Dissertation
Atomic Structure and Thermophysical Properties of Molten Ag-CuOx Air Braze Alloys
Doctor of Philosophy (PhD), Washington State University
01/2011
Handle:
https://hdl.handle.net/2376/3506
Abstract
The Ag-CuOx materials system is the basis for a family of filler alloys used in a recently developed ceramic-metal joining technique referred to as air brazing, which is a brazing process that can be carried out in ambient air rather than under the vacuum or inert to reducing gas conditions required for conventional brazing methods. This research was conducted to elucidate the atomic coordination and selected thermophysical properties of these materials as a function of temperature when they are in the salient liquid state in air, since this is when the critical steps of wetting and spreading occur in the joining process. A series of alloys was selected spanning the entire length of the phase diagram including the pure end members, Ag and CuOx; alloys that form the two constituent single phase liquids; and alloys for which the two liquid phases coexist in the miscibility gap of the phase diagram.
The oxygen content of the liquid alloys in air was measured using thermogravimetry. The oxidative weight gain of 99.999% pure metallic precursors was measured while simultaneously accounting for the concurrent silver volatility using a method that was developed in the course of the study. The surface tension and mass density were measured using the maximum bubble pressure method. The number density was calculated based on the information gained from the oxygen content and mass density measurements. For compositions that were amenable to laser heating, containerless high energy x-ray scattering measurements of the liquid atomic coordination were performed using a synchrotron beamline, an aerodynamic levitator, and laser heating. For the remaining compositions x-ray scattering measurements were performed in a beamline-compatible furnace.
The two liquid phases that form in this materials system have distinct atomic coordinations characterized by an average of nearly two-fold coordinated ionic metal-oxygen pairs in the CuOx-rich liquid and nearly eight-fold coordinated atomic metal-metal pairs in the Ag-rich liquid. Over the temperature range investigated, many of the properties exhibited no significant temperature dependence, however all were strongly dependent on composition.
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Details
- Title
- Atomic Structure and Thermophysical Properties of Molten Ag-CuOx Air Braze Alloys
- Creators
- John Hardy
- Contributors
- Amit Bandyopadhyay (Advisor)Susmita Bose (Committee Member)Aurora E Clark (Committee Member)Kenneth S Weil (Committee Member)Larry R Pederson (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Materials Science and Engineering Program
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 169
- Identifiers
- 99900581858401842
- Language
- English
- Resource Type
- Dissertation