阅读说明：本技术 一种测量沥青材料的中间相沥青的含量的方法 (Method for measuring content of mesophase pitch of asphalt material ) 是由 蒋复国 段春婷 韩志华 李永龙 于 2020-05-26 设计创作，主要内容包括：本发明提供一种测量沥青材料的中间相沥青的含量的方法沥青材料的显微图像的采集方法,包括：1)利用扫描电子显微镜采集沥青材料样品的显微图像,其中所述沥青材料样品未经过喷金处理；2)依据一个显微图像中的中间相沥青的占比得出沥青材料的中间相沥青的含量,或依据多个显微图像中的中间相沥青的占比的平均值得出沥青材料的中间相沥青的含量,其中,步骤1)中,所述扫描电子显微镜的工作电压为0.1kV～1.0kV。通过不对沥青材料样品进行喷金处理,同时采用0.1kV～1.0kV,获得了分辨率能够达到1nm的沥青材料的显微图像,从而可以依据该显微图像获知中间相沥青的结构、形状大小与在沥青材料的的分布情况。(The invention provides a method for measuring the content of mesophase pitch of a pitch material, which comprises the following steps: 1) acquiring a microscopic image of an asphalt material sample by using a scanning electron microscope, wherein the asphalt material sample is not subjected to gold spraying treatment; 2) obtaining the content of the mesophase pitch of the bituminous material according to the proportion of the mesophase pitch in one microscopic image, or obtaining the content of the mesophase pitch of the bituminous material according to the average value of the proportions of the mesophase pitch in a plurality of microscopic images, wherein in the step 1), the working voltage of the scanning electron microscope is 0.1 kV-1.0 kV. By not carrying out metal spraying treatment on the asphalt material sample and simultaneously adopting 0.1 kV-1.0 kV, a microscopic image of the asphalt material with the resolution of 1nm is obtained, so that the structure, the shape and the size of the mesophase asphalt and the distribution condition of the asphalt material can be obtained according to the microscopic image.)

1. A method of measuring the mesophase pitch content of a bituminous material, comprising:

1) acquiring a microscopic image of an asphalt material sample by using a scanning electron microscope, wherein the asphalt material sample is not subjected to gold spraying treatment;

2) the content of mesophase pitch of the bituminous material is derived from the proportion of mesophase pitch in one microscopic image, or the content of mesophase pitch of the bituminous material is derived from the average of the proportions of mesophase pitch in a plurality of microscopic images,

wherein, in the step 1), the working voltage of the scanning electron microscope is 0.1 kV-1.0 kV.

2. The method according to claim 1, wherein the scanning electron microscope has an operating voltage of 0.1 to 0.5kV, preferably 0.1 to 0.3 kV.

3. Method according to claim 1 or 2, characterized in that the sample of bituminous material has a thickness of 10 μ ι η or more, preferably 20 μ ι η or more, more preferably 20 μ ι η to 2 cm.

4. A method according to any of claims 1-3, characterized in that the sample of bituminous material has not been subjected to a grinding treatment and/or a polishing treatment.

5. The method according to any one of claims 1 to 4, wherein in step 1), the linear distance between an electron probe of the scanning electron microscope and the surface of the sample of bituminous material close to the electron probe is controlled to be 5mm to 10mm when the microscopic image of the sample of bituminous material is acquired.

6. The method according to any one of claims 1 to 5, wherein the contrast of the acquired microscopic images is adjusted so that the area in which the mesophase pitch is located is emphasized before performing step 2).

7. The method according to claim 6, characterized in that the contrast of the microscopic image is adjusted to 90% or more, preferably 90-95%.

8. The method according to any one of claims 1 to 7, wherein the fraction in step 2) is a percentage of the area of mesophase pitch in the microscopic image in the total area of the microscopic image.

9. The method according to any one of claims 1 to 7, wherein the fraction in step 2) is a percentage of the total pixel value of mesophase pitch in the microscopic image in the total pixel value of the microscopic image.

10. Use of the method according to any one of claims 1-9 in the field of measurement of the content of mesophase pitch.

Technical Field

The invention relates to a method for measuring the content of mesophase pitch of a bituminous material and to the use of the method for measuring the content of mesophase pitch.

