Ceramic molds suitable for rapid forming of CFRP composites via microwave irradiation

Carbon fiber reinforced plastic (CFRP) composites have been considered quite eminent structural materials. For more extensive applications, however, more rapid forming methods of the CFRP composites are required. As for CFRP composites with thermoplastic matrices, microwave heating and pressing with ceramic molds should be promising. In the present work, zirconia molds with varied thermal conductivity were employed to give a desired shape to the CFRP composites heated with microwave irradiation. Experimental results showed that use of the zirconia molds with smaller thermal conductivity results in shorter necessary time for the forming process. Mechanism of the notable change in the heating efficiency is discussed as well.     

Recent Advances in Mathematical Modeling of Flow and Heat Transfer Phenomena in Glass Furnaces

This paper reviews significant advances in the mathematical modeling of flow and heat transfer phenomena in glass furnaces during the period 1996–2000. It describes developments in both the fundamental/scientific and practical aspects of modeling. The topics reviewed include developments in (a) model formulation and modeling techniques, (b) postprocessing modeling of glass quality and environmental emissions, (c) measurement of thermodynamic and transport properties of melt relevant to modeling, and (d) incorporation of model-based knowledge into process control schemes. These developments are critically examined and assessed from an industrial perspective, and topics needing further research and development efforts are identified.     

Comparison of Microwave Hybrid and Conventional Heating of Preceramic Polymers to Form Silicon Carbide and Silicon Oxycarbide Ceramics

Six different preceramic polymers were pyrolyzed via conventional and microwave hybrid heating; these polymers provide a range of carbon content and local atomic coordination. The products were compared with each other using X-ray diffractometry and transmission electron microscopy. Nanocrystalline β-SiC was the principal crystal phase detected, and the amount and size of the nanocrystals increased as the processing temperature increased. Differences were observed in the amount and size of the β-SiC nanocrystals and the graphitization of residual carbon between the microwave hybrid heating and the conventional oven heating of polycarbosilanes. Conventional heating of a high-carbon polysiloxane in an oven (in flowing argon) produced a greater amount of β-SiC from carbothermal reduction at high temperature. Microwave hybrid heating led to better β-SiC nanocrystal development for polyureasilazane.     

Studies on Thermal Properties of Selected Aprotic and Protic Ionic Liquids

Abstract

We describe herein the thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) investigations of the thermal properties of selected room-temperature ionic liquids (RTILs). The dependence of the thermal properties on both cation and anion structures of RTILs was systematically studied. The ionic liquids (ILs) investigated here include 28 different imidazolium-based ILs, 22 ammonium-based ILs, and 16 amide-based ILs. In general, these three cation classes exhibit different thermal behaviors but follow a quite systematic trend as expected from the corresponding structural variation. The ILs with bromide as the conjugate anion have lower thermal stabilities than those with bis(trifluoromethane sulfonyl) imide or bis(perfluoroethyl sulfonyl) imide as the conjugate anion. The mass of TGA samples and scan rate were found to have a systematic effect on the decomposition temperature of ILs, highlighting the caution needed in reporting TGA results.     

Effect of Heating Rate on the Sintering Behavior and the Piezoelectric Properties of Lead Zirconate Titanate Ceramics

The effect of heating rate on the sintering behavior and the piezoelectric properties of lead zirconate titanate (PZT) ceramics was investigated. Two different types of PZT (pure and doped with Nb₂O₅) were sintered at 1150°C for 2 h with a wide range of heating rate (0.5°–100°C/min). The densification of pure PZT was improved significantly by increasing the heating rate. The improvement was attributed to the suppression of PbO volatilization and grain coarsening during heating. In contrast, the densification behavior of a PZT specimen doped with Nb₂O₅ was not much influenced by the heating rate. These densification behaviors affected the piezoelectric properties of the specimens. The piezoelectric properties of pure PZT were enhanced significantly by increasing the heating rate, while those of doped specimens were improved only moderately.     

己内酰胺类离子液体的热力学性质(英文)

A series of caprolactam ionic liquids(ILs) containing incorporated halide anions were synthesized.Their physical properties,such as melting points,heats of fusion and heat capacities,were measured by differential scanning calorimeter(DSC).The results indicate that these ionic liquids exhibit proper melting points,high value of heats of fusion,and satisfying heat capacities which are suitable for thermal energy storage applications.     

Thermodynamic Properties of Caprolactam Ionic Liquids

A series of caprolactam ionic liquids (ILs) containing incorporated halide anions were synthesized. Their physical properties, such as melting points, heats of fusion and heat capacities, were measured by differential scanning calorimeter (DSC). The results indicate that these ionic liquids exhibit proper melting points, high value of heats of fusion, and satisfying heat capacities which are suitable for thermal energy storage applications.     

