Search

Na2O-GeO2 glasses containing 25∼35 mole% Na2O can be crystallized to give a new sodium germanate crystal together with Na4Ge9O20, Na2GeO3 and/or Na2Ge4O9 crystals. The new crystal is obtained as a principal crystallization product from the glass containing 33.3 mole% Na2O, and is given a composition of Na2Ge2O5. This sodium digermanate crystal is monoclinic with lattice parameters; a0 = 8.421, b0 = 4.962, c0 = 12.67 A and β = 103.5°, and isostructural with β-Na2Si2O5. It is shown that the crystal is thermodynamically metastable.

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.

The glass-forming regions in the ternary systems LiX (X=F and Br)-Li2O-TeO2 were established in the present study. For X=Br the glass-forming region was found to be widened up to about 75mol% LiBr on the LiBr rich side compared to the system containing LiCl which was studied previously, while the region for X=F was restricted to the Li2O side, and no glass was formed in the binary LiF-TeO2 system. These results were interpreted based on the glass structure which was mainly deduced from the IR measurement.

Superconducting YBa2Cu3O7-x fibers and coating films have been prepared using solgel method. Homogeneous viscous sol was prepared by concentrating an aqueous solution of metal acetates. Gel fibers of 5μm - 2 mm in diameter and of more than 50 cm in length could be drawn from the sol. Heat-treated fibers had a hollow structure and were fragile, but showed superconductivity of Tc(end) at 73 K. For preparation of YBa2Cu3O7-x coating films, metal alkoxide solution was prepared using triethanolamine to dissolve copper alkoxide. Repeated application of the solution on a zirconia substrate and heat treatment in O2 resulted in the formation of a superconducting coating film of 1.5 μm in thickness having Tc(end) at 56 K. Factors affecting the properties of the fibers and coating films have been discussed.

The effect of the addition of tetramethylammonium ions on the distribution of silicate species in the methanolic solutions was studied by the trimethylsilylation technique. Tetramethylammonium ions affected silicate species formed in the hydrolysis of tetraethoxysilane, causing the singular formation of the cubic octameric silicate species in the methanolic solution. The recovery was higher in the methanolic solution than in the aqueous system. It was found that the presence of water was necessary for the singular formation, suggesting an interaction among silicate species, tetramethylammonium ions and water. It was also found that the formation of the cubic octamer started immediately after preparation of the solution.

Stability problems encountered in the sol-gel for glass synthesis have been listed. Among a large number of problems, three distinct subjects have been discussed in some detail: the stability of solution viscosity relative to the possibility of fiber drawing, the stability of dry gel monolith to fracture in various solvents and the stability of a silica network structure in the solution, gel and glass.

Kinetics of hydration of CaOAl 2 O 3 P 2 O 5 and Na 2 OCaOB 2 O 3 Al 2 O 3 glasses in an autoclave at high temperatures and high pressures has been investigated. The hydration of the phosphate glasses may occur as a result of hydrolysis of glass constituents to form orthophosphate crystals. Cabal glasses which do not contain any alkali oxides have shown a quite high resistance to water. Substitution of sodium for calcium deteriorates the chemical durability of Cabal glasses.

The present state and the future of glasses anf glass-ceramics synthesized by the sol-gel method from metal alkoxides have been critically reviewed and discussed. Glasses and glass-ceramics can be prepared in forms of bulk, fiber, sheet, coating film and particulate. Advantages and disadvantages in applying the sol-gel method for each form are discussed. It is shown that this method is very prospective and many materials will be manufactured by this method in the year 2004.

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.

A large amount of solids of (2-hydroxyethyl)trimethylammonium silicate, whose silicate skeleton has the double four-membered ring structure, was abruptly separated out from the mixed solution of (2-hydroxyethyl)trimethylammonium hydroxide aqueous solution and tetraethoxysilane after a few hours of stirring.

