Effect of CaF2, B2O3 and the CaO/SiO2 mass ratio on the viscosity and structure of B2O3-containing calcium-silicate-based melts

The relationship between the viscosity and structure of B₂O₃-containing calcium-silicate-based mold fluxes and the effects of fluidizers including CaF₂, CaO, and B₂O₃ on the viscosity and their correlation with the structural aspects were studied using a rheometer with Fourier transformation infrared and Raman spectroscopy. The viscosity decreased with increasing CaF₂ addition up to 28 wt% at a fixed CaO/SiO₂ ratio of 0.3, which was related to depolymerization. Furthermore, CaF₂ addition also affected the apparent activation energy for viscous flow, which decreased with increasing CaF₂ content to 105.1 from 151.1 kJ/mol. At higher C/S ratios, the viscosity decreased in the presence of greater Ca²⁺ and O²⁻ supplied from CaO, which subsequently increased the activation energy to 149.7 from 122.0 kJ/mol. With regard to the B₂O₃-melt, polymerization of the network structure was observed by comparing the B₂O₃-free to 4.4 wt% B₂O₃ content. However, the viscosity was relatively constant with increasing B₂O₃ addition. However, the viscosity decreased due to greater simplification of the network structure above 4.4 wt% B₂O₃. The break temperature decreased with greater B₂O₃ addition as the crystallization was inhibited. Furthermore, the apparent activation energy decreased as depolymerization of the network structures occurred above 4.4 wt% B₂O₃.     

Enhancing mechanism of improved slag resistance of Al2O3-spinel castables added with pre-synthesized (Al,Cr)2O3 micro-powder

In order to enhance the slag resistance of Al₂O₃-spinel castables, (Al,Cr)₂O₃ is added into Al₂O₃-spinel system as a pre-synthesized micro-powder. Firstly, (Al,Cr)₂O₃ micro-powder is synthesized by sintering under reduction conditions to prevent the formation of hexavalent chromium. The Al₂O₃-spinel castables are prepared using tabular alumina, fused spinel, α-Al₂O₃ micro-powder, calcium aluminate cement and (Al,Cr)₂O₃ micro-powder as the raw materials. The bulk density, porosity, mechanical properties, and slag resistance of the samples are tested. Afterward, the effects of (Al,Cr)₂O₃ micro-powder (0–3 wt%) on the slag resistance and microstructures of the Al₂O₃-spinel castables are assessed by X-ray diffraction (XRD) and energy-dispersive (SEM-EDS) analysis. The results show that the addition of (Al,Cr)₂O₃ micro-powder can could inhibit the deteriorating effects of Cr³⁺ on the mechanical properties of the samples. The microstructure results also shows that with the addition of the (Al,Cr)₂O₃ micro-powder, a secondary solid solution of Ca(Al,Cr)₁₂O₁₉ formed, causing the unit cell to become larger. In the slag erosion area, CA₆ crystals formed with network-like interwoven structures, high density, and greater thickness. These characteristics significantly reduce the erosion and permeability indices of the castables, and improve the slag erosion resistance of the material.     

Al2O3-SiC-C耐火材料抗CaO-SiO2-K2O渣侵蚀性能研究

研究了Al2O3-SiC-C耐火材料的抗CaO-SiO2-K2O渣侵蚀性能,以及添加Cr2O3对Al2O3-SiC-C材料抗渣侵蚀性能的影响.研究结果表明CaO-SiO2-K2O熔渣对Al2O3-SiC-C材料具有明显的侵蚀作用;在Al2O3-SiC-C材料中添加适量的Cr2O3可以有效地抑制CaO-SiO2-K2O熔渣向耐火材料内部的渗透,降低耐火材料的侵蚀速度.     

