A sample preparation method for scanning electron microscope analysis of three-dimensional porous materials

Abstract

The application discloses a sample production method for three-dimensional porous material scanning electron microscope (SEM) topography analysis, and takes three-dimensional porous material with rich micro-pore structure as a topography observation object. The method utilizes good ion conductivity of room-temperature ionic liquid and non-destructive infiltration of the sample to comprehensively increase the conductivity of the sample, so that a high-quality SEM image without charging effect is obtained. The method can solve the problem that, when a conductive film is plated to increase the conductivity of the sample at the present stage, each pore wall, net and sheet layer of the three-dimensional porous material cannot be sputtered with conductive particles, and the conductivity of the material cannot be comprehensively and non-dead-angle increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of increasing the conductivity of three-dimensional porous materials in the SEM test process with an ionic liquid mixture. More specifically, it relates to a method of infiltrating a three-dimensional porous sample with an ionic liquid mixture to increase the conductivity, thereby reducing or even eliminating the charging effect generated in the SEM test process and improving the quality of the observed SEM images. BACKGROUND

[0002] Three-dimensional porous, structured porous materials have a wide range of applications in catalysis, adsorption, energy storage, and biomedical fields due to their high specific surface area, high porosity, low density, and good diffusion performance. The geometric characteristics of three-dimensional materials greatly affect many basic properties and use functions of the materials, especially for high porosity and high specific surface area materials, the microtopography is one of the important factors affecting their application and performance. Therefore, the analysis and characterization of the microtopography of three-dimensional materials is of great significance. However, for three-dimensional materials with complex microstructure, the elasticity and brittleness of the three-dimensional skeleton and the poor conductivity make it difficult to observe the SEM morphology, resulting in obvious shaking, drifting and obvious charging whitening phenomenon, which reduces the image quality. Therefore, the problems of difficult fixation and poor conductivity of three-dimensional materials need to be solved by changing the sample preparation method and improving the conductivity of the sample.

[0003] The most common method to reduce the charging effect in the SEM test process is to use an ion sputtering instrument to sputter a conductive layer to change the conductivity of the sample surface, so that the charge accumulated on the sample surface can be discharged through the sample stage, thereby effectively eliminating or reducing the influence of the charging effect on the test results, and also improving the sample imaging quality. However, the method of using a sputter coater to sputter a conductive film can only sputter a conductive film on the sample surface, and for three-dimensional porous, network, and sheet structure solids with complex spatial structure, the conductive film is mainly concentrated on the surface layer, and the sputtering efficiency of the sample's subsurface and side surface is poor, which can easily lead to uneven conductivity of the sample as a whole and poor observation effect. Therefore, the sample preparation method for improving the uniformity and integrity of the conductive film of three-dimensional porous, network, and sheet structure samples has become a difficult point.

[0004] Currently, due to the negligible vapor pressure and relatively high ionic conductivity of room temperature ionic liquids at room temperature, the room temperature ionic liquid can be used to replace the conductive layer sputtered by the gold spraying instrument to conductive treatment of the sample. The dilution of 1-ethyl-3-methyl imidazole tetrafluoroborate ionic liquid and ethanol and / or acetone is used for conductive pretreatment of the insulating sample, which has the advantages of low cost and simple operation, but it does not pay attention to the structural stability and polarity of the sample. First, the dilution of the ionic liquid is directly added on the surface of the sample, which is easy to deform the sample, resulting in the accuracy of the analysis data being affected. Second, the polarity of a single ionic liquid is fixed, and it is difficult to have good wettability for the sample that does not match the polarity, and it is impossible to obtain uniform wettability of the ionic liquid on the three-dimensional material surface, so as to improve the conductivity of the sample. Therefore, the polarity of the sample and the dilution of the ionic liquid is also a decisive factor affecting the uniformity and integrity of the conductive film of the ionic liquid. SUMMARY

[0005] Based on the above problems, the purpose of the present application is to provide a three-dimensional porous material scanning electron microscope topography analysis sample preparation method. The sample preparation method in the present application is simple, efficient and low in cost, and the method can significantly improve the scanning electron microscope image quality of the three-dimensional porous material, which has a very important significance for the analysis and characterization of the microstructure of the three-dimensional material.

