Yongjiao Zhang

This study investigates the continuous cooling crystallization behavior and melting properties of CaF ₂ -CaO-Al ₂ O ₃ -MgO quaternary slags and CaF ₂ -CaO-Al ₂ O ₃ -MgO-B ₂ O ₃ quinary slags during electroslag remelting. Experimental methods include X-Ray diffraction for phase analysis, scanning electron microscope for microstructure observation, the rotating cylinder method for viscosity measurement, and the hemispherical method for melting temperature determination, aiming to clarify the intrinsic relationship between slag composition and properties and provide a basis for ESR slag optimization and process control. Results show that in the quinary slag, as B ₂ O ₃ content decreases (from 3.0% to 1.2%), precipitated Ca ₁₂ Al ₁₄ O ₃₃ crystals transform from elongated strips to large blocks. When B ₂ O ₃ content is below 2.1% (B3-B4), Ca ₃ B ₂ O ₃ crystals no longer precipitate, confirming B ₂ O ₃ ’s refining effect. B ₂ O ₃ reduces both slags’ melting temperature, which decreases continuously with composition changes. The quaternary slag’s viscosity decreases, while the quinary slag’s viscosity remains stable, as B ₂ O ₃ regulates polymerization to offset viscosity fluctuations from other components.

To investigate the influence of B ₂ O ₃ on the microstructure of the CaO–Al ₂ O ₃ –CaF ₂ slag, molecular dynamics were employed. Various performance parameters such as radial distribution functions, coordination numbers, oxygen distribution, and Q ⁿ distributions were considered. The results indicate that Al ³⁺ predominantly adopts a [AlO ₄ ] ^5– tetrahedral structure within the slag, with a minority of Al ³⁺ existing in the forms of [AlO ₅ ] ^7– and [AlO ₆ ] ^9– . B ³⁺ primarily manifests as a [BO ₃ ] ^3– planar triangular structure in the CaO–Al ₂ O ₃ –CaF ₂ slag. The microstructure of the CaO–Al ₂ O ₃ –CaF ₂ slag is characterised by a simple network of Al–O–F. The addition of B ₂ O ₃ content in the slag promotes the incorporation of [BO ₃ ] ^3– into the O–Al–F simple network, thereby displacing F ^– ions, and leading to the emergence of a substantial amount of complex B _III –O–Al _IV network structures within the Al–O–F simple network. This leads to an increase in the degree of polymerisation of the slag structure. Furthermore, the viscosity of slag system increases.

The temperature dependence of the frequencies and linewidths of the Raman-active longitudinal optical (LO) phonons in GaAs and AlAs have been measured. The low-temperature lifetime of the LO phonon in AlAs is found to be 9.7 ps, very close to the corresponding GaAs value of 9.5 ps. This contradicts early theoretical predictions. The agreement between theory and experiment can be restored when the accidental degeneracy between the AlAs LO phonon frequency and a feature in the two-phonon density of states is taken into account.