WO2014189065A1

WO2014189065A1 - Water-based lubricant

Info

Publication number: WO2014189065A1
Application number: PCT/JP2014/063398
Authority: WO
Inventors: 博木之下; 勇太仁科
Original assignee: 国立大学法人岡山大学
Priority date: 2013-05-20
Filing date: 2014-05-20
Publication date: 2014-11-27
Also published as: JPWO2014189065A1

Abstract

Provided is a water-based lubricant that is water-based in order to resolve the problem of flammability, and in which the need for additives such as surfactants can be minimized to reduce the cost associated with processing the waste liquid after use. A water-based lubricant in which graphene oxide, obtained by performing a separation process on graphite and separating the graphene oxide from the graphite, is dispersed in water. The separation process causes the separation by the graphite being mixed into an aqueous solution containing an oxidation agent, and caused to oxidize. The graphite is a fine powder having an average grain size of 100 μm or less and contains graphene oxide at a concentration of 0.1wt% or above. If the average grain size of the graphite is 50 μm or less, the graphene oxide is contained at a concentration of 0.01 wt% or above.

Description

Water based lubricant

The present invention relates to an aqueous lubricant containing graphene oxide.

Conventionally, oil-based materials such as machine oil and machining oil are used as lubricants. Further, in order to improve lubricity, a coating made of a highly lipophilic material is provided on the contact surface. For example, it has been proposed to use a carbon atom-containing inorganic material such as graphite, diamond-like carbon, or carbon nanotube as a highly lipophilic material (see, for example, Patent Document 1). In particular, these coatings are formed on the inner surface of the surface texturing by innumerable recesses formed on the contact surface.

Oil-based lubricants are extremely inexpensive and are widely used. However, when an oil-based lubricant is used as, for example, cutting oil, it is necessary to degrease the workpiece, and various chemicals for this degreasing treatment are necessary, and it is easy to increase the cost in the post-treatment. It was.

Also, since oil-based lubricants have a problem of flammability, water-soluble lubricants that are used by mixing with water are also used recently. However, even when a water-soluble lubricant is used, a cleaning process using an appropriate chemical is necessary, and an aqueous lubricant that can be easily post-processed has been demanded.

Therefore, an aqueous lubricant containing a nanocarbon material such as fullerene in an aqueous solvent (see, for example, Patent Document 2), or processing in which ultrafine particles such as fullerene and carbon nanotubes are dispersed in water containing a surfactant. A working fluid (see, for example, Patent Document 3) has been proposed.

JP 2012-197900 A JP 2009-173814 A JP 2004-331737 A

However, water-based lubricants in which carbon materials such as fullerenes are dispersed originally have low dispersibility of carbon materials such as fullerenes in water, so various additives such as surfactants are necessary and are flammable. Although this problem has been solved, the waste liquid treatment is not easy, and the waste liquid treatment after use has a problem of increasing costs.

On the other hand, one of the inventors of the present invention has invented a production method that makes it possible to produce graphene oxide highly dispersed in water at a lower cost than before. The inventors of the present invention have been studying the use of graphene oxide produced by this production method. As a result, they have found that it can be used as a lubricant, and have achieved the present invention.

The aqueous lubricant of the present invention is an aqueous lubricant in which graphene oxide formed by exfoliating graphite and exfoliating it from graphite is dispersed in water. The exfoliation treatment is performed by mixing graphite with an aqueous solution containing an oxidizing agent. In this way, peeling is caused by oxidizing graphite.

The aqueous lubricant of the present invention is also characterized by the following points.
(1) The graphite should be fine powder with an average particle size of 100 μm or less.
(2) Containing graphene oxide at a concentration of 0.1 wt% or more.
(3) Graphite should contain graphene oxide at a concentration of 0.01 wt% or more as a fine powder with an average particle size of 50 μm or less.

According to the present invention, an aqueous lubricant using graphene oxide that is highly dispersed in water can be used as a lubricant without using an extra additive. Furthermore, in the water-based lubricant of the present invention, graphene oxide itself is harmless in post-treatment after use as a lubricant, so that it can be disposed of easily and at low cost.

