Nobuo Takusagawa

Crystallization process and some properties of calcium mica–apatite glass-ceramics

Abstract A feature of calcium–mica is the great glass stability of the melt. However, the calcium–mica glass-ceramic disintegrates naturally in air. If the disintegration is hindered by the separation of other materials, glass-ceramics containing calcium–mica become usable. In this study, mica–apatite glass-ceramics with the different ratio of fluoroapatite (Ca10(PO4)6F2) to calcium–mica (Ca0.5Mg3(AlSi3O10)F2), were prepared and the crystallization process, microstructure development and some properties were investigated. Mica crystals first appeared and then apatite crystals in all specimens. This crystallization process was different from that of Bioverit®I and the other mica–apatite glass-ceramics. Specimens, in which the mica crystals formed interlocking microstructure and fine apatite crystals were dispersed on the surface of the mica crystals, showed good machinability but disintegrated naturally in air or distilled water. On the other hand, specimens consisting of fine mica and fine apatite crystals, showed higher bending strength and hardness than Macor® and high chemical resistance in distilled water. But they showed inferior machinability because the mica crystals formed incomplete interlocking microstructure.

Fluorescence spectra and chemical species of fluorescein molecules adsorbed on a calcinated porous Vycor glass

Properties of fluorescence and the excitation spectra of fluorescein molecules adsorbed onto a calcinated (773 K) porous Vycor glass have been investigated as a function of the amount of adsorbed dye (the surface coverage, θ = 0.00051 and 0.0098). The fluorescence and fluorescence-excitation spectra of fluorescein adsorbed onto Vycor glass showed the spectrum only due to cation species at θ = 0.00051. On the other hand, the spectra observed at θ = 0.0098 suggested the presence of cation, anion, and dianion species on the surface of Vycor glass. These results indicated the existence of at least two different types of adsorption sites involving the Brønsted acid site on the surfaces of Vycor glass.

Infrared absorption spectra and structure of fluorine-containing alkali silicate glasses

Infrared absorption spectra were studied in the 800-700 cm−1 range for fluorine containing alkali silicate glasses. Only one absorption maximum appeared in that range for SiO2, R2OSiO2 (RLi,Na,K,Rb or Cs) and RFSiO2 (RLi or Na) glasses. In the case of RFSiO (RK,Rb or Cs) glasses, two maxima appeared. The higher and lower frequency peaks were tentatively interpreted as corresponding to symmetric stretching vibrations of SiO2 and SiO4−αFα(α<4) tetrahedra, respectively. Owing to more extensive formation of SiO4−αFα tetrahedra in the KFSiO2, RbFSiO2 and CsFSiO2 glass system, these could be prepared with larger amounts of fluoride than the LiFSiO2 and NaFSiO2 glasses.

Effect of titania addition on crystallization process and some properties of calcium mica-apatite glass-ceramics

Abstract In order to obtain calcium mica–apatite glass-ceramics having high water resistance and excellent machinability, TiO 2 was added to the starting materials of glass-ceramics with chemical composition of 3:7 weight ratio of fluoroapatite to calcium–mica. A large number of fine spherical particles in which mica and apatite should be included were generated uniformly. The mica and apatite were crystallized at lower temperatures and at narrower temperature ranges than those in the undoped specimen. However, the crystallization quantity ratio of apatite to mica was smaller, compared with that of apatite to mica for the undoped specimen. These results suggest that TiO 2 acted as a nucleation agent of mica but impeded the crystallization of apatite. Mica in the fine spherical particles became plate-like when TiO 2 was separated at ⩾900 °C. The plate-like mica with size of 0.5–2 μm was surrounded by apatite, TiO 2 and residual glass, and formed the interlocking microstructure at 1000 °C. Such a microstructure resulted in high water resistance and excellent machinability. Particularly, a large number of fine TiO 2 particles surrounded the mica uniformly, which was very effective in the deterrence of disintegration.

Liquid phase sintering of bimodal size distributed alumina powder mixtures

Fine and coarse alumina powder mixtures (non-additive specimen) and those containing the additive formed liquid phase during firing (additive specimen) were compacted and fired at 1400–1600°C. Liquid phase sintering proceeded markedly at 1400–1500°C and additive specimens had much higher relative density than non-additive specimens at 1500°C. As the liquid phase sintering proceeded, the open pore volume decreased abruptly, but the open pore size changed depending on the packing structure. The open pore size decreased in the specimens where the fine particles formed matrix structure, while it increased in the specimens where the coarse particles formed skeletal structure. At 1600°C all additive specimens having different mixing ratios of fine and coarse powders had similar microstructure and the same relative density of 97%. However, spherical large pores were formed and remained in all additive specimens even at 1600°C. The bending strength of those specimens was about 400 MPa.

Structure of porous glass prepared from fluorine-containing sodium borosilicate glasses

Porous glasses were prepared from Che original glasses in the system of fluorine-containing Na2O-B2O3-SiO2 by the phase separation and leaching process. The original glasses contained 0–3.1 wt% of fluorine and 67.5 wt% of SiO2 and the atomic ratio of B/Na in the glasses was 3.0. Porous glass specimens having the thickness of 5 mm and no crack were obtained from the F-containing glasses after phase-separated at 500°C for 100 hr. Density, porosity, surface area, pore size and chemical composition were measured for the porous glasses prepared from the F-containing glasses and the F-free glass. SiO2 content in all-of the porous glasses prepared were 94–95 wt% but less than 0.5 wt% of fluorine was determined in the porous glasses prepared from the F-containing glasses. Bulk density and porosity were 1.58–1.59 g/ml and 27–28 %, respectively. By the addition of fluorine to the original glass the pore size was increased and consequently the surface area was decreased. For the porous glass prepared from the glass containing 2.8 wt % of fluorine the pore size and the surface area were about 300–400 A and less than 50 m2/g, respectively. Immiscible temperature was increased in some degrees by the addition of fluorine.

