Fabrication of transparent silica glass by powder sintering

Transparent silica glasses were obtained by sintering a green compact (fabricated by slip-casting methods for high-purity silica glass powder) in diverse atmospheres. The relationships between sintering atmosphere and sintering temperature that result in transparent, sintered silica glass were shown. The results indicate that there are four forming phases for each sintering atmosphere and temperature: (1) nontransparent glass resulting from an overabundance of pores (2) crystal, such as cristobalite or β-quartz, (3) moganite, and (4) transparent glass. Optimum sintering temperature for fabricating transparent silica glass was above 1673 K in a high-vacuum (10⁻⁴ Pa: p(O₂)=10⁻¹⁴) atmosphere. We investigate the fabrication of transparent and hydroxyl-free silica glass by a powder-sintered method. After studying the effect of sintering schedule on residual [OH⁻] concentration for transparent, sintered silica glasses, we sintered a green compact prepared by silica powders with a mean particle size of 1.6 μm, first heating it to 1523 K for dehydration and then to 1873 K for densification. This typical fabricated condition resulted in a transparent, sintered silica glass with <1 ppm [OH⁻] concentration.     

Influence of sintering atmosphere on the microstructure and water durability of SnO–MgO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glass

Effects of sintering atmosphere (Ar, air, and O₂) on the sinterability and crystallization at 380–470 °C of 60SnO, 10MgO, 30P₂O₅ (mol%) glass powder, and the water durability of the sintered glass were investigated. Increasing the oxygen partial pressure (P_\textO2 ) (P_{{{\text{O}}_{2} }} ) in the sintering atmosphere enhanced the oxidation tendency of Sn²⁺ to Sn⁴⁺ near the surface region of the glass particles. Therefore, the glass viscosity was increased, resulting in the increase in both the temperature of densification and the temperature at which crystalline phases developed. Phase assemblage and the amounts of crystalline phases were also affected by P_\textO2 . P_{{{\text{O}}_{2} }} . The water durability of the sintered glasses is discussed in terms of the above microstructural parameters.     

Microstructure and dielectric properties of glass/Al2O3 composites with various low softening point borosilicate glasses

The effects of various low softening point borosilicate glasses on both the sintering behavior and dielectric properties of glass/Al₂O₃ composites were investigated by FTIR, DSC, XRD, SEM and EDS. Results show that the addition of alkali oxides and PbO can decrease the glass softening temperature. While, the addition of Al₂O₃ and more SiO₂ content in the glass can increase the continuity of glass network and further increase the glass softening temperature of samples. Glass with lower softening temperature has more time to flow to finish the densification of samples, and that can contribute to get better sintered composites. By contrast, CaO–PbO–B₂O₃–SiO₂–Na₂O–K₂O glass/Al₂O₃ composites sintered at 875?°C for 15?min exhibit better properties of a bulk density of 3.06?g/cm³, a porosity of 0.17?%, a λ value of 2.47?W/m?K, a ε _r value of 8.05 and a tan δ value of 8.8?×?10^?4 at 10?MHz.     

The effect of glass addition on the dielectric properties of barium strontium titanate

Ba_0.7Sr_0.3TiO₃ (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B₂O₃ lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10⁻³ and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.     

Sintering, crystallization, and properties of a low-viscosity SnO–MgO–P2O5 glass

A lead-free, low-viscosity SnO–MgO–P₂O₅ glass powder was fabricated. Sinterability, wetting, flowability, crystallization, and the resulting properties of the glass powder were investigated. It is shown that the powder compact can be fully densified above 362 °C and show good wet to the substrate above 417 °C. The properties (coefficient of thermal expansion and chemical durability) of the sintered glass depend on the sintering temperature and are discussed in terms of the development of crystalline phases during sintering.     

