Effect of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass addition on the microwave dielectric properties of BaO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The effect of ZnO-B₂O₃(ZB) glass addition on the sintering behavior, microstructures and microwave dielectric properties of BaO-Nd₂O₃-TiO₂-Bi₂O₃ (BNTB) system was investigated with the aid of X-ray diffraction, scanning electron microscopy and capacitance meter. It is found that the ZB glass addition, acting as a sintering aid, can effectively lower the sintering temperature of BNTB system to 850 °C. The dielectric constant of BNTB-ZB ceramics increases with the increase of soaking time and the value of dielectric loss decreased with increasing soak time. The optical dielectric properties at 1 GHz of ɛ=74, tan δ=4×10⁻⁴, and TCC=25 ppm/°c were obtained for the BNTB system doped with 25 wt% ZB glass sintered at 850 °C for 2 h, representing that the BNTB-ZB ceramics could be promising for multilayer low temperature co-fired ceramics applications.     

Influences of heat treatments on crystallization in SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-K<Subscript>2</Subscript>O-F glass-ceramics

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO2-Al2O3-MgO-K2O-F glass ceramics samples.The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques.The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 ℃ for 3 h.The phase separation can accelerate the precip...     

Preparation and properties of crystallizable Glass/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites for LTCC material

The investigated low temperature Co fired ceramics(LTCC) composite of 60wt% CaO-Al2O3-B2O3-SiO2 glass and 40wt% α-Al2O3 as a filler is a non-reactive system, which is a critical part of the low temperature Co fired ceramics process. Through a study on densification process, the phase transformation and microstructure can be revealed. Its composites typically consist of CaO-Al2O3-B2O3-SiO2 glass and α-Al2O3 powders of average particle size (D50=3.49 mm). The sintering behavior, phase evaluation, sintered morphology, and microwave dielectric properties were investigated. In the fire range of 800 to 900 ℃, the composites were crystallized after completion of densification. It is found that the composites start to densify at 825 ℃, simultaneously, the dielectric constant (εr) reaches its maximum. With increasing heat-treatment temperatures, due to the loose microstructure of the material, tanδ increases slightly. The last of the sintered samples were identified as partly Anorthite at 850 ℃. At that temperature it has εr of 7.9 and tanδ less than 1×10-3, and can be used as a promising LTCC material.     

Effect of temperature on polishing and flatting time of float-formed Li<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass

Li₂O-Al₂O₃-SiO₂ glass prepared from traditional melting and cooling process was investigated. The surface characteristic of LAS glass was studied by simulating tin bath with different temperature and time, and the effect of surface tension/viscosity ratio on flatting time was analyzed. The results demonstrated that LAS glass can polish effectively when polishing at 1 300 for 8 °C min, and the optimum flatting and polishing temperature was 1 250–1 300 °C.     

Preparation and optical properties of Er<Superscript>3+</Superscript>: Na<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> transparent glass-ceramics

Na₂O-Al₂O₃-SiO₂ glass-ceramics doped with Er³⁺ ions were synthesized by the conventional melt quenching technique at a low melting temperature. The samples were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis-NIR scanning spectrophotometry, and fluorescence spectrometry. The results show that the main crystalline phase of glass-ceramics is nepheline.The best heat-treatment process is at 520 °C for 2 h. Because the up-conversion luminescence and near infrared luminescence properties of glass doped with Eu³⁺ are studied in detail.     

Effect of nucleating agents and heat treatments on the crystallization of magnesium aluminosilicate transparent glass-ceramics

The crystallization behavior and transparent property of MgO-Al2O3-SiO2 (MAS) glasses with TiO2 and TiO2+ZrO2 as nucleating agents were discussed by differential thermal analysis, X-ray diffraction, field emission-environment scanning electron microscope, energy dispersive spectrum and UV-VIS-NIR scanning spectrophotometer. It was found that the glass crystallized at 950 ℃ with ZrO2 less than 3% could obtain transparent glass ceramic, which presented purple to colorless. With the nucleating agent additives (5% TiO2+3% ZrO2), the colorless transparent glass-ceramics with spinel as the main crystal phase could be prepared, and the transmittance reached about 80% . As the crystallized temperature increase to 1 000 ℃, besides spinel(MgAl2O4), sapphirine (Mg3.5Al9Si1.5O20) and ZrTiO4 precipitated from matrix glass, and the transmitance of glass-ceramic decreased.     