Processes and kinetics of mass gain in archeological brick following drying and reheating

The mass gain behavior of archeological bricks was examined following drying (130°C)/reheating (500°C) and aging at a range of temperatures (25°C, 35°C, 45°C). For drying or reheating, samples exhibit a two‐stage mass gain behavior, the second stage, Stage 2, continuing indefinitely and better described by a t^1/n model (1/n=1/6‐1/2); a correlation between the 1/n value and the specific surface area/pore volume demonstrates diffusion mechanisms with some pore geometry/morphology dependence. Stage 2 is shown to have an Arrhenius temperature dependence with activation energies of similar orders of magnitude following both drying and reheating. Supported by thermogravimetric‐mass spectrometry (TG‐MS), Stage 2 is demonstrated as likely due to the recombination of chemisorbed water, previously removed, whereas following reheating due to two components, a chemisorbed component associated with drying and a component associated with rehydroxyls removed at higher temperatures during reheating. Differences between activation energies of chemisorption and rehydroxylation components support this. Evidence for a fundamental compositional relationship between these processes is presented by a strong linear relationship between the drying and reheating mass gain rates. Stage 1, following drying or reheating, is shown to be likely associated with physisorption processes alone.     

The Anisotropy of the Surface Tension of Polar Liquids: The Case of Liquid Crystals

The contact angle of the liquid crystal (LC) 4-phentyl, 4'-cyano biphenyl (5CB) on glass or polyethylene does not correspond to the value expected from its surface tension measured by the “du Nouy” method (29 × 10^-3 JM^-2). The value deduced from the Young-Dupre law is 40 × 10^-3 JM^-2.

Both these values have already been reported in the literature. Their apparent discrepancy is explained by the LC surface tension anisotropy. We show that 5CB as many other LCs orient perpendicular to the free surface but parallel to glass or polyethylene Thus both values of the surface tension correspond to two different molecular orientations.

The LC oriented perpendicularly has a surface tension of 29 × 10^-3 JM^-2 and 40 × 10^-3 JM when it lies parallel to the surface. We suggest that the anisotropy between the perpendicular and parallel state of LCs also exists between two perpendicular orientations. Furthermore, such anisotropy associated with any polar molecules explains the difference of the interfacial energy of similar polar or non polar (i.e., octanol-octane) compounds and water.     

The preparation of Yttrium Aluminosilicate (YAS) Glass Fiber with heavy doping of Tm3+ from Polycrystalline YAG ceramics

Yttrium aluminosilicate (YAS) glass core fibers with different doping concentration of Tm³⁺ were fabricated by a “Melt‐in‐Tube” method from YAG polycrystalline ceramics. The effect of Tm³⁺ concentration on the spectroscopy of YAG ceramics and laser performance of YAS fibers were discussed. A homemade linear all‐fiber laser based on the obtained 15% Tm³⁺‐doped YAS fiber shows an optimized slope efficiency of 12.8%. The YAS fibers have been proven to be practical to achieve extremely high Tm³⁺ doping concentration and are a promising option for the 2.0 μm laser.     

六烷基胍TADC含能离子液体的合成与表征

采用离子交换法合成了4种六烷基胍4,5-二氰基-1,2,3三唑([Cn-guan][TADC],n=3,4,5,6)含能离子液体,用红外光谱和核磁共振对结构进行了表征,测试了其在常用有机溶剂中的溶解性,用表面界面张力仪和TG、DSC分别研究了其密度和热性能。结果表明,六烷基胍TADC离子盐在极性较大的有机溶剂中具有良好的溶解性,最大分解温度在370℃左右,表明[C3-6-guan][TADC]具有良好热稳定性,([Cn-guan][TADC],n=3,4,5)在DSC的二次升温过程中经历了玻璃态、过冷态、结晶固态和液态4种相态。     

高密度聚乙烯／木粉复合材料熔融性能及表面张力的研究

探讨了木粉及马来酸酐接枝聚乙烯(MAPE)对高密度聚乙烯(HDPE)/木粉复合材料熔融性能及表面张力的影响。结果表明:复合材料的起始熔融温度均略高于纯HDPE的,熔融峰的面积及形状介于纯木粉与纯HDPE之间,复合材料的表面张力及其极性组分均随木粉的质量分数逐渐增加。使用MAPE将提高复合材料熔融峰的面积,复合材料更难被熔化。质量分数为5%、10%的MAPE的复合材料的表面张力较低;而质量分数为15%及20%的MAPE的复合材料的表面张力与无MAPE的复合材料的基本相等。     

