JP2014163709A - Ph sensor, and oil deterioration level detection method using the sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a deterioration of an oil itself accompanied by a change in pH by directly immersing a pH electrode into a sample oil, and as a result, to enable a deterioration state of the oil such as a lubricating oil to be continuously detected on line.SOLUTION: A ph semiconductor sensor manufactured by using a glass electrode or an ISFET (Ion-Sensitive Field-Effect Transistor) structure directly immerses a pH sensor part, which is formed by coating a non-oil-soluble and electrically-conductive ion liquid film 15 on an outer surface of a sensor support body between a liquid junction part 23 at the side of a comparison electrode 20 serving as an active area and a pH responsive glass thin film 12 (or an ISFET electrode 10b), into an oil and determines a deterioration of the oil itself accompanying a change in pH. Preferably, a thickening agent is contained in a range of 1 to 50 mass% with respect to an ionic liquid 15.

Description

  The present invention relates to a pH sensor for detecting the deterioration level of oils generally used as lubricating oils such as engine oil, turbine oil, hydraulic hydraulic oil, and gear oil, and more particularly at normal temperature (−20 ° C. to 100 ° C.), diesel The present invention relates to a pH sensor that detects the deterioration of oil such as engine lubricating oil over time.

Conventionally, oils such as lubricating oils have been determined for total acid number and total base number by a method of measuring the pH of a solution dissolved in a mixed solvent.
The total acid value indicates the total amount of acidic components in the oil, that is, the total amount of acidic substances in the additives, organic acids generated during use, and the like. It is widely used as a guideline for the refinement degree of lubricating oil with the total acid number, as a guideline for manufacturing process control index, management of used lubricant oil, or for knowing deterioration state after oxidation test and practical test of lubricant oil. In general, as the lubricating oil degrades, the total acid number usually increases.

  The total acid value of such an oil has been conventionally used as an index of deterioration of the oil. However, since the oil is a non-aqueous liquid, the pH of the oil cannot be directly measured. As shown in "Products and Lubricating Oils-Neutralization Test Method", dissolve the oil in a mixed solvent of toluene, 2-propanol and a small amount of water, and monitor hydrochloric acid standard 2-propanol solution or potassium hydroxide while monitoring the pH. A method of titration with a standard 2-propanol solution is employed.

Such pH is measured using a pH electrode sensor 1 having a configuration including a glass electrode 10 and a comparative electrode 20 as shown in FIG. 6 (principle diagram).
That is, the glass electrode 10 is formed with a pH-responsive glass thin film 11 that responds sensitively to pH at the tip (the pH-responsive glass used at the tip of the glass electrode 10 is mainly composed of silicon and lithium, and is used for other pH measurements. For the purpose of improving the performance as glass, several elements are used as subcomponents, and the pH-responsive glass thin film 11 is well known and will not be described in detail.) Inside, potassium chloride (KCl) and neutral pH A glass electrode 10 internal solution 12 made of a buffer solution is filled. The reference electrode 20 is filled with a reference electrode internal solution 22 made of a potassium chloride solution, and has a so-called delicate junction (a porous ceramic such as alumina or zirconia is often used) called a liquid junction 23 at the tip. Formed and in electrical communication with the solution sample. In the figure, 26 is an internal liquid replenishment port. 14 and 24 are AgCl electrodes, respectively.

  When the pH electrode sensor 1 comprising the glass electrode 10 and the comparison electrode 20 is immersed in the solution sample, the glass electrode 10 generates an electromotive force according to the pH of the solution sample on the surface of the pH responsive glass thin film 11, and the comparison electrode 20. Always generates a constant electromotive force while being in electrical contact with the sample via ions at the liquid junction 23. The pH measuring device main body 5 having the calculation unit 3 measures the difference (voltage) of the electromotive force generated between the glass electrode 10 of the pH electrode 1 and the comparison electrode 20 with the potentiometer 4, and performs calculation processing with the calculation unit 3. Display the pH of the sample. Such a pH measurement method is called a glass electrode A method (see Non-Patent Document 1: JISK2501).

  Moreover, the technique which integrated the comparison electrode and the glass electrode is disclosed by patent 4733588 (patent document 1). However, as shown in FIG. 1 and FIG. 6, if the glass electrode and the comparative electrode are separated from each other, when the gap is oil, the electrodes are not electrically communicated with each other, so that measurement cannot be performed.

  This technique will be described with reference to FIG. 1 (a prerequisite technique of the present invention). In the prerequisite technique shown in FIG. 1, the integrated electrode sensor is integrated so that the comparison electrode 20A surrounds the support tube 34 of the glass electrode 10A. The glass electrode 10 </ b> A includes a cylindrical glass support tube 34 and a glass response film 31 bonded to the tip of the support tube 34. Specifically, the support tube 34 of the glass electrode 10A has a slightly protruding tip portion than the support tube 24A of the comparative electrode, and the glass response film 31 is joined to the tip portion.

  The support electrode 34 of the glass electrode 10A contains an internal electrode 31, and is filled with, for example, a KCl solution having a pH of 7 as the internal liquid 32 of the glass electrode 10A. In the comparison electrode 20A, the liquid junction 23A is provided on the bottom side of the outer peripheral wall of the support tube 24 of the comparison electrode 24A. Lead wires 11A and 21A are connected to the internal electrode 14A of the comparison electrode 20A and the internal electrode 24A of the glass electrode 10A, respectively, and these lead wires extend from the base end of the support tube 2 to the outside as a cable bundle. It is designed to be connected to a pH measuring device main body 5 (not shown).

