JP2001264282A - METHOD AND DEVICE FOR MEASURING ζ POTENTIAL ON METALLIC MATERIAL SURFACE AND SURFACE CHARACTERISTIC EVALUATION METHOD FOR METALLIC MATERIAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for accurately measuring a ζ potential on a metallic material surface and to provide a surface characteristic evaluation method for the metallic material based on this ζ, potential measurement. SOLUTION: A water solution C containing an electrolyte maintaining a fixed dielectric constant is stored in a cell 1, and the metallic material X is brought into contact with the solution C, while a monitor particle B charged at a known ζ potential is arranged inside the solution. From a change in mobility of the monitor particle B between the mobility of the monitor particle B in the solution in no contact with the metallic material and that in the solution C in contact with the metallic material, a ζ potential matching the change of the mobility is measured as a ζ potential of the metallic material surface. A part of the solution contact side surface of the metallic material X is insulated, so that the monitor particle B in the solution is charged, and then, the change of mobility of the monitor particle B in the solution is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the zeta potential of a metal material surface, an apparatus for measuring the zeta potential, and a method for evaluating the surface characteristics of a metal material.

[0002]

2. Description of the Related Art The zeta potential (ζ potential) represents the charged state of a surface of a substance (solid) in a solution such as colloidal particles. It is widely used in scientific fields. More specifically, in the fields of paper pulp, photography, paints, oils, fats, cements, etc., the agglomeration and dispersion of individual colloidal solutions are measured by measuring the zeta potential of the colloidal particles, and the interaction between these colloidal particles and the solution is measured. Various characteristics that are related to each other are evaluated, and JP-A-10-121039, JP-A-8-1697
No. 38, JP-A-7-116484, JP-A-7-45600, JP-A-6-600
No. 48735, JP-A-6-220, JP-A-5-337351, JP-A-5-337351
It is also disclosed in publications such as 5-67601 together with the measurement method.

This zeta potential (ζ potential) is described in “Physical Chemistry at Zeta Potential Particle Interface” (Scientist, 19
As disclosed in U.S. Pat. No. 5,953,955), it can be measured as a potential obtained from electrokinetic phenomena such as electrophoresis of colloid particles, electroosmosis, streaming potential, sedimentation potential and the like.

FIG. 1 schematically shows the principle of measuring the zeta potential of colloidal particles by electrophoresis. In FIG.
When a certain electric field (±) is applied to the solution (dispersion liquid) C in the cell 1 to disperse the particles A, the particles are charged so as to have a constant zeta potential on the surface of the particles A [in Fig. 1, the charge has (-)]. Then, in accordance with this charged state (ζ), it moves at the speed U in the direction of the counter electrode.

The moving speed U of the colloidal particles A in the solution
(Moving speed in the direction of the electrode (+) in Fig. 1)
The zeta potential of the colloidal particle surface A is given by the following equation 1, U = (εE
ζ) / (4πη) (where, ε; dielectric constant of the solution, E: electric field of the solution, ζ; zeta potential on the surface of the colloid particles A, η; viscosity of the solution).

On the other hand, in the field of surface treatment of metal materials,
In the case where the colloidal particles are used for the surface treatment of the metal material, if the relationship between the zeta potential of the colloidal particle surface and the zeta potential of the surface of the metal material to be treated is known,
The surface treatment property of the metal material can be evaluated. In some surface treatments, it is difficult to perform an evaluation test by actually treating the surface, or it may be expensive or it may take a long time, so if it is possible to evaluate the material metal without actually performing the surface treatment And can be promptly reflected in the improvement of the surface treatment property of the material.

[0007] This is not only due to the surface treatment property of the metal material, but also the metal material such as the corrosion resistance of the metal material or the contamination resistance of the surface of the metal material (the surface of the metal material is easily contaminated by a specific substance). Other surface properties of the material can also be said.

[0008] As an example of the surface treatment of metal materials,
Al alloy wrought material has surface treatment properties. In recent years, aluminum alloy wrought materials for automobiles have been used such as rolled aluminum alloy plates for panels and extruded aluminum alloy materials for frames and members. These aluminum alloy wrought materials, like the steel materials used conventionally, in the automobile production line, after forming, assembling, joining, after being subjected to a coating base treatment such as zinc phosphate, Coating such as cationic electrodeposition coating, intermediate coating, and top coating is applied.

[0009] At this time, if the zinc phosphate treatment property of the wrought Al alloy is poor, the adhesion of the coating film formed by coating thereafter is reduced. As a result, rust-like corrosion or blistering of the coating film occurs after coating, and the corrosion resistance and appearance of the automobile may be reduced. For this reason, it is necessary to evaluate the zinc phosphate treatability of the wrought Al alloy on the material producing side before putting the material on the automobile production line, and reflect the zinc phosphate treatability on the material.

[0010] In such a case, the wrought aluminum alloy is not subjected to zinc phosphate treatment without equipment on the material production side, and
It would be a very useful technique if the zeta potential of the wrought aluminum alloy surface could be used as a method for evaluating the zinc phosphate treatability.

[0011]

However, the measurement of the zeta potential up to now has been described in the field of colloid science.
There is no known example of measuring the zeta potential of the surface of a conductive metal material such as Al or iron, which is limited to the zeta potential of particles or an insulating plate surface in a solution.

[0012] The reason for this is that, first, the characteristic evaluation based on the zeta potential is limited to the field of colloid science, and is applied until the characteristic of the surface of a conductive metal material such as Al or iron is evaluated based on the zeta potential. It is presumed that they did not exist or that there was no necessity.

