JPH06151145A - Magnetic fluid to be used for confirmation of underground cracking - Google Patents

Abstract

PURPOSE:To provide a magnetic powder material which can be practically used for confirmation of underground cracking by magnetic fluid. CONSTITUTION:Magnetic fluid used for confirming underground cracking is Sendust powder with +#60, powder thickness of 30 to 40mum, average of several hundred mum of quick liquid-cooling powder; or #400 Sendust powder after annealing at 600 deg.C; or a magnetic fluid used for confirming underground cracking comprising iron powder with the particle size of less than #150 powdered by atomization from molten substance of iron. From the above, as the magnetic fluid for confirming the underground cracks, the Sendust powder having +#60, powder thickness of 30 to 40mum and quick liquid-cooling powder with the average of several hundred mum is effective.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder material used in a method for confirming underground cracks by magnetic fluid. In particular,
Regarding the magnetic permeability of various magnetic powders, by investigating the influence of the powder particle size and the heat treatment temperature on the magnetic permeability, it is possible to obtain the most excellent magnetic fluid material used for the underground crack confirmation method by the magnetic fluid. To aim.

[0002]

2. Description of the Related Art As one of the methods for confirming underground cracks using a magnetic fluid, the inventors of the present invention have applied to Japanese Patent Application No. 340184, "3D Detecting System for Crack Shape in Crust and Existence State Using Artificial Magnetic Field". In order to analyze the crack shape and the existing state in the crust near the well three-dimensionally, a granular magnetic material with high dispersibility in water and high magnetic permeability was developed from the inside of the well to the inside of the formation. A crack (fracture) shape in the crust, groundwater flow by injecting and flowing into a hydrothermal layer, an oil layer, etc. in a rock pore and detecting and analyzing the moving and diffusing state from the same well or from another well We propose a three-dimensional analysis of state endowment.

As the granular magnetic fluid, one having a high magnetic permeability (initial magnetic permeability of about 100) and a particle size of 1 to several tens of microns is used, which is coated to improve the water dispersibility. That is, as the high magnetic permeability material, manganese ferrite, PB-permalloy, PC-permalloy,
Among substances such as sendust, 5A1, 10OSi, Fe8
No. 5 composition, initial magnetic permeability in ingot μ0 = 30,000
The powder having the maximum magnetic permeability of 0 and the maximum magnetic permeability of μm = 120,000 showed the highest initial magnetic permeability of 40 to 45 in the powder, and excellent results were obtained.

[0004]

However, the high-permeability materials used in the past cannot always give sufficiently satisfactory results, probably because of a slight deterioration in sensitivity in actual use. In addition, since the unit price is high and there is a problem in its economic efficiency, the inventors of the present invention further continued the research, and arrived at a magnetic fluid for underground crack confirmation that could be practically used.

[0005]

Therefore, the coarsely crushed Sendust powder was classified into # 60 and # 100 and then heat-treated at 600 ° C. to measure the magnetic permeability. As a result, the magnetic permeability did not depend on the particle size, It was found that the magnetic permeability was about 21, and the magnetic permeability when the heat treatment temperature was 800 ° C. was about 24, and it was found that increasing the heat treatment temperature does not lead to a significant improvement in the magnetic permeability. Therefore, after crushing the thin plate prepared by the liquid quenching method,
As a result of conducting a heat treatment at 00 ° C. and measuring the magnetic permeability, it was found that the magnetic permeability was approximately doubled at + # 60, and when it was finer than this, the magnetic permeability decreased to about 20 to 25.

[0006]

According to the present invention, sendust or another material is used as a material, and a particle size and heat treatment or a liquid quenching powder is used to perform a sample test. A high magnetic permeability has been achieved that was not previously possible.

