Abstract
This study aimed to investigate the effect of impregnation pressure on the decrease in porosity of impregnated bulk graphite. The correlation between pitch impregnation behavior and the pore sizes of the bulk graphite block was studied to determine the optimal impregnation pressure. The densities and porosities of the bulk graphite before and after pitch impregnation under various pressures between 10 and 50 bar were evaluated based on the Archimedes method and a mercury porosimeter. The density increased rates increased by 1.93–2.44%, whereas the impregnation rate calculated from the rate of open porosity decreased by 15.15–24.48%. The density increase rate and impregnation rate were significantly high when the impregnation pressures were 40 and 50 bar. Compared with impregnation pressures of 10, 20, and 30 bar, the minimum impregnatable pore sizes with impregnation pressures of 40 and 50 bar were 30–39 and 24–31 nm, respectively. The mercury intrusion porosimeter analysis results demonstrated that the pressure-sensitive pore sizes of the graphite blocks were in the range of 100–4500 nm. Furthermore, the ink-bottle-type pores in this range contributed predominantly to the effect of impregnation under pressure, given that the pitch-impregnated-into-ink-bottle-type pores were difficult to elute during carbonization.
Highlights
Artificial graphite is widely used in various industries due to its high thermal and electrical conductivity, chemical resistance, high mechanical strength, low thermal expansion, excellent thermal shock resistance under rapid temperature changes, de-wetting, selflubrication, air-tightness, and machinability [1,2,3]
Bulk graphite blocks with a bulk density of 1.76 g/cm3 were impregnated with pitch
Bulk graphite blocks with a bulk density of 1.76 g/cm3 were impregnated with pitch under pressures of 10, 20, 30, 40, and 50 bar
Summary
Artificial graphite is widely used in various industries due to its high thermal and electrical conductivity, chemical resistance, high mechanical strength, low thermal expansion, excellent thermal shock resistance under rapid temperature changes, de-wetting, selflubrication, air-tightness, and machinability [1,2,3]. There are two forms of artificial graphite: powder and bulk. The general manufacturing process of bulk graphite starts with mixing petroleum- or coal-tar-pitch-derived cokes with a binder pitch or resin. The mixture is manufactured into bulk graphite through molding, carbonization, impregnation, graphitization, and purification [10,11,12]. When the molded mixture is carbonized, volatile compounds are released from the pyrolysis or evaporation of a binder pitch or resin components, generating pores with various sizes inside the bulk graphite that degrade the graphite’s mechanical, electrical, and thermal properties [12]. Impregnation followed by heat treatment is required to minimize these pores to produce the desired properties of the bulk graphite
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