Boron Oxide를 添加한 炭素/炭素 複合材의 酸化擧動 = Oxidation Behavior of Boron Oxide Implanted Carbon/Carbon Composites

다국어 초록 (Multilingual Abstract)

The effects of boron oxide as an oxidation inhibitor on C/C composites and structural characteristics of boron-implanted C/C composites were investigated. In order to understand the oxidation properties of the C/C composites, four different preparation methods were employed by varying the B_2O_3 introduction time. The first was an unmodified C/C composite (XX), which had no boron component. The second was a modified C/C composite where the carbon fiber preform was infiltrated by boron oxide solution (OX). The third was a C/C composite prepared with carbon precursor which contained boron oxide during the carbonization process (XO). The fourth was a C/C composite both the second and the third method were employed together (OO). The preparation conditions for all the specimens were the same, except for the introduction time of boron oxide into the carbon precursor. Also, the influence of HTT on the carbon/carbon composites was observed at 2300˚C and 2800˚C, respectively.
After severe HTT, most amount of boron oxide was evaporated only to have less than 0.4B/C% in all specimens. The higher the HTT, the less the content of boron. At the temperature of 2300˚C, relatively large amount of B_2O_3 was detected while significant amount of B_2O_3 were converted into substituted boron and B_4C at 2800˚C.
Small amount of boron increased not only the graphitization efficiency but also the oxidation resistance. Thus, boron containing carbon material need not to be treated as high temperatures as non-containing materials to get enough graphitization. In the latter, the heat treatment temperature played very significant roll in the graphitization procedure. If boron existed in the composites, ultra high temperature was of no use in order to obtain highly graphitized composites.
During the preparation of composites, the introduction time of boron oxide was not important in terms of oxidation behavior. In other words, in both specimens that boron oxide was added on carbon fiber preform and that boron oxide added during carbonization process showed almost the same oxidation behavior. However, the former was slightly better than the latter as the time went by. Thus, boron oxide should be treated on carbon preform so as to get longer lasting oxidation resistance.
At the early stage of oxidation reaction, boron-implanted material seems to promote its reactivity on oxygen according to activation energy. However, boron oxide increased the activation energy of oxidation reaction as the reaction proceeds. Boron atoms on the graphite layer plane catalyzed oxidation at first stage of reaction then boron oxide barrier was formed by reacting with oxygen, which blocked the active sites of C/C composites. Enough carbon atoms surrounding boron atom must be gasified by reactant gas in order to form boron oxide film at the active sites of carbon surface.

목차 (Table of Contents)

• 목차
• I. 서론 = 1
• II. 이론 = 3
• 1. 탄소 표면의 특성 = 3
• 1-1. 탄소의 반응성 = 4
• 1-2. 선택적 기체화 = 4
• 2. 반응 동력학과 메커니즘 = 7
• 2-1. 화학 율속 단계와 확산 율속 단계 = 7
• 2-2. 반응 속도 = 10
• 2-3. 화학흡착 및 이탈 = 10
• 2-4. 활성 표면적(ASA)의 반응성에 대한 중요성 = 13
• 2-5. 반응성의 개념 = 14
• 3. 탄소의 기체화 반응 비교 = 17
• 4. 탄소의 기체화 반응 억제 방법 = 18
• 5. 붕소의 산화 억제 메커니즘 = 21
• 5-1. 흑연 구조로의 변환 = 21
• 5-2. 특정 자리 봉쇄를 통한 기체 확산 억제 = 21
• 5-3. 전자 전이를 통한 산화 억제 = 22
• 6. 붕소 산화물의 특징 = 26
• 6-1. 물리적 성질 = 26
• 6-2. 화학적 성질 = 28
• III. 실험 = 31
• 1. 실험재료 = 31
• 1-1. 보강재 = 31
• 1-2. 기지 전구체 = 31
• 1-3. 붕소 첨가제 = 32
• 2. 4 방향성 (4D) 탄소/탄소 복합재의 제작 = 33
• 2-1. 4 방향성 탄소 섬유 프리폼의 제작 = 34
• 2-2. 붕소 산화물의 침윤 과정 = 34
• 2-3. 가압 함침 과정 (PIC) = 36
• 2-4. 후 탄화 과정 = 37
• 2-5. 중간 흑연화 = 37
• 2-6. 최종 흑연화 = 37
• 3. 시험 및 분석 = 38
• 3-1. 기공률 측정 = 38
• 3-2. 붕소 정량 분석 (EPMA) = 38
• 3-3. 붕소 정성 분석 (XPS) = 38
• 3-4. 열 중량 분석 (TGA) = 39
• 3-5. 결정화도 분석 (XRD) = 39
• 3-6. 미세 조직 분석 (SEM) = 39
• IV. 결과 및 고찰 = 40
• 1. 밀도 변화 및 기공도 = 40
• 2. EPMA 분석 = 42
• 3. XPS 분석 = 45
• 4. 열 중량 분석 = 48
• 4-1. 시편 제조 방법에 따른 비교 = 48
• 4-2. 열처리 온도에 따른 비교 = 49
• 4-3. 활성화 에너지 = 52
• 5. X선 회절 분석 = 61
• 6. 미세 조직 분석 = 68
• 6-1. 붕소 산화물이 흑연화에 주는 영향 = 68
• 6-2. 붕소 산화물이 산화에 주는 영향 = 68
• V. 결론 = 72
• VI. 참고문헌 = 74
• ABSTRACT
• 감사의글