Thermal cycling and hot corrosion behavior of a novel LaPO4/YSZ double-ceramic-layer thermal barrier coating

LaPO₄ powders were produced by a chemical co-precipitation and calcination method. The ceramic exhibited a monazite structure, kept phase stability at 1400?°C for 100?h, and had low thermal conductivity (~ 1.41?W/m?K, 1000?°C). LaPO₄/Y₂O₃ partially stabilized ZrO₂ (LaPO₄/YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were fabricated by air plasma spray. The LaPO₄ coating contained many nanozones. Thermal cycling tests indicated that the spallation of LaPO₄/YSZ DCL TBCs initially occurred in the LaPO₄ coating. The failure mode was similar to those of many newly developed TBCs, probably due to the low toughness of the ceramics. LaPO₄/YSZ DCL TBCs were highly resistant to V₂O₅ corrosion. Exposed to V₂O₅ at 700–900?°C for 4?h, La(P,V)O₄ formed as the corrosion product, which had little detrimental effect on the coating microstructure. At 1000?°C for 4?h, a minor amount of LaVO₄ was generated.     

An isothermal oxidation behaviour of atmospheric plasma and high-velocity oxy-fuel sprayed nickel based coating

This paper describes the isothermal oxidation behaviour of NiCrBSiFe coatings on SS 316 L deposited by the atmospheric plasma (APS) and high-velocity oxy-fuel (HVOF) processes. As-sprayed coatings were oxidised isothermally in the air at 900 °C temperature for 1000 h. The thermogravimetric analysis was performed to measure the oxidation rate. The coating and oxide scale characterisation was carried out using SEM, EDAX, XRD, porosity analysis, and nanoindentation. The HVOF sprayed NiCrBSiFe coating shows better oxidation resistance than the APS coating, due to high density, less porosity, and formation of more protective oxide scale.     

Evolution mechanism of the microstructure and mechanical properties of plasma-sprayed yttria-stabilized hafnia thermal barrier coating at 1400 °C

Yttria stabilized hafnia (Hf_0.84Y_0.16O_1.92, YSH16) coatings were sprayed by atmospheric plasma spraying (APS). The effects of thermal aging at 1400 °C on the microstructures, mechanical properties and thermal conductivity of the coatings were studied. The results show that the as-sprayed coating was composed of the cubic phase, and the nano-sized monoclinic (M) phase was precipitated in the annealed coating. The presence of M phase effectively constrained the sintering of the coating due to its superior sintering-resistance. The Young's modulus kept at a nearly same level of ~78 GPa even after annealing, and the coating annealed for 6 h yielded a maximum value of hardness but revealed a declining tendency in the Vicker's hardness with prolonged sintering time. The thermal conductivity increased from 0.8-0.95 W m^-1 K^-1 at as-sprayed state to 1.6 W m^-1 K^-1 after annealing at 1400 °C for 96 h. The dual-phase coating is promising to serve at temperatures above 1400 °C due to its excellent thermal stability and mechanical properties.     

Chamber bioaerosol study: human emissions of size‐resolved fluorescent biological aerosol particles

Humans are a prominent source of airborne biological particles in occupied indoor spaces, but few studies have quantified human bioaerosol emissions. The chamber investigation reported here employs a fluorescence‐based technique to evaluate bioaerosols with high temporal and particle size resolution. In a 75‐m³ chamber, occupant emission rates of coarse (2.5–10 μm) fluorescent biological aerosol particles (FBAPs) under seated, simulated office‐work conditions averaged 0.9 ± 0.3 million particles per person‐h. Walking was associated with a 5–6× increase in the emission rate. During both walking and sitting, 60–70% or more of emissions originated from the floor. The increase in emissions during walking (vs. while sitting) was mainly attributable to release of particles from the floor; the associated increased vigor of upper body movements also contributed. Clothing, or its frictional interaction with human skin, was demonstrated to be a source of coarse particles, and especially of the highly fluorescent fraction. Emission rates of FBAPs previously reported for lecture classes were well bounded by the experimental results obtained in this chamber study. In both settings, the size distribution of occupant FBAP emissions had a dominant mode in the 3–5 μm diameter range.     

