How to visualize voids in a sample

Abstract

To provide a method for visualizing cavities, which can distinguish between water and an organic matter, which have low X-ray absorption rates.SOLUTION: A method for visualizing cavities of a sample using X-ray CT, comprises preparing a target obtained by filling the cavities of the sample with ionic liquid containing a highly X-ray absorptive component, irradiating the prepared target with X-rays, detecting X-rays that have passed through the target, and obtaining an image of the target with emphasized contrast between the cavities area and other areas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for visualizing voids in a sample, a method for treating a sample for the same, and a composition used therefor. The present invention is useful in various fields, including microstructural analysis of samples such as geological layers. [Background technology]

[0002] It is important to closely observe the geological environment, which is a complex web of minerals and organic matter. For this reason, methods for obtaining information on the fine structure of geological samples have been studied. For example, Patent Document 1 describes a porosity measuring device and measuring method using radon to accurately grasp the internal structure of rocks in three dimensions. This porosity measuring device measures the porosity of a medium based on changes in the concentration of radon gas that occur when radon gas fills the pores of the medium.

[0003] In addition, the resin embedding method commonly used in the field of microscopic observation of biological samples has been applied to the processing of soft, water-rich geological samples, and the resin-embedded geological samples are smoothly cut with a microtome and observed with a scanning electron microscope (SEM), or cross-sectional images are obtained from resin-encapsulated samples by microfocus X-ray CT (Non-Patent Document 1).

[0004] On the other hand, ionic liquids are also called the third liquid, and because of their unique properties, they are used as solvents in separation and purification processes, synthesis and catalytic reactions, and polymer polymerization and depolymerization, and are also used as new electrolytes in electrochemical devices such as lithium-based secondary batteries and non-humidified fuel cells. Furthermore, because ionic liquids have an extremely low vapor pressure, they are used in electron microscope observations as solvents that can be used in a vacuum (Patent Document 2, Non-Patent Document 2).

[0005] There is a report on the use of ionic liquids to investigate the internal structure of seeds that have absorbed water using X-ray micro-CT. In this study, it was reported that by treating the seeds with a high concentration of ionic liquid after fixation with osmium tetroxide, it was possible to prevent deterioration of image quality due to the presence of water, suppress shrinkage of the seeds due to drying during imaging, and enable good observation (Non-Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-52580 A [Patent Document 2] International Publication WO2007 / 083756 (Patent No. 4581100) [Non-patent literature]

[0007] [Non-Patent Document 1] Goichiro Uramoto et al.: Observation of microstructures and microbial cells in marine sediments, Microscope, vol. 51, No. 2: 108-113 (2016) [Non-Patent Document 2] Susumu Kuwahara: Application of ionic liquids as liquid conductive agents to electron microscope observations, Microscope, vol. 48, No. 2: 100-106 (2013) [Non-Patent Document 3] Yamauchi D, et. al. Use of ionic liquid for X-ray micro-CT specimen preparation of imbibed seeds. Microscopy, Vol. 68, No. 1: 92-97 (2019) DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0008] In three-dimensional structural analysis using microfocus X-ray CT, voids and material parts can be distinguished by the difference in X-ray absorption coefficients of the materials that make up the sample. Specifically, in the three-dimensional structure of the sample visualized by the difference in X-ray absorption coefficients, the parts that appear dark due to low X-ray absorption coefficients are recognized as voids. However, in the case of geological samples containing minerals with low X-ray absorption coefficients, organic matter consisting of carbon, nitrogen, oxygen, and hydrogen has low X-ray absorption coefficients, just like the water present in the voids. Therefore, in the case of geological samples containing minerals with high X-ray absorption coefficients, it is not expected that contrast sufficient to distinguish voids from organic matter can be obtained, and it can be said that there is no method to visualize true voids. There is a need for a method to distinguish water and organic matter, both of which have low X-ray absorption coefficients, and to visualize voids. [Means for solving the problem]

[0009] The present inventors have been actively studying the development and improvement of sample processing techniques related to the microstructural analysis of geological samples, etc. As a result, they have now devised a method for visualizing pores in a geological sample by permeating the sample with an ionic liquid containing iodine and observing the sample with an X-ray CT, thereby completing the present invention. The present invention provides the following.

