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Although g-C3N4/BiPO4 heterojunctions have shown high photocatalytic performance experimentally, understanding is far from satisfactory on the relevance of the interlayer interaction and energy levels at interface. Herein, the energy level alignment at g-C3N4/BiPO4 interface is systematically explored by first-principles calculations incorporating semiempirical dispersion-correction schemes. The results indicate that a stable interface with the chemical adsorption can be formed between g-C3N4 and BiPO4. Interestingly, a typical type-II band alignment at g-C3N4/BiPO4 interface is found based on the analysis of the energy band structures and work functions, where the valence and conduction band edges of the BiPO4 layer are higher than those of the g-C3N4 layer after the actual contact of BiPO4 and g-C3N4, respectively. Especially, both charge density difference and Mulliken population show that a built-in electric field is formed with the direction from g-C3N4 to BiPO4 after interfacial equilibrium, and fac...

Bi2WO6 nanosheets were synthesized by a hydrothermal method with H2WO4 for the first time. The band structure of Bi2WO6 was investigated on the basis of density functional theory calculations. Bi2WO6 photocatalysts showed photocatalytic activity for the degradation of methylene blue under visible light irradiation. Kinetic studies using radical scavenger technologies suggested that holes were the dominant photo-oxidants. After hybridization with C3N4, the photocatalytic activity of Bi2WO6 was obviously enhanced. The enhanced photocatalytic activity of the C3N4/Bi2WO6 photocatalysts could be attributed to the effective separation of photogenerated e-/h+ pairs. The photogenerated holes on the valence band of Bi2WO6 can transfer to the highest occupied molecular orbital of C3N4via the well-developed interface, causing a reduction in the probability of e-/h+ recombination; consequently, large numbers of photogenerated holes led to the enhancement of the photocatalytic activity.

Workpiece deformation in stack drilling can lead to interlayer gaps and non-coaxiality, which bring adverse effects to the hole quality and assembly quality. Nowadays, large numbers of fasteners are required to assemble the stacks for satisfactory hole qualities, which will also lead to extreme low efficiency and high cost. This study aims to reveal the formation and quantitative evaluation of the non-coaxiality, and to explore how the pre-installed fasteners reduce the interlayer gaps and non-coaxiality, thus to contribute in designing more efficient layout of the fasteners. First, a simplified 2-D model that involves effects of the pre-installed fasteners in stack drilling is built and the deformation of the stacks is theoretically analysed. Based on the calculation results, three types of patterns of non-coaxiality are revealed and explained, i.e., Type I caused by pure bending, Type II caused by horizontal displacements and Type III caused by local deformations at the holes. With consideration of these characteristics, a combined evaluation criterion for non-coaxiality in stack drilling is proposed and a method of measuring the non-coaxiality is developed. Then, the outcomes of the pre-installed fasteners brought to the deformations of the stacks are explained using theoretical analysis for the simplified 2-D model. As the accurate deformations of the 3-D stacked structures cannot be obtained in 2-D model, finite element simulations are also adopted to study the non-coaxiality and the interlayer gaps quantitatively. Finally, the demonstration experiments of stack drilling are conducted and the results agree with the simulation results that the non-coaxiality of neighbouring holes of the fasteners can be reduced.

Interfacial interactions and electronic properties of graphene/CH3NH3PbI3 heterojunctions were investigated by first-principles calculations incorporating semiempirical dispersion-correction scheme to describe van der Waals interactions. Two lattice match configurations between graphene and CH3NH3PbI3(0 0 1) slab were constructed in parallel contact and both of them were verified to form remarkable van der Waals heterojunctions with similar work functions. Our calculated energy band structures show that the Dirac-cone of graphene and the direct band gap of CH3NH3PbI3 are still preserved in the heterojunctions, thus graphene can be a promising candidate either as a capping or supporting layer for encapsulating CH3NH3PbI3 layer. It is identified that the Schottky barrier of graphene/CH3NH3PbI3 heterojunctions can be controlled by the interlayer distance and affected by the stacking pattern of graphene and CH3NH3PbI3. The 3D charge density differences present the build-in internal electric field from graphene to CH3NH3PbI3 after interface equilibrium and thus, a low n-type Schottky barrier is needed for high efficient charge transferring in the interface. The possible mechanism of the band edge modulations in the heterojunctions and corresponding photoinduced charge transfer processes are also described.

