JP2607640B2 - Magnetometer and magnetic property inspection system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic flux sensor using a superconducting quantum interferometer, and particularly to a ferrite-containing stainless steel used in a high-temperature environment such as a chemical plant and a nuclear power plant. The present invention relates to a probe coil and a probe coil core suitable for detecting high temperature aging embrittlement damage of a metal material.

[Conventional technology]

Conventionally, a superconducting quantum interference device (hereinafter, referred to as a SQUID) equipped with a small probe coil is referred to as a one-chip type SQUID in 1988, International, Solid State Circuits Conference (1988).
International Solid-State Circuits Conference
(ISSCC 88)) discussed on pages 289-291.

On the other hand, as a method for detecting the degree of high-temperature embrittlement damage of an actual ferrite-containing stainless steel member, there is a method described in JP-A-61-28859. This is a method of detecting the degree of embrittlement of the relevant part by magnetically measuring the change in the amount of ferrite after long-time use at a high temperature of a real machine member using a ferrite scope.

Although it is not a deterioration diagnosis, a method of manufacturing a superconducting sheet coil which exhibits high critical current characteristics in a high magnetic field region used for magnets for a superconducting generator, etc.
62-277704.

[Problems to be solved by the invention]

In the above prior art, since the detection area for taking in the magnetic flux from the object to be measured is large, extremely small particles such as α 'phase and G phase precipitated by high-temperature aging in the ferrite phase of the duplex stainless steel used for the actual parts of the nuclear power plant. There was a problem that the magnetic properties of the precipitates could not be investigated, and the correlation between the magnetic properties of the material and the structural change affecting the material degradation could not be clarified sufficiently.

In addition, the above-described prior art was generally able to measure the magnetic properties of the entire material when examining changes in the internal structure of the material accompanied by changes in the magnetic properties. There is a problem that the magnetic properties of the changing part cannot be measured.

Further, in the above prior art, when the size of the internal structure change portion that directly causes a change in the magnetic characteristics of the material is extremely small, the size of the internal structure change portion is determined separately from the magnetic characteristics by a micro-analysis device. There was a problem that it had to be checked using.

An object of the present invention is to clarify the correlation between the change in the magnetic properties of a material and the change in the structure that affect the change in the material of a duplex stainless steel used in a real machine member of a nuclear power plant or the like, and to enhance the reliability of deterioration diagnosis. It is an object of the present invention to provide a magnetometer capable of measuring magnetic characteristics with a positional resolution of the order of Å, and having extremely high magnetic signal sensitivity.

[Means for solving the problem]

In order to achieve the above object, in a magnetometer having a SQUID and a magnetic flux transmission circuit for taking in magnetic flux into the SQUID,
A probe coil provided in a magnetic flux transmission circuit and facing a sample to be measured is formed at the tip of a needle-shaped core having a small radius of curvature at the tip.

Further, in order to reduce the radius of curvature of the tip of the needle-shaped core, the core material is cut into a rod shape, and the end of the rod-shaped material is subjected to electrolytic polishing or scientific polishing.

Further, in order to increase the sensitivity of the magnetic flux signal taken into the SQUID, the needle core is made of a soft magnetic material having a high magnetic permeability.

達成 In order to achieve the purpose of measuring magnetic properties with a positional resolution of the order, an insulating thin film inserted between the probe coil and the needle core is not formed inside the probe coil ring of the needle core, The needle core is driven in a three-dimensional direction by an epizo element so that a tunnel current between the tip of the core and the sample to be measured is constant.

[Action]

Cut a piece of soft magnetic material into a square piece with a length of 15 mm 0.25 mm square, immerse one end of the square piece in an electrolytic solution such as hydrochloric acid or nitric acid, and apply an AC voltage of 2 to 3 V to raise and lower it.
A needle-like core of a degree is completed. An insulating thin film is formed by vacuum evaporation or the like on the entire surface except directly above the needle-shaped core, and a superconducting thin film probe coil is mounted thereon. The probe coil has a diameter of about 160 ° and a very small magnetic flux detection area.

