Eylem Seç
Electric Field Effects on Microstructure Evolution in Oxide Ceramics
Başlık:
Electric Field Effects on Microstructure Evolution in Oxide Ceramics
Yazar:
Qin, Wei, author.
ISBN:
9780355969832
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (125 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: Klaus van Benthem Committee members: Ricardo H. R. Castro; Yayoi Takamura.
Özet:
The application of electric fields can enable the accelerated consolidation of ceramic materials during field assisted sintering. Although such techniques are already employed for the synthesis of a wide variety of microstructures with unique macroscopic properties, a fundamental understanding of the mechanisms for the evolution of microstructures in the presence of electrostatic potentials is mostly absent from the literature. The work of this dissertation has addressed systematic microstructural analysis of ceramics that were sintered with the aid of an externally applied electric field. Microstructural evolution in the ionic conductor yttria-stabilized zirconia (YSZ) and the insulator magnesium aluminate spinel were studied using flash sintering and a home-built electric field assisted sintering apparatus, respectively. Microstructure analysis is crucial in understanding both the sintering process and macroscopic properties. Conventional analysis techniques are limited by efficiency, accuracy, and field of view, and may thus be challenging in obtaining a holistic understanding of the material. Therefore, the available microstructure analysis framework needs to be improved to obtain statistics that more accurately represent the microstructures of materials.
Microstructure analysis using scanning electron microscopy (SEM) was done by acquiring hundreds of partially overlapping images that were stitched together using cross-correlation function to obtain a large field of view representing the microstructure. This task was accomplished using MAPS software package. Custom trained edge detector by deep learning algorithm with convolutional neural network was employed to retract grain boundary networks from SEM images with unprecedented efficiency and accuracy. Microstructural evolution during sintering as well as microstructure gradient within each sample as a function of the applied electric field/current were studied in flash sintering of YSZ and field assisted sintering of spinel using this advanced microstructure analysis framework.
Systematic microstructural statistics for 3 mol% yttria-stabilized zirconia (3YSZ) synthesized by both conventional sintering and flash sintering with AC and DC current demonstrated enhanced diffusion kinetics across grain boundaries under flash condition. Within the gauge section, flash sintered microstructures were indistinguishable from those synthesized by conventional sintering procedures while the processing durations were at least 240 times shorter. Finite element modeling revealed a temperature gradient from the surface to the volume of the sintered body. Microstructure gradients, across the width of gauge section, were discovered for the AC flash sintered sample. Classical grain growth models due to Joule heating were revealed to be insufficient in justifying the microstructural evolution under the simulated temperature distribution. Faster grain growth mechanisms activated by electric field/current occurred during flash sintering and were responsible for the instantaneous grain growth. In addition, from both AC and DC flash sintered specimens, heterogeneous grain size distributions and residual porosity were observed in the proximity of the electrodes suggesting electrode effects can cause significant heterogeneities in microstructural evolution during flash sintering.
Grain growth in MgAl2O4 was studied under an applied DC electric field strength up to 2 kVcm--1. Free sintering of green bodies showed an accelerated grain growth by about 20% in the presence of an applied nominal field strength of 0.95 kVcm--1. In contrast to previous reports, annealing of dense microstructures in the presence of electric fields as high as 2 kVcm--1 revealed no additional grain growth. From the experimental results, it was concluded that applied electrostatic fields affect grain growth during sintering more strongly at lower green body densities, suggesting an enhancement of surface diffusion.
Notlar:
School code: 0029
Konu Başlığı:
Tüzel Kişi Ek Girişi:
Mevcut:*
Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(678579.1) | 678579-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
On Order
Liste seç
Bunu varsayılan liste yap.
Öğeler başarıyla eklendi
Öğeler eklenirken hata oldu. Lütfen tekrar deneyiniz.
:
Select An Item
Data usage warning: You will receive one text message for each title you selected.
Standard text messaging rates apply.