Microstructure, phase and electrical conductivity analyses of spark plasma sintered boron carbide machined with WEDM

Electrical conductivity is an essential property for machining of sintered boron carbide especially by wire electrical discharge machining (WEDM) process. Pure boron carbide was spark plasma sintered to full density at 2050 degrees C. Rietveld refinement on XRD analysis confirmed presence of B13C2 as the major phase in the powder as well as in the sintered samples.Electrical conductivity was found to be similar to 48 Omega(-1) m(-1). The sintered specimens were successfully machined using WEDM technique. The microstructure of powder, machined and fractured surfaces of the sintered boron carbide were analyzed. At low power of WEDM with pulse current less than 140 A formation of molten, oxidized phases of boron carbide was observed as well as the development of surface cracks were minimum on the machined surface. Thus this work is aiming at achieving better product quality with sintered boron carbide specimens which are machined by WEDM

Phase determination of ZrB2-B4C ceramic composite material using XRD and rietveld refinement analysis

In this work, the Spark plasma sintering technique has been used to sinter ZrB2-B4C (20 wt%) composite at 2100 degrees C and 50 MPa uniaxial pressure for 15 min soaking in an argon atmosphere. XRD analysis has been carried out on the sintered sample to analyze the different phases present in the ZrB2-B4C composite. The Rietveld refinement technique has been used to analyze the crystal structure, the unit cell information such as space group, cell position, cell angles and atomic distances of the composite material using FULLPROF software. (C) 2019 Elsevier Ltd. All rights reserved

Optimization of wire electrical discharge machining parameters for cutting electrically conductive boron carbide

In this work, Pure boron carbide (B4C) was consolidated using spark plasma sintering (SPS) at 2050 degrees C with a dwell of 10 min under 50 MPa uniaxial pressure in Argon atmosphere. The sintered specimen was >99% dense and offered characteristic Vickers hardness and fracture toughness of 31.4 GPa and 4.21 MPa-m(0.5), respectively, at 4.9 N indentation load. The specimen showed satisfactory wire electrical discharge machining (WEDM) performance because of its good electrical conductivity. The design of experiment (DOE) was arranged by 132 orthogonal array (OA) between the machining input parameters namely pulse on-time, pulse off-time, pulse peak current, dielectric fluid pressure and servo feed rate and the output responses like machining speed and surface roughness (R-a). Regression models were employed to establish the numerical correlation between the machining parameters and output responses. Experimental observations were utilized to formulate the first-order regression models to predict responses of WEDM. The optimized input parameters were 27 mu s pulse on time, 48 mu s pulse off time, 180 A pulse peak current, 7 kg/cm(2) water pressure and 2200 min/min servo feed rate for the WEDM performance to produce an optimum machining speed and Ra. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Comparative analysis for the prediction of WEDM responses for machining spark plasma sintered boron carbide ceramic sample by RSM and ANFIS

Unconventional wire electrical discharge machining (WEDM) process is successfully used to cut different metals, alloys, composites and recent addition is engineered ceramics which possess sufficient electrical conductivity. Boron carbide is one of the hardest ceramic materials that unable to be processed with conventional machine tools and can be machined by WEDM compulsorily with proper selection of machine parameters. This study is based on boron carbide samples which were prepared using spark plasma sintering (SPS) furnace and machined with WEDM. Five machining parameters were analyzed such as pulse on time, pulse off time, peak current, water pressure and servo feed rate. Surface roughness (R-a) and machining speed were considered as output parameters and design of experiment was derived using central composite design (CCD) of response surface method (RSM) with 32 numbers of different test runs. Adaptive neuro-fuzzy inference system (ANFIS) was used with a new set of 16 numbers of experiments to predict results and seen to be more reliable than predicted results of response surface method. (C) 2019 Elsevier Ltd. All rights reserved

WEDM process optimization of sintered structural ceramic sample by using fuzzy-MPCI technique

Sintered boron carbide is an extremely hard, structural ceramic material and it is difficult to be machined with conventional techniques. To overcome the machining problem, the spark plasma sintered (SPS) monolithic boron carbide (B4C) was successfully machined by wire electrical discharge machining (WEDM) as the material is electrically conductive. The effects of five different machining parameters of WEDM were carefully observed to check their effect on the useful responses, namely machining speed and surface roughness (R-a) for cutting sintered B4C samples. A number of experimental operations were derived by using the concept of central composite design (CCD) and fuzzy logic was implemented to predict the response for a particular input parameter set. Also, a multi objective optimization was performed by fuzzy logic rule based multi performance characteristics indices technique (MPCI). (C) 2020 Elsevier Ltd. All rights reserved

