a positive pressure or a reduced pressure. From the viewpoint of suitably discharging the molybdenum oxide precursor compound from the roasting furnace to the cooling pipe, roasting is preferably carried out under reduced pressure. As a specific degree of reduced pressure, it is preferably -5000 Pa to -10 Pa, more preferably -2000 Pa to -20 Pa, and further preferably -1000 Pa to -50 Pa. If the degree of reduced pressure is -5000 Pa or more, the high airtightness and mechanical strength of the roasting furnace are not overly required, and the manufacturing cost can be reduced, so it is preferred. On the other hand, if the degree of reduced pressure is -10 Pa or less, clogging of the molybdenum oxide precursor compound at the discharge port of the roasting furnace can be prevented, so it is preferred.

[0143] It should be noted that when blowing air into the roasting furnace during roasting, the temperature of the blown air is preferably 5 to 500 °C, more preferably 10 to 100 °C.

[0144] In addition, the blowing speed of the gas is preferably 1 L / minute or more and 500 L / minute or less, more preferably 10 L / minute or more and 200 L / minute or less, relative to the effective volume of 100 L of the roasting furnace.

[0145] The temperature of the vaporized molybdenum trioxide varies depending on the type of molybdenum oxide precursor compound used and is preferably 200 to 2000 °C, more preferably 400 to 1500 °C. It should be noted that if the temperature of the vaporized molybdenum trioxide is 2000 °C or less, there is usually a tendency to be easily granulated by blowing external air (0 to 100 °C) in the cooling pipe.

[0146] The discharge speed of the molybdenum trioxide vapor discharged from the roasting furnace can be controlled according to the amount of the above-mentioned molybdenum oxide precursor compound used, the amount of the above-mentioned metal compound, the temperature of the roasting furnace, the blowing of gas into the roasting furnace, and the diameter of the exhaust port of the roasting furnace. It also varies depending on the cooling capacity of the cooling pipe. The discharge speed of the molybdenum trioxide vapor from the roasting furnace to the cooling pipe is preferably 0.001 g / minute or more and 100 g / minute or less, more preferably 0.1 g / minute or more and 50 g / minute or less.

[0147] In addition, the content of the molybdenum trioxide vapor contained in the gas discharged from the roasting furnace is preferably 0.01 mg / L or more and 1000 mg / L or less, more preferably 1 mg / L or more and 500 mg / L or less.

[0148] Then, the above molybdenum trioxide vapor is cooled and granulated.

[0149] The cooling of the molybdenum trioxide vapor is carried out by keeping the cooling pipe at a low temperature. At this time, as the cooling mechanism, cooling based on the blowing gas into the cooling pipe as described above, cooling using the cooling mechanism of the cooling pipe, cooling using an external cooling device, etc. can be cited.

[0150] The cooling of the molybdenum trioxide vapor is preferably carried out in an air atmosphere. By cooling the molybdenum trioxide vapor in an air atmosphere to form molybdenum trioxide particles, the above ratio (I / II) can be set to be greater than 1.1, and it is easy to obtain the β crystal structure of MoO3 in the molybdenum trioxide particles.

[0151] The cooling temperature (the temperature of the cooling pipe) is not particularly limited, preferably -100 to 600 °C, more preferably -50 to 400 °C.

[0152] The cooling rate of the molybdenum trioxide vapor is not particularly limited, preferably 100 °C / s or more and 100000 °C / s or less, more preferably 1000 °C / s or more and 50000 °C / s or less. It should be noted that there is a tendency that the faster the cooling rate of the molybdenum trioxide vapor, the smaller the particle size and the larger the specific surface area of the obtained molybdenum trioxide particles.

[0153] When the cooling means is cooling based on the blowing gas into the cooling pipe, the temperature of the blowing gas is preferably -100 to 300 °C, more preferably -50 to 100 °C.

[0154] In addition, the blowing speed of the gas is preferably 0.1 m 3 / min or more and 20 m 3 / min or less, more preferably 1 m 3 / min or more and 10 m 3 / min or less. When the blowing speed of the gas is 0.1 m 3 / min or more, a high cooling rate can be achieved and blockage of the cooling pipe can be prevented, so it is preferred. On the other hand, when the blowing speed of the gas is 20 m 3 / min or less, an expensive first blowing mechanism (exhaust fan, etc.) is not required, and the manufacturing cost can be reduced, so it is preferred.

[0155] The particles obtained by cooling the molybdenum trioxide vapor are transported to a recovery machine for recovery.

[0156] The above method for manufacturing molybdenum trioxide particles can calcine the particles obtained by cooling the above molybdenum trioxide vapor again at a temperature of 100 to 320 °C.