Bismuth vanadate (BiVO4)-based photocatalysts as a typical solar-water-splitting material have attracted much interest due to their moderate band gap, fine hole conductivity and good stability. In this work, we perform a comprehensive first-principles study of the structural, electronic and optical properties of a black phosphorus BP/BiVO4 heterostructure, which was realized with remarkable performance in pure water splitting in a very recent experiment. Firstly, the optoelectronic properties and charge transport between BP and BiVO4 are systematically elucidated. We find that the positions of the valence/conduction band edge of BP and BiVO4 change with the Fermi level and form a type-II heterostructure with a high optical absorption coefficient. Furthermore, the charge density difference and Bader charge analysis indicated that the internal electric field will facilitate the separation of e−/h+ pairs at the BP/BiVO4 interface and restrain the carrier recombination. Therefore, the present work provides insightful understanding of the physical mechanism and superior photocatalytic performance of this new synthesized system and offers instructions for fabricating superior BiVO4-based heterostructure photocatalysts.

The manipulation of the constituents of novel hetero-photocatalysts is an effective method for improving photocatalytic efficiency, but a theoretical understanding of the relationship between interlayer interaction and photocatalytic activity is still lacking. Herein, the interfacial interactions and electronic properties of MoS2/graphene oxide (GO) heterojunctions with various O concentrations were explored systematically by first-principles calculations. The results indicate that MoS2 and GO can form a stable van der Waals heterojunction, and enhance the built-in internal electric field from GO to the MoS2 surface with the increase in O concentration after interfacial equilibrium. It is inferred that the photogenerated electrons and holes naturally accumulate in the conduction band of GO and the valence band of MoS2, respectively, under the built-in internal electric field driving, indicating the formation of direct Z-scheme heterojunctions. In addition, a red shift of the light absorption edge and the shift up of the conduction band edge of MoS2/GO heterojunctions are observed with an increase in O concentration. It can be concluded that the O atom plays a crucial role in the energy band alignment of MoS2/GO heterojunctions for the improvement of photocatalytic performance. These results are beneficial to understand and design layered MoS2/GO photocatalytic systems or as cocatalysts with other semiconductors.

Topological semimetals, in which conduction and valence bands cross each other at either discrete points or along a closed loop with symmetry protected in the momentum space, exhibited great potential in applications of optical devices as well as heterogeneous catalysts or antiferromagnetic spintronics, especially when the crossing points/lines matches Fermi level (E F). It is intriguing to find the ‘ideal’ topological semimetal material, in which has a band structure with Dirac band-crossing located at E F without intersected by other extraneous bands. Here, by using angle resolved photoemission spectroscopy, we investigate the band structure of the so-called ‘square-net’ topological material ZrGeS. The Brillouin zone (BZ) mapping shows the Fermi surface of ZrGeS is composed by a diamond-shaped nodal line loop at the center of BZ and small electron-like Fermi pockets around X point. The Dirac nodal line band-crossing located right at E F, and shows clearly the linear Dirac band dispersions within a large energy range >1.5 eV below E F, without intersected with other bands. The obtained Fermi velocities and effective masses along Γ–X, Γ–M and M–X high symmetry directions were 4.5–5.9 eV Å and 0–0.50 m e, revealing an anisotropic electronic property. Our results suggest that ZrGeS, as a promising topological nodal line semimetal, could provide a promising platform to investigate the Dirac-fermions related physics and the applications of topological devising.

