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Congratulations on “United Nations International Year of Glass 2022.” I would like to acknowledge the efforts made by the International Commission on Glass with the Community of Glass Associations and the Glass Art Society to promote the status of glass. I am very much pleased to contribute an article on the birth of the sol–gel method and its growth in early times for a Special Issue of Journal of Sol–Gel Science and Technology, which is published to celebrate the Year of Glass. At present, the sol–gel method is employed not only for manufacturing optical glass fibers for communication, but also for processing a wide range of functional, high technology materials, such as photonic, electronic, micromechanical, chemical, and bionic materials. The sol–gel method typically involves the following steps: (1) starting from a solution containing pure precursors, (2) conversion of the solution to a sol and then to a gel by hydrolysis and polycondensation, (3) forming into desired shapes such as bulk, film, and fiber during gelation of the sol, and (4) thermal treatment of the gel into a solid material at low temperatures. It should be noted, however, that there are many variants. For instance, the method of fabrication of a solid material by heating the shaped compact of gel powders prepared from a solution or sol is also called the “sol–gel method.” In this case, “starting from a solution” is important.

In order to fabricate sol–gel products with desired microstructure in the form of bulk, fiber and coating film, the appropriate selection of the composition of the starting solution is of primary importance. In this paper, the effects of the composition of the starting solution on the reaction in alkoxysilane solutions, the formation of bulk and fiber, and the microstructure of a particular coating film are reviewed, based on our experiences. It is shown in the alkoxysilane and alkylalkoxysilane solutions that, besides hydrolysis and random polymerization, various reactions take place. Among them, the formation of a four-membered ring molecule in dimethyldialkoxysilane solution, formation of a cage-like cubic octamer in an tetraalkoxysilane solution containing, for example, tetramethylammonium ion and stabilization of a solution for polycomponent oxides by the addition of tartaric acid are discussed. It is also shown that the composition of the starting solution suitable for fiber drawing is different from that for the formation of crack-free bulk gels: for the fiber drawing acid catalyst and low water content are required in various oxide systems including silica, while for the bulk silica gels ammonia-catalyzed alkoxysilane solution with dimethylformamide solvent or highly acidic solution works well for bulk silica gel. Finally, it is shown that the control of microstructure of coating films can be realized by selecting the composition of the starting solution. As an example, the change of the acid content of the starting solution produces three different microstructures of polycrystalline, crystal-oriented and amorphous structure in the lithium borate coating film. As another example, the size of precipitated noble metal particles in the coating film is controlled by the water and acid content of the solution. The mechanism of the above phenomena is also discussed.

In Japan, sol-gel research activities are very prosperous and there are many successful commercial products. It appears that this trend will continue into the future. In this article, basic sol-gel research carried out in Japanese universities and applications of the sol-gel method to industrial production will be described. It should be noted that many unique studies, including photocatalysts and products involving coatings applied to automobiles and display panels, are found in Japan.

The sol-gel method is, first of all, characterized by the low temperature processing. Since this method starts from solutions, the product is essentially nanomaterials. So far, various kinds of microstructures, including dense, porous, hybrid, amorphous, crystalline microstructures have been realized. Accordingly, sol-gel materials cover a wide range of functions, such as optical, electronic, mechanical, chemical and bio-functions. All these features are highlighted in this article. Finally, the future of the sol-gel method is discussed.

Journal of Sol-Gel Science and Technology started as unique journal devoted to sol-gel science and technology in 1993. First, papers so far published in the Journal were intoduced. It was shown that the titles of invited papers and special issues show the broadening of the sol-gel area. Second, the change of the research tendency was conjectured from the four proceedings volumes. It was shown that the increase of importance of a particular class of materials and appearance of emergent materials are reflected in the title of the paper.