[0157] That is, the molybdenum trioxide particles obtained by the above-described method for manufacturing molybdenum trioxide particles can be calcined again at a temperature of 100 to 320°C. The calcination temperature for the re-calcination can be 120 to 280°C, and can be 140 to 240°C. The calcination time for the re-calcination can be set, for example, to 1 minute to 4 hours, can be set to 10 minutes to 5 hours, and can be set to 100 minutes to 6 hours. Among them, by performing the re-calcination, a part of the β crystal structure of molybdenum trioxide disappears. If calcined at a temperature of 350°C or higher for 4 hours, the β crystal structure in the molybdenum trioxide particles disappears, and the above ratio (β(011) / α(021)) becomes 0, and the reactivity with sulfur is impaired.

[0158] Through the method for manufacturing molybdenum trioxide particles described above, molybdenum trioxide particles suitable for manufacturing the above-described molybdenum disulfide particles can be manufactured.

[0159] <Lubricating composition>

[0160] The lubricating composition of the present embodiment contains the above-described molybdenum disulfide particles and a base oil composed of one or more of mineral oil, synthetic oil, and semi-synthetic oil.

[0161] As the base oil that is a mineral oil, it includes oils obtained by rock drilling, oils obtained from plants or animals, and mixtures thereof. For example, as such oils, castor oil, lard, olive oil, peanut oil, corn oil, soybean oil, linseed oil, liquid petroleum, and base oils of paraffinic, naphthenic, or paraffin-naphthene mixed types can be cited, but are not limited to these. In a desired case, such a base oil can be partially or completely hydrogenated.

[0162] As the base oil that is a synthetic oil, for example, base oils of poly-α-olefin type, hydrocarbon type, ester type, ether type, silicone type, alkylnaphthalene type, or perfluoroalkyl polyether type can be cited.

[0163] The base oil that is a semi-synthetic oil refers to a base oil obtained by mixing these mineral oils and synthetic oils.

[0164] The above-described lubricating composition can use, without limitation, the base oils commonly used in lubricating compositions as the base oil.

[0165] The kinematic viscosity at 40°C of the base oil used in the lubricating composition of the present embodiment can be 1 mm 2 / s or more and 1000 mm 2 / s or less, can be 5 mm 2 / s or more and 200 mm 2 / s or less, and can be 10 mm 2 / s or more and 150 mm 2 / s or less. In the lubricating composition of the present embodiment, the median particle size D of molybdenum disulfide particles determined by the dynamic light scattering method 50 is as small as 10 nm or more and 1000 nm or less. Therefore, even when a base oil with a relatively low viscosity is used, sedimentation of molybdenum disulfide particles can be suppressed.

[0166] In the above lubricating composition, relative to 100% by mass of the total mass of the above lubricating composition, it is preferably contained 0.0001% by mass or more and 10% by mass or less of molybdenum disulfide particles as the above lubricant, more preferably 0.01% by mass or more and 10% by mass or less, and still more preferably 0.01% by mass or more and 1% by mass or less.

[0167] The lubricating composition of the present embodiment may be a lubricating composition further containing organometallic complex particles in the above lubricating composition. In this lubricating composition, relative to 100% by mass of the total mass of this lubricating composition containing the above lubricating composition and organometallic complex particles, it is preferably contained 0.0001% by mass or more and 10% by mass or less of organometallic complex particles, more preferably 0.01% by mass or more and 10% by mass or less, and still more preferably 0.01% by mass or more and 1% by mass or less. By containing 0.0001% by mass or more and 10% by mass or less of organometallic complex particles, the coefficient of friction can be significantly reduced, and in addition, a low coefficient of friction can be maintained for a long time.

[0168] As the organometallic complex constituting the organometallic complex particles, representative substances include organomolybdenum complexes such as molybdenum dialkyldithiocarbamate (MoDTC) and molybdenum dialkyldithiophosphate (MoDTP). In addition, organozinc complexes such as zinc dialkyldithiophosphate (ZnDTP) may also be contained. In addition, a plurality of these known organometallic complex particles may be contained in combination.

[0169] The above lubricating composition and the above lubricating composition may further contain known additives such as detergents, viscosity modifiers, antifoaming agents, corrosion inhibitors, rust inhibitors, antioxidants, antiwear agents, and friction modifiers.

[0170] The above lubricating composition may further contain a known dispersant contained in a normal lubricating oil. By the presence of the dispersant, storage stability can be more reliably ensured by further suppressing sedimentation.

[0171] Examples

[0172] Examples of the present invention will be described below. The present invention is not limited by the following examples.

[0173] [Synthesis Example] (Manufacture of molybdenum trioxide particles)

[0174] Prepare a roasting furnace equivalent to a heat-resistant container, a cooling pipe provided with an external gas supply port, and a dust collector for recovering molybdenum oxide. As the roasting furnace, use an RHK simulator (manufactured by NORITAKE CO., LIMITED), and as the dust collector, use a VF-5N dust collector (manufactured by AMANO Corporation) to manufacture metal oxides.

