Tellurium Thermodynamics in Ferrous Alloys

为了开发更安全、更有效的合金化实践，需要建立预测钢液中碲活度的热力学模型。这将提高碲作为自由加工钢中铅的替代品的可行性。然而，人们对高温Fe-Te体系知之甚少，稀Fe-Te熔体的热力学也完全未知。对于三元系统和高阶系统也是如此。Fe-C-Te和Fe-Mn-Te特别重要，因为大多数钢中都含有碳，而且在含碲钢中经常注意到溶解的锰和碲之间存在强烈的相互作用。该研究计划通过测量碲蒸气在这些熔体中的溶解度作为温度和成分的函数来研究稀Fe-(C, Mn)- te熔融合金的热力学。实验方案的中心是使用一个自密封的两区炉管，熔融碲在底部，铁合金在顶部的坩埚中。改变碲的温度会改变它的蒸气压（从而改变它的溶解度）；这就确定了碲相对于液体参考状态的活度。分析平衡后的铁合金，确定碲的摩尔分数，从而确定活度系数。测量是在纯铁和铁碳（达到饱和水平）和铁锰（10 wt.%）熔体中进行的，温度范围在液相和1600摄氏度之间。实验结果将与由Bale和Pelton开发的非稀释金属溶液的热力学模型相吻合。该模型可以预测铁熔体中碲的活度（以及分压）作为成分和温度的函数。随着在自由加工钢中使用铅的环境问题日益严重，人们越来越关注潜在的替代添加剂。其中一种替代品是碲，添加少量（通常小于0.5 wt.-%），在提高可加工性方面甚至比铅更有效。然而，由于碲的沸点低（989摄氏度），它既昂贵又难以制成合金；它在炼钢温度下的高蒸汽压除了潜在的粉尘损失外，还带来了工作场所卫生问题

0096619SchlesingerA thermodynamic model for predicting the activity of tellurium in molten steels is needed to develop safer and more effective alloying practice. This would improve the viability of tellurium as a replacement for lead in free-machining steels. However, little is known about the high-temperature Fe-Te system in general, and the thermodynamics of dilute Fe-Te melts are entirely unknown. The same is true for ternary and higher-order systems. Fe-C-Te and Fe-Mn-Te are of particular importance, given the presence of carbon in most steels and the strong interaction between dissolved manganese and tellurium often noticed in tellurium steels. The research program investigates the thermodynamics of dilute Fe-(C, Mn)-Te molten alloys by measuring the solubility of tellurium vapor in these melts as a function of temperature and composition. The experimental program centers on the use of a self-sealing two-zone furnace tube with molten tellurium at the bottom and the ferrous alloy held in a crucible at the top. Varying the temperature of the tellurium changes its vapor pressure (and thus its solubility); this sets the activity of tellurium with respect to the liquid reference state. Analyzing the ferrous alloy after equilibration determines the mole fraction of tellurium, and thus the activity coefficient. Measurements are made in both pure iron and in iron-carbon (up to saturation level) and iron-manganese (10 wt.%) melts, at temperatures ranging between the liquidus and 1600 degrees C. The experimental results will be fitted against the thermodynamic model developed by Bale and Pelton for non-dilute metallic solutions. This model allows the prediction of tellurium activity (and thus partial pressure) in ferrous melts as a function of composition and temperature. %%%As environmental concerns over the use of lead in free-machining steels grow, increasing attention is being paid to potential alternative additions. One of these alternatives is tellurium, which, added in small quantities (generally less than 0.5 wt.-%), is even more effective than lead at promoting machinability. However, tellurium is expensive and difficult to alloy, given its low boiling point (989 degrees C); its high vapor pressure at steelmaking temperatures presents workplace hygiene concerns of its own in addition to potential losses to the dust.***