Hydrolysis and polymerization of dimethyldiethoxysilane (DMDE), methyltrimethoxysilane (MTMS) and tetramethoxysilane (TMOS) in the presence of aluminum acetylacetonate (Al(acac)3) have been investigated by infrared and NMR spectroscopy. In the absence of acidic catalyst, Al(acac)3 catalyzes the hydrolysis of all the silanes. The catalytic activity of Al(acac)3 is less than that of HNO3, but larger than that of NH3. The hydrolysis rate increases with increasing concentration of Al(acac)3 in DMDE. The hydrolysis of TMOS occurs rapidly after an inductive period, which becomes longer with addition of Al(acac)3. The results are explained by assuming an Al(acac)3 catalyzed hydrolysis and a silanol catalyzed hydrolysis. The addition of Al(acac)3 causes changes in polymerization of the resultant silanols. In DMDE and MTMS, it stabilizes the silanols at the early stage, and then enhances their polymerization. The polymerization in TMOS leads to the formation of precipitates that have a high degree of polymerization. The polymerization appears to proceed via a deprotonation mechanism including transfer of protons from silanols to Al(acac)3. The present results strongly suggest that, besides acids and bases, metal complexes can be used as catalysts for the formation of siloxanes under ambient conditions.

Coating films containing Au, Ag, Pt and Pd metal colloids have been prepared by sol-gel processing. It is shown that for oxide films the temperature where the metal particles are precipitated by heating in air depends on metal species: 200°C for Au, 600°C for Ag, 800°C for Pt and 1000°C for Pd. The use of reducing atmosphere lowers the temperature for formation of noble metal colloids. This procedure can be used for direct formation of metal colloids from metal ions in the film as well as reduction of oxide particles to metal particles in the film. For an organic-inorganic matrix, noble metal colloids are precipitated by thermal reduction or photo-reduction. Thermal reduction occurs as a result of reduction by decomposing organic matter. Photo-reduction occurs as a result of UV irradiation.

Electrical properties of Bi-Ba-Cu-O glasses have been systematically investigated, and possible conduction mechanisms are discussed. Conductivity behavior is described by a small-polaron hopping mechanism. log σo, the slope of the log σ-W straight line, and the magnitude of the polaron bandwidth reveal that adiabatic hopping is dominant in the glasses. The Seebeck coefficient, S, of the Bi16BaCu3Oy glass is positive, indicating that the glass is a p-type hole conductor. The positive deviation of the observed S value from the theoretical S value is explained by assuming that the only oxygens bonded to both Cu2+ and Cu+ ions mediate indirect Cu+-O-Cu2+ hopping.

A suitable relationship between the linear refractive index n0, the energy gap Eg, and the nonlinear refractive index n2 has been looked for on the basis of experimental and theoretical data reported in the literature for numerous simple oxides. It has been established that the nonlinear refractive index increases with increasing linear refractive index and decreasing energy gap of the oxides. This is related to the increasing metallicity of the oxides. Oxides with a high nonlinear refractive index posses a metallization criterion of approximately 0.30–0.45.

The average electronic oxide polarizability α02− of numerous single component oxides has been calculated on the basis of two different properties: linear refractive index n0 and energy gap Eg, which have demonstrated remarkable correlation. The optical basicity Λ of the oxides has been estimated on the basis of average electronic oxide polarizability calculated from the refractive index Λ(n0) and the energy gap Λ(Eg). A good agreement has been observed between the optical basicity data obtained using independent initial quantities. The simple oxides have been separated into three groups according to the values of their oxide polarizability. The α02− values (above 3 A) obtained for PbO, Sb2O3, and Bi2O3 have been attributed to the high cation polarizability and the presence of a lone pair in the valence shell of the cation.

ZnO films were prepared on silica glass substrates by the sol-gel method from Zn(CH3COO)2⋅2H2O-2-methoxyethanol solutions containing monoethanolamine (MEA) or diethanolamine (DEA). Smooth and transparent ZnO films were obtained by heating at temperatures from 200 to 500°C for 10min after each coating and finally at the same temperatures for 1h. The films prepared from coating solutions containing MEA were strongly oriented along the (002) plane. The effects of heating temperature and ethanolamines on the film morphology, grain size distribution and crystallographic orientation are discussed based on X-ray diffraction and scanning electron microscopy.

The sol-gel method starts from solutions, leading to formation of dry gels, glasses and ceramics of different microstructures through various transformations, such as solution to sol, sol to wet gel, wet gel to dry gel and dry gel to glass and ceramics. Various microstructures are formed during the process of these transformations. The microstructure of the product is controlled mainly by the type and content of the catalyst, acid or base, although other processing conditions may affect to some degree. In this article, control of pore sizes of bulk silica gels and application of the silica gels with controlled pore sizes are discussed. It is also shown that glassy, randomly crystalline and crystal-oriented Li2B4O7 coating films can be prepared by controlling the composition of the starting solution.