[0175] Mix 1.5 kg of aluminum hydroxide (manufactured by Nippon Light Metal Company) and 1 kg of molybdenum trioxide (manufactured by Nippon Inorganic Co., Ltd.), then put them into a crucible. Connect the roasting furnace, the cooling pipe, and the dust collector, and roast at a temperature of 1100 °C for 10 hours. During roasting, introduce external gas (blowing speed: 150 L / minute, external gas temperature: 25 °C) from the side and bottom of the roasting furnace. After molybdenum trioxide evaporates in the furnace, it is cooled near the dust collector and precipitates in the form of particles, so it is recovered by the dust collector.

[0176] After roasting, take out 1.0 kg of alumina as a blue powder and 0.8 kg of molybdenum trioxide recovered by the dust collector from the crucible.

[0177] The primary particle size of the recovered molybdenum trioxide is 1 μm or less, and it can be confirmed by fluorescent X-ray measurement that the purity of molybdenum trioxide is 99.8%.

[0178] (Manufacture of molybdenum disulfide particles)

[0179] [Example 1]

[0180] Add 40.0 g (277.9 mmol) of molybdenum trioxide prepared in Synthesis Example 1 and 40.0 g (1250 mmol, 4.5 equivalents relative to Mo atoms) of sulfur powder (manufactured by Kanto Chemical Co., Inc.) to an aluminum crucible, and mix with a stirring rod to make the powder uniform. After mixing, cover the aluminum crucible with a lid, put it into a high-temperature atmosphere roasting furnace (manufactured by Motoyama Corporation, SKM-2030P-OP), evacuate the inside of the furnace and then replace it with nitrogen, and then carry out roasting. The roasting conditions are: starting from the room temperature condition of 25 °C, raise the temperature at a rate of 5 °C / minute, and hold for 4 hours after reaching 500 °C. During the roasting process, blow nitrogen at 0.5 L / minute. After that, cool the furnace to room temperature by natural cooling to obtain 44.5 g of molybdenum disulfide particles.

[0181] For the sample of the molybdenum disulfide particles, measure it with a specific surface area meter (manufactured by MicrotracBEL Corporation, BELSORP-mini), and calculate the surface area of the measured average 1 g sample from the nitrogen adsorption amount based on the BET method. As the specific surface area, the result is 44.5 m 2 / g.

[0182] [Example 2]

[0183] Molybdenum disulfide particles were produced in the same manner as in Example 1. Thereafter, 3.39 g of the molybdenum disulfide particles were added to an alumina crucible (manufactured by Tokyo Glass Apparatus Co., Ltd., BA-0), and the lid was covered. The molybdenum disulfide particles were calcined in a nitrogen atmosphere at a heating rate of 5 °C / minute and a calcination temperature of 950 °C for 4 hours using a tubular furnace (manufactured by YAMADA DENKI Co., Ltd., TSS-1130-P), and then naturally cooled to obtain 3.27 g of molybdenum disulfide particles.

[0184] [Example 3]

[0185] The calcination temperature of the molybdenum disulfide particles was changed to 1100 °C. Otherwise, it was the same as in Example 2, and 3.13 g of molybdenum disulfide particles were obtained with a feed amount of 3.41 g.

[0186] [Comparative Example 1]

[0187] Commercially available molybdenum disulfide (MoS2) particles (manufactured by Kanto Chemical Co., Inc., molybdenum disulfide reagent) were prepared.

[0188] The molybdenum disulfide particles obtained in Examples 1 to 3 and Comparative Example 1 were measured and evaluated by the following method.

[0189] [Identification and Analysis of Crystal Structure]

[0190] The sample of the molybdenum disulfide particles was filled into a SUS-made holder for measurement specimens with a thickness of 2.4 mm and an inner diameter of 27 mm, and the measurement surface was smoothed. It was set on a multi-purpose X-ray diffraction (XRD) apparatus (manufactured by Malvern Panalytical Ltd., Empyrean 3) and measured under the following conditions: Cu / Kα ray; 45 kV / 40 mA; a monochromator was used on the incident side and a semiconductor high-speed detector (1D mode) was used on the detector side; focusing method; a rotating platform was used; the measurement time was 8 minutes (Examples 1 and 2, Comparative Example 1) or 10 minutes (Example 3); the step size was 0.066 degrees (Examples 1 and 2, Comparative Example 1) or 0.026 degrees (Example 3); the scanning range was 5 degrees or more and 100 degrees or less.

[0191] Rietveld analysis including microcrystalline size evaluation was performed using software (manufactured by Malvern Panalytical Ltd., HighScore Plus).

[0192] The crystallinity of molybdenum disulfide particles is calculated as follows: (1) Determine the background A from the apparatus and the boundary line of the obtained diffraction pattern in the range of 10 to 95°, and subtract the background A from the obtained diffraction pattern; (2) In the range of 10 to 95°, determine the broad peak B called the amorphous halo derived from the amorphous phase, and further subtract the background B from the obtained diffraction pattern; (3) Divide the sum of the peak intensities derived from the crystal, which is higher than the background A and the amorphous halo B, by the sum of the intensities in the XRD pattern except for the background A. The maximum value of the crystallinity is 99.95%, indicating the state where all molybdenum disulfide particles are crystallized.

