Viscosity of Heterogeneous Silicate Melts: A Review
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INTRODUCTION
SILICATE melt is a general term to represent a mixture of various oxides which mainly consists of silicate. Common silicate melts include metallurgical slags (e.g., steelmaking slag, blast furnace slag), coal ash slags, and magmas. The properties of silicate melts have long been investigated due to their scientific and industrial value. The viscosity has been identified as a probe of the structure (i.e., particle fraction, spatial distribution of particles, particle shape, and size diversity) of heterogeneous silicate melts (i.e., melts containing solid phases) and a key parameter in understanding or controlling natural and industrial processes, e.g. steelmaking,[1] combustion and gasification,[2,3] volcano eruption.[4,5] Numerous mathematical models have been proposed to predict the viscosity of a fully liquid silicate, including the well-known Urbain,[6] Riboud,[7] and Iida[8] models. However, not all silicate melts are fully liquid at the operating temperatures. Metallurgical slags may become quite viscous due to the precipitation of solid crystals, leading to problems with slag tapping.[9] In the entrained flow gasification (for power production), the early precipitation of solid crystals from coal ash slag deteriorates the slag fluidity, resulting in erratic slag flow from the gasifier.[10] In volcanology, the viscosity of solid-containing magmas is a critical factor
ZHUANGZHUANG LIU, LIEVEN PANDELAERS, BART BLANPAIN, and MUXING GUO are with the Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001, Leuven, Belgium. Contact e-mail: [email protected] Manuscript submitted March 15, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
controlling magma ascent and emplacement in the Earth’s crust and eruptive volcanoes.[11,12] It is therefore essential to investigate the effect of solids on the viscosity of silicate melts. Many efforts have been made to study the effect of the fraction, shape, and size of the solid phase particles on the viscosity of various suspensions (e.g., biological fluid,[13] food product,[14] and silicate system). Numerous viscosity models have been established to correlate the viscosity and solid fraction, e.g., the Einstein,[15] Einstein-Roscoe[16] (ER) and Krieger-Dougherty[17] (KD) equations. However, no universally valid viscosity model has been established. One of the primary reasons is that most of the existing models only take into account the solid fraction and assume that the particles are spherical, e.g., the Einstein equation[15] and Roscoe equation,[16] whereas the actual heterogeneous silicate melt is a complicated system with particles of various shapes and sizes. Secondly, different methods employed in measuring and calculating the solid fraction and particle morphology (shape and size) lead to incomparable results between different studies.[18–21] Thirdly, the silicate system is frequently treated as a Newtonian fluid for the sake of simplicity.[21] Although this assumption greatly simplifies the viscosity measurement and modeling, the obtain
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