几种醇溶液表面张力的测定与分析

采用圆环法对不同浓度的甲醇溶液、乙醇溶液、正丙醇溶液、正丁醇溶液的表面张力进行测定,并通过对溶液密度、铂丝半径和铂丝环半径的修正,研究几种醇溶液表面张力与浓度及烷基链长的变化情况,从而分析醇溶液表面张力变化情况与溶度和烷基键长的关系。     

Metal Reference Line Technique for Obtaining Dihedral Angles from Surface Thermal Grooves

A metal reference line (MRL) technique is described for the measurement of surface–grain-boundary dihedral angles, Ψ_s, from thermal grooves at a sample surface using scanning electron microscopy (SEM). Metal lines deposited onto a thermally grooved surface using photolithography conform to the contours of the grain-boundary groove and provide a high-contrast reference line for measuring Ψ_s by SEM. Measurements of Ψ_s from optical interferometry and calculated from groove dimensions using surface diffusion models of thermal grooving are compared with the metal reference line measurements from the same thermally grooved surface of MgO-doped Al₂O₃. Distributions of Ψ_s are found to shift to lower angles and approach the true Ψ_s value as the resolution of the technique increases, with the MRL technique having the highest resolution, a median angle of 113°± 1° and a distribution of angles from 90°± 5° to 139°± 3°.     

Development of optical grade (TbxY1−x)3Al5O12 ceramics as Faraday rotator material

Super full dense (Tb_xY_1?x)₃Al₅O₁₂ (x=0.5‐1.0) ceramics with optical grade (pore‐free) were successfully produced by solid‐state reaction between Tb₄O₇ and Al₂O₃ raw powders. Transparent sintered bodies were obtained by sintering at 1720°C for 5 hours in vacuum furnace. By additional HIP treatment, optical scattering centers were effectively removed, and finally the optical quality of the sintered bodies was improved to optical grade. Optical loss of the obtained samples at 1064 nm was approximately 0.1%/cm, and optically inhomogeneous parts were not observed inside the materials. Gaussian mode laser beam quality was not deteriorated after passing through the sample. Transmitted wavefront distortion inspected by interferometry was as excellent as λ/12. Verdet constant increased with an increase of Tb content in the garnet composition. When x=1.0, the Verdet constant was 307, 196, and 60 rad T^?1 m^?1 for 532, 633, and 1064 nm, respectively, at each measuring wavelength. These values were about 1.5 times higher than that of the commercially available TGG (Tb₃Ga₃O₁₂) crystal. Insertion loss of the produced (Tb_0.6Y_0.4)₃Al₅O₁₂ and TAG ceramics at 1064 nm was 0.01 and 0.05 dB, respectively, and extinction ratio was 39.5 and 40.3 dB, respectively. These properties were superior to that of the commercial high‐quality TGG single crystal (insertion loss: 0.05 dB, extinction ratio: 35.0 dB).     

Surface Tension of Calcium Aluminosilicate Glass Using Computerized Drop Shape Analysis

Numerical analysis is used in this study to derive surface tension from the shape of a liquid silicate sessile drop. The speed afforded by the drop shape analysis package facilitates analysis of experimentally derived drop profiles. Drop symmetry, contact angles, and local shape variations can be readily determined, thereby permitting the detection of experimental errors. The experimental and analytical technique was first validated by determining the surface tension of high-purity gallium and aluminum under carefully controlled furnace atmospheres. Results for a calcium aluminosilicate melt are compared to pendant drop and maximum-bubble pressure measurements reported in the literature. The use of an internal scaling factor and the effect of substrate interactions are discussed.     

Fused silica contamination layer removal using magnetic field-assisted finishing

Fused silica optics used in lasing systems requires a high laser-induced damage resistance. Processes typically used to polish fused silica lenses induce subsurface and surface damage that collect ceria abrasive, creating a layer of contamination. The contamination can be a precursor to laser damage during use. A preliminary study showed the feasibility of magnetic field-assisted finishing (MAF) for polishing fused silica and suggested possible beneficial effects of the MAF-polished surface on the laser-induced damage threshold (LIDT). This paper proposes a method to examine the fundamental polishing characteristics of MAF for fused silica. Using the proposed method, this paper explores the material removal characteristics of the MAF process and improves the understanding of the MAF polishing mechanism. The 45% improvement of LIDT shows the efficacy of MAF for removing the contamination layer of fused silica surfaces with minimal changes in the surface roughness.