However, even an integrated electrode sensor as shown in FIG. 1 cannot measure in the case of oil because the glass electrode and the comparative electrode are separated.
For this reason, in order to measure the total acid value of oil using the measuring device shown in FIG. 1, the difference (voltage) of the electromotive force generated between the glass electrode 10A of the pH electrode 1 and the comparison electrode 20A is measured with a potentiometer. Therefore, the glass response film 31 and the oil to be measured must have an affinity (conductivity). For this reason, conventionally, the oil to be measured is dissolved in a mixed solvent and used.

  That is, even if the pH electrode 1 is directly immersed in the oil, no affinity (conductivity) can be obtained between the pH-responsive glass thin film 31 and the oil, so that the electromotive force cannot be measured. For this reason, sample oil is brought offline into a laboratory such as a lab at predetermined time intervals, and the mixed solvent is added to the sample oil to form an aqueous solution to measure the total acid number of the oil from potential difference and pH measurement. .

  However, in the method of measuring the total acid number of the oil by adding the mixed solvent to the sample oil and measuring the total acid value of the oil, it can only be measured offline at a predetermined time interval as described above. Measurement with is impossible.

  On the other hand, as shown in Patent Document 2 as a technique for continuously determining oil degradation online, an AC voltage is provided between two electrode plates installed in parallel to each other in the oil flow path and the two electrode plates. An ammeter that measures the current that flows when a voltage is applied, a voltmeter that measures a voltage between the two plates when an AC voltage is applied to the two plates, and a measurement by the ammeter and the voltmeter A method has been proposed in which the electrical conductivity and dielectric constant of the oil are obtained based on the results, and the deterioration of the oil is judged based on the electrical conductivity and the dielectric constant.

  However, such prior art determines oil degradation based on conductivity and dielectric constant, and more specifically, it does not “directly” measure changes in the pH of the oil, but rather the electrical characteristics associated with contamination in the oil. The change is captured two-dimensionally from the viewpoint of conductivity and dielectric constant, and the deterioration of the oil itself accompanying the change in pH cannot be determined.

Japanese Patent No. 4733588 (see FIG. 5) Japanese Patent Laying-Open No. 2009-2893 (see paragraphs [0006] and [0007] FIG. 1)

JIS standard document: JISK2501

  In view of the technical problem of the present invention, the pH electrode 1 can be directly immersed in a sample oil such as a lubricating oil to determine the deterioration of the oil itself accompanying a change in pH. A pH sensor capable of continuously detecting an oil deterioration state and an oil deterioration degree detection method using the pH sensor, and particularly a pH sensor suitable for detecting the deterioration degree of lubricating oil or turbine oil of a diesel engine and the sensor An object is to provide a method for detecting the degree of oil deterioration.

  The present invention relates to a pH sensor in which an outer surface of an active sensor area is coated with a non-oil-soluble and conductive ionic liquid film, and in particular, the composite electrode in which the pH sensor is integrated with a reference electrode and a glass electrode The active sensor area is composed of a liquid junction on the comparison electrode side and a pH responsive glass thin film on the glass electrode side, and the ionic liquid film is deposited between the liquid junction and the pH responsive glass thin film. Located in the pH sensor.

  Specifically, according to the first aspect of the present invention, a glass electrode in which a pH-responsive glass thin film that responds sensitively to pH is formed at the tip and the glass electrode internal liquid is filled therein, and the internal liquid of the comparison electrode is contained therein. A pH electrode sensor comprising a reference electrode filled and formed with a liquid junction at the tip, which is insoluble on the outer surface of the sensor support between the liquid junction on the reference electrode side and the pH-responsive glass thin film on the glass electrode side And a conductive ionic liquid film is applied.

  According to the present invention, the pH electrode 1 can be directly immersed in an oil such as lubricating oil to determine the deterioration of the oil itself accompanying a change in pH, and as a result, the oil deterioration state of the lubricating oil or the like can be continued online. Can be detected.

The ionic liquid is a room temperature molten salt that becomes a liquid at room temperature, and the ionic liquid is composed of a combination of various anions and cations. In order to immerse the pH electrode 1 directly in oil such as lubricating oil, a non-ionic liquid is used. It must be oil-soluble and conductive.
The ionic liquid needs to be applied between the pH-responsive glass thin film and the liquid junction on the side of the reference electrode. Further, if a thickener is added to the ionic liquid to form a grease, the application effect is further increased. Rise.

  The second aspect of the present invention is an oil-insoluble material between the outer surface of the sensor support that connects the semiconductor electrode that forms the active sensor area of the pH semiconductor sensor using the structure of an ion-sensitive field effect transistor (ISFET) and the liquid junction. In addition, a conductive ionic liquid film is deposited.

For example, a synthetic diamond semiconductor having a hydrogen-terminated surface becomes a conductive thin film 31 in the electrolyte regardless of its intrinsic or extrinsic shape, and becomes sensitive to the pH and ion concentration of the electrolyte. It is known in Japanese Patent Application Laid-Open No. 2007-78373 and the like that a pH semiconductor sensor can be manufactured using this conductive “Ion Sensitive Field Effect Transistor” (“ISFET”) structure.
Therefore, the second invention is an oil-insoluble and conductive material on the outer surface of the sensor support that connects the semiconductor electrode and the liquid junction, which is an active sensor area of a pH semiconductor sensor using an ion-sensitive field effect transistor (ISFET) structure. The ionic liquid film is deposited.

  According to the second invention, as in the first invention, the pH electrode 1 can be directly immersed in a sample oil such as lubricating oil to determine the deterioration of the oil itself accompanying the change in pH, and as a result, online Thus, it is possible to continuously detect the oil deterioration state of the lubricating oil or the like.