Since the needle-shaped core is driven by the piezo element so as to keep the tunnel current between the tip of the needle-shaped core and the sample to be measured constant, the distance between the two can be reduced to 10 ° or less. As a result, the magnetic flux leakage to the probe coil decreases, the magnetic flux taken in increases, and the signal sensitivity increases.
Further, the fact that the needle-shaped core is made of a soft magnetic material also leads to a reduction in leakage magnetic flux and an improvement in sensitivity. By controlling the voltage applied to the piezo element in a two-dimensional direction while adjusting the voltage applied to the piezo element in a plane perpendicular to the axial direction of the needle core, the surface of the sample to be measured is moved with a positional resolution of the order of Å, and the change in magnetic properties is examined Can be.
Further, when the position control of the needle-shaped core is performed by driving a pulse motor, a coarser scan can be performed as compared with driving the piezoelectric element.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a schematic view of a microprobe coil according to one embodiment of the present invention. A probe coil 2 made of a ring of a superconducting film is formed at the tip of a needle-shaped core 1 having a small radius of curvature at the tip, and a lead wire 3 is derived from the probe coil 2. As shown in FIG. 2, when the two lead wires 3 intersect via the insulating thin film 3-a, the sensitivity of the probe coil is further improved. It is also possible to use the rod-shaped core 3-b as shown in FIG. 3 instead of the needle-shaped core, and to mount the probe coil 2 on the tip of the rod-shaped core 3-b.

SQUID with probe coil as described above
The use of a magnetometer makes it possible to detect magnetic property values in very fine regions of the material. For example, it is effective in the system described below. Duplex stainless steel is used for the reactor walls and primary piping in nuclear plants, but as the operating time of the reactor increases, high-temperature aging embrittlement causes the phase in the ferrite phase of duplex stainless steel to decrease. A minute precipitation phase is generated, and the actual machine member is deteriorated. Because the magnetic properties of the duplex stainless steel change slightly due to the precipitation phase generated in the ferrite phase,
By measuring the magnetic properties using a highly sensitive GQUID and a probe coil for capturing magnetic flux into the GQUID, it is possible to evaluate the degree of deterioration of the members of the actual machine. When an exciting device is arranged near the sample to be measured and a magnetomotive force is applied to the sample to be measured, the fourth
As shown in FIG. 5 and FIG. 5, a magnetic hysteresis loop 4 is drawn corresponding to the change of the magnetomotive force. FIG. 4 is a diagram showing the magnetic properties of the duplex stainless steel receiving material, and FIG.
It is a figure which shows the magnetic characteristic of the deterioration material which performed the high temperature aging of 475 degreeC of the duplex stainless steel. When the magnetic properties of the receiving material and the deteriorated material are compared, the magnetic hysteresis area 5, the magnetic hysteresis form 5-a, the maximum magnetic flux density 6, the residual magnetic flux density 7, the coercive force 8
It can be seen that the characteristic values such as.

In order to actually evaluate the degree of deterioration of actual reactor components, it is necessary to accumulate data on magnetic property changes, strength changes, and internal structure changes with respect to the aging time and aging temperature of duplex stainless steel, and to correlate each characteristic value. Is required. However, when determining the correlation between magnetic characteristics and changes in internal structure, the conventional SQUID magnetometer using a probe coil has a large magnetic flux detection area, and thus cannot directly determine changes in magnetic characteristics due to the minute precipitate phase. Was.

FIG. 6 is a configuration diagram of a magnetic flux measurement unit having a SQUID. The magnetic flux measured from the part to be measured enters the probe coil 2 of the magnetic transmission circuit 9 and is transmitted to the coil S9-a. Coils S9-a and rfSQUID10 have mutual inductance Are joined by Here, Ls and L are the coils S9−
a and the self-inductance of rfSQUID10. Assuming that the number of turns of the probe coil 2 is n _P , the self-inductance per turn is L _PO , the number of turns of the coil S9-a is n _S , and the self-inductance per turn is L _SO , the sensitivity of the SQUID is ε = Given by In the above equation, the maximum sensitivity ε is L _P
= L _S is satisfied. That is, the self inductance of the probe coil and the coil S must be equal. Generally, the self-inductance of a coil is proportional to the cross-sectional area A of the coil wire and inversely proportional to the length of the coil per turn. In the probe coil 2 formed at the tip of the needle-shaped core of the present invention, the length l _P of the coil per turn is very small, but the cross-sectional area A _P can be made sufficiently small, so that L _P = L _S is satisfied. Such a coil S9-a can be manufactured. Further, the magnetic flux signal of the rf SQUID 10 is converted into an electric signal by the LC resonance circuit 11 and transmitted to the control circuit of the SQUID.