[0007]

EXAMPLES First, the effects of sendust powder particle size and heat treatment temperature on magnetic permeability were examined. Sendust (Fe-Si-Al alloy) melted and cast in a predetermined composition was coarsely crushed, and powders classified into # 60 and # 100 were used to investigate the influence of particle size and heat treatment temperature on magnetic permeability. Then, using melted and cast Sendust as a raw material, the liquid quenching method (single roll method) has a thickness of 30 to 40 μm.
A thin plate of a certain size was prepared, and this was crushed, and the classified powder was used to study the influence of the particle size on the magnetic permeability.

Here, the manufacturing method of the liquid quenching powder is, as shown in the conceptual diagram of FIG. 2, the molten sendust alloy 1 is jetted from the hole 3 at the tip of the crucible 2 by the gas pressure, and is rotated for cooling. The thin plate 5 is produced by contact solidification on the surface of the body 4.

The heat treatment was performed in a hydrogen gas atmosphere at a temperature of 600 ° C. as a standard and 800 ° C. as well.

The magnetic permeability is measured by filling a sample powder in a toroidal case and winding the wire, and using an LCR meter as a measuring device, L is measured to measure the inductance relative magnetic permeability (μL). calculate. The measurement conditions are shown in Table 1. Note that, hereinafter, the inductance relative magnetic permeability is simply expressed as magnetic permeability or μL. Also, the powder shape is
It was performed with a scanning electron microscope (SEM).

[0011]

[Table 1]

The effects of the sendust powder particle shape and the heat treatment temperature on the magnetic permeability, particularly the magnetic permeability of the coarsely pulverized powder, were as follows. The coarsely pulverized powder classified into # 60 and # 100 was heat-treated at 600 ° C. to measure magnetic permeability. Also, in order to investigate the effect of heat treatment temperature,
The # 60 powder was heat treated at 800 ° C. to measure the magnetic permeability. The results of these measurements are shown in Table 2. The SEM observation results are shown in FIGS.

[0013]

[Table 2]

From this result, the following is clarified.

1) The magnetic permeability hardly changes even if the powder grain shape is changed.

2) Even if the heat treatment temperature is increased from 600 ° C. to 800 ° C., the magnetic permeability increases only by about 10%.

3) All the powders have an angular shape.

4) In the case of an angular powder, the magnetic permeability has a value of about 21 to 24 regardless of the particle size and the heat treatment temperature, and the influence of the demagnetizing field due to the shape of each powder is considered.

Regarding the magnetic permeability of the powder obtained by crushing the liquid-quenched ribbon (liquid-quenched powder), the liquid-quenched powder classified into various particle sizes was heat-treated at 600 ° C., and the magnetic permeability was measured. Becomes as shown in Table 3.

[0020]

[Table 3]

From this fact, the following facts are clarified.

1) The powders of-# 10 and + # 60 have a shape obtained by crushing a thin flat plate, have a thickness of about 30 to 40 μm, and have an average particle diameter of about several hundred μm. Further, a high value of 112 is obtained.

2) As the particle size becomes smaller, the powder becomes angular and the magnetic permeability decreases to about 20-25. This is considered to be due to the demagnetizing field as in the above.

Next, the magnetic permeability of iron powder, magnetite powder, and Mn-Zn ferrite powder as powders other than Sendust was examined. In addition, the magnetic permeability of iron powder and Mn-Zn
The magnetic permeability of the ferrite powder was also measured.

Iron powders, magnetite powders and Mn-Zn ferrite powders described above were prepared as magnetic powders other than Sendust, which can be reduced in price, and magnetic permeability measurements and SEM observations were performed. Permeability is room temperature and 20-30
It was measured in the temperature range of 0 ° C. Table 4 shows the latter temperature characteristic measurement conditions.

[0026]

[Table 4]

As a result, iron powder, magnetite powder, Mn
-The magnetic permeability of Zn ferrite powder at room temperature is 2 each.
It can be known that they are 4.4, 5.0 and 29.5. Further, the magnetic permeability of the iron powder was almost constant in the range of 20 to 300 ° C., but it was found that the magnetic permeability of the Mn-Zn ferrite powder becomes higher than the magnetic transformation point and the magnetic permeability remarkably decreases at 150 ° C. or higher. Obtained.

