Effects of MgO/CaO on the structural, thermal and dielectric properties of aluminoborosilicate glasses

Glasses with compositions xMgO-(20?x)CaO-10Al₂O₃-20B₂O₃-50SiO₂ (x = 0, 5, 10, 15 and 20 mol%) were prepared by conventional melting method. X-ray photoelectron spectroscopy (XPS) results indicated that the proportion of non-bridging oxygen increased with increasing MgO content. Nuclear magnetic resonance spectra showed that the fraction of the four-coordinated boron ions N_4(B) and aluminum ions N_4(Al) decreased with increasing MgO/CaO. Thus, higher field strength cations were expected to weaken the glass network. However, the increase in the glass transition temperature (T_g) indicated that the magnesium ions strengthened the glass network. The decrease in dielectric constant ε_r and loss tanδ could be attributed to the increase in the rigidity of the glass network as the MgO content increased.     

Conversion of melt-derived microfibrous borate (13-93B3) and silicate (45S5) bioactive glass in a simulated body fluid

Microfibrous bioactive glasses are showing a considerable capacity to heal soft tissue wounds, but little information is available on the mechanism of healing. In the present study, the conversion of microfibrous borate bioactive glass (diameter = 0.2–5 μm) with the composition designated 13-93B3 (5.5 Na₂O, 11.1 K₂O, 4.6 MgO, 18.5 CaO, 3.7 P₂O₅, 56.6 B₂O₃ wt%) was evaluated in vitro as a function of immersion time in a simulated body fluid (SBF) at 37 °C using structural and chemical techniques. Silicate 45S5glass microfibers (45 SiO₂, 24.5 Na₂O, 24.5 CaO, 6 P₂O₅ wt%) were also studied for comparison. Microfibrous 13-93B3 glass degraded almost completely and converted to a calcium phosphate material within 7–14 days in SBF, whereas >85 % of the silica remained in the 45S5 microfibers, forming a silica gel phase. An amorphous calcium phosphate (ACP) product that formed on the 13-93B3 microfibers crystallized at a slower rate to hydroxyapatite (HA) when compared to the ACP that formed on the 45S5 fibers. For immersion times >3 days, the 13-93B3 fibers released a higher concentration of Ca into the SBF than the 45S5 fibers. The fast and more complete degradation, slow crystallization of the ACP product, and higher concentration of dissolved Ca in SBF could contribute to the capacity of the microfibrous borate 13-93B3 glass to heal soft tissue wounds.     

Strength degradation of glass fibers at high temperatures

This article presents an experimental investigation into the effects of temperature and heating time on the tensile strength and failure mechanisms of glass fibers. The loss in strength of two glass fiber types (E-glass and Advantex^®, a boron-free version of E-glass) was investigated at temperatures up to 650 °C and heating times up to 2 h. The tensile properties were measured by fiber bundle testing, and the maximum strength was found to be temperature and time dependent. The higher softening point of the Advantex^® fibers is reflected in superior high-temperature performance. A phenomenological model is presented for calculating the residual strength of glass fiber bundles as functions of temperature and time. The strength reduction mechanism was determined by single-fiber testing. Fracture mirror sizes on the E-glass fibers were related to the fiber strength after high-temperature treatment. Based on fracture mirror measurements, it was established that (1) the mirror constant of the glass, which reflects the network structure, does not change during heat treatment and (2) the strength degradation is a result of larger surface flaws present after heat treatment.     