[0193] Regarding the abundance ratios of the first crystal phase of the 2H crystal structure, the 3R crystal structure, and the second crystal phase of the 2H crystal structure in molybdenum disulfide particles, specifically, in Example 1, it is obtained by performing the following operations: Determine the crystallite size and abundance ratio of the 2H crystal structure through the broad peaks near 40° and 50°, and for the difference, optimize the 3R crystal structure parameters with the two peaks near 33° and the two peaks near 40°, thereby reproducing the overall measured XRD pattern.

[0194] In Examples 2 to 3 where it is not possible to fully fit the XRD pattern even by the above method, a crystal structure with a crystallite size smaller than that of the 2H crystal structure (crystal phase) in the crystal phase is set and the overall measured XRD pattern is reproduced, thereby obtaining it.

[0195] [Evaluation basic formula and calculation of crystallite size]

[0196] Usually, the crystallite sizes of the 2H crystal structure (the first and second crystal phases) and the 3R crystal structure are obtained using the diffraction pattern based on the analysis formula L = Kλ / βcosθ as the basic formula. In the above formula, K is the apparatus constant depending on the XRD optical system (incident side and detector side) and the setting, L is the size of the crystallite [m], λ is the wavelength of the measured X-ray [m], β is the half-value width [rad], and θ is the Bragg angle of the diffracted ray [rad].

[0197] [Median particle size D of molybdenum disulfide particles 50 Determination]

[0198] Add 0.1 g of molybdenum disulfide powder to 20 cc of acetone, perform ultrasonic treatment in an ice bath for 4 hours, and then further adjust the concentration with acetone to a range where it can be measured by a dynamic light scattering particle size distribution measuring device (manufactured by MicrotracBEL Corporation, NanotracWaveII) to obtain a measurement sample. Using this measurement sample, measure the particle size distribution in the range of 0.0001 μm to 10 μm using a dynamic light scattering particle size distribution measuring device, and calculate the median particle size D 50 (z-average). It should be noted that for the median particle size D 50For those over 10 μm (Comparative Example 1), a solution was similarly prepared, and the particle size distribution in the range of 0.015 μm to 500 μm was measured using a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, SALD-7000), and the median particle size D was determined. 50 .

[0199] [Measurement of (I / II) of Molybdenum Disulfide Particles]

[0200] 36.45 mg of molybdenum disulfide particles and 333.0 mg of boron nitride were mixed in a mortar. 123.15 mg of this mixture was weighed and compression-molded into tablets to obtain a measurement sample. Using this measurement sample, extended X-ray absorption fine structure (EXAFS) was measured by the transmission method using BL5S1 of the Aichi Synchrotron Radiation Center. Athena (Internet <URL: https: / / bruceravel.github.io / demeter / >) was used for the analysis.

[0201] In the radial distribution function obtained from this spectrum, the ratio (I / II) of the peak intensity I derived from Mo-S to the peak intensity II derived from Mo-Mo was 1.26 (= 19 / 15).

[0202] [Measurement of Friction Coefficient and Friction Evaluation of Lubricating Composition Containing Molybdenum Disulfide Particles]

[0203] To 90 parts by mass of a lubricating oil (manufactured by JXTG Corporation, SUPER OIL N32), 10 parts by mass of an additive (manufactured by Sanyo Chemical Industries, Ltd., Aclube702) and 0.08 parts by mass of the above molybdenum disulfide particles were added, and ultrasonic dispersion was carried out for 1 hour to prepare a lubricating composition.

[0204] A special platform (tribology-cell) with adjustable temperature for evaluating sliding characteristics was installed on a rheometer testing machine (manufactured by Anton Paar Corporation, MCR-502), and a friction and wear test was carried out. The lubricating composition prepared by the above method was added to a platform where the flat parts of 3 SUJ2 special stainless steel cylindrical pins were inclined at 45 degrees in the height direction and were evenly arranged at 120 degrees in the horizontal direction when viewed from directly above, and the contact surface was immersed. A 1 / 2-inch SUJ2 special stainless steel ball was brought into contact from above, and a specified load was applied in the vertical direction. After standing for 5 minutes, the rotational speed of the SUJ2 ball was changed from 3.0×10 -5 rpm to 3120 rpm, and the friction coefficient at each rotational speed was obtained. When the friction coefficient was less than or equal to the friction coefficient of the comparative example, it was rated as good "〇", when it was the best, it was rated as "◎", and when it exceeded or was equal to the friction coefficient of the comparative example, it was rated as bad "×".

