KR102115607B1 - Nanofluid lubricant for rotating machines using surface-treated alumina nanoparticles - Google Patents

Abstract

The present invention relates to a nanofluid lubricant for rotating devices using surface-treated alumina nanoparticles. According to one aspect of the present invention, the nanofluid lubricant for rotating devices ensures excellent long-term dispersion stability and improved effects of reducing the wear of the rotating devices, thereby greatly contributing to commercialization of lubricants for the rotating devices.

Description

Nanofluid lubricant for rotating machines using surface-treated alumina nanoparticles}

The present invention relates to a nanofluid lubricant for rotating equipment using surface-treated alumina nanoparticles.

Bearings installed in rotating equipment such as traction motors and axle reducers of high-speed / urban railroads are required to use lubricants due to the special driving environment of high loads and long-term use. Through the use of high-performance lubricants, it is possible to improve the lubrication and cooling performance, increase the life of the parts, as well as reduce power consumption to increase machine efficiency. This is directly related to the stable operation and maintenance cost reduction of the railroad vehicle system. In particular, in the case of rail bearings installed on axle reducers or gearboxes, research on the next-generation high-performance lubricant to extend the life of bearings is necessary because they are not manufactured in Korea due to cost and other problems.

The lubricant forms a lubricant film between friction surfaces between metals, such as bearings, to play a variety of roles, such as reducing friction and frictional heat and preventing corrosion through blocking contact with air or moisture. Lubricating oil is largely divided into lubricant oil and grease, which is a solid lubricant, and lubricants are railway vehicles such as couplings, gearboxes, traction motors, wheel flanges, etc. It is used in various parts of my rotating equipment. Lubricant oil has good heat dissipation, excellent efficiency such as rolling resistance, and good lubrication characteristics, while grease can be filled, and it is easy to block and seal foreign substances from entering, making it compact, light-weight, and maintenance-friendly. It has excellent characteristics. The lubricant undergoes physical and chemical transformations during use due to friction / contact heat between metals, metal wear particles, oxygen and moisture in the air, and the like. Problems due to lubricants, such as contaminated lubricants or improper sealing, can develop into bearing wear damage, rehardening, and even cracking or flaking damage. In order to increase the life of the lubricant, there is a need to improve thermal conductivity and minimize friction of the bearing metal surface to cool the contact heat. In order to improve the properties of these lubricants, nanofluid-based high-performance lubricants containing nanoparticles in a lubricant oil or grease have been recently developed.

Nanofluid refers to a fluid made by dispersing and floating functional nanoparticles having a diameter of 100 nm or less in a general fluid (Non-Patent Document 1. E. Ettefaghi, H. Ahmadi, A. Rashidi, A. Nouralishahi, et al. (2013) Preparation and thermal properties of oil-based nanofluid from multi-walled carbon nanotubes and engine oil as nano-lubricant, International Communications in Heat and Mass Transfer, 46, pp. 142-147.). In particular, it has been actively studied as a next-generation cooling fluid due to its high thermal conductivity properties. Nano-fluid-based lubricant means a two-phase fluid stabilized by dispersing nanometer-sized (<100 nm) particles in an existing lubricant with excellent mechanical properties (strength and thermal conductivity, eco-friendliness) in the lubricant. . Nanoparticles in the nanofluid lubricant form a nanometer-sized particle film between a rotating device such as a bearing (ball or cylinder) and a substrate, making the rolling effect by point-contacting the contact surfaces of the two metal surfaces. It serves to improve. And it can play a role of improving lubrication performance and abrasion resistance by filling the fine damaged areas and giving the effect of regenerating the surface smoothly (Non-Patent Document 2. H. Xie, B. Jiang, J. He, X. Xia, F Pan (2016) Lubrication performance of MoS ₂ and SiO ₂ nanoparticles as lubricant additives in magnesium alloy-steel contacts, Tribology International , 93, pp. 63-70.).

In addition, thanks to the high thermal conductivity of the nanoparticles, it has the advantage of cooling the heat rising during operation. However, nanofluid lubricating oil applied to bearings or engine driving parts of high-performance automobiles has been developed, but research on nanofluid lubricating oil for railroad vehicles has not been conducted. In particular, it is necessary to study lubricants of a new concept that can maintain mechanical properties such as stable dispersion and viscosity in a high-load, long-term use environment such as a railroad rolling machine.

An object in one aspect of the present invention is to provide a nanofluidic lubricant for a rotating device including alumina nanoparticles surface-treated with a self-assembled single film, which has excellent long-term dispersion stability and wear resistance.

An object in another aspect of the present invention is to provide a method of manufacturing a nanofluid lubricant for the rotating device.

