Development of Double and Single Hot Thermocouple Technique for in Situ Observation and Measurement of Mold Slag Crystallization.

Kashiwaya, Yoshiaki; Cicutti, C.; Cramb, A. W.; Ishii, Kuniyoshi

doi:10.2355/isijinternational.38.348

Cited by 172 publications

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“…On the other hand, the DHTT can observe the molten sample in situ. As shown in the previous study, 1,2) the solidification of mold slag is complicate phenomena including the bubble formation/breaking and the crystallization. It would be very important to know the sample image during measurement.…”

Section: Methodsmentioning

confidence: 99%

“…1,2) Figure 1 illustrates the principle of the thermal diffusivity measurement and the comparison of the alignment of heat source and detector between the DHTT and the laser flash method. The laser flash method is an excellent method and can predict a relatively suitable value of thermal diffusivity using Parker's method 4) (Eq.…”

Section: Methodsmentioning

confidence: 99%

“…The authors initially have developed the double hot thermocouple technique (DHTT) for in situ observation of mold slag crystallization. 1,2) These studies have indicated that the overall heat transfer rate in the actual process must be very complicated due to the interaction of crystallization of slag with the primary mechanisms of heat transfer: radiation, conduction and convection. The DHTT has a superior feature on the rapid heating and cooling of melted sample during observation, whereas the extremely high sensitivity on the temperature change makes it unamenable.…”

Section: Introductionmentioning

confidence: 99%

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Factors on the Measurement of Effective Thermal Diffusivity of Molten Slag Using Double Hot Thermocouple Technique.

Kashiwaya

Ishii

2002

ISIJ International

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The molten slags that are used not only in the continuous caster but also in every metal industry play an important role and affect the quality of products. The authors initially developed the double hot thermocouple technique (DHTT) for in situ observation of mold slag crystallization.In this study, the DHTT was further developed to allow the measurement of the overall thermal diffusivity of molten slag applying the principle of the laser flash method. The affecting factors (finite pulse time, shape of pulse and heat loss from sample surface) on the measurement of thermal diffusivity using the DHTT were discussed theoretically using both the analytical and the numerical methods. New relationship between the thermal diffusivity a and the time at half-maximum temperature t 0.5 was obtained as follows:a(ϫ10 4 m 2 /s)ϭ0.000707(t 0.5 /t p ) Ϫ1.8946 The thermal diffusivity obtained from the experimental half-maximum time t 0.5 /t p (t p is the time of peak on the heat pulse) was in good agreement with the one from literature.KEY WORDS: thermal diffusivity; thermal conductivity; slag melt; laser flash; hot thermocouple; DHTT.DHTT and the laser flash method. The laser flash method is an excellent method and can predict a relatively suitable value of thermal diffusivity using Parker's method 4) (Eq. (3)). However, it will need a special alignment for the measurement of liquid and/or transparent material. Furthermore, a direct observation during measurement is almost impossible. On the other hand, the DHTT can observe the molten sample in situ. As shown in the previous study, 1,2) the solidification of mold slag is complicate phenomena including the bubble formation/breaking and the crystallization. It would be very important to know the sample image during measurement. The thermal diffusivity obtained from DHTT, however, is not yet established and it is not reported what kinds of factors affected on the measurement until now.For the preliminary approach to the application of the DHTT to the measurement of thermal diffusivity, the affecting factors on the measurement were elucidated from both the theoretical and the experimental method. In the case of laser flash method, an instantaneous laser pulse was used as a heat source and the temperature increase at the rear surface was measured by an infrared pyrometer (IR detector). In the case of DHTT, the temperature of one side thermocouple (CH-1, in Fig. 1) increased in a pulse shape and the other side of thermocouple (CH-2) was used as a detector. The typical temperature profiles of both CH-1 and CH-2 are shown in Fig. 2. The time t 0.5 at the half-maximum temperature (1/2 DT max ) was defined as shown in Fig. 2 and used for the calculation of thermal diffusivity according to the laser flash method (the details will be shown in below). The large differences between the laser flash method and DHTT are as follows: (1) Heat source is the order of several seconds (millisecond order in laser flash method). (2) Shape of pulse is not square. This factor might be decisive in bo...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Factors on the Measurement of Effective Thermal Diffusivity of Molten Slag Using Double Hot Thermocouple Technique.

Kashiwaya

Ishii

2002

ISIJ International

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“…Whereas the 7.5 wt pct MgO-containing CaOAl 2 O 3 -based slag showed a typical 'C'-shaped TTT curve, the 2.5 and 5 wt pct MgO-containing CaO-Al 2 O 3 -based slag showed a half-'C'-shaped TTT curve. The nose, or the critical minimum time required to form a given degree of crystallization, [10] is often analyzed to qualitatively compare the tendency for crystallization and the effects of various chemical compositions of slag systems. In the CaO-Al 2 O 3 -7.5 wt pct MgO slag, the TTT diagram was ''C'' shaped, and the apparent nose of the TTT could be considered to fall approximately at 1563 K (1290°C) and 91 seconds.…”

Section: A Effect Of Mgo Addition On the Crystal Morphology Of Cao-amentioning

confidence: 99%

“…Kashiwaya et al [10] developed the double hot thermocouple technique (DHTT), which is similar to a CLSM, for in situ observation and measurement of mold slag crystallization. The shape and the mode of crystal growth were quite different between the isothermal experiment for TTT diagrams and the non-isothermal experiment for CCT (continuous cooling transformation) diagrams.…”

Section: Introductionmentioning

confidence: 99%

Crystallization Behavior of the CaO-Al2O3-MgO System Studied with a Confocal Laser Scanning Microscope

Jung

Sohn

2012

Metall Mater Trans B

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The crystallization behavior of a calcium-aluminate system with various MgO content from 2.5 to 7.5 wt pct and CaO/Al 2 O 3 ratios between 0.8 and 1.2 has been examined using a confocal laser scanning microscope (CLSM). CCT (continuous cooling transformation) and time temperature transformation (TTT) diagrams were constructed to identify the primary crystal phase of slag at different compositions and at cooling rates between 25 and 800 K/minutes. In the slag at a CaO/Al 2 O 3 ratio of 1.0, crystallization temperature increased during isothermal and continuous cooling with higher MgO content, and the shortest incubation time was observed at 5 wt pct MgO. When MgO content was fixed to be 5 wt pct, crystallization temperature increased with lower CaO/Al 2 O 3 ratio. According to the slag composition, cooling rates and temperature, the primary phase could be CA, or C 5 A 3 , or C 3 A, or C 3 MA 2 , or MgO, and the crystal morphology changes from dendrites to faceted crystals to columnar crystals in this composition range.

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Green Slag System Design During Continuous Casting

Wei¹,

Wang²,

Lu³

et al. 2014

Energy Technology 2014

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Development of Double and Single Hot Thermocouple Technique for in Situ Observation and Measurement of Mold Slag Crystallization.

Abstract: To overcome the limitations of differential thermal analysis (DTA)

Cited by 172 publications

References 0 publications

Factors on the Measurement of Effective Thermal Diffusivity of Molten Slag Using Double Hot Thermocouple Technique.

Factors on the Measurement of Effective Thermal Diffusivity of Molten Slag Using Double Hot Thermocouple Technique.

Crystallization Behavior of the CaO-Al2O3-MgO System Studied with a Confocal Laser Scanning Microscope

Green Slag System Design During Continuous Casting

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