Phenomenon of Whiskers Formation in Al₂O₃−C Refractories

Abstract

Alumina refractories and ceramics are extensively applied in the steelmaking field due to their excellent properties, such as chemical resistance and high wear resistance at high temperature. [1] Besides this, the addition of graphite significantly improves the thermal shock resistance of alumina. Thanks to these properties, the application spectrum of Al 2 O 3 -C materials became very wide-from ladle refractory to submerged nozzle and filters. [2][3][4][5] Khanna et al. [6,7] investigated the interaction between pure Al 2 O 3 , Al 2 O 3 -12.9 mass % C, and molten iron using the sessile drop method at 1550 C between 15 min and 3 h. The authors reported a strong interaction between Al 2 O 3 ÀC and molten iron including COÀgas evolution, extensive iron penetration into the substrate, and refractory degradation, Fe 3 Al formation at the iron refractory interface, and Al 2 O 3 whiskers formation. In contrast, no Al 2 O 3 whiskers formation and penetration of molten iron into the refractory was found in investigations with pure Al 2 O 3 and molten iron. In addition, when a blank Al 2 O 3 -C sample was heated without the presence of molten iron under the same experimental conditions, no Al 2 O 3 whiskers formation could be detected. Khanna et al. [6,7] explained these phenomena through the carbothermic reduction of Al 2 O 3 and dissolution of the reduced aluminum into the liquid iron. Similar investigations with identical results were achieved by Ikram-Ul-Haq et al. [8] However, in earlier publications, the carbothermic reduction of alumina was reported under low pressure (0.08-0.2 atm) with the presence of Sn and Cu as a metallic solvent (from 1700 C to 1850 C) [9] or under vacuum conditions. [10] Nevertheless, the aforementioned explanations for carbothermic alumina reduction at low temperature were not supported by other researchers. [11] If equilibrium concentrations of Al and oxygen in Fe liquid are low, carbothermic reduction is not possible. Zienert et al. [11] conducted a thermodynamic simulation of the Al 2 O 3 ÀC/ Fe system to investigate the process of dissolution of Al and O in Fe liquid in the presence of C across the interface at the conditions of Khanna's [6] investigation. The reaction at every step in this simulation involved the dissolution of small amounts of alumina in liquid iron and the reaction of dissolved oxygen with carbon to CO formation. The amount of dissolved alumina in the simulation was defined from calculated molar densities, the assumed penetration rate, and the contact area and was assumed constant during the simulation. This continuous dissolution of alumina led to pick-up of aluminum in molten iron up to 9.75 at% in 3 h.Wei et al. [12] investigated the interaction between Al 2 O 3 ÀC and Fe in Al 2 O 3 ÀC crucible at 1600 C under argon atmosphere. Yan et al. [13] reported that the aluminum-bearing volatile species released strongly in the Al 2 O 3 ÀCÀFe system in the temperature range 1500-1520 C reacted with iron, which led to the formation of hercynite whiskers on the surface of a...

Effect of Al2O3 and TiO2 on Viscosity, Surface Tension, and Density of Blast Furnace Slag with CaO/SiO2 = 1.13

“…In previous investigations in this high‐temperature microscope using extra pre‐evacuation up to 10 −4 bar, the oxygen partial pressure was measured 10 −21 bar. [ 16 ] For regular measurements, the pre‐evacuation was not used, and oxygen partial pressure was not measured. However the oxygen partial pressure during investigations of flow behavior or during measurement of viscosity, density, and surface tension is expected to be less than 3.75 × 10 −6 bar but greater than 10 −21 bar.…”

“…A detailed description of the high-temperature microscope and the experimental procedure can be found elsewhere. [16,17] The experiments were performed under an argon atmosphere (99.999 mass% Ar). The softening, semispherical, and flow temperatures of the slags were determined according to the German standard DIN 51 730.…”

Formation and Prevention of Nozzle Clogging during the Continuous Casting of Steels: A Review

“…It was found through the chemical interactions in Al 2 O 3 -C/Fe system applying the sessile drop method that Al 2 O 3 whiskers could be generated on the surface of the iron droplet or the Al 2 O 3 -C substrate [97,98] , as shown in Figure 8 [98] , which might be a reason for the formation of nozzle clogging during the continuous casting of Al killed steels.…”

“…7. Proposed formation process of the nozzle clogging originated from the decarburization reaction during the continuous casting of a bearing steel [44,45] [98] Fig. 9.…”

Mechanical strength measurement of needle-shaped CaSO4 microcrystals by a three-point bend test

“…The method of adaptation of the three-point bend test developed for needle-shaped CaSO 4 microcrystals allows direct extraction of numerical estimations of the mechanical bending strength. This novel method can be applied to mechanical testing of various needle-shaped single crystals with suitable shapes and sizes (calcium carbonate (CaCO 3 ) [22,23], silicon carbide (SiC) [24,25], aluminum oxide (Al 2 O 3 ) [26,27] and silicon (Si) [28,29]).…”