JP5604334B2 - Method for analyzing adsorptive compounds - Google Patents

Description

  The present invention relates to a method for analyzing an adsorptive compound adsorbed on a metal surface.

Lubricating oil is widely used for lubrication of sliding portions between metals. Therefore, various compounds are added to the lubricating oil in order to maintain and improve lubricity and the like. For example, metal detergents such as sulfonates, salicylates, and phenates of alkali metals and alkaline earth metals are adsorbed on metal surfaces such as steel to improve lubricity and rust prevention.
In selecting such a compound (additive) that exhibits an effect by adsorption, it is necessary to examine the adsorption / desorption behavior of the additive on the metal surface. For this purpose, a method for analyzing the additive adsorbed on the metal surface is required.
Conventionally, the ATR method (Attenuated Total Reflection) is known as a method for analyzing the surface of a substance (see Non-Patent Document 1). According to the ATR method, it is possible to analyze a very small amount of components present on the surface of a substance.

Wikimedia Foundation, Free Encyclopedia "Wikipedia", [Search February 21, 2011], Internet, <http://en.wikipedia.org/wiki/%E8%B5%A4%E5%A4% 96% E5% 88% 86% E5% 85% 89% E6% B3% 95>

  However, the amount of lubricant additive adsorbed on the metal surface is extremely small, and it is difficult to analyze the trace amount of additive present on the metal surface even by the ATR method described above.

  An object of this invention is to provide the analysis method which can observe in detail the adsorption | suction and desorption behavior with respect to the metal surface of the adsorptive compound contained in the liquid.

As a result of intensive studies, the present inventors have found that the above problem can be solved by applying an ATR-SEIRAS method (Attenuated Total Reflection-Surface Enhanced Infrared Absorption Spectroscopy). .
SEIRA increases the infrared absorption intensity of molecules adsorbed on a metal thin film (gold, silver, copper, platinum, iron, nickel, etc.) having a fine particle structure on the order of nanometers from several tens to several hundred times the usual. It is a phenomenon. When a metal having free electrons becomes fine particles on the order of several tens of nm, absorption derived from surface plasmons appears in the visible range. Fine particles are densely packed on the thin film, and plasmon absorption becomes broad due to the resonance effect and extends to the infrared region. When the absorption of the metal thin film by the plasmon coincides with the infrared vibration frequency of the adsorbed molecule, the dielectric constant of the thin film is greatly modulated. For this reason, the absorption of the metal thin film is greatly attenuated at the wavelength of the molecular vibration, and an effect that the molecular vibration is apparently enhanced is obtained.
That is, the present invention combines this SEIRA with the ATR method and provides the following analysis method.
(1) Among the adsorptive compounds contained in the liquid, a method for analyzing the compound adsorbed on the metal surface, wherein the liquid is a lubricating oil, and the adsorbing compound is an additive for the lubricating oil, The additive is at least one of an alkali metal salt and an alkaline earth metal salt, and each metal salt is at least one of a sulfonate, a salicylate, and a phenate, and is adsorbed on a metal surface by an ATR-SEIRAS method. A method for analyzing an adsorptive compound, comprising analyzing the compound.
(2) In the method for analyzing an adsorptive compound described in (1) above, the adsorbing compound adsorbed on the metal surface is analyzed, and then a desorbing agent that desorbs the adsorbing compound from the metal surface is obtained. An analysis method for an adsorptive compound, characterized by adding to the liquid and analyzing the metal surface.
(3) The method for analyzing an adsorptive compound according to the above (1) or (2), wherein the metal is gold.
( 4 ) The method for analyzing an adsorptive compound according to any one of (1) to (3) above, wherein the alkaline earth metal salt is a calcium salt. Method.
( 5 ) The method for analyzing an adsorptive compound according to any one of (1) to (4) above, wherein the sulfonate is at least one of alkylbenzene sulfonate and alkylnaphthalene sulfonate. Method for analyzing adsorptive compounds.

  According to the present invention, since the ATR-SEIRAS method is used, the adsorption / desorption behavior of the adsorptive compound contained in the liquid on the metal surface can be observed in detail.

