查看更多>>摘要：Tungsten carbide-cobalt (WC-Co) mixtures is the most critical material for cemented carbide. However, traditional preparation methods by using various carbon sources (e, g. carbon black, glucose, methane, carbon monoxide) cause severe carbon deposition. Consequently, traditional WC-Co mixtures exhibits uncontrollable carbon content. To address the challenge, we investigate the in-situ synthesis of WC-Co mixtures by supplying successive liquid methanol as a carbon source and nitrogen gas as a diluent. The as-prepared WC-Co mixture possesses clean surface and controllable carbon content, which are no need for removing excess carbon deposition by washing with water. The carbon nanolayers derived from methanol cracking gas appear on the surface of the intermediates, which can effectively prevent particle aggregation, efficiently increase the intimate contact probability of WC particles and Co particles, and greatly reduce the appearance of excess carbon deposition during subsequent carbonization processes. The present study offers insights on employing quantitative methanol cracking gas as reductive and carbonaceous atmosphere to mediate carbon content in the WC-Co composite powder, which presents a more economical and efficient pathway for large-scale synthesis of high-quality WC-Co mixtures with clean surface and controllable carbon content.
Ismayadi IsmailMuhammad Misbah Muhammad ZulkimiRaba'ah Syahidah Azis
7页
查看更多>>摘要：In the present work, substitution of strontium U-type hexaferrite with the composition of Sr_4Mn_(2-x)Zn_xFe_(36)O_(60) (x= 0.5,0.6,0.8, and 1.0) was prepared via high energy ball milling (HEBM) and sintered at 1100 °C. The phase, microstructure, magnetic, dielectric and electromagnetic wave absorbing properties of U-type strontium hexaferrite composites were measured using XRD, FESEM, and Vector Network Analyzer in the frequency range of 8-18 GHz (X-band and Ku-band). MnZn doping was found to shift the natural resonance of the materials by affecting its magnetocrystalline anisotropy. The reflection loss (RL) indicated that the composite possessed good microwave-absorbing properties with U-type strontium hexaferrite ( Sr_4Mn_(2-x)Zn_xFe_(36)O_(60)) of x = 0.8 resulted in high minimum RL value for all thickness of 1 mm and two peaks at approximately - 32.50 and - 41.50 dB at 14.00 and 15.60 GHz, with bandwidth of 0.60 and 0.80 GHz for losses less than - 10 dB.
查看更多>>摘要：Nowadays, it is still a big challenge to synthesize Mn~(4+)-doped fluoride red phosphors with high water resistance, luminescent intensity and thermal stability simultaneously. Therefore, KSF:M,N@GQ.Ds@KSF (K_2SiF_6:0.06Mn,0.10Na@GQPs (12 mg/mol)@K_2SiF_6 (0.2 wt) KSF: K_2SiF_6, GQDS: OH-contained graphene quantum dots) with high luminescent intensity, high luminescent thermal stability and water resistance have been synthesized via a combination of H_2O_2-free room temperature reaction method, hydrothermal coating method and room temperature surface coating process. Experimental results show that enhancement of negative thermal quenching (NTQ) effect and water resistance can be synergistically induced by double coating of GQPs and KSF. After being immersed in deionized water for 360 min, emission intensities of the KSF:M,N@GQDs and KSF:M,N@GQPs@KSF are decreased from 100% to 70.57% and 91.63%, respectively, indicating that water resistance of the latter is obviously improved by coating of KSF. The improved water resistance is attributed to preventing hydrolysis of [MnF_6]~(2-) on sample's surface by insoluble coating shell of KSF. A prototype WLEDs (white light-emitting diodes) emitted warm white light (CCT = 4546 K and Ra = 91.3, at a driving current of 20 mA) has been assembled by coating mixture of KSF:M,N@GQPs@KSF, yellow emitting phosphor (YAG:Ce~(3+)) and epoxy resin on blue light InGaN chips. The good performances of the WLEDs suggest that the KSF:M,N@GQPs@KSF has potential applications in blue-based warm WLEDs.
查看更多>>摘要：Metal-organic framework (MOF) based materials are a fascinating candidate in the sensor field. In this work, we successfully synthesized Co-MOF/BP-RGO nanocomposite by simple hydrothermal method and fabricated on glassy carbon electrode (GCE) for the detection of chlorogenic acid (CGA). The Co-MOF/BP-RGO nanocomposite was characterized by the powder x-ray diffraction (XRD), micro-Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The electrochemical performance of Co-MOF/BP-RGO was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The Co-MOF/BP-RGO/GCE exposed good sensitivity, and great selectivity towards CGA under optimized conditions. The Co-MOF/BP-RGO/GCE exhibited a wide linear range and excellent LOD 0.001-391 uM and 0.014 uM respectively, and it exposed strong long-term stability also. Hence all these findings indicate that the Co-MOF/BP-RGO nanocomposite is a novel electrocatalyst for the highly sensitive CGA electrochemical sensor. Additionally, our proposed sensor was applied for the detection of CGA in the real samples, such as coffee powder and green tea leaves and it displayed excellent sensitivity and good recovery results.
