A new method to dynamically measure the surface tension, viscosity, and density of melts
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I. INTRODUCTION
KNOWLEDGE of the physical properties of melts is fundamentally important for many metallurgical processes. The term “melt” refers to molten materials such as metals, salts, slags, etc. The productivity and efficiency of many high-temperature applications rely on accurate knowledge of surface tension, viscosity, and density of the melt under consideration. This article will introduce a method that simultaneously calculates all three properties using one experimental setup. Density is required in studies ranging from simple mass balance calculations to the study of natural convection. Other examples include predicting the separation of slag/metal systems or calculating the terminal velocity of inclusions within a melt. Density is also required to quantify other physical properties such as surface tension and dynamic viscosity. Viscosity is a quantity of fundamental importance in fluid transport problems, as well as in issues concerning reaction kinetics in melt processing. The viscosity of molten systems often dictates the castability (or ability to fill a mold cavity) of many metals and their alloys.[1] Furthermore, the mechanisms of solidification often require knowledge of the viscosity of the melt.[2,3] Surface tension is a significant property in atomization and granulation studies for the powder metallurgy industry, because the efficiency of these processes is directly related to the surface tension of the melt.[4] The Marangoni effect has been discussed extensively in the literature and describes convection induced within a liquid from gradients in surface tension. In welding, penetration of the liquid phase is dependent on this phenomenon.[5] The Marangoni effect also plays a crucial role in the corrosion of refractory material at slag-gas and slag-metal interfaces. The rate of nitrogen
absorption in iron is also dependent on this phenomenon in steelmaking.[6] In order to manipulate metallurgical processes, a complete database of these properties should be available. Unfortunately, there is much work that needs to be done in applying property data to many processing environments. Many of the techniques used in measuring physical properties of lowtemperature liquids (water, organic liquids) are not applicable for melts because of a number of factors. Material selection at high temperatures, temperature control and monitoring, and other issues constrain measuring techniques considerably. The reactive nature that molten metals exhibit with oxygen is problematic and great lengths have been made to provide an inert atmosphere for experimentation. In measuring surface tension, contamination has a particularly drastic impact on the surface tension of molten metals. Oxide accumulation has been known to affect the surface tension of these liquids in the presence of very low levels of oxygen.[5,7,8] To further complicate matters, methods used to measure the surface tension of melts are predominantly static, providing an opportunity for contaminants to accumulate. In this study, a new technique will be
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