One of the reasons is that a technique for measuring the zeta potential on the surface of a conductive metal material such as Al or iron has not been established. This is because measuring the zeta potential on the surface of a metal material is more difficult than directly measuring the surface potential of the colloid particles themselves in the field of colloid science.

For example, when the zeta potential on the surface of a metal material is to be measured, a metal plate cannot be electrophoresed (moved) in a solution like colloid particles. Therefore, instead, the zeta potential of the metal material surface interacts with the zeta potential (known or measurable) of its own surface,
Use monitor particles that change the moving speed in the solution.

That is, as shown in FIG. 2, the bottom (part) of the cell 1 is made of a metal plate X and is exposed to the solution C. Then, when other measurement conditions such as an electric field were the same, the moving speed of the monitor particles B in the solution C contacting the metal plate X, and the monitor particles in the solution C in the case of a cell without the metal plate X. Compare with the moving speed of B. Then, the amount of the zeta potential on the surface of the metal plate X corresponding to the amount of change in the moving speed is obtained from the amount of change in both the moving speeds by the above-described equation (1). That is, the indirect determination from the moving speed of the monitor particles B is a basic principle when measuring the zeta potential on the surface of the metal material.

However, when actually measuring the zeta potential on the surface of a conductive metal material based on such a measurement principle, the electrodes 5a and 5b are charged as shown in FIG. Even if an attempt is made to charge the surface of the monitor particles B in the solution C in X, the metal material (plate) E is exclusively charged.
As a result, a problem arises in that the surface of the conductive particle X cannot be measured because the surface of the monitor particle B is not charged or hard to be charged.

On the other hand, there has been no means to prevent the conductive metal material from being charged and to charge the surface of the monitor particles.
It was a common belief that it was not possible to measure the exact zeta potential of a conductive metal material.

The present invention has been made in view of such circumstances, and an object thereof is to provide a zeta potential measuring method and a zeta potential measuring device which can measure an accurate zeta potential on a metal material surface. And to provide a method for evaluating the surface characteristics of a metal material based on these zeta potential measurements.

[0019]

In order to achieve this object, a method for measuring the zeta potential on the surface of a metal material according to the present invention (claim 1)
The gist of the present invention is that an aqueous solution containing an electrolyte for keeping the dielectric constant is accommodated in a cell, a metal material is brought into contact with the aqueous solution, and charged monitor particles having a known zeta potential are arranged in the aqueous solution. A method of measuring the zeta potential corresponding to this change in the movement speed of the monitor particle as the zeta potential on the surface of the metal material from the change in the movement speed of the monitor particles between the aqueous solution where the material is not in contact and the aqueous solution where the metal material is in contact In other words, by insulating a part of the surface of the metal material on the aqueous solution contact side, the monitor particles in the aqueous solution are charged, and the change in the moving speed of the monitor particles in the aqueous solution is detected.

The gist of the present invention for measuring the zeta potential of a metal material surface (claim 5) is to accommodate an aqueous solution containing an electrolyte for dispersing monitor particles having a known zeta potential and keeping the dielectric constant constant. A cell, an electrode for charging the monitor particles, fixing means for contacting a metal material with the aqueous solution, and a monitor particle in an aqueous solution in which the metal material is not in contact with an aqueous solution in which the metal material is in contact. A means for detecting a change in the moving speed, and a device for measuring the zeta potential corresponding to the amount of change in the moving speed as the zeta potential of the metal material surface, and a part of the aqueous solution contact side surface of the metal material. The purpose is to provide an insulating means to charge the monitor particles and detect a change in the moving speed of the monitor particles in the aqueous solution.

According to the gist of the present invention, by insulating a part of the surface of the conductive metal material on the solution contact side, even if the electrode is charged, the metal material is less likely to be charged. The surface of the particles can be charged by an amount sufficient for measuring the moving speed. Then, from the correlation between the monitor particles and the metal material (change in the moving speed of the monitor particles due to the metal material), the known zeta potential of the surface of the monitor particles is used to determine the surface It is possible to determine the zeta potential.

Further, it becomes possible to use the zeta potential of the metal material surface which can be measured thereby to evaluate the surface characteristics of the metal material (corresponding to claim 7).

In order to more accurately evaluate the surface characteristics of the metal material, the evaluation based on the zeta potential is performed by using a specific substance related to the surface of the metal material, or a zeta potential of the surface of the substance in place of the specific substance and the metal. It is preferable to perform the comparison with the zeta potential of the surface of the material (corresponding to claim 8).

The evaluation of the surface characteristics of the metal material is as follows.
It is particularly useful when applied to surface treatment properties of metal materials, corrosion resistance of metal materials, stain resistance of metal material surfaces, etc.
Corresponding).

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below. First, the basic measurement principle of the present invention is as described with reference to FIG. That is, the charged monitor particles B having a known zeta potential are disposed in the aqueous solution C in the cell 1 so that the ordinary aqueous material C is not in contact with the aqueous solution C and the aqueous solution C in which the metallic material X is in contact. In, monitor particles
From the change in the moving speed of B, the amount of the zeta potential on the metal material surface corresponding to the change in the moving speed is measured.

Here, the feature of the present invention is that, as shown in FIG. 3 (b), an insulating spacer E having a gap (window) D in contact with the aqueous solution is provided on the surface of the conductive metal material X on the aqueous solution contact side. By disposing the conductive metal material X, for example, the surfaces on both ends are partially insulated.