A glass in the CaO/MgO/Al2O3/SiO2 System for the rapid laser sealing of alumina

In the field of microelectronics housings made of corundum or sapphire are used, because they resist high mechanical stresses and can be used in extreme environments. For joining these components, sealing materials are necessary, which have a thermal expansion coefficient adapted to corundum or sapphire (8.2×10 ⁻⁶K⁻¹) and resist high temperature. This can be achieved by glass, which is crystallized during the joining process. However, the temperatures in conventional joining processes are not suitable for the encapsulation of temperature “sensitive components”. During a laser joining process only the joining zone is heated up for a short period of time and the components were not destroyed. For this process glasses from the system CaO/MgO/Al₂O₃/SiO₂ were chosen and analyzed with respect to their sintering and crystallization behavior. The glasses could be sintered and crystallized by using the laser joining process. The crystallized glasses have a thermal expansion coefficient between 8.1×10 ⁻⁶ K⁻¹ and 9.3×10⁻⁶ K⁻¹ and hence, show a good match for joining of corundum and sapphire.     

高铝粉煤灰加入量对Al2O3-SiC-C浇注料抗高炉渣性能的影响

以棕刚玉(w(Al_2O_3)≥95.00%,粒度8~1mm,≤1mm),SiC(w(SiC)≥90.00%,粒度≤0.088mm),铝酸盐水泥,α-Al_2O_3微粉,SiO_2微粉,高温沥青等为原料,研究了高铝粉煤灰加入量(质量分数,下同)分别为0、3%、6%、9%和12%时对Al_2O_3-SiC-C质浇注料物理性能和抗渣性能的影响。结果表明随着高铝粉煤灰加入量的增加并达到9%时,Al_2O_3-SiC-C质浇注料的线变化率略有增大,抗渣性能与未添加粉煤灰的浇注料的相当;当高铝粉煤灰添加量增加并达到12%时,试样的抗高炉渣侵蚀的能力开始较明显下降。     

Understanding the effect of nanoparticles TiO2, Al2O3 and SiO2 on damage mechanisms of a polymer composite

In this paper, nanoparticles obtained by Sol-gel method have been incorporated as a filler in glass fiber/polyester composite in order to improve the mechanical properties of the resulting material. This work covered on the characterization and the study of the polymer matrix with 5 wt.%nano TiO₂, 5 wt.%nano Al₂O₃, 5 wt.%nano SiO₂.The results obtained revealed that sol-gel powders with a spherical morphology have excellent thermal stability. Acoustic emission analysis was used to investigate the microscopic damage mechanisms and progression in glass fiber reinforced nanocomposites. Thus, acoustic emission from four modes of approval has been identified: matrix cracking, matrix/fiber decohesion, delamination and fiber breakage. This study shows the increase of mechanical performance and the decrease of damage modes of @Polyester. From the SEM images, the good dispersion of nanofillers, absence of agglomerates, the good affinity with the improving of the interface compatibility were presented.     

Synthesis,crystal structure,photoluminescence of Ba3Y2(BO3)4:Er3+ and thermal expansion of Ba3Y2(BO3)4

The Ba₃Y_2–xEr_x(BO₃)₄ (х = 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were obtained by crystallization from a melt. The Ba₃Y₂(BO₃)₄ crystal structure was refined from single crystal X-ray diffraction data to R = 0.037. Its anisotropic atomic displacement parameters for all atoms were refined for the first time. The borate crystallizes in the orthorhombic crystal system, space group Pnma with unit cell parameters a = 7.673(1), b = 16.44(1), c = 8.977(2) Å, V = 1132.3(3) ų, Z = 4. These phosphors are isotypical to those of the A₃M₂(BO₃)₄ (A = Ca, Sr, Ba, M = Ln, Y, Bi) family. The crystal structure contains the isolated BO₃ triangles, two general and a special one independent crystallographic sites for large cations, which are disordered over sites. Thermal behavior of Ba₃Y₂(BO₃)₄ was investigated by high-temperature X-ray powder diffraction and thermal expansion coefficients are calculated in a wide temperature range. An inflections of temperature dependencies of the unit cell parameters is observed in a range 600–740 °C. Luminescence spectra, excitation and kinetic curves of the Ba₃Y₂(BO₃)₄:Er³⁺ series are reported. A maximum luminescence intensity is observed for the x = 0.1 sample. According to vibrational spectroscopy data no structural changes upon activation of the Ba₃Y₂(BO₃)₄ matrix with the Er ions are observed.     