  According to a third aspect of the present invention, the outside surface of the active sensor area is manufactured using the glass electrode portion or the ISFET structure in which the non-oil-soluble and conductive ionic liquid film is coated on the outer surface of the pH-responsive glass thin film. A method for detecting the degree of deterioration of oil, comprising measuring a pH value of oil by directly immersing a pH semiconductor sensor part, the surface of which is coated with the non-oil-soluble and conductive ionic liquid film, in the oil. is there.

  According to the present invention, the pH electrode 1 can be directly immersed in the sample oil to determine the deterioration of the oil itself as the pH changes, and as a result, the oil deterioration state of the lubricating oil or the like can be continuously detected online. .

It is a schematic diagram of the pH electrode sensor using the glass electrode which concerns on the premise technique of this 1st invention. It is a schematic diagram of the pH electrode sensor using the glass electrode which concerns on 1st Example of this invention. It is a schematic diagram of the pH semiconductor sensor of the structure of "ISFET" concerning the premise technique of this 2nd invention. It is a schematic diagram of the pH semiconductor sensor using the “ISFET” electrode according to the second embodiment of the present invention. It is a calibration curve which shows the relationship between pH (total acid value) and an electromotive force. It is a principle figure of the pH electrode sensor using the glass electrode which concerns on a prior art.

First, the ionic liquid used in the present invention will be described.
The ionic liquid used in the present invention is a non-oil-soluble and electrically conductive, which is also called a room temperature molten salt in a range of −20 to + 100 ° C., preferably in a state where the lubricating oil is operating, at 100 ° C. or less. It is a condition that it is sex.
The ionic liquid is composed of a liquid junction on the comparison electrode side and a pH-responsive glass thin film on the glass electrode side, and the ionic liquid film must be deposited between the liquid junction and the pH-responsive glass thin film. For this reason, by adding a thickener to the ionic liquid to make it grease, the apparent viscosity increases and the deposition effect is further enhanced.

  Such an ionic liquid is composed of a combination of various anions and cations, and as the anion constituting the ionic liquid used in the present invention, phosphinate, imide, carboxylic acid, phosphate, borate, thiocyanate, and thiosalicylate are preferable. . The cation is preferably imidazolium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, morpholine, pyrrole, phosphonium, quaternary ammonium salt, sulfonium or isoxazolium.

Specific examples of non-aqueous and non-oil-soluble ionic liquids (cation / anion)
Trihexyl-tetradecyl-phosphonium / bis (2,4,4-trimethyl-pentyl) phosphinate
1-ethyl-3-methyl-imidazolium / bis (pentafluoroethylsulfonyl) imide
1-butyl-1-methyl-pyrrolidinium / bis (trifluoromethylsulfonyl) imide
Tetrabutyl-ammonium / bis (trifluoromethylsulfonyl) imide
Trihexyl-tetradecyl-phosphonium / decanoate
1-butyl-3- (3,3, ...- tridecafluorooctyl) -imidazolium / hexafluorophosphate
1-methyl-3- (3,3, ...- tridecafluorooctyl) -imidazolium / hexafluorophosphate
1-ethyl-3-methyl-imidazolium / hexafluorophosphate
1-butyl-3-methyl-imidazolium / hexafluorophosphate
1-hexyl-3-methyl-imidazolium / hexafluorophosphate
1-butyl-4-methyl-pyridinium / hexafluorophosphate
1-methyl-3-octyl-imidazolium / hexafluorophosphate
Trihexyl-tetradecyl-phosphonium / hexafluorophosphate
Tetrabutyl-ammonium / nonafluoro-butanesulfonate
Tetrabutyl-ammonium / heptadecafluoro-octanesulfonate
Tetrabutyl-phosphonium / tetrafluoroborate
Tetrahexyl-ammonium / tetrafluoroborate
Tetrapentyl-ammonium / thiocyanate
Trioctylmethylammonium / thiosalicylate
1-hexyl-3-methyl-imidazolium / trifluoromethansulfonate
Is mentioned.

[Thickener]
By adding a thickener to the ionic liquid of the present invention, the apparent viscosity can be increased.
Thickeners are preferably conductive and oil-soluble, and include urea-based thickeners, polytetrafluoroethylene (PTFE), MCA, organic thickeners typified by carbon black, and copper and silver. Metal oxides such as zinc oxide and titanium oxide, and inorganic fine powders such as nitrides such as boron nitride can also be used as thickeners.
The content of the thickener is preferably 1 to 50% by mass, more preferably 3 to 30% by mass with respect to the ionic liquid.

Example 1
The glass electrode type pH electrode 1 sensor applied to the present invention will be described.
FIG. 2 is an oil deterioration (PC) sensor comprising a pH electrode 1 comprising a glass electrode 10A and a comparison electrode 20A according to an embodiment of the present invention, based on FIG. 1, and the glass electrode 10A support tube as in FIG. 34 contains an internal electrode 31 and is filled with, for example, a KCl solution of pH 7 as the internal solution 32 of the glass electrode 10A. In the comparison electrode 20A, the liquid junction 23A is provided on the bottom side of the outer peripheral wall of the support tube 24 of the comparison electrode 24A. Lead wires 11A and 21A are connected to the internal electrode 14A of the comparison electrode 20A and the internal electrode 24A of the glass electrode 10A, respectively, and these lead wires extend from the base end of the support tube 2 to the outside as a cable bundle. It is designed to be connected to a pH measuring device main body 5 (not shown).
Then, the non-oil-soluble and conductive ionic liquid film 15 is coated until the entire surface of the spherical pH-responsive glass thin film 11 and the outer surface of the liquid junction 23A are sandwiched between the support tube 24 of the comparison electrode 24A. .
The ionic liquid 15 is a non-oil-soluble and electrically conductive ionic liquid which is also called a room temperature molten salt in the range of -20 to + 100 ° C. in a state where the lubricating oil is operating. It comprised from the combination of the ionic liquid shown by or several.
The 40 ° C. kinematic viscosity of the ionic liquid 15 is preferably set to 12 mm ² / s or more because it is less than 12 mm ² / s adhesion to the electrode is reduced.
Furthermore, when the thickener is added to the ionic liquid to form a grease, the deposition effect is further enhanced.