The photoelectrochemical properties of g-C3N4 sheet are modified by the π-π stacking interaction with graphene, and the corresponding role of graphene on the surface chemical reactions is investigated by density functional theory. The calculated cohesive energies and the lattice mismatch energies indicate that g-C3N4 and graphene are in parallel contact and can form a stable heterojunction. According to our calculated energy band structures and work functions of g-C3N4/graphene heterojunctions, the band edge modulations by graphene are discussed and corresponding photoinduced charge transfer processes are analyzed in detail. It is found that the incorporating of graphene into g-C3N4 facilitates the separation of photoinduced e–/h+ pairs and the oxidation capacity enhancement of the photoinduced holes with the downshifting of the valence band edge of g-C3N4 layer. It is identified that the inhomogeneous onsite energies between interlayer and the band edge modulations are induced by the inhomogeneous charge redistribution between interlayer caused by graphene. Further, the initial dynamic reaction processes of oxygen atoms in g-C3N4/graphene heterojunctions also confirm the significant role of graphene on the surface chemical reactions.

The deformation of thin-wall stacked structures with low stiffness has been a common problem in the aircraft assembly process, making it difficult to achieve tight tolerance of the countersink depth in one-shot stack drilling. This difficulty is attributed to the complex tool position relative to the workpiece during the machining process. In this paper, an approach to countersink depth control composed of real measurement of the workpiece deformation and compensation of the tool position is presented. The deformation of the workpiece is divided into the following two categories: the rotation angle perpendicular to the feed direction and the deformation along the feed direction. These types of deformation are analysed regarding their influence on the countersink depth error. Effective measures are taken to ensure the countersink depth accuracy; such measures include the adjustment of the normal vector of the drilling position after the clamping process, the error monitoring of the normal vector during machining, and the multi-level compensation during machining. Theoretical analysis and validation of the proposed solution via comparative experiments showed a clear understanding of the coupled interaction of the thrust force with the workpiece deformation and corresponding reduction in the countersink depth error. The compensation solution requires simple computation and is straightforward to implement in industrial automatic drilling applications.

During the robotic drilling of an aircraft assembly, the normal directions of the workpieces are to be measured to guide the robot by aiming the spindle at the real normal directions of the curved surfaces. This paper describes the development of a method of using four laser displacement sensors to measure the normal direction and the implementation of the proposed method in a robotic drilling system to meet industrial application requirements. First, a novel mechanical structure is introduced to achieve a higher installation accuracy for the laser displacement sensors with a micro adjusting method. Next, the hardware structures and a convenient method of calibrating the sensors are introduced. To accommodate the complexity of the industrial circumstance, a procedure of measuring and adjusting is developed with consideration of both an angular deviation threshold and a limited adjusting iteration. Finally, the experiments of measuring and adjusting iteratively show that two iterations can achieve a satisfactory angular deviation of 0.1° for planar workpieces and three iterations are required for curved workpieces, with the perpendicularity errors of the drilled holes being less than 0.3°. The results can meet the required perpendicularity accuracy of 0.5°.

A reflux method to synthesize ultrathin polycrystalline TiO2(B) nanosheets (NSs) which are assembled by single crystals, and further stacked into nanoflower structures, is described. On the basis of the theoretical calculations and experiments, H2O2 can easily substitute the ethylene glycol adsorbed on the surface of TiO2(B) NSs, forming H2O2–NS due to the lower adsorption energy and the unique structural features of ultrathin TiO2(B) nanosheets. TiO2(B) NSs and the H2O2 system can be accelerated to generate superoxide radicals under heat or light and thus exhibit a great degradation property on dye molecules; the total organic carbon (TOC) removal rate was 6 times higher than that for H2O2 alone. Meanwhile, TiO2(B) NSs and the H2O2 system have a good application on the selective oxidation due to the reactive species of superoxide radicals avoiding overoxidization of benzyl alcohol. The conversion of benzyl alcohol oxidized to benzaldehyde in water solution under low temperature and atmospheric pressure w...