Background

Mesophase pitch is an aggregate of aromatic hydrocarbons with optical anisotropy, and is a liquid crystal substance which is generated from heavy aromatic hydrocarbons in the heat treatment process and consists of disc-shaped or rod-shaped polycyclic aromatic hydrocarbons, is a precursor of a high-quality carbon material, and can be widely used for high-performance carbon fibers, activated carbon with ultrahigh specific surface area, high-quality needle coke, foam carbon and the like. The knowledge of the proportion of the mesophase pitch in the pitch material and the structure, shape, size and distribution of the mesophase pitch is a key factor for providing the subsequent high carbon product performance index.

Typically, the mesophase pitch content of a bituminous material is measured using two methods, the first being selective solvent extraction, which uses a specific solvent to dissolve the non-mesophase pitch fraction, the remainder being mesophase pitch. The second is to use quantitative microscope technology, the method can obtain the microscopic picture of the asphalt material, so as to obtain the distribution condition of the mesophase asphalt in the asphalt material, and then the proportion of the mesophase asphalt in the asphalt material is calculated by software, so as to achieve the quantitative effect.

Although the selective solvent extraction method is simple, the method is easy to cause quantitative misalignment due to incomplete extraction or dissolution of part of mesophase pitch, and in addition, after the mesophase pitch is dissolved, the real morphology and distribution of the mesophase pitch are damaged, and the micro particles (microcrystalline structures) cannot be observed, so that the important information of the structure of the mesophase pitch is lost.

The quantitative microscopic technique is to polish the sample to a mirror surface, obtain a polarized light picture by a polarized light microscope, obtain a picture with high contrast by the difference of reflectivity of the mesophase pitch and other parts to the polarized light, distinguish the mesophase pitch to calculate the ratio, and obtain the average value of the content by calculating a large number of pictures. This method is the most common and widely accepted in the industry as a true and effective method. However, although the quantitative microscopy method is simple, it is limited by the optical instrument, and the sample needs a better polishing procedure because the unpolished sample surface is easy to scratch, thereby affecting the image quality of the picture, even the image cannot be quantified, and it is time-consuming and labor-consuming. In addition, the image obtained by the polarizing microscope is influenced by the grain growth direction of the mesophase pitch, so that bright and dark interference fringes appear, and the existence of the fringes also increases the difficulty of calibrating the mesophase pitch, thereby influencing the quantitative result. In addition, when the optical microscope observes the mesophase pitch, the minimum observation size is only about 10 microns due to the limitation of the optical limit, so the microcrystalline structure (less than 5 microns) in the mesophase pitch cannot be observed, and the structure observation is a blind spot.

In view of the above, it is necessary to develop a new method for effectively observing mesophase pitch, so as to obtain the proportion of mesophase pitch in the bituminous material, and simultaneously know the structure, shape and size of mesophase pitch and the distribution of bituminous material.

Disclosure of Invention

In view of the problems in the prior art, an object of the present invention is to provide a method for measuring the content of mesophase pitch of a pitch material, wherein a microscopic image of the pitch material with a resolution of 10 nm is obtained by not performing a metal spraying process on a pitch material sample and simultaneously applying an operating voltage of 0.2kV to 0.5kV, so that the structure, shape and size of the mesophase pitch and the distribution of the mesophase pitch in the pitch material can be known from the microscopic image.

A second object of the invention is an application related to the first object.

In order to achieve one of the above purposes, the technical scheme adopted by the invention is as follows:

a method of acquiring a microscopic image of a bituminous material for measuring its mesophase pitch content, comprising:

1) acquiring a microscopic image of an asphalt material sample by using a scanning electron microscope, wherein the asphalt material sample is not subjected to gold spraying treatment;

2) the content of mesophase pitch of the bituminous material is derived from the proportion of mesophase pitch in one microscopic image, or the content of mesophase pitch of the bituminous material is derived from the average of the proportions of mesophase pitch in a plurality of microscopic images,

wherein, in the step 1), the working voltage of the scanning electron microscope is 0.1 kV-1.0 kV.

In the art, mesophase pitch is generally observed by a polarization microscope, but the effect is not good. The inventors of the present application have found in their research that under certain specific conditions, such as a specific voltage, mesophase pitch can be observed using a scanning electron microscope and microscopic images with a resolution of up to 10 nm can be obtained.

