Contamination Study of Zirconia on the Densification Process and Properties of Transparent MgAl₂O₄ Ceramics.

Yi Li,Qun Zeng,Jian Zhang,Dan Han,Shiwei Wang

doi:10.3390/ma12050749

Abstract

In this paper, transparent magnesium aluminate (MgAl2O4) spinel ceramics are fabricated through pressureless sintering combined with hot isostatic pressing (HIPing). To investigate the effect of zirconia on sintering behavior, microstructure, and optical properties of transparent spinel ceramics, different contents of zirconia were added. The results show that zirconia can promote the densification process by the formation of anion vacancies. The resulting zirconia exists as tetragonal phase along the grain boundaries. The average grain size of resulting ceramics depends on the content of zirconia and HIPing condition. Small zirconia content did not deteriorate the optical properties of samples. A 5-mm-thick sample with 0.05 wt% ZrO2 pre-sintered at 1500 °C followed by HIPing treatment at 1550 °C achieved a high in-line transmittance of 75.5% at 400 nm and 85% at 1100 nm.

Highlights

Transparent magnesium aluminate spinel ceramics have been well studied for more than 50 years, since the first translucent sample was successfully fabricated in the1960s [1,2]
Reducing the porosity to an acceptable level is the main challenge for the fabrication of transparent spinel ceramics
The densification process process was enhanced through the increase of the pre-sintered temperature (Figure was enhanced through the increase of the pre-sintered temperature (Figure 1a)

Summary

Introduction

Transparent magnesium aluminate spinel ceramics (hereafter termed “spinel”) have been well studied for more than 50 years, since the first translucent sample was successfully fabricated in the1960s [1,2]. Transparent magnesium aluminate spinel ceramics (hereafter termed “spinel”) have been well studied for more than 50 years, since the first translucent sample was successfully fabricated in the. To obtain fully dense transparent spinel ceramics, the residual porosity in the sintered sample should be carefully controlled. The pore diameter of resulting samples should be under 40 nm, which markedly decreases the scattering in the visible range. Reducing the porosity to an acceptable level is the main challenge for the fabrication of transparent spinel ceramics. The spinel densification rate is mainly dominated by O2− diffusivity, as it is the largest ion and close-packed lattice [3,10,14,15]. Due to the low diffusivity of O2− in spinel structure, extreme sintering conditions of high temperature and high pressure are usually required to achieve full densification.

Methods

Results

Conclusion