Regarding the magnetic permeability of various magnetic powders, the following results were obtained.

The magnetic permeability measurement results and the SEM observation results of the iron powder, magnetite powder and Mn-Zn ferrite powder at room temperature are shown in Table 5 and FIGS. 12 to 14, respectively.

[0030]

[Table 5]

In Table 5, the Sendust powder added as a reference shows characteristic values when heat-treated at 600 ° C.

Similarly, the results of measuring the temperature characteristics of magnetic permeability of iron powder and Mn-Zn ferrite powder are shown in Table 6 and FIG. (However, since magnetite powder has a very low magnetic permeability, it was excluded from the measurement targets of temperature characteristics.)

[0033]

[Table 6]

In Table 6 above, the sendust powder added as a reference shows characteristic values when heat-treated at 600 ° C. Further, 11 is the case of sendust powder,
12 shows the case of iron powder and 13 shows the case of ferrite powder. The measurement frequency was 1 kHz.

From this result, the following is clarified.

1) The magnetic permeability is about 25 for iron powder, about 5 for magnetite powder, and about 30 for Mn-Zn ferrite powder, all lower than Sendust powder.

2) changing the particle size of these powders,
It is not expected that heat treatment will lead to a significant improvement in magnetic permeability.

Next, regarding the magnetic permeability of the sendust magnetic fluid, the crushed sendust powder (-# 400) was heated to 600 ° C.
The magnetic permeability was measured by using a magnetic fluid made of the powder heat-treated in the above as a test material. The measurement method is
The same as the first method.

The obtained sample was stored in a plastic container in a hermetically sealed state, and was packaged in a container for measuring magnetic properties about every 20 days for measurement. No. 1, No.
2, No. The same sample was numbered 3 and repeated measurements were made every 20 days. After the measurement, the water content of the casingd sample was dried and removed, the weight of the sendust powder was determined, and the cross-sectional area was calculated from this value. As a reference,
The magnetic permeability was calculated when water in the magnetic fluid also had an effective cross-sectional area, and the results are shown in Table 7.

[0040]

[Table 7]

In Table 7, () shows the magnetic permeability when water in the magnetic fluid is calculated as the effective cross-sectional area.

From this fact, the following will become clear.

1) Considering the effective cross-sectional area of water as the dispersion medium, the magnetic permeability of the sendust magnetic fluid is 7-8.

2) Table 7 shows changes in magnetic permeability over time.
The results shown in FIG. 3 were obtained when summarized based on the above results.

In FIG. 3, the ratio in the parentheses indicates the mixing ratio of the sendust powder, the solid line indicates the time series, and the dotted line 14
No. For the sample No. 1 shown in FIG. For the sample No. 2, the dotted line 16 indicates the sample No. 3 is shown.

Here, in the case of the measurement on the measurement date 11/10, when vibration was applied to the sample, as shown in FIG. 1 and No. In No. 2, an increase in magnetic permeability was confirmed.

When the magnetic fluid was taken out of the measuring container after the measurement was completed on the measurement day 11/10, No. 1 and N
o. No. 2 had no fluidity, and it was clear that the water had evaporated. On the other hand, No. Sample No. 3 had fluidity, and it is considered that there was not much evaporation of water.

From these things, No. 1 and No. Two
At the time of measurement on the measurement day 11/10, the evaporation of water in the sample container progressed considerably and the powder was biased in the container, so the powder was uniformly dispersed by applying vibration,
It is considered that the magnetic permeability has increased.

No. 1 and No. 2 is the measurement date 10 /
The measured value of 29 is low, but this is the measurement date 10 /
It is considered that the evaporation of water had already progressed at the time of measurement of 29, and the distribution state of the powder in the container was not uniform.

No. 1, No. 2, No. Sample No. 3 has different sampling dates from the base material (sample in the obtained poly container), but the values measured on the sampling days are different. That is, the first No. Only 1 is lower than the others. It is not clear from this result whether this is the variation that the magnetic fluid itself has or is due to other factors. Although there are various uncertain factors, it is estimated that the time series change of magnetic permeability is not so large.

