Papers by Keyword: Glass-Ceramic

Abstract: In this work, a new microwave dielectric material for LTCC applications, xAl₂O₃+ (1-x) BaO-Al₂O₃-B₂O₃-SiO₂-ZnO (x=0.3, 0.4, 0.5 and 0.6) glass-ceramics, was synthesized. The effect of Al₂O₃ on the microstructure, mechanical properties and electrical properties of BaO-Al₂O₃-ZnO-B₂O₃-SiO₂ glass-ceramics was studied in this paper. The crystallinity was studied by jade6.5 software using the whole pattern fitting method. The XRD analysis showed that the content of BaAl₂Si₂O₈ increased first and then decreased with the increase of Al₂O₃ content. It is found that the formation of phase BaAl₂Si₂O₈ contributes to strong bending strength. The xAl₂O₃+ (1-x) BaO-Al₂O₃-SiO₂-ZnO-B₂O₃ glass-ceramics sintered 2h at 920°C has the excellent microwave dielectric properties at x=0.4, ε_r=7.4, tanσ=1.49×10^-3 at 13.5GHz, τ_f=-42.67ppm/°C, flexural strength= 184MPa.

Abstract: Low temperature sintered MgO-Al₂O₃-SiO₂ glass-ceramic with high mechanical and low thermal expansion was prepared for package. The remarkable influence of B₂O₃ addition on the electrical, mechanical, and thermal properties was fully investigated. A small amount of B₂O₃ promoted the sintering process and improved the densification of MAS. The kinetics via Kissinger method indicated that an appropriate B₂O₃ content decreased the activation energy and helped the occurrence of crystallization. Due to the increase of crystallinity and indialite phase, B₂O₃ addition significantly enhanced flexural strength and Young’s modulus. MAS doped with 3wt% B₂O₃ can be sintered at 900 °C and obtained good properties: σ = 229 MPa, φ = 86 GPa, α = 1.66×10^-6 /°C, ε_r = 5.29, and tanδ = 5.9×10^-4.

Abstract: SrO-Al₂O₃ ceramics has prospective applications due to its photo-luminescence and persistent afterglow properties. Sr₃Al₂O₆-SrAl₂O₄ eutectic glass was prepared by using the aerodynamic levitator equipped with a CO₂ laser device. The prepared Sr₃Al₂O₆-SrAl₂O₄ eutectic glass beads were further heat-treated at temperature from 880°C to 980°C. The phase evolution, crystallization behavior, optical transmittance and mechanical properties of the annealed eutectic glass ceramics were investigated. The as-prepared glass is colorless and transparent over a wide range from ultraviolet to near-infrared region, and the average in-line transmittance is over 80% in the range of 260-3200nm. There were two crystal phases Sr₃Al₂O₆ and SrAl₂O₄ crystallized from the glass beads. With increasing heat-treatment temperature, the transparency of the samples decreased, and the hardness increased. The prepared Sr₃Al₂O₆-SrAl₂O₄ eutectic glass and glass ceramics may be a promising candidate for the development of photo-luminescence and persistent afterglow materials.

Abstract: Transparent glass ceramics containing Na_3.6Y_1.8(PO₄)₃ crystals were successfully synthesized using high temperature melting quenching and subsequent heat treatment of the precursor glass with a composition 15Na₂CO₃-3Y₂O₃-45SiO₂-31H₃BO₃- 5.4P₂O₅-0.6Sb₂O₃ (mol%). The impact of heat treatment is investigated in detail. The glass sample was tested by differential scanning calorimetry analysis to determine the heat treatment system. The ideal heat-treated condition is at 650°C for 2 h. The structure and morphology properties were systematically analyzed by recording X-ray diffraction patterns and scanning electron microscopy images, which indicate that Na_3.6Y_1.8(PO₄)₃ crystal were precipitated homogeneously among the glass matrix. The microstructural of precursor glass and glass ceramic were compared by analyzing FTIR spectra, indicating the formation of phosphate groups in glass ceramic. The refractive index of glass ceramics samples were measured. In the visible region, the transmittance of glass ceramics is up to 85%. Moreover, the relationship between the refractive index of the sample and the transmittance is discussed.

Abstract: Bioactive glass and glass-ceramics have a huge interest in biomedical application due to their high biocompatibility and bioactive property. In this study, macro porous glass-ceramic based on 51.26% SiO₂ - 36.56% CaO - 11.83% P₂O₅ and 42.11% SiO₂ - 18.42% CaO - 29.82% Na₂O - 9.65% P₂O₅ (in mol%) were prepared via sol-gel synthesis and powder sintering method. Sodium nitrate was used as the precursor for sodium oxide (Na₂O) composition in the sol-gel glass. Effect of sodium nitrate addition on the sintered glass (glass-ceramic) properties were studied. The stabilized gel-glasses obtained were compacted into pellets and sintered at 1000 °C for 3 hours. It was found that, Na-contained glass-ceramic (Na-GC) crystallized at 71.5% due to increase in sodium-related crystalline phases. Na-GC showed 72.98% of apparent porosity and densified at 27.02% with macro porous structure with pore sizes in the range of 22.4 μm to 302 μm. The macro porous structure of Na-GC was obtained due to the foaming effect occurred during sintering. Flux effect occurred during sintering also resulted in relatively high compressive strength of Na-GC at 21.53 MPa. The macro porous Na-GC also proved to be bioactive as apatite-like structures were deposited on its surface after immersed into SBF solution for 14 days. The prepared macro porous Na-GC has high potential to be used as a scaffold material in biomedical application due to combination of suitable macro-pore size range, bioactive and has sufficient mechanical strength.

