Investigation Of Viscous Characteristics For Alloy Melts

The knowledge of liquid structure and property is closely related to the progress in science and technology in many fields.It is becoming the focus of condensed physics,material science,life science,metallurgy and chemistry.Viscosity of liquid,one of the physical properties sensitive to structure,is related closely to its structure.In this paper,a torsional oscillation viscometer for high-temperature melts is used to measure the viscosities of tens of melts.The viscous characteristics for these melts are investigated and this present work makes a beneficial attempt at exploring viscosity as an experimental method for studying liquid-liquid(L-L)phase transition.The viscosity measurements for over ten kinds of binary alloy melts are carried out by a torsional oscillation viscometer for high temperature melts.The discontinuity or mutation of structural phase transition is explored based on liquid structure model and fluid cluster diffusion model.There is a discontinuous structural transition in the melts and the characterized parameters are(η₀,ε,d_f).The discontinuous structural transition has the following characteristics:firstly,the structural transition is reversible.The transition temperature and characterized parameters are the same in the heating and cooling process;secondly,it is a discontinuous structural change with two possible forms of thermal contraction or thermal expansion.Furthermore,a comparative integrated liquid structure diagram for Sn-Bi binary alloy melt is present.The temperature dependence of viscosity for eleven multicomponent alloy melts is analyzed based on viscosity measurements.Discontinuous structural transition behavior is observed:the Arrhenius plots are made of discontinuous lines.The viscosity obeys Arrhenius rule in each linear temperature zone.And the transition behavior can be characterized by(η₀,ε,d_f).According to the experimental results and analysis,it can be divided into three temperature zones for some metal or alloy melts at normal pressure: "ambiguous" zone:T＞T_x(T_x—the crossover temperature between ambiguous zone and Arrhenius zone),when the temperature is higher than Tx,the thermal movement of atoms in the melts is so intensive that the data points fluctuate in the ambiguous zone.The phenomenon can be considered to be ambiguous;Arrhenius temperature zone:T_x--T₁, (T₁—liquidus temperature),it can be divided into two kinds,the first,the viscosity of melts obey Arrhenius rule in this temperature zone,the second,there is discontinuous structure transition in the alloy melts and the Arrhenius plots are made of discontinuous lines.The viscosity behavior obeys Arrhenius rule in each linear temperature zone; undercooling zone:T＜T₁,the melts is cooled below the liquidus.Viscosities of Al_1-x/Mg_x(0≤x≤0.10)alloy melts have been measured in the temperature range 973K-1173K by a torsional oscillation cup method.The viscosity dependence on temperature and composition are explored together with the structure of melts.The viscosity dependence on temperature for Al(1-x)Mg_x(0≤x≤0.10)melts obeys Arrhenius equation.The viscosity increases with increasing magnesium concentration in the investigated system.But the increase of viscosity is inconspicuous and fluctuating except an extreme increase at the point of 10%magnesium composition.And the transition of active energy related to the fluid cluster is consistent with that of viscosity.A number of viscosity models on.the concentration dependence for liquid binary alloys are reviewed and simply discussed in this paper.The dependence of viscosity on concentration for the simple binary eutectic Sn-Bi and Bi-Sb solution systems was modeled based on the reviewing and checked against the measured viscosity values.The phenomenological model of viscosity developed by Iida and co-workers and the Kozlov equation demonstrate very good agreement for these two systems.From the concentration dependence of the measured viscosity data for Sn-Bi alloys, one can see that both the excess viscosity and the mixing enthalpy show a slight positive deviation from additivity,which means that the correlation of the excess viscosity with the enthalpy of mixing is not particularly satisfactory.Evidently,an appropriate model should be formulated in terms of both thermodynamic properties and other properties such as differences in atomic size,mass of the components,atomic interaction,bond type and electronegativity.A simple equation:η_alloy=η_SbX_Sb+η_BiX_Bi(η_alloy,η_Sb,η_Bi,X_Sb,X_Biis the viscosity of Sb-Bi alloys,visocisity of pure components and molar fraction of pure components respectively)is attempted to calculate the viscosity of binary Bi-Sb alloy melts and the calculated results accord with that of experiments.It is suggested that we may use this simple equation to calculate the viscosity for Bi-Sb alloy system.