Multi-response optimization of 67Ni18Cr5Si4B coating by HVOF spray using Taguchi-OEC technique

High Velocity Oxygen Fuel (HVOF) spray is being widely used in many industries to deposit erosion-resistant coatings or restore the dimension for components. The porosity, adhesion strength, and hardness are the essential properties commonly used to access the quality of coatings and thus the effectiveness of a HVOF spray process. To achieve desired coating properties and reduce production cost, optimization of process parameters in HVOF spray has developed immensely during last decades. Among the spray parameters, particle velocity, powder feed rate and standoff distance contribute a significant influence on the final properties of the coatings. In the present study, experiments of HVOF thermal spray were prepared for the 67Ni18Cr5Si4B alloy powder. The process parameters including spray velocity, powder feed rate and spray distance were optimized for the objectives of adhesion strength, porosity and microhardness of 67Ni18Cr5Si4B coating. Based on the Taguchi method, signal-to-noise (S/N) ratio and overall evaluation criteria (OEC) are determined to solve the optimization problem considering multiple performance characteristics. Moreover, analysis of variance (ANOVA) was conducted to analyse the contribution percentage of each process parameter. The optimal process parameters in HVOF spray of 67Ni18Cr5Si4B were found for the multi-response optimization as velocity of 1000 m/s, powder feed rate of 30?g/min, and spray distance of 0.2 m. The results of ANOVA indicated that the spray distance was the most significant parameter affecting the output spray quality among the investigated process parameters, subsequently to the powder flow rate and velocity of spray. Finally, a confirmatory experiment was carried out to support the accuracy of optimal process parameters.     

Adsorption of REEs from Aqueous Solution by EDTA-Chitosan Modified with Zeolite Imidazole Framework (ZIF-8)

Chitosan (CS) modified with ethylenediamine tetraacetic acid (EDTA) was further modified with the zeolite imidazole framework (ZIF-8) by in situ growth method and was employed as adsorbent for the removal of rare-earth elements (REEs). The material (EDTA–CS@ZIF-8) and ZIF-8 and CS were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and nitrogen adsorption/desorption experiments (N₂- Brunauer–Emmet–Teller (BET)). The effects of adsorbent dosage, temperature, the pH of the aqueous solution, contact time on the adsorption of REEs (La(III), Eu(III), and Yb(III)) by EDTA–CS@ZIF-8 were studied. Typical adsorption isotherms (Langmuir, Freundlich, and Dubinin–Radushkevich (D-R)) were determined for the adsorption process, and the maximal adsorption capacity was estimated as 256.4 mg g⁻¹ for La(III), 270.3 mg g⁻¹ for Eu(III), and 294.1 mg g⁻¹ for Yb(III). The adsorption kinetics results were consistent with the pseudo-second-order equation, indicating that the adsorption process was mainly chemical adsorption. The influence of competing ions on REE adsorption was also investigated. After multiple cycles of adsorption/desorption behavior, EDTA–CS@ZIF-8 still maintained high adsorption capacity for REEs. As a result, EDTA–CS@ZIF-8 possessed good adsorption properties such as stability and reusability, which have potential application in wastewater treatment.     

Three-dimensional ZIF-67 attached lamellar Ti3AlC2 combined with ZnAl-LDH as cathode catalyst for enhancing oxygen reduction reaction of microbial fuel cells

In this study, a simple hydrothermal method was used to prepare the cathode catalyst of microbial fuel cells (MFCs). The three-dimensional structure of ZIF-67 attached to the lamellar Ti₃AlC₂/ZnAl-layered double hydroxide (LDH) was observed. (010), (012), (015) were the obvious peaks of the composite ZIF-67@Ti₃AlC₂/ZnAl-LDH. Ti, N, C, Al, O, F were relatively uniformly distributed on the surface of the composite material. The maximum voltage of ZIF-67@Ti₃AlC₂/ZnAl-LDH-MFC was 576 mV and the stabilization time was 8 d. The maximum power density of ZIF-67@Ti₃AlC₂/ZnAl-LDH-MFC was 587 mW/m², which was 1.32 times of Ti₃AlC₂/ZnAl-LDH-MFC (446 mW/m²) and 2.69 times of Ti₃AlC₂-MFC (218 mW/m²). Ti₃AlC₂ with large interlayer spacing and high specific surface area were perfectly composited with multi-layer nanosheets of ZnAl-LDH, and ZIF-67 attached to the surface enhanced the reaction center and activity of the composite material, which promoted oxygen reduction reaction and improved MFC performances.     