Since the magnetic fluid used for confirming underground cracks needs to use about 2 tons of magnetic powder per time, it is necessary to use inexpensive powder as much as possible. Then, when the trial calculation was performed in terms of the powder price, the results shown in Table 8 were obtained.

[0052]

[Table 8]

The sendust powders in Table 8 are for pulverization after melting, not for liquid quenching powders. The sendust powder needs to be installed at the time of mass production in the pre-process of crushing to heat treatment. The mass production process for Mn-Zn ferrite powder has not been established, so it is an estimated value. (The prices in Table 8 do not take into account the cost of introducing new equipment.)

As regards Sendust which has been able to obtain the maximum initial relative magnetic permeability as described above, as for Sendust and other high magnetic permeability materials having a medium magnetic permeability (pure iron, ferrite,
For magnetite), the optimum material was selected based on the evaluation of economic efficiency and detectability, and the heat treatment temperature, particle size, and shape of Sendust were examined.

Next, the heat treatment temperature was examined in order to improve the magnetic permeability of Sendust itself.

The sendust powder used for this is-# 4
An undercoat of 00: 400 mesh was used, and this was heat-treated in a hydrogen stream to change the heat treatment temperature at the time of strain removal from room temperature (= before heat treatment) to 1000 ° C. The initial relative magnetic permeability (μ1) at that time is shown in Table 9 and FIG.

[0057]

[Table 9]

As is clear from this result, the initial relative magnetic permeability of the sendust powder is a maximum value of 44.6 to 45 (5.60 to 5.65 × 1/1000) at 600 ° C. to 800 ° C.
00 [H / m] is obtained, but higher temperature (10
It decreased at 00 ° C.

Furthermore, sendust powders (6
Table 10 shows the initial relative magnetic permeability (μ1) of heat treatment at 00 ° C.).

[0060]

[Table 10]

The + # 60 powder has a maximum particle size of 1 mm and has a polyhedral shape. Also, the shape of the-# 400 powder has an average diameter of 1
It has a scale-like shape with a thickness of 7-18 μm and a thickness of 0.5 μm. In this case, the particle size is smaller than the particle size because of the diamagnetic effect due to the shape anisotropy, but the more flat disc-shaped # 400 has a larger particle size (closer to a spherical shape). The initial relative permeability is higher than that of the one.

Next, the particle shape was examined to find the most suitable one.

In order to reduce the diamagnetic effect due to the shape anisotropy, a quenched ribbon (amorphous ribbon) of Sendust alloy was crushed to make a foil-shaped powder. The initial relative magnetic permeability shown in Table 11 was obtained.

[0064]

[Table 11]

The electron micrographs are as shown in FIGS.

As a result, the quenched ribbon powder having a particle size of # 10 to # 60 has the highest initial relative magnetic permeability of 112 so far.
(1.41 × 10 ⁻⁴ [H / m]). However, this method is not practical because the manufacturing cost of the quenched ribbon is added. However, even a substance having a magnetic permeability of about half that of Sendust can be sufficiently used if the sensitivity of the magnetometer system is excellent. Therefore, in consideration of practical use, even a material having a relative magnetic permeability (20 to 30) which is about half that of sendust can be sufficiently put into practical use depending on the performance of the magnetometer system.

Pure iron (F
e), manganese zinc ferrite (Fe ₂ O ₃ : 50mo)
1%, MnO: 25 mol%, ZnO: 25 mol
%) And magnetite (Fe ₃ O ₄ ) were examined. The results are shown in Table 12.

[0068]

[Table 12]

As is clear from Table 12, pure iron is 24,
An initial relative permeability of 29 was obtained with manganese zinc ferrite. The manufacturing costs of both are about 1/10 and 1/3, respectively, compared with the case of Sendust powder, and if the cost is the same, 10 times to 3 times the amount of magnetic powder can be injected into the fracture in the crust. Therefore, it is highly possible to obtain an effective magnetic field response.

