Method for evaluating mesophase pitch

Abstract

The present invention discloses a method for evaluating mesophase pitch, comprising the following steps: taking a mesophase pitch bulk sample for polishing, photographing the polished mesophase pitch bulk sample using a polarized light microscope, statistically analyzing the stripes of the obtained photograph through a graphic processing software, and calculating the length, superposition angle and tortuosity; grinding the polished mesophase pitch bulk sample into mesophase pitch powder, spreading the mesophase pitch powder in a single layer on the crucible of the hot stage microscope stage, performing hot state observation under the hot stage microscope and calculating its maximum hot spreading area ratio; evaluating the mesophase pitch according to the above calculation results. The method for evaluating mesophase pitch of the present invention can quickly judge the spinnability of mesophase pitch.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the spinning performance of mesophase pitch, belonging to the technical field of rapid detection of carbon materials. Background Art

[0002] Mesophase pitch is mainly composed of aromatic-rich compounds, coal tar, coal-based petroleum asphalt, etc. As raw materials, through co-carbonization reaction or polycondensation reaction, the aromatic lamellae are stacked and arranged to form a compound with a macromolecular aromatic lamella structure. Mesophase pitch has anisotropy, high micro-order degree, and easy graphitization, and is an excellent precursor for producing high-quality carbon fiber materials. Mesophase pitch can be used as raw material to prepare many high-performance carbon materials: such as high-modulus pitch-based carbon fiber, needle coke, carbon microspheres, high-temperature lubricants, etc. Among them, mesophase pitch as a precursor for high-modulus pitch-based carbon fiber needs to have spinnability, and in addition, it needs to have sufficient pre-oxidation reaction activity in the subsequent pre-oxidation stabilization stage. To ensure the mechanical properties of mesophase pitch-based carbon fiber after carbonization and graphitization treatment, the mesophase pitch for spinning needs to have sufficient micro-order degree, manifested as having a high mesophase content. Therefore, the requirements for the spinnability of mesophase pitch are relatively high. Through a series of detection and analysis of mesophase pitch, the above-mentioned conventional indexes can be obtained. In previous patents, the description of the spinnability of mesophase pitch mainly starts from the softening point. For example, CN108181344A "Method for Determining the Softening Point of Solid Asphalt" focuses on the determination of the softening point by the traditional ring and ball method. The temperature at which the steel ball wrapped with asphalt falls is the softening point temperature. CN109709060A "Method for Determining the Softening Point, Penetration and Mass Loss of Asphalt" introduces the determination of the softening point by the penetration method, and uses the penetration at a certain temperature as a key parameter to determine the softening point of asphalt. Patents such as CN202928972U "A Component of Softening Point Determination System", CN107748175A "An Apparatus and Method for Determining the Softening Point of Mesophase Pitch" and CN110108746A "A Test Method for the Softening Point of Mesophase Pitch" also conduct research and explanation on the determination of the spinnability of mesophase pitch. The above methods all require a relatively large number of samples for high-temperature heating, and evaluate the spinnability of mesophase pitch through the softening point or penetration. Repeated heating and cooling make it impossible to test quickly. Therefore, it is necessary to develop a simple and easy method for evaluating the spinnability of mesophase pitch. Summary of the Invention

[0003] The present invention provides a method for evaluating mesophase pitch, by which the spinnability of mesophase pitch can be quickly judged.

[0004] To achieve the above object, the method for evaluating mesophase pitch of the present invention includes the following steps:

[0005] Take a block sample of mesophase pitch for polishing. Use a polarized light microscope to take pictures of the polished block sample of mesophase pitch. Statistically analyze the stripes in the obtained pictures through graphic processing software, and calculate the length, superposition angle, and tortuosity; Grind the polished block sample of mesophase pitch into mesophase pitch powder, spread the mesophase pitch powder in a single layer on the crucible of the hot stage microscope stage, conduct hot state observation under the hot stage microscope, and calculate its maximum hot spreading area ratio; Evaluate the mesophase pitch according to the above calculation results.