[0205] The results of the above measurements and evaluations are shown in Tables 1 to 2 and Figures 2 to 11B .

[0206] [Table 1]

[0207]

[0208] [Table 2]

[0209]

[0210] First, a part of the X-ray diffraction (XRD) patterns of the molybdenum disulfide particles obtained in Examples 1 to 3 is shown in Figure 2 . As shown in this figure, the main peaks (A in the figure) are consistent around 2θ: 14° in Examples 1 to 3. In addition, they are also consistent with the main peaks of the 3R crystal structure and 2H crystal structure as references. In addition, the peaks (B in the figure) are consistent around 2θ: 39.5° and 2θ: 49.5° in Examples 1 to 3, and the peak positions are also almost the same as those of the 3R crystal structure and 2H crystal structure as references, but the peak shapes are different. Thus, it is confirmed that the heating conditions result in different ratios of the existence of the 3R crystal structure and 2H crystal structure and different crystallite sizes.

[0211] In addition, in this figure, the diffraction patterns of Examples 1 to 3 are different from each other. Thus, it is confirmed that the crystal state of the molybdenum disulfide particles changes according to the presence or absence of post-calcination and the post-calcination temperature.

[0212] Then, an attempt was made to separate the waveforms of the diffraction patterns of Examples 1 to 3, and according to Figure 3 the results, it was confirmed that both the 3R crystal structure and 2H crystal structure exist in Example 1 (calcination temperature 500 °C, no post-calcination). In addition, in Example 2 (calcination temperature 500 °C, post-calcination temperature 950 °C) and Example 3 (calcination temperature 500 °C, post-calcination temperature 1100 °C), Figure 2 the diffraction patterns are different from those of Example 1. Therefore, it is assumed that in addition to the 3R crystal structure and 2H crystal structure, there is also a second crystal phase of the 2H crystal structure with a small crystallite size, and an extended Rietveld analysis was performed. As a result, it was confirmed that in addition to the first crystal phase of the 3R crystal structure and 2H crystal structure as crystal phases, there is also a second crystal phase of the 2H crystal structure with an extremely small crystallite size in Examples 2 to 3 ( Figure 4 , Figure 5 ).

[0213] On the other hand, as Figure 6As shown, it was confirmed that a certain amount of 3R crystal structure was present in the commercially available molybdenum disulfide particles of Comparative Example 1, but it was confirmed that almost all were composed of the 2H crystal structure (see Table 2). In addition, the crystallinity was 99.95%, and it was confirmed that all the commercially available molybdenum disulfide particles were composed of crystalline phases. In addition, the median particle size D 50 was 13340 nm.

[0214] Then, the relationship between the final calcination temperature and the crystallite size in Examples 1 to 3 is shown in Figure 7 . As Figure 7 shown, in Example 1, the crystallite size of the 2H crystal structure (crystalline phase) was 9.6 nm, and the crystallite size of the 3R crystal structure (crystalline phase) was 11.8 nm. It can be seen that the crystallite size of the 2H crystal structure (crystalline phase) was as small as less than 10 nm. In addition, in Example 2, the crystallite size of the 2H crystal structure (the first crystalline phase) was 134.9 nm, the crystallite size of the 3R crystal structure (crystalline phase) was 12.5 nm, and the crystallite size of the 2H crystal structure (the second crystalline phase) was 3.0 nm. In Example 3, the crystallite size of the 2H crystal structure (the first crystalline phase) was 118.3 nm, the crystallite size of the 3R crystal structure (crystalline phase) was 36.3 nm, and the crystallite size of the 2H crystal structure (the second crystalline phase) was 4.3 nm. From this, it can be seen that by post-calcination, the crystallites of the 2H crystal structure (crystalline phase) grow significantly to form the crystallites of the 2H crystal structure (the first crystalline phase). In addition, the crystallite size of the newly formed 2H crystal structure (the second crystalline phase) by post-calcination is smaller than that of the 2H crystal structure (crystalline phase) before post-calcination.

[0215] Then, the X-ray diffraction (XRD) spectra used in the calculation of the crystallinity of the molybdenum disulfide particles obtained in Examples 2 and 3 are shown in Figure 8 and Figure 9 . In addition, the relationship between the calcination temperature and the crystallinity in Examples 1 to 3 is shown in Figure 10 .

[0216] As a result of calculating the crystallinity from the obtained diffraction spectra, the crystallinity in Example 1 (calcination temperature 500 °C, no post-calcination) was 78.7%, the crystallinity in Example 2 (calcination temperature 500 °C, post-calcination temperature 950 °C) was 89.1%, and the crystallinity in Example 3 (calcination temperature 500 °C, post-calcination temperature 1100 °C) was 94.4%. From this result, it was confirmed that the crystallinity increased by post-calcination. In addition, when the calcination temperature was the same and the post-calcination temperature was increased, the crystallinity of the molybdenum disulfide particles further increased.