FIG. 2 shows a state in which the ionic liquid 15 is deposited between the liquid junction 23A on the comparison electrode side and the pH-responsive glass thin film 31 on the glass electrode side. Although the representative example of the ionic liquid has been described above, the state of FIG. 2 is a conceptual diagram. Actually, the ionic liquid 15 needs to be held between the liquid junction 23A on the comparison electrode side and the pH-responsive glass thin film 31 on the glass electrode side. Therefore, if the ionic liquid 15 is made semi-solid, that is, in the form of grease, the application becomes easy. A method of making a grease with a thickener such as Li soap based on the ionic liquid 15 is described in Kyodo Yushi Invention International Publication No. 2012/018137. In addition, as a method of making a semi-solid without using a thickener, a method of mixing an ionic liquid with an inorganic fine powder can be considered.
As the inorganic fine powder, it is preferable to use metal oxides such as zinc oxide and titanium oxide, ceramics such as alumina and silicon nitride, nitrides such as boron nitride, and fluorine resins such as PTFE.

And the result of having measured the electromotive force of the pH sensor with the potentiometer 4 by immersing the said pH sensor 1 in the engine oil containing carboxylic acid (weakly acidic component) and sulfuric acid (strongly acidic component) is shown in FIG. The vertical axis in FIG. 5 is the electromotive force measured by the present invention, and the horizontal axis is the total acid value measured by the JIS standard method.
This shows that the electromotive force of this pH sensor is associated with the conventional total acid value.

  According to the present embodiment, when directly measuring the pH of the oil, the pH sensor shown in FIG. 2 is directly immersed in the oil, and the entire surface of the pH-responsive glass thin film 11 and the support tube 24 of the reference electrode 24A are sandwiched. If the relationship between the total acid value and the electromotive force is calibrated in advance using the calibration diagram of FIG. 5 with the ionic liquid covered up to the outer surface of the liquid junction 23A, the total acid value is unknown. Since the total acid value can be obtained from the electromotive force of the oil, it is possible to detect oil deterioration online.

(Example 2)
FIG. 3 shows a conventional example of a pH semiconductor sensor using an ion-sensitive field effect transistor (ISFET) which is a precondition for the present invention.
In FIG. 3, a support tube 34 enclosing an Ag / AgCl electrode 24 </ b> B that is an internal electrode is filled with, for example, a KCl saturated solution having a pH of 7 as the internal liquid 32 together with the internal electrode 24 </ b> B. A liquid junction 23B is provided on the bottom side of the outer peripheral wall of the support tube 24, and an ISFET semiconductor electrode 10B is provided on the outer periphery of the support tube 24 near the bottom liquid junction 23B. Lead wires 11B and 21B are connected to the ISFET semiconductor electrode 10B and the Ag / AgCl electrode 24B, respectively, and these lead wires extend to the outside from the base end portion of the support tube 24 as a cable bundle and have a pH not shown. It is designed to be connected to the measuring instrument body 5.

  FIG. 4 shows a second embodiment of the present invention using the base technology of FIG. 3, in which the ionic liquid is deposited on the support tube between the liquid junction on the comparison electrode side and the ISFET semiconductor electrode 10B. Similar to Example 1.

  According to the present embodiment, when directly measuring the pH of the oil, the pH sensor shown in FIG. 4 is directly immersed in the oil, and the entire surface of the pH-responsive glass thin film 11 and the support tube 24 of the comparison electrode 24A are sandwiched. If the relationship between the total acid value and the electromotive force is calibrated in advance using the calibration diagram of FIG. 5 with the ionic liquid covered up to the outer surface of the liquid junction 23A, the total acid value is unknown. Since the total acid value can be obtained from the electromotive force of the oil, it is possible to detect oil deterioration online.

  As described above, according to the pH sensor or the PH semiconductor sensor for detecting the degree of deterioration of the oil according to the present invention, the pH electrode is directly immersed in sample oil such as lubricating oil, which is accompanied by a change in total acid value (change in pH). It is possible to determine the deterioration of the oil itself, and as a result, it is possible to continuously detect the oil deterioration state of the lubricating oil or the like online.

DESCRIPTION OF SYMBOLS 1 pH electrode sensor 3 Calculation part 4 Potentiometer 10, 10A Glass electrode 20, 20A Comparison electrode 15 Non-oil-soluble and electroconductive ionic liquid film 1B pH semiconductor sensor 23A, 23B Liquid junction part

  The present invention relates to a pH sensor for detecting the deterioration level of oils generally used as lubricating oils such as engine oil, turbine oil, hydraulic hydraulic oil, and gear oil, and more particularly at normal temperature (−20 ° C. to 100 ° C.), diesel The present invention relates to a pH sensor that detects the deterioration of oil such as engine lubricating oil over time.

