Crystal growth kinetics in BaOAl2O32SiO2 and SrOAl2O32SiO2 glasses

Crystallization kinetics of BaOAl₂O₃2Si0₂ (BAS) and SrOAl₂O₃2SiO₂ (SAS) glasses in bulk and powderforms have been studied by non-isothermal differential scanning calorimetry (DSC). The crystal growth activation energies were evaluated to be 473 and 451 kJ mol^–1 for bulk samples and 560 and 534 kJ mol^–1 for powder specimens in BAS and SAS glasses, respectively. Development of crystalline phases on thermal treatments of glasses at various temperatures has been followed by powder X-ray diffraction. Powder samples crystallized at lower temperatures than the bulk and the crystallization temperature was lower for SAS glass than BAS. Crystallization in both glasses appeared to be surface nucleated. The high temperature phase hexacelsian, MAl₂Si₂O₈ (M = Ba or Sr), crystallized first by nucleating preferentially on the glass surface. Also, monoclinic celsian does not nucleate directly in the glass, but is formed at higher temperatures from the transformation of the metastable hexagonal phase. In SAS the transformation to monoclinic celsian occurred rapidly after 1 h at 1100 °C. In contrast, in BAS this transformation is sluggish and difficult and did not go to completion even after 10 h heat treatment at 1400 °C. The crystal growth morphologies in the glasses have been observed by optical microscopy. Some of the physical properties of the two glasses are also reported.     

Electron microscopy and EDX-microanalysis of photochromic silver halide glasses of the composition systems Al2O3-B2O3-SiO2 and Na2O-CaO-SiO2

The microstructure and microanalysis study of two glasses containing AgCl precipitated particles have been carried out by transmission electron microscopy (TEM, replica method), scanning electron microscopy (SEM) and SEM/EDX (energy dispersive X-ray spectrometry). The composition of these glasses doped with silver halide and CuO was formulated from the Al₂O₃-B₂O₃-SiO₂ and Na₂O-CaO-SiO₂ systems respectively. In both glasses the seeds, nuclei, crystals and matrix were analysed, and the mean size and number of crystals were evaluated from the TEM and SEM observations. The microstructure in both glasses is different because of the different shape of the silver halide particles; the particles of the Al₂O₃-B₂O₃-SiO₂ glass are rounded while Na₂O-CaO-SiO₂ shows square precipitated particles. Likewise, the darkening behaviour is basically different; the Al₂O₃-B₂O₃-SiO₂ glass shows a higher darkening velocity than the Na₂O-CaO-SiO₂ glass, showing for this glass a very small slope value.     

The relative influences of Al2O3 and Fe2O3 on the chemical durability of silicate glasses at different pH values

The influence of the pH of aqueous solutions on the chemical durability of two glasses in the system Na₂O-FeO-Fe₂O₃-SiO₂ has been compared with that of two glasses in the system Na₂O-MgO-Al₂O₃-SiO₂ where equimolar substitution of MgO for FeO and Al₂O₃ for Fe₂O₃ have been made. The presence of Fe₂O₃, and particularly of Al₂O₃, in glass reduces its alkali extraction in the pH range 4 to 9. The extraction results have been discussed and interpreted in the light of the available standard thermochemical data for the component oxides of these glasses.     

Formation and properties of glasses in the CaF2AlF3P2O5 system

Glasses from the system CaF₂AlF₃P₂O₅ have been synthesized. Glass formation characteristics, thermal expansion, and optical transmission of these glasses in the visible and infrared regions are described. Incorporation of P₂O₅ in the system greatly suppressed the spontaneous crystallization tendencies of the CaF₂AlF₃ binary system. The glasses obtained from the system transmit in the mid-infrared range. A strong absorption band centerd at 4.8 microns is a characteristic of these glasses. The absorption band is related to the presence of P₂O₅ in the glass.     