Preparation and characterization of nanocomposite MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

Nanocomposites MgFe₂O₄/SiO₂ were successfully synthesized by the sol-gel method in the presence of N, N-dimethylformamide (DMF). The formation of pure MgFe₂O₄ was confirmed by powder X-ray diffraction (XRD) and electron diffraction. The structural evolution of MgFe₂O₄ nanocrystals was followed by powder X-ray diffraction and IR absorption spectroscopy. The formation of spinel structure of MgFe₂O₄ started at 800 °C, and completed at 900 °C. The transmission electron microscopy (TEM) measurements suggest that the particle sizes increase with the increasing annealing temperature, and the mean particle sizes of the spherical samples annealed at 800 °C, 900 °C and 1 050 °C are ca. 3 nm, 8 nm and 11 nm, respectively. Magnetization measurements at room temperature and 78 K indicate superparamagnetic nature of these MgFe₂O₄ nanocrystals. Funded by the National Natural Science Foundation of China(No. 30771676), the Natural Science Foundation of Jiangsu Province (No. BK20081842), and the Foundation of Nanjing Bureau of Personal for the Returned Overseas Chinese Excellent Scholars     

Effect of aluminum addition on microstructure and properties of SiO<Subscript>2</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO vitrified bond

Influence of aluminum addition on the structures and properties of SiO₂-B₂O₃-Al₂O₃-CaO vitrified bond at low sintering temperature and high strength was discussed. FTIR and XRD analyses were used to characterize the structures of the basic vitrified bond with different contents of aluminum. The bending strength and the thermal expansion coefficients were also tested. Meanwhile, the microstructures of composite specimens at sintering temperature of 660 °C were observed by scanning electron microscope (SEM). The experimental results showed that the properties of vitrified bond with 1wt% aluminum were improved significantly, where the bending strength, Rockwell hardness, and thermal expansion coefficient of the vitrified bond reached 132 MPa, 63 HRB, and 6.73×10^-6 °C^-1, respectively.     

Effect of Electron Beam on the Structure and Crystallization Features of BaO-SrO-TiO2-SiO2 Glass

Glasses of BaO-SrO-TiO2-SiO2 after electronic radiation treatment of 50-1000 kgy were studied by means of IR spectra, DTA and visible light absorption method. The result shows that the glass structure is changed due to the formation of structue defect from oxygen vacancy and E‘color center, which resultsd in the crystallization process and new precursors, and decreasement of Tg temperature and crystallization peaks by 20 -50℃.     

Preparation and Performance of Si<Superscript>4+</Superscript>-doping Rod-shaped TiO<Subscript>2</Subscript> Powder by Nonhydrolytic Sol-gel Method

Titania (TiO₂) nanorod powder was prepared by nonhydrolytic sol-gel method using titanic chloride (TiCl₄) as titanium source, methylene dichloride (CH₂Cl₂) as solvent, absolute ethyl alcohol (CH₃CH₂OH) as oxygen donor. The effects of Si⁴⁺ doping on the TiO₂ nanocrystalline phase transformation temperature were systematically researched. The results showed that when the molar ratio of Ti⁴⁺ to Si⁴⁺ is 1 to1.3, TiO₂ prepared by calcination at 1100 °C for 1 hour exhibits rod shape and has good photocatalytic activity. Doping of Si⁴⁺ makes glass phase core-shell structure forming on the surface of anatase crystal particles, which can inhibit crystal phase transformation and raise the transformation temperature, making TiO₂ stable in anatase phase at 1200 °C.     

Microstructure and mechanical properties of TiB<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites

Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.     

Effects of nucleating additives on crystallization and properties of CaO-B2O3-SiO2 glass-ceramics

ZrO₂, TiO₂ and P₂O₅ were doped in CaO-B₂O₃-SiO₂ glass-ceramics as nucleating additives. Effects of different nucleating additives on the phase separation and crystalline behaviors were investigated by using gradient temperature furnace, DTA and XRD. Then, sintering process of the glass-ceramics was investigated by testing sintering shrinkage, dielectric constant and loss. The experimental results shows that the glass-ceramics doped with nucleating additives represents higher crystallization, with ZrO₂ as an exceptional effective dopant to promote the precipitation of wollastonite crystal. Finally, ZrO₂ containing glass-ceramics was chosen to study the influence of sintering temperature and soaking time with the help of X-ray diffraction analysis and density measurement. The glass-ceramics can be well consolidated at 850 °C for 10 min, with low dielectric constant (5.87) and loss (3.21 × 10⁻⁴), which is desirable for LTCC application.     

