טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGabay Amir
SubjectThe Influence of Electrical Fields on Grain Growth in
SiC
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Wayne D. Kaplan


Abstract

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During (electromagnetic) field assisted sintering a green body is exposed to an electric field and elevated temperature. The exposure to an electric field causes faster sintering rates compared to conventional sintering methods.  Assuming the microstructure of the sintered body is controlled, this process can result in improved material properties (e.g. strength, transparency, and conductivity). However, there is a debate in the literature regarding the mechanism(s) of electromagnetic field assisted sintering, and understanding the mechanism is critical to implementation of the method. 


This research focuses on the influence of electromagnetic fields on grain growth, rather than on sintering. As a model system, SiC was first sintered using conventional pressure-less sintering at 2100°C under He.  Samples from the sintered bodies then underwent annealing treatments in the same conventional furnace, and the grain size as a function of annealing time was characterized.  In parallel, identical samples were annealed using a spark plasma sintering (SPS) device without pressure, at identical and at lower temperatures, and the grain size as a function of annealing time was characterized. 


From these experiments, the grain boundary mobility of SiC at 2100°C under conventional heating versus SPS was determined. Conventional heating resulted in a grain boundary mobility of 3.53∙10-17 m2/sec. SPS resulted in a grain boundary mobility of 1.36-4.79∙10-14 m2/sec at 2100°C and 6.22∙10-17 m2/sec at 1800ºC. While the aspect ratio of grains as a function of time during conventional and SPS annealing showed different trends, the aspect ratio as a function of grain size after conventional versus SPS annealing showed the same trend. This indicates that the same (or similar) mechanism(s) which promotes rapid sintering during SPS also significantly increases the rate of grain growth.