[0006] The present application provides a three-dimensional porous material scanning electron microscope topography analysis sample preparation method, comprising the following steps:

[0007] Shearing the porous material into a suitable size;

[0008] The porous material is adhered in the conductive groove, and the conductive groove is an open-top container prepared from a conductive material;

[0009] A miscible solution of room temperature ionic liquid and solvent is prepared;

[0010] The room temperature ionic liquid refers to one or more than two (melting point ≤ 30℃) of the molten salt which is in liquid state at room temperature or near room temperature (20-30℃); usually composed of specific organic cations and inorganic anions or organic anions, the organic cations are one or more than two of imidazole (structure formula is ), piperidine (structure formula is ), pyrrolidine (structure formula is ), pyridine (structure formula is ) and the like, wherein R1, R2, R3 are alkyl substituents with carbon chain length n, 0 ≤ n ≤ 8, and the carbon chain length n of R1, R2, R3 is not 0 at the same time; wherein R8, R9, R 10 are alkyl substituents with carbon chain length n, 0 ≤ n ≤ 8, and R8, R9, R 10wherein R4, R5, R6, R7 are alkyl substituents with carbon chain length n, 1≤n≤8, and n is not simultaneously 0;

[0011] The anion is one or more of halogen ion, tetrafluoroborate ion, hexafluorophosphate ion, bistrifluoromethanesulfonylimide, etc.

[0012] The contact angle of the room temperature ionic liquid mixture with the sample to be measured Between Preferably between More preferably ;

[0013] The above mixed solution is added into the conductive groove, so that the solution slowly infiltrates the entire porous material, i.e. each external surface of the material is completely wetted;

[0014] The above infiltrated porous material is dried to remove the solvent, and a porous material sample placed in the conductive groove is obtained for scanning electron microscope topography analysis.

[0015] The above mixed solution is loaded into a syringe;

[0016] The above syringe is installed on a high-precision syringe pump, and the flow rate is set to 0.05-0.5 mL / min, so that the solution slowly infiltrates the porous material;

[0017] The conductive groove with the porous material adhered thereto is placed in an oven, and the temperature is set to 30-90°C, and the drying time is set to 8-24 hours.

[0018] Preferably, the pre-set length* width* height dimensions of the porous material are 0.5*0.5*0.1 cm 3 1*1*1 cm 3 ;

[0019] The material of the conductive groove is one or both of conductive copper foil or aluminum foil, and the thickness is 0.01-0.2 cm. The internal cavity of the conductive groove is a cuboid, and the length of the internal cavity size of the conductive groove is 0.4-2.0 cm (preferably 0.5-1.5 cm, more preferably 0.8-1.2 cm) larger than the length of the porous material, the width of the internal cavity size of the conductive groove is 0-1 cm (preferably 0-0.5 cm, more preferably 0.01-0.4 cm) larger than the width of the porous material, and the height of the internal cavity size of the conductive groove is 0-0.5 cm (preferably 0-0.05 cm, more preferably 0-0.02 cm) smaller than the height of the porous material

[0020] Preferably, the thickness of the conductive groove material is 0.05-0.15 cm, the length of the preset size of the conductive groove is 0.5-1.0 cm larger than the size of the porous material, and the width and height of the preset size of the conductive groove are 0-0.5 cm larger than the size of the porous material; the length of the preset size of the conductive groove is 0.5-1.0 cm larger than the size of the porous material, the width of the preset size of the conductive groove is 0-0.4 cm larger than the size of the porous material, and the height of the preset size of the conductive groove is 0-0.2 cm smaller than the size of the porous material;

[0021] The room temperature ionic liquid is one or more of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazole dicyanamide salt, N-propyl-N-methylpiperidine bis(trifluoromethanesulfonyl) imide salt, and N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl) imide salt.

[0022] The solvent is one or more of water, methanol, ethanol, ethyl acetate, and dichloromethane.

[0023] The volume ratio of the room temperature ionic liquid to the solvent in the prepared miscible solution of the room temperature ionic liquid and the solvent is 1:1-1:20 (preferably 1:2-1:16, and more preferably 1:5-1:10).

[0024] Preferably, the contact angle between the room temperature ionic liquid mixture and the sample to be tested is 0°. In ;

[0025] Preferably, the preparation of the miscible solution of the room temperature ionic liquid and the organic solvent comprises the following steps:

[0026] According to the volume ratio of the room temperature ionic liquid to the organic solvent, the volume ratio is room temperature ionic liquid: organic solvent = 1:2-1:10.

[0027] Preferably, the injection speed of the miscible solution injected by the high-precision syringe pump is 0.01-1 mL / min.

[0028] Preferably, the removal of the volatile solvent in the porous material infiltrated by the miscible solution comprises the following steps:

[0029] Preferably, the temperature of the oven drying is 50-80°C, and the drying time is 12-24 hours.

