抽采孔液态CO2预裂效果显微CT实验研究

为研究液态CO2预裂爆破后,煤体内裂隙发育情况,采用高精度微焦点显微CT系统,对预裂后不同区域的煤样进行CT扫描,并利用Photoshop进行孔裂隙占比统计学分析。研究结果显示,距预裂孔4 m处的煤体裂隙发育明显,孔裂隙占比增加了一倍,而在5 m处的煤体裂隙则发育较弱。表明抽采孔内采取液态C2预裂技术后,4 m范围内的煤体裂隙得到了充分发育,为瓦斯抽采提供了有利条件。     

Effects of sintering in a high magnetic field on properties of vitrified bond and vitrified CBN composites

Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6?T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6?T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5?MPa in 6?T high magnetic field.     

AlF3-modified LiCoPO4 for an advanced cathode towards high energy lithium-ion battery

Surface-interface reaction between the electrode and electrolyte plays a key role in lithium-ion storage properties, especially for high voltage cathode such as LiCoPO₄ and Ni-riched cathode. Generally, surface modification is an effective method to improve the electrochemical performance of electrode materials. Herein, in order to revise the LiCoPO₄ cathode with desirable properties, uniform AlF₃-modified LiCoPO₄ (LiCoPO₄@AlF₃) cathode materials in nano-sized distribution are synthesized. XRD result indicates that there is no structural transformation observed after AlF₃ coating. TEM characterization and XPS analysis reveal that the surface of LiCoPO₄ particle is coated by a nano-sized uniform AlF₃ layer. Further, the electrochemical results indicate that AlF₃ layer significantly improves the cycling and rate performances of LiCoPO₄ cathode within the voltage range of 3.0–5.0 V. After a series of optimization, 4 mol% AlF₃-coated LiCoPO₄ material exhibits the best properties including an initial discharge capacity of 159 mA h g^?1 at 0.1 C with 91% capacity retention after 50 cycles, especially a discharge capacity of 90 mA h g^?1 can be obtained at 1 C rate. CV curves indicate that the polarization of cathode is reduced by AlF₃ layer and EIS curves reveal that AlF₃ layer relieves the increase of resistance to facilitate Li-ion transfer at the interface between electrode and electrolyte during the cycling process. The enhanced electrochemical performances are attributed to that the AlF₃ layer can stabilize the interface between the cathode and electrolyte, form steady SEI film and suppress the electrolyte continuous decomposition at 5 V high voltages. This feasible strategy and novel characteristics of LiCoPO₄@AlF₃ could promise the prospective applications in the stat-art of special lithium-ion battery with high energy and/or power density.     

铅锌多金属矿分段浓缩选别技术的研究与应用

通过多碎细磨、原矿分级溢流优先浓缩脱水,进行了高浓度选铅银、选锌,锌尾矿再浓缩脱水选硫、选锰,同时匹配合理的选矿药剂,原矿浓缩水回用于磨矿分级和选铅,锌尾浓缩水回用于选锌,尾矿浓缩水回用于选硫、选锰,剩余各种废水经适度处理回用于选铅和磨矿分级等,使一段磨矿细度-74μm从70%提高到80%,铅、锌、硫入选初始浓度分别提高到50%、40%、50%,选矿废水全部分质回用。铅锌硫银回收率分别提高了1.5、2.83、13.57、1.01个百分点,硫精矿主品位从38.9%提高到46.5%,设备减少40%、能耗降低25%,节约了选矿药剂消耗和废水处理费用,实现了铅锌多金属矿产资源的高效回收和节能环保。     

Impact of hydrogen fueled hypersonic airliners on the O3 layer depletion

The promising opportunity to reach intercontinental long distances in a few hours is a remarkable issue for both private companies and public organizations: teams of scientists, technicians and researchers in Europe, USA, China, Russia and India are working at national and international programs on long range high speed civil transport. The Space X's CEO also announced, at the IAC 2017 conference, the growing interest in developing a 30-min transatlantic passenger flight by means of a 2-stage rocket-based vehicle. Meeting the dwell requirement of antipodal ranges and high speeds is realistic through a new era of hydrogen-fuelled hypersonic airbreathing vehicles. The interest in hydrogen as aviation fuel has recently increased not only due to the growth of worldwide air travel and time reduction requirements, also for the dramatic rise of common aviation fuel prices, and the continuously increasing restrictive environmental issues.In the light of these changes that have occurred in fuel prices, emissions reduction imperatives and the currently higher demand for supersonic airline travels, hydrogen-fuelled hypersonic airbreathing airliners are a valuable chance with respect to other means of transport (i.e., a rocked based passenger transport). In fact, hydrogen is one of the most environmental friendly fuels, since no particulate and carbon oxide emissions are produced. Past objections on hydrogen as fuel for civil transport, such as safety, liquefying and storing hydrogen are now overcame and its technological maturity opens a large worldwide market for hydrogen as “green” fuel. However, since the opportunity for hydrogen as fuel for future fleets of airline transport resides in its “green” peculiarity, the investigation of the impact of the H₂/air hot exhausts on the ozone layer depletion is mandatory. In fact, a lot of hypersonic cruise vehicles fly at an altitude of 25000–30000 m that corresponds to the ozonosphere. In this region, the concentration of ozone is maximum and NOx emissions may catalyse the ozone destruction.In this context, the goal of this paper is to estimate the effect of the H₂/air emissions (i.e., nitrogen oxides, hydroxide and water vapor) of a fleet of 200 hydrogen fuelled hypersonic airliners flying once a day for 360 days from Brussels to Sydney, on the ozone layer and on the global temperature increase.     

