Volatilisation problems in the measurement of mould fluxes crystallisation by hot thermocouple technique

ABSTRACT

Since it is first verified that saturating the room temperature quartz tube with fluoride gas is not effective for inhibiting the NaF volatilization, the effects of fluorides volatilization on crystallization properties of mold fluxes are studied under the open condition of hot thermocouple technique. The volatilization ratio is analyzed by sintering the mold fluxes at an appropriate temperature to weigh the sample accurately. The results show that, at high holding temperatures (1400 - 1500°C), with the increase of fluoride losses and proportion of SiF₄ in the volatiles, the initial crystallization temperature, crystalline fraction, and relative crystallization rate reduced, which leads to the whole C curve shift to the bottom-right. At low holding temperatures (1300°C), the initial crystallization temperature increases with the increase of fluoride losses, and the crystallization could begin during the holding stage. Therefore, it is infeasible to study the crystallization behavior of mold fluxes using hot thermocouple technique.

KEYWORDS:

• Mould fluxes
• volatilisation ratio
• crystallisation
• holding temperature
• holding time

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The State Key Program of National Natural Science of China (Grant No. U1660204), China Postdoctoral Science Foundation (2016M592119) and Postdoctoral Science Foundation of Jiangxi Province (Grant No. 2016KY19) are acknowledged for supporting this work.