Thermal Conductivity of the Silicate Melts. The University of Tokyo Institute of Industrial Science 〇 YoungJo Kang and Kazuki Morita

Transcription

1 Thermal Conductivity of the Silicate Melts The University of Tokyo Institute of Industrial Science 〇 YoungJo Kang and Kazuki Morita

2 Agenda Introduction Thermal conductivity of liquid oxide Previous studies and Objectives Experimental Apparatus, Experimental procedure, Sample preparation Results and Discussion Temperature and Composition dependence Amphoteric behavior of Al 2 Relationship of thermal conductivity to silicate structure

3 Introduction Thermal Conductivity of Liquid Oxides An important physical property in material production processes Thermal conductivity of liquid oxide in iron- and steelmaking Thermal conductivity of Na 2 O-SiO 2 system (Nagata et al.) Schematic representation of mold powder and slag film layer in continuous casting (M. Susa et al., Ironmaking and Steelmaking, 21(1994)) Heat

4 Introduction Thermal Application of Molten Slag Utilization of blast furnace slag and latent heat Optimization of BF slag recovery process

5 Introduction Previous Studies COMPOSITION (mass%) METHOD TEMPERATURE RANGE (K) THERMAL CONDUCTIVITY (W/mK) AUTHORS 40CaO-20Al 2-40SiO 2 373~ ~1.50 K. Nagata et al. 25CaO-15Al 2-60SiO 2 hot wire 373~ ~1.60 K. Nagata et al. 40CaO-20Al 2-40SiO 2 method ~1.00 K. Nagata et al 40CaO-20Al 2-40SiO 2 373~ ~1.70 M. Susa et al. 40CaO-20Al 2-40SiO 2 273~ ~1.20 M. Kishimoto et al. 45CaO-15Al 2-40SiO 2 laser 273~ ~1.20 M. Kishimoto et al. 50CaO-15Al 2-35SiO 2 flash 273~ ~1.00 M. Kishimoto et al. 50CaO-15Al 2-35SiO 2 method 1273~ T. Sakuraya et al. 35CaO-20Al 2-45SiO ~ ~0.80 T. Sakuraya et al. 40CaO-20Al 2-40SiO 2 radial 1573~ ~2.00 K. Ogino et al. 40CaO-20Al 2-40SiO 2 heat flow 1273~ ~2.00 T. El Gammal et al. CaO-Al 2 -SiO 2 system m.p ~2.80 D. Sommerville et al. limitation in the compositions and temperature

6 Introduction Previous Studies Results of thermal conductivity measurement of the CaO-Al 2 -SiO 2 system (left) after Slag Atlas and (right) by D.Sommerville et al, Trans. of the ISS,1991 reliable thermal conductivity data in pure liquid region: insufficient

7 Introduction Measurement of Thermal Conductivity Measurement methods for liquid oxide Stationary methods Non-stationary method Laser flash method, Hot-wire method

8 Introduction Objectives Measurement the thermal conductivity of the CaO-Al 2 -SiO 2 system using hot-wire method from liquidus temperature to 1873K Better understanding on the relationship between the thermal conductivity and silicate structure from its temperature and composition dependences

9 Experimental Hot-wire Method Equation for thermal conductivity Q ( ΔT) λ = 4 π (ln t) Q : Heat generation of unit length of hot-wire γ : Euler constant slope ΔT against lnt Minimization of the effects of convection and radiation ΔV electric power heat flow sample line heat source temperature change linear onset of range convection ( ΔV ) (ln t) ln t

10 Experimental Sample Preparation weighing, mixing pre-melting at 1873K for 20min. crushing to powder CaO/SiO 2 =0.39 CaO/SiO 2 =0.58 CaO/SiO 2 =0.90 CaO/SiO 2 =4.50 Phase diagram of Na 2 O-SiO 2 system and measurement range ternary phase diagram of the CaO-Al 2 -SiO 2 system

11 Experimental Experimental Procedure Measurement Standard Resistor Supply constant power (1.5A) to hot-wire Measure temperature change of hot-wire PC V Potentiostat Silicon stopper Plot ΔT against ln t Calculate thermal conductivity Experimental cell Furnace Analysis SiO 2 : gravimetry., Others: ICP-AES Reaction tube Crucible Sample Crucible Temp. Alumina or Pt-10%Rh L.T.~1873K, every 50K Alumina brick Schematic diagram of hot wire measurement apparatus

