Microstructure green body

The development of the microstructure is strongly affected by the perfection of the Si green body. Inhomogeneities in density, pore size and distribution are... 

To assess the uniformity of the microstructure in a green body, the variance, is used [91]. 

As a result, a picture of the microstructure is a valuable tool in diagnosing drying problems in green body manufacture and predicting problems during binder burnout and sintering. 

SEM photographs of the surfaces of the sintered samples are shown in Fig. 4 (A). The surface microstructure reveals uniform and fine grain growth about 2-3 pm. No pores were observed on the surface of the sample, but there were some pores from the fracture surface of the sample, as shown in Fig. 4 (C). The sintered density is 6.6 g/cm, which is over 95% of the theoretical value. The residual pores may be partly attributed to the agglomerates in the source powders that lowered the sinterability of the green bodies. It can also be seen that there are no great changes between the pellets sintered in air before and after heat treatment at 750°C for 5h in H2. This result is in aecordance with that of XRD. It confirms that the samples are chemically stable in H2 atmosphere at least below 750°C. 

A commercially available fully dense Na "-(3"-alumina disc was used as the solid electrolyte. The working electrode (sink) of the system is a screen-printed platinum thick film of 7 pm in thickness. The porosity of the Pt thick film is in the range of 65 to 75 %, and the average pore size is about 2 pm and ranges from 0.5-5 pm according to microstructure studies. A source Na COj disc was made by pressing Na COg powder. The green body was then cosintered onto a Pt mesh with a spot-welded Pt lead. 

Because of their strong chemical bonds, bulk ceramics are most efficiently fabricated by means of densification of powders. The fabrication process involves two main stages (1) consolidation of the powder to form a porous, shaped article (the green body), also referred to as forming, and (2) heating of the shaped powder form to produce a dense article, referred to as firing or sintering. The final product commonly consists of a relatively dense polycrystal with some residual porosity (Fig. 1). The microstructure, which... 

After the porous green body has been dried and the organic phases have been removed, the component is sintered at elevated temperature below the melting point of the material. This process step is generally one of the most important, whereby the microstructure of the material is tailored to meet specific, end-use properties. 

The microstructure of the green body as observed by SEM is shown in Fig. 4. After consolidation, powders in green body compact closely and homogeneously. However, the polymer network was not observed via SEM. The pore diameter distribution, obtained by Hg intrusion porosimetry, showed a monomodal distribution type. The relative density, porosity, and the median pore diameter of green samples were 57.67%, 35.02%, and 10.6nm, respectively. 

Ceramic processing typically consists of three main steps (i) synthesis or preparation of precursor powders, (ii) consolidation or packing of the powders into green bodies, and (iii) sintering [44]. Every step has a significant effect on the microstructure and optical performance of the final transparent ceramics. There are a number of parameters relevant to the quality of the powders, facility, and way of consolidation and techniques of sintering, which can be used to optimize the fabrication process as a whole. 

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