JP2014126546A - Method for preparing thin section of fragile sample by dry polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin section used for a scanning electron microscope, an energy dispersive x-ray spectroscopy, an electron probe microanalyzer, a reflecting microscope and the like for which a thin section with a highly smooth surface is required, for a fragile sample which is heat sensitive, or swells and is damaged in water or oil, and is made of natural minerals such as pumice stones, clay, diatom earth, manganese nodules, non-mineralized fossils and minerals containing sulfur and salt.SOLUTION: A fragile sample is embedded with a resin and solidified, and molded and cut into a rectangular parallelepiped shape. Thereafter, rock or mineral is attached to four surfaces of the sample orthogonal to a surface to be polished or to five surfaces in which a surface opposite to the one surface to be polished is added to the four surfaces, and then the surface is polished. This enables the surface to be polished while flatness is maintained and thickness of a thin section is judged. For the resin for the embedding and solidifying, a resin curable at room temperature or low temperature and having a short solidifying time is used, and in a final polishing step for the fragile sample, silk cloth having alumina powder impregnated therein is used.

Description

  The present invention is a sample for an analytical electron microscope such as a scanning electron microscope or an electron beam microanalyzer in a fragile sample that is vulnerable to heating such as pumice and clay among natural minerals or swells and breaks with water or an organic solvent. The present invention relates to a method for producing a flake having a highly smooth surface that can be used as a thin film.

  In general rock flake production, a wet flake production method using water or oil during sample cutting and polishing is used. However, in the case of a fragile sample that swells with water or oil, there is a problem that if water or oil is used in the thin piece manufacturing process, the sample is destroyed due to swelling. In addition, fragile samples that tend to collapse are generally embedded with epoxy or acrylic resin to increase the hardness of the sample, but thermosetting resins are cured by heating, and some of the cold curable resins are The sample is exposed to a high temperature of about 100 ° C. because it is cured by natural heat generation. Therefore, fragile samples that contain a lot of water, such as pumice (including allophane and imogolite), clay, diatomaceous earth, manganese nodules, unfossilized fossils, minerals containing sulfur and salt, can be used to cure the above general samples. When embedding with the resin used, the water vapor contained by heating evaporates, causing cracks or dissolution, leaving uncured parts and destroying the sample during cutting or polishing was there.

As described above, for fragile samples that are cracked or broken by heating, or swelled and destroyed by water or oil, etc., there is no need for high-temperature heating, and the methyl methacrylate monomer and azobis that generate 50 ° C or less A method for producing flakes by a dry method using an embedding resin kit (Osteoresin (registered trademark), manufactured by Wako Pure Chemical Industries, Ltd.) comprising an organic polymerization initiator V-601 has been developed (Non-patent Document 1). Since this resin is a room temperature curing type and does not need to be heated at high temperature, the sample is not destroyed at the time of solidification with the resin, and a thin sample for observation with a transmission microscope can be produced.
In the development at that time, a scanning electron microscope and energy dispersion that require polishing with white molten alumina (white alundum) using kerosene as a lubricant on the agate plate at the final polishing stage and further smoothing the surface of the flakes are required. In the case of producing a thin piece used for X-ray spectroscopy, electron beam microanalyzer, reflection microscope, etc., it was attempted to perform final polishing by applying diamond paste to a rotating table of a variable automatic polishing table.

Clay Science Vol. 50, No. 2, p63-68 (2011)

However, the technology at that time had some problems, although it became possible to produce a thin film for a transmission microscope.
In the process of polishing the flakes, the resin in which the sample is embedded has the disadvantage that it is difficult to maintain flatness because it is scraped from the periphery of the sample chip. In addition, the thickness adjustment of the flakes is usually judged by the interference color of the mineral in the polarization microscope observation. For example, when imogolite, which is a transparent gel-like mineral, is embedded in a resin, a standard such as quartz is used. In the sample containing no mineral, there was a fatal problem that there was no means for identifying the thickness of the flakes.

