Direct Observation of Molten Silver Penetration into Porous Alumina Refractories

摘要

The penetration of molten silver into porous refractories was observed directly using a high temperature X-ray radiographic apparatus. Experimental phenomena were analyzed using equations derived from a capillary model. Measured data, such as surface tension, density and sessile drop contact angle of molten silver on an Al_2O_3 plate were obtained under the same conditions as the penetration experiments. Molten silver penetrates rapidly into porous refractories and reaches a maximum penetration height in a short time. The penetration height then remains almost constant. Molten silver penetrates unevenly into porous refractories due to the uneven pore size distribution. The minimum external pressure under which molten silver can penetrate into porous refractories, that is the critical pressure, depends on the structure of the porous refractories. Below the critical pressure, molten silver cannot penetrate into porous refractories. Above the critical pressure, the maximum penetration height of molten silver increases linearly with increasing external pressure. Experimental and theoretical investigations on the penetration height were performed in relation to factors such as external pressure, pore structure and pore radius in the refractory and surface tension, density and contact angle of molten silver with the refractory. The penetration of molten metal into a porous refractory can be suppressed by the following: increasing the contact angle of molten metal with the refractory, making the pores smaller than a certain pore radius and a more uniform and sharper pore size distribution. The latter can be obtained by adjusting the constituents and particles size distribution of the raw materials.