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The present work reports data for TiO2 thin films on borosilicate glass and (001) single-crystal TiO2, annealed at 200–550 °C for 8 h. Characterization included GAXRD, laser Raman microspectroscopy, AFM, UV–Vis, XPS, SIMS, TEM, ellipsometry, and methylene blue (MB) dye degradation. The substrate determined the TiO2 polymorph that formed, while the annealing temperature and boron contamination from the substrate determined most of the associated properties. The films on glass substrates were amorphous following annealing at 200 °C but were anatase at higher temperatures. The films on rutile exhibited epitaxial growth at all annealing temperatures. Annealing caused diffusion of glass component elements into the films and counterdiffusion of Ti into the glass substrates. Since aqueous MB testing caused decreased glass ion concentrations, the diffusion mechanism is via the grain boundaries. Volatilization of boron occurred during annealing at 550 °C. The morphological features dominated the optical properties; the anatase films exhibited high transmissions and low reflectances, while the rutile films exhibited the converse. The band gap decreased slightly with increasing annealing temperatures, reflecting increasing crystallinity. The refractive indices showed an anomalous trend of decrease with increasing annealing temperature and associated crystallinity; this is attributed to the effects of boron volatilization and associated air-filled pore formation. Although the anatase films outperformed the rutile films, the effect of annealing temperature is likely to have been dominant in that it determined the relative extents of crystallinity, grain size, RMS roughness, optical indirect band gap, and oxygen vacancy concentration.

Industrial borosilicate glasses containing fission products and minor actinides can be subjected to structural damage caused mainly by $$\alpha $$ -self-irradiation effects. In this field of glasses under extreme conditions, we present an X-ray Absorption Near-Edge Structure investigation of two six-oxide borosilicate curium-doped glasses (based on the International Simplified Glass (ISG) composition). The first sample is an 8-year ISG damaged glass, which has already accumulated an $$\alpha $$ -decay dose greater than 6.10 $$^{18}$$ $$\alpha $$ g $$^{-1}$$ , a value corresponding to a damaged but stabilized structural state. The second sample results from annealing of the latter ISG damaged glass. Three species, Cm, Pu and Zr were probed at $$L_{3}$$ -edge, $$L_{3}$$ -edge and K-edge, respectively. From the experimental results, Cm and Pu species appear respectively in +3 and +4 oxidation states in both glasses. No Cm local environment changes are observed. In contrast, a small variation in Pu local environment appears between the damaged and annealed glasses, reflecting a possible coordination variation or Pu–Zr substitution. A more drastic effect appears for Zr local environment, where a sevenfold coordinated site grows over time under $$\alpha $$ -self-irradiation effects, at the expense of the initial major sixfold site of symmetry. Moreover, annealing the damaged glass does not permit to retrieve a similar structural state to the one of a just melted curium-doped ISG.

A long-term disposal of a nuclear waste package requires a matrix material that possesses a high thermal conductivity in order to release the decay heat from the fission products. In this study, the thermal diffusivity (α) of alumina borosilicate glass (ABG), encapsulating surrogated tristructural-isotropic (TRISO) particles, has been measured experimentally using the laser flash analysis (LFA) methodology. Image-based models were developed using X-ray computed tomography for glass samples bearing different proportions of TRISO particles. Simpleware software generated finite element (FE) models which then were solved using Abaqus software. The matrices were examined at different waste loadings (10, 20 and 30 wt%) at a temperature of 50 °C. The modelling results were in close agreement with the experimental results and the deviations were within the bounds of standard numerical error (

Joining of carbon fiber reinforced C–SiC dual matrix composite (denoted by C/C–SiC) is critical for its aeronautical and astronautical applications. Joining of C/C–SiC has been realized through a reaction joining process using boron-modified phenolic resin with micro-size B4C and nano-size SiO2 powder additives. The effect of the heat-treatment temperature on the retained strength of the joints, calculated by dividing the strength of the heat-treated joints by the strength of the joints before heat-treatment, was studied. The maximum retained strength of the joints is as high as 96.0% after the heat-treatment at 1200 °C for 30 min in vacuum, indicating good heat resistance of the joints. The thickness of the interlayer of the joint after the heat-treatment is about 18 μm and it is uniform and densified. There are no obvious cracks or pores at the interfaces. During the heat-treatment, carbon, oxygen, silicon, and boron diffuse at the interfacial area. The interlayer is composed of B4C, SiO2, glassy carbon, amorphous B2O3, and borosilicate glass. SiC appears in the interlayer of the joint heat-treated at 1400 °C for 30 min in vacuum. The addition of B4C and SiO2 powders contributes to the densification of the interlayer, the bonding at the interfaces and the heat resistance of the joints.

Tungsten tools used in the glass-forming industry undergo complex damage process resulting from cyclic contact with molten glass and atmospheric air and from friction between glass and tungsten. The damage process involving oxide scale growth and wear has been studied on W rods of two different diameters, in contact or not with glass, with different friction velocities. Damage is characterized quantitatively and the contributions of oxidation, borosilicate glass–tungsten reaction, and wear are discussed.