[0030] The beneficial effects of the present application are as follows:

[0031] The sample preparation method is simple, efficient and low in cost, and the method can not only maintain the original morphology of the three-dimensional material, but also can make each pore wall, network and sheet layer of the three-dimensional porous material infiltrate the conductive particles, realize all-around and dead-angle-free increase of the material conductivity, and significantly improve the quality of the scanning electron microscope image, which has very important significance for the analysis and characterization of the three-dimensional material microstructure.

[0032] The application takes the three-dimensional porous material with rich microporous structure as the morphology observation object, uses the good ion conductivity of the room temperature ionic liquid and the non-destructive infiltration of the sample, all-round increases the conductivity of the sample, and thus obtains the SEM image with high quality and no charging effect, which is beneficial to the SEM morphology observation.

[0033] The application can solve the problem that the sputtering of the conductive particles cannot be realized on each pore wall, network and sheet layer of the three-dimensional porous material when the conductive film is used to increase the conductivity of the sample at the present stage, and the conductivity of the material is all-round and dead-angle-free. BRIEF DESCRIPTION OF DRAWINGS

[0034] The specific embodiments of the application will be further described in detail below with reference to the accompanying drawings.

[0035] Figure 1 The optical images of SiO2 aerogel before (a) and after (b) being infiltrated with the room temperature ionic liquid in Example 1 are shown.

[0036] Figure 2 The SEM images of the SiO2 aerogel after sputtering (a-c) and after being infiltrated with the room temperature ionic liquid (d-e) in Example 1 are shown, and the magnifications are 4K, 20K and 20K respectively. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the application, the application will be further described below with reference to the preferred embodiments and the accompanying drawings. Similar components are denoted by the same reference numerals in the drawings. Those skilled in the art should understand that the specific description below is illustrative rather than limiting, and should not limit the protection scope of the application.

[0038] Example 1

[0039] Herein, SiO2 nanofiber aerogel and 1-ethyl-3-methylimidazolium dicyanamide-acetic acid ethyl ester mixed solution are taken as examples:

[0040] The preparation method of the SiO2 nanofiber aerogel is prepared according to the method of the reference literature ACS Appl. Mater. Interfaces 2019, 11, 29056-29064, and the specific steps include the following:

[0041] First, a SiO2 precursor sol solution was prepared by mixing TEOS (tetraethyl orthosilicate), H2O, EtOH and C2H2O4 (oxalic acid) in a molar ratio of 1:3.57:0.71:0.016 at room temperature for 8 hours. Then, 0.26 g of SiO2 was uniformly dispersed in the above SiO2 precursor sol solution and homogenously dispersed for 10 minutes under high-speed stirring to prepare a SiO2 sol. At the same time, a PVB powder (polyvinyl butyral) was dissolved in EtOH at room temperature for 8 hours to prepare a 23 wt% PVB / EtOH solution. Subsequently, the SiO2 sol and the PVB / EtOH solution were mixed in a mass ratio of 3:1 and stirred for 4 hours to obtain an electrospinning precursor solution. Subsequently, an electrospinning process was performed using a DXES-1 spinning device (inner diameter of the nozzle: 0.1-1.6 mm, inner diameter used in this example: 0.8 mm) at a high voltage of 15 kV, a receiving distance of 15 cm, and a constant feeding rate of 1 mL / h. The spun composite PVB / TEOS composite nanofiber was gradually heated to 800°C at a heating rate of 5°C / min in a muffle furnace to perform calcination, thereby obtaining a pure SiO2 nanofiber aerogel.

[0042] The above SiO2 nanofiber aerogel was cut into a size of 0.62*0.51*0.33 cm 3 in length* width* height;

[0043] The aerogel was adhered to an electrically conductive groove made of a copper foil (an open container at the upper end) using a Rixin 732 aluminum-based double-sided carbon conductive tape, and the thickness of the copper foil was 0.1 cm, and the size of the inner chamber of the electrically conductive groove was 1.14*0.53*0.30 cm 3 in length* width* height;

[0044] A mixed solution of a room temperature ionic liquid and an organic solvent was prepared:

[0045] The 1-ethyl-3-methylimidazolium dicyanamide salt was mixed with ethyl acetate to prepare a mixed solution of 200 uL in a volume ratio of 0.2, and the contact angle of the room temperature ionic liquid mixed solution with the sample to be measured was

[0046] The above mixed solution was loaded into a 200 uL syringe;

[0047] The above syringe was mounted on a high-precision syringe pump, and the advance speed was set to 0.1 mL / min and the advance time was set to 1.5 min, so that the solution slowly infiltrated the pores, i.e., each outer surface of the material was completely wetted;

[0048] The above infiltrated aerogel was placed in a clean oven at 50°C and dried for 12 hours to remove volatile solvents such as ethyl acetate.

