深部软岩巷道围岩变形特征及数值模拟分析

针对深部煤矿开采条件下软岩巷道围岩出现持续流变时间长、变形大、地压高、巷道难以维护等特点，首先分析了深部软岩巷道变形特征，采用FLAC^3D数值模拟软件，分析了不同埋深条件下巷道围岩垂直应力分布、水平应力分布以及巷道围岩塑性区扩展规律。研究得出，深部软岩巷道的围岩岩块呈松散破碎形态，相互翻转和滑移，岩体的模量和强度低；随着巷道埋深的逐渐增加，巷道围岩应力集中系数逐渐减小，巷道垂直、水平应力峰值逐渐变大，塑性破坏范围扩展速率逐渐增加。研究为深部软岩巷道支护提供理论基础。     

Pollen morphological investigations of family Cactaceae and its taxonomic implication by light microscopy and scanning electron microscopy

The family Cactaceae is the diversified group of angiosperm plants whose pollen statistics has been used for taxonomic identification. In this article, we present the pollen morphology of eight species belong to seven taxonomically complex genera of Cactaceae including Astrophytum, Cylindropuntia, Echinocereus, Echinopsis, Mammillaria, Opuntia, and Thelocactus using light and scanning electron microscopy. The pollen grains were acetolyzed, measured, described, and electron photomicrographs were taken. Cactaceae can be characterized by presenting different palynomorphological features including pollen type, sculpturing, polar and equatorial diameter, aperture orientation, exine thickness, P/E ratio, and echini features. Four types of pollen shapes, that is, prolate spheroidal (three species), subprolate (two species), prolate (two species), and oblate spheroidal in Echinocereus reichenbachii were observed. The polar and equatorial diameter observed maximum in O. ficus indica 116.95 and 112.27 μm while minimum in M. compressa 38.42 and 21.05 μm. Pollen of two types, tricolpate in members of subfamily Cactioideae and pantoporate in the Opuntioideae were examined. The fertility percentage has been observed maximum in Opuntia macrocentra (83.84%) and minimum in Opuntia ficus‐indica (57.89%). Exine sculpturing showing great variations such as granulate, reticulate, granulate perforate and micro‐echinate foveolate ornamentation was examined only in Echinopsis eyriesii. A key to species, based on pollen micromorphological attributes, has been constructed for correct identification of complex cactus species.     

Microstructure transformation of a crystallized glass from the system BaO-SrO-ZnO-SiO2

Glass-ceramics from the studied system are able to precipitate a crystalline phase with an anomalous and low coefficient of thermal expansion. Besides the crystalline phase called LEAZit (Low Expansion Alkaline Earth Zinc Silicate), other phases appear within those glass-ceramics. In order to understand the thermal expansion behavior of the whole material, the phase content has to be known as a function of the composition and the chosen heat treatment. In this paper, a glass with the molar composition 5 BaO · 12 SrO · 35 ZnO · 46.2 SiO₂ · 1.5 Sb₂O₃ · 0.3 Ag is studied using X-ray tomography. With this method, the phase content can be studied in detail together with the microstructure. An ex-situ workflow was used to study one and the same sample after different heat treatments, which makes it possible to characterize the structures (crystalline phase, residual matrix, and porosity) inside the sample in a nondestructive way. The size of the different phases was characterized with a strut thickness analysis of the three-dimensional datasets. The tomographic results are supported by results from X-ray diffraction as well as scanning electron microscopy in combination with elemental analysis.     

Heat transfer analysis of receiver for large aperture parabolic trough solar collector