The interface properties of the hybrid graphene/BiVO4(001) heterojunction were investigated by first-principle calculations incorporating semiempirical dispersion-correction schemes to correctly describe van der Waals interactions. The results indicate that graphene and BiVO4 are in contact and form a stable heterojunction. After equilibration of the graphene/BiVO4 interface, their energy levels are adjusted with the shift of their Fermi levels based on calculated work functions. In addition, electrons in the upper valence band of BiVO4 can be excited to the conduction band under irradiation, and then arrive at the C pz orbital of graphene, in which the electrons cannot migrate back to BiVO4 and thus are trapped in graphene. Thus, substantial holes are accumulated in the BiVO4(001) surface, facilitating the separation of photogenerated e−/h+ pairs. The calculated charge density difference unravels that the charge redistribution drives the interlayer charge transfer from graphene to the BiVO4(001) surface. It is identified that the hybridization between the two components induces an increase of optical absorption of BiVO4 in the visible-light region. A deep understanding of the microcosmic mechanisms of interface interaction and charge transfer in this system would be helpful for fabricating BiVO4-based heterojunction photocatalysts.

The surface modification to inhibit charge recombination was utilized in dye-sensitized solar cells (DSSCs) and self-powered ultraviolet (UV) sensors based on SnO 2 hierarchical microspheres by TiO 2 modification. For DSSCs with SnO 2 photoelectrodes modified by TiO 2 , the power conversion efficiency (PCE) was improved from 1.40% to 4.15% under standard AM 1.5G illumination (100 mW/cm 2 ). The electrochemical impedance spectroscopy and open-circuit voltage decay measurements indicated that the charge recombination was effectively inhibited, resulting in long electron lifetime. For UV sensors with SnO 2 photoelectrodes modified by TiO 2 layer, the self-powered property was more obvious, and the sensitivity and response time were enhanced from 91 to 6229 and 0.15 s to 0.055 s, respectively. The surface modification can engineer the interface energy to inhibit charge recombination, which is a desirable approach to improve the performance of photoelectric nanodevice.

A ternary composite photocatalyst CdS/Au/g-C3N4 was synthesized by a facile two-step photoreduction method. In this hybrid structure, CdS nanoparticles and CdS@Au core–shell nanoparticles are homogeneously deposited on the surface of g-C3N4 to produce two different structures CdS–g-C3N4 and CdS@Au–g-C3N4. The microstructure analysis results of the composition, chemical states, and optical properties of as-prepared ternary hybrid reveal that a strong interaction exists between CdS nanoparticles, CdS@Au nanoparticles and the g-C3N4 bulk. The ternary composite CdS/Au/g-C3N4 exhibits significantly enhanced photocatalytic activity for RhB degradation under visible light irradiation compared with the binary composites CdS/g-C3N4, Au/g-C3N4 and pure g-C3N4. Meanwhile, CdS/Au/g-C3N4 also demonstrates good photostability in the recycling test of RhB degradation. The active species in the photocatalytic reaction over CdS/Au/g-C3N4 are detected as O2˙− and h+. The superior photocatalytic performance of CdS/Au/g-C3N4 should be attributed to the enhanced separation efficiency of photogenerated electrons–holes induced by the formed heterojunctions CdS–g-C3N4 and Z-scheme structure CdS@Au–g-C3N4 where Au nanoparticles serve as electrons mediator.