[0006] The present invention can also be described in detail as follows:

[0007] Take a block sample of mesophase pitch for polishing and grind a small amount into powder; Take pictures and scans of the block sample using a polarized light microscope, and calculate the length and measure the tortuosity of the stripes in the pictures through mapping software; Spread a small amount of the ground mesophase pitch powder in a single layer on the crucible of the hot stage microscope stage, record the sample under the hot stage microscope, and calculate its maximum hot spreading area ratio.

[0008] The present invention does not limit the polishing method of the sample, as long as the surface can be made mirror-like to provide a high-definition sample for further structure calculation. If not polished, the surface of the sample will be unclear, making it difficult to accurately calculate the length and measure the tortuosity of the stripes.

[0009] The present invention does not limit the size of the mesophase pitch powder, as long as the particle size is uniform. The preferred particle size of the mesophase pitch powder in the present invention is <50μm. At this particle size, the melting speed of the mesophase pitch particles is moderate and they are not prone to scattering.

[0010] The present invention does not limit the type of software for calculating the stripe length, as long as it can effectively calculate the stripe length. The preferred software for calculating the stripe length in the present invention is Frange 3D and VoL 3D.

[0011] The present invention does not limit the software used for calculating the tortuosity, as long as it can calculate the tortuosity. The preferred software for calculating the tortuosity in the present invention is MATLAB.

[0012] The maximum hot spreading area ratio of the present invention is the area ratio of the area where the mesophase pitch powder spreads to the blank area after melting to the blank area before melting.

[0013] According to the above calculation results, the present invention evaluates the spinnability of the mesophase pitch as follows:

[0014] When the heat flow temperature is 170 - 230°C, the tortuosity is 0 - 50°, the crystal texture length is 10 - 30μm, and the maximum hot spreading area ratio is 65 - 100%, the spinnability of the mesophase pitch is very good;

[0015] When the heat flow temperature is 230 - 290 °C, the tortuosity is 50 - 110 °, the crystal texture length is 30 - 60 μm, and the heat flowability spreading area ratio is 40 - 65%, the spinnability of the mesophase pitch is better;

[0016] When the heat flow temperature is 290 - 350 °C, the tortuosity is 110 - 140 °, the crystal texture length is 60 - 75 μm, and the maximum heat spreading area ratio is 15 - 40%, the spinnability of the mesophase pitch is average;

[0017] When the heat flow temperature is 350 - 400 °C, the tortuosity is 140 - 180 °, the crystal texture length is 75 - 100 μm, and the maximum heat spreading area ratio is 0 - 15%, the spinnability of the mesophase pitch is poor.

[0018] The method for evaluating mesophase pitch of the present invention has the following advantages compared with the prior art:

[0019] Through the evaluation method provided in the present invention, it is possible to judge the spinnability of mesophase pitch in a very short time, so as to quickly evaluate the feasibility of producing carbon fiber from a certain mesophase pitch, and provide a reliable basis and production index for the reaction of spinnable mesophase pitch; the amount of mesophase pitch required for this method is small, time - saving and labor - saving, reasonable and scientific, and there is no complicated analysis process. Detailed implementation manners

[0020] In order to make the technical solutions described in the present invention clearer and more understandable, the technical solutions in the present invention will be further described below in combination with specific examples and implementation manners.

[0021] Example 1:

[0022] Select massive mesophase pitch from different positions of the reaction kettle. Take a part of the crushed sample and pass it through a 300 - mesh sieve, control the particle size powder size to be <50 μm, and keep the other part in a massive form and perform polishing treatment to facilitate observing its optical structure;

[0023] Take pictures of the massive polished sample under a polarized light microscope, use software Frange 3D and VoL 3D to calculate the length of the sample; and use MATLAB to calculate the tortuosity of the sample, and the calculated stripe tortuosity is 0 °, and the crystal stripe length is 10 μm;

[0024] Put the powdered sample into a loading crucible, conduct hot - state observation under a hot - stage microscope, perform nitrogen purging treatment on the surface, and when the measured fluidity temperature is 170 °C, its maximum heat spreading area ratio reaches 100%. The spinnability evaluation standard of this mesophase pitch is very good.

