Effects of the Pore Size of Graphite on the Mechanical Properties and Permeability of a Porous Nozzle for Continuous Casting Process

Abstract

To analyze the effect of the pore size of graphite in a pore-forming agent, graphite was added to porous ceramics of Al 2 O 3-SiO 2-ZrO 2 systems. The graphite had 45~75, 100~125, 150~180, and 75~180㎛ dimensions. The properties of the ceramics, such as apparent porosity, density, dynamic elastic modulus, mechanical strength, and permeability, were investigated. The average pore size increased from 15.35㎛ to 22.32㎛ with the increase of the graphite size. The sample with the largest average pore size showed the highest mechanical strength and gas permeability. This was due to the sample with the largest pore size at the same porosity having fewer pores and larger distance between the pores than the sample with the smallest pore size, making cracks less likely to propagate. In addition, the large pore size reduced the repulsive power originating from the drag force between the gas and internal pore walls.

Thermal Shock Behavior of Porous Nozzles with Various Pore Sizes for Continuous Casting Process

“…When ∆T is 0 o C (before the thermal shock test), the results were as similar to our previous study. 13) The samples all have virtually the same porosity, but they show large differences in pressure drop depending on the pore size. The results which showed low pressure drop might be attributed to the rapid change of internal fluid flow, which could increas the rate of thermal shock relaxation.…”

“…Consequently, the spaces become too thin to endure external stress, thus weakening the overall strength of the materials. 13,19) Fig. 2 shows SEM micrographs of the three samples (in the order of sample A, B, and C) after the thermal shock test at 600 o C (Figs.…”

“…Porous nozzle samples with various pore sizes were prepared with the same method as our previous study. 13) The starting powders were Al 2 O 3 (AES-11, SUMITOMO, Japan) 92 wt%, SiO 2 (SIGMA-ALDRICH, USA) 4.5 wt%, and ZrO 2 (ZRO02PB, Kojundo Chemical Lab. Co.,Ltd, Japan) 3.5 wt%.…”

“…18) In our previous study, the durability of porous nozzles with different porosities was investigated through a thermal shock test, 12) and an experimental approach was used to characterize the effects of pore size on the properties of porous nozzles. 13) For further investigation, we herein report how pore size can affect the thermal shock behavior of porous nozzles by preventing the propagation of cracks. To control the pore size, graphite was used as a pore forming agent.…”