Apatite bone cement reinforced with calcium silicate fibers

Several research efforts have been made in the attempt to reinforce calcium phosphate cements (CPCs) with polymeric and carbon fibers. Due to their low compatibility with the cement matrix, results were not satisfactory. In this context, calcium silicate fibers (CaSiO₃) may be an alternative material to overcome the main drawback of reinforced CPCs since, despite of their good mechanical properties, they may interact chemically with the CPC matrix. In this work CaSiO₃ fibers, with aspect ratio of 9.6, were synthesized by a reactive molten salt synthesis and used as reinforcement in apatite cement. 5 wt.% of reinforcement addition has increased the compressive strength of the CPC by 250 % (from 14.5 to 50.4 MPa) without preventing the cement to set. Ca and Si release in samples containing fibers could be explained by CaSiO₃ partial hydrolysis which leads to a quick increase in Ca concentration and in silica gel precipitation. The latter may be responsible for apatite precipitation in needle like form during cement setting reaction. The material developed presents potential properties to be employed in bone repair treatment.     

Synthesis and properties of multicomponent fluoride glasses containing phosphorus and arsenic

Several compositions from the (Al+Y+Gd)F₃(Ca+Sr+Ba)F₂Na(P or As)F₆ system have been melted. Cast specimens of 2–5 mm thickness have been obtained for characterization of properties such as the IR transmission, coefficient of thermal expansion, glass transition temperature, and chemical durability with respect to moisture attack. Additions of fluorides of phosphorus and arsenic enhance the glass formability; however, these also contribute to the oxygen contamination of the fluoride melt. Infrared absorption bands at 2170 and 1750 cm^?1 reveal the oxygen contamination related to phosphorus and arsenic, respectively. Incorporation of tetrafluoroethylene in the glass batch helps in reducing the oxygen related absorption bands. The synthesized glass compositions have glass transition temperatures above 400°C, thermal expansion in the range of 141 to 160 × 10^?7/°C, and exhibit good resistance to moisture attack.     

Boron-containing phenolic–siloxane hybrid polymers through facile click chemistry route

Realization of easily processable, tough phenolic functional polymer materials is of high demand for composite applications. Herein, we report the synthesis of boron-containing phenolic–siloxane hybrid polymers through a facile copper-catalysed azide–alkyne click chemistry (CuAAC) approach. For this, phenolic resoles incorporated with boron (PFB) was propargyl-derivatized and then bridged through triazole moieties using telechelic α, ω azidated polydimethylsiloxane (AZ-PDMS). The propargylated boronated PF (PFBPr) resins exhibited high heat of reaction during thermal cure due to the prevalence of multiple reactions. PFBPr-siloxane hybrid co-polymers exhibited glass transitions in the ranges – 100 to – 75 °C and at 25–35 °C corresponding to soft segment and hard segments. Pyrolysed PFBPr-siloxane products showed mixed phase heterogeneous systems of B and SiC. Introduction of boron and silicon improved the degree of graphitization and reduced the graphite crystallite size of the carbonization products. The pyrolysed compounds of silicon and boron formed during high temperature were conducive for creating a layer of void-free graphitic ordered carbon that improved with boron and silicon content, as revealed by SEM images.     

Structural and mechanical properties of zinc aluminoborate glasses with different content of aluminum oxide

The glass samples were prepared according to the following formula: (35 ? x) ZnO, 55B₂O₃, 10Li₂O, x Al₂O₃, where (x = 0.5; 1; 1.5; 2; 2.5; 3; 3.5; 4 mol%) by melt quenching method. Structural parameters such as density, molar volume, cation–anion bond length, and packing density were studied and were correlated to the structural changes. It is found that the density decreases and the molar volume increases with increasing Al₂O₃ content. FT-IR spectra were measured to investigate the glass structure of these samples and to confirm the formation of non bridging Al–O–B bond with the addition of Al₂O₃ content. The FT-IR spectra were deconvoluted using curves of Gaussian shape at approximately the same frequencies. The fraction of fourfold coordinated boron atom (N₄) was calculated from the deconvoluted data. The longitudinal and transverse ultrasonic wave velocities were measured using the pulse-echo technique. The longitudinal L, shear S, Young’s E and bulk B module were calculated from the measured velocity and density values of the prepared samples and were correlated with the structural changes and all reflects that addition of Al₂O₃ to present glasses results in de-polymerization of the glass network and formation of non-bridging oxygen (NBOs).     

