Development of a High Temperature Maximun Bubble Pressure Apparatus for Measuring Surface Tension of Molten Metals

冶金过程的计算机建模可用于提高过程控制和产品质量。充分利用当前可用的高级计算工具需要提高物理属性输入数据的准确性。特别是熔融金属的表面张力对金属加工的特性有重要的影响。为了高质量地测量表面张力，必须确定熔体中存在的表面活性元素的浓度。最普遍存在的物种是氧气；它存在于所有涉及熔融金属的实际条件下，是影响表面张力的主要因素，即使在百万分之一的水平上也是如此。由于几乎不可能完全消除反应堆和容器中的氧气，因此需要密切监测氧势。该奖项来自材料研究仪器项目，支持一个项目，该项目将建造一个高温最大气泡压力（MBP）设备，该设备配备了基于固体电解质的传感器/控制器，以监测探头中的氧势。这种组合非常适合测量反应性合金的表面张力，因为：(1)MBP探针位于熔体表面下，探测表面积与熔体体积相比很小；(2)通过氧传感/控制装置监测产生探测表面的气流中的氧势。在该项目下开发的仪器将提供给卡内基梅隆大学的学生，用于研究熔融状态下金属的结构和性质。此外，预计建立氧势对表面张力的影响以及二维表面相存在的影响的能力，将对卡内基梅隆大学正在进行和未来研究合金表面热力学的研究项目做出重大贡献。为了充分认识计算机模型在预测冶金过程过程控制和产品质量方面所提供的工具，有必要将过程建模的进步与用作输入的物理数据的精度提高相并行。熔融金属的表面张力是一个关键的性能，因为它影响(1)在金属合金粉末生产过程中液滴向固体的转化；(2)铸造过程中气孔的形成，降低了最终的金属强度；(3)钢加工过程中杂质夹杂物的形成和形状。然而，在实验上对熔融反应性合金（如不锈钢和高温合金）进行精确的表面张力测量是极其困难的。这是由于氧气总是以微量的形式存在，它会与金属发生反应。因为即使金属中溶解氧含量很低，也能显著改变表面张力，因此准确控制其浓度至关重要。该奖项来自材料研究仪器仪表项目，仪器仪表支持一种新型组合的开发，该组合用于测量金属表面下的表面张力，以及控制和监测氧气水平的氧气泵/传感器。该仪器将有利于金属加工业，增加对熔融状态下表面物理化学的理解，从而对材料化学的研究和教育产生积极影响。在这个项目下建造的仪器将在卡内基梅隆大学的实验课上实施，改变了迄今为止学生们很少研究材料的重要熔融状态的事实。

Computer modeling of metallurgical processes can be used to enhance process control and product quality. Full exploitation of the high-level of currently available computational tools requires improved accuracy of the physical property input data. In particular, surface tension of molten metals critically influences the characteristics of metals processing. For high-quality measurements of surface tension, it is mandatory to establish the concentration of surface-active elements present in the melt. The most ubiquitous species is oxygen; it is present under all practical conditions involving molten metals and is a major factor effecting surface tension, even at parts per million levels. Since it is practically impossible to totally eliminate the presence of oxygen in reactors and vessels, the oxygen potential needs to be closely monitored. This award from the Instrumentation for Materials Research program support a program to build a high temperature maximum bubble pressure (MBP) device equipped with a solid electrolyte based sensor/control to monitor the oxygen potential in the probe. This combination is uniquely suited for measuring surface tensions of reactive alloys since: (1) the MBP probes beneath the surface of the melt and the probed surface area is small compared to the volume of the melt; and (2) the oxygen potential in the gas stream responsible for creating the probed surface is monitored through an oxygen sensing/controlling device. The instrumentation developed under this program will be made available to students at Carnegie Mellon during laboratory session designed to study the structure and properties of metals in their molten state. Furthermore, it is expected that the ability to establish the effect of the oxygen potential on the surface tension and the effects of the presence of 2D surface phases, will significantly contribute to ongoing and future research projects at Carnegie Mellon that study the surface thermodynamics of alloys.In order to fully appreciate the tools offered by computer models in predicting metallurgical processes for process control and product quality, it is necessary to parallel the advances in process modeling with improved accuracy of the physical data that are used as input. Surface tension of molten metals is a key property since it influences (1) the conversion of liquid droplets to solids during the production of metal-alloy powders; (2) the formation of gas pores during casting which diminish the final metal strength; and (3) the formation and shape of impurity inclusions during the processing of steels. However, it is experimentally extremely difficult to perform accurate surface tension measurements of molten reactive alloys such as stainless steels and superalloys. This is due to the fact that oxygen is always present in trace amounts, which will react with the metals. Since even low levels of dissolved oxygen in the metal can change the surface tension significantly, it is critical to control its concentration accurately. The award from the Instrumentation for Materials Research program instrumentation supports the development of a novel combination of a probe that measures the surface tension under the surface of metals and an oxygen pump/sensor that controls and monitors the oxygen level. The instrument will benefit the metals processing industry and increase the understanding of the physical chemistry of surfaces in the molten state and thereby positively impacting research as well as education in materials chemistry. The instrument built under this program will be implemented in laboratory classes at Carnegie Mellon changing the fact that the important molten state of materials has so far been little studied by students.