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研究生： 黃惟聖
Huang, Wei-Sheng
論文名稱： 以有機金屬化學氣相沈積技術及熱壓製程製備奈米級碳化鉻/氧化鋁複合陶瓷之研究
Investigation of chromium carbide/alumina Nano-composite via Metal Organic Chemical Vapor Deposition and Densification Process
指導教授： 黃肇瑞
Huang, Jow-Lay
學位類別： 碩士
Master
系所名稱： 工學院 - 材料科學及工程學系
Department of Materials Science and Engineering
論文出版年： 2003
畢業學年度： 91
語文別： 中文
論文頁數： 94
中文關鍵詞： 有機金屬化學氣相沈積法 、氧化鉻 、碳化鉻 、氧化鋁 、奈米複合材料
外文關鍵詞： alumina, MOCVD, chromium carbide, chromium oxide, nanocomposite
相關次數： 點閱：86  下載：2 
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    • 本研究利用有機金屬化學氣相沈積法（MOCVD）與流體床（Fluidized Bed）技術，成功製備出奈米碳化鉻（Cr3C2、Cr7C3）/氧化鋁（Al2O3）陶瓷複合粉體，並研究熱壓燒結過程中，環境對材料內部發生的反應及微結構之影響，並探討氧化鉻（Cr2O3）/氧化鋁（Al2O3）固溶材料中之微結構。

    實驗結果顯示，利用有機金屬化學氣相沈積法（MOCVD）與流體床（Fluidized Bed）技術，流體化效果較佳時，先導物經裂解後，以顆粒狀的型態沈積於氧化鋁的顆粒表面，反之，沈積型態則以島狀或鍊狀的方式居多。其中，島狀或鍊狀披覆物，相當於許多顆粒狀披覆物相互連結，單顆尺寸大約為30nm，經由成分分析判定沈積相為非晶質之氧化鉻。

    氧化鉻與碳化鉻的轉換反應，將受反應物碳活性影響。氧化鉻/氧化鋁複合粉體，在高溫通以氬氣作為保護氣氛之石墨爐體中，一方面可藉由與粉體接觸之活性較大的碳，使氧化鉻反應成Cr3C2；另一方面，亦可於爐體中，由爐體或坩鍋等提供之碳游離基，藉氣體攜帶擴散進入粉體中，雖活性較小，卻可使氧化鉻反應成Cr7C3。另外，當粉體密度較高，因使氣體不易進入，粉體中之碳游離基少，故相同的粉末於熱壓燒結環境中，將無法形成Cr3C2。

    氧化鉻/氧化鋁之複合粉體於1400℃真空環境中進行熱壓燒結時，將有兩反應同時進行，一為氧化鉻與氧化鋁之間之固溶反應，二為氧化鉻與碳游離基之碳化反應，其中又以固溶反應速率較快，故此時燒結體為碳化鉻及氧化鋁固溶體之複合材料。其中碳化鉻將以三種型態存在於材料中，包含微米、次微米且位於晶界上；奈米（約80nm）位於晶界上，及奈米（約30nm）位於晶粒內。燒結體強度可達464 MPa，破壞韌性達5.32 MPa*m1/2。

    The metal-organic chemical vapor deposition (MOCVD) conducted in a fluidized bed has been employed for the preparation of nano-sized chromium carbide and alumina composites. Chromium hexacarbonyl(Cr(CO)6) was decomposed and successfully deposited onto alumina particles. The phase and amount of deposition depend on the deposition time and the state of fluid.

    The crystalline phase and microsturcture of as-deposited powders were characterized by XRD、ESCA and TEM. The result indicated the deposition was amorphous Cr2O3 exastinagas island-like (chain) type or individual type.

    In order to obtain Cr3C2/Al2O3 composite powder, heat treatment in graphite furnace is required. The Cr7C3/Al2O3 composite was produced from as-deposited powder by hot-pressed at 1400℃ in vacuum for 1h due to carbonization by the of carbon radicals from graphite mould. At high temperature, the conversion of chromium oxide to Cr3C2 or Cr7C3 depends on the activity of carbon.

    The microstructure of the dense composites was also discussed. The inclusion(Cr7C3) in Cr7C3/Al2O3 composite existed as three types. The matrix Al2O3 transformed into solid solution with a small quantity of Cr2O3. Some pores inside grain induced dislocation cell or low angle grain boundary because of large internal stress generated during cooling from the fabrication temperature 1400℃.

