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Doctor's Theses (authored and supervised):

B. Schwarz:
"Construction of a high temperature sessile drop device for wettability studies in the Copper/Carbon system";
Supervisor, Reviewer: C. Eisenmenger-Sittner, H.P. Degischer; Festkörperphysik, 2008; oral examination: 04-25-2008.



English abstract:
The objectives of this thesis were wettability studies in the Carbon - Copper system. Therefore the overall aim was the construction of a High Temperature Sessile Drop Device (HTSDD) to study the wettability of a liquid metal on a solid substrate. Sessile drop means to melt a metal on a plane substrate and to image the curvature of the droplet, gaining informations on the contact angle, liquid surface energy and identifying the wetting regime. The contact angle in a liquid/solid system is the main property to describe the wetting behavior in the system. After a comparative literature survey about high temperature wetting we planned and constructed a sessile drop device with the ability of melting metals up to approx. 1100°C under high vacuum and the capability of in-situ imaging of the liquid drop. A novelty of this custom-built device is the resistance heated substrate holder, which is also suitable for sputter deposition in a physical vapor deposition (PVD) plant. The imaging of the liquid drop is done by a webcam with an additional optic and for the determination of the contact angle a self-written software is available. With the HTSDD wetting experiments of Cu and a Cu-based active brazing alloy (CuABA) were performed on TiN and Mo coatings. In the case of TiN also substoichiometric films were investigated and in the case of Mo the carbide formation in the Mo-film during heat treatment was investigated and compared with a model. The identfication of the reactive wetting regime in the C/CuABA system can be deduced from the time evolution of the droplet. The structure of this thesis is as follows:
In the chapter "Introduction" the reasons for the choice of C/Cu are described, also the application of wetting promoting thin films in the joining of plasma facing components in future fusion reactors is presented. The chapter "High Temperature Sessile Drop Device" deals with the planning and construction of the sessile drop device. The individual parts of the device (substrate holder, manipulator, thermocouple) are described here. The next chapter "Information from the liquid drop" deals with some information gained from the curvature of the droplet: the contact angle and the liquid surface energy can be calculated. The mass loss of the molten metal during the experiments was compared with theoretical predictions (Knudsen model). In the chapter "Physical vapor deposition" the basics of sputtering are explained and the deposition of substoichiometric TiN films is described. A comparison with a theoretical model for reactive sputtering from literature is given. The chapter "Carbon with interlayers" describes surface energy measurements of the glassy carbon and gives the first wetting experiments with di˙erent interlayers deposited onto the carbon substrate. The following chapter "Substoichiometric TiN as wetting promoters" deals with the results of the wetting experiments of stoichiometric and substoichiometric TiN films. The concept of reactive wetting is presented with the distinction between diffusion limited and reaction limited reactive wetting. The brazing results of the sputter deposited films on graphite and CFC (Carbon Fiber reinforced Carbon) are shown as well. In the chapter "Molybdenum as wetting promoter" wetting experiments on pure Mo and on Mo coatings are presented. Also the carbidization process during the heat treatment of thin Mo ˝lms was studied. Experimental results of the carbide layer formation are compared with a mathematical model using a Cellular Automaton. In the last chapter "Conclusion" the results of this thesis are shortly summarized and an outlook on further work is given.

Created from the Publication Database of the Vienna University of Technology.