[0049] As Figure 1The optical images of SiO2 nanofiber aerogel before and after being infiltrated in Example 1 are shown, it can be seen that each outer surface of the aerogel is wetted, which indicates that the aerogel has been completely infiltrated by the room temperature ionic liquid mixture, and the length, width and height change before and after the infiltration is less than ±0.02 cm, it is preliminarily considered that the three-dimensional configuration is well maintained (the volume change is less than 5%).

[0050] The sample in Example 1 is subjected to SEM detection, and the SEM model is SU8230 produced by Hitachi Company;

[0051] The test conditions during the SEM detection are as follows: the vacuum degree is 0.0001 Pa, the acceleration voltage is 10 kV, the electron beam current is 10 pA, and the working distance is 10 mm. The secondary electron detector is used to accept the signal, and the morphology of the SiO2 nanofiber aerogel is analyzed.

[0052] The morphology of the SiO2 nanofiber aerogel is as follows Figure 2 As shown in d-f, the fiber staggered structure of the SiO2 nanofiber aerogel is well maintained without collapse; no obvious charge accumulation and drift phenomenon occurs at a magnification of 50K during the test, so that the high-quality morphology of the SiO2 nanofiber aerogel is obtained. It can be seen from the SEM image that the diameter of the SiO2 nanofiber is 100-200 nm. It is indicated that the treatment of the SiO2 aerogel by the 1-ethyl-3-methyl imidazole dicyanamide salt-ethyl acetate mixture not only has simple operation and low cost, but also can increase the conductivity in all directions, reduce or eliminate the charging effect, and improve the imaging quality.

[0053] Example 2

[0054] Herein, the SiO2 nanofiber aerogel and the 1-ethyl-3-methyl imidazole dicyanamide salt-ethanol mixture are taken as examples:

[0055] The SiO2 nanofiber aerogel prepared in Example 1 is cut into a size of 0.7*0.6*0.3 cm 3 ;

[0056] The aerogel is adhered to a conductive groove made of copper foil (an open container at the upper end) by using the Rixin 732 aluminum-based double-sided carbon conductive tape, the thickness of the copper foil is 0.1 cm, and the size of the internal chamber of the conductive groove is 1.2*0.7*0.3 cm 3 ;

[0057] The miscible solution of the room temperature ionic liquid and the organic solvent is prepared:

[0058] The 1-ethyl-3-methyl imidazole dicyanamide salt is mixed with ethanol to prepare a miscible solution with a volume ratio of 0.2, and the contact angle of the room temperature ionic liquid mixture with the sample to be tested is

[0059] The mixed solution is loaded into a 500 uL syringe;

[0060] The syringes are installed on a high-precision syringe pump, and the pushing speed is set to 0.2 mL / min and the pushing time is set to 1.0 min, so that the solution slowly infiltrates the pores, i.e. each external surface of the material is completely wetted;

[0061] The infiltrated aerogel is placed in a clean oven at 50°C for 12 h to remove volatile solvents such as ethanol.

[0062] The height of the SiO2 nanofiber aerogel in Example 2 changes little before and after infiltration, and the configuration is well maintained.

[0063] The sample in Example 2 is subjected to SEM detection, and the SEM is an SU8230 produced by Hitachi Company;

[0064] The test conditions during SEM detection are: vacuum degree is 0.0001 Pa, acceleration voltage is 10 kV, electron beam current is 10 pA, and working distance is 10 mm. The present application uses a secondary electron detector to accept signals, and the morphology of the SiO2 nanofiber aerogel is analyzed.

[0065] The SiO2 nanofiber aerogel structure is well maintained and does not collapse; during the test, when the magnification is 35K, the fiber surface abnormally brightens due to charge accumulation, causing part of the image to abnormally brighten and another part to darken; but no charging effect is observed at magnifications below 30K, the image brightness is uniform, and the interweaving of the fibers can be clearly seen; from the figure, it can be seen that the diameter of the SiO2 nanofiber is 100-200 nm. It is shown that treating the SiO2 nanofiber aerogel with a 1-ethyl-3-methylimidazolium dicyanamide salt-ethanol mixed solution can increase its electrical conductivity, effectively reduce the charging effect, and improve the imaging quality.