ZIF-67-derived Co,Ni and S co-doped N-enriched porous carbon polyhedron as an efficient electrocatalyst for oxygen evolution reaction (OER)

Rational fabrication of highly efficient and non-precious metal electrocatalysts for oxygen evolution reaction (OER) are of great importance for renewable energy exploitation to solving the energy crisis and environmental problems. In this paper, we report a novel hybrid nanostructure with Co, Ni and S co-doped N-enriched porous carbon polyhedron (CoNi_xS_y/NCP) via a absorption-pyrolysis-sulfuration strategy derived from zeolitic imidazolate framework-67 (ZIF-67) and explored its electrocatalytic performance for OER. During the synthesis process, Ni²⁺ is abosrbed within the pores or surface of ZIF-67 and Ni/ZIF-67 can be transformed into the Co and Ni co-doped porous carbon frameworks when it is sulfurazed at 800 °C. NiS₂ and NiCo₂S₄ nanoparticles formed at high temperature are homogeneously dispersed in porous carbon and can activate its electrocatalytic performance. The porous carbon can enhance the electrochemical surface area and charge transfer efficiency. Benefiting from the synergistic effects between highly active NiS₂, NiCo₂S₄, and porous carbon, CoNi_xS_y/NCP electrocatalyst exhibits excellent electrocatalytic performance. The results show that CoNi_xS_y/NCP also exhibits a potential as low as 1.51 V to achieve 10 mA/cm² current density and extremely stability towards OER. The good electrocatalytic activity of CoNi_xS_y/NCP further suggest its great potential as an efficient eletctocatalyst for sustainable energy applications.     

Enhanced electrochemical performance of nickel intercalated ZIF-67/rGO composite electrode for solid-state supercapacitors

Ni (Nickel) doped zeolitic-imidazolate framework (ZIF-67) has been prepared in presence of reduced graphene oxide (rGO) to realize a ZIF-67/rGO composite. The doping level of Ni and the ratio of rGO (wt%) in the composite have been optimized to attain desirable redox activity and electrical conductivity. A partial incorporation of redox active Ni ions to substitute Co (cobalt) ions in ZIF-67 has resulted in better electrochemical characteristics by inducing additional pseudocapacitance. A finalized composite with 33% Ni and 20% of rGO (i.e, Ni₃₃/ZIF-67/rGO₂₀) has been used as a supercapacitor electrode material to achieve a high specific capacitance of 304 F/g at a current density of 1 A/g in the presence of 1 M H₂SO₄ as an aqueous electrolyte. The above electrode has also been tested for an all-solid-state symmetric supercapacitor in the presence of a polymer gel electrolyte (PVA/1 M H₂SO₄). This device delivered high values of power and energy densities, i.e., 1 kW/kg and 21.5 Wh/kg, respectively. The device also exhibited an excellent cyclic stability. About 87% of capacitance could be retained even after 4500 charge-discharge cycles. The device has shown superior results for a working potential window of 0–2 V. The practical usefulness of the device has been demonstrated by preparing a symmetrical supercapacitor, which could energize a white LED for 8 min upon a charging of only 40 s.     

部分非晶态Fe_(33)Zr_(67)合金条带的表观晶化动力学

利用示差扫描量热卡计（ＤＳＣ），结合Ｘ射线衍射分析（ＸＲＤ）及透射电子显微镜分析（ＴＥＭ）等实验，研究了部分非晶态Ｆｅ３３Ｚｒ６７合金条带的晶化动力学结果表明：晶化过程为晶粒长大过程所控制，尽管在条带中淬态核分布明显不均匀，与经典Ａｖｒａｍｉ分析的基本假设相矛盾，但该晶化过程仍然与ＪＭＡ反应动力学结论一致．     

Atomic Layer Deposition Inducing Integration of Co,N Codoped Carbon Sphere on 3D Foam with Hierarchically Porous Structures for Flexible Hydrogen Producing Device