Parabolic trough solar collector (PTSC) is one of the most proven technologies for large‐scale solar thermal power generation. Currently, the cost of power generation from PTSC is expensive as compared with conventional power generation. The capital/power generation cost can be reduced by increasing aperture sizes of the collector. However, increase in aperture of the collector leads to higher heat flux on the absorber surface and results in higher thermal gradient. Hence, the analysis of heat distribution from the absorber to heat transfer fluid (HTF) and within the absorber is essential to identify the possibilities of failure of the receiver. In this article, extensive heat transfer analysis (HTA) of the receiver is performed for various aperture diameter of a PTSC using commercially available computational fluid dynamics (CFD) software ANSYS Fluent 19.0. The numerical simulations of the receiver are performed to analyze the temperature distribution around the circumference of the absorber tube as well as along the length of tube, the rate of heat transfer from the absorber tube to the HTF, and heat losses from the receiver for various geometric and operating conditions such as collector aperture diameter, mass flow rate, heat loss coefficient (HLC), HTF, and its inlet temperature. It is observed that temperature gradient around the circumference of the absorber and heat losses from the receiver increases with collector aperture. The temperature gradient around the circumference of the absorber tube wall at 2 m length from the inlet are observed as 11, 37, 48, 74, and 129 K, respectively, for 2.5‐, 5‐, 5.77‐, 7.5‐, and 10‐m aperture diameter of PTSC at mass flow rate of 1.25 kg/s and inlet temperature of 300 K for therminol oil as HTF. To minimize the thermal gradient around the absorber circumference, HTFs with better heat transfer characteristics are explored such as molten salt, liquid sodium, and NaK78. Liquid sodium offers a significant reduction in temperature gradient as compared of other HTFs for all the aperture sizes of the collector. It is found that the temperature gradient around the circumference of the absorber tube wall at a length of 2 m is reduced to 4, 8, 10, 13, and 18 K, respectively, for the above‐mentioned mass flow rate with liquid sodium as HTF. The analyses are also performed for different HTF inlet temperature in order to study the behavior of the receiver. Based on the HTA, it is desired to have larger aperture parabolic trough collector to generate higher temperature from the solar field and reduce the capital cost. To achieve higher temperature and better performance of the receiver, HTF with good thermophysical properties may be preferable to minimize the heat losses and thermal gradient around the circumference of the absorber tube.     

Carbon nanotube reinforced pyrocarbon matrix composites with high coefficient of thermal expansion for self-adapting ultra-high-temperature ceramic coatings

The mismatch in the coefficients of thermal expansion (CTE) of the carbon fiber reinforced pyrocarbon (Cf/C) composites and their thermal barrier coatings (TBCs) has significantly restricted the service life of Cf/C composites in high-temperature environments. Owing to the high CTE of TBCs, it is vital to find a material with similar mechanical properties and higher CTE than Cf/C composites. In this work, carbon nanotube reinforced pyrocarbon (Ct/C) nanocomposites with high CTEs were prepared to self-adapt to the TBCs. Different CTEs (～4.0–6.5 × 10^?6/°C) were obtained by varying the carbon nanotube (CNT) content of the Ct/C composites. Owing to the decreased mismatch in the CTEs, no cracks were formed in the TBCs (SiC and HfB₂-SiC-HfC coatings) deposited on the Ct/C composites. After heat treatment at 2100 °C, several wide cracks were found in the TBCs on the Cf/C composite, whereas the TBCs on the Ct/C composites were intact without cracks. We found that the CTE-tunable Ct/C composites can self-adapt to different TBCs, protecting the composites from oxidation at high temperatures.     

Improvement on thermophysical and mechanincal properties of LaMgAl11O19 magnetoplumbite by Nd2O3 and Sc2O3 co-doping

LaMgAl₁₁O₁₉-type magnetoplumbite holds great promise to be used above 1300 °C as thermal barrier coatings (TBCs), but its practical application has been restricted because of inferior thermophysical properties. Herein, we focus on optimizing the thermophysical properties of LaMgAl₁₁O₁₉ by simultaneously substituting La³⁺ and Al³⁺ ions with Nd³⁺ and Sc³⁺ ions, respectively. Results show that the effects of co-substitution on reducing thermal conductivity are pronounced. The thermal conductivities of La_1-xNd_xMgAl_11-xSc_xO₁₉ (x = 0, 0.1, 0.2, 0.3) ceramics decrease progressively with dopant concentration and a lowest thermal conductivity of 2.04 W/(m·K) is achieved with x = 0.3 at 1000 °C, which is a value superior to pure LMA and even lower than YSZ. The mechanisms behind the lowered thermal conductivity are investigated. Increase of the thermal expansion coefficient is also realized (8.53 × 10⁻⁶ K⁻¹ for pure LMA, 9.07 × 10⁻⁶ K⁻¹ for x = 0.3, 1300 °C). Most importantly, Nd³⁺ and Sc³⁺ combination doping indeed facilitates mechanical properties of La_1-xNd_xMgAl_11-xSc_xO₁₉ solid solutions as well. It should be noted that Sc³⁺ doping at Al³⁺ site plays more effective role in improving thermal properties than Nd³⁺ does at La³⁺ site. This work provides a path to simultaneously integrate low thermal conductivity, good phase stability, moderate thermal expansion behavior and excellent mechanical properties on LMA for the next generation TBCs.     