Preparation and characterization of binary V2O5-Bi2O3 glasses

Characterization of the binary V₂O₅-Bi₂O₃ glasses prepared by rapidly quenching the melt has been made from the studies of X-ray diffraction, scanning electron microscopy, infrared absorption, differential thermal analysis, electron paramagnetic resonance, chemical analysis, density and electrical properties. Stable glasses are obtained for 95 to 75 mol % V₂O₅ by quenching on a stainless steel substrate, while quenching on a copper substrate extends the glass formation range from 95 to 70 mol % V₂O₅. The V-O bond vibration in the glasses occurs at 1020 cm^–1 and the V^5% ion exists in six-fold coordination as in crystalline V₂O₅. All the glasses appear to be in single phase. The spin concentration in the glasses is found to be independent of temperature. A second heat-treatment at 255° C develops crystalline phase in the glasses. Unlike infrared absorption, electron paramagnetic resonance, density and chemical compositions, the electrical and thermal (DTA) properties are found to be slightly sensitive to the thermal history of preparation of the glasses. The high-temperature (300 to 500 K) conduction in the glasses seems to be due to adiabatic hopping of polarons. The thermopower is observed to be independent of temperature and provides evidence for small polaron formation in the glasses.     

Vaporization of glasses in the R2O-Cs2O-B2O3-SiO2 (R = Li,Na, K and Rb) system

A mass-spectrometric Knudsen effusion method has been used for thermochemical study of the vaporization of alkali borosilicate glasses in the R₂O-Cs₂O-B₂O₃-SiO₂ system, where R = Li, Na, K and Rb. Vapours of RBO₂(g), CsBO₂(g), R₂(BO₂)₂(g) and RCs(BO₂)₂(g) have been identified. Over the glasses in which the molar ratio of (R₂O + Cs₂O)/B₂O₃ is slightly larger than unity, vapours of R(g), except for Li(g), have been further observed in the initial stage of heating; over the glass containing lithium, however, the vaporization of Cs(g) has been found. Neither R(g) nor Cs(g) has been identified over the glasses in which the molar ratio is equal to unity. Partial pressures of CsBO₂(g) over the glasses containing lithium and sodium are lower than those with potassium and rubidium, indicating that chemical activities of the CsBO₂ pseudo-component in the glasses with lithium and sodium are small. Enthalpies of formation as well as dissociation energies for dimeric vapours of alkali metaborates are not very different from one another, except that the dissociation energies for the dimeric vapours containing lithium are larger than for those containing the other elements.     

Optical absorption of nickel (II) in Na2O-NaCl-B2O3 and Na2O-NaBr-B2O3 glasses

The optical absorption spectra of nickel(II) have been studied in Na₂O-NaX-B₂O₃ glasses X = Cl or Br); the absorption bands have been interpreted in terms of Ligand Field Theory. In halide-free B₂O₃-rich glasses nickel(II) is octahedral, and halide substitution is accompanied by the formation of a tetrahedral nickel(II)-oxide-halide complex. In alkali-rich glasses nickel(II) is square planar and/or tetrahedral and no halide substitution can be observed. It is suggested that the halide ions are unable to substitute for oxygen in the predominantly covalent nickel(II)-oxygen bonds of the complex formed in basic glasses.     

Estimated immiscibility isotherms of the Li2O-Al2O3-SiO2 system

Using the immiscibility temperature estimation method, recently developed by the present author and Tomozawa, immiscibility isotherms of the Li₂O-Al₂O₃-SiO₂ system were estimated. High reliability of the estimated immiscibility isotherms was confirmed by observing the morphologies of phase-separated glasses, and also by comparing the estimated and observed immiscibility temperatures at several compositions. The determined immiscibility isotherms revealed that, in the Li₂O-Al₂O₃-SiO₂ system, only composition regions near the Li₂O-SiO₂ and Al₂O₃-SiO₂ binary edges are phase-separable. In composition regions where base glasses for commercial glass-ceramics are located, the immiscibility temperatures were much lower than the glass transition temperatures, implying that no phase separation actually occurs. Accordingly the phase separation in practical glasses for producing glass-ceramics may be attributed to increased immiscibility resulting from various additives.     

Spectroscopic investigations of Cu2+ in Li2O-Na2O-B2O3-Bi2O3 glasses

Pure and copper doped glasses with composition,x Li ₂ O-(40-x)Na ₂ O-50B ₂ O ₃-10Bi ₂ O ₃,have been prepared over the range 0 ≤ x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu²⁺ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, α² and β², have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO₃ and BO₄ units in the disordered manner.     

