Fabrication and Characterization of Slag Fiber by Melt Extraction

Yeong Hwan Song1,a, Hwan Goo Seong1,b, Soo Han Park1,c ,

Duck-kyu Ahn1,d,Chang Hwan Seo1,e, and Bo Young Hur1,f 1 i-Cube Center, School of Nano and Advanced Materials Engineering,

Gyeongsang National University, 900, Gazwa-dong, Jinju, 660-701, Korea

ayhsong4u@nate.com,

buw98hgs@gnu.ac.kr,

csuhan2121@nate.com,

dxan2a@nate.com,

eanduckkyu@nate.com,

fhurby@gnu.ac.kr

Keywords: melt extract method, blaster furnace slag fiber, fiber, rock wool

Abstract. The influence of wheel speed and melt temperature on the surface characteristics of slag

fibers were examined in mineral fibers synthesized from the steel-making slag, using a modified melt

extraction method, i.e. melt spinning. The synthesized fibers were characterized by optical

microscope and scanning electron microscopy. It was found that the wheel speed of 700 rpm

generated better quality of mineral fibers in terms of diameter and length. This was attributed to the

relative extent of contact width between the flowing melt and the rotating wheel. The thickness of the

slag fibers were also decreased with increasing the slag melt temperature due mainly to significant

decrease in the viscosity of the slag melt. In addition, the lower melt temperature caused an increase in

number of shots plus the mineral fibers.

Introduction

Artificial mineral fibers have been used in a form of mineral wool for various applications requiring

thermal resistance, sound absorption and semi-permanent properties. However, the consumption of

mineral wool is increased with expansion of the commercial market [1-3]. Although mineral wool

was generally made by natural stone, in recent researches the recycled materials, including slag,

construction waste and dust, are being utilized due to strict environmental regulations.

In fabricating mineral fibers from slag, the formation of shots, termed as unfiberized small particles,

has been noticed as one of main problems. The shots formed in making mineral fibers are shown to

degrade mechanical and physical properties of the mineral fiber-based wool [4]. The formation of

shots is found to be controlled by adjusting the cooling rate and fluidity of the mineral melt [5-10].

The present study is to fabricate the mineral fibers from the blast furnace slag, using the modified melt

extraction method, in an attempt to improve the quality of mineral fibers with minimized shots. For

detailed characterization of the resultant mineral fibers, their structural features were characterized by

optical microscope and scanning electron microscopy.

Experimental Procedure

Materials. The as-received blast furnace slag was used as raw material to fabricate slag fibers. The

slag was water-quenched and pulverized by the mill. This slag was spherical and has about 1mm

diameter. The chemical composition of the finalized slag is given in Table1.

Table1. Chemical composition of the as-received blast furnace slag [11].

Composition CaO SiO2 Al2O3 MgO MnO T.Fe P2O5 TiO2 S

Blast furnace slag 42~44 34~36 14~16 3~5 < 1 0.2~0.4 < 1 0.5~0.7 < 1

Materials Science Forum Vols. 544-545 (2007) pp 499-502Online available since 2007/May/15 at www.scientific.net© (2007) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/MSF.544-545.499

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Fabrication. The slag of 200 g was melted in an induction furnace. Individual molten slag melts

were poured onto the peripheral surface of the rotating steel wheel as can be illustrated in Fig.1. Prior

to the melt pouring, the steel wheels were adjusted with designed positions. Each wheel was arranged

at about 10 cm to 15 cm distance. Then the angle between the flowing melt and the axes of the first

wheel was adjusted in the range of 40o to 60

o so as to ensure continuous collision of the flowing melt

onto the rotating wheels. In order to evaluate the effect of rotor speed and slag melt temperature on the

quality of the slag fibers, the wheel speed and melt temperature were varied in the range of 500 rpm to

1,000 rpm and at different temperatures (1360, 1380, 1400 and 1450oC), respectively.

Fig.1. Actual and schematic diagrams of 4-wheel apparatus for fabrication slag fibers.

Results and Discussion

Fig.2 shows the macrostructure of slag fibers produced at various wheel speeds. As shown in Fig 2(a)

through 2(d), it was observed that there was no significant change in shape and diameter of slag fibers,

irrespective of low and high wheel speed. At a 700 rpm wheel speed, however, the amount of slag

fibers produced were much lager compared to those produced in other wheel speeds. According to

previous researches [4], the better quality of the produced fibers was often obtained at wheel speeds

greater than 4000 rpm. Under the present fabrication conditions, however, the wheel speeds (500,

900, 1000 rpm) less and greater than 700 rpm generated slag fibers plus shots at its increasing

amounts. This is likely to be due to the relative extent of contact width between flowing melt and

rotating wheels as a function of wheel speeds, e.g., the cooling rate [5,6].

