Effect of sintering temperatures on properties of BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass/silica composites for CBGA package

BaO–B₂O₃–SiO₂–Al₂O₃ (BBSA) glass/silica composites synthesized by solid-state reaction method were developed for CBGA packages, and the effects of sintering temperature (900–950 °C) on the phase transformation, microstructure, thermal, mechanical and electrical properties were investigated. XRD results show that the major phases quartz and cristobalite, and the minor phase BaSi₂O₅ are detected in BBSA composites. Furthermore, it was found that the quartz phase transforms to cristobalite phase at 930–940 °C. The formation of cristobalite phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of BBSA composites. However, excessive cristobalite phase content would degrade the mechanical properties and the linearity of thermal expansion of the ceramics. BBSA composites sintered at 920 °C exhibited excellent properties: low dielectric constant and loss (ε_r = 6.2, tanδ = 10^?4 at 1 MHz), high bending strength (179 MPa), high CTE (12.19 ppm/°C) as well as superior linearity of the thermal expansion.     

Synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> nanocomposite powder by sucrose process

Nanocrystalline alumina–zirconia powders were prepared by a modified chemical route using sucrose, polyvinyl alcohol (PVA) and metal nitrates followed by a post calcination process. The process involved dehydration of Al³⁺–Zr⁴⁺ ions-sucrose–PVA solution to a highly viscous liquid which on decomposition process produced a black precursor material. The obtained precursor were then calcined at various temperatures: 1,050, 1,100, 1,150, 1,200 and 1,250 °C for different soaking times (1, 2, 4 h) in air. The formation of a nanocomposite composed of α-alumina (~20 nm) and tetragonal (t) zirconia (~19 nm) crystallites were confirmed for the sample calcined at 1,200 °C for 2 h, based on our XRD and TEM results. However, for the samples calcined below 1,150 °C the composite formed were composed of metastable alumina (γ, δ, θ) as well as t-zirconia phases. Interestingly, the zirconia phase retained its tetragonal structure for all the samples calcined above 1,050 °C. This is possibly related to the “size effect” and reduction of surface enthalpy of the zirconia crystallites surrounded by Al³⁺ cations.     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

Wear and friction of Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites at various sliding speeds

The present study addresses the dry wear behavior of Al₂O₃ 6061 Aluminum particulate composite under different sliding speeds and applied load using pin-on-disk tribometer at room temperature. Three grades of the submicron particle composites containing 10, 20, and 30 vol.% Al₂O₃ were tested. The results illustrate that higher load and higher concentration of Al₂O₃ particles lead to higher wear rates. For 10 and 20% Al₂O₃ concentrations, the wear rate decreases with increasing sliding speed, while it increases for 30% Al₂O₃. The surface morphologies of the worn composites indicate that at lower sliding speeds abrasion is dominant, while at higher sliding speeds delamination and adhesion increases. Results also indicate that the friction coefficient between the composite and the mating steel surface decreases with increasing sliding speed to a steady state.     

Microstructure,interfaces and creep behaviour of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZrO<Subscript>2</Subscript>) eutectic ceramic composites

New compositions in the melt-grown eutectic ceramics field are investigated for thermomechanical applications. This paper is focused on the Al₂O₃–Sm₂O₃–(ZrO₂) system. The studied compositions give rise to interconnected microstructures without anisotropy along the growth direction. At variance with the binary eutectic Al₂O₃–SmAlO₃, the homogeneity of the microstructure of the Al₂O₃–SmAlO₃–ZrO₂ ternary eutectic is less sensitive to the growth rate. Interfaces between the alumina and perovskite phases are investigated by high-resolution transmission electron microscopy (TEM). They are semi-coherent. In stepped interfaces, the facets are parallel to dense planes of each phase. The steps have a dislocation character and may accommodate both misfits. The ternary eutectic displays a very good creep behaviour with strain rates very close to those obtained on other previously studied eutectics in the Al₂O₃–RE₂O₃(RE = Y, Gd, Er)–ZrO₂ systems. The deformation micromechanisms are analysed by TEM in the three eutectic phases. After creep, dislocations are present in every phase. The activation of unusual slip systems (pyramidal slip in the alumina phase) shows that high local stresses can be reached. The presence of dislocation networks with low energy configurations is consistent with predominance of dislocation climb processes controlled by bulk diffusion.     

