Al2O3 B2O3 SiO2 Research Articles

Study on the physics and dielectric property of K2O–B2O3–SiO2/Al2O3 glass + ceramic

Effects of different glass/ceramic weight ratio on the physics and dielectric properties of Al2O3–B2O3–SiO2 (ABS) glass/Al2O3 ceramic composites were investigated. The results show that when glass/ceramic = 50:50 (mass fraction), the composite had the excellent comprehensive properties. Then the lower softening temperature CaO–B2O3–SiO2 (CBS) glass was added to the ABS glass as sintering flux on this composite. When the CBS glass content was 2 wt%, the composites showed good properties: er = 4.98, tanδ = 3.59 × 10−3 (which was 10 % lower than sample without CBS glass), and the flexural strength was 154.77 MPa (which was 16.2 % higher than the sample without CBS glass).

Luminescence properties of Tb3+-doped borosilicate scintillating glass under UV excitation

Transparent Li2O–BaO–La2O3–Al2O3–B2O3–SiO2 glasses doped with Tb3+ ion were prepared by high temperature melting method. Luminescence properties of Tb3+-doped borosilicate glasses have been investigated by transmission, excitation, emission and luminescence decay measurements. The transmission spectrum shows the glass has good transmittance in the visible region. Under the 236nm UV excitation the intense green emission from 5D4 level is observed in Tb3+-doped borosilicate glass, comparable in intensity to the violet–blue emission starting from the 5D3 level. The green emission intensity of Tb3+ ion firstly increases and then decreases with the decreasing B2O3/SiO2 ratio in glass matrix. 5D4→7FJ (J=6, 5, 4 and 3) transitions of Tb3+ ion in borosilicate glass are greatly enhanced with increasing concentration of Tb3+ through the cross relaxation [Tb3+ (5D3)+Tb3+ (7F6)→Tb3+ (5D4)+Tb3+ (7F0)] between two Tb3+ ions. Luminescence decay time of 2.13ms is obtained for the emission transitions starting from 5D4 level in 2.5Li2O–20BaO–20La2O3–2.5Al2O3–20B2O3–35SiO2–0.5Tb4O7 glass. The results show that Tb3+-doped borosilicate glasses would be potential candidates for scintillating material for static X-ray imaging.

Application of BaO–CaO–Al2O3–B2O3–SiO2 glass–ceramic seals in large size planar IT-SOFC

BaO–CaO–Al2O3–B2O3–SiO2 (BCAS) glass–ceramics can be used as sealant for large size planar anode-supported solid oxide fuel cells (SOFCs). BCAS glass–ceramics after heat treatment for different times were characterized by means of thermal dilatometer, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the coefficients of thermal expansion (CTE) of BCAS glass–ceramics are 11.4×10−6K−1, 11.3×10−6K−1 and 11.2×10−6K−1 after heated at 750°C for 0h, 50h, and 100h, respectively. The CTE of BCAS matches that of YSZ, Ni–YSZ and the interconnection of SOFC. Needle-like barium silicate, barium calcium silicate and hexacelsian are crystallized in the BCAS glass after heat-treatment for above 50h at 750°C. The glass–ceramics green tape prepared by aqueous tape casting can be directly applied in sealing the cell of SOFCs with 10cm×10cm. The open circuit voltage (OCV) of the cell keeps 1.19V after running for 280h at 750°C and thermal cycling 10 times from 750°C to room temperature. The maximum power density is 0.42W/cm2 using pure H2 as fuel and air as oxidation gas. SEM images show no cracks or pores exist in the interface of BCAS glass–ceramics and the cell.

Long-term oxidation behavior of carbon/carbon composites with a SiC/B4C–B2O3–SiO2–Al2O3 coating at low and medium temperatures

To achieve the long-term oxidation protection of carbon/carbon composites at low and medium temperatures, a SiC/B4C–B2O3–SiO2–Al2O3 coating was applied on the composites. The coating exhibits a dual-layer structure with a dense SiC inner layer and B4C–B2O3–SiO2–Al2O3 multi-phase outer layer. The effects of Al2O3 contents and oxidation temperatures on the oxidation behavior of the coated C/C were investigated. The results shows that the coating with 7.7wt.% Al2O3 performs excellent self-healing ability and can protect the C/C composites with weight losses of less than 1% for 250h at 800°C and for 90h at 900°C and 1000°C.