Next, in this example, sendust powder (− # 400, heat treatment at 600 ° C.) was used as a sample, and a solid-liquid weight ratio of 1: 1 (sendust powder weight: solution weight = 1: 1) was used to obtain dispersibility. In order to stabilize, the sample sendust powder was subjected to a surface treatment. The iron powder (-
# 150), this process was performed and the results were compared.

In the treatment of dispersion stability, the following three kinds of treating agents were examined.

Surfactant (water dispersion type)

Emulsion (oil dispersion type)

Resin

In addition, in the case of hydraulic fracturing, if it is assumed that the fluid is injected into the ground at the same time as the fracturing fluid, the fracturing fluid (viscous fluid) is used, so there is no need to perform a dispersion treatment on the surface of the magnetic powder. The surface treatment is only for oxidation prevention. At this time, as the treatment agent for the surface treatment for preventing oxidation (when mixed with the crushing fluid is assumed), the following 2 agents are used.
I examined the types.

Oxide compound coating formed naturally on the surface of magnetic powder metal

Antioxidant coating (resin etc.)

First, the dispersion stability of (1) to (4) will be examined, and then the surface treatment for preventing oxidation of (3) will be examined.

As a qualitative standard, the following procedure was tested.

A) Stock solution storage stability test (left at room temperature for 1 month) Examination of stability, fluidity, and oxidizability of a dispersion liquid (= stock solution) having a solid-liquid weight ratio of 1: 1

(B) Water dilution stability test (left at room temperature for 1 week) Dispersion stability due to diffusion when the stock solution was diluted with water (tap water) (aggregation, coagulation, etc. from stock solution to 10 times water diluted solution) Is it stable without occurrence?)

C) Saline dilution stability test (1 at room temperature
Dispersion stability due to diffusion when the stock solution is diluted with saturated saline

D) Dilution stability test with geothermal water (left at room temperature for 1 week) Dispersion stability due to diffusion when diluting stock solution in geothermal water

E) Heating stability test Whether the stock solution is altered or aggregated when heated at 90 ° C. for 5 hours

F) Heating stability test Whether or not there is alteration / aggregation when the stock solution is heated in the range of 100 ° C to 300 ° C by an autoclave

The tests (a) to (e) above were conducted on the magnetic fluid tracer used in the scale model experiment. The results are shown in Table 13.

[0087]

[Table 13]

In a scale model experiment previously performed,
Since the magnetic fluid tracer was placed in a tank filled with saturated saline solution, the phenomenon that the sendust surface chemically changed in saturated saline solution and the magnetic permeability decreased. Therefore, in order to reduce these chemical changes in the material, foaming,
A stable magnetic fluid tracer with no separation was selected. Table 1
4 shows the compositions of the previous sample (Sample No. 000) and the magnetic fluid tracer (Sample No. 306) used this time.

[0089]

[Table 14]

In this test, the storage stability of the stock solution of the sample was continuously observed for 2 months, but there was no change and no decrease in magnetic permeability.

Next, in consideration of use under geothermal conditions, there is a problem that the magnetic permeability of the magnetic powder having high magnetic permeability changes due to heat and chemical components in hot water, resulting in a decrease in magnetic permeability.
For this reason, in this embodiment, it is necessary to take measures against high temperature on the surface of the magnetic fluid tracer that is made to flow into the hydrothermal fracture in the crust, and the following surface treatment agents have taken measures against the high temperature.

Surfactant (water dispersion type) → antioxidation treatment or improvement of heat resistance of surfactant

Emulsion (oil dispersion type) → Improvement of high temperature stability of emulsion (however, if PH or other dispersion medium changes, emulsion is easily broken)

Resin coating → Thermoplastic resin (silicone resin, fluorine resin, polyimide resin) easily forms a uniform film on the particle surface. Of these, the polyimide resin is the most feasible material because it is easy in the manufacturing process. The heat resistance of the polyimide resin in air is 380 ° C.