Thus, even if the cell is charged, the conductive metal material X is less likely to be charged, and the surface of the monitor particles B can be charged in an amount sufficient for measurement. Then, the change in the moving speed of the monitor particles B in the aqueous solution in which the metal material is not in contact and in the aqueous solution in contact with the metal material (in the aqueous solution corresponding to the portion of the gap D) indicates that the portion of the gap D The amount of zeta potential (charge) on the surface of the metal material X corresponding to the amount of change in the moving speed can be obtained.

First, the principle of obtaining the zeta potential on the surface of the metal material X will be described. Now, the zeta potential ζ1 on the surface of the monitor particle B in a normal aqueous solution where no metal material is in contact is
2, U1 = (εEζ1) / (4πη) (where U
1; speed of movement of monitor particles B in a normal solution not in contact with metal material, ε; dielectric constant of aqueous solution, E; electric field of aqueous solution, ζ1; zeta potential of monitor particle B surface, η; viscosity of aqueous solution) . Further, the zeta potential の 2 on the surface of the monitor particle B in the aqueous solution in contact with the metal material is given by the following equation 3, U2 = (εE
ζ2) / (4πη) (where U2 is the moving speed of the monitor particles B in the aqueous solution in contact with the metal material, ε is the dielectric constant of the aqueous solution, E is the electric field of the aqueous solution, ζ2 is the surface of the monitor particles B Zeta potential, η; viscosity of aqueous solution). Therefore, the zeta potential (ζ) on the surface of the metal material X is determined by the change in the movement speed of the monitor particles between the aqueous solution not in contact with the metal material and the aqueous solution in contact with the metal material. Correspondingly, ζ2 − ζ1.

However, in order to accurately and reproducibly determine the zeta potential on the surface of the metal material X in an actual instrumental analysis, the electroosmotic flow (aqueous solution side) used for ordinary measurement of the zeta potential on the surface of colloidal particles is used. It is necessary to consider the factor (effect) of the flow rate of the metal material X, and the method of obtaining the zeta potential on the surface of the metal material X including this point will be described in more detail below.

That is, as schematically shown in FIG.
When an electric field is applied to the solution between B and B (the cell wall B is the surface of the metal material X), a flow of an aqueous solution called an electroosmotic flow occurs in the aqueous solution due to the influence of the surface (wall surface) of the charged metal material X. This electroosmotic flow affects the speed of movement of the monitor particles in the aqueous solution.

Now, a model that is Z away from the wall B of the metal material X
The observed (apparent) velocity of the_obs
(Z) in aqueous solution when metal material is not in contact (existing)
Increase the observed movement speed of the monitor particles of the metal material X
The velocity of the electroosmotic flow at a position Z away from the wall B
U_osm(Z), the following equation 2, U
_obs(Z) = U_osm(Z) + Up, rewrite, U_osm(Z) = U
_obs(Z) -Up, the relationship holds. Of this monitor particle
The observation (measurement) of the movement speed is performed by laser as described later.
Do.

Here, since the surface (wall surface) of the metal material X is Z = 0, the velocity U of the electroosmotic flow on the surface of the metal material X is
_osm (0) is the velocity U of the electroosmotic flow at an arbitrary position
_{From osm} (Z), known hydrodynamic extrapolation methods (for example, Mori,
Okamoto's formula). Therefore,
The zeta potential (ζZ = 0) on the surface of the metal material X is expressed by this U _osm (0)
Is substituted into U of U = (εEζ) / (4πη) in the above equation (1), and can be obtained as ζ in the equation (1).

As shown in FIG. 7, since the moving speed of each monitor particle B is also affected by the distance from the metal material X and the cell, in order to measure the moving speed accurately, it is necessary to measure the zeta potential. As is well known, the average moving speed of each monitor particle B at a certain position at a different distance from the metal material X or the cell is measured, or the moving speed of each monitor particle B is calculated as described above. Insert,
It is preferable to measure the moving speed.

FIGS. 5 (a) and 5 (b) are front views (partial cross sections) of the apparatus for measuring the zeta potential on the surface of a metal material according to the present invention, which is a more specific example of FIG. 3 (b). 5 (a) shows the entire cell unit for measuring the zeta potential on the surface of the metal material, and FIG. 5 (b) shows an enlarged front view (partial cross section) of the main part of FIG. 5 (a). .

In FIG. 5 (a), the cell for measuring the zeta potential on the surface of the metal material is basically a quartz cell 1a, a resin cell.
1b and flow path 2 (monitor particles B)
Is contained and supported in a cell holder (not shown). In addition, the zeta potential measuring device is provided with platinum electrodes 5a and 5b attached to this cell for charging the monitor particles, and a conductive material for contacting and fixing the metal material of the quartz cell 1a cell to the aqueous solution. It has known fixing means such as a heat sheet 6, a constant temperature block 7, and a cap screw 8, and detection means such as a laser (not shown) for detecting a change in the moving speed of the monitor particles in the aqueous solution and the monitor particles.

In the quartz cell 1a, a part of the bottom is opened so that the aqueous solution C can be in contact with the surface of the metal material X.
A (horizontal) flow path 2a is provided. Further, the flow path 2a communicates with the (vertical) flow paths 2b and 2c at the end, and the flow paths 2b and 2c
Are the inlet 3 for the aqueous solution C and the outlet 4 for the cell, respectively.
Communicating. FIG. 4 (b) is a perspective view of these channels provided in the quartz cell 1a in a see-through manner.

