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The effects of sulphur substitution for oxygen on the structure and properties of nonsuperconducting La2−xSrxCuO4, where x=0.26 and 0.30, have been studied. In La2−xSrxCuO 4−y-Sy, the sulphur-doped samples exhibit superconducting transition at 37–39 K and a larger Meissner effect than undoped samples. It was found that the superconductivity of La2−xSrxCuO4−ySy is apparently determined by the value of x−y and the strontium concentration region in which La2−xSrxCuO4 shows superconductivity shifts to higher strontium concentrations with sulphur doping.

The corrosion of alkali-containing fluorozirconate glasses in water and acidic and alkaline solutions was studied with glasses of the compositions (100−x) (0.6ZrF4·0.1AlF3·0.3BaF2)· xLiF and 48ZrF4·8AlF3·24BaF2·xLiF·(20−x)NaF. The corrosion of the glasses in deionized water and 0.1 n HCl solution is mainly controlled by diffusion with an inductive period due to the passage from reaction-controlled to diffusion-controlled mechanisms, and the weight loss of glass increases with increasing LiF content in the single-alkali glasses. There was no appreciable effect of alkali mixing on the corrosion of glasses in deionized water and 0.1 n HCl solution. The glasses exhibited good stability in alkaline solution. The weight loss due to corrosion of the glasses in acidic buffered solution increased exponentially with increasing LiF content.

Glass-ceramic monoliths with a composition of Li2O·Al2O3·4SiO2 have been synthesized by the sol-gel technique using metal alkoxides as starting materials. Heating dried gel monoliths of about 36 mm diameter and height to appropriate temperatures gave glass-ceramic monoliths of about 20 mm diameter and height without the occurrence of cracks, while a melt-derived glass body of the same composition was cracked or softened on heating. The glass-ceramic monoliths obtained by heating gel monoliths at 1000 ‡C for 40 h were a porous body, whose bulk density and porosity were 1.62 g cm−3 and 34%, respectively. On heating gel monoliths, Β-eucryptite crystals were first precipitated around 750 ‡C, followed by precipitation of Β-spodumene crystals at 830 ‡C. At higher temperatures the latter grew at the expense of the former phase. The crystallized specimens exhibited very low thermal expansion coefficient ranging from −13-12×10−7 ‡C−1 at temperatures from room temperature to 700 ‡C depending on the heat-treatment temperature of gels, indicating that a porous glass-ceramic monolith with ultra-low thermal expansion can be prepared using the present sol-gel method.

X-ray radial distribution analysis and Raman spectroscopic measurement were carried out on Na2O-2TiO2 glass prepared by twin-roller quenching method. It is found that four-coordinated Ti4+ ions may be predominant over six-coordinated ones in the present glass. It is also found that the fraction of six-coordinated Ti4+ ions is larger in the present glass than in K2O·2TiO2 and Cs2O·2TiO2 glasses. Poorer glass-forming ability of the Na2O-TiO2 system compared with the K2O-TiO2 and Cs2O-TiO2 systems is ascribed to a larger fraction of TiO6 octahedron for the former system.

Superconducting Bi-(Pb)-Sr-Ca-Cu-O ceramics were prepared through the sol-gel method using an aqueous solution of metal acetates containing acetic acid and tartaric acid. The conditions of gelation and conversion of gel to Bi2Sr2CaCu2Ox phase were studied by thermal analysis, infrared absorption spectroscopy and X-ray diffraction technique. It was found that transparent gels were obtained from the solutions containing tartaric acid, with a molar ratio of C4H6O6/Cu of about 0.4. The gel matrix was assumed to be composed of carboxylate anions and metal cations. A gel of molar composition Bi∶Sr∶Ca∶Cu = 2∶2∶2∶3 was decomposed to CaCO3, CaO, CuO and Bi1-x SrxOy (x = 0.2 to 0.3) at low temperatures of 270 to 600 ° C and produced Bi2Sr2CaCu2Ox phase at 800 ° C via complex intermediate states. A rapid cooling of the heated product increasedT c (end) in the gel of molar composition Bi∶Sr∶Ca∶Cu = 2∶2∶2∶3, while a slow cooling increasedT c (end) in the lead-containing gel of molar composition Bi∶Pb∶Sr∶Ca∶Cu = 1.85∶0.35∶1.9∶2.0∶3.1. The latter showedT c (onset) at 115 K andT c (end) at 105K.

The elastic moduli of silica gel monolith prepared by the sol-gel method from a tetramethoxysilane solution have been measured before and after heat treatment. The elastic moduli showed a drastic change with heat treatment; for example, Young's modulus changed from 0.95 GPa for the gel before heating to 72.5 GPa for the densified product after heating to 1050 ° C. The change in the Young's modulus of the gel with heating temperature is discussed on the basis of changes of porosity and strength of the silica skeleton.

