稀土金屬被廣泛應用在半導體、太陽能電池以及各種催化劑的製備領域中。本篇碩論介紹了氧化物冶金的技術背景、技術原理，稀土金屬的化學性質、物理性質，稀土金屬對於鋼的微觀組織的影響。
熱力學計算在研究稀土鈰對介在物形成影響的研究中被應用到預測SS400鋼液中介在物的形成。當鋼液中的鈰含量在70ppm，鋼中起始氧硫含量都為110ppm時，鋼中鈰的氧化物會經歷由Ce2O3轉變為CeO2， 含鈰的硫化物也會經歷由CeS轉變為Ce2S3再轉變為 Ce3S4。在2000K以下，熱力學上最穩定的含Ce的介在物為CeO2 以及最不穩定的介在物為CeS. 只有在鋼中氧含量很低，硫和鈰的含量相對比較高的情況下才會有Ce2S3的形成。
不同鈰含量鋼中的主要介在物在凝固過程中可以在軟體的幫助下被預測出來，這些預測業已經過實驗的驗證。隨著鋼中的氧/硫比從0.137提高到1.157，介在物的平均尺寸越來越趨近於5μm。在鋼中發現的含Ce2O3的複雜介在物會有一層MnS的顆粒包覆，在這中介在物裡面會有大量的奈米Fe3O4顆粒其尺寸從幾納米到180奈米不等。根據TEM下的SAD觀測，這些Fe3O4顆粒的形狀接近於圓球狀。

Rare earth metals are used in semiconductors, solar cells and catalysts. This thesis introduced the background of oxide metallurgy technologies, the chemical and physical properties of rare earth (RE) metals, the background of oxide metallurgy, the functions of RE metals in steelmaking, and the influences of RE metals on steel microstructures.
Thermodynamic calculation has been applied to predict the inclusion formation in molten SS400 steel. When the Cerium addition in liquid iron is 70 ppm and the initial Oxygen and Sulphur are both 110ppm, the formation of oxides containing Cerium would experience the transformation from Ce2O3 to CeO2 and also the formation of sulfides containing Cerium would experience the transformation from CeS to Ce2S3 and then to Ce3S4. Below 2000K the most thermodynamic stable matter CeO2 and the less thermodynamic stable inclusion is CeS. Only when the amount of [O] is extremely low and the amount of [S] and [Ce] is relatively high, Ce2S3 has the possibility to form.
With the help of Factsage, the inclusion formation with different cerium amount could be predicted during solidification, which is also certified by the experiment. It is found that the inclusion size trends to be 5 μm with the increase ratio of [O]/[S] from 0.137 to 1.157. The nano-Fe3O4 particles found in the complex Ce2O3 inclusion, which has a MnS-particles covering layer, ranges from several nanometers to about 180 nm. According to the SAD analysis with TEM, the shapes of nano-Fe3O4 particles could be deciphered as near sphere.

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