[0010] [1] A method for visualizing voids in a sample using X-ray CT, comprising: A specimen is prepared by filling the voids in the sample with an ionic liquid containing a highly X-ray absorbing component. The prepared specimen is irradiated with X-rays, and the X-rays that pass through the specimen are detected to obtain an image of the specimen in which the contrast between the void areas and other areas is emphasized. A method comprising the steps of: [2] The method according to claim 1, wherein the highly X-ray absorbing component is a component containing iodine. [3] The method according to 1 or 2, wherein the X-ray CT is a microfocus X-ray CT or a synchrotron source X-ray micro-CT. [4] The method according to any one of 1 to 3, wherein the step of preparing a specimen in which the voids of the sample are filled with an ionic liquid containing a component having high X-ray absorption is carried out by a treatment including the steps of: The sample is embedded in an aqueous gel, and the voids in the sample are filled with the aqueous gel; A process in which a sample embedded in an aqueous gel is immersed in an ionic liquid, replacing the water with the ionic liquid, thereby filling the voids in the sample with the ionic liquid. [5] A method for preparing a specimen for X-ray CT, comprising the steps of: Embedding a sample having voids with an aqueous gel, filling the voids of the sample with the aqueous gel, The sample embedded in the aqueous gel is immersed in ionic liquid, and the voids in the sample are filled with ionic liquid by replacing the water with ionic liquid. A method of making the same, comprising the steps of: [6] A method for visualizing voids in a sample using X-ray CT, comprising: Embedding a sample having voids with an aqueous gel, filling the voids of the sample with the aqueous gel, The sample embedded in the aqueous gel is immersed in an ionic liquid, and the water is replaced with the ionic liquid to create a specimen in which the voids in the sample are filled with the ionic liquid. The prepared specimen is irradiated with X-rays, and the X-rays that pass through the specimen are detected to obtain an image of the specimen in which the contrast between the void areas and other areas is emphasized. A method comprising the steps of: [7] A composition for preparing a specimen for X-ray CT, comprising: A. Ionic liquids containing iodine, and An ionic liquid that is miscible with BA and has lower X-ray absorption than A. [8] The composition according to 7, wherein the mass ratio of A (A / (A+B)) is 20 to 40%. Effect of the Invention

[0011] By using an ionic liquid containing a highly X-ray absorbing component in the method of the present invention, voids in a sample can be brightly displayed in a CT image (contrast is enhanced).

[0012] By using an ionic liquid containing a highly X-ray absorbing component together with an ionic liquid for dilution that does not contain a highly X-ray absorbing component, the X-ray absorption efficiency of the voids in the sample can be controlled.

[0013] In addition, in the case of geological samples in which water exists in the pores, the method of the present invention replaces the water with an ionic liquid, which prevents the water from being gasified by the energy of the X-rays and the resulting deformation of the sample. X-ray micro-CT scanning using a synchrotron light source such as SPring-8 is also possible, enabling multi-scale structural analysis of samples. In addition, in measurements using a synchrotron light source, iodine-specific contrast enhancement is possible by taking the difference between tomographic images scanned around the K-absorption edge energy of iodine (33.169 kiloelectron volts), where the X-ray absorption coefficient changes sharply, enabling more selective visualization of pores. [Brief description of the drawings]

[0014] [Figure 1] Microfocus X-ray CT images of a geological sample. (A) The geological sample was photographed as is. (B) The sample was photographed after being infiltrated with an ionic liquid containing iodine. In (A), the dark gray areas are voids. Without ionic liquid, the voids absorb very little X-rays, so they appear dark in the CT image. In (B), the ionic liquid has infiltrated the voids, increasing X-ray absorption in the voids, so the voids appear brighter in the CT image (enhanced contrast). [Diagram 2] Microfocus X-ray CT image of a simulated geological sample taken without using ionic liquid. [Diagram 3] Microfocus X-ray CT image of a simulated geological sample taken after being infiltrated with an ionic liquid that does not contain iodine. [Figure 4] Microfocus X-ray CT image of a simulated geological sample taken after being infiltrated with an ionic liquid containing iodine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention relates to a method for visualizing voids in a sample using X-ray CT.

[0016] [Ionic Liquid] In the present invention, ionic liquid is used to treat samples observed by X-ray CT. Ionic liquid is a salt having a melting point near room temperature, and is a liquid consisting of only ions. In ionic liquid, one or both of the cation and anion are organic ions with a variety of structural changes, and the number of types of ionic liquid is enormous because it is the number of types of cations x the number of types of anions.

[0017] It is important that the ionic liquid used in the present invention is liquid under the conditions for treating the sample. As long as it is liquid when treating the sample and can fill the voids in the sample, there is no problem if it is solid when scanning with X-ray CT. In the present invention, a mixture of multiple ionic liquids can be used.

