A cathode support structure for use in a magnetron oscillator experiment

A low temperature co-fired ceramic (LTCC) material system has been used to develop a protype field emission cathode structure for use in an experimental magnetron oscillator. The structure is designed for used with 30 gated field emission array (GFEA) die electrically connected through silver metal traces and electrical vias. To approximate a cylinder, the cathode structure (48 mm long and 13.7 mm in diameter) is comprised of 10 faceted plates which cover the GFEA dies. Slits in the facet plates allow electron injection. The GFEA die (3 mm × 8 mm) are placed in axial columns of 3 and spaced azimuthally around a cylindrical support structure in a staggered configuration resulting in 10 azimuthal locations. LTCC manufacturing techniques were developed in order to fabricate the newly designed cathode with seven layers wrapped to form the cylinder with electrical traces and vias. Two different cathode wrapping techniques and two different via filling techniques were studied and compared. Two different facet plate manufacturing techniques were studied. Finally, four different support stand configurations for firing the cylindrical structure were also compared with a square post stand having the best circularity and linearity measurements of the fired structure.     

Novel thermal-sensitive properties of NBT-BZT composite ceramics for high-temperature NTC thermistors

We found for the first time that (1 − x) Na_0.5Bi_0.5TiO₃-xBiZn_0.5Ti_0.5O₃ (NBT–BZT) composite ceramics showed negative temperature coefficient (NTC) at a high temperature. The NBT–BZT nanopowders were successfully prepared by Pechini method. Their ceramics were sintered at 1100°C. The NBT–BZT ceramic exhibited a good linear relationship between logarithm of electrical resistivity (Inρ) and reciprocal of absolute temperature (1000/T) at 250°C–1050°C. The obtained ρ₆₀₀, ρ₉₀₀, and B_600/900 constants of the NBT–ZBT NTC thermistors are approximately 5.92 × 10⁶ to 3.01 × 10⁴ Ω cm, 7.03 × 10³ to 7.60 × 10² Ω cm and 2.3 × 10⁴-1.3 × 10⁴ K, respectively. The electrical characteristics can be tuned to the desired value by changing the Na_0.5Bi_0.5TiO₃ content in the compound. The electrical conductivity in these compounds is due to the electron jumps between Ti³⁺ and Ti⁴⁺ and oxygen-ion conductivity. Results demonstrate a tremendous potential of the studied system for perovskite materials with NTC performance.     

Static fatigue of Hi-Nicalon™-S fiber at elevated temperature in air,steam, and silicic acid-saturated steam

A facility for testing SiC fiber tows in static fatigue and creep at elevated temperatures in air and steam was developed. Static fatigue of Hi-Nicalon™-S fibers was investigated at 800°C-1100°C at applied stresses between 115 and 1250 MPa in air, in Si(OH)₄(g)-saturated steam, and in unsaturated steam. Fibers tested in Si(OH)₄(g)-saturated steam and in air had silica scales throughout the test sections, but those tested in unsaturated steam did not develop scales near the steam injection point. Fiber lifetimes in static fatigue were shortest in unsaturated steam, intermediate in Si(OH)₄(g)-saturated steam, and longest in air. Failure strains did not exceed 0.3%. Steady-state strain rates and static fatigue lifetimes are modelled empirically by the Monkman-Grant relationship. Failure mechanisms are discussed.     

Short SiC fiber/Ti3SiC2 MAX phase composites: Fabrication and creep evaluation

The compressive creep of silicon carbide fiber reinforced Ti₃SiC₂ MAX phase with both fine and coarse microstructure was investigated in the temperature range of 1000-1300°C. Comparison of only steady-state creep was done to understand the response of fabricated composite materials toward creep deformation. It was demonstrated that the fibers are more effective in reducing the creep rates for the coarse microstructure by an increase in activation energy compared to the variant with a finer microstructure, being partly a result of the enhanced creep rates for the microstructure with larger grain size. Grain boundary sliding along with fiber fracture appears to be the main creep mechanism for most of the tested temperature range. However, there are indications for a changed creep mechanism for the fine microstructure for the lowest testing temperature. Local pores are formed to accommodate differences in strain related to creeping matrix and predominantly elastically deformed fibers during creep. Microstructural analysis was done on the material before and after creep to understand the deformation mechanics.     

Crystal structure,phase compositions,and microwave dielectric properties of malayaite-type Ca1−xSrxSnSiO5 ceramics

Low-permittivity Ca_1−xSr_xSnSiO₅ (0 ≤ x ≤ 0.45) microwave dielectric ceramics were prepared via traditional state-reaction at 1400°C-1450°C for 5 hours. Moreover the microwave dielectric properties of SnO₂ ceramic were obtained for the first time. SnO₂ ceramic was difficult to densify, and SnO₂ ceramic (ρ_rel = 65.1%) that was sintered at 1525°C exhibited the optimal microwave dielectric properties of ε_r = 5.27, Q × f = 89 300 GHz (at 14.5 GHz), and τ_f = −26.7 ppm/°C. For Ca_1−xSr_xSnSiO₅ (0 ≤ x ≤ 0.15) ceramics, Sr²⁺ could be dissolved in the Ca²⁺ site of Ca_1−xSr_xSnSiO₅ to form a single phase, and the partial substitution of Ca²⁺ by Sr²⁺ could improve the microwave dielectric properties of CaSnSiO₅ ceramic. Secondary phases (SnO₂ and SrSiO₃) appeared at 0.2 ≤ x ≤ 0.45 and could adjust the abnormally positive τ_f value of CaSnSiO₅ ceramic. The highest Q × f value (60 100 GHz at 10.4 GHz) and optimal microwave dielectric properties (ε_r = 9.42, Q × f = 47 500 GHz at 12.4 GHz, and τ_f = −1.2 ppm/°C) of Ca_1−xSr_xSnSiO₅ ceramics were obtained at x = 0.05 and 0.45, respectively.     

