The lattice and radiation conductivities have been determined for commercial mould fluxes in glassy and partially crystalline states as functions of the degree of crystallinity to confirm whether or not more crystallisation of mould fluxes is always effective in slow cooling in continuous casting. Lattice conductivities, refractive indices and absorption/extinction coefficients were measured on glassy and partially crystallised samples from commercial mould fluxes. The lattice conductivities of mould fluxes increased with increasing the degree of crystallinity at temperatures around 773 K and more prominent increase was observed where the degree of crystallinity exceeded about 20 %, which would be due to the contact between crystal grains precipitated. However, fluxes having higher degrees of crystallinity showed negative temperature coefficients in the lattice conductivities, particularly at higher temperatures, and thus there was a case where the lattice conductivities decreased with increasing the degree of crystallinity at higher temperatures. On the other hand, the radiation conductivities tended to decrease with increasing the degree of crystallinity and became almost constant where the degree of crystallinity exceeded about 15 %. As a consequence of this, more crystallisation does not always lead to slow cooling in continuous casting: the degree of crystallinity should be controlled to be about 15 % where the partially crystalline phase exists around 773 K.KEY WORDS: lattice conductivity; radiation conductivity; mould flux; crystallisation; hot wire method. air gap i.e., a thermal resistance, at the mould/flux interface 2) due to the fact that the density of the crystalline phase is greater than that of the glass.Thus, the degree of crystallinity of the flux film is a key factor in the control of horizontal heat flux. Consequently, when casting slabs of MC steel, it is customary to use a mould flux which gives a film with a high degree of crystallinity to reduce the horizontal heat transfer. However, when casting round billets, it is important to minimise the shrinkage of the flux film to support the billet and in this case it is necessary to use a flux giving a glassy film.3) The heat transfer is reduced by introducing transition metal oxides, which increases the absorption coefficient a and thus decreases l R . Paradoxically, l L increases as the degree of crystallinity increases because of the increased packing density and regularity in crystal structure but the enhancement of the total heat transfer across the mould flux by these effects would be much smaller than the decrease in the heat transfer due to (i) pore and air gap formations and (ii) the reduction of l R . The present work primarily focuses on qualitative investigation about the effect of crystallisation on lattice and radiation conductivities for mould fluxes. From such a viewpoint, several attempts have been made to measure values of l L of silicates in liquid and solid states, [4][5][6][7][8][9][10] suggesting that more crystallised samp...

Thermal conductivities of Na 2 O-CaO-SiO 2 slags have been determined using the non-stationary hot wire method over a wide temperature range between room temperature and 1773 K, to propose a prediction equation for the thermal conductivities of this slag system. Samples used were xNa 2 O-yCaO-zSiO 2 (xzyzz5100 mol-%), where 5,x,40 mol-% and 10,y,40 mol-%. With increasing temperature up to glass transition temperatures, the thermal conductivities of the samples increased and then decreased even beyond liquidus temperatures. The thermal conductivities of slags having the same SiO 2 concentration, i.e. the same NBO/T (number of bridging oxygens per tetrahedrally coordinated atom), decreased by replacement of CaO with Na 2 O but took almost the same value at their liquidus temperatures T L , irrespective of the (%Na 2 O)/(%CaO) ratio. Furthermore, plotting the thermal conductivities against T/T L (temperature normalised by T L ) shows that the thermal conductivities in the temperature range T/T L .0 . 9 are not dependent upon the (%Na 2 O)/(%CaO) ratio as long as the SiO 2 concentration is kept constant. This finding indicates that in this system the relationship between thermal conductivities at T L and NBO/T also applies at temperatures other than T L using the temperature scale of T/T L . On the basis of this relationship, the following prediction equation has been proposed for thermal conductivities l of this slag system in liquid and supercooled liquid states: l5a[1/(T/T L )]zb, where a and b are constants specified by the concentration of SiO 2 . This equation applies, for example, in the temperature range 0 . 9,T/T L ,1 . 3 for slags containing 70 mol-%SiO 2 and 0 . 9,T/ T L ,1 . 1 for slags containing 40 mol-%SiO 2 .

Thermal conductivities of CaO-SiO 2 -Al 2 O 3 glassy slags have been determined using the nonstationary hot wire method as functions of (mol.-%Al 2 O 3 )/(mol.-%CaO) and (mol.-%SiO 2 )/ (mol-%Al 2 O 3 ) ratios over a temperature range 300-1270 K. The thermal conductivities of the samples investigated were in the range between 1 . 0 and 1 . 6 W m 21 K 21 . The thermal conductivities of samples having a constant concentration of SiO 2 increased with increasing the (mol.-%Al 2 O 3 )/ (mol.-%CaO) ratio as long as the constant pressure heat capacity per unit volume was kept constant. This increase in thermal conductivities would be due to increases in the speed of sound and/or the phonon mean free path by re-polymerisation of the network structure of silicate glasses by Al 2 O 3 . On the other hand, the thermal conductivities of samples having a constant value of NBO/T (the ratio of the number of non-bridging oxygen ions per tetrahedrally coordinated cation) decreased with increasing the (mol.-%SiO 2 )/(mol.-%Al 2 O 3 ) ratio. This decrease in thermal conductivities would be dominated by the constant pressure heat capacities per unit volume of the samples.

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A fine x‐ray beam, less than 10 μm in diameter, was produced using a small x‐ray tube and an x‐ray guide tube (XGT) with a parabolic inner contour. The beam was directed vertically on to the sample, which was mounted on an x–y scanning stage. The transmitted x‐rays were measured with an NaI(Tl) scintillation detector and the fluorescent, back‐scattered and diffracted x‐rays were simultaneously detected by an hp‐Si detector. The scanning images of transmitted, fluorescent and other x‐rays were obtained by accumulating the detected signals. A scanning image of the lower layer of a four‐layer, printed‐circuit board was obtained by subtracting the fluorescent x‐ray image from the x‐ray transmitted image. Using diffracted x‐rays, distribution images of crystal grains could be made. The method for fabricating the XGT is described and examples of applications of a desk‐top scanning x‐ray analytical microscope are shown. © 1997 John Wiley & Sons, Ltd.