The mechanical stability of a dried silica gel monolith (with micropores a16 nm average diameter, prepared from an Si(OCH3)4-(CH32)NCHO-CH3OH-H2O-NH4OH solution) on exposure to vapour and subsequent immersion in liquid, was examined using various solvents. The surface tension of the test solvent ranged from 17.1 dyn cm−1 for diethyl ether, to 72.8 dyn cm−1 for water. It was found that there is a distinct critical surface tension of the solvent in causing cracks in the gel on exposure to vapour and immersion in liquid for a particular shape of gel monolith. It has also been shown that the critical surface tension shifts to lower values when the gel is directly immersed in liquid, without prior exposure to solvent vapour, and that the critical surface tension also changes with the shape of the gel. The stability of the dried gel monolith to crack formation on exposure to solvent vapour and immersion in liquid solvent may be caused by the capillary force of the solvent filling pores on pore walls consisting of silica skeletons. The capillary force may be largely determined by the surface tension of the solvent. This may also explain the role of dimethylformamide as a component of the starting solution in producing dried gel rods used in this study without crack formation during the drying process.

On a prepare des monolithes de gel de composition: Li 2 O.Al 2 O 3 .4SiO 2 comme precurseur de vitroceramiques d'aluminosilicate de lithium, par hydrolyse et polycondensation d'alcoolates metalliques mixtes dans des solutions contenant LiOCH 3 , Al(O-sec C 4 H 9 ) 3 , Si(OC 2 H 5 ) 4 , des alcools et de l'eau. Des concentrations en eau elevees dans la solution de depart, un controle des conditions reactionnelles et des vitesses de sechage lentes produisent des monolithes sans fissure, de forme cylindrique (diametre=37 mm, hauteur=35 mm). On a etudie les proprietes du monolithe et ces changements avec le chauffage

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.

The coordination state of Ti4+ and Ge4+ ions in Na2O-TiO2-GeO2 glasses has been investigated. Upon crystallization of the glasses, the thermodynamically metastable hexagonal GeO2 crystals containing 4-fold coordinated Ti4+ ions together with stable Na4Ge9O20 crystals containing 6-fold coordinated Ti4+ ions were precipitated. The distribution of Ti4+ ions between these two crystalline phases is a reflection of the coordination state of Ti4+ ions in the starting glass. The majority of Ti4+ ions are in 6-fold coordination at a small TiO2/Na2O ratio and they are contained in Na2Ge9O20, while the majority of Ti4+ ions are in 4-fold coordination at a large TiO2/Na2O ratio and they are contained in GeO2 crystals. Concentrations of 4- and 6-fold coordinated Ti4+ ions have been confirmed to be similar to that in Na2O-TiO2-SiO2 glasses as measured by the X-ray absorption spectrometry of Ti4+ ions. The coordination state of Ge4+ ions in the glasses have been examined by infrared (IR) spectrometry. It is found that in Na2O-TiO2-GeO2 glasses Ge4+ ions have 6-fold coordination preferentially, while Ti4+ ions have 4-fold coordination except at small contents of TiO2, indicating that the addition of TiO2 to Na2O-GeO2 glasses leads to the replacement of 4-fold coordinated Ge4+ ions by 4-fold coordinated Ti4+ ions.

A method for determining the activation energy for crystal growth was calculated on the basis of the heat balance in the differential thermal analysis (DTA) measurements and the mechanism of nucleation and growth. The theoretical analysis showed that the term ln[C pd(δT)/dt+KδT] should be a linear function of l/T, whereC p is the heat capacity of sample and sample holder,K is the heat transfer coefficient,δT is the temperature difference between the sample and reference substance andt is the time. The energy term,E D, obtained by multiplying the slope of the resulting straight line byR is indicative of the activation energy for crystal growth. It was shown thatE D should be three times the activation energy for crystal growth when bulk nucleation is dominant, and equal to that for crystal growth only when surface nucleation predominates. The result of the analysis was tested by comparing the experimentally determinedE D's with the activation energy for viscous flow, which was known to represent that for crystal growth. TheE D for Li2O·2SiO2 glass with dominant bulk nucleation, approached three times the activation energy for viscous flow, as the heating rate in DTA decreased. TheE D for 33.3Li2O·66.7SiO2·3TiO2 glass with dominant surface nucleation approached the activation energy for viscous flow as the heating rate increased, suggesting the validity of the analysis.