An object of another aspect of the present invention is to provide a method of improving the dispersibility of a nanofluid lubricant for a rotating device including alumina nanoparticles by surface-treating alumina nanoparticles with a self-assembled single film.

Another object of one aspect of the present invention is to provide a method of reducing wear of a rotating device using a nanofluid for a rotating device including alumina nanoparticles surface-treated with a single self-assembled film.

In order to achieve the above object,

In one aspect of the present invention, in a nanofluid lubricant for a rotating device comprising alumina (Al ₂ O ₃ ) nanoparticles surface-treated with a self-assembled monolayer (SAM),

The self-assembled single film,

Characterized in that the compound represented by the formula (1),

It provides a nano-fluid lubricant for rotating equipment.

[Formula 1]

Si (OR ¹ ) ₃ R ²

(In the formula 1,

R ¹ is C _1-5 straight or branched chain alkyl; And

R ² is C _1-8 straight or branched chain aminoalkyl).

Another aspect of the present invention is the step of forming a first mixture by adding a self-assembled monolayer (SAM) to a solution containing alumina (Al ₂ O ₃ ) nanoparticles;

Centrifuging the first mixture to recover surface-treated alumina nanoparticles;

Forming a second mixture by adding the surface-treated alumina nanoparticles to a base oil; And

A method of manufacturing a nanofluid lubricant for a rotating device, comprising the step of ultrasonically treating the second mixture, wherein the surface-treated alumina nanoparticles are characterized in that the alumina nanoparticles are surface treated with the self-assembled single film. Provided is a method for manufacturing a base nanofluid lubricant.

In another aspect of the present invention, in a method for improving the dispersibility of a nanofluid lubricant for a rotating device including alumina (Al ₂ O ₃ ) nanoparticles, the alumina nanoparticles self-assembled monolayer, SAM) to provide a method of improving the dispersibility of nanofluid lubricant for rotating equipment by surface treatment.

In another aspect of the present invention, in a method of reducing wear of a rotating device using a nanofluid for a rotating device including alumina (Al ₂ O ₃ ) nanoparticles, the alumina nanoparticles self-assembled into a single film (self- It provides a method of reducing the wear of rotating equipment by surface treatment with assembled monolayer (SAM).

The nanofluid lubricating oil for a rotating device provided by one aspect of the present invention is a self-assembled single film having a hydrophobic group and includes hydrophilic spherical alumina nanoparticles whose surface is modified. Can make a great contribution to the commercialization of.

1 is a view showing the principle of a nano-fluid lubricant used in a rotating machine.
Figure 2 is a view showing a photo of Example 1 and Comparative Example 1 (a) thermal gravimetric analysis, (b) transmission electron microscope analysis, (c) energy dispersion spectrum analysis to determine the surface treatment of the alumina nanoparticles to be.
Figure 3 in Experimental Example 2.1 for evaluating the dispersion stability of Example 2 and Comparative Example 2 (a) immediately after the sample was prepared, (b) 1 hour, (c) 1 day, (d) 2 days elapsed , (e) 3 days, and (f) 8 days.
4 is a view showing the actual image of the Turbiscan AGS equipment used in Experimental Example 2.2 and a conceptual diagram of transmission and scattering measurements.
Figure 5 is a long-term using Turbiscan of Comparative Example 2 ((a) ~ (c)) and Example 2 ((d) ~ (f)) of the concentration of alumina nanoparticles 0.1vol%, 0.3vol% and 0.5vol%, respectively. This diagram shows the results of dispersion stability experiments.
FIG. 6 is a graph showing the results of long-term dispersion stability experiments of Example 2 and Comparative Example 2 as Turbiscan stability index (TSI).
Figure 7 is (a) 0.1vol% Comparative Example 2, (b) 0.3vol% Comparative Example 2, (c) 0.1vol% Example 2, and (d) 0.3vol% to test the wear characteristics of Example 2 It is a graph showing the results of the four-ball test and the diameter of the worn parts of (e) Experimental Example 2 and Comparative Example 2.

Hereinafter, the present invention will be described in detail.

Meanwhile, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art. Furthermore, "including" a component throughout the specification means that other components may be further included, rather than excluding other components, unless otherwise specified.

As described above, the nanofluid lubricant serves to enhance the rolling effect by making the nanoparticles in the lubricant form a nanometer-sized particle film between the rotating machine and the base surface to make point-to-contact contact between the two metal surfaces, and to improve the rolling effect. This has the advantage of being able to cool the rising heat. Accordingly, it is necessary to research and develop high-performance nano-fluid lubricants for extending bearing life.