Etudes du mecaniqme de photooxydation sur une electrode a couche mince de TiO 2 preparee par la methode sol-gel, dans des solutions de differents pH, en vue de determiner l'influence de la structure poreuse du film de TiO 2 , forme par procede sol-gel sur la formation de H 2 O 2 et sur ses etats chimiques sur l'electrode

The absorption spectra of 3d transition elements Cr, Mn, Fe, Co, Ni and Cu were studied in SiO 2 R m O n compositions (R: a transition element), which were prepared at 500°C as coating films through the sol-gel process from a solution consisting of Si(OC 2 H 5 ) 4 , H 2 O, HCl and the nitrate of a transition metal. Generally speaking, the characteristic features of the peaks corresponding to a particular valence and coordination state of an element were similar to those reported for silica glass prepared at a high temperature of 1450°C, although the concentration of the particular valence and coordination state was not equal. This indicates that the SiO 2 network similar to that prepared at high temperatures is already constructed at low temperatures around 500°C. The oxidation state of copper in glasses prepared or treated in air atmosphere was studied with melt-derived silicate and gel-derived silica glasses by measuring the optical absorption due to Cu 2+ ions and making chemical analysis. It has been shown that the redox equilibrium of copper in glass shifts towards the higher valence state as the temperature decreases in the wide temperature range from about 1550°C to 500°C and that at least a portion of the copper is present as Cu 2+ ions in SiO 2 glass prepared at low temperatures up to about 500°C.

The electrical conductivities of (1− x ) Li 2 O · x BaO · 2 SiO 2 , (1− x ) Na 2 O · x MgO ·2 SiO 2 , (1− x ) Na 2 O · x CaO · SiO 2 and (1− x ) Na 2 O · x BaO · 2SiO 2 glasses were measured at temperature ranging from room temperature to 450°C. The transport numbers for Na + ion in (1− x ) Na 2 O · x BaO · 2 SiO 2 glasses were measured. It was found that the alkali ion carried a significant part of the current in these glasses except one that had no alkali ions, and the conductivity decreased markedly as the alkali oxide was substituted by an alkaline earth oxide. The results of conductivity measurements combined with the data hitherto reported on mixed alkali glasses led to the proposal that the so-called mixed alkali effect could be explained on the basis of the independent path model in which it is assumed that cations can move only through vacant sites left by those of the same type.

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.

Tetraethoxysilane was treated with Amberlyst 15 cation-exchange resin in the presence of butyl alcohols. On treating the mixture of tetraethoxysilane and 1-butanol, the transesterification took place in which butoxyl groups were substituted for ethoxyl groups in tetraethoxysilane. The degree of the transesterification depended on the molar ratio of tetraethoxysilane to 1-butanol of the mixture. The distribution of alkoxysilane species present in the tetraethoxysilane–1-butanol solution was compared with the tetrabutoxysilane–ethanol solution, and it was found that the degree of the transesterification depended on the ratio of numbers of alkyl groups in tetraalkoxysilane and alcohol used. The time required for equilibrium in the distribution of alkoxysilane species in the solution was different with the variety of butyl alcohols used, suggesting the presence of steric effect of butyl alcohols on this reaction.

EXAFS spectra and X-ray radial distribution curves were determined for Li2OGeO2, Na2OGeO2 and K2OGeO2 glasses to elucidate the glass structure. The formation of 6-coordinated Ge atoms on the addition of an alkali oxide R2O to GeO2 glass was confirmed. The concentration of 6-coordinated Ge atoms N6 increased with an increase of the R2O content, exhibited a maximum around 20 mol% R2O and decreased again with a further increase of the R2O content. No essential dicrepancies between the techniques employed and between the glass systems investigated were found in the N6 value and the R2O content of glass at the maximum. The small discrepancies were attributed to the different assumptions made for the calculations. It was concluded that the concentration of 6-coordinated Ge atoms N6 follows the formula N6=x/(100-x), where x is mol% R2O. The maximum value of N6 was about 25% for the composition of about 20 mol% R2O.