    論文摘要……………..……………………………………………..Ⅰ Abstract……..……………………………………………………….Ⅲ 總目錄………..……………………………………………………..Ⅴ 圖目錄……………..………………………………………………..Ⅷ 表目錄……..……………………………………………………..ⅩⅢ 第一章 緒論…………………………………...……….…………....1 1-1 前言……………….……………………………………….….…1 1-2研究目的及重點….…………………...………………………...2 第二章 理論基礎…………….…………………….………………4 2-1 陶瓷基複合材料…………………..….…………….…………...4 2-1-1 陶瓷基複合材料韌化方式……….…………………….…...4 2-1-2 奈米複合材料……………………….……………………....5 2-2 化學氣相沈積法及流體床技術…………………….…….…...10 2-2-1 CVD製程………………………………………….……...11 2-2-2 MOCVD製程中六羰鉻使用之探討……..…….…….…..14 2-3 鉻之碳化物或氧化物與氧化鋁複合材料…………….……....15 2-3-1 碳化鉻（Cr3C2）/氧化鋁（Al2O3）複合材料…………..15 2-3-2 碳化鉻（Cr7C3）/氧化鋁（Al2O3）複合材料……..…....15 2-3-3氧化鉻（Cr2O3）/氧化鋁（Al2O3）合金材料…………..16 第三章 材料與實驗步驟…...……………..……..……………....20 3-1 實驗設計…………………………………………….………....20 3-2 實驗設備及合成複合粉體之製程…………………….….…...22 3-2-1 MOCVD與流體床之實驗設計…………………….….....22 3-2-2 實驗材料……………………………………………...…...24 3-2-3合成複合粉體之製程………………………………...…...24 3-3 複合粉體熱處理之製程………………………….……….…...26 3-4 複合材料之燒結製程……………………………………….....26 3-4-1起始粉末的製備………………………………………......28 3-4-2熱壓燒結參數…………….…………………………….....28 3-5 複合粉體熱處理前後之性質分析……………….……….…...28 3-5-1 複合粉體之相分析……………………………..….……...28 3-5-2 複合粉體之表面型態之觀察………………………...…...30 3-5-3 複合粉體之ESCA成分分析……………………….…....30 3-5-4 碳硫分析儀…………………………………..…………....31 3-6 燒結體的性質測定…………………………….……………....31 3-6-1密度的測定…………………………………..…………....31 3-6-2 X光繞射分析………………….………………………....32 3-6-3 掃瞄式電子顯微鏡（SEM）試樣之製作及觀察……….32 3-6-4穿透式電子顯微鏡（TEM）試樣之製作及觀察……….33 3-7 機械性質之量測…………………………………….………....33 3-7-1彎曲強度的測定…………………………..……………....33 3-7-2表面微硬度測試……………………..…………………....34 3-7-3破壞韌性分析…………………………………..………....35 第四章 結果與討論…………………………..…..……………....37 4-1複合粉體的特性…………………………………….………....37 4-1-1合成奈米複合粉體……………………………..………....37 （a）晶相分析---六羰鉻的熱分解………………...………..37 （b）沈積物微結構觀察………………………….…...…….40 （c） 球磨後粉末之表面型態…...………………...…….….45 4-1-2 複合粉體之熱處理………….……………….....………....47 4-2 碳化鉻/氧化鋁燒結體之特性…………………………….…...57 4-2-1 碳化鉻/氧化鋁複合粉體之燒結……...………….……....57 4-2-2氧化鉻/氧化鋁複合粉體之燒結……...…….....………….61 4-2-3 微結構觀察………………………………….……..……...63 4-2-4 披覆相對燒結體之影響………………….….....…….…...79 第五章 結論…………………………………………………….….85 參考文獻…….……………..…………………………………….…88 致謝… … … … … … … … … … … ...… … … … … … … … … … … … … ..93 作者簡歷… … … … … … … … ..… … … … … … … … … … … … … … ..94 Fig. 2.1 The classification of ceramic nanocomposites[3]….…………..7 Fig. 2-2 Schematic diagram of internal stresses around the particles and crack propagations in the case of SiC/Al2O3 matrix.[21]……...9 Fig. 2-3 The five consecutive processes of metal-organic chemical vapor deposition.[29]…………………...……………….……12 Fig. 2-4 Cr-C phase diagram…………………………………………18 Fig. 2-5 Cr2O3-Al2O3 phase diagram…………………………………19 Fig. 3-1 The flowchart of experiment…………………………...……21 Fig. 3-2 Schematic diagram of MOCVD and fluidized bed reactor….23 Fig. 3-3 Schematic diagram of hydrogen reducing furnace……..…...27 Fig. 3-4 The temperature and pressure profiles for hot-pressed alumina composite……………………………………………………29 Fig. 4-1 XRD patterns of as-deposited powders prepared by MOCVD at 400℃ for 1hr………………………………………….….38 Fig. 4-2 TEM image of Cr2O3 deposited alumina powder. (400℃ for 1 hr.), (a) bright-field image; (b) diffraction pattern of A in (a); (c) EDS analysis of A in (a)…………………………………39 Fig. 4-3 ESCA spectrum of as-deposited Cr2O3 – Al2O3 composite powders. (400℃,1hr)…………………………………….….41 Fig. 4-4 TEM micrographs of Cr2O3/Al2O3 composite powder prepared by MOCVD at 400℃ in N2 for 1hr. (a) island like deposited; (b) individual deposited…….……………………………….42 Fig. 4-5 Schematic illustration of nucleation and thin film formation[59]. (a) Nucleation (b) Grain Growth (c) Coalescence (d) Filling of Channels (e) Film Growth[44,45]……...……………………....44 Fig. 4-6 TEM micrograph of Cr2O3-Al2O3 composite powder prepared by MOCVD in newly design chamber at 400℃ in He for 1hr…………...……………………………………………....46 Fig. 4-7 TEM image of composite powders. Samples were ball milled (a) individual ;(b) island-like second phase……….…...……48 Fig. 4-8 Influence of the CO pressure on the temperature of the Cr2O3-Cr3C2-C equilibrium……...