ELECTRORHEOLOGY OF Ti-BEARING SLAG WITH DIFFERENT COMPOSITION OF TiC AT 1723K
Tao Jiang1,2, Hongrui Yue1, Xiangxin Xue1,2, and Peining Duan1,2
1School of Metallurgy, Northeastern University, Shenyang 110819, China
2Liaoning Key Laboratory of Metallurgical Resources Recycling Science; Engineering and Technology Research Center for Boron Resource Comprehensive Development and Application of Liaoning Province; Liaoning Key Laboratory for Ecological Comprehensive
Utilization of Boron Resources and Materials, Shenyang 110819, China
Keywords: Electrorheology, Fluid type, Ti-bearing slag, TiC.
Advances in Molten Slags, Fluxes, and Salts: Proceedings of The 10th International Conference on Molten Slags, Fluxes and Salts (MOLTEN16) Edited by: Ramana G. Reddy, Pinakin Chaubal, P. Chris Pistorius, and Uday Pal TMS (The Minerals, Metals & Materials Society), 2016
Abstract
Electrorheology of Ti-bearing slag was investigated by a reconstructive equipment at 1723K. The slag samples were based on slag of Panzhihua Steel and the viscosity was measured with different composition of TiC. The constitutive equations which simulated the Herschel-Bulkley model were established by the relationship between shear rate and shear stress of slag, thus the fluid type was confirmed under the condition of different electric field intensity. The result was that the slag sample containing TiC had an obvious phenomenon of electrorheology, the increase of electric field intensity gave rise to the increase of viscosity and shear stress. It can be extracted from the constitutive equations of 4% TiC slag that the fluid type converted into a Bingham fluid with application of the electric field.
Introduction
Electrorheology (ER) is a typical property of kinds of non-Newtonian fluids. The ER behavior, a rapid and reversible response on application of a direct or alternating electric field, has been the object of a number of studies[1,2]. In an ER fluid, the solid particles are randomly distributed within a non-conducting liquid. However, when an electric field is applied, the solid particles start to create highly organized structures due to the electric field. At this moment the viscosity and shear stress change rapidly. ER response is controlled not only by the magnitude and characteristics of the applied electric field but also by a wide range of properties of the slag system itself, such as the dielectric constant, the particle conductivity, and the volume fraction of particles. The rapid and reversible property of ER fluid is not limited to the study for academic researches, at the same time it has lots opportunity for application in industry, such as electrical clutches, locks, valves and shock absorbers[3-5].
Numerous studies have been conducted in the past to investigate the viscosity of slag containing TiC. As found by D. Xie[6], the viscosity showed a rapid increase with the appearance of TiC. The relationship between torque and shear rate was investigated by Y.L.
Zhen[7]. The conclusion was that 2wt% TiC slag can be considered as a Newtonian fluid for the slight viscosity change with the shear rate. The result of fluid type in our previous study[8] was that the 8wt% TiC slag, as a liquid dispersed with solid phase, behaved as a non-Newtonian fluid. In another hand, an obvious ER response had been observed for kinds of liquids dispersed with TiC, such as epoxy[9]. So it is reasonable and necessary to investigate the behavior of Ti- bearing slag containing TiC with the application of an electric field.
Experimental
Synthetic slag samples (Table 1) based on the chemical composition of on-site slagfrom Panzhihua steel (Table 2) were prepared from chemical reagents such as CaO, SiO2, MgO, Al2O3, TiO2 and TiC. The grain size of TiC is in range of 3.18-33.43μm and its mean grain size is 14.1μm (Figure 1). The mixtures of CaO, SiO2, MgO, Al2O3, TiO2 and TiC were packed into a Mo crucible and pre-melted in an electric resistant furnace under an Ar gas atmosphere at 1773 K for 20 min to ensure uniformity of the compositions.
Table 1. Experimental composition of slag examples, wt%.
No. CaO SiO2 MgO Al2O3 TiC TiO2 ∑TiO2 CaO/SiO2
a 30.03 27.30 8.00 14.00 4.00 16.67 22.00 1.10 b 30.75 27.95 8.00 14.00 8.00 11.33 22.00 1.10
Table 2. Chemical composition of BF slag from Panzhihua Steel, wt%.