[0217] Then, the relationship between the calcination temperature and the ratio of the presence of the 2H crystal structure and the 3R crystal structure in the crystalline phase in Examples 1 to 3 is shown in Figure 11AThe calculation results of the existence ratios of the respective crystal structures are as follows. In Example 1, the existence ratio of the 2H crystal structure (crystallite size of 20 nm or less) in the crystal phase was 71.5%, and the existence ratio of the 3R crystal structure was 28.5%. In Example 2, the existence ratio of the first crystal phase of the 2H crystal structure (crystallite size exceeding 20 nm) in the crystal phase was 23.5%, the existence ratio of the 3R crystal structure was 49.3%, and the existence ratio of the second crystal phase of the 2H crystal structure (crystallite size of 20 nm or less) was 27.2%. Further, in Example 3, the existence ratio of the first crystal phase of the 2H crystal structure (crystallite size exceeding 20 nm) in the crystal phase was 21.3%, the existence ratio of the 3R crystal structure was 57.7%, and the existence ratio of the second crystal phase of the 2H crystal structure (crystallite size of 20 nm or less) was 21.0%. From these results, it can be seen that when molybdenum trioxide particles are calcined at a calcination temperature of 500°C, the existence ratio of the 3R crystal structure in the crystal phase can be made as high as about 30%. It was also confirmed that when post-calcination is carried out at 950°C, the existence ratio of the amorphous phase of molybdenum disulfide particles is as low as 10.9%, and the existence ratio of the 3R crystal structure in the crystal phase is further increased. In addition, when the calcination temperature is the same and the post-calcination temperature is raised to 1100°C, the existence ratio of the amorphous phase of molybdenum disulfide particles is as low as 5.6%, and the existence ratio of the 3R crystal structure in the crystal phase is further increased.

[0218] Figure 11B FIG. showing the relationship between the calcination temperature and the existence ratios of the first and second crystal phases of the 2H crystal structure, the 3R crystal structure, and the amorphous phase in the particles in Examples 1 to 3 and Comparative Example 1. As Figure 11B shown, in Example 1, the existence ratio of the 3R crystal structure in the particles was significantly increased compared to Comparative Example 1. It was also found that the existence ratio of the 2H crystal structure including the crystal phase with a crystallite size of 20 nm or less was higher compared to Examples 2 to 3, and the existence ratio of the amorphous phase of molybdenum disulfide particles was also higher compared to Examples 2 to 3.

[0219] It can be seen that in Examples 2 and 3, by promoting the crystallization of the amorphous phase, the existence ratio of the amorphous phase was lower compared to Example 1, but higher compared to Comparative Example 1. Additionally, concomitantly, the existence ratio of the 3R crystal structure was higher compared to Comparative Example 1.

[0220] It was also found that in Examples 2 and 3, when the amorphous phase became the 2H crystal structure due to post-calcination, the second crystal phase with a crystallite size of 20 nm or less was formed. When calcined at 500°C, the crystallites of the 2H crystal structure with a crystallite size of 20 nm or less grew into crystallites of 100 nm or more due to post-calcination (see Table 2).

[0221] The results of the friction coefficient calculations and friction evaluations in Examples 1 to 3 and Comparative Example 1 are shown in Table 2. From the results in Table 2, it can be seen that in Example 1, the occupancy ratio of the 3R crystal structure in the crystal phase was 28.5% and the crystallite size of the 3R crystal structure was 11.8 nm. Compared with Comparative Example 1 where the occupancy ratio of the 3R crystal structure in the crystal phase was 2.9% and the crystallite size was 88.3 nm, the friction coefficient was smaller and the friction characteristics were improved. Additionally, it was found that in Example 1, the occupancy ratio of the 2H crystal structure containing crystallites with a crystallite size of 20 nm or less in the crystal phase was 71.5%, and the occupancy ratio of the amorphous phase in the particles was 21.3%. Compared with Examples 2 to 3, the friction coefficient became smaller and the friction characteristics were further improved.

[0222] In Examples 2 and 3, the occupancy ratios of the 3R crystal structure in the crystal phase were 49.3% and 57.7% respectively, and the crystallite sizes of the 3R crystal structure were 12.5 nm and 36.3 nm respectively. It can be seen that the friction coefficient was smaller and the friction characteristics were improved compared with Comparative Example 1. Additionally, it was found that in Examples 2 and 3, the occupancy ratios of the 2H crystal structure in the crystal phase containing crystallites with a crystallite size of 20 nm or less and the occupancy ratio of the amorphous phase in the particles were less than those in Example 1. However, the occupancy ratio of the 3R crystal structure and the crystallite size of the 3R crystal structure were larger than those in Example 1. As a result, a good friction coefficient was obtained compared with Comparative Example 1.