[0018] (Ionic liquid containing components with high X-ray absorption) Furthermore, the ionic liquid used in the present invention may contain at least one type of highly X-ray absorbing component (anionic component or cationic component). In the present invention, when referring to an ionic liquid or a component thereof as being highly X-ray absorbing, unless otherwise specified, it means that the ionic liquid or a component thereof is at least more X-ray absorbing than water, and preferably more X-ray absorbing than a component contained in a relatively large amount in a target sample, and therefore when the ionic liquid is filled into the voids of the sample and subjected to an X-ray CT scan, the voids can be displayed bright enough in the image to be distinguishable from other parts.

[0019] An example of a component with high X-ray absorption is a component containing any one selected from the group consisting of iodine, bromine, and chlorine. Iodine is preferable. Iodine has a large atomic number and a high X-ray absorption rate. A reagent containing iodine is used as a contrast agent in general-purpose CT imaging, and by permeating the sample, it is possible to enhance the image contrast between the iodine permeation site and the rest. Note that when a component is contained, the component is included in the form of ions or atoms.

[0020] An example of the ionic liquid containing a highly X-ray absorbing component used in the present invention is an iodine-based ionic liquid. Note that, although the present specification may be described by taking as an example a case where the ionic liquid containing a highly X-ray absorbing component is an iodine-based ionic liquid, the description also applies to the case where other ionic liquids containing a highly X-ray absorbing component are used.

[0021] The cationic component of the iodine-based ionic liquid used in the present invention is not particularly limited. Examples of the cationic component include ammonium-based, imidazolium-based, phosphonium-based, pyridinium-based, pyrrolidinium-based, etc.

[0022] More specifically, examples of ammonium-based cations include tributylmethylammonium, ethyldimethylpropylammonium, 2-hydroxyethyl-trimethylammonium, methyltrioctylammonium, tributylammonium, tetraethylammonium, tetraheptylammonium, triethylmethylammonium, and tris(2-hydroxyethyl)methylammonium. Examples of imidazolium-based cations include 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-ethyl-3-propylimidazolium, 1-propyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-methyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1-hexyl-2,3-dimethylimidazolium, and 1-octyl-2,3-dimethylimidazolium. Examples of phosphonium-based cations include tributylmethylphosphonium, ethyldimethylpropylphosphonium, 2-hydroxyethyl-trimethylphosphonium, methyltrioctylphosphonium, tributylphosphonium, tetraethylphosphonium, tetraheptylphosphonium, triethylmethylphosphonium, and tris(2-hydroxyethyl)methylphosphonium. Examples of pyridinium-based cations include 1-butyl-3-methylpyridinium, 1-butyl-4-methylpyridinium, 1-ethyl-1-methylpyrrolidinium, 1-octyl-4-methylpyridinium, 1-methylpyridinium, 1-butylpyridinium, and 1-hexylpyridinium. Examples of pyrrolidinium-based cations include 1-butyl-1-methylpyrrolidinium, 1-butyl-1-methylpyrrolidinium, and 1-ethyl-1-methylpyrrolidinium. Other examples of cations include 1-butyl-1-methylpiperidinium, choline, and triethylsulfonium.

[0023] Particularly preferred examples of the ionic liquid containing a component with high X-ray absorption used in the present invention are ionic liquids containing ammonium salts such as tetraethylammonium iodide, tetrapropylammonium iodide, and tetrabutylammonium iodide, imidazolium salts such as dimethylpropylimidazolium iodide, 1-methyl-3-propylimidazolium iodide, and 1-ethyl-3-butylimidazolium iodide, methyltriphenylphosphonium iodide, and isopropyltriphenylphosphonium iodide. Note that although some of these iodine-containing substances are solid at room temperature, they can be used in the present invention as components of ionic liquids as long as they are in a liquid state when a sample is treated, for example by mixing with another ionic liquid.

[0024] <Other ionic liquids> Examples of anion components other than iodine contained in the other ionic liquid used in the present invention include bisfluorosulfonylimide-based anions, fluorinated sulfonic acid-based anions, fluorinated carboxylate-based anions, thiocyanate-based anions, dicyanamide-based anions, and tetracyanoborate-based anions.

[0025] More specifically, examples of the bisfluorosulfonylimide anion include bisfluorosulfonylimide, bistrifluoromethylsulfonylimide, and bistrifluorobutanesulfonylimide. Examples of fluorinated sulfonic acid anions include tetrafluoroborate, hexafluoroborate, and trifluoromethylsulfonate. An example of a fluorinated carboxylate anion is trifluoroacetic acid. The cation component of the ionic liquid having such an anion component used in the present invention is not particularly limited, and may be any of the anion components listed for the iodine-based ionic liquid.