Tin fluorophosphate nonwovens by melt state centrifugal Forcespinning

This report describes the direct melt processing of inorganic tin fluorophosphate (TFP) glass fibers with average diameters ranging from 2 to 4 µm via centrifugal Forcespinning. This was accomplished by using a TFP glass with low glass transition temperature (T _g) and the melt processing capability of Forcespinning. The thermal behavior of TFP glass fibers was investigated by differential scanning calorimetry and thermogravimetric analysis, while the compositional evolution of the fibers was studied using energy-dispersive spectrometry and Fourier-transform infrared spectroscopy. These fibers exhibited excellent thermal stability after thermal post-treatment at 300 °C. The T _g of the thermally treated fibers increased by 100 °C compared to the bulk material. The fibers were found to undergo dehydration and loss of fluorine during thermal treatment, resulting in a rigid and crosslinked glass network with enhanced thermal stability and increased T _g. The enhanced thermal stability demonstrated the potential of TFP fibers for high temperature catalysis and chemical filtration applications.     

Bioactivity potential of calcium alumino-silicate glasses and glass–ceramics containing nitrogen and fluorine

Calcium alumino-silicate glasses of general composition (in eq.%) 28Ca:57Si:15Al:[100 ? (x + y)]O:xN:yF (x = 0 or 20 and y = 0, 3 or 5) and their glass–ceramic counterparts were immersed in simulated body fluid (SBF) at 37 ± 0.5 °C for 28 days to assess their potential bioactivity. The glasses showed no Ca release or surface calcium phosphate deposition due to their high network connectivities (>2.55). The glass–ceramics all showed potential bioactivity, as the SBF became enriched in Ca and calcium phosphate deposits formed on their surfaces. This was a result of Ca release from crystalline phases (predominantly wollastonite in the case of CaSiAlOF glass–ceramics and gehlenite in the case of CaSiAlONF glass–ceramics). No aluminium was leached from the glass–ceramics into the SBF, due to its pH always exceeding 7.0.     

Sintering, densification and crystallization of Ca–Al–B–Si–O glass/Al2O3 composites for LTCC application

Ca–Al–B–Si–O glass/Al₂O₃ composites were prepared based on the borosilicate glass powders (D₅₀ = 2.84) and Al₂O₃ ceramic powders (D₅₀ = 3.26), and the sintering, densification, crystallization of samples were investigated. The shrinkage of sample starts to have a sharp increase at 600 °C. The shrinkage of sample starts to have a further rapid increase after the glass softening temperature of about 713 °C. Glass/Al₂O₃ composites can be sintered at 875 °C/15 min and exhibit better properties of a relative density of 98.4 %, a λ value of 2.89 W/mK, a ε _r value of 7.82 and a tan δ value of 5.3 × 10^?4. The interface between glass and Al₂O₃ grains and the interface between anorthite and glass phase depicts a good compatibility according to transmission electron microcopy test. It is the low sintering temperature, high density and good compatibility with Ag electrodes that, guarantee borosilicate glass/Al₂O₃ composites suitable for low temperature co-fired ceramic materials.     

Microstructural transitions and dielectric properties of boron-doped amorphous alumina thin film