Formation of aragonite from amorphous, gelatinous CaCO 3 and CaCO 3 · H 2 O precipitated in the solution containing Mg 2+ ion was investigated. Amorphous CaCO 3 was converted to aragonite via CaCO 3 · H 2 O formation on drying in air. The stability of CaCO 3 · H 2 O in air depended on how long it has been immersed in the mother solution. Effect of Mg 2+ ion on the formation of aragonite was discussed on the basis of surface energy of a small particle.

The dc electrical conductivities, the activation energies for conduction and the high frequency dielectric constants were measured on glasses of compositions (100−χ)(0.6ZrF4·0.1AlF3·0.3BaF2)·χRF, where χ ranges from 0 to 55, 35 and 25, respectively, for R = Li, Na and K. The elastic moduli of some of the glasses were also measured. A minimum of electrical conductivity and a maximum of activation energy for conduction were found around 20 mol% in the alkali fluoride (RF) concentration, when these preperties were plotted against the RF concentration. The occurrence of the minimum and the maximum was attributed to the change of the conducting species. That is, it was assumed that the conduction of these glasses is governed by the motion of fluoride ions in the low RF concentration region and by the migration of alkali ions in the high RF concentration region. The electrical conductivities of glasses with the same RF concentration were changed in the order of Li glass

Phototropic glasses in which TlCl crystallites play an active role were developed. When glasses containing Tl and Cl were reheated at 420° to 480°C for 3 to 20 h, phototropic glasses were obtained which were transparent, translucent, or opaque, depending on the temperature and time of heat treatment. X-ray powder diffraction patterns of these glasses indicated the presence of TlCl crystallites. The optical absorption in the visible region which developed in the glass after uv exposure was similar to that developed in TlCl crystals prepared by melting TlCl powder. These facts suggest that the phototropy is caused by TlCl crystallites precipitated in the glass by heat treatment. Optical absorption was measured during both darkening and bleaching of the glass.

Generally, on the repeating of lithia-silica glass, it starts to crystallize at the temperatures near or below the softening point to convert into the polycrystalline material without deformation (M. A. Matveev, V. V. Velya. Steklo i Keramika, 16 [10] 14 (1959)).In the present study, various oxides were added as the third component to a lithia-silica glass of the composition, Li2O 25, SiO2 75mol%, and their effects on the crystallization of the base glass on repeating were investigated.It was found that there is a limit in the amount for each oxide, and the addition over the limit inhibits the crystallization of the glass giving rise to the deformation or surface crazing of the sample during repeating (Fig. 2 and Fig. 3). The limit of the amount of addition in mol%, for each of the oxides varied with the own property of the oxides as follows:(1) For each of the series of alkali- and alkaliearth-oxide, which acts as the glass network modifier in the glass structure, the limit decreases with the increase of the size of cation, i.e., The value of limit: NaO0.5>KO0.5>RbO0.5, MgO>CaO>SrO>BaO.For the oxides with the cation of about the same size but of the different valency, the oxide with the cation of the higher valency has always the higher limit, i.e., The value of limit: CaO>NaO0.5, SrO>KO0.5, BaO>RbO0.5(Fig. 6 and Table 8).(2) For the glass network formers (BO1.5, AlO1.5, PO2.5 and AsO2.5) and also for the imtermediates (BeO, PbO, CdO, ZrO2, CeO2, LaO1.5) the limit was generally low compared with that for the glass network modifiers, with the exception for the oxides of transition element (TiO2, MnO1.5, VO2.5, CrO1.5, FeO1.5, CoO, NiO) (Fig. 7 and Table 8).The structural explanations were made of the above results in terms of the polarizing power, and the ability of strengthening the glass network, of the cation in the oxides introduced.