查看更多>>摘要：The combination of active materials and carbon nanotubes (CNTs) provides an effective way to enhance battery capacity and optimize cycle performance. In the present study, the powder electrodeposition technology is employed to synthesize the NiO-Ni/CNTs composite for the first time. This technique contains the following steps. The CNTs are negatively charged by pre-discharge in lithium-ion batteries. Then, the negatived CNTs are uniformly dispersed in the NiCl_2 plating solution by electrostatic repulsion, and the Ni ions are in situ reduced and deposited onto the CNTs. The close combination of CNTs and NiO-Ni improves the overall conductivity and structural stability. As electrode of lithium-ion battery, the reversible capacity is improved due to the coordination of the Ni metal in the mixture of the composite electrode. Besides, the reversible capacity of the composite electrode is 851 mA h g~(-1) at 50 mA g~(-1) after 50 cycles. The "Powder electrodeposition" method in the current work provides a new way for the preparation of other similar powder composite materials. Furthermore, the problem that the traditional electrodeposition process is difficult to apply in the powder materials will be solved.
查看更多>>摘要：A photostable Ag_3PO_4/BCN type-II p-n heterojunction has been demonstrated by loading nano Ag_3PO_4 on B-doped g-C_3N_4 nanosheet (BCN). The photocatalysts were successfully characterized by various physico-chemical techniques and their photocatalytic activities were tested towards the water oxidation reaction to produce oxygen and Cr (VI) reduction under visible light. The HRTEM confirms Ag_3PO_4 with a particle size of 15 nm has been deposited on BCN to construct a p-n heterojunction. The BCNS-50 absorbs more visible light in the solar spectrum as compared to other catalyst, demonstrating the ability to generate 587 umol h~(-1)g~(-1) O_2 and reduces 98% of 20 ppm Cr (VI) solution in 1 h. The lower PL intensity as well as lower arc value in case of BCNS-50 suggests the maximum e-h separation and lower charge transfer resistance across the semiconductor/electrolyte interface. The BCN sheet provides a compact heterojunction where the oxidation peak of Ag_3PO_4 decreases gradually and disappear in case of BCNS-50 suggesting the enhance stability of Ag_3PO_4 in the heterojunction. BCNS-50 could able to produce -139 and 3087.5 uA photocurrent both in cathodic and anodic direction which is approximately 7 and 2.4 folds higher as compared to nano Ag_3PO_4. The generation of photocurrent in both cathodic and anodic direction confirms the formation of p-n heterojunction which further supported by Mott-Schottky analysis. Furthermore the construction of the p-n heterojunction is verified via Mott-Schottky study. DFT calculation explains the contribution of various atomic orbital of Ag_3PO_4 and BCN towards the formation of hybrid orbital in the heterojunction and the path for charge derealization between them. This work may provide a limelight and alternative pathway for enhanced photocatalytic performance on construction of the p-n heterojunction in a simple way.
查看更多>>摘要：Plastic deformation is always inhomogeneous and complicated during hot processing of the superalloy component, making it hard to accurately predict the flow behavior and microstructure evolutions which may deviate greatly from those results obtained during traditional compression tests with a constant strain rate. The hot deformation behavior of a Ni-Cr-Mo based superalloy C276 in shifted strain rate conditions was investigated and a comparison with the constant strain rate compressions was conducted. The flow stress was found to immediately change after varying the strain rate. The strain rate sensitivity (m), which is the exponent of stress change against the strain rate, was calculated to about 0.16-0.24 for C276 superalloy at 1323 K with strain rate in the range of 0.001-1 s~(-1). The strain rate variation affected the microstructure evolution greatly, leading to different dynamic recrystallization (DRX) tendencies from the compressions with a constant strain rate. Shifting the strain rate from high value to low value resulted into a higher extent of DRX in comparison with the reverse process. A cellular automaton (CA) model, considering the evolutions of dislocation density, recrystallization nucleation and grain growth in deformation procedure, was developed to simulate the microstructure evolution and stress response in shifted strain rate compressions. The successful predictions by the CA model showed a good potential application of this approach in understanding the DRX behavior in non-constant hot processing of C276 superalloy.