Synthesis and characterization of barium borosilicate glass–Al2O3 composites

Barium borosilicate glass with composition 30BaO–60B₂O₃–10SiO₂ glass was prepared by melt-quenching technique. Different weight % of crystalline Al₂O₃ was mixed with the glass powder and sintered at optimum temperature. The changes in the structure and thermal properties of the glass with alumina content were investigated by X-ray powder diffraction, FT-IR spectroscopy and differential thermal analysis. The variations in the coefficient of thermal expansion and dielectric properties with composition were also studied and correlated with the structural changes.     

Characterization of microstructure and properties of Al–Al<Subscript>3</Subscript>Zr–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

Aluminium-based metal matrix composite strengthened by in situ Al₂O₃ and Al₃Zr particles were synthesized by powder metallurgy route. Phase analysis by X-ray diffraction and scanning electron microscopy revealed that the reaction between Al and ZrO₂ produced Al₂O₃ and Al₃Zr phases in the sintered composites. The hardness of the composite is a strong function of sintering temperature as well as the volume fraction of reinforcements. The dry sliding wear test results clearly indicated that increasing the volume fraction of zirconia particles in the composite improved the wear resistance. Microcutting, ploughing, delamination and oxidation were the main mechanisms of wear.     

Synthesis and characterization of porous platelet-shaped α-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> with enhanced photocatalytic activity for 17α-ethynylestradiol

The porous platelet-shaped α-Bi₂O₃ photocatalyst was successfully synthesized by a novel hydrothermal–calcination method assisted with ethylenediamine and polyvinylpyrrolidone. The physical and chemical properties of α-Bi₂O₃ photocatalyst were characterized based on XRD, XPS, SEM, TEM, EDS, UV–Vis DRS, and PL techniques. The influence of preparation conditions on the formation of α-Bi₂O₃ photocatalyst was investigated, and the effect of catalyst dosage and pH value on the EE2 removal rate was also investigated. The synthesized porous platelet-shaped α-Bi₂O₃ photocatalyst exhibited excellent photocatalytic activity for 17α-ethynylestradiol (EE2), and 97.8% of EE2 was removed after 75 min of visible light irradiation using α-Bi₂O₃ as photocatalyst. The reaction rate constant over the porous platelet-shaped α-Bi₂O₃ photocatalyst was 11.6 and 11.4 times of that of traditional α-Bi₂O₃ and N-TiO₂, respectively. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. The porous platelet-shaped α-Bi₂O₃ was a stable and efficient photocatalyst, proving that it is a promising photocatalyst.     

Development and characterization of Al/MWCNT–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hybrid composite by accumulative roll bonding

A high-strength hybrid composite was produced by eco-friendly accumulative roll bonding (ARB) process. Multiwall carbon nanotubes and alumina layers as reinforcements were embedded in a matrix of aluminum 1100. The produced hybrid composite was evaluated for structural changes and mechanical properties. The structural micrographs showed that by increasing the rolling cycles, a more uniform distribution of the reinforcements is obtained. After ten cycles of ARB, the composite material reached strength of about 300% higher than that of the annealed aluminum 1100. The elongation of the composite material is decreased by adding reinforcements. However, at a constant value of reinforcements, the elongation slowly increased during sequential rollings. A shear ductile rupture type failure was responsible for fracture of tensile test specimens of both composite and monolithic specimens.     