FIG. 7 is a schematic view of a multi-turn probe coil according to an embodiment of the present invention. A multi-turn probe coil 12 is formed at the tip of the needle-shaped core 1, a lead (1) 13 and a lead wire (2) 14 are led out from the tip, and furthermore, between the lead (2) 14 and the multi-turn probe coil 12. And an insulating material 15 interposed therebetween.

FIG. 8 shows an acicular core made of an insulating thin film and a soft magnetic material,
FIG. 9 is a sectional view of a wound microprobe coil, and FIG. 9 is a sectional view of a needle-shaped core made of an insulating material and a single wound microprobe coil. As shown in FIG. 8, polyethylene or Teflon having a uniform magnetic permeability of about 1 is placed on a needle-shaped core 16 of a soft magnetic material such as an iron-nickel alloy such as permalloy (PC) or high-hardness permalloy (HPC) having a high magnetic permeability. When a one-turn probe coil 18 is formed by coating an insulating thin film 17 such as an organic insulating material such as an inorganic insulating material or the like, and a single-turn probe coil 18 is formed on the insulating thin film 17, leakage is reduced as compared with a case where a material having a low magnetic permeability is used for an iron core. There is an effect that the magnetic flux decreases, the magnetic flux taken in increases, and the sensitivity of the SQUID improves. As shown in FIG. 9, when the insulating material is directly machined or chemically polished to form an insulating needle-like core 19, and a one-turn probe coil 18 is formed thereon, the result is as compared with the case of FIG. Although it is not so desired to reduce the leakage magnetic flux, there is an effect that the process of manufacturing the probe coil is simplified.

FIG. 10 shows an embodiment of a procedure for manufacturing a needle-shaped core made of an insulating film and a soft magnetic material and a one-turn microprobe coil. Cut a soft magnetic material into rods with a length of 15 mm and a cross section of 0.5 mm square.
When immersed in an electrolytic solution such as hydrochloric acid or nitric acid and subjected to electrolytic polishing with alternating or direct current of several volts, a sharp needle core 16 having a tip with a radius of curvature of about R = 500 ° is formed. When this needle-shaped core 16 is introduced into an ultra-high vacuum and a positive high voltage of several kilovolts is applied, the surface atoms at the tip of the needle-shaped core are subjected to a high electric field to make the field evaporation close to an ideal hemisphere. A tip shape is obtained. Next, the insulating material is deposited while rotating the needle core 16 in the axial direction in a vacuum to form an insulating thin film 17 having a uniform film on the surface. Subsequently, a resist 20 is applied on the insulating thin film 17 as shown in FIG. 10, and a superconducting material is deposited again in a vacuum to form a superconducting film 21 as a whole. Finally, when the resist 20 is removed, a very small one-turn probe coil having a diameter of about 1000 ° is completed.

FIG. 11 is a schematic diagram when a magnetic flux of a deteriorated material of duplex stainless steel is measured using a one-chip type probe coil, and a diagram showing the corresponding residual tight bundle density. As described above, the ferrite phase 22- of the duplex stainless steel 22, which is the sample to be measured,
In a, microprecipitated phases such as α 'phase 23 and G phase 24 are generated as the aging time increases. The size of these precipitated phases is as small as several hundred square meters. In the case of a laminated probe coil 25 mounted on a 2 mm x 3 mm 1-chip type SQUID, the sample to be measured is a duplex stainless steel. The laminated probe coil 25 could not be brought sufficiently close to the 22, and the leakage magnetic flux was large and the magnetic flux taken in was small. Further, even if the difference in the magnetic properties between the receiving material and the deteriorated material can be measured, as shown in FIG.
Is not sensitive enough to detect changes in

