Electrolytic properties and element migration behavior in a Fe-TiB2/Al2O3 composite cathode
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摘要: 以氧化鋁溶膠為黏結劑、金屬Fe為燒結助劑, 采用冷壓-燒結制備出鋁電解用Fe-TiB2/Al2O3復合陰極材料, 利用20A電解試驗研究其電解性能; 利用能譜儀(EDS) 對電解試驗前后的復合陰極材料進行了成分物相分析, 研究電解過程中各種元素遷移行為.研究結果表明: 金屬Fe作為燒結助劑在燒結過程中能有效的填充骨料之間的空隙, 使該復合陰極材料的燒結致密度顯著提高; 20 A電解試驗過程電壓穩定, 電流效率93. 2%, 原鋁中鋁元素質量分數為99. 47%, 雜質元素質量分數為0. 53%.在電解試驗后, 鋁液能有效潤濕陰極表面, 表明Fe-TiB2/Al2O3復合陰極材料具有較理想的可潤濕性; 從復合陰極電解后的能譜分析可知, 在電解過程中, 堿金屬主要是通過液態電解質滲透進入陰極材料中, 隨后又逐漸滲透進入黏結劑相中, 并在骨料之間氧化鋁溶膠和金屬燒結助劑均未能充分填充的空隙進行富集. K元素較Na元素對黏結相的滲透力更強; 與此同時, 陰極表面生成的Al通過復合材料的空隙進入陰極內部, 而Fe金屬會利用材料內部的空隙反向擴散至鋁液層中.在試驗中, 陰極表面的鋁液層的穩定存在是該陰極高效穩定運行的基礎.Abstract: Wettable cathodes are a very important part of the non-carbon electrolysis process. This study prepared Fe-TiB2/Al2O3 composite cathode materials by cold pressing and sintering using alumina sol as a binder and metal Fe as a sintering agent for aluminum electrolysis. The electrolytic performance of aluminum electrolysis was studied using a 20 A electrolysis test, and the composite cathode materials before and after the test were analyzed via EDS. The migration behavior of various elements in the electrolysis process was studied by composition analysis. The results show that Fe metal can effectively fill the gap between the aggregates during the sintering process. Hence, the sintering density of the composite cathode material can be significantly improved. In the 20 A electrolysis test, the voltage is stable, the current efficiency is 93.2%, the original aluminum quality is 99.47%, and the impurity in the aluminum liquid is 0.53%. After the electrolysis test, the aluminum liquid can moisten the cathode surface effectively. Therefore, the Fe-TiB2/Al2O3 composite is an ideal wettable cathode material. Based on the EDS analysis of the composite cathode electrolysis, the alkali metal in the liquid electrolyte permeates into the cathode material during the electrolysis process. Subsequently, alkali metals gradually penetrate into the binder phase and fill the voids that are not completely filled by alumina sol or metal sintering additives. As the electrolysis proceeds, the penetration depth of the element K is greater than that of Na. The Al generated at the cathode surface also enters the cathode through the gap of the composite material. However, owing to the gap in the cathode, the Fe metal in the cathode will also be reversely dispersed into the liquid aluminum. This study indicates that the stability of the aluminum liquid layer on the cathode surface is the foundation for efficient and stable operation of the cathode.
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Key words:
- TiB2 composite /
- aluminum electrolysis /
- wettable cathode /
- alumina sol /
- sintering /
- element migration
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圖 2 兩種復合陰極燒結樣品微觀組織形貌圖. (a) Fe-TiB2; (b) Fe-TiB2/Al2O3
Figure 2. Microstructure of the two composite cathode sintered samples: (a) Fe-TiB2; (b) Fe-TiB2/Al2O3
圖 4 復合陰極電解實驗后形貌圖. (a) 陰極表面宏觀形貌; (b) 試驗所出鋁塊
Figure 4. Macroscopic pictures after the composite cathode electrolysis experiment: (a) macroscopic appearance of the cathode surface; (b) aluminum block from the test
圖 5 陰極表面鋁液層微觀組織及能譜圖. (a) 微觀組織; (b) 取樣點1的能譜圖; (c) 取樣點2的能譜圖
Figure 5. Microstructural diagram of the aluminum liquid layer on the cathode surface: (a) microstructure; (b) energy spectrum of sampling point 1; (c) energy spectrum of sampling point 2
圖 6 電解后陰極表面的微觀組織形貌及能譜圖. (a) 微觀組織; (b) 取樣點3的能譜圖; (c) 取樣點4的能譜圖
Figure 6. Microstructural morphology and energy spectrum of the cathode surface: (a) microstructure; (b) energy spectrum of sampling point 3; (c) energy spectrum of sampling point 4
圖 7 TiB2骨料間微觀組織形貌及能譜圖. (a) 微觀組織; (b) 取樣點5的能譜圖; (c) 取樣點6的能譜圖; (d) 取樣點7的能譜圖; (e) 取樣點8的能譜圖
Figure 7. Microstructure and energy spectrum of the TiB2aggregate: (a) microstructure; (b) energy spectrum of sampling point 5; (c) energy spec-trum of sampling point 6; (d) energy spectrum of sampling point 7; (e) energy spectrum of sampling point 8
表 1 三種材料的相對密度
Table 1. Relative density of the three materials
材料 相對密度/% Fe-TiB2/Al2O3復合材料 94.21 Fe-TiB2復合材料 91.14 文獻[12]的TiB2/Al2O3復合材料 92.48 
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表 2 電解后陰極各元素的能譜統計結果
Table 2. Statistical analysis of the EDS spectra of each element at the edge of the sample
元素 能譜結果(質量分數)/% 取樣點3 取樣點4 Fe 65.91 — Al 19.68 — Ti 14.41 89.54 B — 10.46
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表 3 圖 7取樣點對應各元素的能譜統計結果
Table 3. Statistical results of the EDS energy spectrum of the element corresponding to the sampling points in Fig. 7
元素 取樣點能譜分析結果(質量分數)/% 取樣點5 取樣點6 取樣點7 取樣點8 O — 4.48 37.35 6.42 F — 11.62 — 27.97 Na — 1.91 — 3.53 Al — 13.36 47.49 29.01 K — 0.55 1.47 9.93 B 10.46 7.07 — — Ti 89.54 61.01 13.69 23.15
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