WO2014017544A1

WO2014017544A1 - Element analyzing device

Info

Publication number: WO2014017544A1
Application number: PCT/JP2013/070066
Authority: WO
Inventors: 晋今宿; 直人冬野; 潤河合
Original assignee: 国立大学法人京都大学
Priority date: 2012-07-25
Filing date: 2013-07-24
Publication date: 2014-01-30
Also published as: JPWO2014017544A1

Abstract

It is an object of the present invention to provide a portable element analyzing device able to separate the various rare earth elements of the lanthanide series, and to identify and quantify each element. The element analyzing device of the present invention includes: a vacuum chamber; a pyroelectric crystal arranged inside the vacuum chamber; a conductive stage having a sample surface facing one surface of the pyroelectric crystal, while also being connected electrically to the other surface of the pyroelectric crystal and grounded; a Peltier element for heating or cooling the pyroelectric crystal; a characteristic X-ray spectrum detecting means for detecting the characteristic X-ray spectrum emitted by the sample placed on the stage; and a fluorescence spectrum detection means for detecting the fluorescence spectrum emitted by the sample.

Description

Elemental analyzer

The present invention relates to an element analyzer capable of detecting various elements contained in a sample, particularly rare earth elements.

The rare earth element is a general term for a group consisting of a total of 17 elements in which two elements of scandium (Sc) and yttrium (Y) are added to 15 elements of the lanthanoid series from lanthanum (La) to lutetium (Lu). Rare earth elements are indispensable for cutting-edge technology because they can improve their performance by adding a very small amount to steel materials, magnetic materials, phosphor materials, superconducting materials, etc. .

However, at present, the area where rare earth elements are produced is concentrated, and the supply of rare earth elements is interrupted or the price rises depending on the intention of the producing country. For stable and inexpensive supply of rare earth elements, discovery of new veins that produce rare earth elements is indispensable. There are satellite exploration, vegetation exploration, geological exploration, geophysical exploration, chemical analysis, etc. for discovering mine veins, where a rough area is discovered, where exploration, ore is extracted, crushed, and analyzed. In order to save these troubles as much as possible, there is a long-awaited need for a portable rare earth element analyzer that can immediately analyze the mined ore.

The present inventor has so far developed a small EPMA (electron beam microanalyzer) using a pyroelectric crystal (Non-Patent Document 1). EPMA is an apparatus that detects an element contained in a sample from a spectrum of characteristic X-rays generated by irradiating the sample (object to be measured) with an electron beam. The apparatus of Non-Patent Document 1 uses a pyroelectric crystal and a Peltier element as the electron beam generating means.

A pyroelectric crystal is a crystal having spontaneous polarization, and in an equilibrium state, the charged particles floating around it adhere to the surface, so that the electric charge on the surface of the pyroelectric crystal due to polarization is canceled, and an electric field does not appear outside. The sexual state is maintained (the middle figure in FIG. 5). When the pyroelectric crystal is heated from this state, the polarization in the pyroelectric crystal is reduced and the surface charge of the pyroelectric crystal is reduced. Therefore, the charge of the attached charged particles is relatively increased, and the surface is positively polarized (hereinafter referred to as “polarized surface”). , “+ Z plane”), and negatively charged plane (hereinafter referred to as “−z plane”) is positively charged (left figure in FIG. 5). When the pyroelectric crystal is kept at the temperature after heating, the decrease in polarization stops, but excess charged particles are separated from the + z plane and the −z plane of the pyroelectric crystal, so that the pyroelectric crystal returns to the equilibrium state again ( Not shown). On the other hand, when the pyroelectric crystal is cooled from the equilibrium state, the polarization in the pyroelectric crystal is increased and the surface charge is increased, so that the charge of the attached charged particles is relatively reduced, and the + z plane is positively charged. The z plane is negatively charged (the right figure in FIG. 5). If the pyroelectric crystal is kept at the temperature after cooling, the increase in polarization stops, but the floating charged particles adhere to the + z plane and the −z plane of the pyroelectric crystal, so that the pyroelectric crystal returns to the equilibrium state again. While there are many floating charged particles in the atmosphere and the pyroelectric crystal quickly returns to an equilibrium state, there are few floating charged particles in a vacuum and the state gradually returns to an equilibrium state (not shown).