Glass formation, structure of glass and some basic and topical properties have been reviewed for gallium oxide based systems which are free from conventional glass-forming oxides. Glass-forming ten...

The current state of sol-gel technology has been reviewed mainly from the standpoint of microstructures of materials which can be achieved by the sol-gel method. It has been shown that the sol-gel method makes it possible to produce a great variety of high technology materials by providing the existing substances with a significant microstructure and producing the material with a novel microstructure. There are microstructures characterized by micropores, preferential crystal orientation, inorganic-organic and inorganic-inorganic composites of hybrid nature and gradient composition. These characteristic microstructures are related to the properties and applications of the materials.

In sol–gel method, materials are produced through the gelation of solutions or sols. Accordingly, this method is characterized by the low-temperature processing. Also, it is noted that the sol–gel products are essentially nanomaterials. Sol–gel processing can realize various kinds of microstructures, such as dense, porous, hybrid, organic–inorganic, amorphous, crystalline microstructures, and so, it covers a wide range of functional materials, such as optical, electronic, mechanical, chemical and biochemical, and biomedical materials. This versatility has led to a great many applications in both advanced technology and novel advanced materials.

The structure of lead vanadate glasses, x PbO · (100 - x )V 2 O 5 ( x = 55, 50, 40, 30) has been investigated by means of infrared and 51 V static and magic angle spinning nuclear magnetic resonance (MAS-NMR) and 207 Pb MAS-NMR spectroscopies. The 51 V NMR spectral parameters of various constituent vanadate groups in lead vanadate glasses were determined by spectrum simulation on the basis of our previous results on alkaline earth vanadate glasses. The structure of 55PbO · 45V 2 O 5 glass mainly consists of VO 4 tetrahedra, which are composed of V 2 O 7 4− and (VO 3 ) n single chains. The structure of x PbO · (100 - x )V 2 O 5 glasses ( x = 30, 40, 50) consists of both VO 4 tetrahedra and VO 5 trigonal bipyramids. These VO n polyhedra ( n = 4, 5) compose at least four types of vanadate group, i.e., V 2 O 7 4− (VO 3 ) n single chains, branched VO 4 group and (V 2 O 8 ) n zigzag chains depending on the PbO content.

The structure and properties of nitrided silicate glasses have been reviewed mainly on the basis of the works made by the author's group. Neutron diffraction analysis and 29Si and 27Al nuclear magnetic resonance spectroscopy have shown that in NaSiON and YAlSiON oxynitride glasses there exist N atoms bonded to two Si atoms as well as N atoms bonded to three Si atoms. It is also shown that N atoms hardly make bonds with Al atoms in glasses containing both Si and Al atoms and that N atoms do not enter into the glass network but form clusters consisting of AlN4 units in aluminate glasses. The elastic moduli and hardness markedly increase with increasing N content. The increase in elastic moduli with increasing nitrogen content is attributed to the presence of N atoms bonded to three Si atoms. This has been confirmed by an ab initio molecular orbital calculation, which shows that the bending force constant for model molecule N[Si(OH)3]3 is very large compared with that for O[Si(OH)3]2. It is shown that a drastic improvement in chemical durability by nitriding is seen in some glasses but not in others. The ionic conductivity of alkali silicate glasses increases with increasing nitrogen content. Finally, a brief explanation is made on the attempts in Japan for applying oxynitride glasses as industrial products.

TiO2 coating films of 0.3–0.4 μm in thickness that contain fine Pd particles have been prepared by sol-gel method using Ti(OC3H 7 )4 and PdCl2 as starting materials in an attempt to obtain optical materials that show surface plasma resonance in the visible range. A temperature higher than 900°C was required for formation of Pd metal particles when the heat-treatment was conducted in air. Heat-treatment of pre-heated amorphous films in air at 800°C resulted in precipitation of PdO particles, the size of which could be varied by changing the time of heat-treatment, and subsequent heat-treatment in H2/Ar gas converted the PdO particles into Pd metal particles. Heat-treatment of pre-heated amorphous films in H2/Ar gas also resulted in precipitation of Pd metal particles. The size of the Pd metal particles precipitated in the films was 6 to 90 nm, depending on the conditions of heat-treatment. The resultant TiO2 films containing Pd metal particles were brownish grey in color and showed optical absorption in the visible range over 400 nm, which is attributed to surface plasma resonance of Pd metal particles.