Dielectric Properties of Vitreous Silica with Various Hydroxyl Concentrations

We investigated the temperature dependence of the dielectric susceptibility of amorphous silica below 300 mK. The influence of glass matrix and hydroxyl concentration ( ^– >) was studied to investigate the suitability for thermometry. We obtained Suprasil samples with ^– > between 200 and 1000 ppm by annealing in vacuum. We also measured commercial Homosil glass. The sensitivity is proportional to ^– >, but saturation of the dielectric susceptibility occurs at the same temperature for all samples.     

TiO2氧空位形成的影响因素

为了研究TiO2氧空位形成的影响因素,用管式电阻炉在空气、Ar及不同温度下对TiO2烧结.采用扫描电子显微镜(SEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)对烧结TiO2样品的微观形貌、物相组成、元素及价态进行了表征,研究了烧结温度、烧结气氛和Ar+刻蚀对TiO2样品氧空位形成的影响.结果表明:相同气氛下,随着烧结温度的升高,TiO2氧空位浓度逐渐增大;相同温度下,惰性气氛有利于TiO2氧空位的产生;Ar+刻蚀有利于TiO2氧空位的形成.     

Effects of glass additions on the dielectric properties and energy storage performance of Pb0.97La0.02(Zr0.56Sn0.35Ti0.09)O3 antiferroelectric ceramics

In this work, CdO–Bi₂O₃–PbO–ZnO–Al₂O₃–B₂O₃–SiO₂ low softening point glass powders were prepared and employed as sintering aid to improve the dielectric breakdown strength and reduce the sintering temperature of Pb_0.97La_0.02(Zr_0.56Sn_0.35Ti_0.09)O₃ antiferroelectric ceramics. The effects of glass content and sintering temperature on the densification, microstructure, dielectric properties and energy storage performance of Pb_0.97La_0.02(Zr_0.56Sn_0.35Ti_0.09)O₃ antiferroelectric ceramics have been investigated. With inclusion of glass, sintered densities comparable to those obtained by conventional sintering are achieved at only 1,050 °C. The breakdown strength of glass-added samples was notably improved due to the reduction of the grain size. The antiferroelectric to ferroelectric switching field and the ferroelectric to antiferroelectric field both increased with increasing glass content. The dielectric constant and dielectric loss decreased gradually with increasing glass content. As a result, the highest recoverable energy density of 3.3 J/cm³ with an energy efficiency of 80 % was achieved in 4 wt% glass-added sample sintered at 1,130 °C.     

烧结温度对硼硅基质荧光玻璃发光性能影响

采用共烧结法制备了硼硅基质Ce: YAG荧光玻璃,研究了烧结温度在600℃~900℃范围内, Ce: YAG荧光玻璃的发光强度变化和色坐标漂移规律。结果表明, 随着烧结温度的升高, Ce: YAG荧光玻璃发光强度先增强后减弱, 700℃烧结时, 荧光玻璃获得最大发光强度; 超过850℃烧结时, 荧光玻璃无发光性能; 同时, 色坐标(x, y)发生漂移, 且比相同烧结温度的荧光粉漂移幅度大。通过X射线粉末衍射仪、差示扫描量热分析仪和X射线光电子能谱分析仪测试分析表明: 随着烧结温度升高, 荧光粉中的Ce³⁺被玻璃基质氧化成Ce⁴⁺, 玻璃液体腐蚀破坏了荧光粉YAG晶体结构, 降低了荧光玻璃的发光强度, 从而导致色坐标劣化漂移。     

Effects of F− on the optical and spectroscopic properties of Yb3+/Al3+-co-doped silica glass

Yb³⁺/Al³⁺-co-doped silica glasses with different F⁻ content were prepared in this work by sol–gel method combined with high temperature sintering. XRF, FTIR and XPS methods were used to confirm the presence of F⁻. The effects of F⁻ on the optical and spectroscopic properties of these glasses have been investigated. It is worth to notice that the F⁻/Si⁴⁺ mass ratio equal to 9% is a significant value showing a real change in the variation trends of numerous following parameters: refractive index, UV absorption edge, absorption and emission cross sections, scalar crystal-field N_J and fluorescent lifetimes. Furthermore, introduction of F⁻ can adjust the refractive index of Yb³⁺/Al³⁺-co-doped silica glass and it is useful for large mode area (LMA) fibers.     