………………………………....50 Fig. 4-9 XRD patterns of the composite powders. Samples were heated in Al2O3 crucible at (a)700℃; (b)800℃; (c)900℃; (d)1000℃. in alumina furnace in 10H2/90N2 atmosphere for 2hr...….…52 Fig. 4-10 XRD patterns of the composite powders. Samples were heated in graphite crucible at (a)600℃; (b)700℃; (c)800℃; (d)900℃. in alumina furnace in 10H2/90N2 atmosphere for 2hr…………...………………………………………………55 Fig. 4-11 XRD patterns of the composite powders heated at 1250℃ for 2hr………...…………………………………………………56 Fig. 4-12 XRD patterns of the composite powders. Samples were heated at 1250℃ in Ar atmosphere for 2hr before sintering..58 Fig. 4-13 Isothermal section of the system of Cr-C-O at 1200℃……59 Fig. 4-14 XRD patterns of chromium carbide/alumina composites. Samples were heated at 1250℃ in graphite crucible and furnace for 2hr.and hot pressed at 1400℃ in vacuum for 1hr …………………………………………………………..60 Fig.4-15 XRD patterns of chromium carbide/alumina composites. Samples were hot pressed at 1400℃ in vacuum for 1hr…....62 Fig.4-16 TEM micrograph bright field image of chromium carbide / alumina nanocomposite. Sample were hot press at 1400℃ in vacuum for 1hr……...…………………………………….…64 Fig. 4-17 TEM micrograph bright field of nanocomposites (a) micron inclusion; (b) sub-micron inclusion……...………………….66 Fig. 4-18 (a) TEM micrograph bright field of nanocomposites with nano-sized inclusion. (b) micrograph in higher magnification of P in (a)…………...……………………………………….67 Fig. 4-19 TEM micrograph of chromium carbide/alumina nano-composites. Samples were hot pressed at 1400℃ in vacuum for 1hr(a) bright field image; (b)、(c) dark-field image…....68 Fig. 4-20 (a) TEM mocrograph bright image of chromium carbide/alumina nanocomposites. Samples were hot pressed at 1400℃ in vacuum for 1hr. (b) micrograph in higher magnification of P in (a)………………...…………………..69 Fig. 4-21 Forming mechanism of the inter-Cr7C3/(Cr,Al)2O3 nanocomposites during sintering……...…………………….71 Fig. 4-22 Forming mechanism of the intra-Cr7C3/(Cr,Al)2O3 nanocomposites during sintering……………...…………….73 Fig. 4-23 TEM micrograph bright field image of chromium carbide/alumina nanocomposites. Samples were hot pressed at 1400℃ in vacuum for 1hr…………………........………......74 Fig. 4-24 TEM micrograph of chromium carbide/alumina nanocomposites. Samples were hot pressed at 1400℃ in vacuum for 1hr. (a) bright field image. (b) dark field image. (c) EDS of A in (a)…………………………...…………………75 Fig. 4-25 TEM lattice image of interface between partA and Al2O3 grain in chromium carbide/alumina nanocomposites. Samples were hot pressed at 1400℃ in vacuum for 1hr……………...77 Fig. 4-26 TEM micrograph bright image of chromium carbide/alumina nanocomposites. Samples were hot pressed at 1400℃ in vacuum for 1hr………………...…………………………….78 Fig. 4-27 SEM micrograph of fracture surface of chromium carbide/alumina nanocomposites. Samples were hot pressed at 1400℃ in vacuum for 1hr.(a) intergranular fracture; (b) transgranular fracture………………...……………………...80 Fig. 4-28 SEM micrograph showing the propagation crack of chromium carbide/alumina nanocomposites Arrows indicate crack bridging in (a); crack deflection in (b); micro-crack in (c) respectively.. ………………………………………………..81 Fig. 4-29 XRD patterns of Cr2O3/Al2O3 solid solution. Samples were prepared by newly designed fluidized bed and hot pressed at 1400℃ in vacuum for 1hr.………………………………….82 Fig. 4-30 OM macrographs of samples after hot pressed at 1400℃ in vacuum for 1 hr. (a) composite powders with more island-like Cr2O3; (b) composite powders with more individual Cr2O3...84 Table 2-1 Summary of the reported phase of coating from Cr(CO)6...13 Table 3.1 Characteristics of Al2O3 powders（supplied by Alcoa）…25 Table.4-1 Carbon content of composite powders after heated in 10H2/90N2 atmosphere in Al2O3 crucible in for 2hr. Samples were at 700℃, 800℃,and 1000℃ respectively…….……..53

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