Influence of modifier oxides on some physical properties of antimony borate glass system doped with V2O5

Three series of glasses, of the composition 20 MO (M = Ca, Pb, Zn)–40 Sb₂O₃–(40 − x) B₂O₃:xV₂O₅, with six values of x ranging from 0 to 1 mol% were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy, EDS and differential scanning calorimetric techniques. The comparison of DSC data among the three series has indicated high glass forming ability for ZnO mixed glasses. Dielectric properties over a range of frequency and temperature, optical absorption, ESR spectra at room temperature and IR spectra have been investigated. The variations observed in all these properties due to different modifiers as a function of the concentration of V₂O₅ have been analyzed in the light of different oxidation states and environment of vanadyl ions in these glasses. The analysis of these results indicated that the ZnO mixed glasses are more stable against devetrification and possess high insulating strength when compared with PbO and CaO mixed glasses.     

Phase separation in tellurite glass-forming systems containing B2O3,GeO2,Fe2O3,MnO,CoO,NiO and CdO

The boundaries between the regions of single-phase and two-phase glasses were established in tellurite glass-forming systems containing B₂O₃ and one of the following oxides: GeO₂, Fe₂O₃,CoO, NiO, MnO and CdO. The character of the microstructures inside and outside the regions of stable phase separation were determined by electron microscopy. It was shown that the existing microheterogeneities may either result from incomplete liquid immiscibility during melting and supercooling or be due to typical metastable separation.     

Infrared spectra and composition dependence investigations of the vitreous V2O5/P2O5 system

A series of glasses in the V₂O₅-P₂O₅ system was prepared and their compositions analysed. The glass densities and molar volumes were determined. The results obtained revealed three compositional regions. In addition, the infrared absorption spectra of these glasses were measured at room temperature in the frequency range 1600–200 cm^–1. The compositional dependence of the bands present, attributed to a given band and mode of vibration, was investigated. However, the infrared data confirmed the results obtained from the density and molar volume measurements.     

The crystallisation of glasses from the ternary CaF2-CaAl2Si2O8-P2O5 system

A study of glasses from the ternary system CaF₂-CaAl₂Si₂O₈-P₂O₅ has been carried out. It has been shown that glasses with low phosphorus contents and high fluorite contents crystallise to fluorite. Fluorine reduces the glass transition temperature and is also required for the formation of fluorapatite (FAP). In the absence of fluorine in the glass no apatite phase is formed. Bulk nucleation of FAP is favoured for glasses with Ca:P ratios close to the apatite stoichiometry of 1.67 and with low crosslink densities. Thermal gravimetric analysis showed significant weight losses attributable to the formation of volatile silicon tetrafluoride to occur on crystallisation of the aluminium containing phases, anorthite and mullite, which supports the view that silicon tetrafluoride formation is hindered by fluorine bonding to the aluminium atoms of the glass network. Anorthite crystallisation always occurred by a surface nucleation mechanism and appeared to be favoured by the higher silicon to aluminium ratio in these glasses compared to previously studied glass compositions.     

Dielectric behaviour of glasses and glass ceramics in the system BaO-PbO-TiO2-B2O3-SiO2

Glasses with varying molar ratios of PbO/BaO in the system BaO-PbO-TiO₂-B₂O₃-SiO₂ were prepared keeping (BaO + PbO)/TiO₂ ratio equal to one. The glasses were ceramized by two-stage heat treatment. X-ray diffraction indicates that PbTiO₃ crystallizes in lead-rich glasses while BaTiO₃ precipitates in barium-rich compositions. Solid solution (Ba, Pb)TiO₃ does not seem to crystallize over the entire range of compositions. Simultaneous presence of PbO and BaO in the initial glass composition reduces the yield of ferroelectric phase. Dielectric properties have been interpreted in terms of microstructural features.     

