硫化鐵礦物常見的包括四方硫鐵礦 (mackinawite)、硫複鐵礦 (greigite) 以及黃鐵礦 (pyrite) 等，上述硫化鐵礦物本身的獨特性除了在材料領域上有所應用外，它們的相轉變序列也於古環境以及古地磁具有指標性，在合成實驗中指出相轉變路徑以四方硫鐵礦 → 硫複鐵礦 → 黃鐵礦之序列最為普遍接受，發生的條件是硫化氫等多硫化物或者氧氣做為氧化劑存在時，目前文獻提出硫化氫以及氧氣都具有促使相轉變發生之能力，然而若同時存在此兩種不同氧化劑，硫化鐵礦物是否有優先使用的氧化劑以及相轉變是否皆會以硫複鐵礦為中間相；黃鐵礦為最終產物之序列發生等相關研究還未被詳細探討，因此本研究先合成出相轉變序列之前驅物：奈米晶粒硫鐵礦 (nanocrystalline FeS)，配置鐵硫莫耳數比為3:4、1:1以及4:3之溶液分別代表“硫多”以及“硫少”之條件，再藉由改變pH值至酸性而產生去硫化氫，並分別在厭氧和微氧環境進行實驗，觀察硫化氫或者環境中氧氣有無對於其硫化鐵礦物相轉變序列之影響；以及鐵硫莫耳數和溫度如何影響相轉變之速率，另外利用即時X光繞射分析其相轉變過程中連續變化。結果顯示：硫化氫含量充足系統中會以黃鐵礦成核之反應優先，因此硫複鐵礦在此系統中其形成速率較慢；環境中氧氣或者水中溶氧對於相轉變之影響也只於當減少硫化氫含量之條件中才得以觀察到，因即時實驗之手法是利用針筒吸取非即時實驗中配置之溶液，導致即時實驗中硫化氫含量遠小於非即時實驗條件，並且有效抑制了黃鐵礦成核，因此四方硫鐵礦 → 硫複鐵礦 → （黃鐵礦） 之序列只出現在即時實驗之厭氧環境中80oC和100oC下；若在無硫化氫系統中，則將鐵莫耳數提高可促使硫複鐵礦出現，在無硫化氫系統中提高氧氣濃度則出現針鐵礦。

Iron sulfide minerals spread wildly in sediments, including mackinawite, greigite and pyrite etc. Besides their brilliant properties in the field of material applications, the transformation sequence also plays a critical role on paleoenvironment and paleomagnetism. Most studies indicated the commonly known transformation pathway is mackinawite → greigite → pyrite and oxidants embarking transformation include hydrogen sulfide, polysulfide and oxygen. However, previous studies focused on single oxidant in solution system, the contribution of each one and whether transformation sequence always present as the intermediate phase: greigte; final phase: pyrite with existing two or more oxidants in system is less concerned and discussed. Therefore, co-precipitation was used to synthesize precursor (nanocrystalline FeS) first and prepared solution with three Fe/S values, representing “rich-sulfide” as well as “less-sulfide” conditions to observe the rate of transformation. Besides Fe/S value, oxygen was took into account by conducting experiment in anaerobic and aerobic environment, then altering pH to create the H2S system in each Fe/S condition to understand the contribution of hydrogen sulfide and oxygen to transformation. Moreover, in-situ X-ray diffraction analysis was used to obtain continuous transformation process. This study shows: the formation of greigite and the influence of oxygen in environment are limited in the abundant-H2S system where nucleation of pyrite became primary reaction. Due to synthesis method for in-situ experiment, only dropping a little amount of initial solution into capillary resulting in less amount of hydrogen sulfide in capillary, forbidding pyrite from nucleating in solution, therefore, the sequence of mackinawite → greigite → pyrite only can be observed at 80oC and 100oC from in-situ experiment. Without hydrogen sulfide and oxygen as oxidant, the formation of greigite by enhancing the molar value of iron is possible; however, goethite appeared instead not greigite as increasing oxygen concentration in environment.

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