Conventionally, oils such as lubricating oils have been determined for total acid number and total base number by a method of measuring the pH of a solution dissolved in a mixed solvent.
The total acid value indicates the total amount of acidic components in the oil, that is, the total amount of acidic substances in the additives, organic acids generated during use, and the like. It is widely used as a guideline for the refinement degree of lubricating oil with the total acid number, as a guideline for manufacturing process control index, management of used lubricant oil, or for knowing deterioration state after oxidation test and practical test of lubricant oil. In general, as the lubricating oil degrades, the total acid number usually increases.

  The total acid value of such an oil has been conventionally used as an index of deterioration of the oil. However, since the oil is a non-aqueous liquid, the pH of the oil cannot be directly measured. As shown in "Products and Lubricating Oils-Neutralization Test Method", dissolve the oil in a mixed solvent of toluene, 2-propanol and a small amount of water, and monitor hydrochloric acid standard 2-propanol solution or potassium hydroxide while monitoring the pH. A method of titration with a standard 2-propanol solution is employed.

Such pH is measured using a pH electrode sensor 1 having a configuration including a glass electrode 10 and a comparative electrode 20 as shown in FIG. 6 (principle diagram).
That is, the glass electrode 10 is formed with a pH-responsive glass thin film 11 that responds sensitively to pH at the tip (the pH-responsive glass used at the tip of the glass electrode 10 is mainly composed of silicon and lithium, and is used for other pH measurements. For the purpose of improving the performance as glass, several elements are used as subcomponents, and the pH-responsive glass thin film 11 is well known and will not be described in detail.) Inside, potassium chloride (KCl) and neutral pH glass electric in-electrode portion liquid 12 is filled consisting buffer. The reference electrode 20 is filled with a reference electrode internal solution 22 made of a potassium chloride solution, and has a so-called delicate junction (a porous ceramic such as alumina or zirconia is often used) called a liquid junction 23 at the tip. Formed and in electrical communication with the solution sample. In the figure, 26 is an internal liquid replenishment port. 14 and 24 are AgCl electrodes, respectively.

  When the pH electrode sensor 1 comprising the glass electrode 10 and the comparison electrode 20 is immersed in the solution sample, the glass electrode 10 generates an electromotive force according to the pH of the solution sample on the surface of the pH responsive glass thin film 11, and the comparison electrode 20. Always generates a constant electromotive force while being in electrical contact with the sample via ions at the liquid junction 23. The pH measuring device main body 5 having the calculation unit 3 measures the difference (voltage) of the electromotive force generated between the glass electrode 10 of the pH electrode 1 and the comparison electrode 20 with the potentiometer 4, and performs calculation processing with the calculation unit 3. Display the pH of the sample. Such a pH measurement method is called a glass electrode A method (see Non-Patent Document 1: JISK2501).

  Moreover, the technique which integrated the comparison electrode and the glass electrode is disclosed by patent 4733588 (patent document 1). However, as shown in FIG. 1 and FIG. 6, if the glass electrode and the comparative electrode are separated from each other, when the gap is oil, the electrodes are not electrically communicated with each other, so that measurement cannot be performed.

This technique will be described with reference to FIG. 1 (a prerequisite technique of the present invention). In the prerequisite technique shown in FIG. 1, the integrated electrode sensor is integrated so that the comparison electrode 20A surrounds the support tube 34 of the glass electrode 10A. The glass electrode 10A includes a cylindrical glass support tube 34 and a glass responsive film (hereinafter also referred to as a pH responsive glass thin film) 31 bonded to the tip of the support tube 34 . I have. Specifically, the support tube 34 of the glass electrode 10A has a slightly protruding tip portion than the support tube 25 of the comparative electrode, and the glass response film 31 is bonded to the tip portion.

Further, the support tube 34 of the glass electrode 10A accommodates an internal electrode 14A and is filled with, for example, a KCl solution having a pH of 7 as the internal liquid 12A of the glass electrode 10A. In the comparison electrode 20A, the liquid junction 23A is provided on the bottom side of the outer peripheral wall of the support tube 25 of the comparison electrode 20A . Lead wires 11A and 21A are connected to the internal electrode 24A of the comparison electrode 20A and the internal electrode 14A of the glass electrode 10A, respectively, and these lead wires are connected to the outside from the base ends of the support tubes 25 and 34 as cable bundles. And is connected to a pH measuring device body 5 (not shown).

However, even an integrated electrode sensor as shown in FIG. 1 cannot measure in the case of oil because the glass electrode and the comparative electrode are separated.
Therefore, in order to measure the total acid value of oil using the measuring device shown in FIG. 1, the difference (voltage) of the electromotive force generated between the glass electrode 10A of the pH electrode 1A and the comparison electrode 20A is measured with a potentiometer. Therefore, the glass response film 31 and the oil to be measured must have an affinity (conductivity). For this reason, conventionally, the oil to be measured is dissolved in a mixed solvent and used.

That is, even if the pH electrode 1A is directly immersed in the oil, the affinity (conductivity) cannot be obtained between the pH-responsive glass thin film 31 and the oil, so that the electromotive force cannot be measured. For this reason, sample oil is brought offline into a laboratory such as a lab at predetermined time intervals, and the mixed solvent is added to the sample oil to form an aqueous solution to measure the total acid number of the oil from potential difference and pH measurement. .

  However, in the method of measuring the total acid number of the oil by adding the mixed solvent to the sample oil and measuring the total acid value of the oil, it can only be measured offline at a predetermined time interval as described above. Measurement with is impossible.