Wire electrical discharge machining and microstructural analysis of hot-pressed boron carbide

Boron carbide powder was hot-pressed at 2070 degrees C with 30 MPa uniaxial pressure and 90 min soaking. The mechanical, microstructure and other related properties were evaluated. XRD of the boron carbide powder and sintered samples, shows the presence of B13C2 phase of high electrical conductivity. Crystal lattice parameters, space group, cell angle, cell parameters, etc. were found from Rietveld refinement. The micro Vicker's hardness was 26.98 +/- 0.98 GPa at 4.9 N load, fracture toughness 3.54 +/- 0.26 MPa/Mt and Young's modulus 461.50 +/- 4.5 GPa. The hot-pressed boron carbide was found to be electrically conducting, which can be machined using a wire electrical discharge machine (WEDM)

An Azoaromatic Ligand as Four Electron Four Proton Reservoir: Catalytic Dehydrogenation of Alcohols by Its Zinc(II) Complex

Electroprotic storage materials, though invaluable in energy-related research, are scanty among non-natural compounds. Herein, we report a zinc­(II) complex of the ligand 2,6-bis­(phenylazo)­pyridine (L), which acts as a multiple electron and proton reservoir during catalytic dehydrogenation of alcohols to aldehydes/ketones. The redox-inactive metal ion Zn­(II) serves as an oxophilic Lewis acid, while the ligand behaves as efficient storage of electron and proton. Synthesis, X-ray structure, and spectral characterizations of the catalyst, ZnLCl₂ (<b>1a</b>) along with the two hydrogenated complexes of <b>1a</b>, ZnH₂LCl₂ (<b>1b</b>), and ZnH₄LCl₂ (<b>1c</b>) are reported. It has been argued that the reversible azo-hydrazo redox couple of <b>1a</b> controls aerobic dehydrogenation of alcohols. Hydrogenated complexes are hyper-reactive and quantitatively reduce O₂ and <i>para</i>-benzoquinone to H₂O₂ and <i>para</i>-hydroquinone, respectively. Plausible mechanistic pathways for alcohol oxidation are discussed based on controlled experiments, isotope labeling, and spectral analysis of intermediates

Exclusively Ligand-Mediated Catalytic Dehydrogenation of Alcohols

Design of an efficient new catalyst that can mimic the enzymatic pathway for catalytic dehydrogenation of liquid fuels like alcohols is described in this report. The catalyst is a nickel­(II) complex of 2,6-bis­(phenylazo)­pyridine ligand (L), which possesses the above requisite with excellent catalytic efficiencies for controlled dehydrogenation of alcohols using ligand-based redox couple. Mechanistic studies supported by density functional theory calculations revealed that the catalytic cycle involves hydrogen atom transfer via quantum mechanical tunneling with significant <i>k</i>_H/<i>k</i>_D isotope effect of 12.2 ± 0.1 at 300 K. A hydrogenated intermediate compound, [Ni^IICl₂(H₂L)], is isolated and characterized. The results are promising in the context of design of cheap and efficient earth-abundant metal catalyst for alcohol oxidation and hydrogen storage

Exclusively Ligand-Mediated Catalytic Dehydrogenation of Alcohols

Design of an efficient new catalyst that can mimic the enzymatic pathway for catalytic dehydrogenation of liquid fuels like alcohols is described in this report. The catalyst is a nickel­(II) complex of 2,6-bis­(phenylazo)­pyridine ligand (L), which possesses the above requisite with excellent catalytic efficiencies for controlled dehydrogenation of alcohols using ligand-based redox couple. Mechanistic studies supported by density functional theory calculations revealed that the catalytic cycle involves hydrogen atom transfer via quantum mechanical tunneling with significant <i>k</i>_H/<i>k</i>_D isotope effect of 12.2 ± 0.1 at 300 K. A hydrogenated intermediate compound, [Ni^IICl₂(H₂L)], is isolated and characterized. The results are promising in the context of design of cheap and efficient earth-abundant metal catalyst for alcohol oxidation and hydrogen storage