非晶質碳質物之石墨化現象

Abstract

由碳質物轉變而成的石墨化現象是一個受溫度大幅影響的過程，且其反應被認為是不可逆的，能夠記錄岩石中石墨形成時的最高溫度。因此，這是一種能夠廣泛用於決定地層中變質作用發生時之峰值溫度的溫度計。石墨在不同變質地區的最高變質溫度是以石榴子石-黑雲母、鐵-鎂元素分配地質溫度計以及磷灰石核飛跡溫度計來進行估算。結果顯示峰值溫度與拉曼光譜中之三個拉曼光譜帶參數G band（Graphite band）、D1 band（Defect band 1）與D2 band（Defect band 2）之間呈線性關係。除了變質區域外，近幾年對於2008年汶川地震的研究中顯示，石墨化作用能夠在地震斷層的滑移帶出現（Togo et al., 2011），指示石墨可能不僅只在傳統的變質條件下形成。 本研究以非晶質碳質物作為原始材料，並在400°C至900°C的溫度範圍內通氮氣進行處理，實驗時間為2至6小時。每個實驗分別以改變溫度和實驗時間進行處理來避免偏差，並以拉曼光譜、X光繞射與穿透式電子顯微來分析非晶質碳質物之石墨化過程。實驗結果顯示，當非晶質碳質物在經過2小時處理後，隨著溫度的升高，拉曼光譜的R1比例（D1 / G）與溫度之間存在線性關係，然而當回到室溫後，高溫處理過程無法完整記錄在碳質物中。X光繞射資料顯示石墨晶格面（100）和晶格面（101）在處理之後出現峰值，表示天然的石墨化從晶格面（100）和晶格面（101）這兩種結構開始產生，而不是從人造石墨的特徵晶格面（002）結構面開始。因此本研究顯示石墨化現象可能無法記錄最高溫度，並且一部分石墨化現象在冷卻後是可逆的。

Graphitization, the conversion of carbonaceous material to graphite, is considered to be an irreversible process that is independent of pressure but strongly dependent on temperature and records the highest temperature of graphite genesis. Therefore, it is often used as a geothermometer to determine the peak temperature of metamorphism in the strata. The highest temperatures achieved in different metamorphic areas were mainly estimated by the results of garnet-biotite Fe-Mg partitioning geothermometer, and apatite fission track thermometers. Studies show that the peak temperature has a linear relationship with Raman bands：G band（Graphite band）、D1 band（Defect band 1）and D2 band（Defect band 2）. Graphitization has been reported in slip zones of seismic faulting, e.g. the 2008 Wenchuan earthquake, insinuating that graphite may form outside of traditional metamorphic conditions. In this study, amorphous carbon samples were chosen as starting materials and treated at temperatures ranging from 400°C to 900°C for 2 to 6 hours. In each experiment, either temperature or experiment time was chosen as the control variable in order to avoid deviation. The TEM, Raman spectra analyzer, and X-ray diffraction were used to analyze the graphitization process of amorphous carbon. In-situ analyses indicate a positive correlation between temperature and Raman R1 ratio (D1/G) as the temperature increases during 2 hours of treatment. However, this correlation seems to be not preserved once annealed to room temperature. After being treated, the X-ray diffraction patterns of graphite (100) and (101) peaks are significant, suggesting that natural graphitization initiates at (100) and (101) instead of the synthetic graphite characteristic (002) peak. Graphitization, therefore, might not record the highest temperature, and a portion of graphite may be reversible after cooling.