Laboratory production of   and   alumina grains and their characteristic infrared spectra

Abstract

The high‐temperature phase of δ‐Al2O3 was produced using smoke by the gas evaporation method in a mixture gas of O2 and Ar. The θ‐ and α‐Al2O3 were produced by heating the δ‐Al2O3 powder. The θ‐phase was also produced directly by burning a mixture of Al and Cr metal powders in O2–argon gas. On the basic peaks of δ‐Al2O3, the characteristic infrared peaks were observed at 10.4, 10.8, 11.4, 11.9, 12.4, 12.7, 13.0, 13.6, 14.2, 15.2, 15.8, 16.2, 17.0, 17.9 and 19.0 μm. The peak positions are distinct from the well‐known modes of corundum (α‐Al2O3), and from θ‐Al2O3 which has λ= 11.7, 12.0, 12.1–12.6, 13.6, 13.9–14.0, 15.8–16.0, 16.3, 17.1 and 18.5–19.2 μm. The alternation of the characteristic peaks from δ→θ→α is clearly shown in this paper.

Morphological effects on IR band profiles

“…Both samples showed a double peak at approximately 12.4 and 13.9 μm. Similarly, Kurumada et al (2005) carried out transmittance measurements of commercial γ-Al 2 O 3 particles, and they detected a double peak at about 12.5 and 13.5 μm in wavelengths as well. These results fit well with our measurements (aerosol 12.3-13.1 μm & CsI 12.7-13.6 μm).…”

“…Barker 1963;Loewenstein et al 1973;Querry 1985;Gervais 1991) as well as γ-Al 2 O 3 (e.g. Chu et al 1988;Koike et al 1995), δ-and θ-Al 2 O 3 (Kurumada et al 2005), and amorphous Al 2 O 3 (e.g. Chu et al 1988;Begemann et al 1997 ions surrounded by 32 O 2− ions in a unit cell of the spinel.…”

“…One is the medium effect since all observations utilized different substances as a medium. Koike et al (1995) and Kurumada et al (2005) used KBr powder whereas we applied N 2 gas for the aerosol measurements and CsI for the pellet measurements. Another factor is the morphological effect.…”

“…Though it is obvious to confirm the morphological differences among these Al 2 O 3 samples via the SEM and TEM images, these band profiles are significantly affected by differences in the crystal structures, in this case more than by the morphological effects. Kurumada et al (2005) produced nano-sized spherical δ-Al 2 O 3 particles by the gas evaporation method and measured the transmittance spectra by making use of the KBr pellet technique. They detected 15 absorption peaks in the wavelength range between 10 and 19 μm.…”

Morphological effects on IR band profiles: Experimental spectroscopic analysis with application to observed spectra of oxygen-rich AGB stars

“…Both samples showed a double peak at approximately 12.4 and 13.9 µm. Similarly, Kurumada et al (2005) carried out transmittance measurements of commercial γ-Al 2 O 3 particles, and they detected a double peak at about 12.5 and 13.5 µm in wavelengths as well. These results fit well with our measurements (aerosol 12.3-13.1 µm & CsI 12.7-13.6 µm).…”