Accordingly, the present invention is to select a spherical alumina (Al ₂ O ₃ ) nanoparticles having excellent hardness as nanoparticles capable of maintaining high dispersibility in lubricating oil even when the rotating device is not driven, and self-assembled a single membrane ( Self-assembled monolayer (SAM) was used for surface treatment. The alumina nanoparticles have an oxide group on the surface, which shows a strong hydrophilic property. To increase the dispersibility in the lubricant, the triethoxysilane group which reacts well with the oxide group on the surface of the alumina nanoparticles, and the metal material and interface of the rotating machine The surface treatment was performed using a self-assembled single film into which an amine group having a polarity capable of improving properties was introduced.

In one aspect of the present invention, in a nanofluid lubricant for a rotating device comprising alumina (Al ₂ O ₃ ) nanoparticles surface-treated with a self-assembled monolayer (SAM),

The self-assembled single film,

Characterized in that the compound represented by the formula (1),

It provides a nano-fluid lubricant for rotating equipment.

[Formula 1]

Si (OR ¹ ) ₃ R ²

(In the formula 1,

R ¹ is C _1-5 straight or branched chain alkyl; And

R ² is C _1-8 straight or branched chain aminoalkyl).

At this time, the diameter of the alumina nanoparticles may be 20 nm to 100 nm, 25 nm to 95 nm, 30 nm to 90 nm, 35 nm to 85 nm, and 40 nm in several aspects. To 80 nm, 45 nm to 75 nm, 50 nm to 70 nm, preferably about 45 nm in diameter.

The alumina nanoparticles may be spherical alumina nanoparticles.

On the other side,

The rotating device may be a railway vehicle rotating device.

Another aspect of the present invention is the step of forming a first mixture by adding a self-assembled monolayer (SAM) to a solution containing alumina (Al ₂ O ₃ ) nanoparticles;

Centrifuging the first mixture to recover surface-treated alumina nanoparticles;

Forming a second mixture by adding the surface-treated alumina nanoparticles to a base oil; And

A method of manufacturing a nanofluid lubricant for a rotating device, comprising the step of ultrasonically treating the second mixture, wherein the surface-treated alumina nanoparticles are characterized in that the alumina nanoparticles are surface treated with the self-assembled single film. Provided is a method for manufacturing a base nanofluid lubricant.

On the other side,

The rotating device may be a railway vehicle rotating device.

Hereinafter, a method of manufacturing a nanofluid lubricant for a rotating device provided in one aspect of the present invention will be described in detail step by step.

In the method of manufacturing a nanofluid lubricating oil for a rotating device provided in one aspect of the present invention, step 1 is a step of forming a first mixture by adding a self-assembled single film to a solution containing alumina nanoparticles.

As the solvent of the solution, ethanol and distilled water may be used in a volume ratio of 1: 1, but this is only an exemplary description, and a solvent in which alumina nanoparticles can be dispersed may be used without particular limitation.

The self-assembled single film,

It may be a compound represented by the formula (1).

[Formula 1]

Si (OR ¹ ) ₃ R ²

(In the formula 1,

R ¹ is C _1-5 straight or branched chain alkyl; And

R ² is C _1-8 straight or branched chain aminoalkyl).

The self-assembled monolayer may be 3-aminopropyl triethoxy silane (APTES).

The step of forming the first mixture may be performed by physically stirring the alumina nanoparticles in a solvent, sufficiently dispersing the particles through ultrasonic treatment, and adding a self-assembled single film to reflux and stirring. At this time, the stirring time, ultrasonic treatment time, and reflux temperature are different depending on the type of the solvent and the self-assembled monolayer, and in one specific example, agitation is performed for 3 to 12 hours, ultrasonic treatment for 1 hour, and 80 ° C. Can be refluxed.

In the method of manufacturing a nanofluid lubricant for a rotating machine provided in one aspect of the present invention, the second step is a step of recovering the surface-treated alumina nanoparticles by centrifuging the first mixture.

The centrifugation is different depending on the type of the solvent and the self-assembled monolayer, and in one embodiment, the centrifugation can be performed under 5000 rpm for 50 minutes. The nanoparticles recovered through the centrifugation can be dried in a vacuum oven at room temperature and 60 ° C. for 12 hours to obtain surface-treated alumina nanoparticles.

In the method of manufacturing a nanofluid lubricant for a rotating machine provided in one aspect of the present invention, step 3 is a step of forming a second mixture by adding the surface-treated alumina nanoparticles to the base oil.

The base oil is not particularly limited as long as it is a base oil suitable for dispersing the surface-treated alumina nanoparticles. By way of example, it can be selected from synthetic or natural oils or mixtures thereof, synthetic oils comprising dicarboxylic acids, polyglycols and alcohols of alkyl esters, polybutene, alkyl benzene, phosphoric acid with terminal hydroxyl groups modified by esterification and etherification, etc. Organic esters, polysilicon oils, and poly-alpha-olefins, including alkylene oxide polymers, copolymers and derivatives thereof. In this case, the synthetic oil includes a gas to liquid synthetic oil based on natural gas. Natural oils include animal and vegetable oils, liquid petroleum and fertilizers in the form of paraffin, naphthene and mixed paraffin-naphthene, solvent treated or acid treated mineral lubricants. Oils of lubricating viscosity obtained from coal or shale may also be included.