It is a scanning electron microscope (SEM) photograph in a state where graphene oxide (SP1GO) made from graphene called SP1 and graphene oxide (X100GO) made from graphene called X100 are dropped onto a silicon oxide film substrate. (A) is a graph showing a change in friction coefficient when reciprocating sliding is performed 60,000 times with a friction tester of purified water alone, SP1GO dispersion water, X100GO dispersion water, and a commercially available water-soluble lubricant. (B) is a graph showing the change in the coefficient of friction when the reciprocating sliding is performed 60,000 times by the friction tester due to the difference in SP1GO concentration in SP1GO dispersion water, and (c) is the X100GO dispersion. It is a graph which shows a friction coefficient change when performing 60,000 reciprocating slidings by the friction test machine by the difference in the density | concentration of X100GO in water. There is a graph with a cross-sectional curve measured using a confocal laser microscope on the sliding surface of the substrate (SUS304) after 60,000 sliding tests with a friction tester, where (a) is only purified water, b) is the case of 1 wt% SP1GO dispersed water. It is a SEM image of the sliding surface of the ball after only 60,000 sliding tests with a friction tester in the case of purified water only. It is a SEM image of the sliding surface of the ball after 16,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water. (A) is an SEM image of the sliding surface of the ball after 60,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water. (B) is the sliding surface of (a). It is a measurement result of carbon element component distribution by energy dispersive X-ray spectroscopic analysis (EDX). (A) is an SEM image of the sliding surface of the substrate (SUS304) after 60,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water, and (b) is (a) 3 is a measurement result of a carbon element component distribution by energy dispersive X-ray spectroscopy (EDX) on a sliding surface of the steel. It is a graph which shows a friction coefficient change when performing reciprocating sliding 60,000 times only with purified water with a friction test machine using a SUS304 ball and a SUS304 substrate, and SP1GO dispersion water. It is an SEM image of the sliding surface of a ball (SUS304) after purified water only and 60,000 sliding tests with a friction tester. It is a SEM image of the sliding surface of a ball (SUS304) after 60,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water. It is a graph which shows a friction coefficient change when performing reciprocating sliding 60,000 times only with purified water with a friction test machine using a ball made of SUJ2 and a substrate made of SUS304, and SP1GO dispersion water. It is a SEM image of the sliding surface of the ball (SUJ2) after pure water only and after 60,000 sliding tests with a friction tester. It is a SEM image of the sliding surface of the ball (SUJ2) after 60,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water. This is a graph showing the change in friction coefficient when reciprocating sliding of only purified water in a friction tester using a SUS304 ball, a DLC substrate and a single crystal diamond substrate and SP1GO dispersed water. is there. SEM images of the sliding surface of the ball (SUS304) after 21,000 sliding tests using a friction tester, (a) with purified water only, (b) with 1 wt% SP1GO dispersed water It is. SEM images of the sliding surface of the substrate (single crystal diamond substrate) after 21,000 sliding tests with a friction tester, (a) with purified water only, (b) with 1 wt% SP1GO dispersion This is the case with water.

The aqueous lubricant of the present invention is an aqueous lubricant in which graphene oxide obtained by subjecting graphite to exfoliation and exfoliating from graphite is dispersed in water. In particular, in the exfoliation treatment, exfoliation is caused by mixing graphite in an aqueous solution containing an oxidizing agent to oxidize the graphite.

Thus, by dispersing graphene oxide formed by peeling from graphite into water to form an aqueous lubricant, the graphene oxide can be suitably maintained in a dispersed state without any other additive, and used as a lubricant. Can function.

Moreover, since graphene oxide itself is harmless and functions as a lubricant even without other additives, it can be disposed of easily and at low cost in post-treatment after use as a lubricant. If necessary, graphene oxide can be decomposed by adding an appropriate acid to the waste liquid after use as a lubricant, and the graphene oxide itself can be lost.

The graphite to be exfoliated is desirably a fine powder having an average particle diameter of 100 μm or less, and preferably a fine powder having an average particle diameter of 50 μm or less.

By setting the average particle size of graphite to 100 μm or less, the average particle size of graphene oxide also becomes 100 μm or less, and the graphene oxide concentration in the aqueous lubricant can be used as a lubricant by setting it to 0.1 wt% or more.

Furthermore, by setting the average particle size of graphite to 50 μm or less, the average particle size of graphene oxide also becomes 50 μm or less, and the concentration of graphene oxide in an aqueous lubricant can be set to 0.01 wt% or more and can be used as a lubricant. That is, by using graphene oxide having a smaller diameter, the concentration of graphene oxide can be reduced, and the amount of graphene oxide used can be reduced, so that a less expensive aqueous lubricant can be provided.

The water-based lubricant of the present invention will be described in detail below with reference to specific examples.

First, a friction tester was used as a method for evaluating the aqueous lubricant of the present invention. The friction tester used in this example is composed of a flat substrate, a ball arranged in contact with the upper surface of the substrate, and a sliding mechanism for reciprocatingly sliding the ball on the substrate. . In the friction tester, the ball is reciprocated on the substrate without rotating at all.

