Application of flake nanographite in lubricating oil

Nano- graphite was used as a liquid paraffin additive and tested on friction and wear to investigate its lubricating properties. The results show that the friction coefficient of liquid paraffin with a certain amount of flake nanographite is significantly reduced.

In the development of the modern national economy, especially in the field of machinery industry, lubricating oil has a wide range of applications, and some people have compared it to "keeping the blood of normal operation of the machinery." Proper use of lubricating oil is a basic measure to ensure and improve the energy-saving, efficient and long-term normal operation of mechanical equipment. The lubricity and wear resistance of lubricating oils are important indicators of the quality of lubricating oils. In order to compensate for the defects of lubricating oil, the quality of oil products from the refining process alone cannot meet the requirements of harsh conditions such as low speed, high speed, high load, high power, high temperature, low temperature and high vacuum, but must be added to the lubricating oil. Various additives. Currently, is used as lubricating oil additives to be studied nanoparticles mainly elemental nano powder, nano-oxides, nano hydroxide, sulfide nano, nano borate, polymeric nanospheres and nanometer rare earth compound.

First, the test

(1) Pretreatment of flake nanographite

The flake nanographite used in this experiment contains about 65% of water, and the water will play a role in corrosion during the rubbing process, so it must be pretreated before the experiment.

Add a certain amount of nano-graphite slurry to the beaker, add a small amount of liquid paraffin, and perform ultrasonic vibration for about 10 to 20 minutes. The water on the graphite surface is mostly replaced, and the water does not contain graphite and liquid paraffin. The upper layer of water is separated by a tilting method. At this time, the surface of the graphite and the liquid paraffin still contained part of the water, and in order to remove the remaining water, a method of heating under reduced pressure in a DZF-6050 vacuum drying oven was employed.

(2) Screening of dispersants

After removing the water, some dispersion stabilizers will be added, and a certain proportion of base oil and flake nanographite will be selected to investigate the dispersibility of the nano-graphite and the stability of the suspension, and it is necessary to continuously screen and adjust the formulation.

The base oil used in this experiment is liquid paraffin, and its physical and chemical properties are shown in Table 1.

Table 1 Physical and chemical properties of liquid paraffin

1, the dispersion performance test process

Six different dispersants were selected during the experiment, namely polypropylene glycol (1#), polyoxyethylene (2#), polyhexylene glycol (3#), Siban 80 (4#), oleic acid ( 5#), benzylamine (6#), the specific operation process is as follows:

Add 200 ml of liquid paraffin as a base oil in a beaker, then add 1 ml of dispersing agent, and mix the two by magnetic stirring;

After mixing, 0.1 g of the pretreated flaky nano-graphite is added, and the dispersion is forced by a T18 disperser for about 20 to 30 minutes, and then ultrasonic vibration is performed for about 20 to 30 minutes;

The above-mentioned base oil to which nanographite has been added is centrifuged, and the rotation speed is set to 1000 rpm, and the time interval is 30 minutes;

After centrifugation every 30 minutes, a portion of the supernatant was aspirated and subjected to absorbance detection at a 721 visible spectrophotometer, and data was recorded.

2, dispersion performance test data analysis

The absorbance data results for lubricating oils with different dispersants are shown in Figure 1. From the analysis in the figure, Siban 80 (4#) and benzylamine (6#) still have high absorbance after centrifugation, and the curve is relatively flat with the separation time. Combined with the experimental process, it is found that after centrifugation for 300 minutes. No delamination of the flaky nano-graphite and the base oil was found, indicating that the two dispersants have stable dispersing ability. The curves of polypropylene glycol (1#) and oleic acid (5#) are relatively flat, but the spectrophotometry is not very high. During the experiment, it was found that some of the flake graphite precipitated after several centrifugation. It is estimated that the addition of graphite should be reduced. The amount can achieve a good dispersion effect. After the centrifugal separation of polyoxyethylene (2#) and polyethylene glycol (3#), the nano-graphite and the base oil are layered, which has a very low absorbance, and it is difficult to obtain a good stable dispersing ability.

Figure 1 Comparison of absorbance of different dispersant base oils

Other different levels of Siban 80 were added under the same conditions, and the absorbance was measured. The results are shown in Fig. 2. In general, Siban 80 has a good dispersing ability. The experimental results show that when the content of Shiban 80 is 5.0 ml and 8.0 ml, the curve is relatively flat.

Figure 2 Comparison of absorbance of different content of Siban 80 base oil

Other different amounts of benzylamine were added under the same conditions, and the absorbance was measured. The results are shown in FIG. The analysis shows that the curve obtained by adding 0.5 ml of 1.0 ml of benzylamine to the base oil is relatively flat, and the absorbance platform is very high. As the amount of benzylamine added increases, the curve falls greatly, and it is found during the experiment. The nanographite is partially separated.

Figure 3 Comparison of absorbance of different concentrations of benzylamine base oil

(3) Friction test

The base oil used in this experiment was a chemically pure liquid paraffin, which was prepared with a dispersion of 25 ppm, 50 ppm, 100 ppm, 150 ppm, and 200 ppm of flakes with Siban 80 and benzylamine as dispersants. Under the same conditions, the MMW-1 vertical universal friction and wear testing machine Friction wear test, a copper block diameter used was 20 mm and a thickness of 6 mm and a hardness of 148HV, hardness of the steel pin is 263HV, alloy The composition is GCr15.