[0026] In a preferred embodiment of the present invention, a mixture of an ionic liquid having high X-ray absorption, such as an iodine-based ionic liquid, and another ionic liquid is used. According to the inventor's study, when a sample is treated using only an iodine-based ionic liquid and X-ray CT is performed, the X-ray absorption of the voids may increase too much, resulting in a significant decrease in the X-ray transmittance of the entire sample. Therefore, by using an ionic liquid having low X-ray absorption as an ionic liquid for dilution, the X-ray absorption of the voids can be controlled.

[0027] From this viewpoint, in a preferred embodiment of the present invention, examples of the ionic liquid used together with the ionic liquid having high X-ray absorption include salts of alkyl-, hydroxyalkyl- and / or aryl-substituted imidazolium cations and tetrafluoroborate anions. Specific examples of such salts include 1,3-dimethylimidazolium tetrafluoroborate, 1-benzyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-methyl-3-propylimidazolium tetrafluoroborate, and 1,3-dimethylimidazolium tetrafluoroborate. imidazolium tetrafluoroborate, 1-methyl-3-octylimidazolium tetrafluoroborate, 1-methyl-3-tetradecylimidazolium tetrafluoroborate, 1-methyl-3-phenylimidazolium tetrafluoroborate, 1,2,3-trimethylimidazolium tetrafluoroborate, 1,2-methyl-3-octylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-hexyl-2,3-methylimidazolium tetrafluoroborate, and 1-(2-hydroxyethyl)-2,3-dimethylimidazolium tetrafluoroborate.

[0028] Examples of the ionic liquid in another preferred embodiment include salts of alkyl-, hydroxyalkyl- and / or aryl-substituted imidazolium cations and bis(trifluoromethylsulfonyl)imide anions. Specific examples of the ionic liquid include 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, 1-benzyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-methyl ... imide, 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide, 1-methyl-3-tetradecylimidazolium bis(trifluoromethylsulfonyl)imide, 1-methyl-3-phenylimidazolium bis(trifluoromethylsulfonyl)imide, 1,2,3-trimethylimidazolium bis(trifluoromethylsulfonyl)imide, 1,2-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-2,3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-(2-hydroxyethyl)-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide.

[0029] Examples of ionic liquids in another preferred embodiment include salts of alkyl-, hydroxyalkyl- and / or aryl-substituted imidazolium cations and cyanate anions, specifically 1,3-dimethylimidazolium dicyanate, 1-benzyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium tricyanomethane, 1-ethyl-3-methylimidazolium dicyanate, 1-hexyl-3-methylimidazolium thiocyanate, and 1-methyl-3-propylimidazolium tricyanomethane. , 1-methyl-3-octylimidazolium dicyanate, 1-methyl-3-tetradecylimidazolium thiocyanate, 1-methyl-3-phenylimidazolium dicyanate, 1,2,3-trimethylimidazolium thiocyanate, 1,2-methyl-3-octylimidazolium tricyanomethane, 1-butyl-2,3-dimethylimidazolium dicyanate, 1-hexyl-2,3-methylimidazolium thiocyanate, and 1-(2-hydroxyethyl)-2,3-dimethylimidazolium tricyanomethane.

[0030] Examples of the ionic liquid in another preferred embodiment include salts of alkyl-, hydroxyalkyl- and / or aryl-substituted imidazolium cations and tetracyanoborate anions. Specific examples of the ionic liquid include 1,3-dimethylimidazolium tetracyanoborate, 1,3-dimethylimidazolium tetracyanoborate, 1-benzyl-3-methylimidazolium tetracyanoborate, 1-butyl-3-methylimidazolium tetracyanoborate, 1-ethyl-3-methylimidazolium tetracyanoborate, 1-hexyl-3-methylimidazolium tetracyanoborate, 1-methyl-3-propyl ... imidazolium tetracyanoborate, 1-methyl-3-octylimidazolium tetracyanoborate, 1-methyl-3-tetradecylimidazolium tetracyanoborate, 1-methyl-3-phenylimidazolium tetracyanoborate, 1,2,3-trimethylimidazolium tetracyanoborate, 1,2-methyl-3-octylimidazolium tetracyanoborate, 1-butyl-2,3-dimethylimidazolium tetracyanoborate, 1-hexyl-2,3-methylimidazolium tetracyanoborate, and 1-(2-hydroxyethyl)-2,3-dimethylimidazolium tetracyanoborate.