Dielectric Al_2?x B _x O_Y thin films were deposited onto Pt (100)/Ti/SiO₂/Si substrates via sol–gel and spin-coating technology. The microstructural transition occurred at ~500 °C due to boron loading was confirmed by DSC and XRD. FTIR, ²⁷Al MAS NMR and XPS measurements were employed to investigate the microstructural transition caused by different boron concentrations. The results revealed that Al–O–B bonds and [AlO₄] tetrahedrons were produced resulting in the reinforcement of structure with relatively low boron concentrations. With the increase of boron concentration, [BO₃] chains and new surfaces crossing over the internal structure gradually produced and disrupted the structural stability. Meanwhile, hydroxyl groups were accumulated in the internal structure owing to the hydrophilic property of boron. According to the reinforced structure with low boron concentrations, the current density decreased and the breakdown strength was enhanced. Typically, the current density was decreased two orders of magnitude at 100 MV m^?1 and the breakdown strength of the 0.5 mol% B-doped alumina thin film was increased by 59% (from 293 to 465 MV m^?1) in comparison with that of the undoped alumina thin film, whereas the dielectric properties gradually become poor due to the weak structure with the increase of boron concentration. Moreover, the dielectric constant increased owing to hydroxyl groups when the boron doping increased. This work may provide a general strategy for enhancing dielectric properties of the alumina thin film.     

Nanoclays reinforced glass ionomer cements: dispersion and interaction of polymer grade (PG) montmorillonite with poly(acrylic acid)

Montmorillonite nanoclays (PGV and PGN) were dispersed in poly(acrylic acid) (PAA) for utilization as reinforcing filler in glass ionomer cements (GICs). Chemical and physical interaction of PAA and nanoclay (PGV and PGN) was studied. PAA–PGV and PAA–PGN solutions were prepared in different weight percent loadings of PGV and PGN nanoclay (0.5–8.0 wt%) via exfoliation-adsorption method. Characterization was carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fourier transform infrared (FTIR) spectroscopy. XRD results of PAA–PGN demonstrated that the interlayer space expanded from 12.83 to 16.03 Å indicating intercalation whereas the absence of the peak at d ₀₀₁ in PAA–PGV indicated exfoliation. XPS scans of PGV and PGN nanoclays depicted the main peak of O 1s photoelectron due to Si–O–M (M = Mg, Al, Fe) whereas, Si–O–Al linkages were identified by Si 2p or Si 2s and Al 2p or Al 2s peaks. The disappearance of the Na peak confirmed that PAA molecules exchanged sodium ions present on surface of silicate layers and significantly reduced the electrostatic van-der-Waals forces between silicate plates resulting in intercalation or exfoliation. FTIR spectra of PAA–nanoclay suspensions demonstrated the presence of a new peak at 1,019 cm^?1 associated with Si–O– stretching vibrations which increased with increasing nanoclays concentration. Information concerning the dispersion of nanoclay in PAA aqueous solutions, chemical reaction and increase interlayer space in montmorillonite nanoclay is particularly useful regarding dispersion and reinforcement of nanoclay in PAA.     

TiO<Subscript>2</Subscript> hybrid polypropylene/nickel coated glass fiber conductive composites for highly efficient electromagnetic interference shielding

A highly efficient electromagnetic interference shielding composite based on nickel coated glass fibers (NCGFs) and titanium dioxide (TiO₂) filled polypropylene (PP) is fabricated via the simple melt blending method. Superior shielding effectiveness of 44.5 dB can be achieved with only 1.12 vol% Ni and 0.8 vol% TiO₂ loadings owning to the well-formed conductive network and interfacial polarization effect of TiO₂. The conductive Ni layer coating on the surface of glass fibers constructs an efficient conductive network due to its interfacial distribution between GF and PP. This interconnected Ni network provides fast electron transport channels to absorb the electromagnetic waves. Meanwhile, TiO₂ dispersed among the network of NCGFs induces more interfacial polarization, and thus produces a synergistic effect to enhance the shielding effectiveness of composite. Such composite would be considered as a promising electromagnetic shielding material in aerospace and electronics.     