The crystallographic orientation relationship between Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in the composite material Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al–Mg–Si alloy

The formation mechanism of spinels on Al₂O₃ particles in the Al₂O₃/Al–1.0 mass% Mg₂Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic orientation relationship. A thin sample of the Al₂O₃/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al₂O₃ and MgAl₂O₄, which was formed on the surface of Al₂O₃ particles, was discovered by the TEM technique as follows:

High-damping and high-rigidity composites of Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript>–MgTi<Subscript>2</Subscript>O<Subscript>5</Subscript> ceramics and acrylic resin

High-damping materials are widely used in engineering fields. In order to increase the precision of vibration control to different levels, high-damping materials with high-rigidity are required. This study attempts to develop a new high-damping high-rigidity material using ductile ceramics based on the Al₂TiO₅–MgTi₂O₅ system, which has many continuous microcracks along the grain boundaries. Ductile ceramics have high internal friction (Q ⁻¹ = 0.01–0.037), but very low rigidity (<10 GPa). The rigidity of Al₂TiO₅–MgTi₂O₅ ceramics was improved by combining them with a polymer such as acrylic resin. The Young’s modulus and internal friction of the composites of Al₂TiO₅–MgTi₂O₅ ceramics and acrylic resin are investigated. They show high-damping capacity (Q ⁻¹ = 0.03–0.04) with high rigidity (E = 50–60 GPa), and their properties depend on those of the polymer. Thus, the composites fabricated using the above method can serve as high-damping high-rigidity materials.     

Electrical properties of R<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass–ceramics for anodic bonding

Temperature and frequency dependence on electrical properties (dielectric constant, dielectric loss and conductivity) of Li₂O–Na₂O–K₂O–Al₂O₃–SiO₂(R₂O–Al₂O₃–SiO₂) system glass–ceramics used as anodic bonding materials were discussed. The results showed that the main crystal phase of glass–ceramics was lithium metasilicate (Li₂SiO₃). Compared with the parent glass, both the dielectric constant and dielectric loss of glass–ceramics decreased, the dielectric constant and dielectric loss increased gradually with the increasing of the test temperature from room temperature to 400 °C, Testing frequency (30–300 MHz) had very little influence on the dielectric properties of samples. The electrical conductivity of glass–ceramics showed a trend of first decrease and then increase with the increasing of temperature. The glass–ceramics which has a lower dielectric constant, dielectric loss and better stability under high frequency was obtained after an appropriate heat treatment; it could be used as anodic bonding materials under very high frequency.     

Synthesis and properties of nanocrystalline 90 wt % ZrO<Subscript>2</Subscript>〈Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, CeO<Subscript>2</Subscript>〉-10 wt % Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powder

Using hydrothermal treatment of coprecipitated hydroxides, we have prepared nanocrystalline ZrO₂-rich ZrO₂-Y₂O₃-CeO₂-Al₂O₃ powder. The effect of heat treatment on the properties of the powder has been studied in the temperature range 400–1300°C. The powder has been shown to have a metastable phase composition, which is attributable to structural and size factors and also to the fact that the ZrO₂ and Al₂O₃ crystallites inhibit the growth of each other. Sintering the powder under various conditions, we have obtained ceramics with fracture toughnesses from 6.4 to 16.8 MPa m^1/2.     

Synthesis of LaB<Subscript>6</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powders via ball milling-assisted annealing

In this study, LaB₆–Al₂O₃ nanocomposite powders were synthesized via ball milling-assisted annealing process starting from La₂O₃–B₂O₃–Al powder blends. High-energy ball milling was conducted at various durations (0, 3, 6 and 9 h). Then, the milled powders were annealed at 1200 °C for 3 h under Ar atmosphere in order to obtain LaB₆ and Al₂O₃ phases as reaction products. X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) and transmission electron microscopy (TEM) techniques were utilized to carry out microstructural characterization of the powders. No reaction between the reactants was observed in the XRD patterns of the milled powders, indicating that high-energy ball milling did not trigger any chemical reactions even after milling for 9 h. LaAlO₃ and LaBO₃ phases existed in the annealed powders which were milled for 0, 3 and 6 h. LaBO₃ phase was removed after HCl leaching. 9-h milled and annealed powders did not exhibit any undesired phases such as LaAlO₃ and LaBO₃ after leaching step, and pure nanocrystalline LaB₆–Al₂O₃ composite powders were successfully obtained. TEM analyses revealed that very fine LaB₆ particles (~?100 nm) were embedded in coarse Al₂O₃ (~?500 nm) particles.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.     