[0031] Examples of the ionic liquid in another preferred embodiment include salts of alkyl-, hydroxyalkyl- and / or aryl-substituted imidazolium cations and tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate anions, specifically, 1,3-dimethylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-benzyl-3-methylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-Butyl-3-methylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-Ethyl-3-methylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-Hexyl-3-methylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-Methyl-3-propylimidazolium 1-Methyl-3-octylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-Methyl-3-tetradecylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-Methyl-3-tetradecylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-Methyl-3-phenylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate 1,2,3-trimethylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1,2-methyl-3-octylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-butyl-2,3-dimethylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate, 1-hexyl-2,3-methylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate and 1-(2-hydroxyethyl)-2,3-dimethylimidazolium tetrakis-(p-(dimethyl(1H,1H,2H,2H-perfluorooctyl)silyl)phenyl)borate.

[0032] In another preferred embodiment, examples of the ionic liquid include salts of alkyl-, hydroxyalkyl- and / or aryl-substituted imidazolium cations and hexafluorophosphate anions, specifically, 1,3-dimethylimidazolium hexafluorophosphate, 1-benzyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-methyl-3-propylimidazolium hexafluorophosphate, 1 1-methyl-3-octylimidazolium hexafluorophosphate, 1-methyl-3-tetradecylimidazolium hexafluorophosphate, 1-methyl-3-phenylimidazolium hexafluorophosphate, 1,2,3-trimethylimidazolium hexafluorophosphate, 1,2-methyl-3-octylimidazolium hexafluorophosphate, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-hexyl-2,3-methylimidazolium hexafluorophosphate, and 1-(2-hydroxyethyl)-2,3-dimethylimidazolium hexafluorophosphate.

[0033] Examples of ionic liquids in other preferred embodiments include 1-ethyl-3-methylimidazolium tetrachloroaluminate, 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-butyl-3-methylimidazolium methyl sulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-butyl 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium tetracyanoborate, 1-butyl-1-methyl-pyrrolidinium dicyanamide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoroacetate, and 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide.

[0034] Composition for preparing specimens for X-ray CT In one preferred embodiment of the present invention, an ionic liquid having high X-ray absorption, such as an iodine-based ionic liquid, is mixed with another ionic liquid. This makes it possible to control the X-ray absorption efficiency of the voids in the sample. That is, the present invention also provides a composition for treating a sample to be scanned by X-ray CT, comprising: A. Ionic liquids with high X-ray absorption, such as iodine-based ionic liquids, and An ionic liquid that is miscible with BA and has lower X-ray absorption than A.

[0035] The mixing ratio of the ionic liquid with high X-ray absorption and the other ionic liquid can be appropriately set according to the sample. For example, when mixing an iodine-based ionic liquid (A) with an ionic liquid with low X-ray absorption (B), the content mass ratio of A (A / (A+B)) may be 1 to 90%, 5 to 80%, 10 to 60%, or 20 to 40%. When measuring with a general-purpose microfocus X-ray CT scanner, it is preferable to use a high concentration of an ionic liquid with high X-ray absorption from the viewpoint of making the ionic liquid have as high a contrast as possible from the sample constituents. On the other hand, when measuring with a microCT using synchrotron radiation X-rays at energies around the iodine K absorption edge, it is preferable to mix the ionic liquid so that it has a lower contrast than the sample constituents before the K absorption edge and a higher contrast than the sample constituents after the K absorption edge. From this viewpoint, the content mass ratio (A / (A+B)) is recommended to be 20 to 40%.

[0036] When measuring a sample such as a geological layer containing water, it is preferable that the iodine-based ionic liquid (A) and other ionic liquids with low X-ray absorption (B) are also miscible with water.

[0037] [Sample processing and specimen preparation] In the present invention, a specimen is prepared by filling the voids in the sample with an ionic liquid having a large X-ray absorption coefficient. Preparation can be rephrased as manufacturing or production (Article 2, Paragraph 3, Item 3 of the Patent Law).

[0038] The preparation of the specimen in the present invention can be carried out by various means so that the voids in the sample are filled with the ionic liquid and the water contained in the sample is replaced with the ionic liquid, but preferably, the preparation is carried out by embedding the sample in an aqueous gel, filling the voids in the sample with the aqueous gel, and then immersing the aqueous gel-embedded sample in the ionic liquid. By immersion in the ionic liquid, the water contained in the sample is replaced with the ionic liquid and the voids in the sample are filled with the ionic liquid.