Interlayer gap formation during through-hole drilling in stacked structures is a common problem in large assembly operations. The resulting interfacial burrs and non-coaxial stacked holes deteriorate the machining quality and increase the overall assembly time and costs. This study presents both experimental work and theoretical analysis to understand the interlayer gap formations and non-coaxiality occurrences in the drilling of stacked structures of broad skins and narrow stringers, which imitate typical structures of large assemblies. First, some stack drilling experiments are specially designed and are performed to observe that the stacked holes are non-coaxial in a regular fashion by measuring the hole diameters of the upper layer, lower layer and interface. Then, a simplified mechanical model of the stacks is built in 2-D to study how the interlayer gaps and non-coaxiality are formed during stack drilling. Through quantitative analysis based on the simplified model, it is noted that the stack stiffness, drilling thrust force and pressing force have important impact on the interlayer gaps and non-coaxiality. Finally, finite element methods are adopted to present the deformations in 3-D. The calculation results agree with the theoretical explanations for non-coaxiality given by the analytical simplified model. In addition, the beneficial effects of the fasteners and ribs are discussed based on the calculation results, and thus, they could contribute to proposals for better designs for stack drilling.

In this work, a special hybrid structure with 2D configuration comprising of g-C3N4, reduced graphene oxide (RGO), and BiOI (g-C3N4/BiOI/RGO) was rationally constructed and immobilized on Ni foam with RGO functioned as electron transfer mediator and binder. The immobilized 2D g-C3N4/BiOI/RGO hybrid structure exhibited the enhanced photocatalytic CO2 reduction to CO and the methyl orange (MO) degradation efficiency under visible light irradiation. Particularly, the hybrid heterojunction with a mass ratio 6% of BiOI to g-C3N4 displayed the highest CO yield and degradation rate constant for MO, which was 1.6 times and 3 times of g-C3N4/RGO binary heterojunction immobilized on Ni foam. The enhanced photocatalytic activity was ascribed to the rapid charge separation. More importantly, combined with the theoretical calculations on the work functions of g-C3N4, rGO and BiOI, the experimental results clarified the charges transfer route of g-C3N4/BiOI/RGO heterojunction conforming to the Z-scheme mechanism.

The manipulation of the constituents of novel hetero-photocatalysts is an effective method for improving photocatalytic efficiency, but a theoretical understanding of the relationship between interlayer interaction and photocatalytic activity is still lacking. Herein, the interfacial interactions and electronic properties of MoS

Visible light mineralization ability is of great importance for the practical use of a photocatalyst. As a promising visible light photocatalyst, BiOI has relatively weak mineralization ability and is not efficient enough for the removal of some organic pollutants. In this work, the visible light mineralization ability of BiOI was improved via charge transfer between BiPO4 donor and BiOI acceptor. This charge transfer in BiPO4/BiOI composite photocatalyst produced more oxidative holes than that produced by pure BiOI, thus significantly improved its mineralization ability. Under visible light (λ > 420 nm) irradiation, the most effective BiPO4/BiOI could degrade phenol to small molecular organic acids more rapidly than BiOI and its removal efficiency for phenol and TOC were about 2 and 4 times as high as that of pure BiOI, respectively. The enhancement of photocatalytic performance is attributed to the enhanced oxidation ability of the hole and the increased separation and migration efficiency of photogenerated electrons and holes, which is resulted from the relatively large dipole moment of BiPO4.

The photoelectrochemical properties of g-C

A reflux method to synthesize ultrathin polycrystalline TiO

The electronic structures of ZnO were calculated using density functional theory, in which the electronic interactions are described within the GGA+U (GGA = generalized gradient approximation) formalism, where on-site Coulomb corrections are applied on the Zn 3d orbitals (Ud) and O 2p orbitals (Up). The relaxed GGA+U calculation can correct completely the band gap, the position of Zn 3d states, the transition levels of O vacancy in band gap, and so on, which is different from other GGA+U (equivalent LDA+U) calculations partially correcting the energy band structure for fixed lattice constants. By comparing with experimental data, the pair of Ud = 10 and Up = 7 eV was identified as an optimum choice for the energy band structure of W-ZnO. Then, the proper pair of Ud and Up parameters was taken to predict the energy band structure of ZB- and RS- ZnO, of which the former is in good agreement with experimental values, and the latter is in dispute, relating to the decrease of the octahedral symmetry. Subsequen...