  On the other hand, as shown in Patent Document 2 as a technique for continuously determining oil degradation online, an AC voltage is provided between two electrode plates installed in parallel to each other in the oil flow path and the two electrode plates. An ammeter that measures the current that flows when a voltage is applied, a voltmeter that measures a voltage between the two plates when an AC voltage is applied to the two plates, and a measurement by the ammeter and the voltmeter A method has been proposed in which the electrical conductivity and dielectric constant of the oil are obtained based on the results, and the deterioration of the oil is judged based on the electrical conductivity and the dielectric constant.

  However, such prior art determines oil degradation based on conductivity and dielectric constant, and more specifically, it does not “directly” measure changes in the pH of the oil, but rather the electrical characteristics associated with contamination in the oil. The change is captured two-dimensionally from the viewpoint of conductivity and dielectric constant, and the deterioration of the oil itself accompanying the change in pH cannot be determined.

Japanese Patent No. 4733588 (see FIG. 5) Japanese Patent Laying-Open No. 2009-2893 (see paragraphs [0006] and [0007] FIG. 1)

JIS standard document: JISK2501

In view of the technical problem of the present invention, the pH electrode 1A can be directly immersed in a sample oil such as a lubricating oil to determine the deterioration of the oil itself accompanying a change in pH. A pH sensor capable of continuously detecting an oil deterioration state and an oil deterioration degree detection method using the pH sensor, and particularly a pH sensor suitable for detecting the deterioration degree of lubricating oil or turbine oil of a diesel engine and the sensor An object is to provide a method for detecting the degree of oil deterioration.

  The present invention relates to a pH sensor in which an outer surface of an active sensor area is coated with a non-oil-soluble and conductive ionic liquid film, and in particular, the composite electrode in which the pH sensor is integrated with a reference electrode and a glass electrode The active sensor area is composed of a liquid junction on the comparison electrode side and a pH responsive glass thin film on the glass electrode side, and the ionic liquid film is deposited between the liquid junction and the pH responsive glass thin film. Located in the pH sensor.

  Specifically, according to the first aspect of the present invention, a glass electrode in which a pH-responsive glass thin film that responds sensitively to pH is formed at the tip and the glass electrode internal liquid is filled therein, and the internal liquid of the comparison electrode is contained therein. A pH electrode sensor comprising a reference electrode filled and formed with a liquid junction at the tip, which is insoluble on the outer surface of the sensor support between the liquid junction on the reference electrode side and the pH-responsive glass thin film on the glass electrode side And a conductive ionic liquid film is applied.

According to the present invention, the pH electrode 1A can be directly immersed in an oil such as lubricating oil to determine the deterioration of the oil itself accompanying a change in pH, and as a result, the oil deterioration state of the lubricating oil or the like can be continued online. Can be detected.

The ionic liquid (hereinafter also referred to as ionic liquid) is a room temperature molten salt that becomes liquid at room temperature, and the ionic liquid is composed of a combination of various anions and cations. In order to directly immerse the electrode 1A , it is necessary to be non-oil-soluble and conductive.
The ionic liquid needs to be applied between the pH-responsive glass thin film and the liquid junction on the side of the reference electrode. Further, if a thickener is added to the ionic liquid to form a grease, the application effect is further increased. Rise.

  The second aspect of the present invention is an oil-insoluble material between the outer surface of the sensor support that connects the semiconductor electrode that forms the active sensor area of the pH semiconductor sensor using the structure of an ion-sensitive field effect transistor (ISFET) and the liquid junction. In addition, a conductive ionic liquid film is deposited.

For example surface synthetic diamond semiconductor, which is hydrogen-terminated, the intrinsic, regardless of exogenous form, becomes conductive thin film by the electrolyte, be sensitive to pH and ion concentration of the electrolyte. It is known in Japanese Patent Application Laid-Open No. 2007-78373 and the like that a pH semiconductor sensor can be manufactured using this conductive “Ion Sensitive Field Effect Transistor” (“ISFET”) structure.
Therefore, the second invention is an oil-insoluble and conductive material on the outer surface of the sensor support that connects the semiconductor electrode and the liquid junction, which is an active sensor area of a pH semiconductor sensor using an ion-sensitive field effect transistor (ISFET) structure. The ionic liquid film is deposited.

According to the second invention, as in the first invention, the pH electrode 1A can be directly immersed in a sample oil such as a lubricating oil to determine the deterioration of the oil itself accompanying a change in pH. Thus, it is possible to continuously detect the oil deterioration state of the lubricating oil or the like.

  According to a third aspect of the present invention, the outside surface of the active sensor area is manufactured using the glass electrode portion or the ISFET structure in which the non-oil-soluble and conductive ionic liquid film is coated on the outer surface of the pH-responsive glass thin film. A method for detecting the degree of deterioration of oil, comprising measuring a pH value of oil by directly immersing a pH semiconductor sensor part, the surface of which is coated with the non-oil-soluble and conductive ionic liquid film, in the oil. is there.

According to the present invention, the pH electrode 1A can be directly immersed in the sample oil to determine the deterioration of the oil itself accompanying the change in pH. As a result, the oil deterioration state of the lubricating oil or the like can be continuously detected online. .

It is a schematic diagram of the pH electrode sensor using the glass electrode which concerns on the premise technique of this 1st invention. It is a schematic diagram of the pH electrode sensor using the glass electrode which concerns on 1st Example of this invention. It is a schematic diagram of the pH semiconductor sensor of the structure of "ISFET" concerning the premise technique of this 2nd invention. It is a schematic diagram of the pH semiconductor sensor using the “ISFET” electrode according to the second embodiment of the present invention. It is a calibration curve which shows the relationship between pH (total acid value) and an electromotive force. It is a principle figure of the pH electrode sensor using the glass electrode which concerns on a prior art.