Mechanical and dielectric properties of spark plasma sintered Si3N4/SiO2/Eu2O3 composite

In this work, effect of Eu₂O₃ (by 0, 3, 5, and 7 wt%) on mechanical and dielectric properties of Si₃N₄–SiO₂ composites (denoted by E0, E3, E5, E7) was studied. Samples were sintered by spark plasma at 1750 °C - 15 min by 100 °C/min heating rate and 40 MPa pressure under a vacuum atmosphere. The SEM micrographs confirmed the β-Si₃N₄ rod-shaped grains growth. The α to β phase transformation was completed in samples. The E5 and E7 samples have about 180.8 MPa flexural strength due to β-Si₃N₄ rod-shaped grains and increased grain aspect ratio compared to other samples. With the increase of Eu₂O₃ additive, due to an increase in grain size and β phase concentration the average dielectric constant and dielectric loss at 10 GHz frequency growth from 6.6 to 8 and from 0.125 to 0.160, respectively. High hardness values due to the dissolution, diffusion, and precipitation mechanism, and the α phase concentration was developed in these samples.     

Studies on surface tension of poly(vinyl alcohol): Effect of concentration,temperature, and addition of chaotropic agents

It is generally considered that the H‐bonds are responsible for the stabilization of network of PVA in water. The major types of intermolecular interactions from inorganic salts are responsible for the network of poly(vinyl alcohol) (PVA) and water, which ruptures the multiple H‐bonds between the ? OH groups of the polymer chains; therefore, various ions possessing abilities to affect these bonds result in salting out. It has been suggested that water molecules in the region of ionic hydration spheres must have strong orientation preferences, which could considerably restrict their ability to reorient and form hydration shells around nearby nonpolar solutes and thus affect the microstructure. In this article, our primary objective was to study the variation of surface tension, as it reflects the change in short‐range forces. Apart from this, we have also studied the surface tension behavior with the variation of concentration and temperature for different molecular weights of PVA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 122–130, 2004     

The effect of viscosity on surface tension measurements by the drop weight method

Viscosity is one of the parameters affecting the measured surface tension, as fluid mechanics affects the measurement process using conventional methods. Several methods including the selected planes (SPM) and WDSM which combines the weight drop method (WDM) and SPM, are applied to surface tension measurement of high viscous liquids. Yet, none of them treats the viscosity effect separately. The current publication presents a simple, easy to apply empirical approach of satisfactory accuracy, for evaluation of surface tension of liquids having wide range of viscosities up to 10 Pa s. The proposed method is based on Tate's law and the “drop weight” method using calibration curves of known liquids having similar surface tensions but different viscosities. Drop weight of liquids having viscosity ≥0.05 Pa s, was found to be significantly affected by the liquid viscosity. The shape factor, f, of high viscosity liquids was found to correlate linearly with the logarithm of viscosity, pointing the importance of viscosity correction. The experimental correlation presented in the current work can be used as a tool for the evaluation of surface tension for high viscosity liquids such as prepolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Mechanical behavior of 2.5D (shallow straight-joint) and 3D four-directional braided SiO2f/SiO2 composites

The effect of two different fiber architectures on the mechanical properties and mechanical behavior of the SiO_2f/SiO₂ composites processed by silicasol-infiltration-sintering has been investigated. The composites were sintered at relatively low temperature (450 °C). The fiber/matrix interface strength was weak. The characteristics of 2.5D (shallow straight-joint) structure and 3D four-directional braided structure were determined. The tensile strength, flexural strength, shear strength and failure mechanisms of both 2.5D (shallow straight-joint) and 3D four-directional braided SiO_2f/SiO₂ composites were characterized. It was found that the fiber placement in the preform will strongly affect the mechanical property and failure behavior of the composite. The results of the tests and microstructural observations indicated that 3D four-directional braided SiO_2f/SiO₂ composite had better mechanical properties than 2.5D (shallow straight-joint) SiO_2f/SiO₂ composite. 3D four-directional braided SiO_2f/SiO₂ composite exhibited more graceful failure under loading than 2.5D (shallow straight-joint) SiO_2f/SiO₂ composite.     

