Electrical Resistance of Composites and Coatings Based on Boron and Silicon-Containing Compounds in the Temperature Rang
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Electrical Resistance of Composites and Coatings Based on Boron and Silicon-Containing Compounds in the Temperature Range 20–1000°C D. V. Kolovertnova, I. B. Ban’kovskayaa, *, and A. N. Nikolaeva aGrebenshchikov
Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, 199034 Russia *e-mail: [email protected] Received February 14, 2019; revised January 16, 2020; accepted April 3, 2020
Abstract—The electrical resistance of graphite samples with coatings based on Si–B–ZrB2 with different binders and coating components in the temperature range 20–1000°C is determined. Keywords: electrical resistance, coatings on graphite, zirconium boride DOI: 10.1134/S1087659620040070
Graphite is a unique material and serves as the base of products often used in the metallurgy industry, in particular, as electrodes during melting. Taking into account its high oxidizability during heating, its protection with coatings is an urgent problem. Earlier [1], the patent was obtained for the composition and method of fabrication of protective coatings on graphite formed in air and protecting it from oxidation at temperatures above 1000°C. Since graphite is used at increased temperatures in electrodes, it is important to know the electrical properties of the coatings. EXPERIMENTAL The aim of the present work is to determine the specific electrical resistance of graphite samples with coatings and coating components. Silicon powders of the maximum particle size up to 50 μm of the KR00 grade, zirconium boride powders of up to 30 μm and a specific surface area of 6 m2/g of the reagent grade, amorphous boron powder of a specific surface area of 20 m2/g of the B-99A grade and their mixture in the ratio 70Si · 10B · 20ZrB2 in wt %, and coatings on graphite of the GMZ brand of two compositions using different binders (2% aqueous solution of carboxymethylcellulose (CMC) and silicic acid acetone solution (SAA)), were used as the initial components. The following modes of coating formation in the air were used: 600–700°C 10 deg/min + 700°C 15 min, 1000–1300°C 10 deg/min + 1000°C 105 min, 1000– 1300°C 10 deg/min + 1000°C 180 min, 1000–1300°C 10 deg/min + 1300°C 15 min* (*the mode can be described as follows: samples were placed in a furnace
at 1000°C, then the temperature was increased to 1300°C at a rate of 10 deg/min (preformation). Then, the samples were removed and cooled in air to room temperature. This was followed by annealing at 1300°C for 15 min (test) with subsequent cooling. Thereafter, the electrical resistance was measured during heating from room temperature to 1000°C). The data from the differential, thermal, thermogravimetric, and X-ray diffraction analyses obtained earlier [2] were used to interpret the results of the measurement of the specific electrical resistance. RESULTS AND DISCUSSION The dependences of the specific electrical resistance of graphite with coatings of two compositions and the initial coating components in the powder form on the temperature were obtained. The specific electri
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