Therefore, the metal material X is pressed from the bottom of the quartz cell 1a to the (horizontal) flow path 2a of the aqueous solution C by the fixing means 8 or the like, so that the aqueous solution C and the surface of the metal material X on the aqueous solution C side are brought into contact with each other. Contact is ensured. Up to these basic configurations, they are the same as conventional or commercially available zeta potential measuring devices.

FIG. 5 (b) shows a characteristic configuration of the apparatus for measuring the zeta potential on the surface of a metal material according to the present invention. That is,
In FIG. 5 (b), as a means to insulate a part of the surface of the metal material X which is in contact with the aqueous solution C, the resin shown in FIG. An insulating spacer E such as rubber or rubber is provided. The spacer E has a gap (window) D in contact with the aqueous solution C on the surface of the conductive metal material X in contact with the aqueous solution C. Except for the gap D, the spacer E has The surface in contact with the aqueous solution C is insulated.

As a result, even when the cell and the aqueous solution C are charged by the platinum electrodes 5a and 5b, the conductive metal material X is hardly charged, and the surface of the monitor particles B in the aqueous solution C has a sufficient amount for measurement. , Can be charged.

Then, an aqueous solution of the charged monitor particles B
During movement in C, the normal aqueous solution (of the part insulated from metal material X) and the aqueous solution in contact with metal material X
The moving speed of the monitor particles B in C (in the aqueous solution corresponding to the gap D) is measured by a detection means such as a laser.

Further, based on the moving speed of the monitor particles B, the zeta potential on the surface of the metal material X is determined in consideration of the electroosmotic flow (flow rate on the solution side).
It is possible to calculate the amount of zeta potential (charge) on the surface of the metal material X corresponding to the amount of change in the moving speed of the metal.

The insulation of the metal material X is provided not only by the means shown in FIGS. 5 (a) and 5 (b) but also by the gap D at a part of the spacer E which is in contact with the aqueous solution C. It is also possible to embed a metal material X of an appropriate size, and to employ a means for pressing the spacer E against the flow path 2 of the aqueous solution C from the bottom of the quartz cell 1a. Even in this case, since the spacer portion other than the portion where the metal material X is embedded is insulative, the platinum electrode 5a,
By 5b, even when the cell and the aqueous solution C are charged, the conductive metal material X is unlikely to be charged, and the surface of the monitor particles B in the aqueous solution C can be charged in an amount capable of measuring the zeta potential. .

At this time, the length (width) of the gap D provided in the spacer E and the length of the metal material X to be buried in the spacer E
It is preferable to set so that the change in the moving speed of the monitor particles B occurs more than the amount detectable by a laser or the like.
If the length (width) of the gap D provided in the spacer E or the metal material X to be buried in the spacer E is too large, bubbles and liquid flow due to the electrolysis of the aqueous solution C occur, and the monitor particles B Is disturbed to the moving speed of the vehicle, and the upper limit of the magnitude is determined from this point.

As in the case of FIGS. 5A and 5B, when the charged monitor particles B move in the aqueous solution C, the monitor particles B are mixed with the normal aqueous solution C and the metal material X.
It is possible to calculate the amount of zeta potential (charge) on the surface of the metal material X corresponding to the change in the moving speed by measuring the moving speed in the aqueous solution C in contact with Become.

At this time, an aqueous solution in which the monitor particles are dispersed
As with the conventional zeta potential measurement method,
Contain a small amount of electrolyte to keep the
Is necessary. As this chloride, the conventional zeta
Similar to the method for measuring the position, Na itself has no chemisorption ability.
Cl, KCl, NaClO_FourPrefer to be more selected
New (corresponding to claim 2). And the concentration of these electrolytes
Is 1 to 100 mmol / l (dm ^Three) Can be selected from a very small range.
preferable.

As the monitor particles, commercially available latex particles such as polystyrene having a particle diameter of 300 to 700 nm (coated with hydroxypropyl cellulose) used in the conventional zeta potential measurement method.
Is preferred (corresponding to claim 3). If the latex particles are too small, the moving speed cannot be detected by the laser light, while if too large, the laser light will be scattered and become disturbances in detecting the moving speed. The amount of the monitor particles added (dispersed) in the aqueous solution is determined from the sensitivity of the moving speed by the laser, and the optimum amount is determined for each commercially available zeta potential measurement / measurement device, and is determined in accordance with the present invention.

(Procedure for measuring zeta potential on the surface of metal material using apparatus) A procedure for measuring the zeta potential (ζ potential) on the surface of a metal material using this apparatus will be described below. First, the metal material is installed in contact with the (horizontal) flow path 2a engraved in the quartz cell 1a, and the apparatus shown in FIGS.
2a, the monitor particles are introduced through the inlet 3 and the flow path 2b.
An aqueous solution C containing an electrolyte in which B is dispersed is introduced and stored.

Then, the cell and the aqueous solution C are charged by the platinum electrodes 5a (+) and 5b (-), and only the surface of the monitor particles B in the aqueous solution C is charged. The charge amount at this time is preferably such that the change in the moving speed of the monitor particles B is equal to or more than the amount that can be detected by a laser or the like. Further, it is preferable that the charge amount is set such that the liquid bubbles are disturbed by the bubbles generated by the electrolysis of the aqueous solution C and do not disturb the moving speed of the monitor particles B.

Due to this charging, the monitor particles B in the aqueous solution C move from the platinum electrode 5a (+) to the platinum electrode 5
b Move in the direction of (-) (from left to right in Fig. 5). When the charged monitor particles B move, the normal (metal material X
The movement speed of the monitor particles B in the aqueous solution C (in a portion insulated from the liquid) and the aqueous solution C in contact with the metal material X (in the aqueous solution corresponding to the portion of the gap D) is measured by a laser. Measure.