查看更多>>摘要：A novel organic-inorganic hybrid compound based on iron fluoride, formulated as (H_2Piper)_4 [(FeF_6)_2FeF_5(H_20)(H_20)4] (Piper = Piperazine), C1, has been synthesized through hydrothermal method and characterized by X-ray single-crystal diffraction, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and dielectric measurements. Single-crystal X-ray study demonstrated that C1 crystallizes in P 1 space group with lattice parameters: a =12.5535(5) A, b =12.8715(4) A, c =22.2774(8) A, a = 92.321(3)°, p = 95.957 (3)°, y = 91.946(3)°, V = 3574.6 A~3 and Z= 4. In the molecular arrangement, [FeF_6]`(3-) and [FeF_5(H_20)]~(2-) anions are connected to [H_2Piper]~(2+) cations and free water molecules through hydrogen bonds (O-H-F and N-H--F) generating 3D network. Thermal analysis (DSC and TG) of C1 confirmed the presence of two phase transitions as well as the temperature of the decomposition of the hybrid material. The complex impedance of C1 was investigated in the temperature range 410-530 K and in the frequency range 200-2.106 Hz. Additionally, an electrical equivalent circuit was reported to explain the impedance results. The variation of the dc and ac conductivity corroborated two phase transitions of the title compound. Furthermore, the frequency dependence of alternative current (ac) conductivity was interpreted in terms of Jonscher's law. The alternative current (ac) electrical conduction in C1 material was accounted for in terms of two processes that can be assigned to the hopping transport mechanism (CBH and NSPT model). The temperature dependences of dielectric permittivity indicated a relaxation process and highlighted the good protonic conduction of this material.
查看更多>>摘要：The promising candidates for high-performance electrode materials, transition metal species@N-doped mesoporous carbon composites (M/MO/M(OH)_2@NDMCs), were synthesized by carbonization of metal ion-doped polyaniline (PANI) functionalized mesoporous silica SBA-15, followed by etching the mesoporous silica template. The yielded M/MO/M(OH)_2@NDMC can be further converted into sulfide via a simple hy-drothermal sulfidization treatment. The mesoporous structure, large amount of the accessible electro-chemically active nitrogen species, partially graphitic structure, and transition metal compounds of transition metal species@NDMC composites will increase the electronic and ionic conductivity by reducing the internal and ion diffusion resistances resulting in fast diffusion of ions in the electrolyte to the electrode surface. These endowed them good electrochemical performance characteristics for use in supercapacitor electrodes. Correspondingly, NiO/Ni(OH)_2@NDMC, Co/Co(OH)_2@NDMC, and CoS_2@NDMC as the electrodes in 2 M KOH showed specific capacitance of 337, 589, and 1178 F g~(-1) at 2.0 A g~(-1), respectively. Furthermore, the assembled asymmetric supercapacitor device utilizing CoS_2@NDMC as a cathode exhibited a satisfactory energy storage capability (50 Wh kg~(-1) at 750 W kg~(-1)) with an admirable cyclic life (retaining -99% initial capacitance over 6000 repeated cycles). This finding gives these transition metal species@NDMC composites, especially CoS_2@NDMC, prospective applications as high-performance supercapacitor electrode materials, where a fast charge/discharge is required.
查看更多>>摘要：Order parameter coupling associated with the first order, improper ferroelastic (Pm3m - Pbam) transition at -510 K in PbZrO_3 has been analysed from the perspective of strain and elasticity. Formal treatment of spontaneous strains using lattice parameter data from the literature reveals typical coupling with the order parameter for octahedral tilting, Q_R, and stronger coupling with the order parameter for antiferroelectric displacements, QΣ. These indicate that coupling between the two order parameters via common strains is not only biquadratic, λQ_r~2Q_Σ~2, but may also have contributions from a higher order term, λQ_r~2Q_Σ~4- Variations of elastic and anelastic properties obtained by resonant ultrasound spectroscopy (RUS) at frequencies in the vicinity of 1 MHz show softening as the transition point is approached from above, discontinuous stiffening at the transition point and a pattern of further stiffening in the stability field of the orthorhombic structure. Below the transition point, the pattern of stiffening resembles the evolution of Q_R~2 and Q_Σ~2, as is typical of coupling dominated by terms with the form λe~2Q~2, where e is a spontaneous shear strain. The absence of softening due to terms of the form λeQ~2 implies that the relaxation time for changes in the order parameters in response to an induced shear strain is slower than ~10~(-6) s. Also in contrast with measurements from the literature made at lower frequencies, no evidence for mobility of ferroelastic domain walls was observed at RUS frequencies. A peak in acoustic loss observed at the transition point and precursor softening in the stability field of the cubic phase are consistent with evidence for local dynamical polar clusters. Apart from some differences in relaxation times, the antiferroelectric transition in PbZrO_3 does not appear to be overtly different from ferroelectric transitions such as occur in BaTiO_3.
NSTL
Elsevier