Effect of nucleating agent on the crystallization of tailings glass ceramics prepared by one-time sintering

Glass ceramics was made by the one-time sintering method using the main raw material of iron tailings. On the basis of quaternary system of CaO-MgO-Al₂O₃-SiO₂, using DTA, XRD and SEM, the effects of different nucleating agents and mixing amounts as well as heat treatment on the crystallization of tailings glass ceramics were studied. The experimental results show that, nucleating agent and heat treatment are two necessary conditions for one-time sintering preparation of tailings glass ceramics namely, only adding nucleating agent or experiencing heat treatment, the quaternary system can not crystallize. The composite nucleating agent consisting of Cr₂O₃ and TiO₂ can further lead to the crystallization of the CaO-MgO-Al₂O₃-SiO₂ quaternary system at the lower temperature, with the major phase of diopside. In the range of mass content, 0%–4%, crystal intensity and crystal content grow. But when mass content is more than 4%, the crystal size will become coarser and the crystal distribution will be less regular. Different heat treatment regimes do not change the composition of the crystalline major phase in the glass ceramics crystallization of CaO-MgO-Al₂O₃-SiO₂ system. In the range of 30–60 minutes, with the extension of nucleation and crystallization, crystallization degree enhanced, but if the holding time surpasses 60 minutes, the crystallization is worse. Funded by The National Key Technology R & D Program of China for the 11^th Five-Year Plan(2006BAJ04A04)     

High-temperature oxidation behavior of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl matrix composite in air

The oxidation behavior of Al₂O₃/TiAl in situ composites fabricated by hot-pressing technology was investigated at 900° in static air. The results indicate that the mass gains of the composites samples decrease gradually with increasing Nb₂O₅ content and the inert Al₂O₃ dispersoids effectively increase the oxidation resistance of the composites. The higher the Al₂O₃ dispersoids content, the more pronounced the effect. The primary oxidation precesses obey approximately the linear laws, and the cyclic oxidation precesses follow the parabolic laws. The oxidized sample containing Ti₂AlN and TiAl phases in the scales exhibits excellent oxidation resistance. The oxide scale formed after exposure at 900°C for 120 h is multiple-layered, consisting mainly of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner TiO₂+Al₂O₃ mixed layer. From the outer layer to the inner layer, TiO₂+Al₂O₃ mixed layer presents the transit of Al-rich oxide to Ti-rich oxide mixed layer. Near the substrate, cross-section micrograph shows a relatively loose layer, and micro- and macro-pores remain on this layer, which is a transition layer and transferres from Al₂O₃+TiO₂ scale to substrate. The thickness of oxide layer is about 20 μm. It is also found that continuous protective alumina scales can not be observed on the surface of oxidation scales. Ti ions diffuse outwardly to form the outer TiO₂ layer, while oxygen ions transport inwardly to form the inner TiO₂+Al₂O₃ mixed layer. Under long-time intensive oxidation exposure, the internal Al₂O₃ scale has a good adhesiveness with the outer TiO₂ scale. No obvious spallation of the oxide scales occurs. The increased oxidation resistance by the presence of in situ Al₂O₃ particulates is attributed to the enhanced alumina-forming tendency and thin and dense scale formation. Al₂O₃ particulates enhance the potential barrier of Ti ions from M/MO interface to O/MO interface, thereby the TiO₂ growth rate decreases, which is also beneficial to improve the oxidation resistance. Moreover, the multi-structure of the TiO₂+Al₂O₃ mixed layer decreases the indiffusion of oxygen ions and also avails to improve the high temperature oxidation resistance of the as-sintered composites. Supported by the Special Program for Education Bureau of Shaanxi Province, China (Grant No. 08JK240) and Scientific Research Startup Program for Introduced Talents of Shaanxi University of Technology, China (Grant No. SLGQD0751)     

Thermal stability of LiFePO<Subscript>4</Subscript>/C-LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> blended cathode materials

Safety is important to lithium ion battery materials. The thermal stability of LiFePO₄/C-LiMn₂O₄ blended cathode materials is characterized by using TG, XRD, and SEM etc. The results show that LiFePO₄/C-LiMn₂O₄ possesses a worse thermal stability than pure spinel LiMn₂O₄ and pure olivine LiFePO₄/C. When LiFePO₄/C-LiMn₂O₄ blended cathode materials are sintered at 500°C under Ar atmosphere, the sintered cathode materials emit O₂, and appear impurity phases (Li₃PO₄, Fe₂O₃, Mn₃O₄). It is deduced that some chemical reactions take place between different materials, which leads to a worse discharge specific capacity. LiFePO₄/C-LiMn₂O₄ blended cathode materials, therefore, need to be managed and controlled strictly for the sake of thermal stability and safety.     