In addition, in the final polishing stage, when cutting oil is used as a lubricating liquid on the agate plate and polishing with an abrasive material, the brittle sample swells and is destroyed by the lubricating liquid. Polishing was sought.
Furthermore, in a fragile sample, when polishing is performed using diamond paste to make the surface of the flakes smoother, the sample swells due to the liquid contained in the paste, or the diamond paste enters the voids in the sample. Then, since it can be removed only by ultrasonic cleaning, there is a problem that the sample is destroyed by the liquid used for ultrasonic cleaning. In addition, the diamond particles contained in the diamond paste have a high hardness and a cutting angle, and the problem that cutting flaws occur on the sample surface remains as a problem. Furthermore, even if diamond paste is applied to the polishing cloth mounted on the rotary variable automatic polishing machine, it cannot be spread evenly, and the polishing speed of the thick specimen passing through the cloth coated with diamond paste is high. Since it was not stable at a constant speed, the soft part was cut too much, which hindered the production of flakes. In polishing using ordinary diamond paste, the rotating plate is rotated at a high speed while dripping the coolant with a variable automatic polishing machine, and polishing is performed for 1 hour or more. In conventional methods, the resin is deformed by heat. However, the fragile sample has the disadvantage that it is destroyed by the frictional heat due to its rotation and the liquid that becomes the coolant.

  Furthermore, when a brittle sample was solidified using the above resin (osteoresin), it was lost during solidification due to the high content of volatile components in the resin, and all of the sample was initially immersed in the liquid. Nevertheless, the sample may be exposed from the liquid surface. In addition, it takes about 3 months to cure, and in some cases, it may not be completely consolidated.

  The present invention has been made in view of the circumstances as described above. Among the naturally occurring minerals, pumice (including allophane and imogolite), clay, diatomaceous earth, manganese nodules, uncalcified fossils, sulfur and salt Scanning electron microscopes, energy dispersive X-ray spectroscopy, electrons, etc. that require highly smooth surface of thin flakes for fragile samples that are weak to heating or swelled and destroyed by water or oil It aims at providing the thin piece used for a line | wire microanalyzer, a reflection microscope, etc.

In order to achieve the above-mentioned object, the present inventors determined the thickness of the flakes even after forming and cutting the sample after being embedded and solidified with a resin, for example, even a transparent gel-like sample that does not contain standard minerals. We examined methods that can be polished while polishing, a polishing method that can smooth the surface of a thin flake without using diamond paste, and a search for resins that can be cured at normal or low temperatures and have a short solidification time. .
As a result of further diligent investigation, after cutting the sample, the sample thickness was added to the four surfaces perpendicular to the surface to be polished of the sample or the surface opposite to the one surface to be polished. It can be cured at room temperature or low temperature as a resin used for pasting minerals or rocks containing such minerals, polishing with silk cloth impregnated with alumina powder, and embedding solidification By using a resin having a short time, the present invention has been completed which can supply a thin piece of a fragile sample having a high degree of surface smoothness.

That is, the present invention for solving the above-described problems is as follows.
[1] A method for producing a thin sample whose upper and lower surfaces are polished using a weak sample that is weak to heating or swelled by water or oil among naturally occurring minerals, and the weak sample is encapsulated with a resin. After solidifying and forming and cutting into a rectangular parallelepiped, a rock or mineral is pasted on 5 surfaces including the 4 surfaces orthogonal to the polished surface of the sample or the surface opposite to the one surface to be polished. Then, a method for producing a thin sample, which is characterized by polishing.
[2] The method for producing a flake sample according to [1], wherein the thickness of the flake sample is prepared by observing the interference color of the rock or mineral using a polarizing microscope.
[3] The method for producing a thin sample according to [1] or [2], wherein a resin that can be cured at normal temperature or low temperature and has a short curing time is used as the resin.
[4] The method for producing a flake sample according to any one of [1] to [3], wherein polishing is performed using a silk cloth impregnated with alumina powder.
[5] Observation with a scanning electron microscope, energy dispersive X-ray spectroscopy, electron beam microanalyzer, or reflection microscope using the thin sample prepared by the method according to any one of [1] to [4] A method for observing and analyzing fragile samples characterized by performing analysis.