[0223] Examples 1 to 3 and Comparative Example 1 described above confirmed that the 3R crystal structure of the molybdenum disulfide particles, its crystallite size, and the median diameter D determined by dynamic light scattering 50 have a significant impact on the friction characteristics. Additionally, from the results of this example, it can be speculated that when the occupancy ratio of the 3R crystal structure of molybdenum disulfide is 20% or more, its crystallite size is 1 nm or more and 50 nm or less, the effects of the occupancy ratio of the 3R crystal structure and the crystallite size are significant. Even for molybdenum disulfide particles with a median diameter D 50 exceeding 1000 nm determined by dynamic light scattering, a good friction coefficient can be obtained.

[0224] [Friction Coefficient Measurement and Friction Evaluation of Lubricating Compositions Containing Molybdenum Disulfide Particles and Organometallic Complex Particles]

[0225] [Example 4]

[0226] To 90 parts by mass of a lubricating oil (manufactured by JXTG Corporation, SUPER OIL N32), 10 parts by mass of an additive (manufactured by Sanyo Chemical Industries, Ltd., Aclube 702), 0.08 parts by mass of the molybdenum disulfide particles of Example 1, and 0.8 parts by mass of organometallic complex particles (manufactured by ADEKA Corporation, SAKURA-LUBE 525 (MoDTC)) were added, and ultrasonic dispersion was carried out for 1 hour to prepare a lubricating composition.

[0227] [Example 5]

[0228] No organometallic complex particles were added, and 0.08 parts by mass of the molybdenum disulfide particles of Example 1 were added. Otherwise, a lubricating composition was prepared in the same manner as in Example 4.

[0229] [Comparative Example 2]

[0230] Neither the molybdenum disulfide particles nor the organometallic complex particles of Example 1 were added. Otherwise, a lubricating composition was prepared in the same manner as in Example 4.

[0231] [Comparative Example 3]

[0232] No molybdenum disulfide particles of Example 1 were added, and 0.8 parts by mass of organometallic complex particles (SAKURA-LUBE 525 (MoDTC) manufactured by ADEKA Corporation) were added. Otherwise, a lubricating composition was prepared in the same manner as in Example 4.

[0233] A special platform (tribology-cell) with adjustable temperature for evaluating sliding characteristics was installed on a rheometer tester (MCR-502 manufactured by Anton Paar), and a friction and wear test was conducted. The lubricating composition prepared by the above method was added to a platform where the flat parts of three cylindrical pins made of SUJ2 special stainless steel were inclined at 45 degrees along the height direction and were evenly arranged at 120 degrees in the horizontal direction when viewed from directly above, and the contact surfaces were immersed. A 1 / 2-inch SUJ2 special stainless steel ball was brought into contact from above, and a specified load was applied in the vertical direction. After standing for 5 minutes, the temperature of the platform was changed to 25 - 100 °C, and the friction coefficient at each temperature was obtained. The temperature of the platform was equal to the temperature of the lubricating composition, and by changing the platform temperature, the temperature of the lubricating composition could be adjusted. At this time, the rotation speed of the SUJ2 ball was set to 600 rpm. This lubricating composition was set as Example 4, and the friction coefficient was compared with Comparative Examples 2 - 4 shown in Table 3. When the friction coefficient was less than or equal to that of Comparative Example 2, it was rated as good "〇", and when it was the best at the same temperature, it was rated as "◎", and when it exceeded or was equivalent to the friction coefficient of Comparative Example 2, it was rated as poor "×". The results are shown in Table 3.

[0234] [Table 3]

[0235]

[0236] From the results in Table 3, it can be seen that the lubricating composition of Example 4 contains both molybdenum disulfide particles and organometallic complex particles, so that the friction coefficient reduction effects of these two kinds of particles are combined, and the friction coefficient can be significantly reduced in the temperature range of 25 - 100 °C.

[0237] In addition, compared with Comparative Example 2 containing only molybdenum disulfide particles, the friction coefficient can be reduced over the entire temperature range. Especially in the temperature range of 25 to 50 °C, the friction coefficient is significantly reduced.

[0238] On the other hand, in Comparative Example 3 containing only organometallic complex particles, although the friction coefficient is lower over the entire temperature range compared to Comparative Example 2 without molybdenum disulfide particles and organometallic complex particles, compared with Example 4, especially in the temperature range of 25 to 50 °C, the friction coefficient increases.

[0239] Then, the measurement results of the time dependence of the friction coefficient at 75 °C in representative Example 4 and Comparative Example 3 are shown in Figure 12 .

[0240] As Figure 12 shown, in Example 4 containing both molybdenum disulfide particles and organometallic complex particles of Example 1, after 600 seconds, sludge caused by molybdenum dialkyldithiocarbamate (MoDTC) (manufactured by ADEKA Corporation, SAKURA-LUBE 525) used as the organometallic complex particles is generated, and the friction coefficient temporarily increases. However, due to the molybdenum disulfide particles, the friction coefficient decreases, and a low friction coefficient equivalent to that before sludge generation can be maintained for a long time of more than 150 seconds after sludge generation (an increase of about 20%). It can be seen that the time dependence of the friction coefficient is good "〇".