[0025] Example 2:

[0026] Select massive mesophase pitch from different positions of the reactor. Take a part of the crushed sample and pass it through a 300-mesh sieve, control the particle size of the powder to be <50μm, and keep the other part in a massive form and polish it to facilitate the observation of its optical structure;

[0027] Take pictures of the massive polished sample under a polarized light microscope, use software Frange 3D and VoL 3D to calculate the length of the sample; and use MATLAB to calculate the tortuosity of the sample. The calculated stripe tortuosity is 50°, and the length of the crystal stripe is 30μm;

[0028] Load the powdered sample into a carrier crucible, conduct hot-state observation under a hot-stage microscope, perform nitrogen purging treatment on the surface, measure that when its fluidity temperature is 230°C, its maximum hot spreading area ratio reaches 65%, and the spinnability evaluation standard of this mesophase pitch is very good.

[0029] Example 3:

[0030] Select massive mesophase pitch from different positions of the reactor. Take a part of the crushed sample and pass it through a 300-mesh sieve, control the particle size of the powder to be <50μm, and keep the other part in a massive form and polish it to facilitate the observation of its optical structure;

[0031] Take pictures of the massive polished sample under a polarized light microscope, use software Frange 3D and VoL 3D to calculate the length of the sample; and use MATLAB to calculate the tortuosity of the sample. The calculated stripe tortuosity is 0°, and the length of the crystal stripe is 10μm;

[0032] Load the powdered sample into a carrier crucible, conduct hot-state observation under a hot-stage microscope, perform nitrogen purging treatment on the surface, measure that when its fluidity temperature is 230°C, its maximum hot spreading area ratio reaches 100%, and the spinnability evaluation standard of this mesophase pitch is very good.

[0033] Example 4:

[0034] Select massive mesophase pitch from different positions of the reactor. Take a part of the crushed sample and pass it through a 300-mesh sieve, control the particle size of the powder to be <50μm, and keep the other part in a massive form and polish it to facilitate the observation of its optical structure;

[0035] Take pictures of the massive polished sample under a polarized light microscope, use software Frange 3D and VoL 3D to calculate the length of the sample; and use MATLAB to calculate the tortuosity of the sample. The calculated stripe tortuosity is 50°, and the length of the crystal stripe is 30μm;

[0036] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. The surface was purged with nitrogen. When the flow temperature was measured to be 170 °C, the maximum thermal spreading area ratio reached 65%. The spinnability evaluation standard of this mesophase pitch was very good.

[0037] Example 5:

[0038] Block-shaped mesophase pitch was selected from different positions of the reactor. A part of the crushed sample was passed through a 300-mesh sieve, and the particle size of the powder was controlled to be <50 μm. The other part was retained in block form and polished to facilitate the observation of its optical structure;

[0039] The polished block-shaped sample was photographed under a polarized light microscope. Software Frange 3D and VoL 3D were used to calculate the length of the sample; and MATLAB was used to calculate the tortuosity of the sample. The calculated stripe tortuosity was 52°, and the length of the crystal stripe was 33 μm;

[0040] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. The surface was purged with nitrogen. When the flow temperature was measured to be 235 °C, the maximum thermal spreading area ratio reached 63%. The spinnability evaluation standard of this mesophase pitch was good.

[0041] Example 6:

[0042] Block-shaped mesophase pitch was selected from different positions of the reactor. A part of the crushed sample was passed through a 300-mesh sieve, and the particle size of the powder was controlled to be <50 μm. The other part was retained in block form and polished to facilitate the observation of its optical structure;

[0043] The polished block-shaped sample was photographed under a polarized light microscope. Software Frange 3D and VoL 3D were used to calculate the length of the sample; and MATLAB was used to calculate the tortuosity of the sample. The calculated stripe tortuosity was 110°, and the length of the crystal stripe was 60 μm;

[0044] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. The surface was purged with nitrogen. When the flow temperature was measured to be 290 °C, the maximum thermal spreading area ratio reached 40%. The spinnability evaluation standard of this mesophase pitch was good.

[0045] Example 7:

[0046] Block-shaped mesophase pitch was selected from different positions of the reactor. A part of the crushed sample was passed through a 300-mesh sieve, and the particle size of the powder was controlled to be <50 μm. The other part was retained in block form and polished to facilitate the observation of its optical structure;

[0047] The bulk polished sample was photographed under a polarized light microscope, and the software Frange 3D and VoL 3D were used to calculate the length of the sample; the tortuosity of the sample was calculated using MATLAB, and the stripe tortuosity was found to be 52° and the crystal stripe length was 33 μm.