Glass formation in the system CaO-Al2O3-CaF2

The formation of glass in the system CaO-Al₂O₃-CaF₂ has been investigated in sealed platinum capsules having about one atmosphere pressure of AlF₃ vapour. Transparent colourless glass could be obtained in the low-fluoride moderate-alumina region of the system (Al₂O₃ 35 to 60%, CaF₂ 0 to 20%). With the concentration of CaF₂ exceeding 20% considerable amount of quench crystals of CaF₂ appeared in the glass. Moderate-alumina low-lime melts containing more than 35% CaF₂ occur in an immiscibility zone. At the low-fluoride periphery of the liquid immiscibility zone a small zone of metastable liquid immiscibility has been found. The results of electron microscopic and infra-red spectroscopic studies of a few selected glasses have been analysed in combination with the molar refractivity data to reflect upon the co-ordination characteristics of aluminium in these glasses.     

An infrared study of the Na2O-V2O5-Fe2O3 glass system

Structural studies of Na₂O-V₂O₅-Fe₂O₃ glasses have been made from their IR spectra which show that vibrational bands characteristic of the vanadium-oxygen bonds in V₂O₅ are maintained in these glasses, but the addition of Na₂O to these glasses results in a shifting of the higher frequency peaks towards lower wave number due to structural changes produced in V₂O₅. It is inferred that Na⁺ ions make bonds interstitially with isolated V=O bonds and VO₅ polyhedra are destroyed, resulting in the formation of VO₄ polyhedra through intermediate complexes. The variation of Fe₂O₃, however, produces an insignificant structural change in these glasses. The IR spectra of samples heated to their temperature of crystallization confirm the formation of a series of complexes with several isolated V=O bonds.     

Absorption and emission spectra of thallium activated Na2O-NaCl-B2O3 and K2O-KCl-B2O3 glasses

Absorption and emission spectra of two Na₂O-NaCl-B₂O₃ and two K₂O-KCl-B₂O₃ glasses, with large thallium concentrations (about 0.01 mol thallium per litre glass) have been studied. Absorption bands have been observed at 49 000, 44 500 and 40 000 cm^?1 for the Na₂O-NaCl-B₂O₃ glasses, and at 49 000, 43 500 and 38 500 cm^?1 for the K₂O-KCl-B₂O₃ glasses at 300 K. Emission spectra have been recorded at 83, 308, 445 and 485 K; generally two emission bands have been observed in the ultraviolet region, and the intensity of both bands increased with decreasing temperature. The absorption and emission bands have been assigned to electronic transitions in different centres formed by Tl⁺ ions in glass.     

Preparation of MnCo2O4 whiskers and spheroids through thermal decomposition of Mn1/3Co2/3C2O4 · 2H2O

The mixed oxalate Mn_1/3Co_2/3C₂O₄ · 2H₂O has been prepared in the form of whiskers 2–5 μm in diameter and up to 50 μm in length and spheroidal nanofiber arrays 20 μm in diameter using two different coprecipitation procedures. Thermal decomposition of this oxalate in air has led to the formation of MnCo₂O₄ particles very similar in morphology to their oxalate precursor. The materials have been characterized by chemical analysis, thermogravimetry, x-ray diffraction. IR spectroscopy, and scanning electron microscopy.     

Luminescence of 60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium

60B₂O₃-32CaF₂-8Bi₂O₃ glasses codoped with chromium and neodymium have been prepared for the first time, and their luminescence properties have been studied. The glasses have been shown to contain chromium in two oxidation states. We have obtained luminescence spectra of Cr³⁺ in octahedral coordination and Cr⁴⁺ in tetrahedral coordination. Energy transfer from Bi³⁺ to Nd³⁺ and Cr³⁺ has been demonstrated.     

Cluster formation in Ag2O-P2O5-CdCl2 glass system

Ag₂O-P₂O₅ and Ag₂O-P₂O₅-20 wt% CdCl₂ glasses were prepared by melt quenching method and characterized with the help of several experimental techniques. Powder X-ray diffraction study indicated that the glasses are amorphous in nature. DSC studies showed that CdCl₂ doped glass is chemically more durable. Electrical conductivity and ionic transference number measurements have shown that both the glasses are ionic conductors with Ag⁺ ions as the charge carriers. The electrical conductivity of the doped glass is found to be higher than the undoped one. Structures of the glasses have been proposed on the basis of IR spectral analysis. From SEM studies it has been inferred that addition of 20 wt% CdCl₂ modifies the morphology of Ag₂O-P₂O₅ glass and in its presence formation of clusters composed of nanofibers occur.