Sintering and Densification of Transparent Ceramics

After sintering, the specimens were annealed at 1400 C for 2 h in air for decoloring. 

Shanghai Instltute of C ramJcs C EcYa fSTfa piitrent  

Sintering trajectories, i.e., grain size (G) versus relative density (p), of the undoped and silica-doped samples sintered for 2 h at 1450-1800 °C, are shown in Fig. 7.5 [11]. It was observed that grain size increased at a very slow rate until the 

5 G—p sintering trajectraies of the undoped and silica-doped NdiYAG ctaamics sinttaed at vacuum fta 2 h at temptaatures ranging from 1450 to 1800 °C. Reproduced with ptamission from [1]. Copyright 2013, John Wiley Sons 

As a result, when every two Zr ions were substituted, one O was produced, so that [Vy] was increased, while [Yj ] was decreased. The decrease in [Yj ] resulted in a reduction in grain-boundary mobility and sintering rate, which ensured the escape of pores and densification of the ceramics. For example, average grain size of the Zr02-doped ceramics was about 15 pm, which was much smaller than those widely reported in the open literature. In terms of optical performance of the transparent ceramics, 3 at.% Zr02 was the optimized doping concentration. 

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Meir S, Kalabukhov S, Froumin N, Dariel MP, Frage N (2009) Synthesis and densification of transparent magnesium aluminate spinel by SPS processing. J Am Ceram Soc 92 358—364 Frage N, Cohen S, Meir S, Kalabukhov S, Dariel MP (2007) Spark plasma sintering (SPS) of transparent magnesium-aluminate spineL J Mater Sci 42 3273-3275... 

In this paper, novel Nd YAG powders were synthesized via a modified co-precipitation method with alcohol-water as the precipitation solvent. Nd YAG transparent ceramics were fabricated by vacuum sintering using as-prepared ultrafine powders with 0wt%, 0.3wt%, 0.5wt% and 0.7wt% TEOS as additive. The densification and the microstructure evolution of the ceramics were mainly studied. 

MgO is has cubic crystal structure, as shown in Fig. 2.10. MgO ceramics have excellent thermal and mechanical properties with a high melting point of 2850 °C and low density of 3.58 g cm. It has an isotropic cubic crystal strucmre, which meets one of the requirements to be transparent. PolycrystaUine infrared-transparent MgO is a potential substitute for sapphire IR windows and protectors for sensors. Due to the high sintering temperature required for full densification of MgO, fabrication of transparent MgO ceramics is stiU a challenge. Almost aU techniques discussed above have been used to prepare transparent MgO ceramics [3]. 

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