[0048] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. Nitrogen purging was performed on the surface. When the fluidity temperature was measured to be 290 °C, the maximum heat spread area ratio reached 63%. The spinnability evaluation standard of this mesophase pitch is good.

[0049] Example 8:

[0050] Bulk mesophase pitch was selected from different positions of the reactor. A part of the crushed sample was passed through a 300-mesh sieve, and the particle size powder was controlled to be <50 μm. The other part was retained in bulk and polished to facilitate the observation of its optical structure.

[0051] The bulk polished sample was photographed under a polarized light microscope, and the software Frange 3D and VoL 3D were used to calculate the length of the sample; the tortuosity of the sample was calculated using MATLAB, and the stripe tortuosity was found to be 110° and the crystal stripe length was 60 μm.

[0052] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. Nitrogen purging was performed on the surface. When the fluidity temperature was measured to be 235 °C, the maximum heat spread area ratio reached 40%. The spinnability evaluation standard of this mesophase pitch is good.

[0053] Example 9:

[0054] Bulk mesophase pitch was selected from different positions of the reactor. A part of the crushed sample was passed through a 300-mesh sieve, and the particle size powder was controlled to be <50 μm. The other part was retained in bulk and polished to facilitate the observation of its optical structure.

[0055] The bulk polished sample was photographed under a polarized light microscope, and the software Frange 3D and VoL 3D were used to calculate the length of the sample; the tortuosity of the sample was calculated using MATLAB, and the stripe tortuosity was found to be 115° and the crystal stripe length was 65 μm.

[0056] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. Nitrogen purging was performed on the surface. When the fluidity temperature was measured to be 295 °C, the maximum heat spread area ratio reached 35%. The spinnability evaluation standard of this mesophase pitch is average.

[0057] Example 10:

[0058] Select massive mesophase pitch from different positions of the reactor. Take a part of the crushed sample and pass it through a 300-mesh sieve, control the particle size of the powder to be <50μm, and keep the other part in a massive form and perform polishing treatment to facilitate the observation of its optical structure;

[0059] Take pictures of the massive polished sample under a polarized light microscope, use software Frange 3D and VoL 3D to calculate the length of the sample; and use MATLAB to calculate the tortuosity of the sample. The calculated stripe tortuosity is 140°, and the length of the crystal stripe is 75μm;

[0060] Load the powdered sample into a carrier crucible, conduct hot-state observation under a hot-stage microscope, perform nitrogen purging treatment on the surface, and measure that when its fluidity temperature is 350°C, its maximum heat spreading area ratio reaches 15%. The spinnability evaluation standard of this mesophase pitch is general.

[0061] Example 11:

[0062] Select massive mesophase pitch from different positions of the reactor. Take a part of the crushed sample and pass it through a 300-mesh sieve, control the particle size of the powder to be <50μm, and keep the other part in a massive form and perform polishing treatment to facilitate the observation of its optical structure;

[0063] Take pictures of the massive polished sample under a polarized light microscope, use software Frange 3D and VoL 3D to calculate the length of the sample; and use MATLAB to calculate the tortuosity of the sample. The calculated stripe tortuosity is 115°, and the length of the crystal stripe is 65μm;

[0064] Load the powdered sample into a carrier crucible, conduct hot-state observation under a hot-stage microscope, perform nitrogen purging treatment on the surface, and measure that when its fluidity temperature is 295°C, its maximum heat spreading area ratio reaches 15%. The spinnability evaluation standard of this mesophase pitch is general.

[0065] Example 12:

[0066] Select massive mesophase pitch from different positions of the reactor. Take a part of the crushed sample and pass it through a 300-mesh sieve, control the particle size of the powder to be <50μm, and keep the other part in a massive form and perform polishing treatment to facilitate the observation of its optical structure;

[0067] Take pictures of the massive polished sample under a polarized light microscope, use software Frange 3D and VoL 3D to calculate the length of the sample; and use MATLAB to calculate the tortuosity of the sample. The calculated stripe tortuosity is 140°, and the length of the crystal stripe is 75μm;

[0068] The powdery sample is loaded into a carrier crucible and thermally observed under a hot stage microscope. The surface is purged with nitrogen. When the flow temperature is measured to be 350 °C, the maximum thermal spreading area ratio reaches 35%. The spinnability evaluation standard of this mesophase pitch is general.