The concentration of the surface-treated alumina nanoparticles in the second mixture may range from 0.05 vol% to 0.45 vol% in some aspects, from 0.08 vol% to 0.43 vol%, and from 0.10 vol% to 0.40 vol. % Concentration range, 0.13 vol% to 0.38 vol% concentration range, 0.15 vol% to 0.35 vol% concentration range, 0.18 vol% to 0.33 vol% concentration range, 0.20 vol% to It may be in a concentration range of 0.30 vol%, in a concentration range of 0.23 vol% to 0.28 vol%, in a concentration of 0.10 vol%, and in a concentration of 0.30 vol%.

In the method of manufacturing a nanofluid lubricant for a rotating device provided in one aspect of the present invention, step 4 is a step of ultrasonicating the second mixture.

The ultrasonic treatment may vary depending on the type of the self-assembled monolayer and the concentration of the surface-treated alumina nanoparticles. In one embodiment, the ultrasonic treatment may be performed for 1 hour to allow the nanoparticles to be dispersed.

In another aspect of the present invention, in a method for improving the dispersibility of a nanofluid lubricant for a rotating device including alumina (Al ₂ O ₃ ) nanoparticles, the alumina nanoparticles self-assembled monolayer, SAM) to provide a method of improving the dispersibility of nanofluid lubricant for rotating equipment by surface treatment.

Compared to nanofluid lubricating oil containing alumina nanoparticles without surface treatment, nanofluid lubricating oil containing alumina nanoparticles with surface treatment showed good results in a long-term dispersion stability experiment. Specifically, nanofluid lubricating oil containing 0.1 vol% of alumina nanoparticles without surface treatment initially exhibits similar dispersion stability as nanofluid containing 0.1vol% of alumina nanoparticles treated with surface treatment, but has been surface treated after 36 hours. Dispersion stability began to be lower than that of nanofluid lubricants containing alumina nanoparticles. Nanofluid lubricating oil containing 0.3 vol% of untreated alumina nanoparticles begins to deteriorate in stability only after 2 days after dispersion, whereas nanofluid lubricating oil containing 0.3 vol% of surface treated alumina nanoparticles remains after 6 days. The dispersion stability did not drop significantly. The detailed experimental process and data were described later in Experimental Example 2.

In another aspect of the present invention, in a method of reducing wear of a rotating device using a nanofluid for a rotating device including alumina (Al ₂ O ₃ ) nanoparticles, the alumina nanoparticles self-assembled into a single film (self- It provides a method of reducing the wear of rotating equipment by surface treatment with assembled monolayer (SAM).

Compared to nanofluid lubricating oil containing alumina nanoparticles without surface treatment, nanofluid lubricating oil containing alumina nanoparticles with surface treatment showed good results in the lubrication characteristic experiment. Specifically, a nanofluid lubricant containing 0.1 vol% and 0.3 vol% of alumina nanoparticles surface-treated in a 4 ball test for evaluating lubrication properties has an average diameter of 0.597 m and 0.633 m, respectively. While abrasion occurred, nanofluid lubricants containing 0.1 vol% and 0.3 vol% of alumina nanoparticles without surface treatment, respectively, had abrasions with average diameters of 0.678 m and 0.707 m, which were 11% to 13% higher. . The detailed experimental process and data were described later in Experimental Example 3.

Hereinafter, the present invention will be described in detail through examples and experimental examples described below.

However, the Examples and Experimental Examples described below are merely illustrative of the present invention, but the present invention is not limited thereto.

<Example 1> Preparation of surface-treated nanoparticles

In order to manufacture a nanofluid lubricant having excellent properties, functional nanoparticles must be well dispersed in a base-oil without aggregation.

Typical paraffinic lubricating base oils have a molecular structure composed of carbon and hydrogen with straight or branched C _n H _{2n + 2} single bonds. In general, it has a long alkyl group at the level of C ₁₂ -C ₁₆ and thus has hydrophobic properties. The various functional nanoparticles used in the manufacture of nanofluid lubricating oils have an oxide (-OH) or carbonyl (-COOH) group on the surface and thus exhibit hydrophilic characteristics. In order to disperse these hydrophilic nanoparticles well in a lubricating base oil, it is necessary to modify the surface of the nanoparticles to have chemical properties similar to base oil.

The alumina (Al ₂ O ₃ ) nanoparticles used in Example 1 also have an oxide group on the surface, thus exhibiting strong hydrophilicity. Therefore, the surface was treated using a self-assembled monolayer (SAM) material having an oxide group present on the alumina surface and a silane group having excellent reactivity.