CdSxSe1−x nanoparticles or quantum dots (QDs) were grown in borosilicate glass by a two-step heat-treatment process from a melt-quenched color filter glass. We incorporate the results of optical absorption, steady-state photoluminescence (PL), and resonant Raman spectroscopies in the study of growth kinetics of CdSxSe1−x QDs. A modeling of PL spectra employing two Gaussian emission bands and a quantized-state effective mass model in the strong confinement regime reveals that (i) the average particle size ranges from 1.7 to 8.5 nm, (ii) the size dispersion narrows down to 0.22 nm for a single sample, and (iii) QDs form by diffusion-limited growth. We presume that size-dependent higher energy PL band close to the asymptotic absorption edge is due to surface-assisted electron-hole recombination since the difference between optical absorption and PL bands decreases from 239 to 122 meV with increasing average radius.

Soda alumina borosilicate glasses of composition (24-y)Na2O·yAl2O3·14B2O3·37SiO2·25Fe2O3, y = 8, 12, 14, 16 mol%, were melted using Fe2O3 as raw material. Besides, samples with y = 12 and Fe2O3 concentrations of 14.32, 17.8, and 25.0 mol% were prepared from FeC2O4·2H2O as raw material. The X-ray diffraction analyses showed the presence of magnetite for the samples from all the investigated compositions. Transmission electron microscopy (TEM) evidenced that all the samples are phase separated and droplets in the diameter range 100–1000 nm, enriched in iron, are formed. Inside these droplets, numerous small magnetite particles, with size in the 25–40 nm interval, are crystallized.

In this article the selection of more appropriate raw materials applied to alumino-borosilicate glass system for vitrified cubic boron nitride (CBN) grinding wheels was investigated. The selection of raw materials had a major effect on the performance of specimens. Mechanical properties of the specimens were measured by using three-point bending strength tester and microstructure characteristics of specimens were examined by scanning electron microscopy (SEM). The results showed that the elements barium and magnesium in the form of carbonate were more beneficial to the refractoriness and fluidity of glass binder than in the form of hydrate and oxide. Moreover, the element barium in the form of carbonate was more favorable to mechanical property of glass binder than that in form of hydroxide. But magnesium carbonate was harmful to improve the mechanical property of glass binder. Therefore, selection of appropriate raw materials used in glass binder was dependent on their natural characteristic.

Sodium aluminium phosphate (NaAlP) glass–ceramic composites were produced as potential wasteforms for the immobilization of special categories of halide-containing radioactive waste. Sintering conditions for encapsulating a simulated waste (a calcinated mixture of calcium phosphate host and various oxides) in the cold-pressed NaAlP glass–ceramic were first determined and the results were compared with similar samples prepared by hot pressing. In both cases, the conditions aimed to provide a very high-density material, via as low production temperatures as possible, in conjunction with a high waste loading (75 wt.% simulated waste to 25 wt.% glass). It was found that by hot pressing and using a NaAlP glass–ceramic containing 2 mol% B2O3, significantly lower temperatures could be employed compared to the cold pressing and sintering route. The lowest temperature at which a sufficiently dense hot-pressed product was achieved (86% theoretical density), that exhibited mechanical properties similar to those of borosilicate glass (e.g. Young’s modulus 67 ± 2 GPa), was 550 °C. This processing temperature is considerably lower than values reported in the literature for similar systems. As such, hot pressing can be considered as a convenient technique for the fabrication of this type of composite for waste encapsulation.

The Vickers indentation behavior of five commercial glasses has been investigated as a function of temperature. The glasses included: (i) soda-lime-silica Float glass, (ii) lead-alkali silicate, (iii) 7740 Pyrex™ borosilicate, (iv) potassium phosphate, and (v) lanthanum borate. A recording microindentation system was constructed to allow Vickers indentation testing to be conducted at temperatures significantly above room temperature. The Vickers hardness was observed to decrease continuously with increasing temperature for all glasses, with the exception of the 7740 Pyrex™ glass. Decreases in hardness were attributed to decreases in elastic moduli and bond strength with increasing temperature. The lengths of median-radial cracks around indentations in several glasses were observed to first increase, and then decrease, with increasing temperature. The first of this behavior was attributed to initial increases of the crack driving force, characterized by the quantity (E/H), as well as to a decrease in fracture surface energy. Viscous flow at higher temperatures was believed responsible for a reduction in the crack driving force and crack tip stress, resulting in an eventual decrease in crack length. Viscoelastic behavior of the Float glass was characterized by a rate-dependent hardness and indentation crack pattern. Load–displacement traces indicated an increase in the work of indentation and residual indentation depth with increasing temperature for all glasses.

Borosilicate glass matrix composites reinforced with 10 wt% multiwall carbon nanotubes (CNTs) were fabricated using a conventional powder processing route and uniaxial hot pressing. The microstructure of the composites contained aggregates of CNTs which had not been infiltrated by the viscous glass during hot-pressing leaving a ∼9% residual porosity. As a result, the mechanical properties (hardness, elastic modulus, fracture toughness and fracture strength) were not improved in comparison to those of the monolithic glass matrix. However the brittleness index (B), which is the ratio of hardness to fracture toughness, decreased with addition of CNTs, which indicates that the composites should exhibit improved contact damage and wear resistance. Electrical resistivity measurements revealed that the addition of 10 wt% CNTs to the normally insulating borosilicate glass decreased its resistivity to 13 Ω cm in comparison to the high value (1015 Ω cm) of the monolithic glass.

