Characteristics of Composites including Carbon Materials based on Graphite = 흑연 기반의 탄소재료가 포함된 복합체의 특성 연구
저자
발행사항
부산 : 부산대학교 대학원, 2016
학위논문사항
학위논문(박사)-- 부산대학교 대학원 : 재료공학과 2016. 8
발행연도
2016
작성언어
영어
주제어
DDC
620.112 판사항(23)
발행국(도시)
부산
형태사항
viii, 105 장 : 삽화, 표 ; 26 cm
일반주기명
지도교수: 김양도
참고문헌: 장 92-103
DOI식별코드
소장기관
Graphite has excellent in-plane structural, thermal, electrical, and mechanical properties, and as result, graphite-based materials have attracted an increasing amount of attention as viable, inexpensive fillers for composites materials targeting numerous engineering applications. The excellent properties of these materials may also be relevant at the nanoscale if graphite can be exfoliated into thin platelets, even down to the single graphene sheet level.
Graphite exists as a layered material in its bulk state, and its layers must be separated and dispersed throughout a polymeric matrix to efficiently utilize graphite as filler in a polymer composites. Graphite-based materials, such as natural graphite and the basic unit obtained via exfoliation of natural flaky graphite, are a promising low-cost, lightweight alternative to metal- and carbon-based thermally and electrically conducting reinforcements for composites. Graphite does not bear any net charge, and as such, it is different from silicate clay minerals. No reactive ion groups exist on the graphene layers in their natural form, and as a result, it is impossible to intercalate monomers into the graphite galleries via ion exchange reactions as is generally possible for layered silicates.
However, graphite is readily intercalated and can host various atoms, molecules, metal complexes, and salts between expanded graphite sheets to from graphite-based materials. To date, graphite-based materials are mainly obtained from acid-intercalated graphite and graphite oxide (GO). Broadly, three treatment methods have been adopted to modify graphite, and the modified graphitic forms are referred to as graphite oxide, expanded graphite and graphene.
Graphene has excellent thermal, mechanical, electrical, and optical properties, and there has been renewed interest in graphene production since it is the basic building block for all graphitic materials. Although graphene has been studied for the last 60 years, it represents a new class of materials that are only one atom thick, and it is becoming prominent in the fields of materials science, nanoelectronics, and condensed matter physics. Five methods can be used to prepare graphene. The first involves chemical vapor deposition (CVD) of a graphite mono-layer on transition metal surfaces; the second route is the micro-mechanical exfoliation of graphite, which involves peeling off the graphene from graphite using “Scotch” tape; the third route involves the epitaxial growth of graphene on electrically- insulating substrates. Of these, the second and third methods are unsuitable for large-scale graphene production to fabricate composites.
At present, the only routes to prepare bulk quantities of graphene and chemically-modified graphene are through the use of graphite oxide. GO exfoliates readily into colloidal suspensions of single graphite oxide layers. The fourth method involves chemical reduction with reducing agents for GO present in a colloidal suspension to convert the electrically- insulating GO layers back to conducting graphene suitable for composite applications, and the final route by which bulk quantities of graphene can be prepared is by thermally reducing GO. This technique involves rapidly heating GO in an inert environment to produce thermally-reduced expanded GO, which is a black powder with a very low bulk density. In this case, heating is responsible for the exfoliation of the graphene sheets.
In this study, four themes are investigated using graphite-based materials and their composites to confirm the unique properties of graphite.
First, epoxy composites containing natural graphite were manufactured for use as a thermal interface to efficiently remove heat from heating elements. The thermal and mechanical properties of epoxy composites with graphite as filler were examined from a structural perspective.
Second, pristine graphites were treated under strong oxidation conditions to produce GO, and these were subsequently reduced to make reduced graphite oxide (rGO). Oxidation takes place through various processes, including chemical treatment, thermal treatments, or a combination of both, and the treatment sequence also deserves consideration. A series of structural, thermal, and electrical tests are carried out with the as-prepared graphene.
Third, gold-decorated graphite nanosheets (GNs) are prepared through the electrostatic attractive interaction of gold nanoparticles and exfoliated GNs, and their structural and electrochemical properties are then investigated. There are compared with the use of different stabilizers for the gold nanoparticles.
Finally, a reduced graphite oxide coating is produced on a bipolar plate for polymer electrolyte membrane fuel cell (PEMFC) via electro spray coating. The rGO was diffused in an ethanol solvent, and low-carbon steel was used as the substrate. The corrosion resistance and the electrical properties were then confirmed under the operating environment of a PEMFC.
In summary, reduced graphite oxide (i.e., graphene) is exfoliated from graphite, and this study investigates the alteration of its structural characteristic due to the use of various recipes to obtain rGO. Furthermore, the objective of this thesis is to determine the changes in the structural characteristics needed to obtain desirable chemical, electrical, and mechanical properties of graphite-based composites.
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