[0069] Example 13:

[0070] Blocky mesophase pitch is selected from different positions of the reaction kettle. A part of the crushed sample is passed through a 300-mesh sieve, and the particle size of the powder is controlled to be <50 μm. The other part is retained in block form and polished to facilitate the observation of its optical structure;

[0071] The polished block sample is photographed under a polarized light microscope. The software Frange 3D and VoL 3D are used to calculate the length of the sample; and MATLAB is used to calculate the tortuosity of the sample. The calculated stripe tortuosity is 145°, and the length of the crystal stripe is 80 μm;

[0072] The powdery sample is loaded into a carrier crucible and thermally observed under a hot stage microscope. The surface is purged with nitrogen. When the flow temperature is measured to be 355 °C, the maximum thermal spreading area ratio reaches 10%. The spinnability evaluation standard of this mesophase pitch is poor.

[0073] Example 14:

[0074] Blocky mesophase pitch is selected from different positions of the reaction kettle. A part of the crushed sample is passed through a 300-mesh sieve, and the particle size of the powder is controlled to be <50 μm. The other part is retained in block form and polished to facilitate the observation of its optical structure;

[0075] The polished block sample is photographed under a polarized light microscope. The software Frange 3D and VoL 3D are used to calculate the length of the sample; and MATLAB is used to calculate the tortuosity of the sample. The calculated stripe tortuosity is 180°, and the length of the crystal stripe is 120 μm;

[0076] The powdery sample is loaded into a carrier crucible and thermally observed under a hot stage microscope. The surface is purged with nitrogen. When the flow temperature is measured to be 370 °C, the maximum thermal spreading area ratio reaches 2%. The spinnability evaluation standard of this mesophase pitch is poor.

[0077] Example 15:

[0078] Blocky mesophase pitch is selected from different positions of the reaction kettle. A part of the crushed sample is passed through a 300-mesh sieve, and the particle size of the powder is controlled to be <50 μm. The other part is retained in block form and polished to facilitate the observation of its optical structure;

[0079] The bulk polished sample was photographed under a polarized light microscope, and the software Frange 3D and VoL 3D were used to calculate the length of the sample; the tortuosity of the sample was calculated using MATLAB, and the stripe tortuosity was obtained as 145°, and the crystal stripe length was 80 μm;

[0080] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. Nitrogen purge treatment was carried out on the surface. When the fluidity temperature was measured to be 355 °C, the maximum thermal spreading area ratio reached 2%. The spinnability evaluation standard of this mesophase pitch was poor.

[0081] Example 16:

[0082] Bulk mesophase pitch was selected from different positions of the reaction kettle. A part of the crushed sample was passed through a 300-mesh sieve, and the particle size powder was controlled to be <50 μm. The other part was retained in bulk and polished to facilitate the observation of its optical structure;

[0083] The bulk polished sample was photographed under a polarized light microscope, and the software Frange 3D and VoL 3D were used to calculate the length of the sample; the tortuosity of the sample was calculated using MATLAB, and the stripe tortuosity was obtained as 180°, and the crystal stripe length was 120 μm;

[0084] The powdered sample was loaded into a carrier crucible and thermally observed under a hot stage microscope. Nitrogen purge treatment was carried out on the surface. When the fluidity temperature was measured to be 370 °C, the maximum thermal spreading area ratio reached 10%. The spinnability evaluation standard of this mesophase pitch was poor.

[0085] In order to further illustrate that the technical solutions described in the present invention have substantial technical effects compared with the prior art, the following comparative examples are listed in the present invention:

[0086] Comparative Example 1:

[0087] Same as Example 1, the spinnability of the mesophase pitch sample in this comparative example was analyzed by the ring method. 10 g of mesophase pitch was cold-pressed into a mold, and then a small ball was placed above the pitch for heating at a heating rate of 2 °C / min. Its softening point was measured to be 175 °C, and it was also evaluated as having good spinnability, and the test time exceeded 1.5 h.