(Method of Evaluating Surface Properties of Metal Material) The method of applying the present invention to the evaluation of surface properties of metal materials, such as surface treatment properties of metal materials, corrosion resistance of metal materials, and stain resistance of metal material surfaces. Will be described below.

In the case of the surface properties of a metal material, a specific material (colloidal particles or the like) to be surface-treated in the surface treatment property of the metal material, a corrosive substance in the corrosion resistance of the metal material, and a stain resistance in the surface resistance of the metal material. It is necessary that the zeta potential on the surface of a contaminant or the like and the zeta potential on the surface of the metal material correlate with the surface characteristics of the metal material.

For example, the treatment of an Al alloy material with a colloidal dispersion of titanium phosphate, which is used as a pretreatment of the zinc phosphate treatment, involves the adhesion of titanium phosphate to the surface of the Al alloy material.
(Treatability of Al alloy material with colloidal dispersion of titanium phosphate) is based on an electrostatic adsorption reaction between the charge on the Al alloy material surface and the charge on the titanium phosphate surface. In such a case, Al
The zeta potential on the surface of the alloy material has a deep correlation with the adhesion (surface treatment) of titanium phosphate to the surface of the Al alloy material. Therefore, in the case of the titanium phosphate treatment, the surface treatment property of the titanium phosphate treatment can be evaluated based on the zeta potential of the surface of the Al alloy material.

However, as the adhesion of titanium phosphate to the surface of the Al alloy material is improved, the reactivity of zinc phosphate to the surface of the Al alloy material, which is the subsequent treatment, is improved, and the adhesion of zinc phosphate is improved. There is a correlation that the rate improves. Therefore, in such a case, evaluating the adhesion of titanium phosphate to the surface of the Al alloy material by the zeta potential of both leads to the evaluation of the zinc phosphate treatment property of the Al alloy material itself.

That is, even if the surface properties (surface reactivity) of the metal material such as the surface treatment property to be directly evaluated cannot be evaluated by the zeta potential, it correlates with the zeta potential and furthermore, the direct evaluation target If you select a surface reaction or surface treatment that correlates with the surface properties such as the surface treatment properties (such as pretreatment of metal materials, another surface treatment, another corrosive substance, another contaminant, etc.), it will be directly evaluated. It is also possible to evaluate the surface characteristics of the metal material to be evaluated by the zeta potential.

In other words, evaluation of the surface characteristics of the metal material by comparing the zeta potential of the surface of the specific material related to the surface of the metal material, or a substance that can substitute for the specific material, with the zeta potential of the surface of the metal material. Becomes possible.

(Evaluation based on zeta potential) As described above, the evaluation based on zeta potential is basically based on the surface treatment of a metal material,
In the corrosion resistance of metal materials, the stain resistance of the surface of metal materials, etc.
It is performed by comparing the zeta potential of the surface of the metal material with a specific substance related to the surface of the metal material, or the zeta potential of the substance instead of the specific substance.

The evaluation based on the zeta potential is basically as follows.
Perform as follows. First, if the zeta potential between the surface of the metal material and the specific material surface has the same sign, such as plus and plus, minus and minus, the smaller the product of the two zeta potentials, the more the electrostatic repulsion And specific substances are easily adsorbed (adhered) to the surface of the metal material. In addition, when the zeta potential between the surface of the metal material and the specific material surface has a sign different from plus or minus, the larger the difference between the two zeta potentials, the greater the electrostatic repulsion force, Substance easily adheres (adheres) to the surface of the metal material.

Therefore, when it is desired that a specific substance is not easily adsorbed (adhered) to the surface of the metal material, the zeta potential between the surface of the metal material and the surface of the specific material has the same sign, and the product of the zeta potentials of the two. Or the surface of the metal material and / or the surface of a specific substance are controlled so that the sign of the zeta potential is different and the difference between the two zeta potentials is small.

The zeta potential to be compared is a specific substance related to the surface of the metal material, or, in the case of a substitute substance, the substance or the atmosphere or bath liquid that actually relates to the surface of the metal material. It is preferable to set the zeta potential in the measurement aqueous solution having the same pH as the inside. Further, it is preferable that the surface zeta potential of the metal material is actually the zeta potential of the measurement aqueous solution having the same pH as an atmosphere or a bath solution in which the substance is related to the surface of the metal material.

For example, in the case of surface treatment property evaluation, the zeta potential in the aqueous solution, which is the same as the pH of the surface treatment bath solution or atmosphere of the surface of the specific substance (colloidal particles or the like) to be surface treated, and the surface treatment bath Same as pH of liquid or atmosphere,
The comparison is made with the surface zeta potential of the metal material in the aqueous solution.

First, the zeta potential measured by the above-described method and apparatus is greatly affected by the pH in the atmosphere or the bath solution, and the measured value greatly changes. The measured zeta potential is also affected by the amount of coexisting trace ions and the total amount of ions. The latter ion amount affects the measurement accuracy or reproducibility of the zeta potential, and the former pH concerns the problem of whether the evaluation based on the zeta potential correlates with the actual evaluation of properties such as surface treatment properties. For this reason, if the pH conditions for measuring the zeta potential to be compared between the specific substance or a substitute substance and the surface of the metal material are different, a large error may occur in the evaluation of the surface characteristics itself by comparing the zeta potential. Becomes

Therefore, when evaluating the characteristics of the metal material surface by comparing the zeta potentials, particularly when measuring the zeta potential measured by the above-described method and apparatus,
It is preferable that the measurement conditions such as pH have the same pH value or pH range as these actual conditions. Further, it is preferable that the measurement of the zeta potential on the surface of the metal material and the measurement of the zeta potential on the surface of the specific substance to be compared are performed under the same measurement conditions including the above-mentioned pH.