Thermal and structural characterization of erbium-doped borosilicate fibers with low silica content containing various amounts of P2O5 and Al2O3

We report results on the processing and characterization of different glass preforms and single core fibers within the SiO₂–Na₂O–B₂O₃–Er₂O₃–P₂O₅–Al₂O₃ system. Micro-Raman spectroscopy was used to identify post-draw structural modification. The differences in the micro-Raman spectra recorded on the preform and on the fiber glass were attributed to a change in the structure induced by the drawing process. Changes in the silicate network organization and small scale molecular orientation within the glass matrix are suspected to occur during the fiber drawing process. We found that the extent in the changes between the preform and fiber properties depend on the glass composition. The glass network of the Al-containing fiber is expected to be less sensitive to the drawing process than that of the fiber matrix as the network of this Al-containing fiber is formed by a larger number of Si-BO units in the network and neutral three-coordinated boron compared to the network of the fiber matrix. From the micro-Raman spectra, formation of small crystals is suspected to occur in the P-containing glasses during the fiber drawing process. The resulting fibers were found to have propagation losses at 1330 nm and Er³⁺ absorption between (7 ± 1) and (25 ± 1) dB/m and (36 ± 1) and (47 ± 1) dB/m, respectively, depending on the glass composition.     

Compositional effects in the dissolution of multicomponent silicate glasses in aqueous HF solutions

The dissolution rate of multicomponent silicate glasses in a 2.9m aqueous HF solution is investigated as a function of its composition. The glasses studied are composed of SiO₂, B₂O₃, Al₂O₃, CaO, MgO, ZnO, Na₂O and K₂O, covering the compositions of most of the technologically important glasses. Unlike many physical properties, no linear relations are observed between the composition of the glass and its dissolution rate. The dissolution rate of a multicomponent silicate glass is found to be largely determined by two factors: The degree of linkage or connectivity of the silicate network and the concentration of SiO₂ in the glass. It is proposed that the dissolution of the glasses is preceded by the leaching of alkali and alkaline earth components present in the glass, followed by the subsequent dissolution of the leached layer. Probably fluorine species will diffuse into the leached layer to enhance the dissolution rate. Analysis of the activation energy data indicates that in some corrosive glasses the leaching itself becomes rate determining.     

Surface modification of fiber reinforced polymer composites and their attachment to bone simulating material

The purpose of this study was to investigate the effect of fiber orientation of a fiber-reinforced composite (FRC) made of poly-methyl-methacrylate (PMMA) and E-glass to the surface fabrication process by solvent dissolution. Intention of the dissolution process was to expose the fibers and create a macroporous surface onto the FRC to enhance bone bonding of the material. The effect of dissolution and fiber direction to the bone bonding capability of the FRC material was also tested. Three groups of FRC specimens (n = 18/group) were made of PMMA and E-glass fiber reinforcement: (a) group with continuous fibers parallel to the surface of the specimen, (b) continuous fibers oriented perpendicularly to the surface, (c) randomly oriented short (discontinuous) fibers. Fourth specimen group (n = 18) made of plain PMMA served as controls. The specimens were subjected to a solvent treatment by tetrahydrofuran (THF) of either 5, 15 or 30 min of time (n = 6/time point), and the advancement of the dissolution (front) was measured. The solvent treatment also exposed the fibers and created a surface roughness on to the specimens. The solvent treated specimens were embedded into plaster of Paris to simulate bone bonding by mechanical locking and a pull-out test was undertaken to determine the strength of the attachment. All the FRC specimens dissolved as function of time, as the control group showed no marked dissolution during the study period. The specimens with fibers along the direction of long axis of specimen began to dissolve significantly faster than specimens in other groups, but the test specimens with randomly oriented short fibers showed the greatest depth of dissolution after 30 min. The pull-out test showed that the PMMA specimens with fibers were retained better by the plaster of Paris than specimens without fibers. However, direction of the fibers considerably influenced the force of attachment. The fiber reinforcement increases significantly the dissolution speed, and the orientation of the glass fibers has great effect on the dissolving depth of the polymer matrix of the composite, and thus on the exposure of fibers. The glass fibers exposed by the solvent treatment enhanced effectively the attachment of the specimen to the bone modeling material.     