In embodiment, the schematic sectional drawing of the analyzer for performing the analysis by ATR-SEIRAS method. In an Example, the ATR-SEIRA spectrum which shows the adsorption | suction and desorption behavior to the metal surface of alkylbenzene Ca sulfonate. In an Example, the ATR-SEIRA spectrum which shows the adsorption | suction and desorption | desorption behavior to the metal surface of the alkylnaphthalene-type Ca sulfonate.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Configuration of analyzer]
FIG. 1 shows an analyzer 100 for analyzing adsorption / desorption characteristics of an adsorbing compound contained in a liquid on a metal surface.
The analyzer 100 includes a semi-cylindrical (kamaboko-shaped) silicon prism 10 and a mold 30 fixed to the rectangular flat surface portion 11 via an O-ring 20. A metal thin film M is formed on the planar portion 11 of the silicon prism 10. As the metal, for example, gold, silver, copper, platinum, iron, nickel or the like is used. The thickness of the metal thin film M is preferably 8 nm to 100 nm, and more preferably 10 nm to 40 nm. If the thickness of the metal thin film M is less than 8 nm, the effect of enhancing the molecular vibration may be difficult to occur. On the other hand, if the thickness of the metal thin film M exceeds 100 nm, the measurement sensitivity may be lowered. As a method for forming such a metal thin film M, known methods such as electroless plating, vapor deposition, and sputtering can be applied.

[Application of sample solution]
In the analyzer 100, a box-shaped space is formed by the mold 30 and the flat portion 11. The sample liquid L containing the adsorptive compound is applied to the bottom surface of this box-shaped space (the flat portion 11 on which the metal thin film is formed).

[Analysis method]
The spectrum is measured by applying infrared rays to the metal thin film with the ATR arrangement shown in FIG. 1 (ATR-SEIRAS method). Details will be described in an embodiment described later.

In the present invention, the molecular vibration of the adsorbed compound is measured through the vibration of the metal fine particles. Therefore, compared with the conventional high-sensitivity reflection method (IRRAS method) and the normal ATR method, the molecular vibration of the adsorbed molecules can be greatly enhanced. Therefore, the adsorption / desorption state of the compound from the metal thin film can be observed in situ with extremely high sensitivity. Furthermore, the orientation state of the compound molecules adsorbed on the metal thin film can be examined.
For example, when the present invention is applied to a lubricating oil, since the compound (additive) adsorbed on the metal thin film is observed from the metal thin film side, water and various molecules dispersed in the lubricating oil are observed. The influence can be eliminated. Therefore, the moment of adsorption / desorption of the adsorptive compound in the lubricating oil and the orientation state at the time of adsorption can be observed in situ with high sensitivity. Here, that the orientation state can be observed means, for example, that it is possible to estimate whether the alkyl group is vertical or horizontal with respect to the metal surface.
Various additives are blended in the lubricating oil, and are particularly useful for analysis of additives known as metal detergents. Specifically, it is suitable for analysis of sulfonates, salicylates, and phenates of alkali metals and alkaline earth metals. In particular, it is preferably applied to an alkaline earth metal salt, and more preferably applied to a Ca salt. As the sulfonate, alkylbenzene sulfonate and alkylnaphthalene sulfonate can be preferably applied.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by this. Specifically, the adsorption / desorption characteristics of the adsorptive additive contained in the lubricating oil were analyzed using the analyzer 100 shown in FIG.

(Analysis equipment)
In the analyzing apparatus 100, the one obtained by applying electroless gold plating having a thickness of about 20 nm to the planar portion 11 of the silicon prism 10 was used.
(Test oil)
A test oil was prepared by blending the following two types of Ca sulfonate with a hydrocarbon-based lubricating base oil having a kinematic viscosity of 5 mm ² / s (23 ± 3 ° C.) so as to be 5% by mass.
(1) Alkylbenzene type Base number: 0.2 mgKOH / g
Molecular weight: 970
(2) Alkylnaphthalene type Base number: 0.7 mgKOH / g
Molecular weight: 958

(Analysis method)
20 μL of the test oil prepared by the above-described method was applied to the flat portion 11 (gold surface) in FIG. Next, 100 μL of commercial degreasing solution (pH 11) mainly composed of NaOH and sodium silicate was dropped while measuring the spectrum in the ATR configuration (incident angle of infrared light was 69 °), and the change in characteristic absorption over time Was observed. The results are shown in FIGS. In this method, only the vicinity of the interface in contact with the metal thin film is observed, not the entire oil film.

