Effects of basicity and CaF₂ on the viscosity of CaF₂–CaO–SiO₂ slag for electroslag remelting process

Abstract

Effects of the basicity and the CaF2 content on viscosity of CaF2–CaO–SiO2 slag with high CaF2 content for electroslag remelting process were investigated by the rotating cylinder method in the temperature ranging from 1773 to 1533 K. The relationship between the structure and the viscosity variation of the slag was also clarified by the Fourier transform infrared (FT-IR) spectroscopy of water-quenched slags. The results show that the viscosity gradually decreases with the increase in the basicity of the slag from 1 to 3 under the present experimental conditions. It is found that the CaO does not depolymerize all silicate complex anions for the slag with the basicity of 1 at 1773 K and there are still some bridging oxygens. With the increase in the basicity to 3, the silicate complex anions are almost completely depolymerized to simple ions. As the CaF2 content increases from 40 to 80 mass%, the viscosity of the slag decreases due to the dilution of CaF2 for the concentration of the silicate complex anions in unit volume of the slag. Moreover, the effect of the temperature on the viscosity is not remarkable. The activation energy of viscous flow exhibits the decrease from 40.4 to 26.7 kJ · mol−1 with the increase in the basicity from 1 to 3, and also the decrease from 66.6 to 31.0 kJ · mol−1 with the increase in the CaF2 content from 40 to 80 mass%.

Application of Pressure-less Sintering and Dynamic-Slag Treatment to Recover Diamond Wire Saw Silicon Powder

“…As shown in Figure b, it can be noticed that both increased Na 2 O content and increased temperature result in reduced viscosity. High temperature can weaken the bonds among particles and break the network structure in the slag . Because of its small size, Na + could loosen the network structure into a smaller one, and the charge of the [SiO 4 ] − groups could be fully balanced by Na + to form more stable structures .…”

“…High temperature can weaken the bonds among particles and break the network structure in the slag. 43 Because of its small size, Na + could loosen the network structure into a smaller one, and the charge of the [SiO 4 ] − groups could be fully balanced by Na + to form more stable structures. 44 The viscosity is 0.086 Pa s under the condition of 15 wt % Na 2 O and 1500 °C, indicating considerable fluidity.…”

Viscosity of Na–Si–O–N–F Melts: Mixing Effect of Oxygen, Nitrogen and Fluorine

“…。しかしながら，実際のモールドフラック スは様々な成分を含む多成分系であり，最近では，三成分 系以上の多成分系を対象とした測定が進められている [6][7][8] 。 また，モールドフラックスには粘度や結晶化挙動の制御の ため，多くの場合，酸化物成分(例：CaO，Na 2 O，K 2 O)だ けでなく，フッ化物(例：CaF 2 ，NaF)も添加されることが 多い [9][10][11][12][13][14] 。 融体の粘度や構造に及ぼすフッ化物成分添加の影響解明 は，高温冶金学の研究分野において工業的にも学術的にも 重要な課題であり，多数の報告がなされている 15,16) 。融体 中でのフッ化物イオンの役割を融体の陽イオン組成変化の 影響から独立して理解するため，CaO と CaF 2 のモル比を変 化させた際の粘度変化を議論している報告がいくつか存 在する [17][18][19] 。最近では，モールドフラックスの粘度やレオ ロジー挙動を変化させる添加剤として窒化ケイ素(Si 3 N 4 ) が検討されており，窒化ケイ素を添加したオキシナイトラ イド融体の一部では非ニュートン流体としての挙動が報 告されている [20][21][22] 。一方で，オキシナイトライド融体にお ける非ニュートン性の発現機構は不明である。窒化ケイ素 は，ガラス材料の特性改善のための添加剤としても用いら れており 23) ，ガラス科学分野では陽イオンの組成比を一定 とした際の陰イオン組成(酸化物イオンおよび窒化物イオ ンの構成比)がガラスの特性に及ぼす影響が調査されてい る 24) 。この組成設計のコンセプトは，酸化物イオン，フッ 化物イオンおよび窒化物イオンのそれぞれが粘度に与える 影響を明らかにするのに有用である。Hanfi ら 25 6. Parameters obtained by the Gaussian fit to the 29 Si MAS NMR spectra.…”

Viscosity of Na–Si–O–N–F Melts: Mixing Effect of Oxygen, Nitrogen, and Fluorine

“…[9][10][11][12][13][14] The effect of the addition of fluoride, such as CaF 2 , on the viscosity and structure of melts has been a well-studied topic in the metallurgical research field due to its technical and scientific importance. 15,16) To understand the role of fluorine anions in the melts separately from the changes in cationic composition, few papers have discussed the variation in viscosity with the molar ratio of CaO to CaF 2 . [17][18][19] Recently, silicon nitride (Si 3 N 4 ) is also considered as an additive to the mold fluxes in order to vary the melt viscosity and their rheological behavior.…”