Structural and infrared spectral changes of silicon oxide grains by heat treatments

In order to elucidate the relationship between crystallographic structures of amorphous silicon oxide grains and infrared (IR) spectra, ultrafine grains produced by the gas evaporation method have been studied on the basis of IR spectral measurements and electron microscopic (EM) observations. The shifts and disappearance in the IR absorption peaks of specimen heat-treated in air have been found. The spectral changes have been discussed in the relation with the polymorphism of silica

Electron microscopic and infrared spectral studies on the structure of alumina phases

Alumina produced by oxidation of aluminum in air was studied by infrared spectroscopy and electron microscopy. Infrared spectra of both alumina particles and alumina film oxidized in air showed an absorption peak at 10.8μm, though that of γ-Al_2O_3 particles showed a broad 13μm peak. On the basis of the infrared spectra and electron diffraction pattern, it was concluded that alumina produced by the oxidation of aluminum in air is η-Al_2O_3. The phase transition from η-phase to γ-phase and to α-phase took place at 900℃ and 1100℃, respectively. The relationships between infrared spectra and crystal structure of some alumina phases are discussed

太陽系での軽元素の生成

京都大学0048新制・課程博士理学博士甲第1255号理博第261号新制||理||164(附属図書館)3532UT51-47-K29京都大学大学院理学研究科物理学第二専攻(主査)教授 長谷川 博一, 教授 林 忠四郎, 教授 武藤 二郎学位規則第5条第1項該当Kyoto UniversityDA

Mid-infrared spectra of differentiated meteorites(achondrites): comparison with astronomical observations of dust in protoplanetary and debris disks

Mid-infrared (5–25 μm) transmission/absorption spectra of differentiated meteorites (achondrites) were measured to permit comparison with astronomical observations of dust in different stages of evolution of young stellar objects. In contrast to primitive chondrites, achondrites underwent heavy metamorphism and/or extensive melting and represent more advanced stages of planetesimal evolution. Spectra were obtained from primitive achondrites (acapulcoite, winonaite, ureilite, and brachinite) and differentiated achondrites (eucrite, diogenite, aubrite, and mesosiderite silicates). The ureilite and brachinite show spectra dominated by olivine features, and the diogenite and aubrite by pyroxene features. The acapulcoite, winonaite, eucrite, and mesosiderite silicates exhibit more complex spectra, reflecting their multi-phase bulk mineralogy. Mixtures of spectra of the primitive achondrites and differentiated achondrites in various proportions show good similarities to the spectra of the few Myr old protoplanetary disks HD104237A and V410 Anon 13. A spectrum of the differentiated mesosiderite silicates is similar to the spectra of the mature debris disks HD172555 and HD165014. A mixture of spectra of the primitive ureilite and brachinite is similar to the spectrum of the debris disk HD113766. The results raise the possibility that materials produced in the early stage of planetesimal differentiation occur in the protoplanetary and debris disks

Formation of Transition Alumina Dust around Asymptotic Giant Branch Stars: Condensation Experiments using Induction Thermal Plasma Systems

Mid-infrared spectroscopic observations of oxygen-rich asymptotic giant branch (AGB) stars show the common presence of dust species that have a broad feature at similar to 11-12 mu m. Chemically synthesized amorphous alumina (Al2O3) is widely accepted as the source of this emission, although it is not obvious that amorphous alumina can condense in circumstellar conditions. We performed condensation experiments of Al-Si-Mg-O and Mg-Al-O gases using induction thermal plasma systems, in which small particles condense from vapors with a steep temperature gradient. The condensates were analyzed using X-ray diffraction and Fourier transform infrared spectroscopy, and observed with a transmission electron microscope. The condensed nanoparticles from the Al and O gases were transition aluminas based on face-centered cubic (fcc) packed oxygen (delta- and lambda-alumina, and an unknown phase). The fcc oxygen frameworks were maintained in the condensed alumina containing small amounts of Mg and Si. Condensates from the gases of Al:Mg = 99:1 and 95:5 had delta- and gamma-alumina structures. Particles with lambda- and gamma-alumina structures formed from starting materials of Al:Si = 9:1 and Al:Si:Mg = 8:1:1, respectively. Amorphous silica-rich particles condensed from gases of Al/(Si+Al) < 0.75. The condensed transition alumina containing similar to 10% Si showed similar spectral shapes to the observed dust emission from the alumina-rich AGB star T Cep. Based on the present results, it is reasonable that the source of 11-12 mu m broad emission of alumina-rich stars is not amorphous alumina, but is transition alumina containing similar to 10% Si