The brazing of SiC fibre reinforced borosilicate glass matrix composites with Mo plates has been investigated. Molybdenum was chosen as the metallic partner under consideration of system requirements, e.g. thermomechanical stability at temperatures of interest (500–750∘C), and physical properties, e.g. coefficient of thermal expansion close to that of the glass matrix composite. Two brazing filler materials were investigated: a glass braze (Schott G018-174) and an active filler metal (Incusil ABA, brazing temperature = 740∘C). When using the glass braze the surface of the metal had to be roughened to ensure a bond of significant strength. Vacuum brazing with the active filler metal resulted in joints with high strength, which allows to fully utilise the mechanical competence of the glass matrix composite when the joint configuration is adapted to the relevant loading conditions. A novel design of a tool for hot glassware handling, made of glass matrix composite/Mo joints, is presented.

Mullite, Al2[Al2 + 2x Si2 − 2x ]O10 − x , is introduced as a suitable reactive wetting model system for oxide ceramic compounds. Apparent contact angles on single crystal mullite substrates have been measured from sessile drop experiments involving (i) a highly reactive yttrium aluminosilicate (YAS) glass and (ii) a less reactive borosilicate (BS) glass. The apparent contact angles decrease with crystallographic orientation in the following order: (010) > (100) > (001) independent of glass composition. The surface energy, γSV, has been identified as the dominant term controlling reactive wetting with γSV (010) < γSV(100) < γSV(001). This order of surface energy values is rationalized in terms of the high anisotropy of the crystal structure and elastic properties of mullite. The YAS glass reacts stronger with the polycrystalline 3/2 mullite substrate due to the grain boundaries acting as fast diffusion paths. In the YAS/mullite system, analytical electron microscopy shows that for the single crystal 2/1 mullite substrate, a corundum + Y2Si2O7-rich crystalline phase assemblage results upon devitrification while in the case of the polycrystalline 3/2 mullite substrate a 2/1 mullite + Y2Si2O7—rich crystalline assemblage is formed instead. In the less reactive borosilicate system secondary 2/1 mullite microcrystals precipitate at the S/L interface with (i) random orientations established on polycrystalline substrates and (ii) characteristic preferred orientations on the single crystal substrate. A thin Al-rich interdiffusion zone (3 μm) right at the S/L interface is revealed for both glass systems.

The influence of additives of metal compounds (ZrB 2 , MoS 2 ) and nickel to the abrasive masses based on devitrified glasses of ZnO-PbO-B 2 O 3 -SiO 2 system was studied by investigating both the wettability of submicrocrystalline sintered corundum, and the size, structure and chemistry of the interfaces. XRD analysis, scanning electron microscopy with X-ray microanalysis, wettability tests and microhardness measurements were performed. The experimental results were compared with the probability of reaction between the abrasive grain (cBN, submicrocrystalline sintered corundum) and: (1) the additives of metal compounds, (2) devitrified glass binders identified by using a VCS algorithm designed for thermodynamic calculations. It was confirmed that 18-20 compounds (6-9 in condensed phase) out of 230 exhibited chemical stability.

In this study, the possibility of using the glass and glass-ceramic of Al 2 O 3 -containing sodium borosilicate as nuclear waste materials was examined and some infrared measurements were carried out to investigate the Na leaching mechanism as well as the influence of the controlled surface crystallization on effectively increasing the chemical durability.

Glasses from a complex SiO2-Al2O3-P2O5-CaO-CaF2 glass series, known as 'ionomer glasses' were investigated. For comparison, a sodium-boro-silicate (s-b-s) glass system, which is known to undergo amorphous phase separation was also investigated. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and BET surface area and pore distribution analysis were the principal analytical techniques used in this study. SEM analysis of the ionomer glass compositions revealed smooth spherical droplets of 2–15 nm while the background morphology appeared rough and speckled. A classic interconnected structure was observed for the s-b-s glass. EDX analysis of the s-b-s glass confirmed that the sodium-borate phase was removed by leaching with 0.3 M HNO3, leaving behind a silica-rich structure. EDX analysis of ionomer glasses leached with 10% NaOH showed that the calcium and phosphate phases were being removed, although not to completion. For the base s-b-s glass a surface area of m 82 g−1 was recorded. However, the base glass after extraction with 0.3 M HNO3 of the sodium borate rich phase gave a BET surface area of 330 m2 g−1 indicating that it had already undergone phase separation on quenching from the melt, giving rise to a fine scale interconnected structure. The leached s-b-s glasses exhibited type 4 adsorption/desorption isotherms characteristic of mesoporous materials. Glasses which had been heat treated at 580°C for 4 h exhibited a surface area of 62 m2 g−1. This indicates that the as-quenched glass is already phase separated and that the phase separated microstructure is coarsening on heat treatment. A surface area of 4 m2 g−1 was measured for the base ionomer glasses. After leaching with 10% NaOH this value rose 10-fold with a maximum surface area of 44.1 m2 g−1 being recorded. The ionomer glasses also exhibited adsorption/desorption isotherms characteristic of mesoporous materials.

Induced damage in brittle materials due to two interacting Vickers indentations at various orientations was investigated using a three-dimensional finite element model. The model considers ‘tensile cracking and compressive yielding’ behavior of ceramics. Damage evolution due to both the simultaneous and sequential double indentations was studied. The simulation results indicated that the induced damage zone patterns are strongly a function of the relative orientation of the two indenters. The existence of another nearby indentation reduces the crack size on the side closer to the first indentation but increases the overall median damage zone size. These results were validated by sequential Vickers indentation experiments on borosilicate glass. The evolved damage patterns were further rationalized based on Bousinesq and blister field stress fields. Finally, the implication of these results on material removal mechanisms due to simultaneous interaction of several grits in a ceramic grinding process is discussed.

