The effect of oxygen fugacity on the evaporation of boron from aluminoborosilicate melt
Abstract
We present the results of B_2O_3 evaporation experiments from Ca- and Mg-bearing aluminoborosilicate melts. Our experiments were conducted at 1245 to 1249 ∘C and 1350 to 1361 ∘C for different run times (60–1020 min), and at oxygen fugacities (logfO_2) relative to the fayalite–magnetite–quartz (FMQ) buffer of FMQ−6 to FMQ+1.5, and in air. Our results show that with increasing fO_2, 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 B_2O_3 which constrain its speciation in the gas phase to be either 3+ or 4+ (B_2O_3(g) and BO_2(g)). The measured B_2O_3 contents of the B evaporated residual glasses were used to calculate evaporation rate constants (ki) for B_2O_3 in oxidizing conditions (air, kᵢ = 2.09 x 10⁻⁴ cm min⁻¹ at 1350 ∘C) and reducing conditions (FMQ−4, kᵢ = 4.46 x 10⁻⁵ cm min⁻¹ at 1350 ∘C). The absence of diffusion profiles in the experimental glasses suggests that the evaporation rates are slower than B2O3 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 FMQ−4. Show more
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https://doi.org/10.3929/ethz-b-000662878Publication status
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European Journal of MineralogyVolume
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CopernicusMore
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