When observing the morphology of the non-conductive material by using a scanning electron microscope, it is a common practice in the art to spray a metal layer on the surface of the non-conductive material to make the material to be observed conductive. However, in experiments, the inventor of the present application finds that a clear microscopic image can be obtained by using a scanning electron microscope under the working voltage of 0.1kV to 1.0kV, especially 0.1kV to 0.5kV without performing gold spraying treatment on an asphalt material sample, the resolution of the obtained microscopic image can reach 10 nanometers, and the observation size of the asphalt material is greatly improved. Based on the microscopic image obtained by the method, the structure, the shape and the size of the mesophase pitch and the distribution condition of the pitch material can be observed.

The scanning electron microscope utilizes an electron excitation technology, utilizes electron beams to strike the surface of a sample, and electrons on the surface of the material are excited due to the irradiation of the electron beams at the moment, and an image signal is collected by a sensor; the yield of excited electrons of different materials can also have corresponding amount due to different element contents and different conductivity; the mesophase pitch has similar constituent elements to those of the general pitch, and since the mesophase pitch has good electrical conductivity and crystallinity, and is different from the surrounding general pitch, the yield of excited electrons is different, and contrast difference appears on an image, thereby characterizing the distribution of the mesophase pitch.

According to the invention, the bituminous material may be a coal bituminous material or a petroleum bituminous material.

The metal spraying treatment according to the present invention means to spray a metal coating on the surface of the sample, which is a routine operation in the art.

In some preferred embodiments of the present invention, the scanning electron microscope has an operating voltage of 0.1kV to 0.5 kV.

In some preferred embodiments of the present invention, the scanning electron microscope has an operating voltage of 0.1kV to 0.3 kV.

According to the invention, the operating voltage of the scanning electron microscope is the operating voltage of the electron beam.

In practice, the working voltage is selected according to the invention in relation to the type of scanning electron microscope, for example, when the voltage of the scanning electron microscope can only be varied by 0.1KV, the working voltage which can be used according to the invention can be 0.1KV, 0.2KV, 0.3KV, 0.4KV, 0.5KV, 0.6KV, 0.7KV, 0.8KV, 0.9KV or 1.0 KV. When the voltage of the scanning electron microscope can be changed by 0.01KV, the working voltage which can be adopted by the invention can be 0.1KV, 0.11KV, 0.12KV, 0.13KV and the like.

In some preferred embodiments of the present invention, the type of the scanning electron microscope is not particularly limited as long as it can achieve the voltage required by the present invention, and a scanning electron microscope with a working distance between the sample stage and the objective lens that is large enough, for example at least greater than 20mm, is preferred to accommodate and observe a relatively large volume of mesophase pitch.

In some preferred embodiments of the invention, the scanning electron microscope is model FEI Nova Nano SEM 450.

In some preferred embodiments of the invention, the sample of bituminous material has a thickness of 10 μm or more, preferably 20 μm or more.

According to the present invention, sufficient secondary electrons are generated if and only if the thickness of the sample of bituminous material is within the above-specified range, so that a clear microscopic image is obtained.

According to the invention, the thickness of the bituminous material sample should not exceed the lifting limit of the sample table. Generally, the lifting limit of the sample stage is about 20 cm.

According to the invention, the sample of bituminous material has a thickness of between 20 μm and 2 cm.

In some preferred embodiments of the present invention, the sample of bituminous material is not subjected to a grinding treatment and/or a polishing treatment.

According to the invention, when the method is adopted, the asphalt material sample does not need to be finely polished or polished, the natural fracture surface can be imaged, and the interference of grains or scratches on the surface of the sample can be avoided, so that the characterization of the nondestructive fracture surface can be realized, the sample processing time can be saved, the characterization steps can be simplified, and more accurate quantification can be obtained.

In some preferred embodiments of the present invention, in step 1), when the microscopic image of the sample of the asphalt material is acquired, the linear distance between the electron probe of the scanning electron microscope and the surface of the sample of the asphalt material close to the electron probe is controlled to be 5mm to 10mm, preferably 6mm to 8 mm.

According to the invention, in step 1), when acquiring the microscopic image of the asphalt material sample, the imaging mode of the scanning electron microscope is controlled to be secondary electron imaging, and preferably, the large-range magnification is controlled to be 100 to 1000 times, and the small-range magnification is controlled to be 5000 to 20000 times.

