Influence of Heating Temperature on the Electrical Resistivity of Pyrolytic Graphite
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Influence of Heating Temperature on the Electrical Resistivity of Pyrolytic Graphite A. V. Kostanovskiya, *, M. G. Zeodinova, M. E. Kostanovskayaa, and A. A. Pronkina aJoint
Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia *e-mail: [email protected] Received December 18, 2019; revised February 21, 2020; accepted March 10, 2020
Abstract—The influence of the heating temperature on the electrical resistivity of pyrolytic graphite UPV-1 grade is studied in the range T = 2500–3000 K. It is shown that the temperature dependence of the electrical resistivity coincides with the reference data upon heating up to T = 2700 K and has a similar dependence for a single crystal with heating up to T = 3000 K. DOI: 10.1134/S0018151X20040082
INTRODUCTION Pyrolytic graphite (PG) is characterized by a pronounced anisotropy of the values of electrical resistivity. The PG electrical resistivity in parallel ra and perpendicular rc deposition planes were defined in [1] in the temperature range T = 500–1700 K. The dependences ra(T) and rc(T) on the temperature of PG domestic grades UPV-1 and UPV-1T are given in a reference publication [2], but they are limited to a maximum temperature of 2500 K. The temperature dependences ra(T) at T = 300–2000 K and rc(T) at T = 300–1800 K were determined without specification of the domestic PG brand [3, 4]. It should be noted that PG have been studied abroad [1, 5] and in our country since the middle of the last century; however, the properties of this material have not been studied sufficiently. The goal of this work is to study the effect of the heating temperature on the dependence rc(T) for PG brand UPV-1 for the range T = 2500–3000 K. EXPERIMENTAL RESULTS Samples of UPV-1 PG were manufactured at NIIGRAFIT JSC via the thermal decomposition of gaseous hydrocarbons and the deposition of carbon on a heated surface. The studied samples had density of 2.15 g/cm3. The experimental sample, which had a total length of 76 mm, was an assembly of five hollow PG cylinders pressed to each other (with a length of 6.0 mm each and diameters D/d = 10.96/3.1 and 10.96/4.09 mm) and two 23-mm-long side bushings made of graphite of grade MPG-7. The axis of the cylinders coincided with the c direction of the PG. The indicated assembly option made it possible to obtain an isothermal section with a length of at least 16 mm in the central part of the sample. A hole with a diame-
ter of 0.5 mm and a length equal to the thickness of the cylinder wall was made in the center of the isothermal section perpendicular to the axis in the central ring. This hole and the internal cavity of the experimental sample imitated a model of a completely black body (BB). The temperature of the inner surface of the cylinder was measured with the BB model through a camera window with an optical automatic micropyrometer with a spot diameter of 0.3 mm operating at a wavelength of 0.65 μm. In the determination of the actual temperature, a correction was introduced for the absorption by the
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