[0066] Example 3

[0067] Here, a boron nitride microporous material and a N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl) imide salt-methanol mixed solution are taken as examples:

[0068] The boron nitride microporous material is purchased from Qingzhou Haoyu Special Material Co., Ltd., and has a theoretical density of 2.29 g / cm 3 , a molecular weight of 24.81, and a Mohs hardness of 1-2;

[0069] The above boron nitride microporous material is cut into a size of 0.6*0.5*0.4 cm 3 ;

[0070] The above sample is adhered to a conductive groove made of copper foil (an open container at the upper end) with the Rixin 732 aluminum-based double-sided carbon conductive adhesive tape, the thickness of the copper foil is 0.1 cm, and the size of the internal chamber of the conductive groove is length* width* height = 1.3*0.6*0.3 cm 3 ;

[0071] A mixed solution of a room-temperature ionic liquid and an organic solvent is prepared:

[0072] The N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt is mixed with methanol to prepare a mixed solution of 200 uL with a volume ratio of 0.1, and the contact angle of the room-temperature ionic liquid mixed solution with the sample to be tested

[0073] The above mixed solution is loaded into a 200 uL syringe;

[0074] The above syringes are installed on a high-precision syringe pump, and the push speed is set to 0.05 mL / min and the push time is set to 4.0 min, so that the solution slowly infiltrates the sample, i.e., each outer surface of the material is completely wetted;

[0075] The above infiltrated sample is placed in a clean oven at 50°C for 12 h to remove volatile solvents such as methanol.

[0076] The structure of the boron nitride microporous material in Example 3 remains unchanged before and after being infiltrated.

[0077] The sample in Example 3 is subjected to SEM detection, and the SEM model is SU8230 produced by Hitachi Company;

[0078] The test conditions during SEM detection are: vacuum degree is 0.0001 Pa, acceleration voltage is 10 kV, electron beam current is 10 pA, and working distance is 10 mm. The present application uses a secondary electron detector to accept signals and analyzes the morphology of the boron nitride microporous material.

[0079] The structure of the boron nitride microporous material remains good, and there is no structure collapse or micropore blockage; during the test, irregular bright spots and bright lines appear in the image when the magnification is greater than 20K, but a high-quality SEM image can still be obtained at 20K by increasing the scanning speed. From the SEM image, it can be seen that the pore size of the boron nitride microporous material is 80-200 um. It is shown that treating the boron nitride microporous material with the N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt-methanol mixed solution has an effect on increasing the electrical conductivity of the boron nitride microporous material, and can meet the normal test requirements.

[0080] Example 4

[0081] Here, polyurethane foam and 1-butyl-3-methyl imidazole tetrafluoroborate-ethanol mixed solution are taken as examples:

[0082] The polyurethane foam is purchased from Wenzhou Nanpu Sponge Co., Ltd., and has a density of 0.022-0.08 g / cm 3 ;

[0083] The polyurethane foam is cut into a size of 0.65*0.53*0.37 cm 3 ;

[0084] The polyurethane foam is adhered to a conductive groove made of copper foil (an open container at the upper end) with the Rixin 732 aluminum-based double-sided carbon conductive tape, and the thickness of the aluminum foil is 0.5 cm, and the size of the internal chamber of the conductive groove is 1.2*0.55*0.30 cm 3 ;

[0085] A mixed solution of a room-temperature ionic liquid and an organic solvent is prepared:

[0086] The 1-ethyl-3-methyl imidazole dicyanamide salt is mixed with ethyl acetate to prepare a mixed solution of 200 uL with a volume ratio of 0.15, and the contact angle of the room-temperature ionic liquid mixed solution with the sample to be tested is 38°;

[0087] The mixed solution is loaded into a 200 uL syringe;

[0088] The syringe is installed on a high-precision syringe pump, and the pushing speed is set to 0.1 mL / min, and the pushing time is set to 1.5 min, so that the solution slowly infiltrates the polyurethane foam, that is, each outer surface of the material is completely wetted;

[0089] After the polyurethane foam is infiltrated, no structural collapse and deformation occurs;

[0090] The infiltrated polyurethane foam is placed in a clean oven at 50°C for 12 h to remove volatile solvents such as ethanol.

[0091] The sample in Example 4 is subjected to SEM detection, and the SEM is an SU8230 produced by Hitachi Co., Ltd.; the test conditions during SEM detection are: vacuum degree is 0.0001 Pa, acceleration voltage is 10 kV, electron beam current is 10 pA, and working distance is 10 mm. The present application uses a secondary electron detector to accept signals, and performs topographic analysis on the polyurethane foam.

[0092] ​During the test, the image appears slight distortion within 30K magnification, but the scanning speed is accelerated, the morphology of the polyurethane foam can still be obtained, and it can be seen that the pore size of the polyurethane foam is 50-200um. When the magnification is greater than 30K, the image distortion becomes serious, and the real morphology cannot be obtained. It is proved that the treatment of polyurethane foam with 1-butyl-3-methylimidazolium tetrafluoroborate-1-ethyl-3-methylimidazolium dicyanamide-acetic acid ethyl ester-ethanol mixed solution can increase the conductivity of the polyurethane foam, reduce the accumulation of electric charge on the surface of the sample, and thus obtain the required morphology.

