Carbon-Carbon Composition “Expanded Graphite – Multiwalled Carbon Nanotubes”

Sementsov Yurii,Grebel’Na Yulia,Wang Bo,Makhno Stanislav,Strelchuk Victor,Dovbeshko Galyna,Zhuravskyi Serhii,Kartel Mykola

doi:10.11648/j.ijmsa.20190806.16

Sementsov Yurii, Grebel’Na Yulia + Show 6 more

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https://doi.org/10.11648/j.ijmsa.20190806.16

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Abstract

It is given the description of expanded graphite (EG) as a cluster-assembled nanoscale system. It is shown that in the structure of EG there are both extended defects formed by the convolution of one or more graphene layers and orientation defects - disclination. The strength characteristics of EG compacted materials can be controlled by changing the parameters of the production process in a limited interval (the ratio of the amount of oxidizing agent, intercalant, with natural dispersed graphite, its particle size). The procedure for treating multiwalled carbon nanotubes (MW CNTs) with a solution of potassium dichromate in sulfuric acid was carried out according to the known technology of oxidation of natural graphite in order to obtain expandable graphite. It provides for the use of sulfuric acid as an intercalating agent and potassium dichromate (K2Cr2O7) as an oxidizing agent. The aqueous dispersion of oxidized MW CNTs is stable over time: the average particle size is 50 nm; two fractions - from 20 to 100 nm, amount - 99.9%, mass - 10%; from 250 to 500 nm and amount of 0.1%, mass - 90%; high polydispersity ranges from 0.35-0.4, that is, the particles are quite close to the spherical shape. Modification of CNTs by oxygen simultaneously with anodic oxidation of natural dispersed graphite allowed for the first time to create a carbon-carbon composite "EG – MW CNTs" with enhanced physical and mechanical characteristics without additional use of binders.

Highlights

Exfoliated graphite (EG) is a group of materials with a graphite-like structure, which is obtained by rapid heating of graphite intercalation compounds and their hydrolyzed forms
We investigated a possibility of deagglomeration of MWCNT in an ultrasonic disperser UZDN-2 and universal homogenizer using shear deformation together with the effect of cavitation in an aqueous dispersion in the presence of surfactants
The procedure of multiwalled carbon nanotubes (MW carbon nanotubes (CNTs)) treatment with a solution of potassium bichromate in sulfuric acid according to known technology natural graphite oxidation aiming at obtaining expandable graphite, is based on the following scheme, which involves the use of sulfuric acid as an intercalating agent and potassium dichromate (K2Cr2O7) as oxidizer [2]: Cn + 25H2SO4 + K2Cr2O7 →6C24+HSO4−·2.5H2SO4 + Cr2(SO4)3 + K2SO4 + 7H2O + Cn-144

Summary

Introduction

Exfoliated (expanded) graphite (EG) is a group of materials with a graphite-like structure, which is obtained by rapid heating (thermal shock) of graphite intercalation compounds and their hydrolyzed forms. The EGs are characterized by a complex structure with developed surface and a presence of extended slit-like and cylindrical defects with a cross-sectional diameters of 0.7 to 20 nm which occur due to the coagulation and bending of several layers of graphene (Figure 1a, b) [1]. These defects manifest themselves in the Raman spectra, positron annihilation, low-temperature nitrogen adsorptiondesorption experiments which all confirms a nanoscale structure of the EG [1, 2]. The thinnest particles (multilayer graphene’s of about 5...7 layers thick) are exfoliated by the mechanism of “secondary intercalation” (diffusion via defects) and aggregate in 3D structures on conductive substrates

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