The ultraviolet-induced darkening and subsequent bleaching of crystalline thallium chloride was investigated in order to study the processes occurring in a photochromic glass containing TlCl crystalline particles. Doping with a small amount of copper, silver or indium ion was found to be effective in promoting darkenability of TlCl crystals. Exposure to visible light causes bleaching of UV-induced coloring of TlCl crystals. Almost no fading occurs, however, when TlCl crystalline pieces are kept in darkness at room temperature or higher temperatures up to about 70°C, where very quick fading in color is observed in the case of TlCl crystals embedded in a glassy matrix.

When a lithium containing photosensitive glass is exposed to ultraviolet light and then subjected to the heat treatment, it changes into a polycrystalline material characterized by its good mechanical properties (S. D. Stookey. Ind. Eng. Chem., 45, 115 (1953)).The purpose of this paper is to present the relation between the mechanical strength and the grain size of the constituent crystallites of the resultant material.Glass specimens (2.5×5×50mm) of the oxide composition SiO2 81, Li2O 12.5, K2O 2.5, Al2O3 4, CeO2 0.03, Au 0.027% (wt.) were exposed to ultraviolet light by placing them at a distance of 10cm from a 500 watt high pressure mercury lamp for 2 to 1000 min. After the exposure they were heated at three steps; first at 510°C for 30 min. to cause formation of gold nuclei, then at 620°C for 60 min. to cause crystallization of lithium metasilicate partially (40%) from the base glass, and finally at 900°C for 60 min. to convert almost the whole of the base glass to polycrystalline materials consisted of lithium disilicate and β-quartz. The grain size of the constituent crystallites of the resultant material was able to be varied from 0.85 to 2.3μ by changing the U. V. exposure time (Ref. M. Tashiro and S. Sakka. J. Ceram. Assoc. Japan, 67, 263 (1959)).Tests for bending strength and Vickers hardness were made with two classes of specimens, one which completed a whole course of the above heat treatments and the other which completed only the first half of the heat treatments, i.e., heated only up to 620°C.The tests have shown that, for the specimens which completed the whole course of the heat treatments, crystallization increases mechanical strength of the specimens, and the relation between the average grain size of the constituent crystallites (d) and the mechanical properties (M) (both of the bending strength and Vickers hardness) is given by the equation, M=const⋅d1/2.For the specimens heated up to 620°C, partial crystallization of the glass phase was found to increase the mechanical strength of the specimens but in somewhat more complex way. This was attributed to the effects of glass phase still remaining in considerable amounts (60%) in the specimens.

The gamma -ray dose rate distribution in a small closed space, 80 mm in diameter and 110 mm high, was determined by the use of small picees of ordinary plate glass, 15 x 6 x 1.7) mm, as a dosimeter. The technique of the measurement is described. The advantageous features of the glass dosimeter, i.e., its small size, convenient usage, and preciseness in the measurement, are discussed. A brief description of the construction of a small Co/sup 60/ irradiator, in which the measurement was made, is included. (auth)

Most commercial products of ferrites are made by firing preformed powder mixtures of raw materials. This conventional method, however, is not adapted for obtaining products of the special shapes such as fiber and film. In this study we undertook to examine the possibility of obtaining magnetic materials from melted silicates containing Fe2O3 and MnO and of forming the melts into desired shapes by the ordinary glass-forming technique.The compositions of the melts studied were of 7.5-20% Fe2O3, 7.5-20% MnO (or CoO and NiO), 0-5% Li2O (or Na2O and K2O), 0-15% Al2O3, and 55-70% SiO2(mole). The raw materials were ferrous oxalate, manganese dioxide, cobaltic oxide, nickel oxide, lithium-, sodium- and potassium carbonates, aluminium hydroxide and potter's flint powders. Their mixtures to yield about 50 gram of melts were heated in sintered-alumina crucibles in an electric furnace at temperatures from 1300° to 1400°C. Their melting behaviors and the workability of their melts into shapes of fiber or plate during cooling were investigated. X-ray diffraction analysis and magnetic measurement were made on materials quenched in air.The results obtained are as follows:1) The melts of the compositions, 7.5-15% Fe2O3, 7.5-20% MnO, 0-5% Li2O (or Na2O and K2O), 5-15% Al2O3, 55-70% SiO2 (mole) were fluid at temperatures 1300°-1400°C, and were able to be formed into desired shapes during cooling.2) The intensity of magnetization of quenched specimens reached up to 18 gauss/g at the field of 10, 000 oersteds. Magnetization increased with increasing the content of Fe2O3 or Fe2O3+MnO, and decreased with increasing the content of Al2O3. The specimens of high Fe2O3 content saturated magnetically at a fairly weak magnetic field whereas the specimens of Fe2O3 content less than 15mole% did not saturate even at the field as strong as 5, 000-10, 000 oersteds. The followings are some examples of the composition which showed high magnetization and magnetic saturation at a weak magnetic field.3) Separation of fine crystallites of spinel-type ferrites was confirmed by X-ray analysis in some of quenched specimens containing high amount of Fe2O3. The average size of the crystallites estimated from the broadening of X-ray diffraction peaks was 60-150A.4) Reheating quenched specimen generally increased the intensity of magnetization and also accelarated magnetic saturation at weak magnetic field.

