The effect of oxygen fugacity on the evaporation of boron from aluminoborosilicate melt

Flemetakis, Stamatis; Renggli, Christian J.; Pangritz, Paul; Berndt, Jasper; Klemme, Stephan

We present the results of Binline-formula2Oinline-formula3 evaporation experiments from Ca- and Mg-bearing aluminoborosilicate melts. Our experiments were conducted at 1245 to 1249 inline-formulaC and 1350 to 1361 inline-formulaC for different run times (60–1020 min), and at oxygen fugacities (loginline-formulafOinline-formula2) relative to the fayalite–magnetite–quartz (FMQ) buffer of FMQinline-formula−6 to FMQinline-formula+1.5, and in air. Our results show that with increasing inline-formulafOinline-formula2, evaporation of B from the melt increases by a factor of 5 compared to reducing conditions. Using Gibbs free energy minimization calculations, we suggest two possible evaporation reactions for Binline-formula2Oinline-formula3 which constrain its speciation in the gas phase to be either 3inline-formula+ or 4inline-formula+ (Binline-formula2Oinline-formula3(g) and BOinline-formula2(g)). The measured Binline-formula2Oinline-formula3 contents of the B evaporated residual glasses were used to calculate evaporation rate constants (inline-formulaki) for Binline-formula2Oinline-formula3 in oxidizing conditions (air, inline-formula M23inlinescrollmathml k i = normal 2.09 × normal 10 - normal 4 79pt16ptsvg-formulamathimg08692036c59ec4f0d68b4826fabfa8a2 ejm-36-173-2024-ie00001.svg79pt16ptejm-36-173-2024-ie00001.png  cm mininline-formula−1 at 1350 inline-formulaC) and reducing conditions (FMQinline-formula−4, inline-formula M27inlinescrollmathml k i = normal 4.46 × normal 10 - normal 5 79pt15ptsvg-formulamathimg515fd7f02ee2be6e9bad32597e40a769 ejm-36-173-2024-ie00002.svg79pt15ptejm-36-173-2024-ie00002.png  cm mininline-formula−1 at 1350 inline-formulaC). The absence of diffusion profiles in the experimental glasses suggests that the evaporation rates are slower than Binline-formula2Oinline-formula3 diffusion rates and therefore the rate-limiting process. Overall, the rate of B evaporation in air is approximately a factor of 5 higher compared to reducing conditions at FMQinline-formula−4.

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Flemetakis, Stamatis / Renggli, Christian J. / Pangritz, Paul / et al: The effect of oxygen fugacity on the evaporation of boron from aluminoborosilicate melt. 2024. Copernicus Publications.

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