[0039] A preferred example of the aqueous gel used in the present invention is a polysaccharide gel or a protein gel, because these have low X-ray absorption and have little effect on the observation of the sample. Examples of materials constituting the polysaccharide gel include agar (agarose), carrageenan, pectin, gellan gum, alginic acid or a salt thereof. Examples of materials constituting the protein gel include gelatin, collagen, elastin, fibronectin, laminin, entactin, heparin or a salt thereof.

[0040] In a preferred embodiment, agar is used as the aqueous gel material, more preferably agar with a low melting point. Since it is a low-viscosity liquid above a certain temperature, it is easy to fill fine voids in the sample, and since it is easily gelled and solidified by lowering the temperature, and since it has relatively high mechanical strength, it is easy to process it with a cutting tool or the like and shape it. With regard to the melting point of agar, "low" means that it is lower than the melting point of general agar, which is 85 to 93°C, specifically, 80°C or lower, preferably 75°C or lower, and more preferably 70°C or lower. In the following, the process of treating the sample and preparing the specimen may be described using agar gel as an aqueous gel, but the description also applies to the case where other aqueous gels are used.

[0041] When using low-melting agar gel, the concentration of the agar can be appropriately adjusted depending on the sample to be embedded. For example, when embedding a geological sample, the concentration of the low-melting agar can be 0.5 to 3%, preferably 1 to 2%.

[0042] The specimen embedded in the aqueous gel and with the water replaced by the ionic liquid is molded as necessary before scanning with an X-ray CT. The molding is performed taking into consideration the settings of the device used and the pixel size of the CT reconstructed image obtained by the measurement. The CT reconstructed image obtained by many general-purpose microfocus X-ray CT scanners and synchrotron radiation X-ray micro CT has 1024 pixels in both length and width. Therefore, for example, when the pixel size is 5 microns, the length and width of the sample is set to 10 mm or less, preferably 7.5 mm or less, for example 5 mm or less, and when the pixel size is 1 micron, the size is set to 5 mm or less, preferably 2 mm or less, for example 1 mm or less, so that the sample can be measured within the image.

[0043] [X-ray CT scan] The specimen can be mounted on a sample stage and subjected to X-ray CT scanning. The X-ray CT device used in the present invention is not particularly limited in terms of the X-ray source, scanning method, etc., and various types can be used. For example, a microfocus X-ray CT device or a synchrotron light source X-ray micro CT device can be used.

[0044] In the specimen processed and prepared according to the present invention, the voids are filled with an ionic liquid containing a component that is highly X-ray absorbing. In the specimen thus constructed, the voids are brightly displayed and visualized when observed with X-rays.

[0045] In the present invention, even if the sample contains water, the water in the prepared specimen is replaced with a non-volatile ionic liquid, which prevents deformation due to gasification during observation and allows observation of voids in a natural state.

[0046] The present invention also enables X-ray micro-CT scanning of geological samples using a synchrotron light source such as SPring-8, enabling multi-scale structural analysis of samples. In addition, in measurements using a synchrotron light source, iodine-specific contrast enhancement can be achieved by taking the difference between tomographic images scanned around the K-absorption edge energy of iodine (33.169 kiloelectron volts), where the X-ray absorption coefficient changes sharply, enabling more selective visualization of voids.

[0047] 〔sample〕 The present invention makes it possible to visualize the voids in various samples. As long as the voids are connected to the outside and allow the introduction of ionic liquid, it becomes possible to clearly observe various voids. Examples of samples having such voids include strata, rocks, shells, sediments, coagulated materials, foamed materials, dried materials, pathological tissues, bones, plant tissues, microflora, fermented materials, foods, molded products, castings, solidified materials, various materials and ingredients, and instruments.

[0048] Examples of the present invention are shown below, but the present invention is not limited to the following examples. EXAMPLES

[0049] [Ionic liquid impregnation treatment protocol] [Equipment used] ·Electronic balance Incubator (thermostat) Rotator Hot stirrer

[0050] [Equipment used] Spatula A straw or a syringe with the tip cut off ·pipette Plastic rod Plastic tubes ·beaker Scalpel

[0051] [Reagents used] ·Pure water Low melting point agarose Ionic liquids containing iodine · Ionic liquid for dilution (ionic liquid that does not contain iodine)

[0052] [Measuring equipment] Microfocus X-ray CT ·Synchrotron source X-ray micro-CT

[0053] [Processing Procedure] Before sampling, prepare an aqueous solution by dissolving 1-2% by weight of agarose in pure water and dispense it into a plastic tube. The tube is placed in a thermostatic bath (incubator) whose temperature is set to the gelling temperature of the agarose or higher.