According to the present invention, the wide-range magnification means that the field of view is wide and a wide range can be seen because the magnification is small. The small-range magnification means that the magnification is large and thus the area of the region that can be seen is small.

In some preferred embodiments of the present invention, the contrast of the acquired microscopic image is adjusted before step 2) is performed, so that the area where the mesophase pitch is located is emphasized.

In some preferred embodiments of the present invention, the contrast of the microscopic image is adjusted to 90% or more, preferably 90% to 95%. According to the present invention, impurities such as dust on the surface of the asphalt material can be removed using high-pressure air.

In order to achieve the second purpose, the invention adopts the following technical scheme:

use of a method according to the above in the field of the measurement of the content of mesophase pitch.

The invention has the beneficial effects that:

firstly, the minimum observable size of the method provided by the invention is 10 nanometers, so that the observation size of the mesophase pitch (the limit of an optical microscope is 10 micrometers) is greatly improved, and the method has breakthrough on the observation and research of the microcrystal of the mesophase pitch.

Secondly, the method provided by the invention can be used for collecting images of a sample which is not polished, so that the influence of scratches caused by polishing operation is avoided.

Drawings

FIG. 1 is a microscopic image obtained by the measurement method of example 1.

Fig. 2 is a microscopic image obtained by the measurement method of example 2.

FIG. 3 is a microscopic image obtained by the measurement method of example 3.

Fig. 4 is a microscopic image obtained by the measurement method of example 4.

Fig. 5 is a microscopic image (contrast 70%, brightness 40%) obtained by the measurement method of example 5.

Fig. 6 is a microscopic image (contrast 90%, brightness 5%) obtained by the measurement method of example 5.

FIG. 7 is a microscopic image obtained by the measurement method of example 6.

Fig. 8 is a partially enlarged view of a microscopic image obtained by the measurement method of example 6.

Fig. 9 is a microscopic image obtained by the measurement method of comparative example 1.

Fig. 10 is a microscopic image obtained by the measurement method of comparative example 2.

Fig. 11 is a microscopic image obtained by the measurement method of comparative example 3.

Fig. 12 is a microscopic image obtained by the measurement method of comparative example 3, which was adjusted by image software.

Detailed Description

The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to the following description.

Example 1

Step 1: taking blocky coal pitch, directly breaking the blocky coal pitch, and taking a piece of petroleum pitch with a relatively flat fracture surface as a sample to be tested;

step 2: blowing off dust on the surface of the sample by utilizing high-pressure air, then placing the sample on a special sample table, and simply fixing the sample to prevent the sample from moving;

and step 3: putting the sample into an observation chamber, and vacuumizing to 5E-3 Pa;

and 4, step 4: setting the working voltage to be 0.2kV, and adjusting the multiplying power to be 100 times by using a secondary electron imaging mode;

and 5: moving an electron probe of a scanning electron microscope to a position which is 5-10mm away from the surface of the sample, selecting a proper area and adjusting a proper magnification to take a picture to obtain a microscopic image of the sample, wherein the microscopic image is shown in figure 1. In fig. 1, the sample surface texture can be clearly seen. Non-mesophase pitch (dark grey) and mesophase pitch (white) are clearly visible with clear boundaries.

Step 6: and moving the sample stage to acquire images in other areas of the sample, and acquiring more than 5 images in total.

And 7: and (4) carrying out statistical calculation on the average content of the mesophase pitch in each image.

Example 2

In this example, another region of coal pitch obtained in step 1 of example 1 was used as a sample to be tested, and an image was taken in the same manner as in example 1 except that the operating voltage was 0.4kV, and the obtained microscopic image was as shown in FIG. 2.

Comparing fig. 1 and fig. 2, it can be seen that the contrast of fig. 2 is slightly lower than that of fig. 1.

Example 3

In this example, another region of coal pitch obtained in step 1 of example 1 was used as a sample to be tested, and an image was taken in the same manner as in example 1 except that the operating voltage was 1.0kV, and the obtained microscopic image was as shown in FIG. 3.

Comparing fig. 1 and fig. 3, it can be seen that the signal of fig. 3 is inverted, that is, the original mesophase pitch turns to black and gray, and the non-mesophase pitch turns to white, which indicates that the voltage is too high, which causes the electron beam to generate deep interaction with the sample, thus affecting the display, and being not beneficial to obtaining a clear microscopic image.