Influence of sintering conditions on the electrical properties and the PTCR effect of the multilayer Ba1.005(Ti1?xNbx)O3 ceramics with Ni internal electrode

The effects of the Nb-dopant content and the sintering conditions on the electrical properties and the positive temperature coefficient of resistance (PTCR) effect of Ba_1.005(Ti_1?xNb_x)O₃ (BTN) ceramics were investigated, which were sintered at 1,070–1,220?°C for 0.5–6?h in a reducing atmosphere and then re-oxidized at 600–750?°C for 1?h. The results indicated that both the sintering temperature and sintering time affected the electrical properties and the PTCR effect of the multilayer BTN samples, whose room-temperature (RT) resistance first reduced and then increased as a function of the donor–doped concentration at all sintering temperature; moreover, the higher the sintering temperature was, the lower the critical dopant concentration. The BTN ceramics showed a remarkable PTCR effect, with a resistance jump greater by 3.3 orders of magnitude, along with a low RT resistance of 0.3?Ω at a low reoxidated temperature of 600?°C after sintering in a reducing atmosphere.     

Frequency up-conversion luminescence in Yb3+–Ho3+ co-doped PbxCd1−xF2 nano-crystals precipitated transparent oxyfluoride glass-ceramics

Oxyfluoride glasses were developed with composition 30SiO₂·15AlO_1.5·28PbF₂·22CdF₂·(4.9−x)GdF₃·0.1HoF₃·xYbF₃ (x=0, 0.1, 0.2, 0.5, 1, 2, 3, and 4) in mol%. Powder X-ray diffraction analysis revealed that the heat-treatments of the oxyfluoride glasses at the first crystallization temperature cause the precipitation of Yb³⁺–Ho³⁺ co-doped fluorite-type nano-crystals of about 17.8 nm in diameter in the glass matrix. These transparent glass-ceramics exhibited very strong green up-conversion luminescence due to the Ho³⁺: (⁵F₄, ⁵S₂)→⁵I₈ transition under 980 nm excitation. The intensity of the green up-conversion luminescence in the glass-ceramics was much stronger than that in the precursor oxyfluoride glass. The reasons for the highly efficient Ho³⁺ up-conversion luminescence in the oxyfluoride glass-ceramics are discussed.     

Effect of sintering atmosphere on the microstructure and dielectric properties of barium strontium titanate glass–ceramics

The sintering of barium strontium titanate glass–ceramics in nitrogen modified their dielectric properties significantly compared to the sintering in air. The experimental results demonstrate that the glass–ceramics sintered at low temperatures contain a major phase Ba₂TiSi₂O₈ (BTS), known as fresnoite. The fresnoite phase disappeared and the barium strontium titanate perovskite phase became the major phase when the sintering temperature was increased. In addition, the microstructure observation showed that both the proportion of crystal phase and the crystal size increase obviously with the increase of sintering temperature. Most importantly, impedance spectroscopy has been employed to study the electrical responses arising from the glass and the crystal phases in the glass–ceramics sintered at low temperatures and high temperatures. The magnitudes of impedance and modulus changed significantly for the glass–ceramics sintered at the two temperature ranges. The activation energy calculated from the complex impedance, complex modulus and dc conductivity suggests that the dielectric relaxation for the glass phase and the glass–crystal interface may be attributed to the motion of the dipole associated with oxygen vacancy. And for the barium strontium titanate perovskite glass–ceramics, the motion of the electrons from the second ionization of oxygen vacancies leads to dc electrical conduction. The mechanism for the giant dielectric properties of the glass–ceramics sintered at high temperatures in nitrogen is discussed.     