The objective of this work is to test the hypothesis that the failure probability prediction model by Fischer-Cripps and Collins can be used without introducing an empirically derived parameter and therefore can serve as a predictive tool. We examined this hypothesis by Hertz cone crack initiation tests of flat borosilicate glass statically loaded through a spherical indenter. The Weibull parameters characterizing the surface flaw distribution were determined from biaxial flexure experiments using specimens with the same surface condition as in the indentation tests. Elastic moduli of the specimens were determined by using ultrasonic methods. In addition, the crack initiation was determined using stereo microscopy at 20× magnification. The results demonstrated that the model can predict the minimum critical load and cumulative failure probability for small indenters within the 90% confidence level. Therefore, the current work demonstrates that the model can be used as a predictive tool provided the parameters necessary for the model accurately reflect those of the actual sample populations that are used for the experimental setup.

AlN/glass composite is low-fired substrate material for microelectronic packaging material. In this work, AlN/glass sheets were prepared by tape casting process. The dispersion, stabilization and the rheological properties of the slurry were studied. The optimum drying condition and mechanisms of debinding were also investigated. The results showed that powder size influenced the optimum content of dispersant and the viscosity of slurry. The slurry for tape casting exhibited a typical shear-thinning behavior. Smooth green tape without cracking was acquired after it was dried at solvent atmosphere. The binder was fully burned out at 600°C at low heating speed. The lamination with uniform microstructure was achieved by hot-pressed at 900°C.

Oxidation tests of a three-dimensional C/SiC composites with different coatings were conducted in dry air and the effect of defects in the coatings on the oxidation behavior were investigated. There existed two kinds of preparation defects in the CVD SiC coating, including the supporting defects and the machining defects. The former were produced by supporting of the specimens and the later were produced from the matrix pores formed between the fiber bundles after machining. There existed two kinds of deposition defects in the multi-layer CVD SiC coating, including the plane-defects and the net-defects. The former were formed between the layers and the later were produced at the boundaries between the particles. Increasing the coating thickness can seal the machining defects, but it can not seal the supporting defects. Multi-deposition can not completely seal the preparation defects although it decreased remarkably the weight loss. The Si-Zr outer layer can seal completely defects in the multi-layer, but it increases the weight loss at low temperature, and furthermore has a low resistance to oxygen diffusion. The borosilicate glass can seal the coating cracks, but it nearly loses all ability of sealing defects at high temperature. The preparation defects can be completely sealed if there exist no plane-defects in the multi-layer coating. Increasing the deposition temperature and decreasing the deposition pressure will be favorable to removing the plane-defects.

Various glasses in the system (65 − x)[SrO · TiO2]-(35)[2SiO2 · B22O3]-(x)La2O3, where x = 1,5,10 (wt%) were prepared by melting in alumina crucible (1375–1575 K). Heat treatment schedules were selected from DTA plots of respective glasses. X-ray diffraction studies of glass ceramic samples containing different concentrations of La2O3 revealed the formation of Sr2B2O5, Sr3Ti2O7 and TiO2 (rutile) phases. The addition of La2O3 results in the development of well formed, elongated crystallites of different phases. Results of the dielectric behaviour demonstrate higher values of dielectric constant for some of the glass ceramic samples. This can be ascribed to the relaxation polarization at the crystal-glass interface due to conductivity differences between crystalline and glassy phases.

Composites reinforced with hollow glass fibres (HGF) have been shown to display improved performance in flexural and compressive loading over materials reinforced with solid fibres. A major drawback associated with hollow fibre composites is reduced reinforcement cross-section for a given fibre volume fraction. It is suggested that the use of optimised manufacturing parameters may allow fibre strengths to be increased, offsetting the inherent strength reduction predicted for hollow fibre composites compared to solid fibre composites. Tensile tests have been performed on batches of hollow and solid fibres with a variety of geometry's to investigate the effects of fibre hollow fraction and manufacturing parameters on fibre strength. Hollow and solid glass fibres drawn under a variety of conditions display tensile strengths which reflect their manufacturing history. A mechanism is proposed whereby differential strains may be locked into the fibre during manufacture. This mechanism may provide an explanation for the strength variations observed. Average tensile strengths for solid and hollow glass fibres appear to increase according to the degree of residual strain differential. The principal manufacturing parameters influencing residual strain differential are draw rate and temperature. Further investigation is suggested into methods for determining heat transport mechanisms within the fibre neck-down zone.

The preparation of glasses from gels in the ternary system of SiO2-ZrO2-B2O3 has been investigated. The crystallization character of ZrO2 particles and high-temperature structure stability in the SiO2-ZrO2-B2O3 gels were analyzed. The effect of B2O3 as the inhibitor of crystallization was illustrated. Finally, the result that the purified DD3 single crystal superalloy melt can retain high undercooling in the SiO2-ZrO2-B2O3 coating mold indicates that the coating has an ideal non-catalytic nucleation property.