On the other hand, as shown in FIG. 12, a duplex stainless steel 22 was manufactured using a SQUID having the microprobe coil 26-a of the present invention.
When the deteriorated material is measured, the residual magnetic flux density profile 26 with respect to the center position of the probe has a shape that directly reflects the change of the α 'phase 23 and the G phase 24 because of the extremely small detection area of 500 mm in radius. become. Further, since the needle-shaped core of the soft magnetic material is provided, the leakage magnetic flux is reduced and the magnetic flux taken in is increased. Further, if a center hole 27 is opened at the center of the microprobe coil 26-a and handled as a probe of a scanning tunneling microscope (STM), the center hole 27 is moved to a position of several mm which is a distance at which a tunnel current can be measured. Thus, the SQUID can be brought closer to the stainless steel 22, and the sensitivity of the SQUID is further enhanced.

FIG. 13 shows an SQ having a microprobe coil 26-a.
FIG. 2 is a schematic diagram of an STM-SQUID in which a driving mechanism of a scanning tunneling microscope (STM) is applied to a UID magnetometer. A tunnel current is caused to flow between the needle-shaped core 1 having the microprobe coil 26-a and the ferrite phase 22-a having the α 'phase 23 and the G phase 24, and the distance Z is kept constant at about Ｚ. Axial piezo
28 is controlled by the PI control circuit 29, and the X-axis piezo 30
And the Y-axis piezo 31, the structure of the sample surface can be observed at the atomic level on the monitor (1) 33 through the computer (1) 32. According to the present invention, the needle core 1 is cooled to 11 K in a vacuum by the cryogenic refrigerator 34 in parallel with these scans, and the magnetic flux signal measured by the microprobe coil 26-a is output. , Lead wire 3, coil S9
−a, rf SQUID10, SQUID control circuit 35 through LC resonance circuit 11
The computer (2) 36 makes it possible to observe the surface distribution of the molecular size of each magnetic property such as the residual magnetic flux density profile 38 on the monitor (2) 37 by the computer (2) 36. Here, there is an effect that the superconducting material such as the probe coil, the magnetic flux transmission circuit, and the SQUID can be easily lowered to the transition temperature or lower by the refrigerator.

FIG. 14 is a schematic view of a core and a microprobe coil arranged in a multi-needle shape.

As shown in FIG. 14, a large number of microprobe coils 26-a
And the needle-shaped core 1 are arranged at regular intervals on the core stage 39,
If the magnetic flux signal from each microprobe coil 26-a is continuously processed, there is also an effect that the surface distribution of each magnetic property on the surface of the duplex stainless steel 22 can be discretely measured without using the STM driving mechanism.

Also, the SQUI equipped with the microprobe coil of the present invention
The use of the D magnetometer has the effect that the magnetic domain of a magnetic disk or a magnetic head, an initial structural defect, and a structural defect due to aging can be measured.

[Effects of the Invention] According to the present invention, it is possible to produce a SQUID having a probe coil having a very small magnetic flux detection area at the tip of a needle-shaped core, so that α precipitates in the ferrite phase of a duplex stainless steel. As in the 'phase and the G phase, there is an effect that a change in magnetic properties due to a minute structural change inside the material can be measured following the position of the structural change. If the magnetic properties corresponding to minute structural changes such as α 'phase and G phase have been checked in advance, the magnetic flux of the same material can be measured using the probe coil to check the structure of the material in reverse. There is also an effect that can be done.

Further, according to the present invention, there is an effect that the metal can be used as a core without peeling off the probe coil having the probe coil formed at the tip.

Furthermore, since the drive mechanism of the STM can be used together, the probe coil can be brought as close as possible to the sample to be measured, so not only the sensitivity of the SQUID is improved, but also the magnetic characteristics can be investigated with a resolution of the order of the order. This has the effect.

