In Situ High Temperature Environmental Scanning Electron Microscopic Investigations of Sintering Behavior in Barium Titanate

 
 
 
 

In Situ High Temperature Environmental Scanning Electron Microscopic Investigations of Sintering Behavior in Barium Titanate

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Title: In Situ High Temperature Environmental Scanning Electron Microscopic Investigations of Sintering Behavior in Barium Titanate
Author: Subramaniam, Srinivas
Description: First time in situ observations of sintering behavior occurring in barium titanate were carried out in the environmental scanning electron microscope (ESEM). FEI XL-30 ESEM-FEG/LaB6 environmental scanning electron microscopes equipped with a 1500°C hot-stage furnace accessory were used to perform these studies. Barium excess Barium titanate powders (Ba/Ti ratio 1.004) processed using conventional ceramic routes were sintered in the ESEM at temperatures between 1320°C and 1375°C. Silica additions to the powders facilitated observation of liquid phase sintering behavior. Dynamic observations of the materials were made starting at ambient temperatures and following a typical furnace sintering cycle with temperatures exceeding 1300°C. Both solid state and liquid phase sintering mechanisms were observed in the samples with the dynamics of these mechanisms exhibiting similarities found in ex-situ studies in the literature. In all materials, no noticeable changes were observed to occur at temperatures below ~800°C. Phosphate contamination occurred in initial experiments which resulted in vapor-solid interactions with mixed phase end products being formed. A contamination mechanism has been proposed. Corrective measures were implemented to allow sample surface observations. Solid state sintering experiments performed in the ESEM result in poor sintering and densification. This was attributed to changes in the defect chemistry of the sample in the ESEM chamber caused by low vacuum water vapor atmospheres used in the experiments. Liquid phase sintering observations performed in the ESEM resulted in dense largegrained samples with microstructural similarities to conventional furnacesintered samples. Instrument capabilities allowed the capture of rapid sequences at high resolution. Fluid real-time sequences studying ongoing sintering phenomenon were obtained, vastly enhancing the ability to study these dynamic processes in real time. Platinum support materials were observed to vaporize and condense on sample surfaces at temperatures exceeding 1300°C. The use of field emission instrumentation over LaB6 sources is recommended due to their improved imaging characteristics in harsh environments. These studies have clearly demonstrated the versatility of the ESEM techniques and its ability to probe into harsh research environments providing the researcher with a valuable tool to understand them.
Permanent Link: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155575558
http://hdl.handle.net/2374.OX/11996
Date: 2006

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