The Peltier element is for changing the temperature of the pyroelectric crystal. In the apparatus of Non-Patent Document 1, a sample is placed on a conductive sample stage, and a pyroelectric crystal is arranged so that one surface faces the surface of the sample. The other surface of the pyroelectric crystal is electrically connected to the sample stage and grounded. As a result, when the temperature of the pyroelectric crystal is changed by a Peltier element (not shown), an electric field is generated between the pyroelectric crystal and the sample stage (left diagram in FIG. 6). For example, when the surface of the pyroelectric crystal facing the sample stage (the + z plane in the example of FIG. 6) is negatively charged, negative floating charged particles are directed toward the sample stage, and positive floating charged particles are converted to the pyroelectric crystal. Each is accelerated toward the center (the middle diagram in FIG. 6). Among these floating charged particles, electrons irradiated on the sample contribute to the emission of characteristic X-rays. In the atmosphere, electrons collide with suspended charged particles and lose energy, but in a vacuum of several Pa, most of the electrons collide with the sample on the sample stage without losing energy. As a result, characteristic X-rays are emitted from the sample (the right figure in FIG. 6), and the characteristic X-ray spectrum is obtained by detecting the emitted characteristic X-rays with an energy dispersive X-ray detector (EDX) or the like. It is done.

The power source used in the above configuration may be a small battery, such as a dry cell used for driving and controlling the Peltier element, and the overall size of the device may be smaller than the trunk case, so it is excellent in portability.

Rare earth elements are often mined in a mixed state, and among the rare earth elements, lanthanoid series elements are adjacent in atomic number. In the small EPMA of Non-Patent Document 1, when such lanthanoid series elements are targeted, the peaks of adjacent rare earth elements cannot be sufficiently separated, and it is difficult to accurately identify and quantify these individually. Met.

The problem to be solved by the present invention is to provide an elemental analyzer that is excellent in portability and that can separate and correctly identify various lanthanoid rare earth elements.

An elemental analyzer according to the present invention, which has been made to solve the above problems,
A vacuum vessel;
A pyroelectric crystal disposed in the vacuum vessel;
In the vacuum vessel, the surface on which the sample is placed is opposed to one surface of the pyroelectric crystal, and is disposed so as to be electrically connected to the other surface of the pyroelectric crystal and grounded. Conductive sample stage,
A Peltier element for heating or cooling the pyroelectric crystal;
Characteristic X-ray spectrum detection means for detecting a spectrum of characteristic X-rays emitted from the sample placed on the sample stage;
Fluorescence spectrum detection means for detecting a spectrum of fluorescence emitted from the sample;
It is characterized by having.

It should be noted that the term “opposite” as used herein is not limited to the state where the two surfaces are facing each other, but may be the state where the two surfaces are inclined and face each other.

The inventor of the present invention has conceived that cathodoluminescence analysis is used in combination in order to separate rare earth element peaks that overlap in the characteristic X-ray spectrum. The cathodoluminescence analysis is a method for identifying elements contained in a sample from the spectrum of fluorescence emitted from the sample when the sample is irradiated with electrons.
In the analysis by the characteristic X-ray, the electrons in the inner orbit of the atom are ejected by the incident electrons, and the characteristic X-ray generated by the electrons in the outer orbit dropping into the orbit is used. Is used to excite the outer shell electrons (electrons in the valence band or acceptor level) of the atom, and light generated by recombination of the generated electron-hole pairs is used. As described above, since the principle is different between the characteristic X-ray analysis and the cathodoluminescence analysis, there is a possibility that the rare earth element peak that cannot be separated in the characteristic X-ray spectrum can be separated and identified in the fluorescence spectrum.

The present inventor detected rare earth elements that could not be separated in the characteristic X-ray spectrum by cathodoluminescence analysis using an electron beam of a scanning electron microscope (SEM) (a normal tungsten electron gun was used for electron beam irradiation). Preliminary experiments were conducted to see if this was possible. Then, it was confirmed that this was possible, and an elemental analyzer according to the present invention capable of both characteristic X-ray analysis and cathodoluminescence analysis using a pyroelectric crystal and a Peltier element as electron beam generation means was produced. did.

For the characteristic X-ray spectrum detection means, it is desirable to use an energy dispersive X-ray detector (EDX) for high sensitivity and miniaturization of the apparatus, but a wavelength dispersive X-ray detector (WDX). May be used. A spectroscope such as a polychromator can be used as the fluorescence spectrum detecting means.

Note that the intensity of fluorescence emitted from the sample by electron irradiation is weaker than the intensity of characteristic X-rays emitted from the sample by the irradiation. Further, the detection sensitivity of the spectrometer is generally lower than that of EDX. For this reason, in order to efficiently collect the fluorescence, an input end of an optical fiber is arranged near the sample surface, and the fluorescence collected immediately near the sample surface is sent to the spectroscope at the subsequent stage through the optical fiber. It is desirable.