Calcium, strontium, and barium tungstates and their solid solutions, doped with a small amount of bismuth, color remarkably on exposure to ultraviolet light and return to the original white by thermal fading or optical bleaching. The factors affecting the darkening and fading processes were studied experimentally. Under the same irradiation conditions the intensity of uv-induced coloration depended on the Bi content and preparation temperature of the tungstates. Bi contents higher than 0.1 molyo and preparation temperatures higher than 1250°C gave strong coloration. The rate of fading of uv-induced color increased with increasing Bi content. The fading was accelerated by heating; almost all the uv-induced color disappeared at 230°C in 30 min. The fading rate was also increased by visible light exposure. The uv-induced absorption spectra varied systematically with the composition of the tungstates.

In order to make barium titanate ceramics having high dielectric constant by a process of crystallization of glass, a series of glasses with the general composition (100-x-y) BaO⋅TiO2+xSiO2+yAl2O3, in which x and y are within the range of 10 to 60 and 0 to 20 mole per cent, respectively, was investigated, especially with respect to their glass formation tendencies, crystallization behaviors during reheating and dielectric properties of their crystallized products.The glasses were melted, in all cases, in platinum crucibles at 1450°C for one hour and formed into plate of about 2mm thick. They were crystallized by reheating up to 1100°C at a rate of 5°C/min.The results of the experiments are summerized as follows:1) A glass formation region was determined (cf. Fig. 1).2) In general, crystallization of the glasses in this region starts at about 850°C, and is almost completed at 1100°C (cf. Fig. 3 and 5). The resulting crystallized products show flaws such as cracks and surface unevenness when the parent glasses contain BaO⋅TiO2 or Al2O3 in excess (cf. Fig. 2).3) Major constituents of the crystallized products are BaTiO3 (tetragonal), BaAl2Si2O8 (hexagonal), BaTiSiO5 and some unidentified crystalline phases (cf. Table 2).4) For the crystallized products with Al2O3 held constant, their dielectric constant decreases with increasing the SiO2/BaO⋅TiO2 mole ratio. For those with BaO⋅TiO2 held constant, it reaches a maximum when the Al2O3/SiO2 mole ratio is set to 35/65 (cf. Fig. 7). Generally, it increases with increasing the amount of barium titanate crystals separated out in the crystallized products. The composition of the crystallized product which shows a maximum dielectric constant (about 500 at 106c) in the present experiments is BaO⋅TiO2 60, SiO2 26, Al2O3 14 mole per cent.5) On the basis of Bruggeman's theory the crystallized products obtained were assumed to have the structure of prophyritic mixture in which lamellar barium titanate crystals are dispersed in matrix consisting of glass phase and crystal phases of BaAl2Si2O8 and BaTiSiO5 etc. (cf. Fig. 8).