The influence of Poisson contraction on the stresses for propagating a semi-infinite fiber-bridged crack in unidirectional fiber reinforced ceramics is studied in this paper. The situation of bonded fibers that is subjected to compressive pressure due to thermal expansion mismatch between the fiber and the matrix is considered in the present analysis. The results show that the Poisson contraction has profound effects on the matrix cracking stress predictions in the ceramic matrix composites, especially for the composites with high coefficient of friction. The Poisson contraction effects can be evidenced by the comparison of the present analysis with the Aveston, Cooper and Kelly (ACK) model. The roles played by the interfacial properties of the interfacial bonding energy and the coefficient of friction on the stresses for matrix cracking are discussed.

The structural and textural properties of “Two-Phase Porous Silica” consisting of a mesoporous pore system formed by finely dispersed silica-gel inside the original pores of a macroporous glass framework have been carefully investigated. Nitrogen adsorption at 77 K, Mercury Intrusion, Small Angle X-ray Scattering (SAXS), Temperature-Programmed Desorption (TPD) of ammonia and 27Al MAS NMR spectroscopy were used. Different mesoporous glasses investigated show BET surface areas up to 300 m2/g, a total pore volume of about 0.16 cm3/g and pore sizes of

Tensile and bending tests are useful to characterize the mechanical behavior of ceramics. Theoretical comparisons between results of both tests are usually done based on Weibull statistics. In previous experiments on borosilicate glass, no agreement was found between experimental and theoretical values of the ratio of the maximum bending and tensile stresses at 50 percent probability of fracture. In this investigation, additional experiments in bending have been performed, to measure the distribution of fracture initiation points. Good agreement with theory is found. The previous disagreement could be attributed to fatigue effects.

Fiber-matrix interfacial debonding is observed and the debond length is directly measured during flexure tests performed on transparent SiC fiber-reinforced borosilicate glass composites. The relationship among the debond length, applied stress, and interfacial properties is investigated both experimentally and theoretically. A new technique based on debond length measurement is introduced for measuring fiber-matrix interfacial properties such as interfacial shear strength, frictional shear stress, and interfacial debond energy. Analytical models are employed for the new technique to interpret the experimental data. Fiber pushout technique is also employed to measure the interfacial properties independently. It is shown that these two different techniques of debond length measurement and fiber pushout test for measuring the interfacial properties can provide comparable results.

Experiments of dissolution of a soluble boro-silica glass were performed at 37°C in a saline solution without and with 50, 75 and 100 ppm of added silica. After reaction silica concentration was measured by AAS and colorimetry and fibers were investigated by SEM-EDS and XPS. The results give informations on the dissolution velocity of the glass and the factors controlling the formation rate of the gel layer and its composition. The dissolution velocity measured at the unaltered glass-gel interface is not significantly decreased by the silica concentration in solution whatever its origin (leaching of the glass fibres or initial addition). Accordingly, gel formation is controlled by the chemical reactions rate at, or near, the boundary of the unaltered core. The composition and the stucture of the gel layer are depending on the silica concentration in solution above a threshold of about 50 ppm. The framework of the gel appears to play the more important role in the dissolution velocity of the glass.

A transmission electron microscope study has been made of a silicon nitride component with 6 w/o yttrium oxide as a sintering aid hot isostatically pressed (HIP) with an encapsulation glass of borosilicate. The TEM study concentrated on the interface region between ceramic and glass. Two different types of hexagonal boron nitride were formed near the interface. One, with a textured structure, seemed to nucleate heterogeneously on the surfaces of silicon oxynitride grains. The (001) planes of the crystals extended outwards, giving a thickness of approximately 0.5 microns. The other type formed as hexagonally shaped grains separate from the first type and appeared to have grown as several segments in different directions around a nucleus. In each segment BN layers are parallel to each other and perpendicular to their common [001]BM direction. This second type of BN crystal was also detected a little further from the surface within the silicon nitride. The volume fraction of additive glassy phase tended to be lower in this surface region than in the bulk. Possible mechanisms of prevention of encapsulation glass penetration into the porous ceramic component during HIP were discussed.

The effect of Al2O3 on the structure change and the phase separation in Na2O-B2O3-SiO2 glass was investigated using 11B nuclear magnetic resonance (NMR), 29Si MAS NMR, and 27Al MAS NMR together with infrared absorption spectroscopy and field emission scanning electron microscopy (FE-SEM). The results show that the structure change from the introduction of Al2O3 contributes greatly to the inhibition of phase separation. First, the introduction of Al2O3 imparts an ionic character to the boron-oxygen network, resulting in the formation of B-O-Al-O-Si bonds and thus increases the compatibility of the silicon network with the boron-oxygen network. Second, the addition of Al2O3 causes the sodium ion to transfer from the boron-oxygen network to AlO4 tetradedra, changing a number of four-coordinated borons into three-coordinated borons. As the bond energy of the four-coordinated boron is weaker than that of the three-coordinated boron, the -B-O-Si- bond with the four-coordinated boron in Na2O-B2O3-SiO2 glasses is easily broken and results in severe phase separation during heat treatment. However, the -B-O-Al- bond with the three-coordinated boron formed in Na2O-B2O3-SiO2-Al2O3 glasses is difficult to be broken due to the high bond energy. In addition, the silicon network in Na2O-B2O3-SiO2-Al2O3 glasses is also strengthened by the addition of Al2O3, which prevents [BO] groups from further aggregation. As a result, the tendency of the glass towards phase separation is greatly suppressed in the Na2O-B2O3-SiO2-Al2O3 system.