Study on the performance of syntactic foam reinforced by hybrid functionalized carbon nanotubes

Hollow glass microspheres (HGMs)/epoxy syntactic foam were reinforced by hybrid functionalized carbon nanotubes that were synthesized by simultaneous covalent and noncovalent functionalization of carbon nanotubes. The effect of hybrid functionalized carbon nanotubes on density, mechanical properties, and water absorption of HGMs/epoxy syntactic foam was studied. The study indicated that the dispersion of carbon nanotubes in epoxy resin can be improved by hybrid functionalization. The compression strength of syntactic foam reinforced by hybrid functionalized carbon nanotubes was significantly enhanced. The maximum compressive strength of syntactic foam corresponding to chitosan modified carbon nanotubes approached 60 MPa. Hybrid functionalized carbon nanotubes had little effect on the water absorption ability of syntactic foam, and was less than 1%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48586.     

制备工艺对聚氨酯酰亚胺泡沫性能的影响

以均苯四甲酸二酐(PMDA)、多苯基多亚甲基多异氰酸酯(PAPI)、聚醚多元醇为主要原料,分别采用聚酰亚胺(PI)预聚法、聚氨酯(PU)预聚法和一步法制备聚氨酯酰亚胺泡沫,从微观形貌、力学性能、热稳定性能以及阻燃性能方面对上述3种制备工艺进行对比和评估。实验结果表明,采用一步法制备PUI泡沫时,PU链段和PI链段同时增长,容易造成泡孔缺陷,导致泡沫的力学性能较差;在采用PU预聚法制备的PUI泡沫中,PU链段含量较高,因此,泡孔孔径分布较宽且平均泡孔直径较大,对应的热稳定性和阻燃性能较差;采用PI预聚法制备的PUI泡沫的泡孔孔径分布窄且平均泡孔直径较小,对应的压缩性能、热稳定性以及阻燃性能均达到最佳。     

三聚氰胺氰尿酸盐阻燃聚氨酯硬泡

将三聚氰胺氰尿酸盐(MCA)作为阻燃剂,采用一步全水发泡法,制备一系列硬质聚氨酯泡沫/三聚氰胺氰尿酸盐复合材料(RPUF/MCA),采用扫描电子显微镜(SEM)、热重分析(TG)、极限氧指数(LOI)、UL-94垂直燃烧、烟密度测试、傅立叶红外光谱(FT-IR)及拉曼光谱表征,研究了MCA对硬质聚氨酯泡沫(RPUF)泡孔结构、热稳定性、阻燃性及燃烧烟气密度的影响。研究表明,MCA能够显著提高RPUF/MCA的阻燃性能,30份的MCA使RPUF/MCA30达到UL-94 V-1级别,极限氧指数达到22.0%。热重测试结果表明,MCA的添加使成炭率降低;同时发现,MCA的添加降低了RPUF/MCA泡沫复合材料的初始热分解温度和复合材料的燃烧烟气密度,有效地提高了复合材料火灾安全性能。     

谈陶瓷装饰中的婴戏纹饰与西方艺术品中的儿童形象

婴戏纹饰即描绘儿童游戏时的画作,是中国人物画的一种,更是陶瓷装饰中常见的传统题材。其主要以儿童为主要绘画对象,表现儿童纯真,或借以其他物象,组成吉祥图案,在我国陶瓷绘画上广泛运用,有着深刻的社会形态特征和思想文化的背景。其始于唐代,兴盛于宋金,明清两朝日臻成熟,并延续至今。在西方艺术史当中,儿童形象大都通过神话人物或宗教相关的艺术品走进人们视野,用以表现某些宗教思想或精神诉求。本文主要探讨陶瓷婴戏纹饰在我国历史发展历程中的演变概况,以及笔者对我国陶瓷婴戏纹饰和西方艺术品中儿童形象横向对比下的一些思考。     

Wear mechanisms and effects of monolithic Sialon ceramic tools in side milling of superalloy FGH96

FGH96 is one kind of nickel-based superalloy, being widely used in aero engine hot end components due to its superior mechanical properties, while its machinability has been a challenge because of rapid tool wear and low machining efficiency. Recently, ceramic tools have gained widespread attention for their superior performance maintained at high temperatures. This work aims to study the wear mechanisms and the wear effects of monolithic Sialon ceramic tool in the side milling of superalloy FGH96. The specific influences of average flank wear on the side milling forces, machining temperatures, surface quality and micro-hardness of subsurface and the wear modes in the early and serious stage are analyzed. The results indicate that the milling temperatures, machined surface roughness and the depth of hardening layer will increase as the wear increases. While parallel to the cutting direction, the machined surface roughness is about 1.8 μm without significant changes until entering the serious wear stage. The milling force tends to undergo a decrease when the VB is about 0.22 mm, since the temperature is close to the solute temperature of γ’ phase in this stage. The main wear modes of monolithic ceramic tools are adhesive wear and flanking in the flank surface.