An experimental study on K and Na incorporation in dravitic tourmaline and insight into the origin of diamondiferous tourmaline from the Kokchetav Massif, Kazakhstan

Tourmaline was synthesized in the system MgO–Al2O3–B2O3–SiO2–KCl–NaCl–H2O from an oxide mixture and excess fluid at 500–700 °C and 0.2–4.0 GPa to investigate the effect of pressure, temperature, and fluid composition on the relative incorporation of Na and K in dravitic tourmaline. Incorporation of K at the X-site increases with pressure, temperature, and KCl concentration; a maximum of 0.71 K pfu (leaving 0.29 X-vacant sites pfu) was incorporated into K-dravite synthesized at 4.0 GPa, 700 °C from a 4.78 m KCl, Na-free fluid. In contrast, Na incorporation depends predominately on fluid composition, rather than pressure or temperature; dravite with the highest Na content of 1.00 Na pfu was synthesized at 0.4 GPa and 700 °C from a 3.87 m NaCl and 1.08 m KCl fluid. All synthesized crystals are zoned, and the dominant solid solution in the Na- and K-bearing system is between magnesio-foitite [□(Mg2Al)Al6Si6O18(BO3)3(OH)3OH] and dravite [NaMg3Al6Si6O18(BO3)3(OH)3(OH)], with the dravitic component increasing with the concentration of Na in the fluid. In the K-bearing, Na-free system, the dominant solid solution is between magnesio-foitite and K-dravite [KMg3Al6Si6O18(BO3)3(OH)3(OH)], with the K-dravitic component increasing with pressure, temperature, and the concentration of K in the fluid. The unit-cell volume of tourmaline increases with K incorporation from 1555.1(3) to 1588.1(2) A3, reflecting the incorporation of the relatively large K+ ion. Comparison of our results to the compositional data for maruyamaite (K-dominant tourmaline) from the ultrahigh-pressure rocks of the Kokchetav Massif in Kazakhstan suggests that the latter was formed in a K-rich, Na-poor environment at ultrahigh-pressure conditions near the diamond-stability field.

Phase Equilibria of Fluoride‐Free Boracic Mould Flux for Steel Continuous Casting

Development of fluoride‐free mould flux is important for steel continuous casting. Properties of the mould flux depend on the flux crystallinity. This paper analyzes phase composition of fluxes containing B2O3, TiO2, Na2O, and MgO which can be feasible candidates to replace the fluorides. The phase equilibria of these fluoride‐free boracic mould fluxes were calculated using the thermochemical software FACTSage. In the process of crystallization of the CaOSiO2Al2O3B2O3Na2O flux with high CaO/SiO2, combeite (Na2,Ca)Na2CaSi3O9, Ca11B2Si4O22, and nepheline NaAlSiO4 were formed, which can substitute cuspidine in the fluoride‐containing fluxes. At high CaO/SiO2, adding MgO into CaOSiO2Al2O3B2O3Na2OTiO2 mould flux remarkably increased crystallization temperature by forming merwinite (Ca3MgSi2O8), decreasing the relative crystal phase contents of (Na2,Ca)Na2CaSi3O9 and Ca11B2Si4O22. The calculated data were in reasonable agreement with results of XRD and SEM/EDS analyses of selected boracic fluxes.

Joint strength of a solid oxide fuel cell glass–ceramic sealant with metallic interconnect in a reducing environment

Effects of reducing environment and thermal aging on the joint strength of a BaO–B2O3–Al2O3–SiO2 glass–ceramic sealant (GC-9) with a ferritic-stainless-steel interconnect (Crofer 22 H) for planar solid oxide fuel cells are investigated. A technique is developed for conducting mechanical tests at room temperature and 800 °C in H2-7 vol% H2O under shear and tensile loadings. Given an aged condition and loading mode, the joint strength at 800 °C is lower than that at room temperature in the given humidified hydrogen atmosphere. A thermal aging at 800 °C in H2-7 vol% H2O for 100 h or 1000 h enhances both shear and tensile joint strengths at room temperature but degrades them at 800 °C in the same reducing environment. Non-aged specimens show a comparable joint strength and fracture mode when tested in humidified hydrogen and in air under a given loading mode and testing temperature. The shear strength at 800 °C for joint specimens after a 1000-h thermal aging at 800 °C in air or humidified hydrogen is reduced by a similar extent of 19%, compared to the counterpart of non-aged joint specimens tested in the same oxidizing or reducing environment.