Effect of microstructure on KCl corrosion attack of modified AISI 310 steel

Abstract

The effect of microstructure on KCl corrosion attack was studied using a specifically chosen modified AISI 310 austenitic steel in a 15% (v/v) H₂O (g) + 5%(v/v) O₂ (g) + N₂ (g) (balance) atmosphere at 600°C for 168 h. The material was a targeted choice as it allows investigation of different microstructures i.e. as-received (without sigma phase) and heat-treated (29% σ-phase per area) microstructures. The corrosion attack was studied with light optical, scanning electron and transmission electron microscopy as well as X-ray diffraction. The heat-treated sample showed a corrosion attack that was 5 times higher than the as-received sample. In the heat-treated sample, the σ-phase was selectively attacked. At the corrosion front, chlorine (but not potassium) was detected in the selectively attacked σ- phase but not in the unattacked adjacent matrix. Therefore, the corrosion attack was propagated by preferential σ-phase attack by chlorine species.     

Effect of microalloying with silicon on high temperature oxidation resistance of novel refractory high-entropy alloy Ta-Mo-Cr-Ti-Al

Abstract

The effect of 1 at.% Si addition to the refractory high-entropy alloy (HEA) Ta–Mo–Cr–Ti–Al on the high temperature oxidation resistance in air between 900 °C and 1100 °C was studied. Due to the formation of protective chromia-rich and alumina scales, the thermogravimetric curves for Ta–Mo–Cr–Ti–Al and Ta–Mo–Cr–Ti–Al–1Si showed small mass changes and low oxidation rates which are on the level of chromia-forming alloys. The oxide scales formed on both alloys at all temperatures are complex and consist of outermost TiO₂, intermediate Al₂O₃, and (Cr, Ta, Ti)-rich oxide at the interface oxide/substrate. The Si addition had a slightly detrimental effect on the oxidation resistance at all temperatures primarily as a result of increased internal corrosion attack observed in the Si-containing HEA. Large Laves phase particles distinctly found in the Si-containing alloy were identified to be responsible for the more rapid internal corrosion.     

Effect of the Pb–Te–B–O system glass frits in the front contact paste on the conversion efficiency of crystalline silicon solar cells

In the present paper, many monocrystal silicon (Si) solar cells are produced by screen printing a front contact paste prepared with crystalline silver particles, a series of glass frits with the different lead oxide (PbO) contents in Pb–Te–B–O system glass, and an organic medium. Under scanning electron microscopy, the selective etching of cells screen-printed by pastes containing the glass frits of different PbO contents from low to high (37.2–52.5 mol%) reveals the corrosion degree of antireflection coating and the growth of silver crystallite microstructures on Si substrate. When the PbO content is 42.7 mol% in glass frits, the silver crystallites of optimal size were formed to make the conversion efficiency of cells best. By comparing the cross-section microstructures of solar cells, the different transition temperatures (T_g = 283–546 °C) of glass frits are found to have a substantial impact on wetting behavior during the firing cycle. When the glass T_g is medium (T_g = 393 °C), the optimal glass layer will be obtained to derive photoelectrons smoothly.     

Effect of Iron Particle Size and Volume Fraction on the Magnetic Properties of Fe/Silicate Glass Soft Magnetic Composites

Fe/Silicate glass soft magnetic composites (SMC) were fabricated by powder metallurgy with 1000 MPa pressure at room temperature, and then annealed at 750 °C for 90 min. A continuous and discontinuous layer of iron oxygen compounds FeO and Fe₃O₄ exit at the interface. Very fine crystalline phases Na₁₂Ca₃Fe₂(Si₆O₁₈)₂ were formed in silicate glass. Crystallite formation introducing the CTE mismatch between Fe and silicate glass results in thermal stress. Therefore, the magnetic properties decrease. The particle size and volume fraction of iron powder are larger, DC magnetic properties are better, but the core loss is greater. For the Fe/ silicate glass composite, the hysteresis loss plays a leading role in iron.