摘要
　　
台灣東部之蛇綠岩系 (Ophiolite)，原屬於海洋地殼之基性和超基性火成岩，經變質和風化作用 … 等形成之岩石系。本研究之重點在開發該岩石系之蛇紋岩，成為高科技用途材料之新礦源。基於上述之考量，利用其提選之精礦粉，與高嶺石作適當比例之混合，來試驗燒製成為 MgO – Al2O3 – SiO2 三成分系統之工業陶瓷，即菫青石 (Cordierite)。

菫青石是含有鎂鋁之矽酸鹽礦物，其分子式是 Mg2Al4Si5O18‧n H2O，高溫相稱為六方菫青石，其分子式中沒有 H2O，具有高熔點、高強度、低介電常數、低熱膨脹係數、高電阻係數、高熱傳導率、高機械強度與極佳的抗熱震…等優異的特性，故其用途非常廣泛，除了傳統用途如汽車用燃氣輪機的熱交換器，排氣淨化用觸媒載體…等，亦極適合作為積體電路基板材料 (Integrated Circuit Substrates)，其性質較傳統氧化鋁優良。

　　菫青石的計量組成為 2 MgO．2 Al2O3．5 SiO2。本研究以高嶺石補足氧化鋁，與提純之蛇紋岩以適當比例進行固態反應，合成菫青石粉末，並製備其燒結體。探討：(1) 蛇紋岩與磁鐵礦之分選條件對氧化鐵之去除率與蛇紋岩之回收率的影響；(2) 提純後之蛇紋岩的化學組成；(3) 煅燒條件對菫青石粉末與其燒結體之影響；(4) 燒結助劑對燒結體結晶相及對其熱電性質的影響。

根據實驗結果發現：(1) 經由顎式碎礦機與加水球磨的操作程序後，蛇紋岩原礦的粒徑可大幅縮減至 10 um 以下；(2) 以 3.8 N HCl 對粒徑縮減後的蛇紋岩做酸浸漬可有效地降低 Fe 含量至 0.32 wt %，而蛇紋岩的回收率是 84.06 wt %； (3) 將提純的蛇紋岩與高嶺土來合成的粉末以1100 ℃ 持溫 4 小時煆燒，可獲得 μ – Cordierite 的結晶相，其顆粒粒徑約為 48.24 nm；(4) 比較低溫與高溫煆燒所製備之燒結體，發現前者較緻密，且其緻密化發生的溫度比高溫者低約200 ℃，顯示低溫煆燒對後續的燒結行為有較佳的結果；(5) 以氧化鉍 (Bi2O3) 作為燒結助劑，可有效降低 α – Cordierite 結晶相析出的溫度，並降低燒結緻密化溫度。以 1220 ℃ 持溫 6 小時燒結，燒結體之氧化鉍添加量為12 wt % 可得相對密度達 92 % 之 α – Cordierite。

Summary

This study is focus on developing Serpentinite as a new source for making high – tech material. For this reason, the mixture of refined Serpentinite and kaolinite with suitable ratio was sintered to be a ternary compound of MgO – Al2O3 – SiO2, that is, Cordierite.

Cordierite, due to low thermal expansion coefficient, high resistivity, high conductivity and good mechanical strength, is mainly used in the fabrication of industrial heat exchangers for turbines used in automobiles, and catalyst of self - cleaning ovens. Besides, Cordierite is expected to have great potential as substrate materials in the application of integrated circuit board replacing alumina, which has a relatively low dielectric constant (~ 5) at the high frequency region.

Stoichiometric composition of Cordierite is 2 MgO．2 Al2O3．5 SiO2. This study is to investigate precursor of Cordierite powders synthesized by refined Serpentine and kaolinite with suitable ratio via solid reaction. By the way, kaolinite is substitute for alumina. It is studied on (1) separation conditions of Serpentinite and magnetite influence on the elimination of ferric oxide and the recycling of Serpentinite; (2) compositions of refined Serpentinite; (3) effects of sintering conditions on particles size and sintered matrix; and (4) effects of sintering aid on crystalline phase and relative thermionics’ properties of Cordierite.

It is found that (1) particles size of Serpentinite can be decreased below 10 um through a jaw crusher and a ball mill duplex conditions; (2) Fe contents of Serpentine with smaller particles size can be reduced to be 3.2 wt% after soaking it into 3.8 N HCl solution; (3) μ- Cordierite crystalline phase with particle size 48.24 um synthesized by purified Serpentine and Kaolinite is obtained after calcining at temperature 1100 oC; (4) lower temperature calcining contributes to follow-up sintering behavior according to the level of densitification calcining at higher and lower temperature; and (5) growth temperature of α- Cordierite crystalline phase and densitification temperature can be reduced by Bi2O3 addition. In a word, relative density of α - Cordierite can be reached to be 92 % with 12 wt % Bi2O3 addition after sintering at temperature 1220 oC for 6 hrs.

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