Spherical alumina nanoparticles (Al ₂ O ₃ , Alfa Aesar, Nanodur) having an excellent hardness and an average diameter of 45 nm are used. Nanoparticles with a diameter of 100 nm or less have a large surface area to mass and are very likely to aggregate. Therefore, proper surface treatment is required to increase dispersibility. As a surface treatment agent, 3-aminopropyl triethoxy silane (APTES, Sigma-Aldrich), which is a representative self-assembled monolayer, was used.

One end of APTES consists of a triethoxysilane group that is known to react very well with -OH groups existing on the surface of oxide nanoparticles, and the other end improves the interfacial properties with metal materials mainly used in railway rolling machinery. It is a structure in which an amine (-NH2) group having a polarity is introduced.

A total of 200 mL of ethanol and distilled water are added to 5 g of alumina nanoparticles in a volume ratio of 1: 1, mixed, and physically stirred (3 hours), followed by sonication (1 hour) to sufficiently disperse the particles. To the suspension in which the alumina particles were dispersed, 3-aminopropyl triethoxy silane (APTES) 33.75 mM (7.47 g) was added dropwise for 10 minutes using a syringe. After refluxing at 80 ° C. and stirring for 3 hours, the mixture is further stirred at room temperature for 12 hours. The colloid containing alumina nanoparticles is washed three times with ethanol using a centrifuge (5000 rpm, 50 minutes). The nanoparticles recovered by centrifugation were dried in a vacuum oven at room temperature and 60 ° C. for 12 hours to obtain surface-treated alumina nanoparticles (APTES-NP).

<Example 2> Preparation of nanofluid lubricant

In order to manufacture a nanofluid lubricant using the nanoparticles prepared in Example 1, a lubricant for a gearbox of a railway vehicle (Spirax EP 80W, Shell) was selected as a base oil. For the preparation of the nanofluid lubricant, the nanoparticles of Example 1 were added with 0.1, 0.3, and 0.5 vol%, respectively, and after ultrasonic treatment (1 hour), the nanoparticles were sufficiently stirred for 5 hours or more so that the nanoparticles could be dispersed.

<Comparative Example 1>

For comparative experiments, alumina nanoparticles (Pristine-NP) that were not surface-treated were prepared.

<Comparative Example 2>

 For comparative experiments, a nanofluid lubricant having the same composition as Example 2 was prepared, except that the nanoparticles of Comparative Example 1 were used instead of the nanoparticles of Example 1.

<Experimental Example 1> Nanoparticle weight and surface analysis

The surface treatment of alumina nanoparticles can be confirmed by thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM) analysis. The results are shown in FIG. 2.

As shown in Figure 2 (a), the content of the surface-treated APTES of the nanoparticles prepared in Example 1 and Comparative Example 1 was quantitatively analyzed. Alumina nanoparticles have a heat resistance of 1000 ° C or higher, whereas APTES treated on the surface is generally organic and has a heat resistance of 500 ° C or lower. The temperature change was observed while heating up to 700 ° C in a nitrogen atmosphere (heating rate of 10 ° C / min). In Comparative Example 1, the weight loss hardly occurs, whereas in Example 1, it can be confirmed that the weight loss occurs at a 350 ° C point. Weight loss of 0.68% compared to Comparative Example 1 occurred additionally, which means the APTES content present in the Example 1 sample. However, these results do not mean that APTES is present on the surface of alumina nanoparticles.

In order to directly check the surface treatment, Example 1 was observed through TEM. 2 (b), as a result of directly observing the APTES thin film present on the alumina particle surface through high-resolution TEM analysis, it was confirmed that APTES formed a film with a thickness of about 1 nm on the alumina particle surface.

In addition, through the elemental analysis using the Energy Dispersive Spectrometer (EDS) technique, the APTES surface treatment can be more clearly confirmed. 2 (c), elemental analysis of Al, O, Si, and C was performed from the APTES-NP sample. Since it is an alumina particle, it is of course possible to confirm the image of the Al and O elements. In addition, Si and C elements present in the APTES molecule are evenly distributed along the alumina particle surface. Through this, it was confirmed that APTES was well treated on the alumina surface.

<Experimental Example 2> Evaluation of dispersion stability of nanofluid lubricant

2.1. Dispersion stability evaluation-1

In order to evaluate the dispersion stability of the nanofluid lubricating oil in Example 2, the dispersion stability of the nanofluids according to the concentrations of Example 2 and Comparative Example 2 was observed by taking pictures according to the time change from immediately after manufacture to 8 days. The results are shown in FIG. 3. The first of the 7 samples is Spirax EP 80W base oil, and the 2nd to 4th samples were put in Comparative Examples 2 by 0.1, 0.3, and 0.5 vol% concentrations, respectively, and the 5th to 7th samples were Examples 2 and 0.1. , 0.3, 0.5vol% Nanofluid added by concentration.

