Surface Study of Vitreous Carbon Obtained from Glassy Carbon Powder
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Surface Study of Vitreous Carbon Obtained from Glassy Carbon Powder F. Dondeo1, A. J. Damiao1, W. Miyakawa1, F. Nascimento1, L. Fernandes1, S. Oishi2, E. Botelho2 1 Photonics Division/Institute for Advanced Studies/DCTA, Trevo Coronel Aviador José Alberto Albano do Amarante, 1, São José dos Campos, CEP 12228-001, Brazil. 2 Department of Materials and Technology, São Paulo State University, Av. Ariberto Pereira da Cunha, 333, Guaratinguetá-SP, CEP 12516-410, Brazil; e-mail: [email protected] ABSTRACT This work presents a surface study of monolithic vitreous (or glassy) carbon - MVC obtained from vitreous carbon powder. Defective MVC pieces are crushed in a ball mill and size classified by sifting. The MVC powder is mixed with furfuryl-alcohol resin and compacted in a mould using a hydraulic press. Samples with different powder granulometries are produced in this way and carbonized in a furnace under nitrogen atmosphere. Complete carbonization of the “powder” is achieved in only one day and losses due to breakage of the pieces is less than 5%. These results compare very favorably with respect to traditional MVC production methods where full carbonization may require up to seven days and losses due to breakage can be as high as 70%. After carbonization, samples are sanded and polished. Surface roughness and microstructure are characterized by light microscopy. Porosity is quantified from micrographs using ImageJ software and nanometric height variations are measured by atomic force microscopy. INTRODUCTION Vitreous carbon (or glassy carbon) is a carbonaceous material with high stiffness and low density suitable for applications in the aerospace industry. In addition, this material exhibits good electrical conductivity, good resistance to high temperatures in non-oxidizing atmospheres and biocompatibility [1]. Two main forms of vitreous carbon are available: monolithic (MVC) and reticulated (RVC). RVC has extremely high porosity (a95%) and is suitable for electrode manufacturing applications due to the large internal surface area and the electrical conductivity exhibited by this material. Vitreous carbon can also be used in the form of powder for various electrochemical [3, 4] and tribological [5] applications and in the manufacture of conductive glues [6] and carbon activated materials [7]. MVC is a compact material and porosity is usually unacceptable. The main limitation of MVC is that products thicker than 10 mm are difficult to prepare [2]. The traditional method to produce MVC consists in the polymerization of a carbon rich resin, e.g. furfuryl alcohol, phenolic or furfuryl-phenolic resin, followed by slow carbonization in a non-oxidant atmosphere (usually nitrogen gas or vacuum), at temperatures above 1000ºC. However, in this process, irreversible mechanical damage is usually observed for sample thickness exceeding about 10 mm. In this work, a new processing route for the production of monolithic vitreous carbon is developed with the aim of overcoming some of the difficulties usually found in traditional methods
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