[0093] Example 5

[0094] Here, taking porous alumina ceramic and 1-ethyl-3-methylimidazolium dicyanamide-acetic acid ethyl ester mixed solution as an example:

[0095] The porous alumina ceramic is purchased from Jiangxi Yitian Filler Co., Ltd., and its density is 0.42g / cm 3 , and the porosity is 80-90%;

[0096] The above porous alumina ceramic is cut into a size of 0.7*0.6*0.5cm 3 ;

[0097] The porous alumina ceramic is adhered to the conductive groove made of copper foil (an open container at the upper end) with the Rixin 732 aluminum-based double-sided carbon conductive tape, and the thickness of the aluminum foil is 0.5cm, and the size of the internal chamber of the conductive groove is length* width* height = 1.3*0.9*0.30cm 3 ;

[0098] Prepare a mixed solution of room temperature ionic liquid and organic solvent:

[0099] Take the 1-ethyl-3-methylimidazolium dicyanamide and acetic acid ethyl ester mixture, and prepare a mixed solution of 400uL with a volume ratio of 0.15, and the contact angle of the room temperature ionic liquid mixture with the sample to be tested is 34°;

[0100] The above mixed solution is loaded into a 500uL syringe;

[0101] The above syringe is installed on a high-precision syringe pump, and the push speed is set to 0.1mL / min, and the push time is 3.5min, so that the solution slowly infiltrates the polyurethane foam, that is, the various outer surfaces of the material are completely wetted;

[0102] After the porous alumina ceramic is infiltrated, there is no structural collapse and deformation;

[0103] The above infiltrated porous alumina ceramic is placed in a clean oven at 50℃ for 12h to remove volatile solvents such as ethanol.

[0104] The sample in Example 5 was subjected to SEM detection, the model of which was SU8230 produced by Hitachi Company; the test conditions in SEM detection were as follows: vacuum degree was 0.0001 Pa, acceleration voltage was 10 kV, electron beam current was 10 pA, and working distance was 10 mm. The present application used a secondary electron detector to accept signals and analyze the morphology of the porous alumina ceramic.

[0105] A clear morphology diagram of the alumina ceramic was obtained at a magnification of 30 K, and it could be seen from the diagram that the pore size of the porous alumina ceramic was 50-200 um. It was shown that the treatment of the porous alumina ceramic with the 1-butyl-3-methylimidazolium tetrafluoroborate-1-ethyl-3-methylimidazolium dicyanamide-methanol mixed solution could improve the conductivity of the material, effectively reduce the charging effect, and improve the imaging quality.

[0106] Example 6

[0107] Herein, the glass fiber and the 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl) imide-methanol mixed solution were taken as examples:

[0108] The glass fiber was purchased from Shaoguan Haoli Regenerated Resource Utilization Co., Ltd., and the density thereof was 1.63 g / cm 3 ;

[0109] The above glass fiber was cut into a size of 0.8*0.8*0.5 cm 3 ;

[0110] The glass fiber was adhered to a conductive groove made of a copper foil (an open container at the upper end) by using a Rixin 732 aluminum-based double-sided carbon conductive tape, the thickness of the aluminum foil was 0.5 cm, and the size of the internal chamber of the conductive groove was 1.3*1.2*0.30 cm 3 ;

[0111] A mixed solution of the room temperature ionic liquid and the organic solvent was prepared:

[0112] The 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl) imide was mixed with methanol to prepare a mixed solution with a volume ratio of 0.1, and the contact angle of the room temperature ionic liquid mixed solution with the sample to be tested was 38°;

[0113] The above mixed solution was loaded into a 200 uL syringe;

[0114] The above syringe was installed on a high-precision syringe pump, and the pushing speed was set to 0.1 mL / min and the pushing time was set to 4 min, so that the solution slowly infiltrated the glass fiber, that is, each outer surface of the material was completely wetted;

[0115] ​The glass fibers are not collapsed and deformed after being infiltrated.

[0116] The infiltrated glass fibers are placed in a clean oven at 50℃ for 12h to remove the volatile solvents such as methanol.

[0117] The sample in Example 6 is subjected to SEM detection, and the SEM is SU8230 produced by Hitachi; the test conditions in the SEM detection are as follows: vacuum degree is 0.0001 Pa, acceleration voltage is 10 kV, electron beam current is 10 pA, and working distance is 10 mm. The present application uses a secondary electron detector to accept signals and analyze the morphology of the glass fibers.