ZnO photocatalyst with surface oxygen vacancies was obtained via vacuum deoxidation method. The concentration of surface oxygen vacancies could be controlled by tuning the temperature and time in vacuum, which governs the production of visible activity and the enhanced level of photocatalytic activity. The optimum UV photocatalytic activity and photocurrent of vacuum ZnO are almost 1.7 and 2.4 times as high as that of pure ZnO, respectively. Interestingly, the dramatic visible photocatalytic activity and distinct photocurrent both are generated due to the introducing of oxygen vacancies on ZnO surface. The enhancement in performance is attributed to the high separation efficiency of photogeneration electron–hole pairs due to the broadening of the valance band (VB) induced by surface oxygen-vacancies states. The production of visible photoactivity is demonstrated to be the narrow of energy band gap resulting from the rising of VB.

An effective structural doping approach has been described to modify the photoelectrochemical properties of g-C3N4 by doping with nonmetal (sulfur or phosphorus) impurities. Here, the substitutional and interstitial doped models of g-C3N4 systems were constructed with different doped sites, and then their dopant formation energies and electronic properties were performed to study the stability and visible-light photoactivity using first-principles density functional theory, respectively. Our results have identified that an S atom preferentially substitutes for the edge N atom of g-C3N4; however, a P atom preferentially situates the interstitial sites of in-planar of g-C3N4. Furthermore, it is demonstrated that the doping with nonmetal impurities reduces the energy gap to enhance the visible-light absorption of g-C3N4. The increased dispersion of the contour distribution of the HOMO and LUMO brought by doping facilitates the enhancement of the carrier mobility, while the noncoplanar HOMO and LUMO favor the...

An effective codoping approach is described to modify the photoelectrochemical properties of anatase TiO2 by doping with nonmetal (N or C) and transition metal (Nb or Ta) impurities. Here, compensated and noncompensated codoped TiO2 systems are constructed with different proportions and dopant species, and then their dopant formation energies and electronic properties are calculated to study the stability and visible-light photoactivity by first-principles density functional theory incorporating the LDA+U formalism, respectively. The calculated results demonstrate that the codoping with transition metals facilitates the enhancement of the concentration of p-type dopants (N and C) in the host lattice. Especially, both 1:2 compensated Nb/C/Nb and Ta/C/Ta codopings not only reduce the energy gap to enhance the optical absorption and eliminate the local trapping to improve carrier mobility and conversion efficiency but also do not lower the reduction potential of the conduction band edge. Our designated strat...

First-principles density functional theory incorporating the LDA + U formalism has been used to investigate the origin of photocatalytic activation of Ag3PO4. The approach provides an improved band gap and the position of the valence band if both Up and Ud are used. Through examining the energy band structure and density of states, we can understand why Ag3PO4 is a promising photocatalyst for oxidizing water as well as degrading organic contaminants. The results show that Ag3PO4 has a large dispersion of conduction band and the inductive effect of PO43−, which help the separation of electron−hole pairs. It is demonstrated theoretically that Ag vacancies in Ag3PO4 with high concentration have a significant effect on the separation of electron−hole pairs and optical absorbance in the visible-light region. These findings present a reasonable explanation of recent experimental results.

First-principles plane-wave pseudopotential calculations have been performed to study the formation energy, electronic structure and optical properties of V-, N- and V/N-doped TiO2. The calculated results show that V:N defect pairs tend to bind to each other, which facilitates the enhancement of the concentration of N dopant compared with N-doped case. In addition, the incorporation of V into N-doped TiO2 lattice induces the appearance of passivated shallow acceptor and donor levels near the VBM and CBM, which would act as capture traps for photoexcited holes or electrons. Furthermore, the optical absorption coefficient spectra show that V/N codoping can enhance the optical absorption region, which can be attributed to lower excitation energy from the N 2p orbitals to V t 2 g orbitals rather than a band gap narrowing. These findings give a reasonable explanation of recent experimental results.

