Microstructure and formation mechanism of titanium matrix composites coating on Ti-6Al-4V by laser cladding

Laser cladding experiments were done on a 5-kW continuous wave CO2 laser to synthesize TiC and TiB rein- fowed titanium matrix composite coatings on Ti-6AI-4V alloy with a mixture of Ti and B4C precursor powder. The ther- modynamics of the reactions were calculated and analyzed. The microstructure and phase evolution of TiB and TiC com- posites were investigated. The results showed that the chemical reaction between Ti and B4C would release much heat, and these compounds, TiC, TiB, and small amount of TiB2, can be formed on the surface of Ti-6AI-4V alloy if the supplied en- ergy is sufficient to excite the reaction among the initial products. A good metallurgical bond between the coating and the substrate can be achieved. The microhardness of coating was irregular and the maximum value was approximately HV600.

In situ deposited cobalt-magnesium selenates as an advanced electrode for electrochemical energy storage

Currently,bimetallic selenates have attracted much attention as a prominent electrode composite material for supercapacitors owing to their higher redox chemistry and superior electrical conductivity.Herein,we synthesized cobalt-magnesium selenates (CoSeO3-Mg Se O4,CMS) via a facile hydrothermal process,followed by selenization.At first,cobalt-magnesium oxide (Co2.32Mg0.68O4,CMO) was in situ prepared by a one-pot hydrothermal method.An investigation on the morphological change was performed by synthesizing the same CMO samples at different growth times by keeping the temperature constant.The CMO electrode designed for 8 h of growth time (CMO-8 h)with an attractive morphology showed a higher areal capacity of 101.7μAh cm-2(at 3 m A cm-2) than the other CMO electrodes prepared for 6 and 10 h.Further exalted performance was achieved by the selenization of the CMO-8 h sample to form the CMS material.At 3 m A cm-2,the resulted CMS exhibited nearly three times higher capacity,i.e.,385.4μAh cm-2,than the CMO-8 h electrode.Additionally,an asymmetric cell fabricated with CMS as a positive electrode also revealed good energy storage performance.Within the applied voltage between 0 and 1.5 V,the asymmetric cell demonstrated maximum energy density of 0.159 m Wh cm-2(18.6 Wh kg-1) and maximum power density of 18.47 m W cm-2(1938 W kg-1),respectively.Thus,novel magnesium-based metal selenates can act as an efficient electrode for energy storage.

In situ formation of an intimate solid-solid interface by reaction between MgH_(2) and Ti to stabilize metal hydride anode with high active material content

MgH_(2) and TiH_(2) have been extensively studied as potential anode materials due to their high theoretical specific capacities of 2036 and 1024 mAh/g,respectively.However,the large volume changes that these compounds undergo during cycling affects their performance and limits practical applications.The present work demonstrates a novel approach to limiting the volume changes of active materials.This effect is based on mechanical support from an intimate interface generated in situ via the reaction between MgH_(2) and Ti within the electrode prior to lithiation to form Mg and TiH_(2).The resulting Mg can be transformed back to MgH_(2) by reaction with LiH during delithiation.In addition,the TiH_(2) improves the reaction kinetics of MgH_(2) and enhances electrochemical performance.The intimate interface produced in this manner is found to improve the electrochemical properties of a MgH_(2)-Ti-LiH electrode.An exceptional reversible capacity of 800 mAh/g is observed even after 200 cycles with a high current density of 1 mA/cm^(2) and a high proportion of active material(90 wt.%)at an operation temperature of 120℃.This study therefore showcases a new means of improving the performance of electrodes by limiting the volume changes of active materials.

Selective reduction of carbon dioxide to carbon monoxide over Au/CeO_2 catalyst and identification of reaction intermediate

CO2 selective reduction to CO with H2 over a CeO2-supported nano-Au catalyst at atmospheric pres- sure was investigated. A high CO2 conversion, approaching the thermodynamic equilibrium value, and nearly 100% CO selectivity were obtained. The surface formate intermediates generated during the reverse water-gas shift reaction at 400 ℃ were identified using in situ diffuse-reflectance infra- red Fourier-transform spectroscopy. The formate consumption to give CO and H20, determined using mass spectrometry, indicated that the reaction proceeded via an associative formate mecha- nism; this contributes to the high Au/CeO2 catalytic activity at low temperatures.

Strong ozone production at a rural site in the North China Plain: Mixed effects of urban plumes and biogenic emissions

Regional ozone （O3） pollution has drawn increasing attention in China over the recent decade, but the contributions from urban pollution and biogenic emissions have not been clearly elucidated. To better understand the formation of the regional O3 problem in the North China Plain （NCP）, intensive field measurements of O3 and related parameters were conducted at a rural site downwind of Ji＇nan, the capital city of Shandong province, in the summer of 2013. Markedly severe 03 pollution was recorded, with the 03 mixing ratios exceeding the Chinese national ambient air quality standard on 28 days （a frequency of 78%） and with a maximum hourly value of 198 ppbv. Extensive regional transport of well-processed urban plumes to the site was identified. An observation-constrained chemical box model was deployed to evaluate in situ photochemical O3 production on two episodes. The results show that the in situ formation accounted for approximately 46% of the observed O3 accumulation, while the remainder （54%） was contributed by regional transport of the O3-laden urban plumes. The in situ ozone production was in a mixed controlled regime that reducing either NOx or VOCs would lead to a reduction of ozone formation. Biogenic VOCs played an important role in the local ozone formation. This study demonstrates the significant mixed effects of both anthropogenic pollution from urban zones and biogenic emission in rural areas on the regional 03 pollution in the NCP region, and may have general applicability in facilitating the understanding of the formation of secondary pollution over China.

Rechargeable solid-state Li-air batteries： a status report

The theoretical specific energy of lithium-air battery is as high as 3436 Wh.kg^-1, and the possible achieved value may reach 600-700 Wh.kg^-l, which enables this energy storage system as an important propulsion power sources for electric vehicles with the driving range of 500-800 km. Currently, Li-air batteries are facing main challenges at stability, efficiency, applicability and safety. In particular, from a practical view of point, the Li-air batteries should be operated directly in ambient air. Solid-state battery system is the best avenue to eventually solve these main issues. At the heart of the solid state, Li-air technology is the solid-state Li^＋-conducting ceramic material. Developing solid-state lithium-air batteries （SSLAB） can solve the problem of applicability fundamentally and circumvent the safety issues completely, and it is also an important avenue to improve the stability of the battery system. In this paper, we provide a systematical review of the progress in the cell construction, the regulation of the electrode/electrolyte interface, the cell assembly, the electrochemical performance and the mechanism for the SSLAB. In every section, the contributions of the recent research progress in the main challenges and the remained questions will be commented. Based on these reviews, we attempt to propose some alternative approaches for the next stage and suggest a development prospective for the SSLAB.