Zur Viskosität von Glasschmelzen und porösen Sintergläsern

Qn the viscosity of glass melts and porous sintered glasses Suspensions of solid phase particles in molten glasses modify their flow behavior and therefore their viscosity. This work deals with the dependence of the effective viscosity (η_eff) of isotropic suspensions on the concentration of the solid phase particles. Independently of the shape of the inclusions the values of the effective viscosities lie between upper [η_eff = η_L (1 ? C_D)^?14 ]and lower bounds [η_eff = η_L (1 ? C_D)^?3], where η_L is the viscosity of the molten glass and C_D is the volume fraction of solid inclusions. The lower bound is also valid for the effective viscosity of suspensions containing spherical inclusions. Pores present in a glass matrix affect its flow behavior and consequently its creep and sintering behavior. The effective viscosity of porous glasses (η_P) as a function of the volume fraction of pores, or porosity (P), also varies between and upper [η_P = η_M (1 ? P)^1.04] and a lower bound [η_P = η_M (1 ? P)¹⁴], where η_M is the viscosity of the nonporous glass matrix. For spherical porosity the equation is: Measured values for the viscosity of different suspensions as reported in the literature as well as own experimental data on two glass-solid systems are compared with the theoretical values predicted by these equations. In a similar way literature data for the viscosity of porous sintered glasses are compared with the respective equations. In all cases a fair agreement between experiment and theory was found in some cases the agreement was excellent. Therefore the presented equations constitute a reliable approach for the prediction of the viscosity of suspensions and porous sintered glasses and since they do not contain fitting parameters, they are of substantial practical relevance (for a comprehensive english treatment of the matter compare Glastechnische Berichte, Proc. Otto-Schott-Colloquium 1994).     

Er- and Nd-doped yttrium aluminosilicate glasses: Preparation and characterization

The undoped, and Nd-, Er-doped low silica high alumina yttrium aluminosilicate (YAS) glasses were prepared by flame synthesis in the form of transparent glass microbeads with diameters ranging from a few to several tens of micrometers. The silica content ranged between 5 and 20 mol.%. The prepared glass microbeads were characterized by optical microscopy, SEM XRD, FT-IR and UV–VIS–NIR spectroscopy. The glass forming ability of glasses, expressed in terms of the difference between the glass transition temperature, T_g, and the onset of crystallization, T_x, improved with increasing silica content. Doping of YAS15 glass with neodymium or erbium at the level of 1–5 mol.% leads to decrease of both the T_g and T_x. However, the glass forming ability was not affected. The UV–VIS–NIR reflectance spectra in the spectral range from 300 to 1800 nm shows characteristic absorptions, due to the optically active Nd³⁺ and Er³⁺ ions in the host glass.     

Synthesis and properties of bio-waste-based hydroxyapatite via hydrothermal process

In this study, a facile hydrothermal method is applied to produce hydroxyapatite (HA) particles using egg shells as calcium precursors and fruit waste extracts (banana peel) as biomolecular templates at 150 °C for a reaction time period of 12 hours (h) and 24 hours. The sintering of the green samples of hydroxyapatite were conducted at 1250 °C in air for 2 h. The results showed that pectin extracted from banana peel extracts assisted in regulating crystal growth to obtain homogeneous hydroxyapatite powder, with higher purity observed for 24 h hydrothermal reaction time. Fourier-transform infrared spectroscopy (FTIR) spectra revealed the presences of phosphate (PO₄³⁻) and hydroxyl (OH⁻) groups in the powders. A relative density of 89.6 % was achieved for sintered hydroxyapatite compacts produced via hydrothermal method for 24 h. The sintered body was characterized by having high Vickers hardness of 5.35 GPa and good fracture toughness of 1.23 MPa√m, suitable for biomedical application.     