The use of flame hydrolysis deposition (FHD) to fabricate porous silica glass soot in the B2O3-P2O5-SiO2 glass system (BPSG) is described for silica-on-silicon device applications. The deposition conditions with a Si substrate temperature (∼200 °C) and a flame temperature (1300–1500 °C) are appropriate to synthesize the SiO2 and P2O5-SiO2 non-crystalline glass soot. However, further investigations for the B2O3-P2O5-SiO2 glass soot are needed to obtain complete amorphous phases. The densification process of porous silica glass soot in the three systems of SiO2, P2O5-SiO2 and B2O3-P2O5-SiO2 is also described to estimate the onset of sintering temperature. The OH absorption measurements are performed to try to identify incorporation of hydroxyl contaminants in the systems of P2O5-SiO2 and B2O3-P2O5-SiO2.

The rheological behavior of SiC particulate glass composites was investigated in the present study. The nature and extent of flow modifications are addressed with respect to solid content in the suspension, temperature and dispersoid size. A transition from Newtonian to non-Newtonian viscous flow and characteristic shear thinning behavior were observed. With progressive strengthening and deviation from Newtonian flow, a significant loss in rate sensitivity occurred. The apparent viscosity of the composites increased with the concentration and size of reinforcements. The increase in viscosity is explained in terms of hydrodynamic/mechanical interactions between particles in the composites.

Unidirectional-aligned continuous SiCaAlON fiber-reinforced glass matrix composites have been fabricated and their light transmittance was measured. Optically transparent composites with the fiber volume fraction from 0.03 to 0.10 were fabricated by a hot-pressing method. The light transmittance of the composite perpendicular to the fiber axis in the wavelength range from 200 to 700 nm was measured, and found to decrease with the increase of the fiber volume fraction. This decrease is explained by the theory proposed by the authors (Hl and YK). The major source of a light transmittance loss of the composite originates from a phase change of transmitted light in the composite.

The failure process of unidirectional BN-coated HI-NICALONTM SiC fiber reinforced glass matrix composites was examined under tensile loading. In situ observation of the mean matrix crack interval was conducted by the replica observation during tensile testing. Axisymmetric cylindrical models extended to the system considering the strength distribution of fibers were proposed to predict the whole stress-strain curve for comparison with the experimental results.

The luminescent properties of Tb3+ have been studied for borosilicate glasses prepared by a sol-gel method. Gel bodies were formed from solutions consisting of silicon tetraethoxide, triethyl borate, ethanol, water and terbium nitrate, then sintered into a bulk glass. The Tb3+ luminescence in glasses mostly shows green light under UV excitation, because the emission line at 545 nm occupies the main part of the energy emitted. The observed luminescence consisted of four main emission lines originating from the 5D4 level. However, a remarkable spectral change has been observed for the Tb3+ luminescence in borosilicate glasses after firing at about 800°C. This spectral change due to heat treatment was found to be large enough to show yellow or red luminescence, suggesting that the crystal field acting on Tb3+ is very strong. The spectral energy distribution of Tb3+ luminescence in sol-gel derived borosilicate glasses were investigated in relation to the effects of calcination temperature.

A silicon-to-In2O3:Sn coated glass bonding has been developed for the package of field emission arrays fabricated on the silicon wafer, utilizing a conventional silicon-to- silicon anodic bonding using the glass layer. A 1.8 μm Pyrex #7740 glass layer was deposited on the In2O3:Sn coated glass by an electron beam evaporation. It was confirmed that the composition of the glass layer was nearly the same as that of the bulk Pyrex #7740 glass plate. In this work, bonding the silicon and In2O3:Sn coated glass was achieved at a temperature of 190 °C with an applied voltage of 60 Vdc. A secondary ion mass spectroscopy analysis was used to confirm the modeled bonding kinetics of the silicon-to-In2O3:Sn coated glass.

The preparation and properties of gels via borosiloxane polymers formed by the reaction of tetraacetoxysilane (TAS) with boron tri-n-butoxide (BTB) in tetrahydrofuran (THF) was investigated. The reaction formed polyborosiloxanes which underwent further condensation to give heterogeneous gels at room temperature and homogeneous gels with (TAS/BTB ≥ 2) or without (TAS/BTB = 1) cracks at 60 °C. The addition of ethanol to the reaction mixture formed homogeneous gels under milder conditions. In the presence of hydrochloric acid as a catalyst, transparent round gel plates of B2O3 contents up to 34 mol % were obtained by the reaction in the molar ratios of TAS/BTB = 9/2–1/2. Polyborosiloxanes of molecular weight around 1000 were found to be formed. It was found that the consisted of borosiloxanes incorporated with well cross-linked borosiloxane networks, which provided borosilicates containing B2O3 up to 30 mol % on heat treatment.