The material of the substrate is SUS304 and the surface is smoothed by grinding. The material of the ball is a very hard ball for bearings (tansten carbide), with a 1 mm radius. The ball sliding conditions were such that the sliding distance for one cycle was about 2 mm and the sliding time for one cycle was about 0.2 seconds. That is, the sliding speed is approximately 0.02 m / s.

As graphene oxide, graphene oxide created by oxidizing graphite called “SP1” and graphene oxide created by oxidizing graphite called “X100” were used. Hereinafter, for convenience of explanation, the respective graphene oxides are simply referred to as “SP1GO” and “X100GO”.

For producing graphene oxide from graphite, a production method described in Japanese Patent No. 5098064 was used.

That is, first, the raw material graphite is irradiated with microwaves using a microwave oven, and then the graphite irradiated with the microwaves is mixed with an oxidizing agent composed of sulfuric acid, sodium nitrate, and potassium permanganate. It was oxidized by mixing with an aqueous solution to produce exfoliation as graphene oxide.

By preparing graphene oxide by this method, an aqueous graphene oxide solution having high water dispersibility can be prepared, and an inexpensive graphene oxide aqueous solution can be provided.

Conventional graphene oxide has become an expensive material not only due to an increase in manufacturing cost due to a long time required for manufacturing but also due to an increase in manufacturing cost due to a large amount of chemicals used. . Therefore, it has been considered that the use of graphene oxide as a lubricant material is not cost effective. However, one of the inventors of the present invention can provide graphene oxide at a cost practical as a lubricant material by inventing the manufacturing method described in Japanese Patent No. 5098064 as an inexpensive manufacturing method. became.

FIG. 1 shows a scanning electron microscope (SEM) photograph of SP1GO and X100GO dropped on a silicon oxide film substrate. SP1GO is over 50μm in one large size, but X100GO is about 5μm in size. The difference in size is caused by the size of the raw graphite powder, and it is desirable to adjust the size of the graphite powder so that a desired size can be obtained. In particular, graphite is desirably a fine powder having an average particle size of 100 μm or less, and preferably has an average particle size of 50 μm or less.

SP1GO and X100GO were subjected to the following comparative tests as dispersed water adjusted to a desired concentration.

In FIG. 2 (a), as a comparative test of purified water alone, SP1GO dispersed water, X100GO dispersed water, and a commercially available water-soluble lubricant, 60,000 reciprocating slides were performed using the friction tester described above. It shows the coefficient of friction change. Here, the SP1GO dispersion water and the X100GO dispersion water each had a concentration of 1 wt%, and the commercially available water-soluble lubricant was a 1% aqueous solution.

As is clear from the graph of FIG. 2 (a), the friction coefficient of purified water is 0.4 or more, and the friction coefficient of the water-soluble lubricant is around 0.1. On the other hand, the friction coefficients of SP1GO dispersion water and X100GO dispersion water are each around 0.05, indicating that the friction coefficient is lower than that of the water-soluble lubricant and extremely good lubrication characteristics.

Fig. 2 (b) shows the change in the friction coefficient when the reciprocating slide is performed 60,000 times with a friction tester as a comparative test based on the difference in SP1GO concentration in SP1GO dispersed water. As a comparative example, only purified water is shown.

As is clear from the graph in FIG. 2 (b), the friction coefficient of 1wt% SP1GO dispersed water is the lowest at 0.05, the friction coefficient of 0.1wt% SP1GO dispersed water is around 0.1, and 0.01wt% SP1GO dispersed water. It can be seen that the coefficient of friction finally exceeds 0.3. Thus, it was confirmed that there was a lubricating effect even at 0.01 wt%, compared with that of purified water alone. However, if the same level of performance as that of a commercially available water-soluble lubricant is required, the concentration of SP1GO dispersed water is desirably 0.1 wt% or more.

Fig. 2 (c) shows the coefficient of friction change when reciprocating 60,000 times with a friction tester as a comparative test based on the difference in X100GO concentration in X100GO dispersed water. As a comparative example, only purified water is shown.

As is clear from the graph of FIG. 2 (c), the friction coefficient of 1 wt% X100GO dispersed water and the friction coefficient of 0.1wt% X100GO dispersed water are approximately the same, about 0.05 at first, and finally about 0.1. The friction coefficient of 0.01wt% X100GO dispersed water is about 0.15 at first and finally about 0.1, and the friction coefficient of 0.001wt% X100GO dispersed water is almost the same as that of purified water alone. I understand. Thus, it can be seen that X100GO dispersed water has a friction reducing effect at a concentration of 0.01 wt% or more.