[0063]

EXAMPLES (Example 1) Hereinafter, as examples of the present invention,
First, an example in which the present invention is applied to the evaluation of zinc phosphate treatability of a wrought Al alloy by measuring the zeta potential of the surface of an Al alloy plate for an automobile will be described. In addition, as the evaluation of the zinc phosphate treatment, the titanium phosphate treatment as a pretreatment of the zinc phosphate treatment was selected.

That is, from the correlation between the zeta potential on the surface of the titanium phosphate particles in the titanium phosphate treatment and the zeta potential on the surface of the Al alloy material, the titanium phosphate treatment property and the zinc phosphate treatment property of the aluminum alloy wrought material are considered. Was evaluated.

Further, as the metal material (Al alloy wrought material) for evaluating the processability, JIS to AA 5052 (hereinafter JIS to AA)
(Abbreviate | omitted) Al alloy rolled plate and 6016Al alloy rolled plate were selected.
Then, test materials were collected from these Al alloy rolled plates, and commonly immersed in 5% NaOH at 60 ° C. for 30 seconds, and then 5% H _{2 at} 50 ° C. for 30 seconds.
Cleaning with etching immersing in SO ₄ was performed. Thereafter, the zeta potential on the surface of the test material after washing and the zeta potential on the surface of titanium phosphate were measured.

The measurement of the zeta potential was performed by the measuring apparatus shown in FIG. That is, an Al alloy plate X to be measured (length 60 mm × width 20 mm × thickness 3 mm) was brought into contact with an aqueous solution containing an electrolyte contained in a horizontal flow path (capacity: 5 ml) cut in a quartz cell. Insulation of the Al alloy plate X is performed by placing a gap D (length 2 mm x depth 10 mm) on the surface (solution side) of the Al alloy plate X in contact with the solution.
Polypropylene spacer E (length 60 mm × width 30
mm × 45 μm thick), the surfaces of both ends of the Al alloy plate X were partially insulated.

As the monitor particles B, latex particles made of polystyrene (manufactured by Otsuka Electronics Co., Ltd.) coated with the above-mentioned hydroxypropyl cellulose having a known zeta potential were selected and dispersed in an appropriate amount in an aqueous solution containing 10 mmol / dm ³ of NaCl electrolyte. Then, apply an electric field of 20 mV to the cell,
The charged latex particles are moved through the solution,
The change in the moving speed of the latex particles in the portion D is detected by a laser, and the zeta potential on the surface of the Al alloy plate X corresponding to the change in the moving speed in the space D is measured and calculated by the method described above. .

FIG. 5 shows the measured zeta potentials of the surfaces of the 5052 Al alloy plate and the 6016 Al alloy plate in the titanium phosphate colloidal dispersion. FIG. 5 also shows the zeta potential of the titanium phosphate surface in the titanium phosphate colloidal dispersion, which can be directly measured. FIG. 5 shows the change in the zeta potential of the surface of each Al alloy plate corresponding to the change in the pH of the colloidal dispersion of titanium phosphate (horizontal axis).

The 5052-based Al alloy plate has a good formability among 5000-based Al alloys and is widely used as an automobile panel material. In addition, 6016 series Al alloy plate has good formability among 6000 series Al alloys, and each of them is a typical type commonly used as automobile panel material.
Al alloy. The Al alloy plate used in the test was manufactured by a usual rolling process and conditions, and is representative of each Al alloy plate in the Al alloy field.

In FIG. 5, the pH of a colloidal dispersion of titanium phosphate, which is usually used for the surface treatment of an automobile body, is adjusted to pH9.
Looking at the vicinity, the zeta potential of the titanium phosphate surface is −60 mV, while the zeta potential of the 5052 Al alloy plate surface is −10 mV, and the zeta potential of the surface of the 6016 Al alloy plate is −40 mV.
It is. According to this, the product of the zeta potential of the 5052 Al alloy plate surface and the zeta potential of the titanium phosphate surface is 600 (mV) ² , whereas the zeta potential of the surface of the 6016 Al alloy plate is The product of the absolute value and the zeta potential is 2400 (mV)
It becomes ² . That is, the product of the zeta potential of the titanium phosphate surface and the zeta potential of the 5052 Al alloy plate surface is smaller than the zeta potential of the 6016 Al alloy plate surface.

The results correspond well to the adhesion of titanium phosphate to the surface of the Al alloy material when the surface of the Al alloy material was actually treated and tested with a colloidal dispersion of titanium phosphate (pH 9). Was. In other words, the actual processing test results are
The 00 series Al alloy plate has better adhesion of titanium phosphate than the 6000 series Al alloy plate such as 6016. And, in the subsequent zinc phosphate treatment test, the 5000 series Al alloy plate
The adhesion of zinc phosphate was better than the alloy plate, and the results of the subsequent rust-resistant corrosion test showed that the 5000 series Al alloy plate was more excellent in thread rust resistance than the 6000 system Al alloy plate. .