1000 MW二次再热超超临界机组分散控制系统关键技术研究及应用

在分析二次再热机组控制难点的基础上,介绍了1 000 MW二次再热超超临界机组国产自主化分散控制系统关键技术的研发,包括机组分散控制系统的设计及技术特点,机组协调控制技术,汽温控制技术,旁路控制技术及机组自启停(APS)控制技术。示范工程的应用表明,该分散控制系统性能稳定可靠,各项性能指标达到或优于设计值,机组实现了启停全程控制自动化。     

LCC谐振变换器非对称移相控制及效率优化方法

提出一种LCC谐振变换器的非对称移相控制方法。该方法采用PWM移相混合调制方式,有两个控制变量,实现了更高的控制自由度。分析LCC谐振变换器的稳态特性,包括输出功率特性、软开关特性以及谐振电流特性。分析结果表明,不同的控制变量组合能够实现同一输出功率,但会导致软开关及谐振电流特性发生变化。在此基础上提出一种效率优化策略,使谐振变换器在输出功率不变的情况下谐振电流降至最低,同时保证了软开关的实现。所提出的方法能够进一步提升LCC谐振变换器的效率。通过仿真及1.9k W样机验证了理论分析及所提控制方法的可行性和有效性。     

基于CMOS APS高精度太阳敏感器

通过对CMOS APS的简要介绍以及它与CCD的性能比较,揭示出CMOS APS在太阳敏感器的研究发展方面所具有的优越性.在提出CMOS APS太阳敏感器一般方案的同时,对它进行了更进一步的探讨.并在探讨太阳敏感器视场和精度相互制约这一问题的过程中,结合CMOS APS各方面的优点,阐明了这一问题虽然在CCD太阳敏感器中难以解决,但在CMOS APS太阳敏感器中却可以得到有效解决.     

Carbon nanotube–polyaniline composites

The last decade has seen a growing interest in hybrid electrically conducting nanocomposites. This article aims to provide a detailed overview of the present status of research in carbon nanotube–polyaniline (CNT/PANI) composites, from processing to structural and property evaluations. CNT/PANI are synthesized by electrochemical and chemical processing. When chemical methods are used, the main challenge is to obtain processable CNT/PANI in the emeraldine salt (ES) form composites. Stable dispersions of ES–CNT in organic media are prepared using the post doping method, inverse emulsion polymerization, or ex situ polymerizations. On the contrary, stable water dispersions of CNT/ES are prepared using hydrophilization of a preformed CNT/ES composite, direct synthesis of micelle–CNT hybrid templates, interfacial polymerization, covalent functionalization of CNT with a water soluble polymer, or using electrostatic interactions between two oppositely charged ES and CNT aqueous colloids. Moreover, the strategies for the synthesis of ternary CNT/PANI composites incorporating noble metal nanoparticles, metal oxide, or graphene sheets are also presented and analyzed in depth. Finally, we give a review of potential applications, including chemical sensors, capacitors, fuel cells and electronic devices.     

HCPEB轰击对热障涂层结构及抗CMAS腐蚀性能的影响

利用强流脉冲电子束(HCPEB)对大气等离子喷涂(APS)制备的热障涂层进行表面改性,分别对原始涂层和电子束改性涂层进行1250℃的钙镁铝硅酸盐(CMAS)腐蚀试验,采用XRD、SEM和EDS表征腐蚀前后原始涂层和电子束改性涂层的物相组成、微观结构和化学成分变化,对比分析原始涂层和改性涂层的CMAS腐蚀行为及影响规律。结果表明,改性涂层表面粗糙度降低了60.9%,且生成了具有柱状晶的致密重熔层,涂层表面具有更好的结构稳定性及相稳定性,改性涂层经CMAS腐蚀8 h后结构依然完整且表面无m-ZrO₂相生成,涂层并未发生脱落失效,具有较好的抗CMAS腐蚀能力。     

Fabrication and characterization of 8YSZ ceramic based abradable seal coatings by atmospheric plasma spraying

8 wt% yttria-stabilized zirconia (8YSZ) powders are fabricated as high-temperature based materials via a solid-state reaction method and ground into spheres in this paper. Following that, 4 wt% Nickle (Ni), 4 wt% Hexagonal Boron Nitride (hBN) and 4 wt% PHB (Polyphenyl ester) are added to 8YSZ for getting 8YSZ ceramic-based abradable seal powders (8YSZ CAS_p). Then, the 8YSZ CAS_p are sprayed on the stainless steel substrate with a NiCoCrAlY transition layer by an atmospheric plasma spraying (APS) technology. The phase structure, surface morphology and the cross-section topography of the fabricated are analyzed, the indentation hardness and nano-indentation test are conducted. The experiments of 8YSZ ceramic-based abradable seal coatings (8YSZ CAS_c) show that the deposition efficiency and porosity are respectively 78.5% and 21.8%, the bond strength is 4.6 MPa, the cycle number of thermal shock resistance is 37 times, those parameters prove that the fabricated 8YSZ CAS_c are promising abradable seal coatings.