本研究利用不銹鋼於高碳勢環境中的金屬塵化機制製備奈米碳管。取經噴砂處理之304L不銹鋼，於CO/CO2=35/1之混合氣氛中進行不同溫度之塵化實驗，以探討溫度及碳勢(carbon activity)對碳沉積物結構的影響，並作為製備奈米碳管之依據。實驗結果顯示，隨著碳勢的減少，碳沉積物的形貌由實心纖維轉變為空心的多壁奈米碳管，再變成管壁更薄的單壁奈米碳管集束，在碳勢僅5時甚至無法形成管狀石墨結構，因此可發現管狀石墨結構的生成需要一臨界碳勢，小於此臨界值則無法生成。另外，試片上所有碳沉積物的量也可從SEM上觀察到隨碳勢降低而減少的趨勢。而隨著溫度的上昇，碳沉積物的原子規則排列程度也明顯提升，顯示其結晶性隨溫度的升高而提升。

根據表面形貌觀察結果，於600 ℃下之CO/CO2混合氣氛中進行500小時塵化實驗，並收集所生成之多壁奈米碳管，以電化學方法進行儲氫量之量測與儲氫性能提升之研究。本研究以空氣氣氛熱處理、硝酸酸洗及兩種方法交替進行等方式，對奈米碳管原材進行後處理，並發現碳管表面特性會顯著影響其吸附氫原子的效能，適度提升其表面活性可提高吸附量。SEM與TEM照片顯示，空氣氣氛中熱處理有助於非晶質碳的氧化及碳管封閉端的開口，改善氣體在碳管中的流通性，提升吸附氫氣的效能，與原材相比放電量可提高約50 %。硝酸酸洗則可洗去金屬顆粒，氧化非晶質碳達到純化的效果，並可適度增加碳管表面缺陷以提高表面能，進而使放電量提高約80 %。但過度的酸洗卻會造成管狀石墨結構的破壞，破碎的碳管結構彼此團聚減少表面積與可吸附氫原子位置，降低其吸氫效能。

經熱處理再酸洗的碳管由於表面非晶質碳已在熱處理中去除，硝酸全部用於洗去金屬顆粒以及與碳管表面產生反應，故其表面形貌照片顯示碳管結構破碎，而在TEM照片可發現內壁薄化的現象，且酸洗可去除金屬顆粒，充放電實驗結果顯示，其放電量仍略高於僅熱處理之碳管。

經酸洗再熱處理之碳管，由於酸洗時破壞較嚴重的碳管可在熱處理過程中優先氧化，故在拉曼光譜中可發現，其結構中缺陷振動強度與石墨單晶振動強度的比例低於僅酸洗的碳管，顯示其結晶性優於酸洗4小時的碳管，在TEM中觀察到的管狀結構普遍較完整，而其放電量則是略低於僅酸洗的碳管，顯示酸洗4小時已是本實驗中最適合的後處理方式，後續的熱處理並未能使儲氫效能提升。

In this study, carbon nano-materials were grown during the metal dusting of stainless steel in the high carbon activity atmosphere. The sand-blasted 304L stainless steels were exposed in mixed CO/CO2 atmosphere with different exposure temperatures, to investigate effects of temperature and carbon activity.

The SEM and TEM images showed that the diameter of the carbon filament decrease with carbon activity, and there must be a critical carbon activity that the carbon filament would not form with a carbon activity under it. We can also find that the amount of carbon deposits on the substrate increase with the raise of carbon activity. In another way, carbon atoms arrangement is more regular with the raise of temperature. It means the carbon deposits get better crystallization with higher temperature. So the morphology of carbon nano materials could be explained clearly with temperature and carbon activity.

According to former experiment results, we chose multi-walled carbon nanotubes grown at 600 ºC to investigate its hydrogen storage performance. The substrates were exposed in mixed atmosphere at 600 ºC for 500 hours, and then we collected the coke in the chamber for electrochemical hydrogen storage experiment. The surface characteristics of carbon nanotubes (CNTs) determine the interaction with hydrogen, effective surface treatments on carbon nanotubes to gain surface activity is a significant step. Two basic post-treatment are used for purification and surface modification. One is heat treatment in air and the other is nitric acid treatment with different times. At last we mixed the two ways and hoped to combine the advantages of them.

The SEM and TEM images showed that heat treatment in oxidation atmosphere is effective to eliminate amorphous carbon and open the closed-end of tubes. These effects were also reflected with the electrochemical discharge capacity of CNTs after heat treatment which improved by 50% of as-prepared CNTs. Acid treatment can dissolve catalyst particles and eliminate amorphous carbon. And it can also form micro-pores or etch groove on the CNTs to bring in dangling bonds which make CNTs active, so the hydrogen can gather on the CNTs. The charge-discharge experiment results of the acid treatment CNTs showed the highest discharge capacity. But for longer acid treatment time, the structure of the tubes is destroyed gradually and amorphous carbon is formed, so hydrogen adsorption is lower.

Then we combined the two post-treatments. The CNTs with heat treatment followed by acid treatment showed that the amorphous carbon was oxidized during heat treatment, so the following acid treatment would react directly with CNTs structure and cause over pickling of CNTs. But the acid treatment can dissolve metal particles, so it’s hydrogen storage performance still better than the CNTs after heat treatment.

The heat treatment after acid treatment oxidized the amorphous carbon and low crystallization tube walls produced during acid treatment. Micro-Raman spectrum showed that the heat treatment after acid treatment really fostered crystallization. But it’s hydrogen storage performance showed that the heat treatment after 4 hours acid treatment didn’t help hydrogen adsorption on CNTs.

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