First, the ionic liquid used in the present invention will be described.
The ionic liquid used in the present invention is a non-oil-soluble and electrically conductive, which is also called a room temperature molten salt in a range of −20 to + 100 ° C., preferably in a state where the lubricating oil is operating, at 100 ° C. or less. It is a condition that it is sex.
The ionic liquid is composed of a liquid junction on the comparison electrode side and a pH-responsive glass thin film on the glass electrode side, and the ionic liquid film must be deposited between the liquid junction and the pH-responsive glass thin film. For this reason, by adding a thickener to the ionic liquid to make it grease, the apparent viscosity increases and the deposition effect is further enhanced.

  Such an ionic liquid is composed of a combination of various anions and cations, and as the anion constituting the ionic liquid used in the present invention, phosphinate, imide, carboxylic acid, phosphate, borate, thiocyanate, and thiosalicylate are preferable. . The cation is preferably imidazolium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, morpholine, pyrrole, phosphonium, quaternary ammonium salt, sulfonium or isoxazolium.

Specific examples of non- oil-soluble ionic liquids (cations / anions)
Trihexyl-tetradecyl-phosphonium / bis (2,4,4-trimethyl-pentyl) phosphinate
1-ethyl-3-methyl-imidazolium / bis (pentafluoroethylsulfonyl) imide
1-butyl-1-methyl-pyrrolidinium / bis (trifluoromethylsulfonyl) imide
Tetrabutyl-ammonium / bis (trifluoromethylsulfonyl) imide
Trihexyl-tetradecyl-phosphonium / decanoate
1-butyl-3- (3,3, ...- tridecafluorooctyl) -imidazolium / hexafluorophosphate
1-methyl-3- (3,3, ...- tridecafluorooctyl) -imidazolium / hexafluorophosphate
1-ethyl-3-methyl-imidazolium / hexafluorophosphate
1-butyl-3-methyl-imidazolium / hexafluorophosphate
1-hexyl-3-methyl-imidazolium / hexafluorophosphate
1-butyl-4-methyl-pyridinium / hexafluorophosphate
1-methyl-3-octyl-imidazolium / hexafluorophosphate
Trihexyl-tetradecyl-phosphonium / hexafluorophosphate
Tetrabutyl-ammonium / nonafluoro-butanesulfonate
Tetrabutyl-ammonium / heptadecafluoro-octanesulfonate
Tetrabutyl-phosphonium / tetrafluoroborate
Tetrahexyl-ammonium / tetrafluoroborate
Tetrapentyl-ammonium / thiocyanate
Trioctylmethylammonium / thiosalicylate
1-hexyl-3-methyl-imidazolium / trifluoromethansulfonate
Is mentioned.

[Thickener]
By adding a thickener to the ionic liquid of the present invention, the apparent viscosity can be increased.
Thickeners are preferably conductive and oil-soluble, and include urea-based thickeners, polytetrafluoroethylene (PTFE), MCA, organic thickeners typified by carbon black, and copper and silver. Metal oxides such as zinc oxide and titanium oxide, and inorganic fine powders such as nitrides such as boron nitride can also be used as thickeners.
The content of the thickener is preferably 1 to 50% by mass, more preferably 3 to 30% by mass with respect to the ionic liquid.

Example 1
It explained pH electrostatic Gokuse capacitors glass electrode type to be applied to the present invention. In the following, “ionic liquid film” and “ionic liquid” are denoted by the same reference numerals.
Figure 2 is a base technology to Figure 1, an oil degradation (pH) sensor 100 consisting of pH electrodes 1A made of glass electrode 10A and the reference electrode 20A according to the embodiment of the present invention, the glass electrode 10A as in FIG The support tube 34 accommodates an internal electrode 14A and is filled with, for example, a KCl solution having a pH of 7 as the internal liquid 12A of the glass electrode 10A. In the comparison electrode 20A, the liquid junction 23A is provided on the bottom side of the outer peripheral wall of the support tube 25 of the comparison electrode 20A . Lead wires 111 and 201 are connected to the internal electrode 24A of the comparison electrode 20A and the internal electrode 14A of the glass electrode 10A, respectively, and these lead wires are connected to the outside from the base ends of the support tubes 25 and 34 as cable bundles. It is to be connected to the extending and p H meter body 5.
Then, the non-oil-soluble and conductive ionic liquid film 15 is covered until the entire surface of the spherical pH-responsive glass thin film 31 and the outer surface of the liquid junction part 23A are sandwiched between the support tube 25 of the comparison electrode 20A . .
The ionic liquid 15 is a non-oil-soluble and electrically conductive ionic liquid which is also called a room temperature molten salt in the range of -20 to + 100 ° C. in a state where the lubricating oil is operating. It comprised from the combination of the ionic liquid shown by or several.
The 40 ° C. kinematic viscosity of the ionic liquid 15 is preferably set to 12 mm ² / s or more because it is less than 12 mm ² / s adhesion to the electrode is reduced.
Furthermore, when the thickener is added to the ionic liquid to form a grease, the deposition effect is further enhanced.

