Masaki Makihara

Containerless Melting of Glass by Magnetic Levitation Method

The Melting of glass materials levitated in high magnetic fields has been carried out without a crucible by using a hybrid magnet and a CO2 laser. A cubic glass with 6 mm sides has become a complete sphere through melting and cooling in the air. This new method will provide opportunities for obtaining high-purity and new heterogeneous materials.

Magnetic levitation experiments in Tohoku University

Magnetic levitation makes a condition equivalent to non- or microgravity for diamagnetic materials and gives us an opportunity to do similar experiments as those planned for space projects. We have succeeded in the in situ observation of freezing of levitated water, crystal growth of some ionic crystals in a levitated solution and melt of levitated glass without a crucible.

High pressure densification of lithium silicate glasses

Abstract We have carried out neutron diffraction and Raman scattering measurements on the lithium disilicate glass densified by the application of high pressure. The density of the glass increased monotonically with applied pressures up to 6 GPa. A shift of the first sharp diffraction peak (FSDP) toward larger Q vectors was found in the total structure factor S ( Q ) of the neutron diffraction spectra. The Si–O bond length in an SiO 4 tetrahedron elongated by about 0.001 nm after densification under 6 GPa, while the nearest O–O distance did not change. However, an increase in distribution of the O–O distance was found after the densification. A low energy shift of 1080 cm −1 band, which is assigned to Si–O stretching mode, was observed in Raman scattering spectra of the densified glasses. It is consistent with the increase of Si–O bond length. We deduced from these results that the densification is caused by an increase of packing density of SiO 4 tetrahedron, which is accompanied by a distortion of the tetrahedron.

Crystal growth and materials processing in the magnetic levitation condition

Magnetic levitation effects in high magnetic fields and its application to crystal growth and materials processing have been investigated at High Field Laboratory for Superconducting Materials of IMR, Tohoku University. We have succeeded in (1) growing of some ionic crystals in a levitating solution, and (2) melting of levitating glass that makes a perfect sphere and fine particles.

Glass spheres produced by magnetic levitation method

Abstract Melting of glass levitated in high magnetic fields has been performed by using a hybrid magnet and a CO 2 laser. A sphere of an optical glass (BK7) has been obtained through melting and cooling without any crucible. Raman scattering and electron spin resonance (ESR) of the glass sphere showed no spatial anisotropy with respect to the applied field. Microspheres of binary sodium tellurite glass were also obtained for the first time by an evaporation–condensation process in high magnetic fields. Thermal convection was suppressed under a magnetic force of −0.8 g . The size of microspheres produced under the magnetic force was about 500 nm at most. This size is one-half the size of spheres produced without a magnetic field. Raman scattering measurements on microspheres produced under the magnetic field showed different spectra from those without a magnetic field. The difference is due to a deficiency of sodium ions in the spheres produced without a magnetic field.

Coordination structures of implanted Fe, Co, and Ni ions in silica glass by x-ray absorption fine structure spectroscopy

Coordination structures of implanted Fe, Co, and Ni ions were studied in 1.78–2.00-MeV 5 × 10 16 ions/cm 2 -implanted silica glasses by x-ray absorption and optical absorption spectroscopies. It was found from x-ray absorption spectra that the implanted Fe, Co, and Ni ions are coordinated by ca.3 oxygen atoms. The implanted ions dispersed in glass matrix and did not form crystals. The valence of the implanted ions was about 1.5. The Fe–O, Co–O, and Ni–O interatomic distances were 190, 191, and 192 pm, respectively. In addition, it was found from optical absorption spectra that one-fifth of implanted Co ions were present as Co 2+ ions in tetrahedral symmetry.

High pressure effect on optical properties of cerium ion in fluoroaluminate glass

Abstract High pressure effects on optical properties of Ce3+ doped ternary fluoroaluminate (18BaF2·37CaF2·45AlF3) glass have been investigated in terms of ligand field around cerium ion. Five bands due to the 4f–5d transitions were observed in ultraviolet absorption spectra for the glass. A photoluminescence band was observed at around 300 nm under excitation at each band. The photoluminescence band shifted toward smaller energies by densifying the glass using high pressures and temperatures. An energy shift of the band was also found in in situ photoluminescence measurement under high pressure using a sapphire anvil cell. However, the shift observed under high pressure was large compared with that of the densified glass. We deduced that the large peak shift under high pressure is mainly due to a local elastic contraction around cerium ion.

Microspheres of Tellurite Glass Formed by Evaporation–Condensation Process under High Magnetic Field

Sodium tellurite glass was evaporated by irradiating a CO2 laser beam under a high magnetic field with a large gradient. Glass microspheres were formed as a cloud of soot with the condensation of the vapor from the source glass. The flow of the glass soot due to thermal convection was observed when the glass source was evaporated under a zero field, but was suppressed by applying the high magnetic field with a large gradient, which reduces gravity for the glass by a magnetic force of -0.8g in the gravitational scale. The maximum size of the microspheres decreased to about half that of microspheres formed under a zero field. Sodium concentration in the microspheres was found to increase with magnetic field. A disturbance of the motion of evaporated species due to electromagnetic force was suggested as an origin of the suppression of recondensation to the surface of source glass melt under the high magnetic field, resulting in the increase in the sodium concentration of the microspheres and in the decrease in their size.

Structural relaxation of MeV ion-implanted silica glasses by thermal annealing

Abstract Thermal relaxation of Si–O–Si bond angle has been studied in 1 MeV B + -ion, 1 MeV O + -ion and 4 MeV Ni 2+ -ion implanted silica glasses by infrared reflection and visible and near-infrared reflection spectroscopy. It is found that the change in Si–O–Si bond angle is not proportional to the change in molar volume upon annealing. It is deduced that the relaxation mechanism of Si–O–Si bond angle accompanied by little density change has an activation energy of about 100 kJ mol −1 .

X-ray absorption fine structure study on coordination state of implanted gold ions in silica glass

Coordination state of gold atoms implanted in silica glass to an energy of 1.5 MeV and a dose of 1 × 10 17 ions/cm 2 has been studied by x-ray absorption fine structure spectroscopy. It was found that most of the gold atoms form gold clusters in which the nearest neighboring Au–Au interatomic distance is shorter by 0.05 °A than that in bulk gold. The contraction of Au–Au interatomic distance of gold clusters in silica glass is less than that reported in the previous studies on gold clusters within the other substrates. Gold atoms are coordinated by about four gold atoms in average. In addition, it was found that Au–O bonds are formed at the gold clusters/silica glass interface. It was deduced that the formation of Au–O bond at the gold clusters/silica glass interface depresses the contraction of Au–Au interatomic distance.