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Fig.2. Macrostructure of slag fibers fabricated at different wheel speeds.

(a)500 rpm, (b) 700 rpm, (c) 900 rpm, (d)1000 rpm.

a)

b)

D1

D2

D3

D4

500 Eco-Materials Processing and Design VIII

At a 500 rpm, the contact width was relative larger (i.e. higher cooling rate) than the 700 rpm,

leading to partial fiberization and thus larger shots. On the other hand, the contact width at 1000 rpm

was smaller and caused smaller shots along with fibers. Thus, it is indicated that the optimal wheel

speed was around 700 rpm in the present study. The mixture of slag fibers and shots obtained at two

different wheel speeds was shown in Fig. 3. As mentioned above, the size of the shots were larger at

500 rpm than those at 1000 rpm. �

����������������� �

Fig.3. Photographs of slag fiber and shots produced at two different wheel speeds.

(a) 500 rpm, (b) 1000 rpm

Fig.4 shows secondary electron photomicrographs of slag fibers fabricated at different slag melt

temperatures, exhibiting a difference in average fiber diameters. In case of fibers fabricated at

1380oC, average thickness and length was evaluated to 15 µm and 25 µm, respectively. The amount of

shots was less than 5% in total weight percent. In case of fibers fabricated at higher temperatures

(1400oC and 1450

oC), on the other hand, average thickness was 10 µm and 7 µm at almost identical

length. It was apparent that the lower pouring temperature promoted thick fibers at a constant wheel

speed due to a relatively higher viscosity. This observation and interpretation were shown to be

confirmed by experimentally measured viscosity values.

As illustrated in Fig. 5, the viscosity of slag melt was much higher at 1380oC than at 1450

oC; in

detail, 20 poise and 4 poise at 1380oC and at 1450

oC, respectively.

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Fig.4. SEM micrographs of fiber structures produced with different melt temperatures

at constant wheel speed (700 rpm). (a)1350, (b)1380, (c)1400, (d)1450oC

a) b)

c)

a) b)

d)

Materials Science Forum Vols. 544-545 501

Fig. 5. Viscosity of blast furnace slag as a function of temperature [8].

Summary

Slag fibers using the blast furnace slag were synthesized using four-wheel melt extraction apparatus.

The experimental results can be summarized as follows:

1. The amount of slag fiber produced was larger at a 700 rpm wheel speed compared to other speeds

used, resulting in better quality of slag fibers. This was related to the relatively contact width of

melt to the rotating wheel which was proportional to the melt cooling rate. The relatively large

amount of shots was produced at lower and higher wheel speeds than 700 rpm.

2. The diameter of slag fibers produced was increased with decreasing the slag melt temperatures.

This was ascribed to the increased viscosity of the slag melt under the present experimental

conditions at constant 700 rpm wheel speed.

Acknowledgement

This research was conducted under the Development of Functional Composite Panel of Metal Foam

with Good Environment which was supported by the Ministry of Environment of the Korean

Government (112-031-004).

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502 Eco-Materials Processing and Design VIII

Eco-Materials Processing and Design VIII 10.4028/www.scientific.net/MSF.544-545 Fabrication and Characterization of Slag Fiber by Melt Extraction 10.4028/www.scientific.net/MSF.544-545.499

DOI References

[2] W. J. Hwang, Y. T. Park, W. Hwang: Metals and Materials international, 11Vol 3 No (2005), .197~205

doi:10.1007/BF03027442 [3] Young Hyun Paik, Dong Sik Kim, Sung Mo Seo: Metals and Materials international, 7, Vol. 5 No 2001)

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doi:10.1016/S1077-2014(99)80010-2 [2] W. J. Hwang, Y. T. Park, W. Hwang: Metals and Materials international, 11Vol 3 No (2005), p.197~205

doi:10.1007/BF03027442 [3] Young Hyun Paik, Dong Sik Kim, Sung Mo Seo: Metals and Materials international, 7, Vol. 5 No (2001)

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doi:10.1007/BF03027090