Table 15 shows the observation results regarding the surfactant and the emulsion.

[0096]

[Table 15]

As a result, the following is clarified from this table.

Dispersion stability is lowered by heating, and the case where a fluorine-containing surfactant having particularly high heat resistance is used is no exception.

The addition of the antioxidant does not significantly suppress the oxidation of the internal particles (sendust), but the effect is recognized depending on the type.

No difference in heat resistance was observed between the surfactant (water dispersibility) and the emulsion (oil dispersibility).

Next, the resin coating was examined. For this resin coating, a polyimide resin was used.

After the sendust or iron particles were dipped in a solvent solution obtained by melting a polyimide resin, the solvent was evaporated and removed. As a result, in a heating test at 250 ° C., a completely stable state was maintained and it was sufficiently usable under geothermal conditions. However, regarding the dispersion stability, although it was dispersed by stirring, it settled in the stationary state, and the dispersion stability was not perfect. However, it was concluded that this degree of dispersibility is sufficient for practicability when mixed with a crushing fluid and injected.

Next, on the premise of mixing with the crushing fluid (viscous fluid), a surface treatment for preventing oxidation was performed.

Assuming mixing with a crushing fluid (viscous fluid), it is considered that there is no problem even if the magnetic powder itself, which is smaller than the crack retaining agent, is injected, in the extreme theory. However,
In that case, the progress of oxidation on the surface of the magnetic powder and the accompanying decrease in magnetic permeability pose a problem. According to a certain trial, the relationship between the hydrothermal treatment time of the magnetic powder (immersion in hot water at 230 ° C. for 0 to 10 hours) and the initial relative magnetic permeability after the hydrothermal treatment was as follows.
Alternatively, # 100 to # 150) is almost constant. In addition, in sendust powder (-# 400, the initial relative magnetic permeability is halved in the first 5 hours and then becomes constant. Iron powder forms an oxide compound on the particle surface and prevents the progress of internal oxidation. It is considered that the sendust powder containing iron as the main component is scale-like and has a large surface area, so that the scale of oxidation on the particle surface is large. Although treatment is necessary, when iron powder is used, it can be practically used without surface treatment.

[0105]

EFFECTS OF THE INVENTION Coarse crushed Sendust powders are added to # 60, # 10
After classifying to 0, heat treatment was performed at 600 ° C., and the magnetic permeability was measured. As a result, the magnetic permeability was about 21 without depending on the particle size,
Further, the magnetic permeability when the heat treatment temperature was 800 ° C. was about 24, and it was found that increasing the heat treatment temperature does not lead to a significant improvement in the magnetic permeability. Further, as a result of crushing a thin plate prepared by the liquid quenching method and then heat-treating it at 600 ° C. to measure the magnetic permeability, a magnetic permeability of +112 is obtained at + # 60. It has been found that the value drops to about 20 to 25. Further, a method for producing the liquid quenched powder will be described. As shown in FIG. 2, a melt of Sendust alloy is jetted from the hole at the tip of the crucible by gas pressure, and is solidified by contact on the surface of the cooling rotator to produce a ribbon. However, when the manufacturing method shown in FIG. 2 is manufactured for mass production, the ribbon production amount per lot is at most about several kg, which is not suitable for mass production. Furthermore, as powders other than Sendust, iron powder,
As a result of examining the magnetic permeability of the magnetite powder and the Mn-Zn ferrite powder, the magnetic permeability at room temperature was 24.
I knew it was 4, 5.0, 29.5. The magnetic permeability of iron powder was almost constant in the range of 20 to 300 ° C,
It was found that Mn-Zn ferrite powder has a magnetic transformation point or higher at 150 ° C or higher and its magnetic permeability remarkably decreases. What is determined.

For the liquid quench powder, + # 60
Then, a value of 112 was obtained for the magnetic permeability, and the thickness of this powder at this time was about 30 to 40 μm, and it could be known that the average was several hundreds of μm. On the other hand, even if the thickness is the same, if the average diameter becomes smaller, the magnetic permeability becomes 21
Since it tends to decrease to ~ 24, it has been found that the magnetic permeability also increases when the dimensional ratio of (diameter) / (thickness) is larger than a certain value.