The absorption bands of cerium in trivalent and tetravalent states in silicate and phosphate glasses, whose exact positions are still open to discussion, and the effects introduced by the change of composition and of melting condition were investigated.For the measurement of the absorption spectra of silicate glasses with poor ultraviolet transmission the thickness of the sample plates was reduced to 0.12-0.02mm by polishing.The results obtained are as follows: (1) In the silicate glass consisting of K2O, BaO, and SiO2, Ce3+ gives a sharp and weak absorption band at 320mμ, whereas Ce4+ gives a broad and strong absorption band in ultraviolet region below 350mμ. (2) In the phosphate glass consisting of K2O, BaO, Al2O3 and P2O5, Ce3+ gives three sharp and weak absorption bands at 294, 245, and 227mμ, whereas Ce4+ gives a broad and strong absorption band in ultraviolet region, as before.

Two types of silver chloride photochromic glasses, one based on the Na2O-B2O3-Al2O3-SiO2 system (Glass I) and the other on the Li2O-Na2O-B2O3-Al2O3-SiO2 system (Glass II), which were prepared by precipitating AgCl crystals at high temperatures of 560°-580°C, have been reheated at low elevated temperatures ranging from 200° to 520°C, and ultraviolet induced darkening has been measured. It was found that the reheating markedly affected the darkening characteristics of the photochromic glasses and the effect varied with their base composition and thermal history of the glass. Generally, the degree of darkening of Glass I lowered as a result of reheating, regardless of the reheating temperature. Especially, it lowered to the value as low as 50% of that before reheating when the glass was reheated around 520°C. On the other hand, a pronounced increase in the degree of darkening, reaching 100-200% sometimes, occurred when some samples of Glass II were reheated at the temperatures in the range 300°-420°C. No increase in the degree of darkening was seen in Glass II, however, when the condition of heating for precipitation of AgCl crystals was different and the degree of darkening before the reheating was already high. The rate of fading of U. V. -darkened photochromic glasses was also affected by the lower temperature reheating.The occurrence of these variations of photochromic characteristics resulting from the heating at low elevated temperatures seems to indicate that the “AgCl” particles precipitated in glasses are actually mixtures or solid solutions of AgCl and NaCl (or LiCl) and that the reheating alters the state of solid solution within the particles.

Glasses of the compositions, Li2O⋅1.5SiO2, Li2O⋅2SiO2, Li2O⋅3SiO2, and Li2O⋅3SiO2⋅0.1 MmOn (MmOn=Na2O, K2O, Al2O3 or ZrO2) in mole ratio, each with or without platinum, were prepared in a form of rectangular plate of 20×40×2mm. After polished with 1500-grit Al2O3 powder to make smooth surfaces, these glasses were repeated up to 900°C at the constant rate of 5°C/min. The polycrystalline materials thus obtained were exposed to various solutions, mainly to 5% HCl solution of 90°±2°C for various times. The chemical durability was reported in terms of weight loss per unit surface exposed. Identification of crystalline phases in the specimens by an X-ray diffractometer and electron microscopicobservation of the surface of specimens were made before and after the durability test in order to correlate the durability to the microstructure of the crystallized specimens.The results obtained were summarized as follows:1) Effects of the basic composition.For the two component system, i.e., Li2O⋅1.5SiO2, Li2O⋅2SiO2, and Li2O⋅3SiO2, the durability, in general, increased with the increase in SiO2 content, regardless of the presence of Pt. The durability of the crystallized specimens was much higher than that of their mother glasses. An exception was the Li2O⋅2SiO2 crystallized specimen without Pt, which showed the very poor durability.2) Effects of the addition of Pt.The poor durability of the specimen above described was found to be due to the presence of micro-cracks on the surface of the crystallized specimen. The addition of Pt as a nucleating agent in an appropriate amount (0.005-0.01% in weight) was found effective for suppressing the development of the cracks during reheating, thus improving the durability.3) Effects of addition of the third components.Of the four components, e. g., Na2O, K2O, Al2O3, and ZrO2, Na2O and K2O lowered the durability markedly. This was attributed to the concentration of these components in crystal grain boundaries (matrix glass) of the crystallized specimens, which was confirmed by an electron microscope. The matrix glass was easily attacked by 5% HCl.4) Effects of the kind of test reagent.The durability to various test reagents such as pure water, 5% H2SO4, 5% NaCl, 5% NaOH and 5% Na2CO3, besides 5% HCl, was also measured with the glass of the composition Li2O⋅3SiO2 with 0.01% Pt. In general, the attack of the alkaline solutions was much more severe than that of pure water and the acid solutions.