Visually, there is no significant change immediately after preparation, but it can be seen that a large difference in dispersibility appears depending on whether the nanoparticles are surface-treated over time. In particular, when looking at the results of Day 1-2, it can be seen that despite the same amount, the precipitation amount generated in Comparative Example 2 appears larger than in Example 2. This tendency is similarly observed for all compositions.

Therefore, the nanofluid lubricating oil prepared in Example 2 shows better dispersion stability than the nanofluid lubricating oil of Comparative Example 2, and among the six nanofluids prepared in particular, the best dispersion stability when the concentration of Example 2 is 0.1 vol%. It was confirmed to show. In the case of the rest of the nanofluids, it was observed that a sedimentation phenomenon occurred, and the transparent upper layer part and the sedimented bottom layer were clearly separated. Also, when 0.5 vol% of nanoparticles were included, it was found that the amount of precipitation was very high regardless of the surface treatment.

2.2. Dispersion stability evaluation-2

Due to the characteristics of the lubricant used in various driving and rotating equipment, it must maintain stable dispersion in the operation state as well as in times when the rotating equipment is not operating. In particular, the long-term dispersion stability of nanofluid-based lubricating oil that is physically dispersed is more important, unlike additives that are chemically dissolved in base oil.

To quantitatively measure the dispersibility of the nanofluid lubricant of Example 2.2, a Turbiscan AGS (Formulaction) equipment was used. Turbiscan can quantify the dispersion characteristics by measuring complex transmittance (Back Scattering Trasnmittance, BST) through multiple light scattering methods through a sample. By calculating the change in permeability (Delta BST) measured after a certain period of time, the stability index of particles in the fluid can be quantitatively determined. The actual image of the Turbiscan AGS equipment used in Experimental Example 2.2 and the conceptual diagram of transmission and scattering measurement are shown in FIG. 4.

By measuring the dispersion in a dedicated container and scanning closely from the lower part to the upper part of the container, foaming, sedimentation, phase separation, agglomeration, foaming, etc. can be distinguished. In addition, since up to 54 samples can be simultaneously measured at a given time using a robot arm, long-term dispersion stability analysis of samples having various types and compositions can be stably performed.

5 is a result of measuring the change in dispersion stability by scanning the nanofluid lubricants of Example 2 and Comparative Example 2 prepared at room temperature for 6 days every 2 hours. The change in transmittance (ΔT) and change in back-scattering (ΔBS) with respect to the height of the sample (X-axis) with each scan time are shown on the Y-axis. 5 (a) to 5 (c) are the results of Comparative Example 2 at concentrations of 0.1, 0.3, and 0.5 vol%, and FIGS. 5 (d) to 5 (f) are conducted at concentrations of 0.1, 0.3 and 0.5 vol%. The results of Example 2 are shown.

The smaller the change in permeability and scattering degree over time, the higher the long-term dispersion stability, and the larger the amount of change and the rate of change, the lower the dispersibility. In general, in the case of nano-fluid lubricants, since the density of ceramic or metal nanoparticles is significantly higher than that of base oils, when stored for a long period of time without agitation, even if the initial dispersion characteristics are good, the dispersibility due to precipitation phenomenon is expected to decrease over time. The density of the alumina nanoparticles used in Experimental Example 2.2 is 3.60 cm ³ / mL, and the density of Spirax EP 80W, the base oil, is 0.89 cm ³ / mL, which is very likely to cause precipitation.

Looking at the Turbiscan results, it can be seen that the value of ΔBS is significantly increased in the lower part of all samples except for the 0.1 vol% sample (FIG. 5 (d)), and the permeability is changed by the typical precipitation phenomenon as expected. It can be seen that appears. The precipitation phenomenon quickly progressed within the first 24 hours, after which the precipitation phenomenon stabilized. However, in the case of the 0.1 vol% sample of Example 2, although the precipitation phenomenon was observed, it was found to be not only significantly lower than other samples, but also to precipitate very slowly at a uniform rate over 6 days of measuring the dispersion properties. This is because dispersion stability is sufficiently secured and heavy particles gradually sink due to gravity. In addition, when looking at ΔBS of the middle layer of the samples, it can be seen that in the case of Comparative Example 2, the transmittance was uneven depending on the height of the sample. These results indicate that nanoparticles having poor dispersion characteristics are aggregated with each other to increase the size of the particles, and that phase separation occurs between the upper and lower layers, and is a typical appearance when the dispersion characteristics are not good. However, in the case of Example 2, it can be seen that ΔT and ΔBS according to the sample height change uniformly, except for the case where the high concentration of nanoparticles of 0.5 vol% is used (FIG. 5 (d) and FIG. 5). (e)). Since the surface is treated with APTES, the interfacial properties with the base oil are improved, which means that the agglomeration between particles does not occur significantly.

