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Abstract
In this paper, local spark sintering of a ceramic-metal system (SiO2-Sn) during microwave processing was examinedby means of synchrotron-radiation-computed tomography technology. From the reconstructed 3-D and cross-section images of the specimen, adensification process was observed below the melting point of Sn, and then the specimen came into a rapid densification stage. These results may be due to the local spark sintering induced by the high-frequency alternating microwave electric fields. As the metallic particles Sn were introduced, the microstructure of “ceramic-metal” will lead to a non-uniform distribution and micro-focusing effect from electric fields in some regions (e.g., the neck). This will result in high-intensity electric fields and then induce rapid spark sintering within the micro-region. However, in the subsequent stage, the densification rate declined even when the specimen was not dense enough. The explanation for this is that as the liquid Sn permeated the gaps between SiO2, the specimen became dense and the micro-focusing effect of electric fields decreased. This may result in the decrease or disappearance of spark sintering. These results will contribute to the understanding of microwave sintering mechanisms and the improvement of microwave processing methods.
Highlights
Over the last decades, microwave sintering has been under constant development for the rapid preparation of high-performance powder materials, such as ceramics and ceramic matrix composites [1,2,3,4,5]
A densification processwas observed below the melting point of Sn, and the specimen came into a rapid densification stage
An in situ investigation on local spark sintering of ceramic-metal system (SiO2 -Sn) during microwave processing was carried out using synchrotron radiation computed tomography technology (SR-CT).The following conclusions can be drawn: In the experiment, except for the normal sintering phenomenon, a densification process was observed below the melting point of Sn, and the specimen came into a rapid densification stage
Summary
Microwave sintering has been under constant development for the rapid preparation of high-performance powder materials, such as ceramics and ceramic matrix composites [1,2,3,4,5]. Since the first full sintering of metal powders in a microwave field, many experiments on microwave sintering of various kinds of metals, including ceramic-metal materials, have been carried out. Many researchers attribute the advantages of microwave sintering to the effect induced byhigh-frequency alternating microwave fields, such as the enhancement of the diffusion coefficient [7,8], reduction of activation energy [9,10], micro-focusing effect [11] and the eddy current [12] for ceramics or metals
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