CaO SiO2 MgO Al2O3 TiO2
27.0 24.3 8.3 14.4 22.3
0.1 1 10 100
0 2 4 6 8 10
Interval percentage (%)
Partical Diameter (μm)
0 20 40 60 80 100
Cumulative percentage (%)
Figure 1. Grain size distribution of TiC powder.
The rheology of slag samples within an electric field was investigated using a reconstructive equipment[10] which consisted of a Brookfield DV-Ⅲ rheometer, a high- temperature resistance furnace, a direct current (DC) electrical source and data acquisition systems (Figure 2). The crucible, filled with 140g slag was placed in the resistance furnace, heated up to 1773K at the rate of 5K·min-1 and kept there for 60 min. After the melting and reacting sufficiently, the slag was cooled to 1723K at the rate of 3K·min-1 and kept there for 30 min before the measurement. The procedure of rheological measurement was shown in Figure 3.
Figure 2. Schematic diagram of the experimental apparatus.
The Herschel-Bulkley fluid (Formula 1) is a generalized model of a non-Newtonian fluid, in which the strain experienced by the fluid is related to the stress in a complicated, non-linear way[11].
τ=τy+kDn (1) Where τ is shear stress, Pa; τy is yield stress, Pa; k is viscosity factor; D is shear rate, s-1; n is flow index. The fluid is considered to be a Newtonian fluid[12] when τy = 0 and n = 1, a dilatant fluid when τy = 0 and n > 1, a pseudo plastic fluid when τy = 0 and n < 1, a Bingham fluid when τy ≠ 0 and n = 1, a plastic pseudo plastic fluid when τy ≠ 0 and n < 1, and a plastic expansion fluid when τy ≠ 0 and n > 1. Both the process of data fitting and error analysis were noted by our previous paper[8].
Figure 3. Temperature-time schedule of the experiment.
Results and discussion
As illustrated in Figure 4, a considerable influence of electric field on the flow behavior of Ti-bearing slag containing TiC slag has been found. As the slag is applied for the maximum electric field intensity 70V·mm-1, the viscosity of 8% TiC slag is approximately 40 percent higher than that in absence of an electric field. And a 10 percent increasing for 4% TiC slag, although kind of tiny, is greater than the error mentioned above. Perovskite, the first- crystallized phase in a 29.3CaO-26.7SiO2-14Al2O3-8MgO-22TiO2 slag, starts to be crystalized once the temperature below 1709K[13]. So the increasing of viscosity could be attributed to the influence of TiC totally which should be the unique solid phase in the slag at 1723K. In the slag system, a three-dimensional network structure is formed with the core of TiC particle, for kinds of polymer matrix[14], the agglomerates alike the three-dimensional network structure in Ti-bearing slag are present even at low composition of TiC. So the conclusion, extracted from the paper[14] mention above that values of dielectric permittivity increase with TiC content, since the composites become more conductive, their heterogeneity raises, charges accumulate at the interfaces of the system and thus interfacial polarization enhances, may be a reference for the conclusion in the present paper.
The shear rate dependence of the shear stress of slag sample (a) is shown in Figure 5. The shear stress in presence of the electric field is greater than the value without any electric field over the entire range of shear rates. When the curve of 0V·mm-1 is extrapolated to Y axis, the
curve passes the origin, and at the same time the slope keeps at a same value mostly, so the fluid type of the sample (a) without any electric field could be considered as a Newtonian fluid based on the Newton's Law of Viscosity. For the electric field intensity 70V·mm-1, curve of slag turns into a non-zeroaxial line once the electric field is applied. Polarization of disperse phase TiC particles gives rise to the establishment of field-induced structure[15], and then the extrapolate value of shear stress at zero shear rate, known as yield point, is observed in slag system. At a very low shear rate, the shear forces are unable to destroy the field-induced structure. Meanwhile, the resistance to flow is much greater than in the absence of an electric field. Hence, the fluid type should be a non-Newtonian fluid once the electric field is applied in consideration of the slope fluctuates slightly as well.