A zirconia hydrogel prepared by dialysing ZrOCI2 aqueous solution against water buffer was unidirectionally frozen in a cylindrical polyethylene cell which was immersed in a -78° C cold bath at various rates. Freezing rate,R, and temperature gradient,G, at the frozen gel front were continuously measured during freezing. It was found that zirconia fibres longer than 20 mm are formed whenG/R = 2 to 8° C h cm−2. Either lower or higherG/R values gave only fragmental zirconia. The diameter,d, of the long zirconia fibres was changed from 25 to 55 μm with the temperature gradient and the freezing rate according to the equationd − A/(GR) +B, whereA andB are constants. It was concluded that long fibres of the desired diameter are obtained by controlling both the freezing rate and the temperature gradient. These results were interpreted in terms of cellular growth of ice crystals.

The SiKβ fluorescence X-ray and infra-red absorption spectra of Na2O-TiO2-SiO2 and K2O-TiO2-SiO2 glasses have been measured in order to study the Si-O bonding as a function of the composition of glass. The chemical shifts of the SiKβ peak relative to that of silica glass [Δλ=λ(SiO2)-λ(specimen)>0] and the wavenumbers of the infra-red absorption peaks around 950cm−1 and 1100 cm−1 have been determined from the spectra. The SiKβ chemical shift in both series of glasses increased with increasing total content of R2O and TiO2 and with decreasing ratio of TiO2/(K2O+TiO2), where R2O represents Na2O or K2O. The infra-red peaks around 950 cm−1 and 1100 cm−1 shifted towards lower wavenumbers with increasing total content of R2O and TiO2 and with decreasing ratio of TiO2/(R2O+TiO2). These experimental facts were interpreted as showing that the Si-O bond in glass was weakened as the total content of R2O and TiO2 increased and that the Si-O bond was weakened by R2O more than by TiO2.

The SiKβ X-ray emission spectra of silicate and aluminosilicate glasses and crystals have been measured with an X-ray fluorescence spectrometer and the chemical shifts of the SiKβ peak relative to that of SiO2 glass have been determined. Trends in the chemical shift of the SiKβ peak for Na2O-SiO2, Li2O-SiO2 and Li2O-Al2O3-SiO2 glasses were similar to those of their crystalline counterparts, indicating that the strength of the Si-O bond varies in the same way with composition in both glass and crystal. The chemical shift in alkali aluminosilicate glasses containing equal molar proportions of aluminium oxide and alkali oxide increased with decreasing SiO2 content, indicating that the Si-O bond also weakened in aluminosilicate glasses. The same effect was also observed when zirconia was added. The SiKβ bandwidths for Na2O-Al2O3-SiO2 and Li2O-Al2O3-SiO2 glasses with the Al2O3: M2O ratio equal to one, remained almost the same as for SiO2 glass, indicating that the addition of alkali does not result in the formation of non-bridging oxygens in the framework if accompanied by Al2O3.

The use of N,N-dimethylformamide (DMF) was found to be effective in the sol-gel synthesis of silica gel and glass monoliths from tetramethoxysi lane (TMOS) by the sol-gel method. Wet gel bodies prepared by gelation of TMOS-DMF-CH3OH-H2O-NH4OH (or HNO3) solutions could be dried without the occurrence of fracture or cracks when drying conditions were appropriate. Furthermore, the resultant dried gel monoliths could be converted without cracking or bloating to silica glass on heating up to 1050° C and holding there for 2 h, when the composition of the starting solution was appropriate.

A new type of apatite-containing glass-ceramic in the system MgO-CaO-SiO2-P2O5 can form a tight chemical bond with bones and has a high mechanical strength. The cause for its high mechanical strength was examined by comparing mechanical properties of the glass-ceramics which have an identical chemical composition and different microstructures. It was found that the mechanical strength of the apatite-containing glass-ceramics is considerably increased by the precipitation ofβ-wollastonite crystals due to an increase in fracture surface energy resulting in an increase in fracture toughness.

Differential thermal analysis was made of 33.3 Li2O·66.7 SiO2·3 ROn and 25 Li2O·75 SiO2·3 ROn glasses, where ROn is an added oxide. The exothermic temperatures, Tc, due to the precipitation of lithium disilicate crystal, were plotted against the ionic radius of the cation of the added oxide. It was possible to classify the added oxides into a few groups on the basis of the valency of the cation. Within each group, the Tc increased as the ionic radius of the cation increased. It was shown that the temperature, Tη corresponding to the viscosity of 1010 P also increased with increasing the radius of the cation. The relation between Tc and Tη was discussed using the theory on the rates of nucleation and crystal growth. The effect of phase separation on Tc was also discussed.

Densities, molar volumes, refractive indices, molar refractivities, glass transition temperatures and elastic constants of glasses with compositions (100−x) (0.6ZrF4 · 0.1 AlF3 · 0.3BaF2) · xRF, where R = Li, Na or K, were studied. All the properties vary continuously with increasing RF concentration for all three alkali atoms. The calculated molar refractivities of LiF, NaF and KF are constants which are very close to the values of the crystalline compounds LiF, NaF and KF, respectively, throughout the composition range studied, suggesting that no change occurs in the coordination state of the alkali ions by fluorine atoms. The comparison with crystalline compounds suggests that Li+, Na+ and K+ ions are all coordinated by six fluorine atoms.

