The issue of metal-ceramic interfaces is being explored through three interconnected topics. In the first, wetting of ceramics by metals (both liquid and solid) are explored. This is conducted using the sessile drop technique for liquids on solids, and Winterbottom analysis to determine the energy of solid-solid interfaces. The second topic related to metal-ceramic interfaces deals with processing of ceramic matrix composites and ceramic-metal and ceramic-ceramic joins , where data from wetting experiments is used as the basis for process design.
Finally, in-depth electron microscopy of the interfaces formed from the wetting and joining processes is conducted. Major issues include the formation of equilibrium films at metal-ceramic interfaces. Emphasis is placed on analysis of the atomistic structure and chemistry of the same interfaces for which the interface energy is determined. A description of the major methodologies and systems under study is given below.
Wetting and Metal-Ceramic Interfaces
Sessile drop experiments are conducted in a unique UHV Wetting Furnace. This unique system is dedicated to in-situ investigations of sessile drops at very high temperatures (up to 1800°C) under very controlled gas partial pressures. The system is based on a UHV chamber and includes the following; a water cooled tungsten heating system, an ion-sputtering system for cleaning the surfaces of samples in-situ, a residual gas analyzer for monitoring gas partial pressures, mass-flow controllers and various vacuum and pressure gauges for controlling the total pressure and partial pressure within the system, and a CCD linked to a computer for computerized measurements of the sessile drops. Kaplan’s lab includes secondary sessile drop systems for working with metals with high vapor pressures.
Data from the sessile drop experiment are analyzed using image analysis software developed by Kaplan’s group, for the automatic measurement of contact angles, and to extract liquid surface energies from the drop shape. The focus is to analyze the thermodynamic work of adhesion and interface energies of metal-ceramic interfaces, as a function of temperature, chemistry and gas partial pressure.
In addition to liquid-solid wetting, activities have been extended to solid-solid interface energies. These studies are based on Winterbottom analysis, using cross-section TEM of site-specific samples prepared using FIB. Again, the goal of these studies is to obtain a correlation of solid interface energy to processing temperature, gas partial pressure, chemistry, and crystallographic orientation. Systems under study currently include Ni, Pt and Cu (both pure and doped) in contact with ZrO2, Si, SiO2, TiO2, Al2O3, and SrTiO3.
Metal Ceramic Interfaces in Composite and Joint Processing
Data from the wetting experiments are important in their own right, but are also used for designing processing schemes for metal-ceramic joints and composites, which is the second topic related to metal-ceramic interfaces which is studied in Kaplan’s group. Kaplan’s group has developed a unique method for producing nanocomposites.
The process is based on the infiltration of metallic salts into a fired (green) ceramic preform. During sintering, the gas phase in the sintering furnace is controlled to promote reduction of the salts, to form nano-sized metallic particles within the open pores of the ceramic body, which is then sintered to full density.
Current Research Projects
- Kinetic and thermodynamic characterization of Pt thin films on SrTiO3 on a-Al2O3 and their role on electrical properties for memory device application
- Ni-YSZ interface
- Grain boundary migration in Al2O3
- Atomistic structure and thermodynamics at the nanoscale
- The influence of additives on sintering and microstructural evolution of SiC