Effect of B2O3 on Structure and Properties of CaO–MgO–B2O3–Al2O3–SiO2 Glasses

xB2O3-(1 − x) (60SiO2–15Al2O3–15MgO–10CaO) glasses with various x around 5–30 mol% at the step of 5 mol% are prepared by the melting-quenching method at 1,450 °C for 3 h. The IR data indicate that replacing other components by B2O3 levels up the amount of [BO4] tetrahedron and boron-oxygen rings, forcing [AlO4] tetrahedron to drop gradually. The glass transition temperature (Tg), crystallization temperature (Tc) and thermal stability (∆T) rise when B2O3 is present in lower concentrations (≤20 mol%); accordingly the glass network enhances. However, further increase in concentration of B2O3 (>20 mol%) reduces the Tg, Tc and ∆T. We utilize temperature-gradient furnace to measure the G6 glass, while the re-melt sample and crystallized phase are observed from polarizing microscope destroying microstructure. As B2O3 content move up, falls in dielectric constant (er) and loss (tanδ) can be associated with drop of cations polarizability as well as concentration, along with glass network rigidity ascending.

CdSe nanocrystals ingrained dielectric nanocomposites: synthesis and photoluminescence properties

Cadmium selenide (CdSe) nanocrystals ingrained dielectric nanocomposites in a B2O3–SiO2–Al2O3–Na2O–K2O borosilicate glass system were synthesized by a single step in situ melt quenching technique. The sizes of the nanocrystals as well as the band gap of the nanocomposites were controlled by both concentration of CdSe and post thermal treatment duration. The nanocomposites were characterized by different instrumental techniques including detailed photoluminescence studies. The sizes of the CdSe nanocrystals were found to alter in the range 4–16 nm as estimated from the effective mass approximation model and optical absorption spectroscopy. However, the TEM analysis revealed the generation of two different size ranges, 3–4 and 23–45 nm, of the particles within the dielectric matrix. Selected area diffraction (SAED) and x-ray diffraction (XRD) patterns authenticate the formation of hexagonal nanostructures of CdSe. These nanocomposites were found to be capable of exhibiting strong visible red luminescence around 715 nm on excitation at 446 nm. This has originated from the electron–hole recombination of CdSe nanocrystal and defects or traps related transitions. The properties of these nanocomposites advocate their significant applications as semiconductor based luminescent materials.

The influence of glass composition on crystalline phase stability in glass-ceramic wasteforms

Zirconolite glass-ceramic wasteforms were prepared using a suite of Na2O–Al2O3–B2O3–SiO2 glass matrices with variable Al:B ratios. Zirconolite was the dominant crystalline phase only for the most alumina rich glass compositions. As the Al:B ratio decreased zirconolite was replaced by sphene, zircon and rutile. Thermodynamic data were used to calculate a silica activity in the glass melt below which zirconolite is the favoured crystalline phase. The concept of the crystalline reference state of glass melts is then utilised to provide a physical basis for why silica activity varies with the Al:B ratio.

Homogeneity of peraluminous SiO2–B2O3–Al2O3–Na2O–CaO–Nd2O3 glasses: Effect of neodymium content

Considering the interest of developing new glass matrices able to immobilize higher concentration of high level nuclear wastes than currently used nuclear borosilicate compositions, glasses containing high rare earth contents are of particular interest. This study focuses on a peraluminous aluminoborosilicate system SiO2–B2O3–Al2O3–Na2O–CaO–Nd2O3 defined by a peralkaline/peraluminous ratio RP=([Na2O]+[CaO])/([Na2O]+[CaO]+[Al2O3])<0.5. Samples with various contents of Nd2O3 from 0 to 10mol% were studied using DSC, XRD, SEM, TEM, STEM and EMPA methods. The glasses present a high thermal stability even after a slow cooling treatment from the melt. Only a slight mullite crystallization is detected for low Nd2O3 content (≤2.3mol%) and crystallization of a neodymium borosilicate crystalline phase combined to a phase separation occurred at high Nd2O3 content (≥8mol%). The solubility of neodymium in the presence of aluminum is demonstrated, with higher neodymium incorporation amounts than in peralkaline glasses.

Low temperature sintering and characteristics of K2O–B2O3–SiO2–Al2O3 glass/ceramic composites for LTCC applications

The K2O–B2O3–SiO2, K2O–B2O3–SiO2–2 %Al2O3, K2O–B2O3–SiO2–4 %Al2O3 glasses with different Al2O3 content were prepared. Different proportions (50, 55, 60, 65, 70 %) of the three glasses were respectively mixed with alumina ceramic-filler, then the mechanical and dielectric properties were investigated. The results showed K2O–B2O3–SiO2–2 %Al2O3 glass/alumina filler (glass:alumina = 60:40) had the excellent comprehensive properties, so further study was continued with part of alumina ceramic-filler replaced by the silica ceramic-filler on this composite. Then the X-ray diffraction analysis revealed that the alumina and silica fillers existed as the crystal phase, and the densification was seriously damaged when the silica content reached to three quarters of the fillers. With the increase of the silica-filler, the composites’ density and dielectric constant exhibited uniform decrease, but thermal expansion coefficient (TEC) uniformly increased. When the glass:alumina:silica was equal to 60:30:10, a best composite property was presented as a bulk density of 2.582 (g cm−1), a dielectric constant of 6.1 and a dielectric loss of 2 × 10−3 at 1 MHz, a flexural strength of 168 MPa, and a TEC of 8.62 × 10−6 °C−1.