[0118] The uniformly distributed glass fibers can be clearly seen at a magnification of 15K, and the diameter of the fibers is 10-20 um. It is shown that the treatment of the glass fibers with the 1-ethyl-3-methyl imidazoline bis(trifluoromethylsulfonyl) imide-methanol mixed solution can increase the conductivity of the glass fibers, effectively reduce the charging effect, and improve the imaging quality.

[0119] Comparative Example 1

[0120] The SiO2 aerogel prepared in Example 1 is cut into a size of 0.6*0.5*0.3 cm 3 ;

[0121] The porous material is fixed on a sample stage with a Rixin 732 aluminum-based double-sided carbon conductive tape;

[0122] The sample stage is placed in the chamber of a Hitachi MC1000 ion sputtering instrument, the sputtering current is set to 10 mA, the time is set to 90 s, and the platinum metal coating on the surface of the sample is sputtered by clicking start. The thickness of the sputtered metal layer is 5 nm;

[0123] The sample in Comparative Example 1 is subjected to SEM detection, and the SEM is SU8230 produced by Hitachi;

[0124] The test conditions in the SEM detection are as follows: vacuum degree is 0.0001 Pa, acceleration voltage is 10 kV, electron beam current is 10 pA, and working distance is 10 mm. The present application uses a secondary electron detector to accept signals and analyze the morphology of the SiO2 aerogel.

[0125] The morphology of the SiO2 aerogel is as follows Figure 2As shown in a-c, the SiO2 aerogel structure remains good without collapse; obvious charge accumulation and drift phenomenon occurs during the test, and image drift is serious even at 4K magnification with fast scanning, multiple charged black stripes and image distortion are observed, so that high-quality SiO2 aerogel morphology cannot be obtained. It is shown that the method of sputtering metal coating by sputtering instrument is not good for improving the overall conductivity of SiO2 aerogel.

[0126] Comparative Example 2

[0127] Example 1 is repeated (process and conditions are the same as in Example 1), and the difference is that the SiO2 aerogel prepared in Example 1 is replaced by hydrophobic SiO2 nanofiber aerogel, and other conditions remain unchanged. The preparation method of the hydrophobic SiO2 nanofiber aerogel is as follows: the SiO2 nanofiber aerogel of Example 1 is soaked in 5.0g SiF3 ethanol solution (15wt.%) and aged for 3 days, the solvent is exchanged with ethanol, and finally dried with supercritical carbon dioxide to obtain the hydrophobic SiO2 nanofiber aerogel. The contact angle of the hydrophobic SiO2 nanofiber aerogel with the 1-ethyl-3-methylimidazolium dicyanamide-ethyl acetate mixed solution is The mixed solution cannot infiltrate the sample, and during the SEM test, due to the poor conductivity of the sample itself and the ineffective infiltration of the ionic liquid mixed solution, obvious charging effect occurs, the image shakes and drifts during scanning, the morphology shows fiber distortion, stage difference, and abnormal brightening of the fiber edge, which cannot show the details of the sample.

[0128] Comparative Example 3

[0129] Example 1 is repeated (process and conditions are the same as in Example 1), and the difference is that the 1-ethyl-3-methylimidazolium dicyanamide-ethyl acetate mixed solution is replaced by an equal volume ratio of N-hexylpyridine bromide-ethanol mixed solution, and other conditions remain unchanged. Since the melting point of N-hexylpyridine bromide is 46℃, during the SEM test, when the incident electron beam interacts with the sample surface, the temperature of the sample surface will rise, causing the N-hexylpyridine bromide solidified at 46℃ to melt, affecting the stability of the sample, and the SEM image obtained shows deformation and morphology distortion.

[0130] Comparative Example 4

[0131] Example 1 is repeated (process and conditions are the same as in Example 1), and the difference is that the infiltration operation of the high-precision syringe pump with a syringe push speed of 0.1mL / min and a push time of 1.5min is changed to a push speed of 1.8mL / min for 5s, and other conditions remain unchanged. Due to the too fast push speed, the structure of the SiO2 nanofiber aerogel collapses, and the volume distortion is greater than 30%, which cannot be tested.