That is, this tendency is due to the fact that the 6000 series (Al-M) produced by the usual rolling or extrusion process and heat treatment conditions (T4, T6, etc.)
g-Si) It can be said about all wrought aluminum alloys.
The reason why titanium phosphate adhesion is low when a 6000 series (Al-Mg-Si) Al alloy spread material is treated with a titanium phosphate colloidal dispersion is that the 6000 series Al alloy spread It is supposed that this is due to the large electrostatic repulsion between the zeta potential of the material surface and the titanium phosphate surface.

As described above, the adhesion of titanium phosphate to the surface of the Al alloy is an electrostatic adsorption reaction to the surface of the Al alloy. Therefore, when the titanium phosphate is adsorbed and adhered to the 6000 series Al alloy wrought material surface, the zeta potential of the 6000 series Al alloy wrought material surface is changed to the zeta potential of the titanium phosphate surface −60 mV (pH
9) On the other hand, if the zeta potential is the opposite positive zeta potential, or the zeta potential is such that the product becomes small even if it is negative, electrostatic adsorption works and titanium phosphate becomes 6000 series aluminum alloy wrought material surface Works in the direction of better adhesion.

However, the actual zeta potential of the wrought 6000 series aluminum alloy surface is, for example, about −40 mV (pH 9) of 6016 alloy. Therefore, the zeta potential on the surface of titanium phosphate −60 mV (p
H9) is the same minus, and the product is large. As a result, electrostatic repulsion acts between the titanium phosphate which is to adhere to the surface of the Al alloy material and the surface of the wrought 6000 Al alloy material, and acts in a direction in which titanium phosphate does not easily adhere.

From these results, it was found that if the surface was adjusted so that the zeta potential of the surface of the wrought 6000 series alloy was increased to the positive side with respect to the negative zeta potential of the surface of titanium phosphate, the adhesion of titanium phosphate could be improved. It can be seen that the properties and the processability of titanium phosphate are improved.

Example 2 Next, as Example 2 of the present invention, JIS3004Al was measured by measuring the zeta potential on the surface of the Al alloy material.
An example of evaluating the contamination resistance of the alloy piping material by seawater as cooling water is shown below.

A test material was sampled from JIS 3004 Al alloy piping material for evaluating the stain resistance, and sodium chloride (N
(aCl) The zeta potential of the surface of the test material in an aqueous solution (pH was adjusted with hydrochloric acid and / or sodium hydroxide) was measured in Example 1.
The measurement was performed in the same manner as described above.

Separately, when seawater containing a rust inhibitor (organic acid) continues to flow through JIS 3004 Al alloy piping, sludge generated by etching the piping (main component is Al)
And a mixture of a composite oxide and a hydroxide of an alloy component) were actually collected, and the zeta potential of the sludge surface in the NaCl aqueous solution was measured in the same manner as in Example 1. However, the zeta potential on the sludge surface was measured without using the metal material X as shown in FIG.
The measurement was performed according to the measurement principle shown in FIG.

FIG. 6 shows the measured zeta potential of the test material surface and the measured zeta potential of the sludge surface. FIG. 6, like FIG. 5, shows a change in zeta potential corresponding to a change in pH (horizontal axis) of the NaCl aqueous solution.

As can be seen from FIG. 6, the zeta potential on the sludge surface is -20 mV and is constant irrespective of pH. On the other hand, the zeta potential on the 3004Al alloy surface is + 60mV at pH 3
, The pH greatly changes to −50 mV at pH 11.

It can be said from FIG. 6 that the zeta potential of the surface of the 3004 Al alloy material is -10 to 20 mV in the pH range of 6 to 7 which is the pH range of seawater, which is the same as the zeta potential of the sludge surface of -20 mV. It has a sign. Therefore, in this seawater pH range, it is evaluated that the adsorption reaction between the surface of the 3004Al alloy material and the sludge hardly occurs, and the contamination of the pipe by the sludge hardly occurs.

However, when seawater contains a rust inhibitor (organic acid), the pH of the seawater decreases. In this case, for example, in a part where the pH of seawater is 4 or less, the zeta potential on the surface of the 3004Al alloy material is +30 mV or more, and the zeta potential on the sludge surface is −
It has a sign opposite to 20 mV. As a result, it can be seen that in the portion where the pH of the seawater is 4 or less, the adsorption reaction easily occurs between the 3004Al alloy material surface and the sludge. That is, this result indicates that when seawater contains a rust preventive (organic acid), sludge adheres to the surface of the Al alloy piping material and easily contaminates the Al alloy material surface.

Therefore, from FIG. 6, when seawater contains a rust inhibitor, the improved Al alloy piping material is
As indicated by the zeta potential of the alloy material (assumed), it is necessary to make the surface state such that the zeta potential decreases so that the adsorption reaction between the surface of the Al alloy material and the sludge hardly occurs at the pH of 4 or less. It is shown that. In other words, from Fig. 6, when seawater contains a rust inhibitor, the surface treatment of the Al alloy material and alloy design (change of alloy components) were performed, and the zeta on the surface of the Al alloy material at pH 4 or lower was determined. It can be evaluated that the potential needs to be lowered.

From the above examples, according to the present invention, it is possible to measure the zeta potential on the surface of a metal material.
It can be seen that it is possible to evaluate the surface properties of the metal material by the zeta potential.

In the above-described embodiment, measurement of the zeta potential on the surface of the wrought Al alloy and evaluation of the zinc phosphate treatment property and antifouling property of the wrought Al alloy by the zeta potential were described.
However, the present invention, besides Al alloy wrought material containing duralumin, etc., if it is conductive, cast material of Al alloy, or
It is also applicable to the measurement of zeta potential on the surface of other metal materials such as copper and copper alloy materials, steel materials including stainless steel, titanium materials, and welding materials (rods and wires).