Example 4

In this example, another piece of coal pitch having a relatively flat fracture surface obtained in step 1 of example 1 was used as a sample to be tested, and an image (not polished) was taken in the same manner as in example 1, and the obtained microscopic image is shown in fig. 4.

In fig. 4, the natural crack trace of the asphalt surface can be seen invisibly, but the mesophase asphalt can still be clearly distinguished (white part) due to the large contrast of black and white, indicating that the mesophase asphalt is not affected by the surface flatness by electron microscopy.

Example 5

In this example, another coal tar pitch with a relatively flat fracture surface obtained in step 1 of example 1 was used as a sample to be tested, and after the sample was simply polished, an image was collected in the manner described in example 1, with a contrast of 70% and a brightness adjusted to 40%, and the obtained microscopic image is shown in fig. 5. To reflect the effect of contrast and brightness on distinguishing mesophase pitch from non-mesophase pitch, contrast was adjusted to 90% and brightness was adjusted to 5% in fig. 5, so that the region where mesophase pitch was located was prominently strengthened, as shown in fig. 6.

Example 6

In this example, another piece of petroleum asphalt with a relatively flat fracture surface obtained in step 1 of example 1 was used as a sample to be tested, and an image was acquired as in example 1, and the obtained microscopic image is shown in fig. 7. In fig. 7, an area (box) is selected for enlargement, as shown in fig. 8.

In FIG. 8, the secondary particles of mesophase pitch are clearly seen, with a minimum size of about 50 nm, in this mode with a resolution of up to 10 nm, which is not possible with other observation means, such as optical microscopy.

Comparative example 1

In this comparative example, another piece of petroleum asphalt having a relatively flat fracture surface obtained in step 1 of example 1 was used as a sample to be tested, and an image was collected in the same manner as in example 1 except that the operating voltage was 10kV, which is a common operating voltage in the art when the sample was observed with a scanning electron microscope, and the obtained microscopic image is shown in fig. 9.

As can be seen by comparing fig. 1 and 9, fig. 9 does not clearly distinguish between bitumen and mesophase bitumen. The surface is not able to observe mesophase pitch at the voltages typically used. This is one of the reasons for the technical prejudice in the art that mesophase pitch cannot be observed with scanning electron microscopy.

Comparative example 2

In this comparative example, the asphalt sample without grinding and polishing was directly observed by a polarizing microscope.

Another piece of petroleum asphalt with a relatively flat fracture surface obtained in step 1 of example 1 was used as a sample to be tested, and the sample was fixed on a glass slide and placed on a sample stage of a polarizing microscope. The light path is adjusted to be in a reflection mode, the polaroid is adjusted to be in an orthogonal polarization mode, and the objective lens with the power of 20 times is selected. Focusing to obtain the clearest picture as shown in fig. 10.

In fig. 10, since the surface of the sample was not polished, clear mesophase and non-mesophase regions could not be observed by the polarization method.

Comparative example 3

In this comparative example, the buffed and polished asphalt sample was observed using a polarizing microscope.

Another piece of petroleum asphalt with a relatively flat fracture surface obtained in step 1 of example 1 was used as a sample to be tested, and after simple polishing, the sample was fixed on a glass slide and placed on a sample stage of a polarizing microscope. The light path is adjusted to be in a reflection mode, the polaroid is adjusted to be in an orthogonal polarization mode, and the objective lens with the power of 20 times is selected. Focusing to obtain the clearest picture, as shown in fig. 11.

And calculating the proportion of the intermediate phase part in the image by using the calculation software. Due to the refractive index and the mesophase pitch crystalline texture, there is a bright and dark interference shadow (or fringe) in the mesophase portion of the polarization microscope picture, which also causes a quantitative error, like the portion within the circle in fig. 11. The result will be either higher or lower with fine tuning of the image calculation software. In FIG. 11, the shaded portion of the mesophase is not counted, and the content of the mesophase is calculated to be 35.3%, which is lower.

In order to calculate the shadow of the mesophase, the calculation range is adjusted by the image software, which results in that the shadow of the non-mesophase is also adjusted to the mesophase, which results in a higher result, as shown in fig. 12. The mesophase content calculated in fig. 12 was 57.9%.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.