Abstract: Currently, many researchers interested studying waste materials to recycle them or reuse them in new products. From the sustainable perspective development, it is necessary to implement new technologies to help reduce waste and thus minimize the environmental problems associated with disposal. In this study, the preparation of SiO₂-Na₂O-CaO-P₂O₅ (SNCP) glass-ceramic is composed of Soda Lime Silicate (SLS), Clam Shell (CS), Na₂CO₃ and P₂O₅ in the ratio of 50: 25: 20: 5 respectively. The waste materials that were used for fabricate glass-ceramic are SLS and CS. All the compounds were mixed to fabricate the SNCP glass-ceramic through solid state reaction. The samples were investigated through X-ray diffraction (XRD), field emission microscope (FESEM) and density measurement. The samples were sintered at temperature 550°C, 650°C, 750°C, 850°C until 950°C. The main phase obtained from XRD analysis is Sodium Calcium Silicate, Na₂CaSiO₄ with cubic crystal system at 550°C. The highest intensity phase of the diffraction peak is (220) and at the angle 33.7°. There was new peak presence at right side of the main phase Na₂CaSiO₄, which belong to Silicon Phosphate, SiP₂O₇ at 650°C and 750°C. When heat treatment increased at 850°C - 950°C, the main phase is Combeite, Na₄Ca₄(Si₆O₁₈) at diffraction peak (220) with rhombohedral crystal system which is assigned to high crystallization temperature (T_c). The density of samples increases at 550°C - 750°C and decreases when heat treatment 850°C - 950°C. Sample density decreases at heat treatment 850°C - 950°C due to increases of sample lattice parameter. FESEM analysis showed that the grain size and porosity increased when the heat treatment increased.

Abstract: Bone replacements for congenital defects, cancer resections, and traumas are typically performed using bone grafting. However, due to scarcity of the source material, synthetic materials for bone replacements are sometimes used instead. Unfortunately, the ability to engineer anatomically correct pieces of viable and functional human bone are difficult and time-consuming through conventional manufacturing methods. This paper proposes an alternative route which incorporates the use of AM technology for fabricating patient-specific implants. The implants were computer-aided design (CAD) from a stereolithography (STL) file of a mandible. AM method was combined with lost wax casting (LWC) technology to produce the customised A-W glass-ceramic implants. An initial study of sintered A-W was performed on cylindrical samples show on average 19.8% porous with on average 75% of the porosity being open and an average flexural strength of 82.6 MPa. The A-W scaffolds display a degree of macro-and micro porosity. The geometrical shape of the A-W implants shows a close resemblance to the required implant. Additive manufacturing assisted fabrication of A-W glass-ceramic provides a promising method for manufacturing customised medical implants.

Abstract: The composites have a great use in practical application. In common, the phases in composite have different relative dielectric constant and in order to reveal how the phases with different permittivity affect the composite’s dielectric properties, the experiments were carried out using inorganic and organic composite with different dielectric constant phases to make that clear. The barium niobate-based SiO₂ system glass–ceramic and fillers-epoxy resin composites were chosen, and the dielectric properties were tested to compare the difference of those composites. The results show that the existence of high dielectric constant phases in composites can improve the permittivity of composites and make the composites present ferroelectric properties, while the dielectric loss can also increased, and the difference in dielectric constant of the phases can decrease the dielectric breakdown strength.

Abstract: SiO₂, Al₂O₃, MgO, MgF₂, SrCO₃, CaCO₃, CaF₂ and P₂O₅ were used to prepare machinable glass-ceramic with 4 mol% of fluorapatite for restorative dental applications. XRD showed that the glass heat treated at 792°C (the first crystallization temperature+20°C) for 6 hours consisted of calcium-mica, fluorapatite, strontium apatite, anorthite, forsterite, fluorite and stishovite crystalline phases. The microstructures of the resultant glass-ceramic, observed by SEM, were found to exhibit plate-like mica crystals and many tabular particles embedded in the mica phases. The particles, determined by EDS, were rich in calcium. The three-point bending strength (158 MPa) closely matched that of nature tooth. Average Vickers hardness of the received glass-ceramic (2.6 GPa) was lower than that of natural tooth.

Abstract: The glass system of SiO₂-Al₂O₃-MgO-MgF₂-SrCO₃-CaCO₃-CaF₂-P₂O₅ was used to prepare machinable glass-ceramics for restorative dental applications. The aim of this study was to apply various heat treatments to produce mica-based glass-ceramics. Differential Thermal Analysis (DTA) was used to determine the optimal heat treatment conditions for nucleation and growth of the crystalline phases in the quenched glass. It was found that the optimum nucleation temperatures for the first and the second crystallization temperatures (T_p1 and T_p2) were 642°C and 635°C, respectively, and the optimum nucleation times were between 2 and 4 hours. X-Ray Diffraction (XRD) showed the phases developed were anorthite, calcium-mica, fluorapatite, strontium apatite, forsterite, fluorite and stishovite phases. The microstructures of glass-ceramics were observed by Scanning electron microscope (SEM), found to exhibit plate-like mica crystals with high interlocking and randomly oriented with a higher soaking temperature and prolongation of the soaking time for crystallization.