CN111855537A

CN111855537A - HRTEM-based method for measuring micro-pore diameter in coal

Info

Publication number: CN111855537A
Application number: CN202010852224.0A
Authority: CN
Inventors: 李霞; 王小令; 曾凡桂; 边洁晶
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2020-08-21
Filing date: 2020-08-21
Publication date: 2020-10-30

Abstract

The invention relates to the technical field of coal pore structure determination, in particular to a method for determining the micro pore diameter in coal based on HRTEM; the method comprises the following steps: 1) performing demineralization treatment on a coal sample, then performing high-resolution transmission electron microscope analysis, denoising an original image, performing Fourier-inverse Fourier transform, and performing binarization treatment on the image; 2) image inversion (Invert) with ImageJ software; 3) performing watershed segmentation algorithm on the reversed image; 4) calculating the area of each segmented block of the image obtained in the step 3), namely the area of a single micro hole; 5) fitting each obtained block into a square approximately, and calculating the side length of each block to obtain the aperture distribution; the method of the invention reproduces the distribution of the pores in the basic structure unit of the coal macromolecule intuitively, and especially plays a good guiding role in researching the relationship between the distribution of the pores in the coal and the basic structure unit of the coal macromolecule for the specific position of the pores.

Description

HRTEM-based method for measuring micro-pore diameter in coal

Technical Field

The invention relates to the technical field of coal pore structure determination, in particular to a method for determining the micro pore diameter in coal based on HRTEM.

Background

The tiny pores in coal have been proved to be the main space for storing the coal bed gas and also an important tunnel for transporting the coal bed gas, and there is sufficient evidence that the tiny pores in coal provide most of the total pore volume and the total specific surface area, and directly influence the storage, absorption, desorption and diffusion of the free gas. Therefore, the tiny pores in coal have become the focus of current research, and many researchers have conducted research and achieved significant results, and the change of the chemical structure of coal has a significant influence on the nanometer-scale pores in coal, especially on micropores: (<2 nm). Due to the limitation of experimental conditions, micropores are difficult to embody visually, so that the distribution condition of the micropores in different coals can be displayed only by constructing a 3D molecular structure model of the coals. In connection with this work, the earliest scholars, Faulon et al, used three-dimensional (3D) coal molecular structure to study micropore size distribution, confirming the presence within the 3D coal molecular structure<1nm of ultra-micro pores, ultra-micro pore volume and low pressure CO₂The adsorption data were found to be consistent. In subsequent studies, where the nanopore scale has been tapered to a level of 0.6nm, Feng and Bhatia have suggested that small pores (about 0.6 nm) may represent the region between the basal planes of two crystallites, and larger pores (1.3 nm) should represent the space between the edge locations of two crystallites.

At present, most of the research on the micropores adopts a molecular simulation method, but the pore distribution in the coal cannot be more truly reflected. In recent years, various methods have been developed, such as mercury intrusion, liquid nitrogen adsorption, small angle X-ray scattering (SAXS) analysis, neutron scattering (SANS) analysis, and Scanning Electron Microscope (SEM) analysis. Because coal is composed of coal macromolecular Basic Structural Units (BSU), it is difficult to quantify nanometer pores by common technical means, for example, mercury intrusion experiments are mainly used for measuring macropores with a pore diameter of more than 100 nm, liquid nitrogen adsorption experiments are mainly used for measuring pores with a pore diameter of more than 2nm, and atomic force microscopes, scanning electron microscopes and the like are mainly used for observing pore structures and forms. While nanopores smaller than 2nm in coal are less reported.

The advent of High Resolution Transmission Electron Microscopy (HRTEM) opened the micro-world door to the study of materials, the macromolecular structural building blocks of coal have been detected, and quantitative studies have done little on coal nanopores, although quantitative effects on lattice fringes in coal have been achieved.

Disclosure of Invention

The invention aims to provide a method for measuring the pore size of coal based on HRTEM (high resolution transmission electron microscopy), which can be used for visually quantifying the structural information of the pore size of the coal through the HRTEM.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a method for measuring the micro-pore diameter in coal based on HRTEM comprises the following steps:

step 1), carrying out demineralization treatment on a coal sample, then carrying out high-resolution transmission electron microscope analysis on the demineralization coal sample, carrying out processes of denoising, Fourier-inverse Fourier transform, binarization treatment of the image and the like on an original image, and before that, removing the boundary, the mark and the scale of the microscopic image.