0 10 20 30 40 50 60 70
0.2 0.4 0.6 0.8 1.0 1.2
Electric field strength, V·mm-1
Viscosity, Pa·s 41.43974%
a b
(0.78181)
(1.10579)
(0.35592) (0.40191)
12.92144%
Figure 4. Plots of viscosity of slag samples with electric field applying.
0.0 1.4 2.8 4.2 5.6 7.0 8.4 9.8 11.212.614.0 15.416.8 -1.0
-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
Yield point
0V·mm-1
70V·mm-1
0.0 0.5 1.0 1.5 2.0 0V·mm-1
Yield stress, Pa
Shear rate, s-1
Shear rate, s-1
Value of slope
Shear stress, Pa
70V·mm-1
0.0 1.4 2.8
0.0 0.2 0.4 0.6 0.8
0.0 1.4 2.8 4.2 5.6 7.0 8.4 9.8 11.2 12.614.0 15.416.8 -2
0 2 4 6 8 10 12
14 0V·mm-1 70V·mm-1
0 1 2 3 4 5 6
0V·mm-1 non-Newtonian fluid
Newtonian fluid 70V·mm-1
Shear rate, s-1
Shear stress, Pa Value of slope
Figure 5. Rheological curves of sample (a). Figure 6. Rheological curves of sample (b).
The relationship between shear rate and shear stress of sample (b) is depicted in Figure 6.
A typical non-Newtonian fluid behavior, shear thinning[16,17], is observed in the slag system.
The slopes are decreasing with the shear rates both in the absence and presence of the electric field. Once the shear rate is beyond 9.8s-1, the shear stresses decrease hardly and the slag performs as a Newtonian fluid. The decrease range of slope value under the application of an electric field is greater than in absence of an electric field, it is obviously that the application
of electric field is a promotion for the establishment of three-dimensional network structure in Ti-bearing slag due to the formation of field-induced structure. After the yield point is reached, the shear stress maintains a plateau level and, as a consequence, the viscosity shows decrease as a function of shear rate. Due to the non-zeroaxial propriety and shear thinning behavior of the rheological curves, a similar conclusion[18] could be extracted from Figure 6 is that when an electric field is applied, the apparent viscosity and the shear stress increase and the flow curves become slightly pesudoplastic.
The results of constitutive equations are shown in Table 3. Coefficient indexes (R2) of these established equations are all greater than 0.99 to ensure a good fitness between each equation founded and result measured. The conclusion similar with existed research[19,20] could be obtained for 4% TiC slag that without an electric field, the slag behaves as a Newtonian fluid, however, once applying the electric field on slag system, the particles in this system polarize and align parallel to the field vector, thus, the slag behaves as a Bingham fluid. For the 8% TiC slag, the slag performs as a plastic pseudo plastic fluid which possesses yield stress and shear thinning behavior both in the absence and presence of the electric field. The absolute values of k and τy, which mean the viscosity factor and yield stress respectively, increase as the response for the electric field application.
Table 3. Constitutive equations of slag sample (a) and (b)
TiC Electric field Constitutive equations Fluid type R2
4
0V·mm-1
τ=0.4018D1.0000 Newtonian 0.9994
70V·mm-1
τ=0.3592+0.5357D1.0000 Bingham 0.9991
8
0V·mm-1
τ=1.8683+0.6883D0.9098 Plastic pseudo plastic 0.9974 70V·mm-1
τ=2.3175+0.9388D0.8755 Plastic pseudo plastic 0.9968
Conclusions
An obviously ER response is observed in Ti-bearing slag containing TiC, once the electric field is applied, both the viscosity and shear stress increase with the electric field, and the enhancement of 8% TiC slag is greater than 4% TiC slag.
The fluid type of 4% TiC slag converts from a Newtonian fluid to a Bingham fluid with the application of the electric field, at same time, the flow resistance is greater than in absence of the electric field due to the appearance of yield stress. It is already a non-Newtonian fluid even without any external impact for the 8% TiC slag. And as a plastic pseudo plastic fluid, which possesses the shear thinning behavior, the shear stress decreases with the increasing of shear rate among the electric field.
This work was financially supported by the National Science Foundation of China (Nos.
51174051 and 51090383).
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