The formation of a hitherto unknown 4-center, 6π-conjugated trigonal-planar complex, [Bi{Cr(CO) } ] (1), is reported, in which the oxidation state of the Bi atom is +3, as evidenced by XAS, XPS, and DFT calculations. The Bi atom in 1 has dual donor and acceptor properties in its bonding mode. In contrast to the mild Lewis acidity of Bi , the central Bi in 1 functions as a prodigious Lewis acid site to exhibit strong affinity toward F ions, unique solvatochromic properties, intriguing etherification through the C-O bond cleavage of alcohols, and surprising semiconducting characteristics with an ultra-narrow optical band gap of 1.02 eV, which can be attributed to the intermolecular Bi⋅⋅⋅O and O⋅⋅⋅O interactions in the solid state. The tetrahedral Fe(CO) -adduct [{Fe(CO) }Bi{Cr(CO) } ] (1-Fe) allowed the selective demetallation to afford the isoelectronic multiply bonded BiCr -complex 1 and the BiCr Fe-complex, [Bi{Cr(CO) } {Fe(CO) }] (2), which may open a novel pathway for the design of the heterometal-incorporated trigonal-planar Bi-Cr complexes.
The coatings deposited by physical vapor deposition (PVD) technique have found a wide industrial application as protective coatings for their attractive properties such as high hardness, good wear resistance and chemical stability. In order to explore the triboligical performances of CrSiN coatings, CrSiN coatings were prepared o the surface of 316 stainless steel by high power pulse magnetron sputtering (HPPMS) in this paper. Sliding wear tests of CrSiN coatings against Si3N4 ceramic balls and titanium balls have been carried out on a friction abrasion testing machine under reciprocating sliding conditions. nanoindentation and scratch tester, field emission scanning electron microscopy equipped with energy dispersive spectrometer (FESEM/EDS) and a X-ray diffractometer (XRD) was used to study the tribological behaviors of CrSiN coatings systematically. Results showed that CrSiN coatings exhibited good wear resistance, which can be attributed to the smoother and denser surface of CrSiN coatings resulted from much fewer macroparticles and pitting defects. The differences on wear debris removal behaviors and wear mechanism were caused by the different microstructure of CrSiN coatings.
In this paper, we propose a side-absorption concentrated module with diffractive grating as a spectral-beam-splitter to divide sunlight into visible and infrared parts. The separate solar energy can be applied to different energy conversion devices or diverse applications, such as hybrid PV/T solar systems and other hybrid-collecting solar systems. Via the optimization of the geometric parameters of the diffractive grating, such as the grating period and height, the visible and the infrared bands can dominate the first and the zeroth diffraction orders, respectively. The designed grating integrated with the lens and the light-guide forms the proposed module, which is able to export visible and infrared light individually. This module is demonstrated in the form of an array consisting of seven units, successfully out-coupling the spectral-split beams by separate planar ports. Considering the whole solar spectrum, the simulated and measured module efficiencies of this module were 45.2% and 34.8%, respectively. Analyses of the efficiency loss indicated that the improvement of the module efficiency lies in the high fill-factor lens array, the high-reflectance coating, and less scattering.
Material removal mechanisms of Al2O3-based conductive ceramics machined by electric discharge milling in deionized water are investigated. The main components of conductive ceramic samples are Al2O3 (80%), TiC (11%) and WC (9%). The material removal mechanisms by low electric discharge energy are mainly spalling and melting. The material removal mechanisms by high electric discharge energy are mainly melting, evaporation and spalling. With high discharge energy and insufficient cooling conditions, chemical reactions will happen, where TiC and WC are oxidized to dielectric TiO2 and WO3, which will slow down the electric discharge milling processand finally make it stopped.
In order to study the temperature regularity of inter-electrode gap in PECM, the multi-physical coupling model based on COMSOL Multiphysics platform is established. The model of blades was used for this study, and the impact of some factors on the temperature is analyzed. The results show that the duty ratio is smaller or the inlet pressure is greater, the process of electrolyte convective and heat transfer is more sufficient. At the same time, the increase of the voltage and the decrease of the gaps will exacerbate the temperature fluctuations in a single pulse time. The lower voltage and duty ratio with larger inlet pressure should be selected in small gaps of PECM, so that we can effectively avoid the negative influence of high temperature in the processing zone.
Ultrasonic vibration aided electrical discharge milling in deionized
water is proposed and its mechanism is investigated in this paper. The tool electrode is formed to be walled pipe, and high pressure deionized water is supplied through it. Two groups of orthogonal experiments were carried out respectively, one group with ultrasonic vibration on tool electrode and the other without. Research results show that ultrasonic vibration can improve the machining process and surface roughness.
CrN coating possesses high strength, hardness and good resistance to friction. In order to further improve the performance of CrN coating, especially the high temperature resistance, a series of Cr1-xAlxN coatings with different Al content were deposited on the surface of 316 stainless steel by closed field unbalanced magnetron sputtering (CFUBMS). The microstructure, mechanical properties of Cr1-xAlxN coatings were investigated by XRD, FESEM/EDS and microhardness tester, respectively. The oxidation behaviors of Cr1-xAlxN coatings at 800°C were also studied. The results showed that with the increase of Al content, the hardness of the coating increases first and then decreases, and the binding force decreases gradually, and its microstructure is gradually refined. The phases in CrAlN coatings are mainly CrN and AlN. As the amount of Al increases, the number of dense oxide films on the surface of the coating increases, increasing the antioxidant capacity of the coating.
Electric Discharge Machining (EDM) working fluid as a medium can control electrical discharges occur, carry away the heat, compress discharge channel and help remove the corrosion products out of the gap. The main working fluids used in EDM are oil-based working fluid, gas-based working fluid, powder mixed working fluid, gas mixed working fluid and water-based working fluid. In order to improve the green and safety of EDM working fluid, an oil-in-water working fluid is proposed. A gap flow field model of EDM is established by using external flushing fluid. The flow field distribution, pressure distribution and corrosion products distribution of the machining gap are analyzed by using computational fluid dynamics. The effects of inlet pressure, processing depth and electrode size on the flow field are studied. The simulated results show that within a certain range, removal effect of the corrosion products will increase with inlet velocity and the size of electrode and decrease with processing depth.
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