Synthesis and evolution of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanorods for enhanced visible-light-driven photocatalysis

Single-crystalline α-Fe₂O₃ nanorods were prepared by a simple and direct hydrothermal method in large quantities. The 1, 2-propanediamine played the role of shape-control agent for the formation of α-Fe₂O₃ nanorods. The characteristics and the evolution mechanism of α-Fe₂O₃ nanorods were investigated in detail. As reaction time prolonged, the hydrogen ions generated by the hydrolysis of Fe³⁺ could etch the surface of α-Fe₂O₃ nanorods and resulted in the eroded α-Fe₂O₃ nanorods formation. HRTEM results demonstrated that the eroded α-Fe₂O₃ nanorods have rough edges and corners which leading to higher photodegradation ability. Absorption spectra and photocurrent responses indicated that the eroded α-Fe₂O₃ nanorods have a narrow bandgap and higher photocurrent response, which were benefit for absorbing photons and inhibiting the recombination of photogenerated charges. It is expected that the etching of semiconductor materials is an effective way to design the photocatalysts with a high performance, and the α-Fe₂O₃ nanorods with high visible-light photocatalytic activity could find potential applications in the field of environmental management.     

In vitro dissolution behavior of SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass–ceramic system

Herein, we report the results of the in vitro dissolution tests, which were carried out by immersing the selected glass-ceramic samples in artificial saliva (AS) for various time periods of up to 42 days. In our experiments, the SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics with different crystal morphology and crystal content were used and a comparison is also made with the baseline glass samples (without any crystals). The bioactivity of the samples was probed by measuring the changes in pH, ionic conductivity and ionic concentration of AS following in vitro dissolution experiments. High resistance of the selected glass-ceramic samples against in vitro leaching has been demonstrated by minimal weight loss (<1%) and insignificant density change, even after 6 weeks of dissolution in artificial saliva. While XRD analysis reveals the change in surface texture of the crystalline phase, FT-IR analysis weakly indicated the Ca-P compound formation on the leached surface. The experimental measurements further indicate that the leaching of F(-), Mg(2+) ions from the sample surface commonly causes the change in the surface chemistry. Furthermore, the presence of (Ca, P, O)-rich mineralized deposits on the leached glass-ceramic surface as well as the decrease in Ca(2+) ion concentrations in the leaching solutions (compared to that in the initial AS solution) provide evidences of the moderate bioactive or mild biomineralisation behaviour of investigated glass-ceramics.     

Preparation and characterization of Li<Subscript>2</Subscript>O–CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> glasses as bioactive material

The aim of the present investigation was to study the role of Al₂O₃ in the Li₂O–CaO–P₂O₅–SiO₂ bioactive glass for improving the bioactivity and other physico-mechanical properties of glass. A comparative study on structural and physico-mechanical properties and bioactivity of glasses were reported. The structural properties of glasses were investigated by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and the bioactivity of the glasses was evaluated by in vitro test in simulated body fluid (SBF). Density, compressive strength, Vickers hardness and ultrasonic wave velocity of glass samples were measured to investigate physical and mechanical properties. Results indicated that partial molar replacement of Li₂O by Al₂O₃ resulted in a significant increase in mechanical properties of glasses. In vitro studies of samples in SBF had shown that the pH of the solution increased after immersion of samples during the initial stage and then after reaching maxima it decreased with the increase in the immersion time. In vitro test in SBF indicated that the addition of Al₂O₃ up to 1.5 mol% resulted in an increase in bioactivity where as further addition of Al₂O₃ caused a decrease in bioactivity of the samples. The biocompatibility of these bioactive glass samples was studied using human osteoblast (MG-63) cell lines. The results obtained suggested that Li₂O–CaO–Al₂O₃–P₂O₅–SiO₂-based bioactive glasses containing alumina would be potential materials for biomedical applications.     

Fabrication of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.