Preparation of multiple oxide BaTiO3 fibres by the sol-gel method

Multiple oxide BaTiO₃ gel fibres were prepared by the sol-gel method from Ba(OC₂H₅)₂-Ti(O-isoC₃H₇)₄-H₂O-C₂H₅OH-CH₃COOH and Ba(CH₃COO)₂-Ti(O-isoC₃H₇)₄-H₂O-CH₃COOH solutions. Relatively long gel fibres of 10cm length were obtained from both solutions in the limited composition region. The latter solution in particular showed a spinnability even when it contained no water. Therefore, the occurrence of spinnability of the solution was considered to be due to the formation of linear polymers composed of bridging acetate groups such as TiO-C(CH₃)-O-Ti rather than metalloxane bonding as Ti-O-Ti. Addition of water to the solutions seems to break the bridging acetate bonds and replace some of them by bridging oxygen bonds. The as-drawn gel fibres which were X-ray amorphous crystallized into BaTiO₃ ceramic fibres of 5mm average length upon heating above 600 ° C. However, the gel fibres drawn from the sols without water became powdery on heating because of the lack of Ti-O-Ti metalloxane bonds. The crystallization behaviour of the BaTiO₃ gel fibres is discussed based on the infrared spectroscopy, X-ray diffraction analysis and thermogravimetric-differential thermal analysis.     

Structural changes of glass-ceramics of the Cu2O-Al2O3-SiO2 system on heating in air

The behaviour of copper ions in low thermal expansion glass-ceramics prepared from Cu₂O · Al₂O₃ ·_nSiO₂ glasses, or in-spodumene type Cu₂O · Ae₂O₃ ·nSiO₂ crystals included in the glass-ceramics on heating in air was investigated. On hewing at 300 to 500° C, the copper ions behaved as in the corresponding glasses. Cuprous ions in the glass-ceramics or-spondumene type crystals were oxidized into the cupric state, and at the same time an equal amount of cuprous ions to those oxidized were expelled out of the specimen for the requirement of electrical charge neutrality and then reacted with oxygen to form CuO on the surface. The oxidation of cuprous ions and the decrease of the copper content of the-spondumene type crystals brought about a considerable decrease in the lattice spooings.     

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosillcate Glasses in Copper-Containing Molten Salt: I, Monovalent Copper Salt, CuCl

Cu⁺⇌ R⁺ (R = Li, Na, and K) ion exchange experiments were conducted for 20R₂O·10Al₂O₃·70SiO₂ glasses in molten CuCl at 550°C in air and nitrogen atmospheres. The depth profiles of the copper incorporated into glasses were determined with an electron microprobe X-ray analyzer. The total amount of diffusing copper, M _t, strongly depended on the type of alkali ion in the glass and the ion-exchange atmosphere; i.e., M _t increased with increasing cationic size in the order Li < Na < K and M _t was greater in air than in nitrogen. The Cu ⇌ R⁺ ion exchange kinetics are discussed in detail.     

Nitridation of the Sol–Gel-Derived Titanium Oxide Films by Heating in Ammonia Gas

Dip-coated sol–gel-derived TiO₂ films on an alumina substrate were converted to nonstoichiometric titanium nitride (TiN _x ( x ≦ 1)) films by heating at approxmately 1000°C in NH₃ gas. TiO₂ films made from TiO₂ sols prepared from Ti(O– i -C₃H₇)₄ and stabilized by diethanolamine were more easily nitrided than those from sols containing HCl as a deflocculant reagent. This appears to be a result of the more porous structure of the former films.     

Preferred orientation of crystallite in carbons heat-treated under high pressure

A soft carbon and a hard carbon which were prepared from Polyvinylchloride and phenolformaldehyde resin, respectively, both by carbonizing to about 700°C, were obtained as sintered cakes by heat-treatment up to about 1800°C under the quasihydrostatic pressure of 5 kbar. Preferred orientation of crystallites relative to the compressing direction in these cakes was determined by X-ray difraction technique by using the (004) or (002) diffraction line. The soft carbon showed remarkable preferred orientation of crystallites, but the degree of orientation was dependent only a little on heat-treatment temperature (HTT). At 1200°C under 5 kbar, the hard carbon gave a sintered cake which had no appreciably preferred orientation. The degree of preferred orientation of crystallites in the cake of the hard carbon greatly increased with the increase in HTT. The difference in the dependence of preferred orientation of crystallites in the soft and hard carbons on HTT was interpreted by referring to the texture of the original carbons.     

Copper-Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Molten CuCl—An Ion Exchange Controlled by the Cu+→Cu2+ Oxidation Reaction in Glass

The kinetics of copper-potassium ion exchange of potassium aluminosilicate glass have been investigated in molten CuCl at 550°C in air and nitrogen. The presence of oxygen dissolved in molten CuCl has a great effect on the Cu-K ion-exchange kinetics, i.e. ion exchange in nitrogen is controlled by the interdiffusion process of Cu⁺ and K⁺ in the glass, whereas ion exchange in air seems to be controlled by the Cu⁺→Cu²⁺ oxidation reaction.     

Hydration of phosphate and borate glasses at high temperatures and pressures

The kinetics of hydration of CaO-Al₂O₃-P₂O₅ and Na₂O-CaO-B₂O₃-Al₂O₃ glasses in an autoclave at high temperatures and pressures have been investigated. A linear time dependence of the depth of hydrated layer has been found for the glasses used in the present study. This implies that the hydration process is governed by the chemical reaction at the interface between the unhydrated and the hydrated glass phases. It is indicated that the hydration of the phosphate glasses may occur as a result of hydrolysis of glass constituents to form orthophosphate crystals. Water vapour can easily reach the interface through the crystalline aggregates, which are loosely packed. Cabal glasses which do not contain any alkali oxides have shown quite a high resistance to water. Substitution of sodium for calcium has resulted in deterioration of the chemical durability of cabal glasses. This can be explained by the difference in stability between sodium and calcium ions in the hydrated layer.     

Fibrous hydroxyapatite grown in the gel system: effects of pH of the solution on the growth rate and morphology

In the preparation of fibrous hydroxyapatite (HAp), using the gel system consisting of agar gel containing calcium nitrate and over-layered (NH₄)₂HPO₄ solution, the pH of the solution was found to greatly influence the growth rate and morphology of the resultant products. In particular, a pH value of about 9–10 produced straight fibrous HAp in the shortest time. Also, the Ca/P molar ratio of the product increased with the pH value of the starting solution. The growth rate and morphology of the product were correlated to the ion species present in the solution at different pHs.     

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Copper-Containing Molten Salt: II, Divalent Copper Salts, CuCl2 and CuSO4

The ion-exchange mechanism between copper and alkali ions, when 20R₂O · 10Al₂O₃· 70SiO₂ (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl₂, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl₂ decomposes into CuCl and Cl₂ at 550°C and the Cu⁺ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl₂ acts as an oxidizing agent just like oxygen. In the case of molten CuSO₄─₂SO₄, a small amount of Cu⁺ which is present in the molten state plays a primary role in the Cu ⇌ R⁺ ion exchange process, although the contribution of direct Cu²⁺⇌ 2R⁺ ion exchange cannot be ignored.