鎂碳磚在鋼鐵工業廣泛使用，常使用於轉爐和電弧爐的渣線用耐火材料，而鎂碳磚亦為極佳的盛鋼桶渣線耐火材料。由於鎂碳磚在磚爐及盛鋼桶中受鋼液與熔渣的侵蝕而剝落，因此為一耗材。本論文將探討鎂碳磚－渣系統中的礦物反應與這些反應與鎂碳磚剝蝕之關聯。對於盛鋼桶鎂碳磚壽命延長提供重要的參考。
掃描式電子顯微鏡與能量分散光譜儀分析在中國鋼鐵公司盛鋼桶渣線使用70回以上後除役之鎂碳磚，結果顯示在磚－渣過渡間有三種不同礦物組合層，分別為最近渣側之去碳層、反應層渣側與最近磚側之反應層磚側。去碳層之特徵為多大孔洞，已通常被解釋為在加熱過程中，鎂碳磚之石墨氧化後造成多孔洞，孔洞中常填充方鎂石，則來自於由鎂碳磚產生之MgO蒸氣晶出。在去碳層中單純的礦物組成可相較於反應層的複雜礦物相組成。
反應層渣側礦物相組成為鈣黃長石、尖晶石、黃長石、斜矽鎂鈣石、鈣鎂橄欖石與玻璃基質。大多數（9分之18）的玻璃的成分大約相同，Al2O3和CaO約為39%，並有約20% 的SiO2 及少於1% 的MgO。這種玻璃成分可解釋為原來可晶出C3A與C12A7的液態爐渣成分因加入了來自於鎂碳磚SiO2 與MgO而改變而成。其餘之玻璃成分組成有較低的Al2O3（22-8%），這些玻璃的成分在相關的Al2O3–CaO–SiO2–MgO系統相關之相圖中可與實際之共生礦物相互驗證。Al2O3含量較高之液態爐渣冷卻晶出序列為鈣黃長石  尖晶石 + 黃長石  尖晶石 + 黃長石 + 斜矽鎂鈣石  黃長石 + 斜矽鎂鈣石 + 鈣鎂橄欖石，與反應層中之礦物相組成類似。當液態爐渣Al2O3含量約為10% 時，將會與鈣鎂橄欖石礦物群平衡。元素區域分析顯示Al2O3、MgO、SiO2隨接近鎂碳磚系統性的增加，而CaO則降低。基於此種變化及反應於礦物相群，可由兩種模式解釋：（1）受鎂碳磚不同程度汙染的液態爐渣結晶出不同礦物相組合。（2）由均勻液態爐渣結晶分化。
反應層磚側主要由尖晶石、鎂橄欖石、鈣鎂橄欖石組成，鎂橄欖石來自氧化的矽金屬形成之二氧化矽蒸氣與鎂碳磚反應形成，鎂橄欖石在由來自爐渣以或是磚內部提供之氧化鈣而形成鈣鎂橄欖石。
在反應層中的礦物產生，有三種機制可導致鎂碳磚的劣化：（1）鎂碳磚的方鎂石與爐渣中的FeO、MnO形成低熔點的（Mg, Fe, Mn）O固溶體而熔融。（2）燒結方鎂石的間隙相部分熔融使方鎂石剝落。（3）在反應層形成之礦物相造成鎂碳磚剝蝕。上述內容應被視為盛鋼桶鎂碳磚增加使用回數之考量。

MgO-C bricks are widely used in steelmaking industry, usually as linings in basic oxygen furnace and electric arc furnace. They are also the best materials for lining the slag-line in steel ladles. Because the MgO-C bricks are subjected to corrosion by steel melt and molten slag, they flake off from furnace and ladle; therefore, are one of the consumable materials. This thesis investigated the mineral reactions in the MgO-C brick + slag system and addressed the association of these mineral reactions with the corrosion of the MgO-C bricks. The outcome provides critical references for prolonging the lifetime of the steel ladle MgO-C bricks.
SEM and EDS analyses on a MgO-C brick removed from ladle after ~70 times of steel refining process showed three different mineral assemblage zones between the slag–brick transition. They are, from closest to slag toward brick, decarburization zone, slag-side reaction zone, and brick-side reaction zone. The decarburization zone is characterized by relatively large volume of pore space, which has been commonly interpreted as vacancies resulted from carbon removal from the MgO-C bricks during heating. The pore space was filled by periclase originated as crystals from MgO vapor and as relicts from brick degradation. The simple mineral assemblage in the decarburization zone contrasts to the sophisticated ones in the reaction zone.
The slag-side reaction zone is composed of gelhenite, spinel, melilite, merwinite, monticellite and glassy matrix. The majority (9 of 18) of the glass composition analyses resulted in sub-equal amounts of Al2O3 and CaO (~39%) with ~20% SiO2 and < 1% MgO. This composition can be explained as addition of SiO2 and MgO derived from bricks into the molten slag that crystallized C3A and C12A7. Other glass compositions are characterized by lower Al2O3 contents of 22–8%. The association of these glass compositions and coexisting minerals was justified by relevant phase diagrams in the Al2O3–CaO–SiO2–MgO system. The observed mineral assemblage is consistent with crystallization from a melt with composition similar to the high Al2O3 glass in a general sequence of gelhenite  spinel + melilite  spinel + melilite + merwinite  melilite + merwinite + monticellite. Melts with compositions similar to the ~10%-Al2O3 glass were in equilibrium with monticellite-containing mineral assemblages. Element mapping showed systematical increases in Al2O3, MgO, and SiO2 and a decrease in CaO contents toward brick. Based on the fact that such a variation pattern reflects changes in mineral assemblages, this feature is explained by two models: (1) crystallization from melts whose compositions subjected to varying extents of contamination from bricks, and (2) fractional crystallization from a compositionally homogeneous melt.
The brick-side reaction zone is dominated by spinel, fosterite and monticellite. Fosterite formed as a product of interaction between periclase and SiO2 vapor derived from oxidation of Si metal in the bricks. The fosterite then reacted with the slag-derived or brick-derived CaO components to form monticellite.
The formation mechanisms of minerals in the reaction zone lead to three lines of connections to brick degradation. (1) Interaction between periclase in the brick and the FeO and MnO components in the slag formed (Mg, Fe, Mn)O, which subsequently dissolved into the slag for lower melting point. (2) Partial melting of the interstitial phases in the sintered periclase led to gradual disintegration of brick. (3) Dissolution of minerals formed in the reaction zone facilitated brick degradation. These should be considered for extending the lifetime of the steel ladle MgO-C brick.

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