Nanocrystalline γ′-Fe 4 N thin films were synthesized on single crystal Si (1 0 0) substrate by facing target magnetron sputtering at a mixture of Ar/N 2 gas discharge, and their structure, morphology, and magnetic properties at room temperature and low temperature were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM), respectively. The results showed that the films were γ′-Fe 4 N with an average grain size of 55 nm, which had a highly preferred orientation along (1 1 1). The ratio of remanent magnetization M r over saturated magnetization M s at room temperature for γ′-Fe 4 N was 0.528, which indicated that the films had a single easy magnetized direction. In the temperature range of 80–350 K, the saturation magnetization M s and coercive force H c increased, whereas the ratio of M r / M s decreased with decreasing temperature. The relation between the coercive force H c and temperature T observed a T 1/2 law, and the coercivity at T = 0 K of 356.87 Oe and blocking temperature of 667 K were acquired, respectively. However, the relation between M s and T did not observe the Bloch T 3/2 law, which meant that the interaction among spin waves should be considered. Through fitting M s – T equation, the saturation magnetization at T = 0 K of 202 emu/g, Bloch constant of 1.0 × 10 −4 K −3/2 , and exchange interaction constant of 1.537 × 10 −21 were obtained, respectively.

The (γ′-Fe 4 N/Si-N) n ( n : number of layers) multilayer films and γ′-Fe 4 N single layer film synthesized on Si (1 0 0) substrates by direct current magnetron sputtering were annealed at different temperatures. The structures and magnetic properties of as-deposited films and films annealed at different temperatures were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results showed that the insertion of Si-N layer had a significant influence on the structures and magnetic properties of γ′-Fe 4 N film. Without the addition of Si-N lamination, the iron nitride γ′-Fe 4 N tended to transform to α-Fe when annealed at the temperatures over 300 °C. However, the phase transition from γ′-Fe 4 N to ɛ-Fe 3 N occurred at annealing temperature of 300 °C for the multilayer films. Furthermore, with increasing annealing temperature up to 400 °C or above, ɛ-Fe 3 N transformed back into γ′-Fe 4 N. The magnetic investigations indicated that coercivity of magnetic phase γ′-Fe 4 N for as-deposited films decreased from 152 Oe (for single layer) to 57.23 Oe with increasing n up to 30. For the annealed multilayer films, the coercivity values decreased with increasing annealing temperature, except that the film annealed at 300 °C due to the appearance of phase ɛ-Fe 3 N.

While bolt fastening is the most commonly used method for fastening components, hole quality is an important technology standard in modern manufacturing, especially in the aircraft industry. With low stiffness, the machining deformation of aerospace structures has been a striking problem, which makes it difficult to achieve tight tolerance of countersink depth in one-shot drilling of stacked materials. As a result of the manufacturing errors between the workpieces and the digital models, the position of the workpiece surface can hardly be known before drilling. Moreover, the cutting force adds to the deformation of the thin-walled workpiece in the direction of the feed axis. In view of problems mentioned above, a method of position compensation based on the clamp foot displacement is proposed in the paper, which ensures the countersink depth accuracy by compensating for the deformations of clamping and countersinking respectively in different stages of drilling. Some drilling experiments were conducted, in which the forces in the feed direction were real-time monitored and recorded for FEM simulation. The influencing factors of countersink depth error are firstly discussed in this study, which mainly consists of the size of clamping force and the stiffness differences of variable drilling positions. Numerical simulations were carried out to study the deformation characteristics of workpiece under the combining effect of clamping force and cutting force achieved above. Comparing the simulation results and the experiment results, some other influencing factors of countersink depth are discussed.Copyright © 2015 by ASME

