Silica reactivity during reaction‐sintering of Nd:YAG transparent ceramics

Abstract

Silica (SiO2) is widely used as sintering aid during vacuum sintering of YAG (Y3Al5O12)‐based transparent ceramics. These ceramics are mainly used for laser applications when they are doped with rare‐earth luminescent elements such as Yb3+ or Nd3+. By means of microstructural, chemical, dilatometry, and thermogravimetry analyses, this study has evidenced that sufficiently high amount of silica (ie above the solubility limit in YAG) forms intergranular transient liquid phase of mixed composition Y‐Al‐Si‐O that vaporizes rapidly for temperatures higher than 1350°C. As a result, silica content after sintering remains always lower than the solubility limit in YAG ceramics (ie lower than 900 ppm). Finally, vacuum sintering with an external source of gaseous Si was proven to be suitable to manufacture highly transparent Nd:YAG ceramics.

Fabrication and microstructure development of Yb:YAG transparent ceramics from co‐precipitated powders without additives

“…Recently, Boulesteix et al investigated the silica reactivity during reaction‐sintering of Nd:YAG transparent ceramics. They determined Si doping YAG at levels below the solubility limit could not volatilized, meanwhile would result in the equilibrium segregation of Si to the grain boundaries.…”

“…The evidences support the fact that the introduction of SiO 2 additive prominently improves the densification rate of Yb:YAG ceramic due to the existence of liquid phase, [29][30][31][32] previously reported by our group. 22 Recently, Boulesteix et al 33 investigated the silica reactivity during reaction-sintering of Nd:YAG transparent ceramics. They determined Si doping YAG at levels below the solubility limit could not volatilized, meanwhile would result in the equilibrium segregation of Si to the grain boundaries.…”

“…Judging by naked eye, one can clearly see all the Yb:YAG ceramics from co-precipitated powders without additives have good transparency, as inserted in Figure 11. On the other hand, Boulesteix et al 33 recently reported the Nd:YAG ceramics samples fabricated from the primary powders mixtures without sintering aids, but the samples appear smoky, attributable to the small amounts of defects centers such as pores and second phase acting as light scattering centers. However, the sample sintered at 1800°C for 15 hours exhibits the best optical quality in the current study, with the optical transmittance reaching a maximum value of 83.4% at 1100 nm and ~82% in visible region, a value close to that measured for Yb:YAG single crystal (83.8% at 1100 nm), as shown in Figure 11.…”

Effect of different contents of zirconia and yttrium oxide on microstructure and properties of high alumina ceramics

“…The MgO addition could inhibit grain growth and grain boundary diffusion of alumina during sintering . In the sintering process, SiO 2 can promote the formation of liquid phase, and the presence of liquid phase allows the crystal grains to flow sufficiently in the matrix, which is beneficial to the densification of ceramics . In addition, different contents of ZrO 2 and Y 2 O 3 (analytical purity, Qinghe County Kete New Material Technology Co., Ltd.) were mixed with above powders, and the chemical composition of the sample is shown in Table .…”

“…In recent years, the mechanical properties of alumina ceramics have been effectively improved by dispersing appropriate sintering aids in a continuous matrix with alumina ceramics as the matrix, which is a simple and feasible method to obtain alumina ceramics with high hardness, and high wear resistance . For example, adding MgO to alumina ceramic matrix can inhibit grain growth and grain boundary diffusion, adding SiO 2 can generate liquid phase and reduce the sintering temperature . The addition of MgO and SiO 2 is beneficial to inhibit the discontinuous grain growth and to promote the sintering of Al 2 O 3 ‐based ceramics, promoting ceramics to be denser .…”