Also, the intensity of the fluorescence emitted from the sample can be increased by increasing the number of electrons irradiated to the sample per unit time (irradiation current amount). In the elemental analyzer according to the present invention, therefore, it is desirable to provide a conductive needle on the surface facing the pyroelectric crystal sample. As a result, the current generated between the pyroelectric crystal and the sample has the shortest path along the straight line connecting the needle and the portion of the sample facing the needle, so that the resistance is reduced and flows in a concentrated manner on the straight line. Therefore, the amount of irradiation current to the sample increases locally. As the material of the needle, it is desirable to use a highly conductive material, for example, gold or silver can be suitably used. Note that tungsten, molybdenum, or the like may be used when importance is attached to strength or the like.

The elemental analyzer according to the present invention has a configuration using a pyroelectric crystal and a Peltier element, similar to the EPMA of Non-Patent Document 1, and can be downsized and driven by a small battery such as a dry cell. Is excellent. In addition, since cathodoluminescence analysis is used in combination, lanthanoid series rare earth elements that could not be distinguished only by analysis by characteristic X-rays can be individually separated and correctly identified and quantified.

The schematic block diagram of one Example of the elemental analyzer which concerns on this invention. The graph which shows the characteristic X-ray spectrum and fluorescence spectrum with respect to the zircon powder obtained by the elemental analyzer of a present Example. The graph which shows the characteristic X-ray spectrum and fluorescence spectrum with respect to mixed powder obtained by the elemental analyzer of a present Example. The schematic diagram (a) of the elemental analyzer of a 1st modification, The schematic diagram (b) of the elemental analyzer of a 2nd modification. Explanatory drawing which shows the principle which this pyroelectric crystal charges by changing the temperature of a pyroelectric crystal. Explanatory drawing which shows the principle by which a sample on a sample stand is irradiated with electrons by a pyroelectric crystal. The schematic diagram of the elemental analyzer of a 3rd modification.

An embodiment of an elemental analyzer according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an elemental analyzer according to the present embodiment. In the following, the + z direction in the figure is “up” and the −z direction is “down”.

1 includes a stainless steel vacuum vessel 10, a pyroelectric crystal 11 made of a single crystal of LiTaO ₃ , a Peltier element 12 for heating / cooling the pyroelectric crystal 11, and a sample S. A sample table 13 made of brass, an energy dispersive X-ray detector (EDX) 14 that detects the spectrum of characteristic X-rays emitted from the sample S by irradiating the sample S with electrons, and the sample by the electrons And a polychromator (spectrometer) 15 for detecting the spectrum of fluorescence emitted from S.

The vacuum vessel 10 includes a copper exhaust pipe 16 to which a rotary pump (not shown) is connected. The lower surface of the Peltier element 12 is joined to the upper surface of the distal end of the exhaust pipe 16. The lower surface of the pyroelectric crystal 11 is bonded to the upper surface of the Peltier element 12. The Peltier element 12 heats / cools the pyroelectric crystal 11 when power is supplied from the power supply unit 18. The upper surface of the pyroelectric crystal 11 is a + z plane (a surface that is positively polarized), and the lower surface is a −z plane (a surface that is negatively polarized). Thus, the upper surface of the pyroelectric crystal 11 is negatively charged and the lower surface is positively charged.

The copper rod 17 can be inserted and removed from the upper surface of the vacuum vessel 10, and the bottom surface of the sample stage 13 is joined to the lower surface of the tip of the rod 17. The sample mounting surface of the sample table 13 has a 45 ° gradient with respect to the bottom surface of the sample table 13. The energy dispersive X-ray detector (EDX) 14 is disposed so as to be in front of the sample mounting surface, and the polychromator (spectrometer) 15 is further inclined by 45 ° with respect to the sample mounting surface. (Thus, at a position rotated by 90 ° with respect to the surface of the pyroelectric crystal 11). When placing the sample S on the sample stage 13, the rod 17 is removed from the vacuum vessel 10, and the sample S is fixed on a double-sided tape affixed to the sample placement surface of the sample stage 13. Then, the sample stage 13 is directed downward, and the rod 17 is inserted into the vacuum vessel 10. Since the elemental analyzer according to the present embodiment has such an arrangement, as shown in FIG. 1, when the flat sample S is placed on the sample placement surface of the sample stage 13, X-rays emitted from the sample surface Enters the energy dispersive X-ray detector (EDX) 14 from the front, and a large amount of fluorescence also enters the polychromator (spectrometer) 15. The insertion port of the rod 17 of the vacuum vessel 10 is hermetically sealed by an O-ring or the like (not shown).