Structural and compositional modification of a barium boroaluminosilicate glass surface by thermal poling

In addition to inducing second-order nonlinear properties, significant structural and compositional alteration can be imparted to glass surfaces during the process of thermal poling. In this work, we focus on how thermal poling affects a structurally complex, nominally alkali-free boroaluminosilicate display glass composition. We provide evidence for electrolysis of the glass network, characterized by the migration of both cations (Ba2+, Na+) and anions (O−, F−) towards opposing electrode interfaces. This process results in oxidation of the positively biased electrode and forms a network-former rich, modifier-depleted glass surface layer adjacent to the anodic interface. The modified glass layer thickness is qualitatively correlated to the oxidation resistance of the electrode material, while extrinsic ions such as H+/H3O+ at not found in the depletion layer to compensate for the migration of modifier cations out of the region. Rather, FTIR spectroscopy suggests a local restructuring of the B2O3–Al2O3–SiO2 network species to accommodate the charge imbalance created by the exodus of network-modifying cations, specifically the conversion of tetrahedral B(4) to trigonal B(3) as Ba or Na ions are removed from B-related sites in the parent network. The resultant poling-induced depletion layer exhibits enhanced hydrolytic resistance under acidic conditions, and the IR spectra are substantially unlike those produced by acid leaching the same glass.

Synthesis and characterization of chloroborosilicate glasses in the K2O–BaO–Al2O3–B2O3–SiO2–BaCl2 system

Generally borosilicate glasses are rarely used in photonic applications. Here we modified borosilicate glass by incorporating BaCl2 with a view to their application in the area of photonics. Chloroborosilicate glasses in the system with general composition (mol%) (100−x)(42SiO2–30B2O3–20BaO–4K2O–4Al2O3)–xBaCl2 (where x=0–30) were prepared by the melt quench technique. All the glasses were found to be X-ray amorphous and transparent. They were characterized by X-ray diffraction, infrared and UV–vis-NIR spectral analyses, differential scanning calorimetry, dilatometry, refractive index, dielectric constant measurements, etc. Their glass transition temperature (Tg), coefficient of thermal expansion (CTE), refractive index and dielectric constant have been found to vary in the ranges 614–641°C, 73–91×10−7K−1, 1.58–1.63 and 9.79–11.73 respectively. All the properties are found to be controlled by BaCl2 content. Their covalent character, metallization criterion and Abbe number were found to decrease with increasing BaCl2 content whereas the molar volume, average molar refraction and electronic polarizability increase with increasing BaCl2 content. The devitrified materials have been characterized by XRD which manifests the presence of BaCl2 nanocrystals of sizes 15–30nm. Thus these glasses have the potential to develop BaCl2 nanocrystal containing low phonon energy (~350cm−1) glass-ceramics and are promising for different photonic applications.

Fabrication and enhanced photoluminescence properties of Sm3+-doped ZnO–Al2O3–B2O3–SiO2 glass derived willemite glass–ceramic nanocomposites

The transparent willemite, Zn2SiO4 (ZS) glass–ceramic nanocomposites were prepared from melt-quench derived ZnO–Al2O3–B2O3–SiO2 (ZABS) precursor glass by an isothermal heat-treatment process. The generation of willemite crystal phase, size and morphology with increase in heat-treatment time was examined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 80–120nm. The decreased refractive index with increase in heat-treatment time attributed to partial replacement of ZnO4 units of willemite nanocrystals by AlO4 units and simultaneous generation of vacancies in the Zn-site. Fourier transform infrared (FTIR) reflection spectroscopy exhibits the structural evolution of willemite glass–ceramics. The photoluminescence spectra of Sm3+ ions exhibit emission transitions of 4G5/2→6HJ (J=5/2, 7/2, 9/2, 11/2) and its excitation spectra shows an intense absorption band at 402nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 14-fold with crystallization into willemite.