Thick-film resistors are made by screen-printing thick-film paste on insulating, mainly alumina, substrates. After printing and drying, the thick-film pastes are fired in a belt furnace. Thick-film resistor pastes consist basically of a conducting phase, a lead borosilicate-based glass phase and an organic vehicle. The organic material is burned out between 300 and 400 C during the high-temperature processing. The ratio between the conductive and glass phases roughly determines the specific resistivity of the resistor. In most modern resistor compositions the conductive phase is either RuO2 or ruthenates. The glass phase is based on the B2O3–PbO–SiO2 glasses with the molar ratio of SiO2/PbO approximately equal to 2. Some other oxides are also added as modifiers of the temperature coefficient of expansion and/or the glass-transition temperature [1–5]. The well-known European environmental legislation, i.e., the RoHS Directive (restriction of the use of certain hazardous substances), requires the elimination of the lead, or at least a minimising of the lead content in electrical and electronic equipment to below 0.1 wt.%—starting from July 2006. Thick-film materials are currently an exemption from the directive, but the producers of thick-film materials are already developing new material systems in accordance with the directive [6]. While there are many lead-free conductor and dielectric compositions available, the development of thick-film resistors with lead-free glasses is still mainly in the experimental stage. At least to the authors’ knowledge, no commercially available thick-film lead-free resistor series with characteristics comparable to ‘‘conventional’’ resistors is on the market. However, many ‘‘experimental’’ papers have reported on the preparation and investigations of the characteristics of lead-free thick-film resistors where the conductive phase is based, like with ‘‘conventional’’ resistors, on ruthenium oxide or ruthenates [7–11]. In the glass phase the lead oxide is often replaced with the zinc oxide [12–15]. Regardless of the very different melting points (Tm is 886 and 1,975 C for PbO and ZnO, respectively) both oxides share similar characteristics. Both PbO and ZnO are classified as intermediate oxides, i.e., they can be either glass formers or glass modifiers. Some of the characteristics, i.e., the dissociation energy per MOx, the coordination number and the single bond strength, are summarised in Table 1 [16]. The aim of this work was to investigate subsolidus phase equilibria (in air) in the RuO2–ZnO–SiO2 system. The results would indicate possible interactions between silicarich glass with the addition of ZnO and the conductive phase (ruthenium oxide) in lead-free thick-film resistors. The binary Zn2SiO3 compound exists in the SiO2–ZnO system. The melting point of the eutectic on the ZnO-rich side is 1,507 C, and on the SiO2-rich side it is 1,432 C [17, 18]. Morimoto et al. reported a synthesis at a high temperature of 1,400 C and at a high pressure, and a characterisation of the binary compound ZnSiOO3 [19]. Phase equilibria in the RuO2–SiO2 [5] and RuO2–ZnO systems were studied by Hrovat et al. [20]. In both systems there is no binary compound and no liquid phase (eutectic) at temperatures up to 1,405 C, the temperature at which RuO2 decomposes (in air) to metallic ruthenium and oxygen. For the experimental work, RuO2 (Ventron, 99.9%), ZnO (Johnson Matthey, ultrapure), and SiO2 (Riedel de M. Hrovat (&) J. Holc S. Glinsek Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia e-mail: marko.hrovat@ijs.si

Lead ruthenate $(Pb_2Ru_2O_{6.5})$ with pyrochlore structure is one of the phases that form in thick-film resistors, which consist of a conducting oxide dispersed in a lead borosilicate glass with minor additions. Lead ruthenate converts to $RuO_2$ when the PbO concentration in the glass is reduced. $TiO_2$ is added as a modifier to lower the temperature coefficient of resistance of thick-film resistors.

The machining of a composite material comprising silicon carbide (SiC) fibres in a chemical vapour infiltrated SiC matrix has been investigated using a 400 W pulsed Nd–YAG laser. The principal aim of this work has been to determine, by comparison with the results obtained from other ceramic matrix composites optimum processing conditions for these materials with regard to both material removal rate and cut surface quality. Previous trials involving a borosilicate glass matrix composite and a magnesium–alumino–silicate glass-ceramic matrix composite, both incorporating the same SiC fibres, have highlighted the importance of the coupling of the matrix phase with the emitted laser radiation. The various phase's resistance to oxidative degradation at high temperatures is another influential factor. The material considered in this work has been shown to be particularly suitable in these respects, with the result that both cut rate and quality are significantly enhanced. Report is made of the effect of varying the laser pulse parameters such as pulse energy, duration and intensity and concentrates on the material removal rate. Part II of this work addresses the influence of process variables, such as choice and pressure of assist gas and the point of focus of the laser beam on the quality of the cut surface. © 1998 Chapman & Hall

In situ environmental scanning electron microscopy studies of semi-macro indent cracks in borosilicate glass indicate that crack healing occurred at humidities as low as 8% relative humidity and at temperatures as low as about 400°C. The crack morphology changes observed in situ include slow crack regression (at low temperatures) and multiple crack pinch-off (at higher temperatures). Subsurface crack morphology changes were observed using conventional scanning electron microscopy of the fractured healed specimens. Subsurface healing included pinch-off into voids which appear quasi-circular in cross-section. In addition, crack debris were observed to hinder the crack healing process, which has important implications for fatigue of ceramic materials, where debris generation is frequently reported in the literature.

KMg2AlSi4O12 is a phyllosiloxide isostructural with phlogopite mica, but totally free of OH- ions. It decomposes at ≈ 950 °C at atmospheric pressure but remains stable up to at least 1350 °C under high pressures. Its chemical compatibility with α-alumina, MgAl2O4 spinel, forsterite, β-SiC and borosilicate glass selected as representative of fibres and matrices in ceramic matrix composites (CMCs), has been assessed via annealing experiments on multilayers and particulate composites at 900–1200 °C. At T = 900 °C and P = 100 MPa, the phyllosiloxide is chemically stable with respect to all the ceramics. At higher temperatures, interdiffusion occurs with the formation of various reaction products. At T = 1050 °C and P = 2 GPa, the extent of the reaction zone is larger for both α-alumina and forsterite than for spinel and β-SiC, whereas at 1200 °C, the reactivity of the phyllosiloxide with all the ceramics becomes about the same. Borosilicate glass with a softening point lower than the decomposition onset of KMg2AlSi4O12 at relatively low pressures seems to be an ideal model matrix material for assessing the potential of the phyllosiloxide as an interphase material in CMCs.