The overall dispersion stability difference can be quantitatively compared by obtaining the Turbiscan Stability Index (TSI) value. TSI is the distance (d _i ) between each profile measured over time at the specified sample height (H) as shown in Equation 1 below, and is accumulated by integrating the area between each profile due to changes in dispersion stability over time. Say what you ordered.

[Equation 1]

d _i = {∑ _h ｜ scan _i (h)-scan _i-1 (h) ｜} / H

6 shows the TSI values (Y-axis) of the six types of nanofluid lubricants prepared in FIG. 6, and the X-axis represents storage time. The safety of the nanofluid lubricant can be determined through these graphs. The larger the TSI value, the worse the dispersion stability.

As shown in Figure 6, it was confirmed that Example 2 at a concentration of 0.1 vol% shows the best long-term dispersion stability. Generally, when the TSI value is 20 or less, it means that dispersion stability is maintained. When the nanoparticle content is 0.1 vol% or less, it can be seen that the dispersion stability is maintained to some extent regardless of whether the surface is treated. Example 2 with the best dispersion stability When 0.1 vol%, the TSI value is increased by aggregation and sedimentation after 36 hours, but after that, the TSI rise is very small. However, in the case of the 0.1 vol% sample of Comparative Example 2, initially, the behavior was similar to that of the 0.1 vol% sample of Example 2, but the TSI value continuously increased over time to show a value of 20 or more. This means that agglomeration between nanoparticles is continuously occurring, as well as particle precipitation due to initial gravity.

When the nanoparticle content is 0.3 vol% or more, it can be seen that it has a higher TSI value than the 0.1 vol% sample regardless of whether or not it is surface treated. It is understood that this is due to the fact that a large amount of dense alumina particles is contained, and thus precipitation occurs rapidly. In addition, in samples having a particle content of 0.3 vol% or more, surface treatment had a much greater effect on dispersibility. Comparative Example 2 In the case of 0.3 vol% and 0.5 vol% samples, a TSI value of 40 or more was measured in 2 days after dispersion, and after 6 days, it showed a very high value of more than 50. This means that the dispersibility was very deteriorated. Since the content of the particles is also high and the surface treatment is not performed, agglomeration occurs, resulting in a large particle size and rapid precipitation. On the other hand, in the case of Example 2, it can be seen that even if the particle content is 0.3 vol% or more, the TSI value is stabilized at 30 or less even after 6 days. This is because precipitation occurs due to the high particle content, but it prevents aggregation between particles due to surface treatment. In general, when the TSI value of the solution is 20 or less, it can be determined that dispersion stability is maintained. Based on these criteria, it can be seen that only 0.1 vol% of Example 2 secures long-term dispersion stability of 7 days or longer. These results are consistent with the results obtained through observation of dispersibility with the naked eye (FIG. 3) and Turbiscan permeability changes (FIG. 5). Through this, it can be seen that the content and surface treatment of the nanoparticles greatly influence the long-term dispersion stability of the nanofluid lubricant.

2.3. Viscosity evaluation

 Table 1 shows the results of Kinematic Viscosity for Example 2 and Comparative Example 2 4 of 0.1 vol% and 0.3 vol% concentration. Nanofluid lubricant containing 0.5 vol% of nanoparticles with poor dispersibility was not measured for viscosity. Kinematic viscosity is the result of HVM 472 (HERZOG) viscosity measurement according to ASTM D445 standard. The kinematic viscosity of Spirax EP lubricants was measured to be 71.07 (73.4) cSt and 9.323 (9.2) cSt at 40 ° C and 100 ° C, respectively, and the viscosity index was 108. This is a result very similar to the result of the property table provided by the Spirax EP 80W manufacturer, and the manufacturer's results are indicated in parentheses. Looking at the results of the kinematic viscosity and viscosity index of Example 2 and Comparative Example 2, it can be seen that even if the nanoparticles are included in 0.1 vol% and 0.3 vol%, the kinematic viscosity and viscosity index properties are not significantly affected. In addition, there was no significant difference in the change in viscosity characteristics depending on whether the nanoparticles were surface treated.