Effects of AlN on the thermal and mechanical properties of vitrified bond and vitrified CBN composites

The effects of AlN fillers on the thermal and mechanical properties of vitrified bond and vitrified cubic boron nitride (CBN) composites were systematically investigated. The basic vitrified bond (B2O3–Al2O3–SiO2–Li2O–Na2O–ZnO) and AlN fillers make up the vitrified bond, and then constitute the vitrified CBN composites consists together with CBN grains. When the adding amount of AlN rises from 0wt% to 8wt%, the thermal conductivity of the vitrified bond increases from 0.74W/mK to 1.44W/mK. 6wt% AlN-doped-vitrified bond presents the minimum coefficient of thermal expansion and bending strength of 66.35MPa. The substantial improvement of thermal conductivity may be attributed to the formation of thermal conductive path and new crystalline phase—α-tridymite in the vitrified bond. Microstructure characterization indicates that the main crack deflection and divergency are the primary strengthening mechanisms. Such vitrified CBN composites with good thermal conductivity and mechanical strength might be promising in grinding materials for reducing burn.

Study on structural, dielectric, thermal and chemical characteristics of aluminoborosilicate glasses doped by rare earth oxides

Glasses in SiO2–Al2O3–B2O3–RO system doped with different Re2O3 (Re = La, Ce, Nd and Sm) at 4·5 mol.-% were prepared by conventional melt quenching technique. Structural, thermal durability and dielectric properties were investigated by using differential thermal analysis, Fourier transform infrared spectroscopy and precision impedance analyser respectively. Chemical durability was evaluated by weight losses of samples after immersion in HCl solution for varying times. The results showed that with increasing ionic radius of Re3+ ions (La3+<Ce3+<Nd3+<Sm3+), it was found that the fraction of non-bridging oxides and BO3 units increased. Dielectric constant and loss of doped different Re2O3 glasses decreased with the increase in frequency ranging from 40 Hz to 1 MHz, and possessed the lowest values of dielectric properties of ϵr = 3·83, tan δ = 7·93×10−4. In addition, the results of acid resistance showed that doping Re2O3 could improve the chemical durability in the order of La2O3>Ce2O3>Nd2O3>Sm2O3.

Glassy Coatings for Single-Firing Production of Ceramic Facing Tile

Fritted glazes for single-firing ceramic facing tiles have been obtained in the system R2O–RO–Al2O3–B2O3–SiO2 (where R2O = Na2O, K2O; RO = CaO, ZnO, MgO, BaO). The high molar content of calcium oxide (12.5 – 17.5%) in the glaze glasses shifts the formation temperature of the coatings to high values (1060 – 1100°C) and ensures that the degassing process in the ceramic paste is matched with the fusing process in the glaze.

Tuning the interfacial reaction between CaO–SrO–Al2O3–B2O3–SiO2 sealing glass–ceramics and Cr-containing interconnect: Crystalline structure vs. glass structure

Abstract In this paper, Al 2 O 3 was added to CaO–SrO–B 2 O 3 –SiO 2 sealing system to tailor the structure of sealing glass–ceramics and glass–ceramics/metal interfacial reaction. The addition of alumina in glasses contributes to increasing fraction of bridging oxygen in silica tetrahedral as well as the change in boron environment from three-fold to four-fold (BO 4 → BO 3 ). The devitrification tendency of glasses also decreases with increasing Al 2 O 3 content. The condensed glass structure and increasing residual glass content play opposite roles on the interfacial reaction, consequently resulting in a maximum fraction of Cr 6+ in reaction couples between Cr 2 O 3 and glass containing 6 mole% Al 2 O 3 at 700 °C. In addition, the good bonding can be observed at the interface between Cr-containing interconnect (Crofer 22APU) and glass containing 4 mole% Al 2 O 3 , held at 700 °C for 100 h. The reported results support the suitability of the prepared glass–ceramics as sealing materials for SOFC applications.

Microstructure and Strength of Al2O3/Al2O3 Joints Bonded with ZnO–Al2O3–B2O3–SiO2 Glass–Ceramic

ZnO–Al2O3–B2O3–SiO2 (ZABS) glass powder was used as interlayer to join alumina ceramics. The effect of joining temperature on the microstructure and strength of joints was investigated. The results showed that the ZABS glass can react with alumina substrate to form a layer of ZnAl2O4 at Al2O3/glass interface. Bending test exhibited that low joining temperature (1150 °C) led to low joint strength due to the formation of pores in the interlayer, originated by high viscosity of the glass. High joining temperature (1250 °C) also resulted in low joint strength, because of large CTE (coefficient of thermal expansion) mismatch between amorphous interlayer and alumina substrate. Therefore, only when the joining temperature was appropriate (1200 °C), defect-free interface and high joint strength can be obtained. The optimum joint strength reached 285 MPa, which was the same as the base material strength.