Thermal stability of nanometric TiC-carbon composites: effects of carbon allotropes and Zr milling impurities

In the ISOL (Isotope Separator OnLine) method a target at high temperatures (up to 2300?°C), is bombarded with high energy protons in order to produce isotopes through nuclear reactions which are simultaneously extracted from the target, ionized and delivered to physics experiments. Due to the enhanced isotope release properties of nanosized porous materials, titanium carbide-carbon porous nanocomposites have been developed at CERN and tested up to 1500?°C. In the interest of the ISOL application, in this study we extended the range of temperatures up to 1800?°C, to test the sintering hindering capabilities of different carbon allotropes. Carbon black was the most effective with the smallest TiC crystallite size: <80?nm at 1800?°C. Additionally, using thermodynamic modelling, ex-situ X-ray powder diffraction and in-situ gas phase analysis, we show that there are interesting additional phase and lattice parameter changes due to the ZrO₂ impurities from the attrition milling.     

Environmental-barrier coating ceramics for resistance against attack by molten calcia-magnesia-aluminosilicate (CMAS) glass: Part I,YAlO3 and γ-Y2Si2O7

The high-temperature (1500?°C) interactions of two promising dense, polycrystalline EBC ceramics, YAlO₃ (YAP) and γ-Y₂Si₂O₇, with a calcia-magnesia-aluminosilicate (CMAS) glass have been explored as part of a model study. Despite the fact that the optical basicities of both the EBC ceramics and the CMAS are similar, they both react with the CMAS. In the case of the Si-free YAlO₃, the reaction zone is small and it comprises three regions of reaction-crystallization products, including Y-Ca-Si apatite solid-solution (ss) and Y₃Al₅O₁₂ (YAG)(ss). In contrast, only Y-Ca-Si apatite(ss) forms in the case of Si-containing γ-Y₂Si₂O₇, and the reaction zone is an order-of-magnitude thicker. These CMAS interactions are analyzed in detail, and are found to be strikingly different than those observed in Y-free EBC ceramics (β-Yb₂Si₂O₇ and β-Sc₂Si₂O₇) in the accompanying Part II paper. This is attributed to the presence of the Y in the YAlO₃ and γ-Y₂Si₂O₇ EBC ceramics.     

Highly porous nano-SiC with very low thermal conductivity and excellent high temperature behavior

Highly porous nano-SiC is fabricated by partial sintering and decarburizing process using SiC nano-powders as starting materials and graphite flakes as pore forming agents. The prepared porous nano-SiC ceramics possess multiple pore structures, including well-distributed meso-pores in the skeleton and interconnected flakelike micro-pores. The samples prepared at 1800 °C have relatively low thermal conductivities of 5.61 ～ 0.25 W m^?1 K^?1 with porosities of 55.5–76.1%. While the samples sintered at 1500 °C with porosities between 54.0% to 76.3% show very low thermal conductivities of 0.74 ～ 0.14 W m^?1 K^?1, which is attributed to the integrated nano-scale phonon-scattering mechanisms and duplex pore structures. Porous nano-SiC ceramics also show good retention of elastic stiffness up to 1350 °C and low thermal conductivity at 1400 °C. Our results shed light on porous nano-SiC as a promising thermal insulator used in extreme thermal and chemical environments.     

Effects of deformation rate on properties of Nd,Y-codoped CaF2 transparent ceramics

Different deformation rates of Nd,Y-codoped CaF₂ transparent ceramics were prepared by ceramization of single crystals. The deformation rate effects on the crystallization behaviors, microstructures, mechanical properties, and optical performances were investigated for the first time. The results indicate that the comprehensive performances of Nd,Y-codoped CaF₂ ceramic (△a?=?62%) are the most optimal compared with other ceramics having different deformation rates (△a?=?34%, 40%, 50%, and 75%). In further investigations of the optical properties, the Nd,Y-codoped CaF₂ ceramic (△a?=?62%) sample exhibited a high transparency (T_a?>?91%, 3-mm thick，250?～?1200?nm), low light scattering, superior fracture toughness (K_1c?～?0.71?MPa·m^1/2), strong fluorescence emission, long lifetime (τ?=?348.72?μs), and broad FWHM (29.2?nm), promising a good candidate for high-power laser material.