<Experiment 3> Evaluation of wear properties of nanofluid lubricant

In order to analyze the lubricating properties of Example 2 and Comparative Example 2, a 4-ball test was performed. The four-ball test evaluated lubrication and wear characteristics by rotating four metal balls inside the lubricant according to ASTM D4172 standard and measuring the diameter of the worn part at the contact point between each ball. The experiment applied a load of 40 ± 0.2 kgf at a temperature of 75 ° C. and proceeded for 60 minutes at a rotation speed of 1200 ± 50 rpm. After the rotation experiment was finished, the lubricant on the surface of the recovered metal ball was removed, and the worn part was observed using an optical microscope and the diameter was measured. Each sample was repeatedly tested three times under the same conditions, and the diameter of the worn part was measured six times per sample, and an average value was used.

When using Example 2 and Comparative Example 2 of 0.1 vol% and 0.3 vol%, respectively, the optical microscope images of the worn parts generated on the surface of the metal ball are shown in FIGS. 7 (a) to 7 (d). In addition, the average value of the diameter obtained from the results of three times for each sample is shown in Fig. 7 (e). In the case of Example 2, wear of 0.597 ± 0.038 m and 0.633 ± 0.027 m in diameters occurred in the 0.1 vol% and 0.3 vol% samples, respectively. In the case of Comparative Example 2, wear of 0.678 ± 0.045 m and 0.707 ± 0.069 m, which is more than 11-13% larger than this, occurred.

This difference in wear properties can be found in the dispersion properties of nanoparticles. As described in FIGS. 4 and 5, the nanofluid lubricant of 0.1 vol% in Example 2 is dispersed evenly without almost any aggregation of particles, but when particles that are not surface-treated are used or the particle content increases, the particles Liver aggregation and sedimentation occurred, and the size of the nanoparticles increased. When the number of agglomerated nanoparticles increases, the lubricating properties of the nanoparticles decrease and act as an abrasive that wears the surface. As a result, it was found that the lower the dispersibility, the more wear occurred.

As described above, the present invention has been described in detail through preferred manufacturing examples, examples, and experimental examples, but the scope of the present invention is not limited to characteristic examples, and should be interpreted by the appended claims. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

Claims (10)

In the nano-fluid lubricant for a rotating device comprising alumina (Al ₂ O ₃ ) nanoparticles surface-treated with a self-assembled monolayer (SAM),
The self-assembled single film,
Characterized in that the compound represented by the formula (1),
Nanofluid lubricant for rotating equipment:
[Formula 1]
Si (OR ¹ ) ₃ R ²
(In the formula 1,
R ¹ is C _1-5 straight or branched chain alkyl; And
R ² is C _1-8 straight or branched chain aminoalkyl).
According to claim 1,
The alumina nanoparticles,
Characterized in that the spherical alumina nanoparticles having a diameter of 20 nm to 100 nm,
Nano fluid lubricant for rotating equipment.
According to claim 1,
The rotating device is characterized in that it is a rolling stock rolling machine,
Nano fluid lubricant for rotating equipment.
Forming a first mixture by adding a self-assembled monolayer (SAM) to a solution containing alumina (Al ₂ O ₃ ) nanoparticles;
Centrifuging the first mixture to recover surface-treated alumina nanoparticles;
Forming a second mixture by adding the surface-treated alumina nanoparticles to a base oil; And
A method of manufacturing a nanofluid lubricant for a rotating device, comprising the step of ultrasonically treating the second mixture, wherein the surface-treated alumina nanoparticles are characterized in that the alumina nanoparticles are surface treated with the self-assembled single film. Manufacturing method of nano fluid for base oil.
The method of claim 4,
The self-assembled single film,
Characterized in that the compound represented by the formula (1),
Manufacturing method of nanofluid lubricant for rotating equipment:
[Formula 1]
Si (OR ¹ ) ₃ R ²
(In the formula 1,
R ¹ is C _1-5 straight or branched chain alkyl; And
R ² is C _1-8 straight or branched chain aminoalkyl).
The method of claim 4,
The self-assembled single film,
Characterized in that 3-aminopropyl triethoxy silane (APTES),
Method for manufacturing nanofluid lubricant for rotating equipment.
The method of claim 4,
The second mixture,
Characterized in that the concentration of the surface-treated alumina nanoparticles is 0.05vol% to 0.45vol%,
Method for manufacturing nanofluid lubricant for rotating equipment.
The method of claim 4,
The rotating device is characterized in that it is a rolling stock rolling machine,
Method for manufacturing nanofluid lubricant for rotating equipment.
In a method for improving the dispersibility of a nanofluid lubricant for a rotating device comprising alumina (Al ₂ O ₃ ) nanoparticles, the alumina nanoparticles are surface treated with a self-assembled monolayer (SAM) for rotating devices Method for improving dispersibility of nanofluid lubricant.
In a method of reducing abrasion of a rotating device using a nanofluid for a rotating device comprising alumina (Al ₂ O ₃ ) nanoparticles, the alumina nanoparticles are surface treated with a self-assembled monolayer (SAM) To reduce the wear of rotating equipment.

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