The effect of Sm2O3 on the microstructure and electrical properties of SiO2-doped SnO2-Zn2SnO4 ceramic varistors

In this work, Sm₂O₃- and SiO₂-codoped SnO₂-Zn₂SnO₄ ceramic varistors were prepared through traditional ceramic processing, and the effect of Sm₂O₃ on the resulting microstructure and electrical properties was investigated. The results demonstrated that the ceramics were composed mainly of SnO₂ and Zn₂SnO₄, and Sm was distributed homogeneously in the grains and along the grain boundaries. With 0.2 mol% Sm₂O₃ doping, the grain growth was obviously promoted. Further increases in Sm₂O₃ to 0.4 mol% resulted in trace amount of SiO₂ and segregations containing elemental Sm via X-ray diffraction patterns and microstructure photos, respectively. In the sample doped with 0.3 mol% Sm₂O₃, optimal electrical characteristics of α=9.4, E_B=10 V/mm, J_L=46 μA/cm² and ε′=1.2×10⁴ were obtained. Simultaneously, the sample doped with 0.3 mol% Sm₂O₃ had the lowest conductance activation energy of 0.16 eV at temperatures lower than 110 °C. This good performance indicates that Sm₂O₃- and SiO₂-codoped SnO₂-Zn₂SnO₄ composite ceramics are viable candidate for the manufacture of capacitor-varistor functional devices.     

Effects of Al2O3 addition on sintering behaviour,microstructure, and physical properties of Al2O3/vitrified bond CBN composite

The effects of Al₂O₃ content on the sintering behaviour, microstructure, and physical properties of Al₂O₃/vitrified bonds (SiO₂–Al₂O₃–B₂O₃–BaO–Na₂O–Li₂O–ZnO–MgO) and Al₂O₃/vitrified bond cubic boron nitride (CBN) composites were systematically investigated using X-ray diffraction, differential scanning calorimetry, dilatometry, scanning electron microscopy, and X-ray photoelectron spectroscopy. Various amounts of Al₂O₃ promoted the formation of BaAl₂Si₂O₈ and γ-LiAlSi₂O₆, increasing the relative crystallinity of the Al₂O₃/vitrified composite from 85.0 to 93.2%, resulting in residual compressive stress on BaAl₂Si₂O₈, thereby influencing the thermal behaviour and mechanical properties of the Al₂O₃/vitrified composite. The bulk density, porosity, flexural strength, hardness, and thermal conductivity of 57.5 wt% Al₂O₃ sintered at 950 °C were 3.12 g/cm³, 6.1%, 169 MPa, 90.5 HRC, and 4.17 W/(m·K), respectively. The coefficient of thermal expansion of the bonding material was 3.83 × 10^?6 °C^?1, which was comparable to that of CBN, and the number of N–Al bonds were increased, which boosted the flexural strength of the Al₂O₃/vitrified CBN composite to 81 MPa. The excellent mechanical properties, compact structure, and suitable interfacial bonding state with the CBN grains of the Al₂O₃/vitrified composite make it a promising high-performance bonding material for superhard abrasive tools.     