Raman spectra of K2O-Nb2O5-SiO2 glasses are measured in order to compare the coordination state of Nb5+ ions in gallate glasses with that in silicate glasses. It is found that less-distorted NbO6 octahedra with no non-bridging oxygens as well as NbO6 octahedra with non-bridging oxygens and/or with much distortion are present in the K2O-Nb2O5-SiO2 glasses. The Raman band in the 800 to 900 cm−1 region is attributed to the NbO6 octahedra with non-bridging oxygens and/or with much distortion. The broad bands in the 600 to 800 cm−1 region are attributed to less-distorted NbO6 octahedra with no non-bridging oxygens. An increase in the molar ratio Nb2O5/K2O leads to an increase in the oxygens shared by more than two polyhedra and/or a decrease in non-bridging oxygens for the NbO6 octahedra which possess non-bridging oxygens, or to an increase of distortion for much-distorted NbO6 octahedra. At the same time, an increase in the molar ratio Nb2O5/K2O increases the less-distorted NbO6 octahedra with no non-bridging oxygens. In short, GaO4 tetrahedra and NbO6 octahedra compete to attract alkali ions in gallate glasses but such competition is not found in silicate glasses.

Effects of nitrogen incorporation on the crystallization of a 3OLi2O · 70SiO2 glass have been studied in terms of the glass transition and crystallization temperatures, nucleation mechanism and precipitated crystalline phases. Glass transition and crystallization temperatures rise with increasing nitrogen content. Bulk crystallization is dominant in these oxinitride glasses. Precipitated crystallization phases and their relative amounts vary with nitrogen content. The experimental results are discussed assuming the formation of an [((-O-)3Si-)3N] unit and its evolution to an [SiON3] unit in the residual glassy phase during the crystal growth.

The behaviour of copper ions in low thermal expansion glass-ceramics prepared from Cu2O · Al2O3 ·nSiO2 glasses, or inβ-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 orβ-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 theβ-spondumene type crystals brought about a considerable decrease in the lattice spooings.

The elastic properties, such as Poisson's ratios, shear modulus, Young's modulus and bulk modulus, have been determined with glasses of the compositions 48ZrF4 · 24BaF2 · 8AlF3 · 20RF, where RF is the LiF-NaF or NaF-KF pair, and 42ZrF4 · 21BaFe2· 7AIF3 · 30RF, where RF is the LiF-NaF pair, by measuring sound wave velocities. Non-linear variations, i.e. mixed alkali elects, were found in the sound velocities, shear modulus, Young's modulus and bulk modulus. The mixed alkali effect in the present systems is attributed to the strengthening of the glass structure and not to the mere compaction of the glass structure. The thermal expansion coefficient becomes higher when the two alkalis are mixed contrary to expectation from the change of the elastic moduli, indicating that the structural elements controlling the elastic moduli re different from those affecting the thermal expansion.

Glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems containing up to 33 wt% ZrO2 were prepared by a non-melting technique using zirconium n-propoxide, sodium methoxide and silicon tetraethoxide as raw materials. The mixed alkoxide solutions were exposed to moist air for hydrolysis. The fibrous gels were drawn from these solutions in the course of hydrolysis, and converted to the corresponding oxide glass fibres by heating at 500 to 700° C. It was found that chemical durability of the fibres toward alkaline solution increased with ZrO2 content. The weight loss due to the corrosion by 2 N NaOH solution at 96° C for 4 h was around 14 mg dm−2 for the fibres containing 17 to 26 wt% ZrO2, which was comparable to the alkali-resistant glasses so far obtained by the conventional melting technique. The glass fibres containing 33 wt% ZrO2 showed higher resistance.

The chemical durability of a superconducting oxide YBa2Cu3Ox in the aqueous solution was investigated as a function of pH value by measuring the amount of leaching of the cations in the solution by inductively coupled plasma (ICP) analysis. The chemical durability of YBa2Cu3Ox was very low in highly acidic solutions of pH ca, 1, where the cations were dissolved in the same cation ratio as that of the compound. In an ion-exchanged water and NaOH solution, barium ions were leached out preferentially and almost no yttrium and copper ions were leached out. When NH4OH was used as a basic reagent, the amounts of barium ions leached out were higher than in the NaOH solution of the same pH value and the dissolution of copper ions was observed, unlike in the NaOH solution of the same pH value. These observations were explained in terms of the chemical stability of individual oxide components.