  According to the method for producing a thin piece on a fragile sample of the present invention, it can be used for a scanning electron microscope, energy dispersive X-ray spectroscopy, an electron beam microanalyzer, a reflection microscope, etc. that require a highly smooth surface of the thin piece. It has the advantage of becoming.

Photograph of fragile sample impregnated and solidified in embedding resin Photograph of a fragile sample with rocks affixed to five surfaces of the sample excluding the adhesive surface to the slide glass Photograph of silk cloth impregnated with alumina powder Photograph of a thin sample with a highly smooth surface of a fragile sample

The present invention will be described in more detail.
The thin sample preparation method of the present invention is a method of embedding and solidifying a sample using a resin that can be cured at room temperature or low temperature and having a short solidification time. A scanning electron microscope and energy dispersive X-rays that require high-level smoothing of the surface of a thin piece by a polishing method that enables polishing of a fragile sample having high-level surface smoothness. It is characterized by producing a thin piece that can be used in a spectroscopic method, an electron beam microanalyzer, a reflection microscope, and the like. Here, fragile samples are natural minerals such as pumice (including allophane and imogolite), clay, diatomaceous earth, manganese nodules, unfossilized fossils, minerals containing sulfur and salt, water or oil. The sample which swells by is shown.

In the present invention, when solidifying a fragile sample, it is preferable to use a resin that can be cured at room temperature or low temperature and has a short solidification time. As a result of repeated studies on various commercially available resins, the resin contains methyl methacrylate. An embedding resin kit (MMA resin, manufactured by Marto, Inc.) comprising a monomer, a methyl methacrylate polymer, and a polymerization accelerator (benzoyl peroxide BPO), or a resin comprising bisphenol A epoxy resin and 7-dimethyloctanoic acid ( Solidification was performed using Struers, Cardofix). The curing time is less than 2 months by using the MMA resin, and about 1 week for cardofix, which is a significant reduction in time compared to osteoresin, and because there is less loss due to volatilization, there is no exposure of the sample. It became possible to impregnate to a homogeneous state.
In addition, MMA resin and cardofix have water repellency and can avoid swelling due to the coolant used during cutting. Furthermore, since these resins are easy to cut, the cutting time can be shortened, and the heating due to the friction of the cutter blade is suppressed.
In the present invention, MMA resin or cardofix is preferably used as the brittle sample solidifying agent, but as the brittle sample solidifying agent, the sample has excellent permeability and transparency, and does not generate a high temperature during consolidation. Any resin may be used, and the resin is not limited to the above-described solidifying agents, and can be used in the same manner as long as they have the same effect.

In the present invention, after molding and cutting a sample after embedding and solidifying with a resin, the sample is polished after cutting the solidified sample as a method that enables polishing while maintaining the flatness and judging the thickness of the sample. We have developed a method for attaching rocks or minerals to four surfaces that are perpendicular to the surface, or five surfaces that are opposite to the surface to be polished. Surrounding the sample with rocks or minerals has advantages that it can prevent distortion of the sample and missing corners of the sample during polishing, and can suppress part of the sample from being excessively shaved. Furthermore, not only can the thickness of the flakes be judged by the affixed rocks or minerals, but also contamination can be prevented.
In the present invention, granite containing a large amount of quartz, granodiorite containing feldspar, and the like are preferable as the rock or mineral to be attached. These rocks or minerals are not limited to the above-mentioned rocks or minerals, and can be used in the same manner as long as they have the same effect.

In the present invention, polishing using a silk cloth impregnated with alumina powder has been developed as a polishing method that enables fragile specimen flakes having a high degree of surface smoothness. Alumina powder, unlike diamond particles, has low hardness and round particles, so it does not cause cutting flaws. In addition, alumina particles are cheaper than diamond paste, can be reduced in cost, and are readily available. Has advantages. Also, since the alumina particles are impregnated into the silk cloth, the particles are uniformly dispersed and there is no change in the polishing rate, the solvent at the time of impregnation is volatilized, no liquid component remains, and in the silk cloth polishing of the alumina powder impregnation, Since the sample can be cut evenly and quickly, it can be polished for about 10 minutes at a rotation of 50 rpm or less, and the polishing time is about 1/5 to 1/10 when using diamond paste. Therefore, there is an advantage that there is little adverse effect on the sample polishing.
In the present invention, alumina powder is preferably used as an abrasive to be impregnated into silk cloth. These abrasives are not limited to the above-mentioned abrasives, and can be used in the same manner as long as they have the same effect.

  EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited to these at all.

<Example: Preparation of imogolite flakes>
<Moisture removal from imogolite>
If the sample is brittle and fragile, it is usually reinforced with a resin after it has been sufficiently dried, but imogolite shrinks and deforms when dried, so dehydrate the imogolite containing water before impregnating the resin with ethanol. The process to replace with is required.
About soil containing imogolite, what was shape | molded with the knife etc. to the magnitude | size of about 60 mm x 70 mm in length and width and about 30 mm in thickness was used.
1) Put a sample in a container and immerse it in xylene in a sealed state for several days.
2) Remove the sample from the container, absorb the xylene contained in the sample with paper or cloth that is hard to generate dust, avoiding drying of the sample surface, put the sample in the container, and then immerse it in ethanol for several more days. put.
3) Remove the sample from the container, absorb xylene and ethanol contained in the sample with paper or cloth, and immerse in ethanol again for several days in a sealed state.
4) Repeat step 3) and leave it at room temperature until the ethanol has sufficiently penetrated the entire sample.

<Resin embedding>
5) The sample infiltrated with ethanol in 4) is immersed in an embedding resin (manufactured by Struers, cardofix).
6) Vacuum impregnation is performed in a vacuum impregnation apparatus so that the embedded resin penetrates into the sample. At this time, it is necessary to minimize the generation of bubbles by sending outside air in the middle of vacuum impregnation in order to avoid destruction of fragile samples due to bubbles generated in large quantities during vacuum impregnation. .
7) After vacuum impregnation, leave the sample containing uncured embedded resin on polypropylene, vinyl, etc., and remove the embedded resin as much as possible.
8) The sample is vacuum impregnated again by the steps 6) and 7) while suppressing the generation of bubbles with a new embedding resin.
9) After the vacuum impregnation, the whole container containing the sample and the embedding resin is taken out and the whole container is cured at room temperature. For soil samples containing imogolite, soak the entire sample in embedding resin and wait for it to harden at room temperature. On the other hand, for imogolite gel, immerse the entire sample in embedding resin and let it stand at room temperature for 1 week, then transfer the thin-skinned imogolite gel to a small container, put a new embedding resin, and imogolite gel will settle at the bottom of the container And cure at room temperature.
FIG. 1 is a photograph of a fragile sample impregnated in an embedding resin and solidified.

<Molding of sample>
10) Dry-cut the embedded and hardened sample with a band saw using diamond as the blade. Soil samples containing imogolite are cut and molded to about 45 mm x 60 mm and 10 mm thick.
11) Rocks polished to a thickness of about 5mm (those with a certain degree of hardness including standard minerals such as granite, or standard minerals such as quartz themselves) are placed on the four surfaces that are perpendicular to the surface of the sample that is attached to the slide glass. Paste.
12) Polish the surface opposite to the surface to be attached to the slide glass, and apply the polished rock to a thickness of about 5mm. FIG. 2 is a photograph of a fragile sample in which rocks are pasted on the five surfaces of the sample excluding the adhesive surface to the slide glass.