51 V static and magic-angle spinning (MAS) NMR spectra of crystalline monovalent metal metavanadates LiVO 3 , α- and βNaVO 3 , KVO 3 , CsVO 3 , β-AgVO 3 , and NH 4 VO 3 and divalent metal metavanadates M (VO 3 ) 2 ( M = Mg, Ca, Sr, Ba, Zn, Pb) have been measured in order to establish the relationships between the various NMR parameters, such as isotropic chemical shift, δ iso , chemical shift anisotropy, |Delta;δ|, the asymmetry parameter, η, and the crystallographic parameters. When the structural units are the same, in this case VO 4 tetrahedra or VO 5 trigonal bipyramids, the δ iso decrease almost linearly with decreasing average V-O bond length, independent of the polymerization degree and linkage mode of the VO n polyhedra. |Delta;δ|, increases with the polymerization degree and the degree of the structural distortion of the VO n polyhedron. It is found possible to predict the structural unit and the polymerization degree on the basis of the relation between |Delta;δ| and η.

The structure of 50PbO·50GaO1.5 and 80BiO1.5·20GaO1.5 glasses was investigated by neutron and X-ray diffraction. Most Ga3+ ions are four-coordinated in both glasses. PbO3 trigonal pyramids and PbO4 square pyramids are present in 50PbO·50GaO1.5 glass. The stronger glass-forming ability in PbOGaO1.5 is attributed to (PbO3, PbO4)n infinite spiral chains as in crystalline PbSiO3. Bi3+ ions form BiO5 and BiO6 units in 80BiO1.5·20GaO1.5 glass as in α-Bi2O3. This glass may be constructed by (BiO5, BiO6)n layers and GaO33− chains. It is assumed that in these glasses nearly all oxygen atoms bonded to Pb2+ or Bi3+ ions are three- or four-coordinated and most oxygen atoms bonded to Ga3+ ions are three-coordinated. It is found that the structure of the present ‘non-conventional’ glasses are contrary to Zachariasen's rules for glass formation.

Neutron diffraction and magic angle spinning (MAS) 27Al and 29Si NMR have been applied to study the local structure of glasses in the system Y-Al-Si-O with and without addition of AlN. 27Al MAS NMR indicated that in the Y-Al-Si-O-N oxynitride glass there is no Al-N bonding and aluminium atoms occupy various sites within the glass structure. The first peak of the radial distribution function curves obtained by neutron diffraction was deconvoluted into four peaks which are attributable to Si-O, Si-N(Al-O(4)), Al-O(5) and Al-O(6) pairs and the coordination numbers of Si, N, Al and Y were estimated. The glass network is assumed to consist mainly of corner-sharing AlO4 tetrahedra and SiO3N tetrahedra. 86% of N atoms are three-coordinated and 14% of N atoms are two-coordinated in the present oxynitride glass.

Rutile and anatase thin films have been prepared by the sol–gel method using Ti(OC3H7i)4. Third-order nonlinear optical properties of both TiO2 thin films have been investigated by the third-harmonic generation (THG) method and the effect of the polymorph of TiO2 on the third-order nonlinear optical susceptibility, χ(3), has been examined. The measured χ(3) values of rutile and anatase thin films were 1.4 × 10−12 and 9.7 × 10−13 esu, respectively. The χ(3) values corrected for the porosity of the film were 4.0 × 10−12 (rutile) and 2.4 × 10−12 esu (anatase), which are about 100 times as high as that of SiO2 glass used as standard sample (2.8 × 10−14 esu). The measured and corrected χ(3) values were discussed in comparision with those calculated on the basis of several models.

The structure of alkaline earth vanadate glasses, xMO⋅(100-x)V2O5 (M=Ca, Sr, Ba, x=30, 40, 45, 50, 55), has been investigated by means of 51V static and magic angle spinning (MAS) NMR spectroscopies. The 51V NMR spectral parameters of various constituent vanadate groups contained in the vanadate glasses were determined by the spectrum simulation with reference to those of various crystalline vanadates obtained previously. It was found that the structure of alkaline earth vanadate glasses consists mainly of VO4-tetrahedra in accordance with the authors' previous results based on the IR study. It was deduced that for x=50 the glass network is mainly constituted of one dimensional (VO3)n-single chains, and for x≤45 the decrease of the MO content yields a mixture of the V2O5-rich phase constituted of three dimensionally branched VO4-groups and the MO-rich phase constituted of the VO5-trigonal bipyramids, followed by the decrease of (VO3)n-single chains.