Integration of metal–organic frameworks on deformation tolerant substrates exhibits a promising prospect in flexible electrode applications. A straightforward synthesis utilizing atomic layer deposition pretreating to induce the growth of a zeolitic imidazolate framework‐67 (ZIF‐67) layer on carbon foam (CF), which maintains high ZIF‐67 loading with a hierarchically porous structure and large surface area of 453 m² g^?1 is presented. With a subsequent pyrolysis process, three‐dimensional composite structures are obtained with Co, N codoped carbon spheres attached firmly on the CF framework, and CF bridges the individual carbon spheres to construct a conductive pathway. The composites are used as a flexible electrode for hydrogen production both in acid and alkaline electrolytes. The advances in the composite structure, such as the hierarchically porous structure, large surface area, and high loading of active material, lead to excellent electrochemical performance in terms of low overpotential of 142 mV and low Tafel slope of 73 mV dec^?1 in 0.5 m H₂SO₄. Most importantly, the composite structure with outstanding flexible property shows good catalytic performance under remarkable deformation, and after 100 repeated compression–recovery cycles, the performance degrades slightly. This work provides a new design of flexible electrode, which is promising for the hydrogen production industry.     

池窑法玻璃纤维增强PA66性能研究

以池窑法生产的高强玻璃纤维(短切处理过)为改性填料,对尼龙66进行共混改性。结果表明:尼龙66/玻纤复合材料的拉伸强度、弯曲强度、硬度、冲击强度等性能都有了显著提高,其中拉伸强度提高了69%、弯曲强度提高了112%、硬度提高了14%、冲击强度提高了11%,但是材料的断裂伸长率却随玻纤含量的增加而降低。通过分析得出玻纤的最佳含量为30%左右。简要介绍了池窑法生产的玻璃纤维的特点。     

Effect of grain boundary state and grain size on the microstructure and mechanical properties of alumina obtained by SPS: A case of the amorphous layer on particle surface

The work was aimed at the investigation of kinetics of Spark Plasma Sintering (SPS) of the α-Al₂O₃ particles with amorphous surface layers and investigation of the effect of the amorphous layers on the grain growth and on the mechanical properties of alumina. The objects of investigations comprised:(i) submicron α-Al₂O₃ powder, (ii) submicron α-Al₂O₃ powder with the amorphous layers on the particles' surfaces, and (iii) the fine-grained α-Al₂O₃ powder. The submicron powders (i) and (ii) were used to analyze the effect of the amorphous layers on the sintering kinetics. Powders (i) and (iii) were used to analyze the effect of the initial particle sizes on the shrinkage kinetics. The effect of the temperature regime and of the rate (V_h) on the shrinkage kinetics of the submicron and fine alumina powders has been studied. The shrinkage curves were analyzed using the Young–Cutler and Coble models. The sintering kinetics was shown to be determined by the intensity of grain boundary diffusion for the submicron powders and by simultaneous lattice diffusion and grain boundary one for the fine powders. The amorphous layers on the surfaces of the submicron α-Al₂O₃ particles were found to affect the grain boundary migration rate and the Coble equation parameters at the final stages of SPS. The abnormal characteristics of the alumina ceramics sintered from the submicron powder with the amorphous layers on the particles’ surfaces were suggested to originate from the increased concentration of the defects and of the excess free volume at the grain boundaries formed during crystallization of the amorphous layers.     

Reply to Oosterhaven’s: the net multiplier is a new key sector indicator

This paper is a reply to Oosterhaven’s reply of the paper “A critical comment on Oosterhaven–Stelder net multipliers” written by de Mesnard in this issue of The Annals of Regional Science. It is argued that, unlike Oosterhaven’s statement, (1) any coefficient must be stable but Oosterhaven–Stelder final demand ratio is not; (2) the output must be exogenous in Oosterhaven–Stelder net multipliers (NM); (3) the Leontief input–output model can be validly seen as an iterative model, time consistent; (4) there is a valid link with the Keynesian multiplier; (5) the output preservation requirement is satisfied by de Mesnard’s ‘iterative net multiplier’. The paper concludes by agreeing to Oosterhaven’s suggestion that NM is not suitable to examine causalities between endogenous and exogenous variables and that the wording ‘multiplier’ is very bad and confusing for NM. Oosterhaven’s new suggestion of terming it as ‘net contribution’ or ‘net backward linkage’ is very good.