Elsevier

Carbon

Volume 42, Issues 8–9, 2004, Pages 1799-1805
Carbon

Carbonization and graphitization of shavings filed away from Kapton

https://doi.org/10.1016/j.carbon.2004.03.012Get rights and content

Abstract

Two kinds of shavings with different degrees of defect concentration were filed away from Kapton with 50 μm in thickness using two sheets of diamond paper with different diamond particle size. Kapton is known as a starting material for preparation of well-crystallized graphite film. The shavings were carbonized and their graphitization behaviors were investigated by X-ray diffraction and Raman microprobe measurements. The carbonized shavings heat-treated at 3000 °C show lower graphitizability than that of the carbonized Kapton film heat-treated at 3000 °C. Existence of turbostratic structure in the 3000 °C-treated shavings was verified by X-ray diffraction. The results of the Raman microprobe on the 3000 °C-treated shavings indicated inhomogeneous graphitization proceeded during heat treatment. The graphitization degree of the 3000 °C-treated shavings has been found to depend on the average size of the diamond particles of the diamond paper used.

Introduction

Carbonized films prepared from commercially available aromatic polyimide films Kapton, Novax and laboratory prepared aromatic polyimide films PMDA/PPD, PMDA/PDA and BPDA/PDA are known to be graphitizable even though they carbonized through solid-phase [1], [2], [3], [4], [5], [6]. One condition of the aromatic polyimide films from which graphitizable carbon films are obtained is that planner molecules are oriented along the film surface with high degree [7]. Among the aromatic polyimide films, Kapton is a precursor film giving a particularly well-graphitizable carbon film [2], [7], [8]. The graphitization degree of graphite films obtained from the carbonized Kapton depends on the thickness of Kapton, a thinner film providing a carbon film with higher graphitizability [8]. The thickness of the precursor film controls the orientation of polyimide molecules along the film surface [9]. A carbon plate prepared from a sintered plate having the same molecular structure as Kapton is non-graphitizable [1]. On the other hand, carbon particles prepared from aromatic polyimides in powder form are non-graphitizable [10] or show low graphitizability [11]. The graphitizability of the carbon material prepared from an aromatic polyimide is, therefore, governed by whether the form of the starting aromatic polyimide is block or film or powder. Even in the case of thin film, a constraint, such as stretching, during imidization to form a polyimide film was found to have a strong effect on the crystallinity of the resultant graphite film as examined for laboratory prepared Kapton-type polyimide films [12]. However, the effect of mechanical treatment to change the shape of Kapton or those of other polyimide films into very small portions, such as grinding for the films after imidization and before carbonization, on graphitizability of the carbonized films has not been investigated.

In the present study, shavings were prepared by filing away from the surface of Kapton with 50 μm in thickness using diamond papers. The resultant shavings were small and thin pieces in various forms, much different from the flat film. Since the defects introduced in each of the shavings during preparation could be supposed to remain in the carbonized shaving and also even in high-temperature-treated carbonized shaving, lower graphitizability of the carbonized shaving than that of the carbonized Kapton and also existence of crystallites with turbostratic structure in high-temperature-treated carbonized shavings were expected. The expectation was examined with X-ray diffractometry and Raman microprobe.

Section snippets

Samples

The aromatic polyimide film to file away is a 50 μm thick Kapton, and denoted hereafter as Kap-50. It can be expected that the degree of deformation and defect concentration of the shavings depend on average diameter of the diamond paper used. Therefore, two kinds of diamond papers, #80 and #140, were used. Catalog value of average size of diamond particles on each diamond paper was 130 μm for #80 and 60 μm for #140, respectively. The shavings obtained using these diamond papers are denoted as

SEM observation of shavings

According to the SEM observations, shapes of the both kinds of shavings as-filed away were significantly changed from the film, and almost similar to those of thick shavings from pencil wood by a knife. The SEM micrographs for #80-3000 and #140-3000 are shown in Fig. 1. Various shapes of the shavings can be seen. Almost of them are bent or crumpled sheets and bent or twisted thin ribbons. The sizes of the sheets and length of the ribbons are shorter than 50 μm. Therefore, the sheets and ribbons

Summary

The effect of deformation and defects introduced in the shavings filed away from Kapton on graphitization of the carbonized samples were investigated. Two kinds of shavings were obtained from Kapton using two sheets of diamond papers with different diamond particle sizes, #80 and #140. X-ray-diffractometry indicated some degree of molecular orientation in original Kapton. The carbonized shavings heat-treated at 3000 °C show lower graphitizability than that of the carbonized Kapton heat-treated

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