Characteristics of powder and sintered bodies of hydrothermally synthesized Mn-Zn ferrites

To improve the sinterability of powders fabricated by the conventional mixed-oxides method, ultrafine Mn-Zn ferrite powders were hydrothermally synthesized from metal nitrates solution using ammonia as a precipitant. The R value (alkalinity) was introduced to adjust the amount of added OH^– in the reaction suspension. The characteristics of the powders synthesized at different hydrothermal conditions and the properties of the sintered bodies were investigated. The results show that the R value and hydrothermal time have a great effect on the compositions and phases of hydrothermally synthesized Mn-Zn ferrite powders. Powders synthesized from a starting suspension with a higher content of Zn ions (or lower content of Mn²⁺) may approach to a stable spinel structure with a lower Mn/Zn ratio as the hydrothermal time is longer. Factors affecting the position of the diffraction angle (2) of the spinel Mn-Zn ferrite (311) of powders may include both the compositions of spinel ferrite structure and crystallite sizes (or particle sizes) of powders. Some possible reasons were suggested to explain the dependence of composition and phase of hydrothermally synthesized Mn-Zn ferrite powders on the R value and hydrothermal time. The temperature that the green compact begins to shrink at increases with increasing R value, and ranges from 510°C (R = 2) to 650°C (R = 6). After being sintered at 950°C for 2 h in N₂ atmosphere, the relative sintered density of each specimen reaches a value of 94.5–99.8%.     

Broadband infrared fluorescence in Er-doped BaO–SiO2 glasses

Er³⁺-doped SiO₂ glasses with or without BaO were fabricated by containerless processing. Scanning electron microscope observations and the scan profiles of electron-probe microanalysis demonstrated that the Ba-silicate glass was homogeneous and no aggregation of Er³⁺ ions occurred. The infrared fluorescence at around 1.55 μm from Er³⁺ in the Ba-silicate glass excited by a 980-nm laser was broader and its lifetime was longer than that of the silica glass, indicating the difference in the local structures around Er³⁺ ions between the Ba-silicate and silica glasses; this was supported by Raman scattering measurements. These results demonstrated that the Ba-silicate-glass system might be a new candidate for a host glass for Er³⁺-doped fiber amplifiers.     

Slip casting and sintering of monodispersed TiO2 particles

Monodispersed TiO₂ particles were used to prepare a uniformly packed green compact with a high relative density by slip casting. A suspension consisting of monodispersed TiO₂ particles, solvent and binder was cast in the mould. The sintering behaviour of the green compact was investigated. The green compact could be sintered to a relative density of > 99% by treatment at 1050 °C for 120 min. The average grain size of the sintered body was 1.26 m without abnormal grain growth. The green sheet cast on a glass board could be densified with no grain growth. The experimentally obtained relation between densification rate and grain size indicated a volume diffusion mechanism according to Coble's equation.     

Manufacturing of pure and doped silica and multicomponent glasses from SiO2 nanoparticles by reactive electrophoretic deposition

Manufacturing of glasses by shaping of powders and sintering comprises several advantages, like near-shaping of complex structures. Furthermore, sintering to fully transparent glasses is typically obtained at temperatures significantly lower than via melt fabrication. Thus incorporation of functional dopants with lower decomposition stability becomes possible, significantly increasing the variety of possible doping materials and applications. However, nanosized particles with their significantly enhanced sintering activity have to be used for powder manufacturing of glasses to avoid crystallisation. Unfortunately, no suitable nanopowders with appropriate composition are commercially available, and the manufacturing techniques proposed so far are complicated and time-consuming, often resulting in inhomogeneous doping. In contrast, by means of the newly developed reactive electrophoretic deposition (EPD) fast shaping and doping of glasses in only one process step is possible, using pure nanosized fumed silica powders as starting material. Doping is achieved by electrophoretic co-deposition of the nanoparticles and functional ions, surrounding each particle homogeneously in the electrochemical double layer. Thus doping with anions as well with cations was possible, resulting in different colouration of the silica glass (blue or gold ruby), with the coefficient of absorption being a function of the ion concentration within the suspension. Furthermore, a decrease in sintering temperature was achieved by EPR with boric acid. Finally, co-doping with anions and cations resulted in the manufacturing of multicomponent glasses with a decrease in sintering temperature of 450 °C compared to pure silica OX50.