Influence of pore size on the intensity of the monomer and excimer-like fluorescence of pyrene adsorbed onto porous glasses

Abstract The influence of the pore size of calcinated (773 K) porous glasses (average pore diameters, 40, 80 and 300 A) on the ratio R of the emission intensity of the excimer-like fluorescence to that of the monomer fluorescence of pyrene adsorbed on porous glass was examined. R decreased with increasing pore size. The results were interpreted on the basis of the photophysical processes of adsorbed pyrene molecules on the surfaces. The ratio of the quantum efficiency for excimer formation from excited dimeric pyrene was estimated to be 1:0.23:0.11 for PG40, PG80 and PG300. The fractal nature of the surfaces of the individual porous glasses played an important role in the photophysical processes of pyrene encapsulated in the pores.

Dielectric properties of sintered materials prepared from glass-ZrO2-SrTiO3 mixtures

Abstract(Ca,Sr,Ba)O-Al2O3-SiO2-TiO2 glass powder was mixed with 6.7 mol % ZrO2 and 0–11.96 mol % SrTiO3. The mixtures were sintered at 850 °C, 900 °C or 950 °C. Most of the glass phase changed to crystalline phases of (Ca,Sr,Ba)2TiSi2O6TS, (Ca,Sr,Ba)Si2O6AS, ZrO2 and SrTiO3 during sintering. The dielectric properties of samples sintered at 900 °C were measured at 1 MHz using silver electrodes. With increasing SrTiO3 content, the dielectric constant increased from 12 to 19 and the temperature coefficient of dielectric constant, TCD, changed from -30 ppm ^C-1 to -400ppm^C-1. Using mixture equations, dielectric constants and TCD values were estimated for the samples and these values were compared with experimental results.

Effects of Reaction Temperature and Layer Charge on Formation of Chromia Pillared Fluorine Micas.

層電荷の異なるLi+交換型テニオライト系膨潤性合成フッ素雲母[LixMg33-xLixSi4O10F2(x=O.5,0.8)]とOH/Cr比の異なる各種多核ヒドロキソクロム(III)水溶液を室温から95℃ の各所定温度で反応させ,クロミア架橋フッ素雲母の生成と性質に及ぼす挿入反応温度と層電荷の影響を検討した.その結果,OH/Cr=2.0の溶液を用いて層間挿入反応を80℃ 以上で行うと,室温で挿入反応を行う場合よりもかさ高いクロム(III)イオン種を多量に雲母層問域に挿入できることがわかった.特に,層電荷が大きなホスト結晶からも,従来調製することができなかった多量のクロム収容量[2.01mol・(Si4O10)-1]をもつクロミア架橋体が得られた.95℃ での挿入反応により得られる層電荷0.8のクロミア架橋フッ素雲母の底面間隔値は,室温挿入反応で得られる架橋体に比べ0.1nm程度増大し,高温域(400-700℃)まで1.1-1.4nmの底面間隔値を維持した.また,95℃ で挿入反応させると,室温挿入反応の場合よりも200-300℃ の加熱温度範囲では最大100m2g-1程度大きな比表面積をもつクロミア架橋体が得られた.

Effects of Layer Charge on Formation of Chromia Pillared Fluorine Micas.

精密に細孔特性を制御したクロミア架橋フッ素雲母を合成する研究の一環として,イオソ交換容量およびピラー密度を規定する層電荷に着目し,層電荷の異なるLi+交換型テニオライト系合成フッ素雲母[LixMg3-xLixSi4O10F2(x=O.8,0.5)]を調製条件の異なる各種の多核ヒドロキソクロム(III)溶液と反応させ,層電荷が挿入クロム(III)イオン種およびクロミア架橋フッ素雲母の性質に及ぼす影響を検討した。その結果,層電荷が大きいフッ素雲母にはCr(III)単量体やオリゴマーのような単位陽電荷あたりの断面積が小さいクロム(III)イオン種が挿入されやすいのに対し,層電荷が小さいフッ素雲母にはかさ高く陽電荷密度の小きい高重合度のヒドロキソクロム(III)ポリマーイオン種が挿入されやすくなることが判明した。また,挿入クロム(III)イオン種のイオン交換選択性は,層電荷の大きさばかりでなく,用いる溶液中に存在する各クロムイオン種の相対含有率にも依存することが明らかになった。層電荷が大きい雲母から得られる架橋体は,200～300℃ 加熱時にはミクロ細孔が生成し,層電荷が小さい架橋体に比べ大きな比表面積と細孔容積を示した。これに対し,層電荷が小さな雲母から得られる架橋体は,よりかさ高いポリマー種が挿入される結果,底面間隔値が大きく,かつ耐熱性も高くなり,層電荷の大きな架橋体に比べより高温まで比較的大きな比表面積と細孔容積を維持した。