The mechanism in drilling of carbon fiber reinforced plastic (CFRP) is different from that of CFRP and titanium stacks. The evacuation of the titanium chips through the hole causes damage to the CFRP. To investigate the quality characteristics of CFRP-layer in drilling of CFRP/Ti stacks, an automated drilling prototype is developed and the drilling experiments of single CFRP and CFRP/Ti stacks are designed respectively for purpose of analyzing the influence of the titanium chips formation with various cutting parameters on the drilling performance of CFRP-layer. The chips morphology are firstly observed, then the mechanism of entrance spalling, high surface roughness (Ra), and hole diameter out of tolerance is studied. The results show that, low feed rate and high cutting speed generates long and folded chips wrapped around the drill, which damage the CFRP strongly. The damage can be controlled by optimization of the cutting parameters. Low feed rate helps to eliminate the entrance spalling, but enlarger the hole diameters in both the CFRP and the titanium layers. To prevent the chips from wrapping on the drill, the cutting speed should be selected in a moderate range. Therefore, the cutting parameters on the titanium layer can be recommended as the feed rate between 0.09 mm/r to 0.13 mm/r, and the cutting speed in a range of 12 m/min to 24 m/min.

OPTICA APPLICATA; 2/2015; ISSN 1429-7507

The hydrogen adsorption properties of Ti and Ni atoms as media on single-walled carbon nanotube (SWCNT) have been studied by density functional theory (DFT) incorporating a pragmatic method to correctly describe van der Waals interactions. The results show that both Ti and Ni atoms can reliably adhere to single-walled carbon nanotube, respectively, making strong TM[Formula: see text]C bonds. Meantime, it is found that the average adsorption energies of H2 by Ti and Ni atoms are decreased with the increase of the amount of H2 adsorption. Ti or Ni atoms can bind up to no more than six H2 molecules on a carbon nanotube. It is inferred that these transition metals (TMs) can adsorb molecular hydrogen through likely Kubas-type interaction. By comparing the interaction energies among TM and H atoms, it can be identified that the hydrogen adsorption properties of Ti atoms are superior to those of Ni atoms at certain conditions. The present investigation is useful in the wider development of carbon-based nanomaterials as potential high-capacity H2 storage media.

CdWO4 nanorod photocatalysts were synthesized by a hydrothermal method. CdWO4 nanorod photocatalysts showed highly efficient photocatalytic activity for the degradation of methylene blue under ultraviolet light irradiation. On the basis of the experiment results, the difference in photocatalytic activities of the samples was mainly attributed to surface area, surface hydroxyl groups and defects which can act as inactivation centers. Kinetic studies using radical scavenger technologies suggested that OH˙ radicals were the dominant photooxidants.

The effect of stress annealing on magnetic properties and asymmetrical giant magneto-impedance effect of Co-rich glass-covered microwires have been studied. The asymmetrical giant magneto-impedance effect in glass-covered amorphous wires was obtained frequency current biased with a dc current. Under certain annealing conditions(annealing current, Iann=183 A/mm2, applied stress, =140 MPa), the impedance up to about 0.18 % / A/m. The asymmetrical giant magneto-impedance is useful to construct linear field Sensors.

Three kinds of crystal phase BiPO4 (HBIP, nMBIP and mMBIP) were selectively synthesized by a hydrothermal method. The governed factors for the formation of three crystal phase of BiPO4 were both on the acidity of the solution and reaction temperature. The BiPO4 with nMBIP phase structure showed higher activity for degradation of MB solution under UV irradiation than HBIP and mMBIP. The catalytic activity per surface area activity of nMBIP (3.8×105 h−1 m−2) was about ten times higher than that of P25(1.4×104 h−1 m−2). The BiPO4 with nMBIP structure exhibited the highest activity due to the most distorted PO4 tetrahedron. The induce effect of the dipole moment derived from the distorted PO4 tetrahedron promoting the separation of e−/h+ pairs and further benefited for the photocatalytic reaction. This correlation may help to design and develop other oxoacid salt photocatalysts with high activity.