[0054] A straw or a cut-off syringe is then inserted into the core sample to subsample it.

[0055] [Table 1]

[0056] Next, create spaces on both ends of the straw or syringe that was used for subsampling. The space inside the straw is created by using a plastic rod with a thickness that matches the inner diameter of the straw, and the space inside the syringe is created by adjusting the plunger (see diagram below).

[0057] [Table 2]

[0058] Add a drop of agarose into one of the spaces and allow it to solidify. [Table 3]

[0059] After that, place the straw or syringe into the plastic tube containing the melted agarose and leave it for at least half a day. For the syringe, pull out the plunger when putting the sample into the tube. During this time, you can shake the tube in an incubator to promote the penetration of the agarose solution. After half a day or more has passed, lower the temperature of the tube to solidify the agarose.

[0060] [Table 4]

[0061] Meanwhile, prepare a plastic tube into which ionic liquid has been dispensed. Once the agarose has solidified, remove the straw or syringe from the tube. Then, push the sample into the tube into which ionic liquid has been dispensed, and immerse the sample in the ionic liquid. When pushing out the sample, use a plastic rod whose diameter matches the inner diameter of the straw or syringe, or use a plunger for a syringe. Place the tube with the sample immersed in it on a shaker (rotator) and leave it for at least half a day.

[0062] [Table 5]

[0063] The sample permeated with the ionic liquid is molded and then scanned by X-ray CT. Sample molding is performed taking into consideration the settings of the device and the pixel size of the CT reconstructed image obtained by measurement. CT reconstructed images obtained with most general-purpose microfocus X-ray CT scanners and synchrotron radiation X-ray micro CT have 1024 pixels in both length and width. Therefore, for example, if the pixel size is 5 microns, the length and width of the sample should be approximately 5 mm or less, and if the pixel size is 1 micron, approximately 1 mm or less, then measurements can be made with the sample contained within the image. The molded sample is mounted on a sample stage and CT scanning is performed.

[0064] [Experimental Example 1: Preparation of specimens from geological samples and visualization] Using the above procedure, a specimen with a diameter of 5 mm was prepared from a geological sample (quartz sand, Fujifilm Wako Pure Chemical Industries, Ltd.), and observed using a microfocus X-ray CT with a pixel size of 5um / pixel.

[0065] [Materials, equipment, etc.] Low melting point agarose: Sea Plaque GTG Agarose (Lonza Japan Co., Ltd.), melting point is about 65℃ at 1.5% Ionic liquid: 1-propyl-3-methylimidazolium iodide (Kanto Chemical Co., Ltd.) Equipment: Xradia Versa 410 microfocus X-ray CT scanner (Carl Zeiss X-ray Microscopy)

[0066] Figure 1 shows microfocus X-ray CT images of the obtained geological sample. (A) The geological sample was photographed as is. (B) The sample was photographed after infiltrating iodine-containing ionic liquid. In (A), the dark gray areas are voids. When ionic liquid is not used, the voids hardly absorb X-rays, so they appear dark in the CT image. In (B), the ionic liquid has infiltrated the voids, increasing the X-ray absorption in the voids, so the voids appear brighter in the CT image (enhanced contrast).

[0067] [Experimental Example 2: Visualization of simulated geological samples] A simulated geological sample was created by mixing glass beads with voids that are impermeable to liquids with minerals and organic matter. The simulated geological sample was infiltrated with water and ionic liquids with and without iodine, and the brightness of the image components was confirmed by CT scanning.

[0068] [material] <Simulated geological particles> Glass beads (hollow beads made of sodium borosilicate glass): Q-CEL 7014 (registered trademark), Potters-Barotini Co., Ltd. Minerals: Quartz sand (Fujifilm Wako Pure Chemical Industries, Ltd.) Organic material (polystyrene beads (specific gravity 1.04-1.09)): Abacus beads, approx. 4 mm, Daiso Industries Co., Ltd.

[0069] <solvent> ·Ultra pure water (Milli-Q water) · Iodine-free ionic liquid: 1-methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide (Tokyo Chemical Industry Co., Ltd.) · Ionic liquid containing iodine: 1-propyl-3-methylimidazolium iodide (Kanto Chemical Co., Ltd.)

[0070] [method] The quartz sand and plastic beads were crushed in a mortar and sieved through 250um and 100um sieves, and the material remaining on the 100um sieve was used. Q-CEL, quartz sand, and plastic beads were mixed in each solvent and CT scanned using the same device as in Experimental Example 1, and the images obtained were compared.