Note that the reason why X100GO dispersed water is more effective than SP1GO dispersed water is that the average particle size of X100GO is smaller than that of SP1GO, as is apparent from FIG. Conceivable. That is, by using graphene oxide having a particle size as small as possible, it is possible to obtain a graphene oxide dispersed water with a lower concentration, and further cost reduction can be achieved.

FIG. 3 shows a cross-sectional curve obtained by measuring the sliding surface of the substrate (SUS304) after 60,000 sliding tests with a friction tester using a confocal laser microscope. FIG. 3A shows the case of purified water only, and FIG. 3B shows the case of 1 wt% SP1GO dispersed water.

As is clear from the graph in FIG. 3A, a level difference of about 5 μm is observed in the case of purified water alone. That is, it can be seen that wear has occurred. On the other hand, as is apparent from the graph of FIG. 3B, no step is observed in the SP1GO dispersed water, and it can be seen that almost no wear occurs.

Fig. 4 shows an SEM image of the sliding surface of the ball after only 60,000 sliding tests with a friction tester in the case of purified water only. The arrow line in Fig.4 (a) has shown the sliding direction. FIG. 4B is an enlarged SEM image of a part of FIG. The balls are cleaned in acetone using an ultrasonic cleaner after the sliding test.

In FIG. 4 (a), the broken line circled portion is the sliding surface of the ball, which is approximately 300 μm in size and flat, and it can be seen that it is worn. When calculated geometrically, the wear depth is about 5 μm. The ball is synthesized by sintering fine particles of tungsten carbide. From the enlarged view of FIG. 4B, it can be seen that the fine particles are missing and defective.

Fig. 5 shows an SEM image of the sliding surface of the ball after 60,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water. The arrow line in Fig.5 (a) has shown the sliding direction. FIG. 5B is an enlarged SEM image of a part of FIG. The balls are cleaned in acetone using an ultrasonic cleaner after the sliding test.

As is clear from FIGS. 5 (a) and 5 (b), in the case of 1 wt% SP1GO dispersed water, no wear due to sliding was observed on the balls. In particular, as is apparent from FIG. 5B, it can be seen that the tungsten carbide fine particles, which are the same as before the sliding, remain in a densely sintered state.

As can be seen in FIG. 5A, it can be seen that a dark streak pattern is formed along the sliding direction. Further, as can be seen in FIG. 5B, the gaps between the tungsten carbide particles are clearly observed even in the dark imaged area, as if the permeable thin film is adsorbed on the surface. Looks like.

In general, when a few layers of graphene oxide adsorbed on the surface of another substance are observed with an SEM, an electron beam passes through the graphene oxide and forms an image on the lower side. However, in that case, the intensity is weakened, and as a result, the portion where graphene oxide exists is darkly imaged, so the portion imaged like this dark streak adsorbs graphite oxide on the surface of the ball It seems to have done. In order to clarify this, the surface elemental components were examined as follows.

Fig. 6 (a) is an SEM image of the sliding surface of the ball after 60,000 sliding tests with a friction tester in the case of 1wt% SP1GO dispersed water, and Fig. 6 (b) shows Fig. 6 (b). The measurement result of the carbon element component distribution by the energy dispersive X-ray-spectroscopy (EDX) in the sliding surface of a) is shown. In FIGS. 6A and 6B, the vertical direction is the sliding direction.

From FIG. 6 (b), it can be seen that a large amount of carbon component is contained in the area darkly shown in FIG. 6 (a).

Fig. 7 (a) is an SEM image of the sliding surface of the substrate (SUS304) after 60,000 sliding tests with a friction tester in the case of 1wt% SP1GO dispersed water. Fig. 7 (b) The measurement result of the carbon element component distribution by the energy dispersive X-ray-spectroscopy (EDX) in the sliding surface of Fig.7 (a) is shown. 7A and 7B, the vertical direction is the sliding direction.

FIG. 7B also shows that a lot of carbon components are contained in the place darkly shown in FIG. 7A.

Therefore, it seems that one or several layers of graphite oxide are adsorbed on the sliding surface, and it is adhering to some extent firmly because it is not peeled off even if ultrasonic cleaning with acetone is performed. Seem.

From these results, graphene oxide dispersed water not only lowers the coefficient of friction on the practical material surface of SUS304-tanstencarbite but also shows no wear. It was confirmed that the performance was shown.

This seems to have been realized because graphite oxide was adsorbed in one or several layers on the sliding surface, preventing direct contact between the substrate and ball material on the sliding surface, and reducing friction and wear.

In the embodiments described above, the water-based lubricant of the present invention is composed only of water and graphene oxide, but an appropriate preservative, pH adjusting solution, or the like may be added for commercialization.