[0132] Obviously, the above-mentioned embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation manners of the present application. Based on the above-mentioned description, other different forms of changes or variations can be made by those skilled in the art, and it is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A sample preparation method for scanning electron microscope topography analysis of three-dimensional porous materials, characterized by, Includes the following steps: Shear three-dimensional porous materials to the required dimensions; The porous material is bonded to a conductive groove using conductive adhesive. The conductive groove is a container with an open top, made of conductive material. Prepare a mixed solution of a room temperature ionic liquid and a solvent; The room temperature ionic liquid refers to one or more than two kinds of fused salts which are in liquid state at 20-30℃, melting point ≤30℃; usually composed of specific organic cation and inorganic anion or organic anion, structural formula is The organic cation has one or more than two kinds of imidazole, structural formula is Piperidine, structural formula is Pyrrolidine, structural formula is Pyridine, wherein R1, R2, R3 are alkyl substituents with carbon chain length n respectively, 0 ≤ n ≤ 8, and the carbon chain length n of R1, R2, R3 is not 0 at the same time; wherein R8, R9, R 10 are alkyl substituents with carbon chain length n respectively, 0 ≤ n ≤ 8, and the carbon chain length n of R8, R9, R 10 is not 0 at the same time; wherein R4, R5, R6, R7 are alkyl substituents with carbon chain length n respectively, 1 ≤ n ≤ 8; The anions include one or more of the following: halide ions, tetrafluoroborate ions, hexafluorophosphate ions, and bis(trifluoromethanesulfonyl)imide. The contact angle Ѳ between the room temperature ionic liquid mixture and the sample to be tested is between 0 < Ѳ < 90°; The above mixed solution is added into the conductive tank so that the solution slowly wets the entire porous material, that is, all the outer surfaces of the material are completely wetted. The above-mentioned impregnated porous material is dried to remove the solvent, and a porous material sample that can be used for scanning electron microscopy morphology analysis is obtained by placing it in a conductive tank.

2. The method according to claim 1, characterized in that: The contact angle Ѳ between the room temperature ionic liquid mixture and the sample to be tested is between 0 < Ѳ < 60°.

3. The method according to claim 1, characterized in that: The porous material is a cuboid with length, width and height dimensions of 0.1-2 cm * 0.1-2 cm * 0.1-2 cm.

4. The method of claim 1, wherein: The conductive groove is made of one or both of conductive copper foil and aluminum foil, with a thickness of 0.01-0.2 cm. The internal cavity of the conductive groove is a cuboid. The length of the internal cavity is 0.4-2.0 cm larger than the length of the porous material, the width of the internal cavity is 0-1 cm larger than the width of the porous material, and the height of the internal cavity is 0-0.5 cm smaller than the height of the porous material.

5. The method of claim 4, wherein: The internal cavity of the conductive groove is a cuboid. The length of the internal cavity is 0.5-1.5 cm larger than the length of the porous material, the width of the internal cavity is 0-0.5 cm larger than the width of the porous material, and the height of the internal cavity is 0-0.05 cm smaller than the height of the porous material.

6. The method according to claim 1, characterized in that: The room-temperature ionic liquid is specifically one or more of the following: 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium dinitrileamine salt, N-propyl-N-methylpiperidine bis(trifluoromethanesulfonyl)imine salt, and N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imine salt.

7. The method according to claim 1 or 5, characterized in that: The solvent is one or more of water, methanol, ethanol, ethyl acetate, and dichloromethane; The volume ratio of the room temperature ionic liquid to the solvent in the prepared mixed solution of room temperature ionic liquid and solvent is 1:1 to 1:

20.

8. The method according to claim 7, characterized in that: The volume ratio of the room temperature ionic liquid to the solvent in the prepared mixed solution of room temperature ionic liquid and solvent is 1:2 to 1:

16.

9. The method according to claim 1, characterized in that: The process of adding the above mixture into the conductive tank to allow the solution to wet the entire porous material is as follows: Fill the syringe with the above mixture; The syringe is mounted on a high-precision injection pump and the flow rate is set so that the solution slowly wets the porous material, that is, all the outer surfaces of the material are completely wetted. The impregnated porous material was placed in a clean oven to remove volatile solvents.

10. The method of claim 9, wherein: The mixed solution is injected using a high-precision syringe pump at a flow rate of 0.01-1 mL / min until all outer surfaces of the material are completely wetted or the entire conductive groove is filled.

11. The method according to claim 1, characterized in that: The process of removing solvent from porous materials wetted by the mixed solution includes the following steps: Place the conductive groove with porous material into an oven at a temperature of 30-90℃ for 8-24 hours.

12. The method according to claim 1, characterized in that: The porous material includes one or more of the following: foam materials, hydrogels, porous ceramics, porous polymer materials, porous carbon materials, porous glass materials, and other three-dimensional porous materials.

13. The method according to claim 1, characterized in that: The conductive adhesive is one or more of the following: double-sided aluminum-based carbon conductive tape or double-sided non-woven carbon conductive tape. Conductive adhesive is used to bond the sides and bottom surface of the porous material to the inner side and bottom surface of the conductive groove.

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