[Brief description of the drawings]

FIG. 1 is a partial perspective view showing an overview of a microprobe coil according to an embodiment of the present invention, FIG. 2 is a partial perspective view showing an overview of a microprobe coil having crossed lead wires,
FIG. 3 is a partial perspective view showing an overview of a microprobe coil formed at the tip of a rod-shaped core, FIG. 4 is a magnetic characteristic diagram of a duplex stainless steel receiving material, and FIG. FIG. 6 is a circuit diagram of a magnetic flux measuring unit equipped with a SQUID, and FIG. 7 is a schematic view of a multi-turn probe coil according to an embodiment of the present invention. FIG. 8 is a cross-sectional view of a needle-shaped core made of an insulating thin film and a soft magnetic material and one turn of a microprobe coil. FIG. 9 is a cross-sectional view of a needle-shaped core made of an insulating material and one turn of a microprobe coil. Fig. 10 is a process diagram showing a procedure for manufacturing a needle-shaped core made of an insulating film and a soft magnetic material and a one-turn microprobe coil. Fig. 11 shows a one-chip probe coil made of a deteriorated material of duplex stainless steel. Schematic diagram and corresponding residual magnetic flux FIG. 12 is a schematic diagram showing the magnetic flux measurement of the deteriorated material of the duplex stainless steel using the microprobe coil of the present invention, and FIG. 13 is a characteristic diagram showing the residual magnetic flux density, and FIG. Scanning tunneling microscope (ST) with SQUID magnetometer equipped with probe coil
M) Schematic circuit diagram of STM-SQUID to which drive mechanism is applied,
FIG. 4 is a perspective view showing an overview of a core and micro probe coils arranged in a multi-needle shape. 1 ... needle-shaped core, 2 ... probe coil, 3 ... lead wire, 3-a ... insulating thin film, 3-b ... rod-shaped core, 4 ...
Magnetic hysteresis loop, 5 ... magnetic hysteresis area, 5-a ... magnetic hysteresis form, 6 ... maximum magnetic flux density, 7 ... residual magnetic flux density, 8 ... coercive force, 9 ... magnetic flux transmission circuit, 9-a …… rfSQUID, 10 …… rfSQUID, 11 ……
LC resonance circuit, 12 multi-turn probe coil, 13 lead wire (1), 14 lead wire (2), 15 insulating material, 16
... soft magnetic material needle core, 17 ... insulating thin film, 18 ... one-turn probe coil, 19 ... insulating material needle core, 20 ... resist, 21 ... superconducting thin film, 22 ... duplex stainless steel Steel, 22-
a: Ferrite phase, 23: α 'phase, 24: G phase, 25:
... Laminated type probe coil, 26 ... Residual magnetic flux density profile, 26-a ... Micro probe coil, 27 ... Center hole, 28 ... Z piezo, 29 ... PI control circuit, 30
... X-piezo, 31 ... Y-piezo, 32 ... Computer (1), 33 ... Monitor (1), 34 ... Cryogenic refrigerator, 35 ... SQUID control circuit, 36 ... Computer (2 ), 37: Monitor (2), 38: Residual magnetic flux density distribution, 39: Core stage.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-28859 (JP, A) JP-A-1-1244781 (JP, A) JP-A-2-66478 (JP, A) 27880 (JP, U)

Claims (6)

(57) [Claims] A magnetic flux transmission circuit arranged so that a probe coil faces an object to be measured, a superconducting quantum interference element provided within a range where a magnetic flux generated from the circuit reaches, and a needle-shaped core. A magnetometer, wherein the probe coil is provided at the tip of a needle-shaped core. 2. A stylus comprising a magnetic flux transformer in which a pickup coil is arranged to face an object to be measured, a superconducting quantum interference device provided in a range where a magnetic flux generated from the transformer reaches, and a needle-shaped core. A magnetometer, wherein the pickup coil is provided at the tip of a core having a shape of a circle. 3. The magnetometer according to claim 1, wherein the needle-shaped core is made of a soft magnetic material. 4. The magnetometer according to claim 1, wherein the needle-shaped core is positioned in a three-dimensional direction by driving a piezo element. 5. The positioning of the needle-shaped core in a three-dimensional direction by driving a pulse motor.
The magnetometer according to any one of claims 1 to 4. 6. A magnetometer according to claim 1, wherein a magnetic flux signal output from said magnetometer is displayed as a surface distribution of magnetic characteristics on a monitor via a signal processing circuit. A magnetic property inspection system characterized by the following.