稀土电解槽石墨内衬高温氧化过程中孔隙结构演化规律及其分形特征

doi:10.16085/j.issn.1000-6613.2018-1031

摘要/Abstract

摘要：

针对稀土电解槽石墨内衬破损问题，采用显微CT研究稀土电解槽石墨内衬在不同氧化时间下内部微观孔隙结构演化特征，考察了孔隙率、孔喉尺寸、孔喉形状因子、孔隙分形维数等参数的变化规律。结果表明: 石墨内衬氧化0、1h、2h、3h后的平均孔隙率在逐渐增大，分别为4.02%、8.53%、11.18%、13.35%，孔喉尺寸为5～25μm与孔喉形状因子为0.02～0.05的孔喉数量从17903增加到39388。进一步应用分形理论分析发现：氧化不同时间的石墨内衬孔隙构造均符合分形规律，且随着氧化时间的增大，石墨内衬的氧化腐蚀越来越严重，石墨内衬孔隙分形维数从1.5722增加到1.6985。因此可以间接地用分形维数来判断石墨内衬的氧化腐蚀程度。最后建立了石墨内衬渗透率的分形表达式，由此计算氧化0、1h、2h、3h的石墨内衬理论渗透率分别为0.10 $μ$ m²、0.25 $μ$ m²、0.37 $μ$ m²、0.52 $μ$ m²。计算结果与其实际渗透率0.09 $μ$ m²、0.18 $μ$ m²、0.38 $μ$ m²、0.57 $μ$ m²相差不大，可以用此式来预测石墨内衬的渗透率。

关键词: 石墨内衬, 渗透率, 多孔介质, 氧化, 孔隙演化, 分形

Abstract:

In view of the breakage of graphite lining in rare earth electrolytic cell, micro-CT was used to study the evolution characteristics of internal micro-pore structure of rare-earth electrolytic cell graphite lining under different oxidation time. The variation rules of the porosity, pore throat size, pore throat shape factor, pore fractal dimension and other parameters were investigated. The result showed that the average porosity of the graphite lining was gradually increased after 0, 1h, 2h and 3h of oxidation time, and the porosity were 4.02%, 8.53%, 11.18%, and 13.35%, respectively. The number of pore throats with size between 5—25 $μ$ m and shape factor between 0.02—0.05 increased from 17903 to 39388. Therefore, fractal dimension can be used indirectly to judge the degree of oxidation corrosion of graphite lining. Finally, a fractal expression of the permeability of the graphite liner was established. The theoretical permeability of the graphite liner under the oxidation time of 0, 1h, 2h, and 3h was calculated to be 0.10 $μ$ m², 0.25 $μ$ m², 0.37 $μ$ m², and 0.52 $μ$ m², respectively. The calculated result were similar to the actual permeability which were 0.09 $μ$ m², 0.18 $μ$ m², 0.38 $μ$ m² and 0.57 $μ$ m², therefore, it can be used to predict the permeability of graphite lining.

Key words: graphite lining, permeability, porous media, oxidation, pore evolution, fractal

中图分类号:

TF845

刘庆生,段旭,谈成亮. 稀土电解槽石墨内衬高温氧化过程中孔隙结构演化规律及其分形特征[J]. 化工进展, 2019, 38(03): 1468-1475.

Qingsheng LIU,Xu DUAN,Chengliang TAN. Evolution of pore structure and fractal characteristics of graphite lining in rare earth electrolytic cell during high temperature oxidation[J]. Chemical Industry and Engineering Progress, 2019, 38(03): 1468-1475.

图/表 13

表1 显微CT扫描参数

探测器

类型

像素尺寸

/μm

电压（kV）

/电流（μA）

扫描帧数

/耗时

曝光

时间

?

10mm×10mm

表1 显微CT扫描参数

探测器

类型

像素尺寸

/μm

电压（kV）

/电流（μA）

扫描帧数

/耗时

曝光

时间

视场

5.6

60/150

1800/7h

?

10mm×10mm

图1 石墨内衬显微CT扫描实验

图2 不同氧化时间石墨内衬的CT图

图3 原始CT灰度图二值化过程

图4 样品三维CT图像处理

图5 不同氧化时间的石墨孔隙率分布图

图6 孔隙半径分布图

图7 喉道半径分布图

图8 孔隙形状因子分布图

图9 喉道形状因子分布图

图10 不同氧化时间石墨孔隙的分形维数

图11 不同氧化时间石墨的灰度切片及其二值化图

表2 石墨内衬渗透率计算结果

氧化时间 /h	孔隙率 /%	最小孔隙半径/ $μ$ m	最大孔隙半径/ $μ$ m	分形维数	实际渗透率/ $μ$ m²	理论渗透率/ $μ$ m²
0	4.02	5.6	18.67	1.5722	0.09	0.10
1	8.53	5.6	21.79	1.6465	0.18	0.25
2	11.18	5.6	25.80	1.6788	0.38	0.37
3	13.35	5.6	31.53	1.6985	0.57	0.52

表2 石墨内衬渗透率计算结果

氧化时间 /h	孔隙率 /%	最小孔隙半径/ $μ$ m	最大孔隙半径/ $μ$ m	分形维数	实际渗透率/ $μ$ m²	理论渗透率/ $μ$ m²
0	4.02	5.6	18.67	1.5722	0.09	0.10
1	8.53	5.6	21.79	1.6465	0.18	0.25
2	11.18	5.6	25.80	1.6788	0.38	0.37
3	13.35	5.6	31.53	1.6985	0.57	0.52

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