修復用石灰的碳酸鈣含量之檢測方法研究

Method for Measuring Calcium Carbonate Content in Restoration Lime

我國在古蹟灰作修復時所用的石灰其來源多元、品質參差不齊、中性化程度不一，無法掌握所得灰作的品質及耐久性，本研究認為為改善此缺點，對於使用於古蹟灰作修復的石灰，在施工前應對其純度，即有效成分氧化鈣、氫氧化鈣，或無效的成分碳酸鈣加以檢測，以使修復的灰作能有充分的品質保障。本研究所研發的石灰中碳酸鈣的含量檢測方法有質量守恆檢測法和二氧化碳（CO_2）濃度檢測法二種。其中質量守恆檢測法，係根據石灰中之碳酸鈣遇酸產生的二氧化碳氣體會消散，因此依待測石灰實驗前後之質量差異，可以推估其含有二氧化碳比例，進而得到碳酸鈣比例。二氧化碳濃度檢測法，乃根據石灰中的碳酸鈣遇酸會產生二氧化碳，因此可以用二氧化碳濃度檢測儀器，記錄實驗前後二氧化碳濃度變化量，進而推出碳酸鈣比例。本研究亦以X光繞射儀檢測各試樣的碳酸鈣含量，作為比較之參考基準。研究結果顯示，市售之試藥級氧化鈣、氫氧化鈣純度並非如標示所示，疑因製造時間、存放環境等因素，產生水化、碳化反應，使其純度下降。二氧化碳濃度檢測法之穩定度優於質量守恆方法，與X光繞射法相比誤差也較小，且設備簡單、操作迅速，可運用在現地快速檢測修復用石灰之碳酸鈣含量。

This study explored the in-situ measurement of calcium carbonate (CaCO_3) content in lime used for restoring heritage sites (hereinafter ＂restoration lime＂). Restoration lime varies in source, quality, and degree of neutralization. Consequently, the quality and durability of lime work also varies. To address this problem, the purity of the restoration lime - including the active ingredients, such as CaO and Ca(OH)_2, and the inactive ingredients, such as CaCO_3, that it contains - should be measured before construction. This study developed the following two methods for measuring the CaCO_3 content of lime:1. the law of conservation of mass and 2. carbon dioxide (CO_2) concentration. Both the proposed methods are based on the dissipation of the CO_2 gas produced by the CaCO_3 in lime when the lime is exposed to acid. In the conservation of mass method, the concentration of CO_2 in the sample is estimated according to the difference in the mass of the lime sample before and after acid exposure and is used to determine the CaCO_3 content of the sample. In the CO_2 concentration method, a CO_2 concentration detector is used to measure the changes in the CO_2 concentration of a lime sample before and after acid exposure and to convert them into moles of CO_2, which can be used to determine the concentration of CaCO_3. In this study, an X-ray diffractometer was used to measure the CaCO_3 content of lime samples as a reference for comparing the applicability of the two methods. The key findings of the study are as follows: 1. Commercially available reagent-grade CaO and Ca(OH)_2 may not be as pure as indicated on the label. Their purity gradually decreases because of hydration and carbonization during manufacturing and storage. 2. The CaCO_3 measurements obtained using the CO_2 concentration method were more reliable than those obtained using the conservation of mass method and fewer errors than those from the X-ray diffraction measurements. CO_2 concentration detectors are simple and quick to be operated and can be used for rapid in situ measurement of the CaCO_3 content in restoration lime.