(4) Test results and discussion

1. The effect of the same load on the friction coefficient

The test conditions were: load of 100 cattle, experimental time of 10 minutes, rotation speed of 360 rpm, and temperature of room temperature. Figure 4 shows the effect of different nanographite content on the friction coefficient of liquid paraffin base oil with Siban 80 as dispersant.

Fig. 4 Effect of different nanometer graphite content on friction coefficient of added Siban 80 base oil

It can be seen from the figure that under the action of the load of pure liquid paraffin, the friction coefficient is very high, up to 0.1 or more. With the addition of flake nanographite, the friction coefficient is gradually reduced, and nanographite plays a good role in friction reduction. When the graphite content is 100 ppm, the coefficient of friction is the smallest. As the content of nano-graphite increases, the friction coefficient increases gradually, which may be hindered by the deposition of a large amount of flaky nano-graphite on the friction surface.

Figure 5 shows the effect of different nanographite on the friction coefficient of base oil liquid paraffin with benzylamine as dispersant. From the figure we can find that as the content of flake nanographite increases, the friction coefficient decreases gradually. When the content is 150 ppm, the friction coefficient is minimized, and then the friction coefficient is gradually increased.

Fig. 5 Effect of different nanographite content on friction coefficient of benzylamine-added base oil

Table 2 Comparison of Minimum Friction Coefficients of Different Additives

Table 2 shows that under the same load, the minimum friction coefficient obtained by adding the Siban 80 base oil is smaller than that of the benzylamine base oil.

2. Influence of different loads on friction coefficient

The test conditions were as follows: the speed was 360 rpm, and the loads were 100, 150, 200, 250, and 300, respectively. Figure 6 is a comparison of the friction coefficient of base oil with pure liquid paraffin with Siban 80 as dispersant and 50 ppm nanographite under different loads. It can be seen from the figure that the friction coefficient of pure liquid paraffin is compared. It can be seen from the figure that pure liquid paraffin has a high coefficient of friction under different loads, and the friction coefficient increases as the load increases. The friction coefficient of 50ppm nano-graphite content base oil under different loads, the effect of reducing the friction coefficient is very obvious. While the load increases, the friction coefficient increases slightly, indicating that Siban 80 has a high load capacity as a dispersant.

Fig.6 Comparison of friction coefficient of adding Siban 80 base oil under different loads

Figure 7 is a comparison of the friction coefficient of a base oil with a pure liquid paraffin with a benzylamine as a dispersant and a 150 ppm nanographite content under different loads. The results show that the effect of reducing the friction coefficient under low load with benzylamine as a dispersing agent is more effective and more obvious. When the load is increased, the friction coefficient increases sharply and the effect is significantly reduced.

Figure 7 Comparison of friction coefficient of benzylamine base oil added under different loads

3. Friction mechanism of nano graphite additive

Graphite has the characteristics of high temperature resistance, corrosion resistance and self-lubrication. As a good solid lubricant and lubricating additive, it is applied to the lubrication of mechanical equipment and processing technology in various forms, which plays a role in performance maintenance, energy saving and production efficiency. effect. Some research results show that whether it is natural graphite or artificial graphite, graphite fine powder with an average particle size of 4 to 5 microns will produce good lubrication effect, which can minimize the friction and wear of the test piece. According to the relationship between the crystal size ratio of the graphite powder (the ratio of the layer area to the facet area) and the specific wear of the material to be lubricated, it is shown that as the graphite particle size ratio increases, the specific wear of the material to be lubricated decreases significantly. . Therefore, the flaky graphite particles have a better lubricating effect.

During the experiment, some worn copper pieces were selected as scanning electron microscope samples, and the morphology of the friction surface marks was analyzed, as shown in Fig. 8.

(a) pure liquid paraffin

(b) 100ppm nanographite content (Span 80)

Figure 8 SEM image of the friction trace on the copper surface

It can be seen from the electron micrograph that the friction surface of the pure liquid paraffin copper sheet peels off like a snow flake, forming many grooves, which are rough, and the surface of the wear-resistant surface of the added nano-graphite is smooth and flat. The energy spectrum (EDS) analysis shows that there are a lot of C elements on the surface of the wear scar, which indicates that the sheet-like nano-graphite deposits on the friction surface to form a film during the friction process, which plays a role of filling and repairing, so that the friction surface is always in a relatively flat state. This explains that the addition of flake nanographite to liquid paraffin can reduce the coefficient of friction and improve its lubricating properties.

Second, the conclusion

(1) After the pretreatment of the sheet-like nanographite, it is analyzed by scanning electron microscopy, and the size is about 500 nm or less and the thickness is between 10 and 30 nm.

(2) Using the sedimentation method, the absorbances of six different dispersants were tested, and two dispersants with stable dispersing ability, Siban 80 and benzylamine, were obtained.

(3) Using Siban 80 and benzylamine as dispersing agents, a base oil containing a certain amount of flake nanographite was arranged. It was found by friction test that nanographite can reduce the friction coefficient of liquid paraffin.

(d) The effect of Division 80 as a dispersant in reducing the coefficient of friction is more pronounced than that of benzylamine, especially under high loads.

(5) The flaky nano-graphite is deposited on the friction surface during the friction process to form a film, which serves as a filling and repairing function, thereby reducing the friction coefficient and improving the lubricating performance.

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