Four series of photochromic glasses were prepared by heating a glass having the batch composition SiO2 59.5, B2O3 20.6, Al2O3 8.9, Na2O 4.7, Li2O 4.3, Cl 1.5, Ag 0.5, CuO 0.015% in wt. at 570°C for 3hr, at 580°C for 3hr, at 580°C for 8hr and at 580°C for 31hr. The samples of different thicknesses ranging from 0.19mm to 2.73mm obtained from each series were subjected to optical measurements of darkening and fading. The following results were obtained.1. The degree of U. V.-induced darkening increased as the sample thickness increased for all series as expected. However, the features of the curves correlating the degree of darkening with the sample thickness varied with the series, namely, with the conditions of high temperature heat treatment required for precipitation of AgCl particles; the rate of increase in the degree of darkening with increasing thickness of the sample decreased more rapidly as the thickness increased for a series having a large light scattering factor than for a series having a small one. A large scattering factor was caused by large AgCl particles that was produced by prolonged heat treatment. On the other hand, the degree of darkening of very thin samples did not undergo the effect of the light scattering, but depended only upon the light absorption characteristics of the sample.2. The rate of fading of U. V.-darkened glasses varied with the thickness of the sample; in general, thinner samples exhibited higher fading rate than thicker ones for glasses subjected to the same heat treatment for AgCl precipitation.3. No general relation was found between the degree of darkening and the rate of fading.

An opal type of photosensitive glass, when exposed to ultraviolet light and subsequently heated to about its softening temperature, changes in transparency due to the formation of nonmetallic submicroscopic crystallites within the glass. In this study the transparency change of the glass having the following composition was studied in relation to the exposure time: SiO2 81, Li2O 12.5, K2O 2.5, Al2O3 4, CeO2 0.03, Au 0.027% by weight.Glass specimens of 2mm thick plates were exposed to ultraviolet light by placing the near a 500 watt high pressure mercury lamp at a distance of 10cm for various times ranging from 1 to 1000 min. After exposure all of specimens were heated firstly at 510°C for 30 min. and then at 620°C for 60 min. to cause the formation of gold nuclei and lithium metasilicate crystallites at respective temperatures. The measuremeat of light transmittance in the visible region was made of these specimens with a photoelectric spectrophotometer.It was found that (1) the transparency decreases with increasing exposure time up to 30 min. (due to the formation of metasilicate crystallites); (2) between 30 and 180 min., however, it increases with increasing exposure time; the specimen with the exposure time of 180 min. is almost transparent though its color is deep red; (3) over 180 min. it again decreases with increasing exposure time.The peculiar change in transparency with increasing exposure time was discussed on the basis of the size of lithium metasilicate crystallites within the glass. The increase in transparency with increasing exposure time in the range between 30 and 180 min, was attributed to the decrease of the size of crystallites under a limiting value which is too small for scattering visible light within the glass. The density measurement by a sink-float method was also made to support this conclusion.

The ratio of the glass transition temperature T g to the liquidus temperature T l (or T m ) was calculated for a wide variety of inorganic glass forming systems including the elements, oxides and sulfides and technologically important systems such as borates and silicates. It was found that a simple empirical rule T g /T l = 2 3 which was suggested for organic polymers holds suprisingly well for inorganic systems.