As another example, FIG. 8 shows the test results with a friction tester when the ball material is SUS304. Here, the material of the substrate is SUS304, and the surface is smoothed by grinding. The ball had a radius of 1 mm, and the sliding condition of the ball was that the sliding distance of one cycle was about 2 mm and the sliding cycle was 500 rpm. The load acting on the substrate was 1.8N.

In Fig. 8, comparison is made between purified water only (white circle graph) and SP1GO dispersed water (black circle graph). The friction coefficient of purified water is 0.5 or more, and the friction coefficient of SP1GO dispersed water is 0.2. there were. The concentration of P1GO dispersed water was 1 wt%.

FIG. 9 shows an SEM image of the sliding surface of the ball after 60,000 sliding tests with a friction tester using only purified water. FIG. 10 shows an SEM image of the sliding surface of the ball after 60,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water.

As another example, FIG. 11 shows a test result by a friction tester when the ball material is SUJ2. Here, the material of the substrate is SUS304, and the surface is smoothed by grinding. The ball had a radius of 1 mm, and the sliding condition of the ball was that the sliding distance of one cycle was about 2 mm and the sliding cycle was 500 rpm. The load acting on the substrate was 1.8N.

In Fig. 11, comparison is made between purified water only (white circle graph) and SP1GO dispersion water (black circle graph). The friction coefficient of purified water is 0.4 or more, and the friction coefficient of SP1GO dispersion water is 0.1. there were. The concentration of P1GO dispersed water was 1 wt%.

FIG. 12 shows an SEM image of the sliding surface of the ball after 60,000 sliding tests with a friction tester in the case of purified water alone. FIG. 13 shows an SEM image of the sliding surface of the ball after 60,000 sliding tests with a friction tester in the case of 1 wt% SP1GO dispersed water.

As another example, the results of a test using a friction tester on a DLC substrate with diamond-like carbon (hereinafter referred to as “DLC”) as a substrate material and a single crystal diamond substrate with single crystal diamond are shown. As shown in FIG. Here, the material of the ball was SUS304, the radius of the ball was 1 mm, and the sliding condition of the ball was that the sliding distance of one cycle was about 2 mm and the sliding cycle was 500 rpm. The load acting on the substrate was 11.1N.

In FIG. 14, the square dots (■) indicate the case of DLC substrate-SUS304 ball-purified water only, and the diamond-shaped dots (♦) indicate the case of DLC substrate-SUS304 ball-1 wt% SP1GO dispersion water. It was confirmed that the friction coefficient can be reduced by SP1GO dispersed water.

In addition, in FIG. 14, the point x indicates the case of single crystal diamond substrate-SUS304 ball-purified water only, and the triangular point (▲) indicates single crystal diamond substrate-SUS304 ball-1 wt% SP1GO dispersion. The case of water is shown, and in the single crystal diamond substrate, there was no difference in the friction coefficient.

However, the wear states of the sliding surfaces on the ball side and the substrate side are greatly different as shown in FIGS. 15 and 16, and it can be seen that the wear can be greatly reduced in the case of 1 wt% SP1GO dispersed water.

That is, as shown in FIG. 15 (a), the sliding surface of the ball after the sliding test of 21,000 times by the friction tester has a large friction mark in the case of purified water alone, As shown in FIG. 15 (b), when 1 wt% of SP1GO dispersed water is used, almost no friction marks are generated.

On the other hand, the sliding surface of the substrate is larger in the frictional trace when 1 wt% SP1GO dispersed water shown in FIG. 16B is compared with the frictional trace of purified water alone shown in FIG. The thickness can be reduced to half or less.

Thus, it can be seen that the water-based lubricant in which graphene oxide is dispersed has excellent characteristics as a lubricant.

It is a high-performance lubricant that can be used at low temperatures that do not exceed the boiling point of water. It can reduce the cost required for post-processing and disposal, and can be used as a lubricant in metal processing such as cutting.

Claims

An aqueous lubricant in which graphene oxide formed by exfoliating graphite and exfoliating it from graphite is dispersed in water,
The stripping treatment is an aqueous lubricant which is a stripping treatment by mixing graphite in an aqueous solution containing an oxidizing agent to oxidize the graphite.
The aqueous lubricant according to claim 1, wherein the graphite is a fine powder having an average particle diameter of 100 µm or less.
The aqueous lubricant according to claim 2, containing the graphene oxide at a concentration of 0.1 wt% or more.
The aqueous lubricant according to claim 2, wherein the graphite contains the graphene oxide at a concentration of 0.01 wt% or more as a fine powder having an average particle size of 50 µm or less.