12 Results and Discussion Thermal Conductivity and Temperature The Na 2 O-SiO 2 system 1.2 Na 2 O-2SiO 2 m.p. Na 2 O-SiO 2 m.p. Thermal conductivity (W/mK) Na 2 O-0.67SiO 2 Susa et al. 1) Hayashi et al. 3) Nagata et al. 4) 0.5Na 2 O-0.5SiO 2 Nagata, Goto Nagata, Goto 4) Temperature ( o C) in mole fraction Thermal conductivities of the Na 2 O-SiO 2 system as a function of temperature

13 Results and Discussion Thermal Conductivity and Temperature The CaO-Al 2 -SiO 2 system Thermal Conductivity (W/mK) CaO-20Al 2-40SiO 2 after Nagata et al. 25CaO-15Al 2-60SiO 2 after Nagata et al. 11CaO-11Al 2-78SiO 2 26CaO-8Al 2-66SiO 2 24CaO-15Al 2-61SiO 2 22CaO-22Al 2-56SiO CaO-52.5SiO 2 30CaO-18Al 2-52SiO 2 26CaO-30Al 2-44SiO 2 37CaO-22Al 2-43SiO 2 38CaO-20Al 2-42SiO 2 28CaO-40Al 2-32SiO 2 45CaO-45Al 2-10SiO CaO-50.5Al 2-9SiO Temperature (K) in mass percent Thermal conductivities of the CaO-Al 2 -SiO 2 system as a function of temperature

14 Results and Discussion Thermal Conductivity and Basicsity Thermal conductivity (W/mK) K 1773K 1823K K (mass%cao)/(mass%sio 2 ) acid-side: basicity thermal conductivity basic-side: relatively high thermal conductivity influence of Al 2? Relationship between thermal conductivity and CaO/SiO 2 ratio mass%cao mass%sio 2 : basicity

15 Results and Discussion Amphoteric Behavior of Al 2 Thermal Conductivity (W/mK) [AlO 4 ] K Al K CaO/SiO 2 =0.4 CaO/SiO 2 = mass%(al 2 ) 1823K 1873K Maximum value in thermal conductivity with Al 2 addition Change in the role of Al 2 between network former and network modifier Dependence of thermal conductivity on Al 2 content at constant CaO/SiO2 ratios

16 Results and Discussion Silicate Structure and Temperature Debye s expression for thermal conductivity λ = Cvl 3 in crystalline materials l 1 T, C: heat capacity v:sound velocity l: phonon mean free path λ 1 T Thermal Conductivity (W/mK) crystal structure λ 1 T 0 Reciprocal Absolute Temperature (K -1 )

17 Results and Discussion Silicate Structure and Temperature Temperature (K) Thermal Cunductivity (W/mK) change in silicate structure CaO-18Al 2-52SiO 2 λ 1 T Liquidus Temperature X(K -1 ) Dependence of thermal conductivity of 30%CaO-18%Al 2-52%SiO 2 on the inverse absolute temperature

18 Results and Discussion Silicate Structure and Temperature Transmittance (a.u.) [SiO 4 ] tetrahedra 1873K 1773K 1673K change in silicate structure NBO/Si= Wavenumber (cm -1 ) IR transmittance of 30%CaO-18%Al 2-52%SiO 2

19 Results and Discussion Silicate Structure and Temperature low T liquidus temp. thermal vibration 1 l T interaction volume l Ω high T Ω - Bond breakage depends the bonding energy - A broken bond divides the interaction volume λ exp 1 T

20 Results and Discussion Silicate Structure and Temperature %CaO-18%Al 2-52%SiO 2 lnλ ln λ 1 T X1/T (K -1 ) Dependence of logarithm of thermal conductivity of 30%CaO-18%Al 2-52%SiO 2 on the reciprocal absolute temperature

21 Conclusions The thermal conductivity of the Na 2 O-SiO 2 and CaO-Al 2 -SiO 2 system was measured by hotwire method in their pure liquid region The thermal conductivity decrease in more basic silicate, and as temperature rises. And amphoteric behavior of Al 2 was observed in the ternary system Temperature dependence deviates from the linearity at higher temperature than liquidus temperature. The change in silicate structure may cause this disagreement.