Optical absorption spectra of color centers produced in silicate glasses by γ-irradiation were measured before and after application of pressure of 50 kbar to the glass. The two color center peaks, one found at about 400 nm and the other at about 600 nm, shifted toward shorter wavelengths as a result of densification of glass. The local shrinkages around the color centers estimated from the shifts of the peak wavelengths were much larger than the bulk shrinkages of the glasses obtained from the change in density of the glasses due to application of the pressure. Similar shifts of the color center peak wavelengths were observed also when the glass was γ-irradiated after densification. Besides the shift of the peaks, the application of the pressure caused a great increase of broad absorption through the visible region. A tentative explanation was given to this phenomenon on the basis of the formation of unknown defects due to the effect of shear accompanying the application of pressure. The annealing of the various pressure effects was also examined.

Silicate glasses exposed to high-energy radiation develop three visible absorption bands sircilar to the F- and V-band in alkali halide crystals. The fanction of cerium in suppressing formation of these bands was studied spectrophotometrically in glasses with compositions of 20 R/sub 2/O, 10 BaO, 70 SiO/sub 2/, and 0.03 mole% CeO/sub 2/ (R/sub 2/O: Li/sub 2/O, Na/sub 2/O, K/sub 2/ O). Glass specimens of about 0.1 mm in thickness were irradiated with x rays of 42 kev, 10 ma, and changes of their absorption spectra in the range of 230 to 600 m mu were measured with the Beckman photoelectric spectrophotometer. As the absorption changes were found to be caused not only by color centers but also by other sources such as the valency change of cerium ion, the change due to color centers was separated from the others by heating the irradiated specimen at l5O deg C for 30 min; the decrease in absorption intensity by the heating was taken as the absolute change of the absorption dae to formation of color centers. The experimental results showed that trivalent cerium ions suppress development of the three absorption bands equally. Thus trivalent cerium ions are effective in preventing formation ofmore » either of those structural imperfections associated with trapped electrons of positive holes. As to the valency changes of cerium ion itself, a small part of trivalent cerium ions was found to lose their electron upon irradiation by the reaction Ce/sup 3+/ + h nu -- STACe/sup 3+/ with positive holel + e/sup -/. (auth)« less

H. M. Cohen and Rustum Roy reported that silica glass densified under ultrahigh pressures with the opposed anvil apparatus shows no relaxation effects even when heated at 600°C (J. Am. Ceram. Soc., 44 [10] 523 (1961)). J. D. Mackenzie, however, has found recently that marked relaxation occurs at the beginning of reheating at above 300°C for silica glass densified with the high-pressure “Belt” apparatus (J. Am. Ceram. Soc., 46 [10] 461, 470 (1963)). In the present work Mackenzie's result has been confirmed for silica glass and a borosilicate glass both densified with the same opposed anvil type pressure apparatus as used by Cohen et al.Samples of the silica glass were taken from a commercial clear grade silica glass rod. The borosilicate glass with the composition of Na2O 7.5, B2O3 22.5, and SiO2 70% in weight, was melted in a platinum crucible. The glasses were pulverized to 40-50μ, pelleted into a disc of approximately 6-mm diameter and 0.2-mm thickness, wrapped in a platinum foil, and pressed between two opposed anvils of the high-pressure apparatus at temperatures ranging from 25°C to 300°C for various periods. The pressure was released after the temperature of the sample was lowered to room temperature. The annealing of the densified glasses was made by reheating under atmospheric pressure at temperatures ranging from about 130°C to 900°C for various periods. Refractive indices of the reheated glasses were measured as the indication of relaxation.The results showed that the relaxation becomes noticeable by reheating above approximately 300°C for the silica glass and at much lower temperatures than 300°C for the borosilicate glass. In both cases the relaxation completes almost in a few minutes at the beginning of reheating.The activation energies of the relaxation process calculated from the initial changes in refractive indices were approximately 10 and 3kcal/mol for the silica- and borosilicateglasses respectively, which were both much lower than the activation energy of viscous flow in these glasses.