(result of analysis)
FIG. 2 shows the results of a test oil containing an alkylbenzene-based Ca sulfonate, and FIG. 3 shows the results of a test oil containing an alkylnaphthalene-based Ca sulfonate. In all cases, characteristic absorption specific to Ca sulfonate was observed after application of the test oil. And when a degreasing liquid is dripped at the test liquid after application | coating, since Ca sulfonate will detach | desorb from a metal surface, it turns out that the characteristic absorption mentioned above weakens. At the same time, water permeates and adsorbs on the metal surface from which the Ca sulfonate has been desorbed, and water-specific characteristic absorption is observed.

It can be seen that in the system using the alkylbenzene Ca sulfonate, the characteristic absorption disappeared and completely desorbed after 5 seconds under the degreasing droplet. On the other hand, in the system using an alkylnaphthalene-based Ca sulfonate, characteristic absorption is observed even after 60 seconds under a degreasing droplet, indicating that a part of the compound still remains on the metal surface. Specifically, wavelength ^{1450 cm} -1 due to the Ca ^sulfonate, 2800 cm -1, remain absorbed in 2900 cm ^-1.

  The results of alkylbenzene-based Ca sulfonate and alkylnaphthalene-based Ca sulfonate are consistent with the order of degreasing properties in steel in the degreasing process of automakers. That is, according to this example, it can be said that the moment when Ca sulfonate was degreased was observed for the first time. In the past, automobile manufacturers used the degreasing end point when the steel sheet became wet (water repelled when oil remained), but even when wet, water actually became oil (especially highly adsorbed Ca sulfonate). ) Remained, and a defective phenomenon sometimes occurred in the subsequent coating. It is necessary to observe the adsorbed state and the desorbed state in detail in order to achieve both the contradictory properties of lubricity (rust prevention) and degreasing properties possessed by the adsorbing compound such as Ca sulfonate. The method is extremely useful because it can be confirmed at the molecular level whether or not it has really been degreased.

  The analysis method of the present invention can be suitably used in the industrial field using a compound having adsorption / desorption characteristics for metals. For example, it is suitable for the machine field and automobile field in which a metal detergent is used as an additive for lubricating oil.

DESCRIPTION OF SYMBOLS 10 ... Silicon prism 11 ... Plane part 20 ... O-ring 30 ... Formwork 100 ... Analyzer L ... Sample liquid M ... Metal thin film

Claims (5)

Among the adsorptive compounds contained in the liquid, a method for analyzing the compounds adsorbed on the metal surface,
The liquid is a lubricating oil;
The adsorptive compound is a lubricant additive;
The additive is at least one of an alkali metal salt and an alkaline earth metal salt;
Each metal salt is at least one of sulfonate, salicylate and phenate;
A method for analyzing an adsorptive compound, characterized in that the compound adsorbed on the metal surface is analyzed by ATR-SEIRAS (attenuated total reflection surface enhanced infrared spectroscopy). The method for analyzing an adsorptive compound according to claim 1,
Analyzing the adsorptive compound adsorbed on the metal surface,
Next, a desorbing agent that desorbs the adsorptive compound from the metal surface is added to the liquid to analyze the metal surface. In the analysis method of the adsorptive compound according to claim 1 or 2,
The method for analyzing an adsorptive compound, wherein the metal is gold. In the analysis method of the adsorptive compound according to any one of claims 1 to 3,
The method for analyzing an adsorptive compound, wherein the alkaline earth metal salt is a calcium salt. In the analysis method of the adsorptive compound according to any one of claims 1 to 4,
The method for analyzing an adsorptive compound, wherein the sulfonate is at least one of alkyl benzene sulfonate and alkyl naphthalene sulfonate.

Images