The lower surface of the pyroelectric crystal 11 is electrically connected to the exhaust pipe 16 by a conducting wire or the like. The bottom surface of the sample stage 13 is electrically connected by being joined to the rod 17. Further, the exhaust pipe 16 and the rod 17 are electrically connected by a conducting wire or the like and grounded. As a result, the sample stage 13 and the lower surface of the pyroelectric crystal 11 are electrically connected to have the same potential (ground potential). In addition, when the vacuum vessel 10 is comprised with an electroconductive material, this vacuum vessel 10 can also be used instead of conducting wire.

The power supply unit 18 has a function of periodically switching the direction of a current flowing through the Peltier element 12 as well as a function of flowing a current through the Peltier element 12. Thereby, the upper surface of the Peltier element 12 repeats heating and cooling periodically. Accordingly, the pyroelectric crystal 11 bonded to the upper surface of the Peltier element 12 is periodically heated and cooled.

After placing the sample S on the sample stage 13 and inserting the rod 17 into the vacuum vessel 10, the inside of the vacuum vessel 10 is exhausted through the exhaust pipe 16 by a rotary pump (not shown). The vacuum chamber 10 is evacuated until the internal pressure reaches about several Pa (for example, 1 Pa to 2 Pa). When the pyroelectric crystal 11 is heated in this state, an electric field is formed in the direction from the sample stage 13 toward the pyroelectric crystal 11. Thereby, stray electrons in the vacuum are accelerated toward the sample stage 13 and collide with the sample S fixed on the sample stage 13, and characteristic X-rays and fluorescence are emitted from the sample S.
However, pyroelectric crystals cannot be heated indefinitely. In order to increase the sensitivity of the measurement data, the operation of once cooling the pyroelectric crystal, increasing the polarization, and then heating the pyroelectric crystal again is repeated to irradiate the electrons a plurality of times. When the pyroelectric crystal is cooled and the polarization is increased, the floating electrons are accelerated toward the pyroelectric crystal 11.

The detection sensitivity of the polychromator 15 is generally lower than that of the EDX14. Therefore, by arranging the input end of the optical fiber 19 in the vicinity of the sample surface, the fluorescence emitted from the sample S is efficiently collected in the immediate vicinity of the sample S. The collected fluorescence is sent to the polychromator 15 through the optical fiber 19. Further, the EDX 14 has an X-ray entrance in a direction in which the characteristic X-ray is not hindered by the optical fiber 19.

The graph of FIG. 2 shows a characteristic X-ray spectrum (a) and a fluorescence spectrum (b) obtained by the elemental analysis apparatus of this example when a zircon powder containing rare earth elements or the like as a trace component is used as a sample. is there.
In the characteristic X-ray spectrum of FIG. 2 (a), it can be seen that peaks of Cr, Fe, Ni, Cu, and Zn appear, but the rare-earth element peaks are insignificant and are almost invisible (LaLα in the figure). LuLα represents the peak position of the characteristic X-ray of the rare earth element). For this reason, it is determined that the rare earth element is not included only by the characteristic X-ray spectrum of FIG. In contrast, in the fluorescence spectrum shown in FIG. 2 (b), peaks of Sm, Tb, Dy, and Er appear separately from each other. Therefore, it can be seen that this zircon powder contains at least Sm, Tb, Dy, and Er as rare earth elements.

FIG. 3 shows a characteristic X-ray spectrum (a) obtained by the elemental analyzer of this example when a mixed powder of oxides of Nd, Sm, Gd, Dy, Er, and Yb was used as a sample, and a fluorescence spectrum ( b).
In the characteristic X-ray spectrum of FIG. 3A, the peaks of GdLα and ErLβ appear separately from other elements. Therefore, it can be seen from the characteristic X-ray spectrum of FIG. 3A that this sample contains at least Gd and Er.
On the other hand, since peaks other than Gd and Er may contain a plurality of elements, it is difficult to separate and identify them only from this characteristic X-ray spectrum. For example, in the peak around 5.4 keV, any or all of Cr, Nd, and Sm may be included, but it is not known whether any or all of these are included only by this peak. In contrast, in the fluorescence spectrum of FIG. 3 (b), the peak of Sm appears separately. Therefore, it can be seen from the fluorescence spectrum of FIG. 3B that this sample contains at least Sm.
Similarly, in the characteristic X-ray spectrum of FIG. 3 (a), since the DyLα and Fe peaks overlap, it is not known whether this sample contains Dy, but from the Dy peak in the fluorescence spectrum of FIG. 3 (b). It can be seen that this sample contains Dy.
Thus, it can be seen from the characteristic X-ray spectrum of FIG. 3A that Gd and Er are included, and from the fluorescence spectrum of FIG. 3B that Sm and Dy are included.

