CAPACITIVE PROPERTIES OF MODIFIED AND NON MODIFIED THERMALLY EXPANDED GRAPHITE COMPOSITES WITH POLYANILINE

Modified thermally exfoliated graphite with p-nitrophenyldiazonium tetrafluoroborate, followed by reduction of nitrophenyl groups to aminophenyl ones. Composites PAN - graphite, PAN - modified graphite at a constant value of potential 1 V were synthesized by electrochemical method. Their conditional density and electrical conductivity were determined. The electrochemical behavior in 1 M HCl solution was investigated and the capacity of synthesized composites was calculated. The conditional density of PAN composites with modified and non modified graphite increases sharply with increasing graphite content from 0 to 5%. At graphite contents higher than 5%, the density of composites varies very slightly. In the range of graphite contents 0% - 20%, the density is the highest for composites with a graphite content of 5% - 10%. In the case of modified graphite, the density of composites is higher than that of composites with non modified graphite. Analysis of the dependence of the specific conductivity on the content of modified graphite indicates that the conductivity of PAN - graphite composites increases the most with increasing graphite content from 1 to 10%. In this interval, the conductivity increases linearly. This indicates the absence of specific interactions between the components in the synthesized composites, as well as the fact that the nature of the distribution of these components does not change with changes in the graphite content. For a composite with modified graphite, there are two maximum capacities of composites with a graphite content of 2 and 10%. For a composite with non modified graphite on the obtained curves there is a maximum capacity of composites with a graphite content of 2%. Modification of the graphite surface leads to increased interaction between the components of the compo¬site, which resulted in the compaction of its structure. As a result, the capacitive characteristics of modified graphite composites, as well as CVA currents and electrical conductivity, were lower compared to composites with non modified graphite.

Процессы переноса заряда в легировaнном натрием углеродном композите на основе фуллеренов и терморасширенного графита

The results of doping of a carbon composite material, in which fullerenes are located in a conductive matrix based on thermally exfoliated graphite, with a sodium dopant are presented. Charge transfer processes taking place in samples with different initial ratios of components are studied. It turns out that the electrical resistivity of the samples increases with the introduction of sodium and an increase in its content, since the mobility of the main charge carriers, which are holes as in the undoped material, decreases. The concentration of charge carriers in different types of samples varies in both directions and can increase by more than an order of magnitude. It is concluded that Na plays an ambiguous role. It can contribute not only to the generation of free electrons, but also to an additional increase in the concentration of various defects that can generate free holes and can affect, being effective traps and scattering centers, all types of charge carriers.

Магнитные свойства легированных натрием композитов типа фуллерен-терморасширенный графит

The magnetic properties (field range H = 0–50 kOe, temperature range T = 3–300 K), and structural features of a sodium-doped carbon composite material based on fullerene C_60 and thermally exfoliated graphite (TEG) are studied. The material is obtained with different ratios of the components by sintering at a pressure of 7 GPa and T = 600°C, at which it is found that significant amorphization of the crystal lattice of the initial C_60 occurs. The dia-, para-, and ferromagnetic components ( M _D, M _PM, and M _FM) were separated from the total magnetic moment of the samples under study. It is found that a sodium dopant has no effect on the magnetic properties of the composite. Analysis of the M _PM( H ) field dependences by using the Brillouin function for the fullerene-containing sample (i.e., without TEG) makes it possible to determine the quantum number of the total angular momentum of paramagnetic (PM) centers. Its value is found to be J = 1, which corresponds to elementary magnetic moment μ_PM = 2μ_B of a PM center. The concentration of PM centers is estimated at the level of N _PM ≈ (2–5) × 10^18 g^–1 for most samples, including the material without TEG. The introduction of TEG into the initial composition and an increase in its proportion in the composite leads to a strong increase in the magnetic moment, which is explained by an increase in both the J value and the concentration of PM centers.