Crystallization and luminescence properties of Sm<Superscript>3+</Superscript>-doped SrO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

The Sm³⁺-doped SrO-Al₂O₃-SiO₂ (SAS) glass-ceramics with excellent luminescence properties were prepared by batch melting and heat treatment. The crystallization behavior and luminescent properties of the glass-ceramics were investigated by DTA, XRD, SEM and luminescence spectroscopy. The results indicate that the crystal phase precipitated in this system is monocelsian (SrAl₂Si₂O₈) and with the increase of nucleation/crystallization temperature, the crystallite increases from 66 % to 79 %. The Sm³⁺-doped SAS glass-ceramics emit green, orange and red lights centered at 565, 605, 650 and 715 nm under the excitation of 475 nm blue light which can be assigned to the ⁴G_5/2→⁶ H _j/2 (j=5, 7, 9, 11) transitions of Sm³⁺, respectively. Besides, by increasing the crystallization temperature or the concentration of Sm³⁺, the emission lights of the samples located at 565, 605 and 650 nm are intensified significantly. The present results demonstrate that the Sm³⁺-doped SAS glass-ceramics are promising luminescence materials for white LED devices by fine controlling and combining of these three green, orange and red lights in appropriate proportion.     

Low-temperature sintering and microwave dielectric properties of Ba<Subscript>2</Subscript>Ti<Subscript>3</Subscript>Nb<Subscript>4</Subscript>O<Subscript>18</Subscript> ceramics

The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO (< 1 wt%) considerably facilitated the densification of Ba2Ti3Nb4O18 ceramics.Appropriate addition of H3BO3 (< 3.5 wt%) remarkably improved the microwave dielectric properties of ceramics.The addition of H3BO3 and CuO successfully reduced the sintering temperature of Ba2Ti3Nb4O18 ceramics from 1300 to 1050 ℃.B...     

Microstructures and mechanism of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composites fabricated by the reaction between SiO<Subscript>2</Subscript> and molten aluminum

Al₂ O₃/Al composite was fabricated by the reaction between SiO₂ and molten aluminum. The microstructures of the composite obtained under different reaction conditions were analyzed. The formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably by the reaction temperature, reaction time and the quantity of SiO₂. The morphologies of Al₂O₃ have different features, depending on the reaction temperature. The composite has equaxed Al₂O₃ grains when materials reacted below 1200°C, and the composite is composed of a large number of fine Al₂O₃ grains and aluninum. The composite has a frame-shaped Al₂O₃ microstructure at the reaction temperature of above 1250°C. CHENG Xiao-min: Born in 1964 Funded by the National Natural Science Foundation of China (No. 91522)     

Properties of Aluminosilicate Glasses Prepared by Red Mud with Various [Al<Subscript>2</Subscript>O<Subscript>3</Subscript>]/[CaO] Mass Ratios

By introducing other oxide materials (SiO₂, Al₂O₃, CaO) into the red mud, all materials were melted into aluminosilicate glasses. On the basis of 17.2Fe₂O₃-5.7CaO-18.2Al₂O₃-50SiO₂-5.9Na₂O-3TiO₂ system glasses, [Al₂O₃]/[CaO] mass ratio changed further. For each sample, the assignment of IR absorption bands for aluminosilicate glasses was investigated by Fourier transform infrared spectroscopy and the glasstransition temperature and high temperature molten state were studied by differential scanning calorimetry. According to X-Ray diffraction and differential scanning calorimetry, the behavior of crystallization was analyzed. The results show that the glass structures of three-dimensional network are depolymerized and the amount of non-bridging oxygens increases gradually with network modifier CaO replacing network intermediate Al₂O₃ when [Al₂O₃]/[CaO] ratio of aluminosilicate glass decreases from 4.05 to 0.66, resulting in decreasing density, melting temperature, crystallization peak temperature and glass-transition temperature. As [Al₂O₃]/[CaO] mass ratio decreases, the concentration of crystallized phase maghemite (γ-Fe₂O₃) will increase which provides the possibility for production of black glass-ceramic further.     

Microwave sintering of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript>-WC-Co cermets

Composite powders of nanocrystalline WC-10Co (15wt%),Y2O3 (8mol%) stabilized nanocrystalline ZrO2 (30wt%),industrial cobalt powder (4.5wt%) and submicron Al2O3 (55wt%) composite powders were fabricated by high-energy ball-milling process.The nanocomposite powders were consolidated by microwave sintering process at temperature ranged 1300℃-1550℃ for 15min,respectively.The optimum consolidation conditions,such as temperature,were researched during microwave sintering process.Vickers Hardness of the consolidated cermets was measured by using a Vickers indentation test,and density of specimens was also determined by Archimedes’ principle.Microwave sintering process could not only increase the density of Al2O3-ZrO2-WC-Co cermets and reduce the porosity,but also inhibit abnormal grain growth.