[0088] In the evaluation method of the present invention, the optical structure test takes 3 minutes, and the hot stage microscope takes 10 minutes to observe its maximum spreading area, which can greatly save the test time. In addition, the ring method requires a long time to cool the heating medium for soaking the test samples after testing a group of samples, and continuous testing is not possible; while the optical structure test in the evaluation method of the present invention is a cold-state test and can be carried out continuously. In addition, since only 0.5 g of the sample is used in the hot stage microscope, it can be quickly cooled by purging with nitrogen for the next test. Therefore, the evaluation method of the present invention can greatly save the test time.

[0089] Comparative Example 2:

[0090] Same as Example 2-1, in this comparative example, the spinnability of the mesophase pitch was analyzed by the penetration method. 2 g of mesophase pitch powder was placed in a test tube, and a protective gas was introduced simultaneously to prevent oxidation. The test tube was placed in a crucible with molten salt and the crucible was heated at a heating rate of 2 °C / min. During the heating process, the sample was continuously pricked with a fine needle. When the penetration reached the requirement, the flow temperature of this sample was determined to be 220 °C, and the spinnability was evaluated as good. The test time exceeded 1.5 h.

[0091] In the evaluation method of the present invention, the optical structure test takes 3 minutes, and the hot stage microscope takes 12 minutes to observe its maximum spreading area, which can greatly save the test time. In addition, the penetration method requires a long time to cool the molten salt medium after testing a group of samples, and continuous testing is not possible. In addition, the penetration measurement depends on the perception of the human hand and is prone to errors; while the optical structure test in the evaluation method of the present invention is a cold-state test and can be carried out continuously. In addition, since only 0.5 g of the sample is used in the hot stage microscope, it can be quickly cooled by purging with nitrogen for the next test. Therefore, the evaluation method of the present invention can greatly save the test time, and at the same time, the test data is processed by software and is not prone to human errors.

[0092] Of course, the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention. However, these corresponding changes and deformations should all fall within the protection scope defined by the appended claims of the present invention.

Claims

1. A method for evaluating mesophase pitch, characterized in that, It includes the following steps: Take a bulk sample of mesophase pitch for polishing. Use a polarized light microscope to take pictures of the polished bulk sample of mesophase pitch. Statistically analyze the stripes of the obtained pictures through graphic processing software, and calculate the length, superposition angle and tortuosity; Grind the polished bulk sample of mesophase pitch into mesophase pitch powder, lay the mesophase pitch powder in a single layer on the crucible of the hot stage microscope stage, conduct hot state observation under the hot stage microscope and calculate its maximum hot spreading area ratio; Evaluate the mesophase pitch according to the above calculation results; The evaluation criteria are as follows: When the heat flow temperature is 170 - 230 °C, the tortuosity is 0 - 50 °, the crystal texture length is 10 - 30 μm, and the maximum hot spreading area ratio is 65 - 100%, the spinnability of the mesophase pitch is very good; When the heat flow temperature is 230 - 290 °C, the tortuosity is 50 - 110 °, the crystal texture length is 30 - 60 μm, and the hot fluidity spreading area ratio is 40 - 65%, the spinnability of the mesophase pitch is good; When the heat flow temperature is 290 - 350 °C, the tortuosity is 110 - 140 °, the crystal texture length is 60 - 75 μm, and the maximum hot spreading area ratio is 15 - 40%, the spinnability of the mesophase pitch is average; When the heat flow temperature is 350 - 400 °C, the tortuosity is 140 - 180 °, the crystal texture length is 75 - 100 μm, and the maximum hot spreading area ratio is 0 - 15%, the spinnability of the mesophase pitch is poor.

2. The method for evaluating mesophase pitch according to claim 1, characterized in that The particle size of the mesophase pitch powder is <50 μm.

3. The method for evaluating mesophase pitch according to claim 1, characterized in that, The graphic processing software is Frange 3D, VoL 3D and MATLAB; Frange 3D and VoL 3D calculate the length of the stripes of the bulk sample of mesophase pitch; MATLAB calculates the tortuosity of the bulk sample of mesophase pitch.

4. The method for evaluating mesophase pitch according to claim 1, characterized in that, The maximum hot spreading area ratio is the area ratio of the spreading area of the mesophase pitch powder after melting to the blank area before melting.