Kunio Kitajima

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.

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.

Growth of NiWO4 crystals from a Na2W2O7 flux

Well-formed rod crystals of NiWO4 were grown from a Na2W2O7 flux by a slow cooling method. The solubility of NiWO4 in Na2W2O7 increased with increasing temperature. At 1100 °C, NiWO4 was dissolved in Na2W2O7 at a concentration of about 45 mol %. The eutectic temperature was 615± 5 °C. Flux growth was conducted by heating mixtures at 1100 °C for 10 h, followed by cooling to 500 °C at a rate of 5 °C h−1. The brownish and transparent crystals up to 15 mm in length were grown from the mixtures of about 40 g. The most suitable solute content was 30 mol %. The grown crystals were bounded by the {100}, {010}, {110}, {102}, and {111} faces. In certain instances, the {111} faces disappeared. The EPMA data showed that sodium from the flux used was not contained within the grown crystals. The crystals of NiWO4 had a d.c. electrical resistivity of about 1 × 1011 Ω cm.

Effects of particle size on thermal durability and microporous characteristics for sintered bodies of alumina-pillared fluorine micas

Powder compacts of alumina-pillared fluorine micas having different particle sizes were fired at various temperatures in the range of 500–800 °C. Sintered bodies of the alumina-pillared micas were obtained at 500–700 °C with retaining their pillared structure. The pillared structure collapsed at 800 °C, losing microporous characters. Specific surface area and micropore volume of the sintered bodies obtained from coarse particles are larger than those obtained from fine particles. Thermal durability of the pillared structure depends on the particle size of alumina-pillared fluorine micas, especially on the c-dimension of the host mica crystals; thermal durability of the sintered bodies obtained from coarse particles is higher than that from fine particles. The sintered bodies are machinable due to the interlocking microstructure of the flaky mica crystals.

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.

The use of proton-exchanged X-type zeolite in catalysing ring-opening reactions of 2-substituted epoxides with nucleophiles and its effect on regioselectivity

The use of proton-exchanged X-type zeolite in catalysing ring-opening reactions of 2-alkyl substituted epoxides with nucleophiles gives a high regioselectivity and functional-selective catalysis giving allylic products from allylic nucleophiles. Mechanistic aspects are discussed.

Synthesis and properties of alumina-pillared fluorine micas having cation exchangeability

Abstract Alumina-pillared fluorine micas were prepared from synthetic highly layer-charged expandable fluorine mica and polyhydroxoaluminium solutions under different solution loadings (Al mmol in solutions per 1.0 g mica) in order to clarify the effects of solution loading on thermal durability and microporous properties. The intercalated Al content of the pillared micas increased with increased solution loading. The intercalated Al content (i.e. the pillar density) of the pillared micas influenced both the thermal durability and specific surface areas of the pillared micas. The pillared micas obtained from the high solution loadings showed better thermal durability than those obtained from the low solution loadings. Through micropore formation upon heating, the pillared micas exhibit cation exchangeability due to the liberation of residual Na+ ions from steric hindrance in the interlayer pillaring space. The amount of the exchangeable ions depends on the heating temperature of the pillared micas.

Synthesis of Ga2O3-pillared fluorine micas

Synthesis of gallium oxide pillared fluorine micas has been undertaken by using hydroxogallium solutions having different OH/Ga ratios and aging conditions as pillaring agents. The gallium oxide pillared fluorine micas obtained from aged hydroxogallium solutions have larger basal spacings and higher specific surface areas than those obtained from freshly prepared hydroxogallium solutions. Thermal durability of the pillared structure depends on the aging conditions of the hydroxogallium solutions; thermal durability of the pillared micas was enhanced by using the solutions aged under the optimized conditions. The pillared micas obtained from the hydroxogallium solution (OH/Ga = 2.0) aged at room temperature for 24 hours retained larger basal spacings and specific surface areas even after heated up to 750 °C.

Reactivity of synthetic expandable fluorine mica with titania sol: Effects of layer charge and interlayer cation species

Abstract The reactivity of synthetic expandable fluorine micas [M x Mg 3− x Li x (Si 4 O 10 )F 2 ( M = Li , Na , K ), x = 0.4, 0.5, 0.6, 0.8] with titania sol was investigated. The interlayer cation species of host micas have a strong effect on the complex formation, resulting in different titania contents and surface areas of titania-pillared micas in the order K + Na + Li + . This is due to the difference in the expandability of host micas. The layer charge ( x ) also affects the complex formation. The Na x -series gave a maximum of titania content at x = 0.6.

Reduction of interlayer Co2+ ions in fluorine mica using diethylene glycol

Reduction of interlayer Co2+ ions in expandable fluorine mica has been attempted. The polyol process using diethylene glycol as a reducing agent was employed. The co2+ -exchanged mica was refluxed at about 225–235 °C in liquid diethylene glycol for 10–120 minutes. Consequently, zero-valence Co metal (Co0) intercalated mica having a metallic grey colour was obtained by in situ reduction of interlayer Co2+ ions, showing different properties from Co2+ -exchanged mica as a precursor. The layer charge of Co-metal-intercalated mica is compensated by protons which are produced through the course of reduction of interlayer Co2+ ions. The reduced sample heated at 350 °C, which had no organic molecules, exhibited a basal spacing of 1.28 nm, indicating the presence of 0.34 nm cobalt metal clusters after subtracting the thickness of the host silicate layer. During the process of reduction in diethylene glycol, cobalt metal particles were expelled from the interlayers which grew to about 0.5 μm onto the external surfaces of host mica crystals with increasing refluxing time.