FIG. 2 shows a state in which the ionic liquid 15 is deposited between the liquid junction 23A on the comparison electrode side and the pH-responsive glass thin film 31 on the glass electrode side. Although the representative example of the ionic liquid has been described above, the state of FIG. 2 is a conceptual diagram. Actually, the ionic liquid 15 needs to be held between the liquid junction 23A on the comparison electrode side and the pH-responsive glass thin film 31 on the glass electrode side. Therefore, if the ionic liquid 15 is made semi-solid, that is, in the form of grease, the application becomes easy. A method of making a grease with a thickener such as Li soap based on the ionic liquid 15 is described in Kyodo Yushi Invention International Publication No. 2012/018137. In addition, as a method of making a semi-solid without using a thickener, a method of mixing an ionic liquid with an inorganic fine powder can be considered.
As the inorganic fine powder, it is preferable to use metal oxides such as zinc oxide and titanium oxide, ceramics such as alumina and silicon nitride, nitrides such as boron nitride, and fluorine resins such as PTFE.

FIG. 5 shows the results of measuring the electromotive force of the pH sensor with the potentiometer 4 by immersing the pH sensor 1A in an engine oil containing carboxylic acid (weakly acidic component) and sulfuric acid (strongly acidic component). The vertical axis in FIG. 5 is the electromotive force measured by the present invention, and the horizontal axis is the total acid value measured by the JIS standard method.
This shows that the electromotive force of this pH sensor is associated with the conventional total acid value.

According to the present embodiment, when directly measuring the pH of the oil, the pH sensor shown in FIG. 2 is directly immersed in the oil, and the entire surface of the pH-responsive glass thin film 31 and the support tube 25 of the comparison electrode 20A are sandwiched. If the relationship between the total acid value and the electromotive force is calibrated in advance using the calibration diagram of FIG. 5 with the ionic liquid covered up to the outer surface of the liquid junction 23A, the total acid value is unknown. Since the total acid value can be obtained from the electromotive force of the oil, it is possible to detect oil deterioration online.

(Example 2)
FIG. 3 shows a conventional example of a pH semiconductor sensor using an ion-sensitive field effect transistor (ISFET) which is a precondition for the present invention.
In FIG. 3, a support tube 25 containing an Ag / AgCl electrode 24B as an internal electrode is filled with, for example, a KCl saturated solution having a pH of 7 as the internal liquid 22B together with the internal electrode 24B. With the bottom side there is provided the liquid junction 23B of the outer peripheral wall of the support tube 25, it is close to the support tube 25 the outer circumference of the bottom side of the liquid junction 23B is provided with a ISFET semiconductor electrode 10B. The lead wires 11B and 21B are connected to the ISFET semiconductor electrode 10B and the Ag / AgCl electrode 24B, respectively, and these lead wires extend to the outside from the base end portion of the support tube 25 as a cable bundle and have a pH not shown. It is designed to be connected to the measuring instrument body 5.

FIG. 4 shows a second embodiment of the present invention using the base technology of FIG. 3, in which the ionic liquid 15 is deposited on the support tube between the liquid junction on the comparison electrode side and the ISFET semiconductor electrode 10B. The same as in the first embodiment.

According to the present embodiment, when directly measuring the pH of the oil, the pH sensor shown in FIG. 4 is directly immersed in the oil so that the entire surface of the ISFET semiconductor electrode 10B and the outer surface of the liquid junction 23B of the comparison electrode 24B while being coated with the ionic liquid 15 until, using a calibration diagram of FIG. 5, if calibrated in advance total acid number and the electromotive force of the relationships, the total acid number from the electromotive force of an unknown oil all Since the acid value can be obtained, it is possible to detect oil deterioration online.

  As described above, according to the pH sensor or the PH semiconductor sensor for detecting the degree of deterioration of the oil according to the present invention, the pH electrode is directly immersed in sample oil such as lubricating oil, which is accompanied by a change in total acid value (change in pH). It is possible to determine the deterioration of the oil itself, and as a result, it is possible to continuously detect the oil deterioration state of the lubricating oil or the like online.

DESCRIPTION OF SYMBOLS 1 pH electrode sensor 3 Calculation part 4 Potentiometer 10, 10A Glass electrode 20, 20A Comparison electrode 15 Non-oil-soluble and electroconductive ionic liquid film 1B pH semiconductor sensor 23A, 23B Liquid junction part

Claims (5)

  The pH sensor is a composite electrode in which the reference electrode and the glass electrode are integrated, and is non-oil soluble on the outer surface between the liquid junction on the side of the comparative electrode functioning as an active sensor area and the pH-responsive glass thin film on the side of the glass electrode. And a pH sensor which is coated with a conductive ionic liquid film.   A pH sensor comprising a thickener in an amount of 1 to 50% by mass with respect to the ionic liquid.   A pH-responsive glass thin film that responds sensitively to pH is formed at the tip, a glass electrode filled with glass electrode internal liquid, and a liquid inside the comparison electrode is filled inside, and a liquid junction is formed at the tip A non-oil-soluble and conductive ionic liquid film is deposited on the outer surface of the sensor support between the liquid junction on the comparison electrode side and the pH-responsive glass thin film on the glass electrode side. The pH sensor according to claim 1, wherein   A non-oil-soluble and conductive ionic liquid film is coated on the outer surface of the sensor support that connects the semiconductor electrode that is the active sensor area of the pH semiconductor sensor using the structure of an ion-sensitive field effect transistor (ISFET) and the liquid junction. The pH sensor according to claim 1, wherein the pH sensor is worn. The non-oil soluble and non-oil soluble on the outer surface of the active sensor area manufactured using the glass electrode part or the structure of ISFET whose outer surface of the pH responsive glass thin film is coated with the non-oil soluble and conductive ionic liquid film. A method for detecting the degree of deterioration of an oil, wherein the pH value of the oil is measured by directly immersing the pH sensor coated with a conductive ionic liquid film in the oil.

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