Composition dependent structure,dielectric and energy storage properties of Pb(Tm1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3 antiferroelectric ceramics

In order to stabilize the perovskite structure and improve the storage energy density (U) of Pb(Tm_1/2Nb_1/2)O₃ (PTmN) based materials, Pb(Mg_1/3Nb_2/3)O₃ (PMN) was introduced into PTmN to form binary (1-x)PTmN-xPMN solid solution ceramics. The XRD patterns show that all the compositions belong to orthorhombic phase with space group Pbnm. The Curie temperature (T_C) gradually decreases while the dielectric constant (ε') increases for (1-x)PTmN-xPMN with increasing PMN content. The ε' of each composition above T_C obeys the Curie-Weiss law. The appearance double hysteresis loop confirms the antiferroelectric nature of (1-x)PTmN-xPMN (x = 0.02–0.18) ceramics. With the increase of PMN concentration, the maximum polarization slowly increases from 8.58 μC/cm² to 29.5 μC/cm² while the threshold electric field (E_A-F) gradually declines from 290 kV/cm to 120 kV/cm. The maximum of U (3.12 J/cm³) is obtained in 0.92PTmN-0.08PMN ceramic with moderate E_A-F = 220 kV/cm, which makes (1-x)PTmN-xPMN ceramics safe in practical application.     

Effects of Co3(PO4)2 coatings on LiNi0.8Co0.16Al0.04O2 cathodes during application of high current

The electrochemical properties of bare and Co₃(PO₄)₂-coated LiNi_0.8Co_0.16Al_0.04O₂ electrodes after high current damage testing were characterized. Damage was induced by cycling with a high current density of 600 m Ag⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.16Al_0.04O₂ electrodes exhibit lower capacity loss and better charge retention than bare LiNi_0.8Co_0.16Al_0.04O₂ electrodes after damage testing. The discharge capacity reduction of bare and Co₃(PO₄)₂-coated electrodes after damage testing were ∼27 and 15%, respectively. The impedance of cells containing bare electrodes remarkably increased after high current cycling, which may be induced by damage to the electrode surface. However, damage was successfully suppressed by the Co₃(PO₄)₂ coating. Bare LiNi_0.8Co_0.16Al_0.04O₂ electrodes developed large amounts of cracks and other extended defects after high current cycling. In contrast, Co₃(PO₄)₂-coated electrodes maintained stable features after high current cycling, indicating the coating layer effectively protected the surface of the LiNi_0.8Co_0.16Al_0.04O₂ powder.     

Preparation and characterization of materials in the system xCuO-(50-x) CdO-50B2O3

New glassy materials in the system xCuO-(50-x) CdO–50B₂O₃ were prepared by a melting-quench technique. Their UV–vis, FTIR, electrical, dielectric, SEM, XRD patterns and density properties were investigated. SEM and XRD studies confirmed their amorphous nature and the presence of crystalline phases in the sample with 50 mol% CuO. Replacing CdO with increasing concentrations of CuO decreased the density and increased the molar volume. Optical reflectance spectra revealed the presence of Cu²⁺ ions in octahedral coordination, as well as the presence of Cu¹⁺ and Cuº in the samples with greater than 30% CuO. FTIR measurements confirmed the conversion of BO₄ units to BO₃ units with increasing CuO contents. The conduction in the CuO-containing samples increased as the CdO was completely replaced by CuO. The CuO-containing samples exhibited a slight increase in the ɛʹ values with increasing temperature and a decrease with increasing frequency. The ɛʹ values gradually increase upon replacing CdO with up to 40 mol% CuO. An abrupt increase in ɛʹ was recorded for the sample with 50 mol% CuO, particularly at high temperature. The latter sample showed an εʹ value of 927at 100 Hz and 298 K. Prepared samples with high ɛʹ values are promising candidates for capacitor materials in electronic devices.     

二氧化硅对不饱和聚酯树脂浇铸体力学性能的影响

研究了SiO2对不饱和聚酯树脂（UPR）浇铸体拉伸性能的影响．用应变计电测法研究了SiO2填料对树脂浇铸体的拉伸变形特性和弹性模量的作用．运用变形功原理，对添加SiO2后材料的特性作了初步判断。结果表明：在所采取的实验条件下．填料SiO2的添加量对UPR的拉伸强度和弹性模量有显著的影响．其质量分数为8％时得到的强度比纯树脂试样提高了大约4．1％．但SiO2质量分数为8％时却是对应着材料的脆韧转变点。