As described above, the intensity of the fluorescence emitted from the sample by electron irradiation is weaker than the intensity of the characteristic X-ray emitted from the sample by the irradiation. Further, the detection sensitivity of the polychromator 15 is generally lower than that of the EDX 14. Therefore, in order to accurately measure the fluorescence emitted from the sample S, it is desirable to increase the amount of irradiation current to the sample S and cause the sample S to generate fluorescence more strongly. In the elemental analysis apparatus according to the present invention, in order to locally increase the amount of irradiation current, a configuration in which the conductive needle 20 is bonded to the upper surface (+ z plane) of the pyroelectric crystal 11 is used as a first modification. (FIG. 4 (a)). Thus, by providing the conductive needle 20 on the (+ z plane) of the pyroelectric crystal 11, the current generated between the pyroelectric crystal 11 and the sample S (more precisely, the sample stage 13) Since the path is the shortest in the straight line connecting the sample locations facing the needle 20, the resistance is reduced, and the flow is concentrated on the straight line. Therefore, the electron trajectory concentrates as shown by the arrows in FIG. 4A, and the amount of irradiation current to the sample S increases locally. Gold or silver can be suitably used as the material of the needle 20. The characteristic X-rays and fluorescence emitted from the sample S on the sample stage 13 are detected by EDX and a spectroscope provided in a direction of ± 45 ° from the sample placement surface.

As a second modification, as shown in FIG. 4B, the sample placement surface of the sample stage 13 may be curved in a convex shape. As a result, the current generated between the pyroelectric crystal 11 and the sample S (more precisely, the sample stage 13) is a straight line connecting the nearest point (nearest contact point) between the pyroelectric crystal 11 and the pyroelectric crystal 11 of the sample stage 13. Since the path becomes the shortest in (1), the resistance is reduced, and the flow is concentrated on the straight line. Therefore, the electron trajectory is concentrated as shown by the arrows in FIG. 4B, and the amount of irradiation current to the sample S is locally increased. The sample S (for example, the powder of the sample S) is fixed near the closest point of the sample stage 13. Characteristic X-rays and fluorescence emitted from the sample S on the sample stage 13 are detected by EDX and a spectroscope provided in a direction of ± 45 ° from the sample placement surface. The needle used in the first modification may be further added to the second modification.

As a third modification, an electron lens 21 may be provided between the pyroelectric crystal and the sample stage as shown in FIG. The electron lens 21 is used for focusing electrons in an electron microscope or the like, and includes an electrostatic lens using an electric field and a magnetic lens using a magnetic field. FIG. 7 shows an example in which a donut-shaped permanent magnet is used as the electron lens 21. The magnet is not limited to a permanent magnet, and an electromagnet may be used. Thereby, the accelerated stray electrons are concentrated and collide with the point P on the sample S fixed on the sample stage 13. Therefore, the irradiation current amount to the sample S increases locally. Also in this modification, the needle used in the first and / or second modification may be added.

DESCRIPTION OF SYMBOLS 10 ... Vacuum container 11 ... Pyroelectric crystal 12 ... Peltier device 13 ... Sample stand 14 ... EDX
DESCRIPTION OF SYMBOLS 15 ... Polychromator 16 ... Exhaust pipe 17 ... Rod 18 ... Power supply part 19 ... Optical fiber 20 ... Needle 21 ... Electron lens

Claims

A vacuum vessel;
A pyroelectric crystal disposed in the vacuum vessel;
In the vacuum vessel, the surface on which the sample is placed is opposed to one surface of the pyroelectric crystal, and is disposed so as to be electrically connected to the other surface of the pyroelectric crystal and grounded. Conductive sample stage,
A Peltier element for heating or cooling the pyroelectric crystal;
Characteristic X-ray spectrum detection means for detecting a spectrum of characteristic X-rays emitted from the sample placed on the sample stage;
Fluorescence spectrum detection means for detecting a spectrum of fluorescence emitted from the sample;
An elemental analysis apparatus characterized by comprising:
The elemental analyzer according to claim 1, wherein a conductive needle is provided on a surface of the pyroelectric crystal facing the sample.
3. The element analyzer according to claim 1, wherein the sample mounting surface of the sample stage is curved in a convex shape.
The input end of an optical fiber is disposed in the vicinity of the surface of the sample, and fluorescence emitted from the sample is sent to the fluorescence spectrum detecting means through the optical fiber. Elemental analyzer.
The elemental analyzer according to any one of claims 1 to 4, wherein an electron lens is provided between a surface of the pyroelectric crystal facing the sample and the sample stage.