[0241] On the other hand, in Comparative Example 3 containing only organometallic complex particles, after 600 seconds, sludge caused by molybdenum dialkyldithiocarbamate (MoDTC) (manufactured by ADEKA Corporation, SAKURA-LUBE 525) used as the organometallic complex particles is generated, the friction coefficient increases, and a high-load state is formed, so the test cannot be continued. Therefore, the time dependence of the friction coefficient is poor "×".

[0242] Description of reference numerals

[0243] 1 Manufacturing device

[0244] 2 Roaster

[0245] 3 Cooling pipe

[0246] 4 Recovery machine

[0247] 5 Exhaust port

[0248] 6 Opening adjustment damper

[0249] 7 Observation window

[0250] 8 Exhaust device

[0251] 9 External cooling device

Claims

1. A molybdenum disulfide particle having a 2H crystal structure and a 3R crystal structure of molybdenum disulfide, wherein the proportion of the 3R crystal structure in the crystal phase of molybdenum disulfide is 10% or more, the crystallite size of the 3R crystal structure is 1 nm or more and 150 nm or less, and the crystallite size of the 3R crystal structure is calculated as follows; using the spectrum obtained by powder X-ray diffraction (XRD) with Cu-Kα ray as the X-ray source, based on the analytical formula L = Kλ / (βcosθ), it is calculated by the extended Rietveld analysis, in the formula, K is a device constant depending on the XRD optical system and the set-up, the XRD optical system is located on the incident side and the detector side, L is the size of the crystallite [m], λ is the wavelength of the measured X-ray [m], β is the half-value width [rad], and θ is the Bragg angle of the diffraction line [rad].

2. The molybdenum disulfide particles according to claim 1, wherein, The 3R crystal structure obtained by the extended Rietveld analysis is composed of the following crystal phase: a crystal phase composed of crystallites with a crystallite size of 5 nm or more and 50 nm or less calculated based on the analytical formula.

3. The molybdenum disulfide particles according to claim 1, wherein, The 2H crystal structure obtained by the extended Rietveld analysis is composed of the following crystal phase: a crystal phase composed of crystallites having a specified crystallite size, the crystallite size of the crystal phase of the 2H crystal structure is 1 nm or more and 20 nm or less.

4. The molybdenum disulfide particles according to claim 3, wherein, The proportion of the 2H crystal structure and the 3R crystal structure in the crystal phase obtained by the extended Rietveld analysis using the spectrum obtained by the XRD is 10:90 to 90:

10.

5. The molybdenum disulfide particles according to claim 1, wherein, The 2H crystal structure obtained by the extended Rietveld analysis is composed of the following crystal phase: a first crystal phase composed of crystallites having a specified crystallite size and a second crystal phase having a smaller crystallite size than the first crystal phase, the crystallite size of the second crystal phase of the 2H crystal structure is 1 nm or more and 20 nm or less.

6. The molybdenum disulfide particles according to claim 5, wherein, The proportion of the first crystal phase of the 2H crystal structure, the 3R crystal structure, and the second crystal phase of the 2H crystal structure obtained by the extended Rietveld analysis using the spectrum obtained by the XRD in the crystal phase is 30 to 10:10 to 70:80 to 15.

7. The molybdenum disulfide particles according to claim 1, wherein, The molybdenum disulfide particle contains an amorphous phase, and the proportion of the amorphous phase of the molybdenum disulfide particle is 5% or more.

8. The molybdenum disulfide particles according to claim 1, wherein, In the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) spectrum at the K absorption edge of molybdenum, the ratio (I / II) of the intensity I of the peak derived from Mo-S to the intensity II of the peak derived from Mo-Mo is greater than 1.

0.

9. The molybdenum disulfide particles according to claim 1, wherein, The median particle size D of molybdenum disulfide particles determined by dynamic light scattering method 50 is 10 nm or more and 1000 nm or less.

10. The molybdenum disulfide particles according to claim 1, wherein, The specific surface area of the molybdenum disulfide particles measured by the BET method is 10 m 2 / g or more.

11. A lubricating composition containing: the molybdenum disulfide particle according to any one of claims 1 to 10; a base oil composed of one or more of mineral oil, synthetic oil, and semi-synthetic oil; and an additive.

12. The lubricating composition according to claim 11, wherein, The molybdenum disulfide particle is contained in an amount of 0.0001% by mass or more and 10% by mass or less based on 100% by mass of the total mass of the lubricating composition.

13. The lubricating composition according to claim 11, wherein, It further contains organometallic complex particles.

14. The lubricating composition according to claim 13, wherein, The organometallic complex particles are contained in an amount of 0.0001% by mass or more and 10% by mass or less relative to 100% by mass of the total mass of the lubricating composition.

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