And 2) importing the obtained binary image into ImageJ software, intercepting an image containing lattice fringe information, and reversing (Invert) the part except the region.

And 3) carrying out WaterShed segmentation algorithm (WaterShed) on the reversed image.

And 4), setting the obtained image according to the original scale, scribing to define the length of the image, and finally calculating the area of each segmented block, namely the area of a single micro hole.

And 5), approximately fitting each obtained block into a square, and calculating the side length of each block to obtain the aperture distribution.

Further, in the step 3, the set inversion region is a region covered by the black-and-white binary image, and is not all regions of the electron microscope image.

Further, in the step 4, the black blocks after the inversion can be approximated to be micro holes in the coal.

Compared with the prior art, the invention has the following beneficial effects:

the method is simple, reproduces the distribution situation of the pores in the coal macromolecule basic structure unit more intuitively, and plays a good guiding role in researching the relationship between the distribution of the micropores in the coal and the coal macromolecule basic structure unit particularly for the specific positions of the micropores.

Drawings

FIG. 1 is an electron microscope raw image and a binarized image of Ducheng No. 2 coal with the aid of an embodiment of the present invention.

FIG. 2 shows an image processing procedure (a is to segment the binarized image, b is to invert the segmented binarized image, and c is to perform a watershed algorithm on the inverted image to obtain a plurality of independent black blocks) in the embodiment of the present invention.

FIG. 3 is a diagram of a model of the final micro-aperture distribution obtained in the embodiment of the present invention.

FIG. 4 is a diagram illustrating the final distribution of the aperture of the micro-holes according to the embodiment of the present invention.

Detailed Description

The present invention is further illustrated by the following specific examples.

Examples

This example illustrates the processing of high resolution transmission electron microscopy images of coal, Dortella 2, Shanxi.

Taking 5g of No. 2 coal of the Ducheng, measuring the micro pore diameter in the coal based on HRTEM, and carrying out the following steps:

step 1), performing demineralization treatment on the coal sample, and then performing high-resolution transmission electron microscope analysis on the demineralization coal sample to obtain an electron microscope original image of the coal of Ducheng No. 3, as shown in FIG. 1 a. The method comprises the following steps of denoising an original image, Fourier-inverse Fourier transform, binarization processing of the image and the like, and before the process, removing boundaries, marks and scales of a microscopic image.

And 2) importing the obtained binary image into ImageJ software, intercepting an image containing lattice fringe information, and inverting (Invert) the part except the region as shown in FIG. 2a to obtain FIG. 2 b.

And 3) performing a WaterShed segmentation algorithm (WaterShed) on the reversed image to obtain a graph 2c, so that the distribution condition of the segmented holes can be clearly seen.

And 4), setting the obtained image according to the original scale, scribing to define the length of the image, and finally calculating the area of each segmented block, namely the area of a single micro hole. Finally, a pore distribution model diagram of the coal Dunerg No. 2 is obtained, as shown in FIG. 3.

And 5) approximately fitting each obtained block into a square, and calculating the side length of each block to obtain the aperture distribution, as shown in FIG. 4.

Claims

1. A method for measuring the micro-pore size in coal based on HRTEM is characterized by comprising the following steps:

step 1), performing demineralization treatment on a coal sample, then performing high-resolution transmission electron microscope analysis on the demineralization coal sample, removing the boundary of a microscopic image, marking and scaling, and then performing denoising, Fourier-inverse Fourier transform and binarization treatment on an original image;

step 2), importing the obtained binary image into ImageJ software, and intercepting an image containing lattice fringe information for inversion;

step 3), carrying out watershed segmentation algorithm on the reversed image;

step 4), setting the image obtained in the step 3) according to the original scale, scribing to define the length of the image, and finally calculating the area of each segmented block, namely the area of a single micro hole;

2. The HRTEM-based method for measuring the pore size in coal as claimed in claim 1, wherein the reversed region is the region covered by the black-white binary image.

3. The HRTEM-based method for measuring the sizes of the micro pores in the coal as claimed in claim 1, wherein the black blocks after inversion in the step 4 are similar to the sizes of the micro pores in the coal.