The objective of this study was to assess the applicability of an extrinsic carbon coating to tailor the interface in a unidirectional NicalonTM–borosilicate glass composite for maximum strength. Three unidirectional NicalonTM fibre-reinforced borosilicate glass composites were fabricated with different interfaces by using (1) uncoated (2) 25 nm thick carbon-coated and (3) 140 nm thick carbon coated Nicalon fibres. The tensile behaviours of the three systems differed significantly. Damage developments during tensile loading were recorded by a replica technique. Fibre–matrix interfacial frictional stresses were measured. A shear lag model was used to quantitatively relate the interfacial properties, damage and elastic modulus. Tensile specimen design was varied to obtain desirable failure mode. Tensile strengths of NicalonTM fibres in all three types of composites were measured by the fracture mirror method. Weibull analysis of the fibre strength data was performed. Fibre strength data obtained from the fracture mirror method were compared with strength data obtained by single fibre tensile testing of as-received fibres and fibres extracted from the composites. The fibre strength data were used in various composite strength models to predict strengths. Nicalon–borosilicate glass composites with ultimate tensile strength values as high as 585 MPa were produced using extrinsic carbon coatings on the fibres. Fibre strength measurements indicated fibre strength degradation during processing. Fracture mirror analysis gave higher fibre strengths than extracted single fibre tensile testing for all three types of composites. The fibre bundle model gave reasonable composite ultimate tensile strength predictions using fracture mirror based fibre strength data. Characterization and analysis suggest that the full reinforcing potential of the fibres was not realized and the composite strength can be further increased by optimizing the fibre coating thickness and processing parameters. The use of microcrack density measurements, indentation–frictional stress measurements and shear lag modelling have been demonstrated for assessing whether the full reinforcing and toughening potential of the fibres has been realized.

Nicalon fibres were coated with a sol–gel precursor of the KMg2AlSi4O12 phyllosiloxide, by dip-coating. However, both the 1 μm gel coating and the fibres were severely damaged during the phyllosiloxide crystallization under supercritical conditions (700 °C, 50 MPa, 48 h) in glycol monomethyl ether. A 3–5 μm thick coating of KMg2AlSi4O12 was successfully applied from a slurry on SiC chemical vapour deposited- or α-alumina single crystal-monofilaments, in which the phyllosiloxide platelets were oriented parallel to the fibre surface in a first approximation. Small one-dimensional model composites with a borosilicate matrix were prepared from these coated monofilaments, by hot pressing (900 °C, 30 MPa, 10 min). Evidence of fibre pull-out in bending failure tests suggesting a weak fibre matrix bonding, was observed. It is not known whether this weak bonding is related to the layered crystal structure or to the porosity of the phyllosiloxide interphase.

Fracture mechanisms of discontinuous carbon-fibre-reinforced glass matrix composites were experimentally studied for specimens with initial damage induced by thermal shock. First, matrix cracking due to thermal shock was observed using both optical microscopy and scanning acoustic microscopy (SAM) to reveal the damage state. Secondly, tensile stress-strain behaviour and acoustic emission during tensile tests were measured for specimens with and without thermal shock. The progress of microscopic damage during tensile loading was also investigated using both replica and in-situ SAM techniques. Finally, macroscopic transient thermal stresses during thermal shock were calculated using finite-element analysis. It is proved that the fracture process of the composite specimen with thermal-shock-induced cracks is different from that of the virgin specimen. This difference in fracture processes is attributed to the difference in the evolution of matrix cracking, which is affected by pre-existing microcracks in the matrix.

Coating of alumina onto the surface of hollow glass spheres was accomplished by controlled heterogeneous precipitation from aqueous solutions. The processing conditions were optimized to yield thin and uniform precursor coatings. After calcination, converting the precursor to alumina, the alumina-coated hollow glass spheres formed free-flowing powders that were used to produce glass/alumina composites with up to 35 vol% of controlled and well dispersed closed porosity. The dielectric constants and the flexural strengths of such porous composites were determined as a function of porosity.

Glass matrix-fibre and glass infiltrated ceramic composites with interconnected phases have been shown to have the potential for displaying optimum thermal conductivity and dielectric constant at 1 MHz making them useful as substrates for electronic packaging. Ceramic (Nicalon and silicon carbide grade (SCS)) fibre-borosilicate glass composites were fabricated using tape casting processes combined with pressure and pressureless sintering techniques. Experiments were also conducted to process AIN ceramics with interconnected porous channels which were then hot infiltrated with borosilicate glass. Results of optical characterization of the composites indicate that infiltration of Nicalon cloth with glass is achieved by hot pressing, while the tape casting and lamination approach followed by sintering is useful for fabricating composites of glass and Nicalon tows. The sintered aluminium nitride ceramics are comprised of ≈28% (volume fraction) interconnected pores. Hot infiltration yielded ≈100 μm penetration of borosilicate glass into the pores of the nitride ceramic. The paper discusses the various scientific aspects involved in processing the glass-fibre and porous AIN composites containing 3-d interconnected pores. Results of the microstructural characterization of these composites are discussed particularly in regards to the desired microstructure essential for these composites to be useful as substrates in electronic packaging.