The structure of alkaline earth vanadate glasses of the compositions, xMO⋅(100-x)V2O5 (M=Mg, Ca, Sr, Ba, x=30, 40, 45, 50, 55), has been investigated by means of IR spectroscopy with reference to various crystalline alkaline earth vanadates structurally known. It is found that the structure of alkaline earth vanadate glasses is very similar to each other and mainly consists of VO4-tetrahedra which form either (VO3)n-sin-gle chains as found in Sr(VO3)2 and Ba(VO3)2 crystals or the three dimensional arrangement of the cornersharing branched VO4-tetrahedral groups as found in molten and amorphous V2O5. It is stressed that the glass network of the V2O5-rich glasses, 30MO⋅70V2O5, also mainly consists of VO4-tetrahedra.

Silica coating films of 0.5–0.7 μm in thickness doped with gold metal particles were prepared by heating gel coating films obtained from solutions of acid-catalyzed methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) mixture containing chlorauric acid tetrahydrate. Transparent coating films with deep blue, red, and purple colors were obtained. Changes in size and shape of the gold particles with the MTES content were observed. Lower MTES contents gave bigger and non-spherical particles, while higher MTES contents produced smaller and more spherical particles with a more uniform size distribution. The effect of heat-treatment temeprature on the shape, size, and size distribution of the metallic gold particles was also studied.

The present state of our knowledge on sol-gel coating films has been reviewed. A qualitative discussion is made on the limit of the film thickness which can be achieved in the sol-gel method and the factors affecting the film thickness. Considering that properties of the film are intimately related to the microstructure, types of microstructures accomplished by the sol-gel coating are introduced with examples.

It was shown that a single phase YBa2Cu4O8 (124-phase) could be formed from gels at 1 atm oxygen pressure, and the mechanism of its formation was elucidated. It was found that there are two key routes for the sol-gel formation of the 124-phase, one involving the tetragonal YBa2Cu3O y with a low concentration of oxygen defects (tetra-I phase) and the other involving the Ba2Cu3O5.9 as important intermediates of the 124-phase. The rapid formation of these intermediate compounds from the gel was attributed to the small particle size of the oxides and carbonates precipitating at the initial stage of heating. It was thought that the small particles characteristic of sol-gel processing lead to the rapid formation of the intermediate compounds and subsequent precipitation of the 124-phase.

Glass formation in Sb 2 Se 3 MX n (metal halides) has been studied. Glass transition temperatures, crystallization temperature and infrared transmission of some of the glasses were examined. Broad glass-forming regions were found in the Sb 2 Se 3 HgI 2 , Sb 2 Se 3 HgBr 2 and Sb 2 Se 3 CuI with narrow glass-forming regions in Sb 2 Se 3 PbI 2 and Sb 2 Se 3 PbBr 2 . No bulk glass formation was found in Sb 2 Se 3 CdBr 2 , Sb 2 Se 3 AgI, Sb 2 Se 3 AgBr, Sb 2 Se 3 TiI and Sb 2 Se 3 TiBr by quenching a silica glass ampoule (inner diameter 4.5 mm, outer diameter 6 mm) in water. The glass transition temperature ranges from 110 to 180°C and the difference between crystallization and glass transition temperatures ranges from 40 to 60°C. The infrared cut-off wavelengths of the glasses extend to 22 μm. Sb 2 Se 3 -based chalcogenide-halide glasses may have capabilities applicable to infrared optical fiber materials.

The structure of 40NaO0.5⋅20GaO1.5⋅40TiO2 glass has been investigated by X-ray radial distribution analysis. Nearly all the Ga3+ and Ti4+ ions are four coordinated, constructing highly cross-linked three-dimensional glass networks, and that the number of non-bridging oxygens is very small. The degree of medium-range order in this glass is much lower than in the Na2O⋅2TiO2 glass studied in a previous paper, possibly due to the almost complete absence of TiO6 octahedra in the former glass. The higher glass-forming ability of the Na2O-Ga2O3-TiO2 ternary system compared with the Na2O-TiO2 binary system is ascribed mainly to the higher fraction of four-coordinated Ti4+ ions in the former system. It is suggested that in oxide systems glass-forming ability increases with increasing fraction of four-coordinated Ti4+ ions.