Shock/expansion fan interaction with real gas effects for Earth and Mars atmospheric conditions

Numerical simulations are performed to investigate the real gas effects on shock/expansion fan interaction. Initial perfect gas simulations at low enthalpy capture the flow structures efficiently and outcomes are found to have excellent agreement with the analytical calculations. Furthermore, the simulations with the real gas solver for different enthalpies showed that the variation in enthalpy significantly changes the flow structures. It is observed that an increase in enthalpy leads to a decrease and increase in the postshock and postexpansion fan Mach numbers, respectively. Another important observation is the decrement in the peak pressure ratio with an increment in the enthalpy. These effects are noted to be more pronounced for Mars's environment due to the higher dependency of specific heat on temperature.     

High-entropy titanate pyrochlore as newly low-thermal conductivity ceramics

Low-thermal conductivity ceramics play an indispensable role in maximizing the efficiency and durability of hot end components. Pyrochlore, particularly zirconate pyrochlore, is currently a highly promising and widely studied candidate for its extremely low thermal conductivity. However, there are still few pyrochlores that offer both stiffness, insulation, and good thermal expansion properties. In this work, the solidification method was innovatively introduced into the preparation of titanate pyrochlore, and combined it with the compositional design of high-entropy. Through careful composition design and solidification control, the high-density and uniform elements distributed high-entropy titanate pyrochlore ceramics were successfully prepared. These samples possess high hardness (15.88 GPa) and Young’s modulus (295.5 GPa), low thermal conductivity (0.947 W·m^?1·K^?1), excellent thermal expansion coefficient (11.6 ×10^?6/K) and an exquisite balance between stiffness and insulation (E/κ, 312.1 GPa·W^?1·m·K), in which the E/κ exhibits the highest value among the current reported works.     

Preparation and characterization of polynorbornene/sepiolite hybrid nanocomposite films

Polynorbornene/sepiolite hybrid nanocomposite films were prepared using polynorbornene dicarboximide and modified sepiolite with 3‐ aminopropyltriethoxysilane (3‐APTES). Exo‐N‐(3,5‐dichlorophenylnorbornene)‐5,6‐dicarboxyimide (monomer) and their copolymers were synthesized via ring‐opening polymerization using ruthenium catalysts. Subsequently, the surface‐modified sepiolite by 3‐APTES was mixed with the polynorbornene copolymers to prepare hybrid nanocomposite films. The modified sepiolite particles were well dispersed in N,N‐dimethylacetamide and distributed randomly throughout the polynorbornene matrix in the hybrid films, which enhanced the dimensional stability and mechanical and oxygen barrier properties of the polynorbornene/sepiolite hybrid nanocomposite films. © 2014 Society of Chemical Industry     

In_2W_3O_(12)陶瓷的相变特性及其负热膨胀性能(英文)

以分析纯In2O3和WO3为原料,采用固相反应法制备In2W3O12陶瓷。利用X射线衍射仪、场发射扫描电子显微镜、热重分析仪、差示扫描量热仪和热机械分析仪对样品的物相组成、微观结构、相变和热膨胀特性进行了表征。结果表明:在900℃烧结6h可制备出纯的单斜相In2W3O12陶瓷,In2W3O12陶瓷断面晶粒均匀,平均尺寸为4～6μm。In2W3O12陶瓷在253.34℃发生单斜相到斜方相的相转变,单斜相的In2W3O12陶瓷显示正热膨胀,在27～249℃,其平均热膨胀系数为16.51×10-6℃-1,斜方相的In2W3O12陶瓷显示负热膨胀,在273～700℃,其平均热膨胀系数为-3.00×10-6℃-1。