<Polishing the adhesive surface>
The reference surface for attaching the sample to the slide glass is polished. However, when moisture or oil penetrates the sample, imogolite and the like swell, so that the dry method is used here as well.
13) Adhesive is applied to the plate of the variable automatic polishing machine, and circular water-resistant abrasive paper dedicated to precision polishing is applied to the adhesive. For water-resistant abrasive paper, use 320, 500, 800, 1200, 1200, 2400, and 4000 in order. Alternatively, grinding is performed with abrasive paper having finer grain than that, and then washed and dried.
14) Place the sample to be polished in the center of the water-resistant abrasive paper, rotate the disc at a low speed (about 40-50 revolutions / minute), and the abrasive paper once passed from the center of the abrasive paper to the outside or from the outside to the center Polish so that it does not pass repeatedly. When using a fine-grinded abrasive paper, blow off the scraps remaining on the polished surface of the sample with an air gun. In addition, when a sample is dropped on the polished surface, a cyanoacrylate adhesive is dropped to reinforce.
In the polishing process, brushing and cleaning with an air gun are performed so that the abrasive scraps from the previous stage do not remain on the polished surface. In addition, care should be taken to ensure smooth polishing so that there is no step at the boundary between minerals and resins with different hardness.

<Adhesion of sample to slide glass and secondary cutting>
15) A sample is affixed on a slide glass using an epoxy-based room temperature curing type two-component mixed adhesive (cemedine super 60 minute curing type). For slide glass, use 55mm x 78mm.
16) Make the thickness of the epoxy-based room temperature curable two-component mixed adhesive uniform, fix it with a jig so that the sample does not slip and adhere, and let it stand at room temperature for 24 hours to cure the adhesive.
17) Fix the adhesive-cured sample to a dedicated chuck holder and carefully cut it dry using the band saw used in 10). The thickness of the cut sample adhered to the slide glass is about 0.8 mm.
18) In order to prevent the sample from falling off the cut surface, the sample surface is solidified with a cyanoacrylate adhesive.

<Finishing polishing>
19) In the same manner as the polishing process of the adhesive surface by the dry method in 13) and 14), the sample is scraped off while pressing the slide glass with a fingertip at 40 to 50 revolutions. The water-resistant abrasive paper is polished in the order of 320 → 500 → 800 → 1200 → 2400 → 4000 until the thickness of the sample is about 35 microns. Thereafter, polishing is performed with a lapping film No. 6000 (1,5 μm) on which alumina particles are deposited.
The standard thickness of the sample in each polishing step is 100 μm for 320, 80 μm for 500, 60 μm for 800, 40 μm for 1200, 35 μm for 2400 and 4000, and 31 μm for lapping film 6000. If necessary, the sample surface is solidified with a cyanoacrylate adhesive when polishing is finished at No. 320 and the thickness becomes 100 μm.
20) As final polishing, after adding ethyl alcohol to alumina powder (φ1μm) to make a paste, the paste of alumina while rotating the rotating plate on the silk cloth disc attached to the rotating plate of the variable automatic polishing machine Apply evenly. FIG. 3 is a photograph of a silk cloth impregnated with alumina powder. Raise the rotation speed of the turntable and evaporate the alcohol. After that, a slide glass is attached to the holder and polished to 50 μm at 50 revolutions.
FIG. 4 is a photograph of a fragile sample, a flake sample having a highly smooth surface.

Claims (5)

It is a method of making a flake sample whose upper and lower surfaces are polished using a fragile sample that is vulnerable to heating or swells with water or oil among naturally occurring minerals,
After embrittlement of the fragile sample with resin and molding and cutting into a rectangular parallelepiped, 4 surfaces perpendicular to the surface to be polished of the sample, or 5 surfaces including the surface opposite to the one surface to be polished, A method for producing a flake sample, comprising polishing after attaching a rock or mineral.   The method for producing a thin piece sample according to claim 1, wherein the thickness of the thin piece sample is prepared by observing the interference color of the rock or mineral using a polarizing microscope.   The method for producing a flake sample according to claim 1 or 2, wherein a resin that can be cured at normal temperature or low temperature and has a short curing time is used as the resin.   The method for producing a flake sample according to any one of claims 1 to 3, wherein polishing is performed using a silk cloth impregnated with alumina powder.   Observation and analysis by a scanning electron microscope, energy dispersive X-ray spectroscopy, an electron beam microanalyzer, or a reflection microscope is performed using the thin sample prepared by the method according to any one of claims 1 to 4. This is a method for observing and analyzing fragile samples.

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