Control of the optical properties of gel-derived oxide films containing fine metal particles is described. The duration of the aging of Si(OC2H5)4-derived sols and the amount of water for hydrolyzing Si(OC2H5)4 were found to greatly affect the size and the shape of Au particles formed in the silica matrix, and accordingly the optical absorption of the Au/SiO2 composite films. Employing dielectric media with high refractive indices like TiO2 was shown to shift the absorption peak of Au particles to longer wavelengths. Pd/TiO2 and Pt/TiO2 composite films showed absorption in the visible region.

51V static and magic-angle spinning (MAS) NMR spectra of crystalline divalent metal vanadates, M3(VO4)2 (M = Mg, Sr, Ba, Zn, Pb) and Mg2M′(VO4)2 (M′ = Sr, Ba, Pb) and divanadates, M2V2O7 (M = Mg, Ca, Sr, Ba, Zn, Pb) have been measured. In vanadates and dichromate-type divanadates, the 51V isotropic chemical shifts decrease linearly with decreasing electronegativity of divalent metal atom adjacent to the VO4-tetrahedron. This was interpreted by considering that the electron density and the symmetry of VO4-tetrahedron increases with decreasing electronegativity of divalent metal atom. This effect was more significant in vanadates than in divanadates. In divanadates the isotropic chemical shifts of the thortveitite-type configuration appeared at lower frequencies than that of the dichromate-type configuration. This was explained by assuming that the degree of s-hybridization of the oxygen orbitals in the V–O–V bonds is higher in the thortveitite-type than in the dichromate-type.

The third-order nonlinear optical susceptibilities of the xLaO[sub 1.5][center dot](100 [minus] x)TeO[sub 2] binary glasses have been measured by the third harmonic generation (THG) method. In order to investigate the origin of high-intensity third harmonic generation, the various optical properties, such as nonlinear refractive index, Abbe number, dispersion energy (E[sub d]), average excitation energy (E[sub 0]), (energy gap and polarizability have been estimated from the refractive index and UV-visible absorption spectrum measurements). The linear refractive index, polarizability, and E[sub d]/E[sup 2][sub 0] increased, and Abbe number and energy gap decreased, with increasing LaO[sub 1.5] content. The nonlinear optical susceptibility is discussed in relation to these optical parameters.

Dependence of the contents and the states of residual carbon in YBa2Cu3O7−x powders synthesized by the sol-gel method on heating conditions, and effects of residual carbon on the superconducting properties were investigated. The carbon content of the powder heated at 950 °C for 20 h was reduced to 0.02%. It has been found that a large number of carbonaceous materials in the starting materials that are used in the sol-gel method does not affect the carbon content of synthesized superconducting powders. The volume of diamagnetism was increased and the Tc,onset was raised as the carbon contents were reduced to 0.04%. These properties were further improved by O2–HIP treatment at 500 °C.

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.

YBa 2 Cu 3 O 7−x (123 or YBCO phase) films were prepared on YSZ substrates by the sol-gel method. The reaction between the YBCO film and the YSZ substrate, the c-axis orientation of the 123 crystals in the film, and their influence on the critical current density (J c ) and the critical temperature (T c ) have been investigated. When the coating films were fired at temperatures higher than 950°C, the films reacted heavily with the substrate, the c-axis orientation of the 123 crystals in the films perpendicular to the substrate increased, and the 123 phase in the films changed to the 211 phase and further to the 202 phase as the reaction of the films with the substrate progressed

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.

Non-bioactive glass-ceramic A-W(Al) containing apatite and wollastonite in a MgO−CaO−SiO2−Al2O3 glassy matrix did not form an apatite layer on its surface in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma and also in the fluids with small amounts of the calcium and silicate ions added individually, but formed the apatite layer in the fluid with the calcium and silicate ions added simultaneously. This indicates that the calcium and silicate ions dissolved from bioactive glass-ceramic A-W containing the apatite and wollastonite in a MgO−CaO−SiO2 glassy matrix play a cooperative and important role in forming an apatite layer on its surface in the body, to give the glass-ceramic bioactivity. The calcium ion might increase the degree of the supersaturation of the surrounding body fluid, and the silicate ion might provide favourable sites for nucleation of the apatite on the surfaces of glass-ceramic.