Segregation of Magnesium to the Internal Surface of Residual Pores in Translucent Polycrystalline Alumina

Abstract

For the first time direct evidence for Mg segregation to the surface of pores within translucent polycrystalline alumina grains has been found using energy dispersive Xray spectroscopy (EDXS) and convergent beam electron diffraction (CBED) in an analytical electron microscope (AEM) on a submicrometer scale. This supports the model that MgO dopant increases the surface diffusivity which, in turn, increases the pore mobility. The MgO dopant's role in retarding grain growth in combination with the enhanced pore mobility allows the achievement of nearly full density and translucency in alumina. [

Solubility of Magnesia in Polycrystalline Alumina at High Temperatures

“…Fourth, direct evidence of magnesium segregation on pore surfaces was reported in translucent samples of MgO-doped Al 2 O 3 using chemical techniques using analytical electron microscopy. 25 If the sintered samples in most prior works contained a greater number density of residual, micrometer-sized pores than in the present samples, then there could have been a significant amount of magnesium segregation at the surface pores, contributing to increased MgO solubility in their Al 2 O 3 samples.…”

Atomistic modeling of dopant segregation in α-alumina ceramics: Coverage dependent energy of segregation and nominal dopant solubility

“…34) albeit smaller than lanthanides is still larger than the aluminum ion. Grain boundary [51][52][53] and surface [54][55][56][57] segregation of Mg still occurs, the extent being less pronounced than for the larger elements considered above. Experimental values for the Mg bulk solubility in ␣-alumina vary substantially; the most recent value found in the literature (132 ± 11 ppm at 1600 • C) was measured using a wavelength dispersive spectroscopy, 51 whereas Roy and Coble 58 reported a solubility limit of 300 ppm at 1630 • C based on spectrochemical analysis.…”

Precipitation of MgO·nAl2O3 in Mg‐Doped α‐Al2O3 under Electron Irradiation

“…S INCE the discovery of the effect of Mg doping on the sintering of ␣-Al 2 O 3 , 1,2 the grain boundaries of Mg-doped ␣-Al 2 O 3 have been intensively studied by many researchers to determine whether Mg segregates at the grain boundaries, using spark source mass spectrometry (SSMS), 3 Auger electron spectroscopy (AES), 4 X-ray photograph-electron spectroscopy (XPS), 5 high-resolution scanning Auger microprobe (HR-SAM), 6 -8 combinations of transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS), 9 and the combination of scanning transmission electron microscopy (STEM) with spatially resolved electron energy-loss spectroscopy (SREELS). 10 Although the segregation of Mg at the free surfaces of ␣-Al 2 O 3 was successfully detected by AES 11,12 and TEM-EDS, 13 there have been no conclusive reports for Mg segregation at the grain boundaries of ␣-Al 2 O 3 . It was pointed out that at least some of the reported inconsistencies of Mg segregation could be explained by the fact that measurements have mostly been made on fracture surfaces, affected by the presence of spinel precipitation at or near the fracture plane.…”