Considering these matters and economical efficiency, the magnetic fluid used for the magnetic fluid underground crack confirmation method is as follows.
Iron powder (-# 110) or Sendust powder (-# 40)
It was found to be effective to disperse (0,600 ° C heat treatment) in water or a crushing fluid.

[Brief description of drawings]

FIG. 1 is a temperature characteristic diagram of magnetic permeability of various powders.

FIG. 2 is a conceptual diagram of liquid quenching ribbon manufacturing.

FIG. 3 is a diagram showing a change in magnetic permeability of Sendust magnetic fluid.

FIG. 4 is a diagram showing a change in initial relative magnetic permeability with respect to a heat treatment temperature.

FIG. 5 is a copy of an electron micrograph showing the powder shape.

FIG. 6 is a copy of an electron micrograph showing the powder shape.

FIG. 7 is a copy of an electron micrograph showing the powder shape.

FIG. 8 is a copy of an electron micrograph showing the powder shape.

FIG. 9 is a copy of an electron micrograph showing the powder shape.

FIG. 10 is a copy of an electron micrograph showing the powder shape.

FIG. 11 is a copy of an electron micrograph showing the powder shape.

FIG. 12 is a copy of an electron micrograph showing the powder shape.

FIG. 13 is a copy of an electron micrograph showing the powder shape.

FIG. 14 is a copy of an electron micrograph showing the powder shape.

[Explanation of symbols]

 1 Molten Sendust Alloy 2 Crucible 3 Crucible Tip Hole 4 Rotating Body for Cooling 5 Thin Plate

[Procedure amendment]

[Submission date] September 30, 1993

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

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Title of the invention Magnetic fluid Magnetic fluid used for underground crack confirmation method

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FIG. 5 is an electron micrograph showing a particle structure.

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FIG. 6 is an electron micrograph showing a particle structure.

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FIG. 7 is an electron micrograph showing a particle structure.

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FIG. 8 is an electron micrograph showing a particle structure.

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FIG. 9 is an electron micrograph showing a particle structure.

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FIG. 10 is an electron micrograph showing a particle structure.

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FIG. 11 is an electron micrograph showing a particle structure.

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FIG. 12 is an electron micrograph showing a particle structure.

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FIG. 13 is an electron micrograph showing a particle structure.

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FIG. 14 is an electron micrograph showing a particle structure.

Claims (7)

[Claims] 1. A magnetic fluid used in a magnetic fluid underground crack confirmation method, wherein the magnetic fluid is a fine powder obtained from a high magnetic permeability material. 2. The magnetic fluid used in the magnetic fluid underground crack confirmation method according to claim 1, wherein the magnetic fluid is a high-permeability material finely pulverized and then dispersed in water or a crushing fluid. fluid. 3. The magnetic fluid according to claim 1, wherein the magnetic fluid is made of a single material of sendust powder, iron powder, magnetite powder, Mn-Zn ferrite powder, or a mixed material thereof. Magnetic fluid used for underground crack confirmation method. 4. The magnetic fluid underground crack confirmation method according to claim 3, wherein the magnetic fluid has a particle size of # 10 to # 60 obtained by crushing a quenched ribbon of Sendust. Magnetic fluid. 5. The magnetic fluid according to claim 3, wherein the magnetic fluid is a powder obtained by crushing sendust and heat-treated at a temperature of 600 ° C. to 800 ° C. Magnetic fluid. 6. The magnetic fluid used in the magnetic fluid crack confirmation method according to claim 3, wherein the magnetic fluid has a particle size of # 150 or less obtained by pulverizing a melt of iron by a spraying method. 7. The magnetic fluid used in the magnetic fluid subsurface crack confirmation method according to claim 1, wherein the magnetic fluid has a particle surface coated with a thermoplastic resin.