[0071] [result] <Sample using ultrapure water> In the CT image (Figure 2) of the sample mixed with ultrapure water, the brightness of the image for each element was quartz sand (light gray) > ultrapure water (gray) ≒ plastic beads (gray) > voids inside the glass beads (dark gray). The measurement conditions are as follows:

[0072] 100kV, 10W Exposure time 3 seconds Number of projections: 3201 -Pixel size: 4.71um / pixel

[0073] In this case, the ultrapure water and the plastic beads could not be distinguished from each other, resulting in what appeared to be large voids. Therefore, this method cannot distinguish the substances made up of light elements in the strata from voids.

[0074] <Sample using ionic liquid that does not contain iodine> In the CT image of the sample using iodine-free ionic liquid (Figure 3), the brightness of the image for each element was as follows: quartz sand (light gray) > iodine-free ionic liquid (gray) > plastic beads (dark gray) > voids inside glass beads (black). The measurement conditions are as follows:

[0075] 40kV, 10W Exposure time 5 seconds, Number of projections: 3201 -Pixel size: 4.984um / pixel

[0076] In this case, the higher density of the iodine-free ionic liquid made it possible to distinguish between the plastic and the ionic liquid.

[0077] <Sample using ionic liquid containing iodine> In the CT image of the sample using ionic liquid containing iodine (Figure 4), the brightness of the image for each element was ionic liquid containing iodine (light gray) > quartz sand (gray) > plastic beads = voids inside glass beads (dark gray). The measurement conditions are as follows:

[0078] 90kV, 10W Exposure time 3 seconds Number of projections: 3201 -Pixel size: 4.984um / pixel

[0079] In this case, the voids inside the glass beads remain dark because the ionic liquid does not penetrate them, but the brightness of the image in voids other than the voids in the glass beads that have been penetrated by the ionic liquid is inverted from that of the quartz sand, etc. [Industrial Applicability]

[0080] According to the present invention, minute pores in a geological sample can be analyzed. In addition to geological samples, various samples having pores into which an ionic liquid can be introduced can also be analyzed.

Claims

1. 1. A method for visualizing porosity in a mineral-containing sample using X-ray CT, comprising: A specimen is prepared by filling the voids in the sample with an ionic liquid containing a component with high X-ray absorption properties, The prepared specimen is irradiated with X-rays, and the X-rays that pass through the specimen are detected to obtain an image of the specimen in which the contrast between the void area and other areas is emphasized. A method comprising the steps of:

2. The method according to claim 1 , wherein the component having high X-ray absorption is a component containing any one selected from the group consisting of iodine, bromine, and chlorine.

3. The method according to claim 1 or 2, wherein the X-ray CT is microfocus X-ray CT or synchrotron source X-ray micro-CT.

4. The method according to any one of claims 1 to 3, wherein the step of preparing a specimen in which the voids of a sample are filled with an ionic liquid containing a component having high X-ray absorption is carried out by a process including the steps of: The sample is embedded in an aqueous gel, and the voids in the sample are filled with the aqueous gel; A process in which a sample embedded in an aqueous gel is immersed in an ionic liquid, replacing the water with the ionic liquid, thereby filling the voids in the sample with the ionic liquid.

5. A method for preparing a specimen for X-ray CT, comprising the steps of: Embedding a mineral-containing sample having voids in an aqueous gel, filling the voids of the sample with the aqueous gel; The sample embedded in the aqueous gel is immersed in ionic liquid, and the voids in the sample are filled with ionic liquid by replacing the water with ionic liquid. A method of making the same, comprising the steps of:

6. 1. A method for visualizing porosity in a mineral-containing sample using X-ray CT, comprising: Embedding a sample having voids with an aqueous gel, filling the voids of the sample with the aqueous gel, The sample embedded in the aqueous gel is immersed in an ionic liquid, and the water is replaced with the ionic liquid to create a specimen in which the voids in the sample are filled with the ionic liquid. The prepared specimen is irradiated with X-rays, and the X-rays that pass through the specimen are detected to obtain an image of the specimen in which the contrast between the void area and other areas is emphasized. A method comprising the steps of:

7. A composition for preparing a specimen for X-ray CT from a mineral-containing sample, the composition comprising: A. An ionic liquid containing iodine, and B. An ionic liquid that is miscible with A and has lower X-ray absorption than A.

8. The composition according to claim 7, wherein the content by mass of A (A / (A+B)) is 20 to 40%.

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