Further, as a method for evaluating metal surface characteristics,
It can be used to evaluate the surface treatment properties of the metal material, the corrosion resistance of the metal material, the contamination resistance of the metal material surface, etc., where the electrostatic adsorption reaction is the main component of the reaction. More specifically, the adhesion of surface treatment substances such as plating, chemical conversion treatment, and coating of metal materials, the contamination of specific substances such as dust and impurities or contaminants and corrosive substances on the surface of metal materials, It can be widely applied to the evaluation of the affinity with a specific substance, the affinity of a material surface such as an Al alloy, a copper alloy, or steel with a fluid or a cooling medium, and the corrosion resistance.

[0087]

According to the present invention, it is possible to provide a zeta potential measuring method capable of measuring an accurate zeta potential on the surface of a metal material. Therefore, it is possible to evaluate the surface characteristics of the metal material in the fields such as the surface treatment property of the metal material, the corrosion resistance of the metal material, and the contamination resistance of the surface of the metal material. In addition, it is possible to evaluate the material metal without actually performing surface treatment, corrosion, or contamination. Therefore, the present invention has a great industrial value in that new applications of the metal material can be expanded, for example, it can be promptly reflected in the improvement of the surface characteristics of the material.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram schematically showing a principle of measuring a zeta potential (ζ).

FIG. 2 is an explanatory view schematically showing the principle of measuring the zeta potential on the surface of a conductive metal material.

FIG. 3 is an explanatory view showing a method of measuring the zeta potential on the surface of a metal material according to the present invention, and FIG.
3 (b) shows a case where measurement is possible.

FIG. 4 is an explanatory view showing one embodiment of an apparatus for measuring a zeta potential on a metal material surface according to the present invention.

FIG. 5 is an explanatory diagram showing the zeta potential on the surface of a 5052 Al alloy plate for comparison with a 6016 Al alloy plate.

FIG. 6 is an explanatory diagram showing the zeta potential on the surface of a 3004Al alloy plate and etching sludge.

FIG. 7 is an explanatory view schematically showing a method for measuring a zeta potential on a metal material surface according to the present invention.

[Explanation of symbols]

1: cell, 2: flow path, 3: inlet, 4: outlet, 5: platinum electrode,
6: heat transfer sheet, 7: constant temperature block, 8: cap screw, X: metal plate, A: colloid particle, B: monitor particle, C: aqueous solution,

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Reiko Ohara 1-5-5 Takatsukadai, Nishi-ku, Kobe, Japan Inside Kobelco Research Institute Nishijin Office (72) Inventor Tatsuya Osako 1-5-5, Takatsukadai, Nishi-ku, Kobe-shi No. 5 F-term in Kobelco Research Institute Seishin Office (reference) 2G055 AA01 BA09 FA06

Claims (9)

[Claims] An aqueous solution containing an electrolyte for maintaining a constant dielectric constant is accommodated in a cell, a metal material is brought into contact with the aqueous solution, and charged monitor particles having a known zeta potential are arranged in the aqueous solution. From the change in the moving speed of the monitor particles between the aqueous solution where the metal material is not in contact and the aqueous solution where the metal material is in contact, the zeta potential corresponding to this change in the moving speed is measured as the zeta potential of the metal material surface. A method comprising: insulating a part of an aqueous solution contact side surface of a metal material to charge monitor particles in an aqueous solution; and detecting a change in the moving speed of the monitor particles in the aqueous solution. A method for measuring the zeta potential of a material surface. 2. The method according to claim 1, wherein the electrolyte is selected from NaCl, KCl, and NaClO ₄ . 3. The method according to claim 2, wherein the monitor particles are latex particles. 4. The method for measuring the zeta potential of a metal material surface according to claim 1, wherein an insulating spacer having a gap in contact with the aqueous solution is disposed on the surface of the metal material on the aqueous solution contact side. 5. A cell containing an aqueous solution containing an electrolyte for dispersing monitor particles having a known zeta potential and keeping the dielectric constant constant, an electrode for charging the monitor particles, and a metal material in the aqueous solution. And a means for detecting a change in the moving speed of the monitor particles between the aqueous solution in which the metal material is not in contact and the aqueous solution in which the metal material is in contact, and the amount of change in the moving speed It is a device for measuring the zeta potential corresponding to the zeta potential of the metal material surface, provided with means for insulating a part of the aqueous solution contact side surface of the metal material to charge the monitor particles, the monitor particles in the aqueous solution An apparatus for measuring zeta potential on a metal material surface, which detects a change in a moving speed. 6. The apparatus according to claim 5, wherein an insulating spacer having a gap in contact with the aqueous solution is disposed on the surface of the metal material on the contact side with the aqueous solution containing the electrolyte. 7. The method of claim 1, wherein the zeta potential measured by the method according to claim 1 or the apparatus according to claim 5 is used for evaluating the surface property of the metal material. Evaluation method. 8. The evaluation based on the zeta potential is performed by comparing the zeta potential of a specific substance related to the surface of the metal material or the zeta potential of the surface of the substance replacing the specific substance with the zeta potential of the surface of the metal material. 3. The method for evaluating the surface characteristics of a metal material according to item 1. 9. The method according to claim 8, wherein the surface property is a surface treatment property of a metal material,
9. The method for evaluating the surface properties of a metal material according to claim 7, wherein the method is selected from corrosion resistance of the metal material and stain resistance of the surface of the metal material.