Effects of process current density and temperature on electrochemical boriding of steel in molten salts

In this study, the effects of current density and bath temperature on the hardness, thickness, and morphology of boride layer are systematically investigated. The electrochemical boride coating on steel substrates is carried out at various current densities (50–700 mA/cm²) and bath temperatures (800–1000°C) at constant electrolyte composition and electrolysis time. The FeB, Fe₂B, and Fe₃B phases are detected by the x-ray diffraction method. The hardness of the boride layer reaches approximately 1800 HV on the surface and gradually decreases toward the matrix. The optimum current density and electrolyte temperature for the boriding of low-alloy steel are determined as 200 mA/cm² and 900°C, respectively.     

An energy-economic scenario analysis of alternative fuels for personal transport using the Global Multi-regional MARKAL model (GMM)

This paper deals with the long-term prospects of alternative fuels in global personal transport. It aims at assessing key drivers and key bottlenecks for their deployment, focusing particularly on the role of biofuels and hydrogen in meeting climate policy objectives. The analysis is pursued using the Global Multi-regional MARKAL model (GMM), a perfect foresight “bottom-up” model of the global energy system with a detailed representation of alternative fuel chains, linked to the Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC). The analysis shows that biofuels are limited by the regional availability of low-cost biomass, but can be important for meeting mild climate policy targets. If policy-makers intend to pursue more stringent climate policy, then hydrogen becomes a competitive option. However, the analysis finds that the use of hydrogen in personal transport is restricted to very stringent climate policy, as only such policy provides enough incentive to build up the required delivery infrastructure. An analysis of costs additionally shows that “keeping the hydrogen option open” does not take considerable investments compared to the investment needs in the power sector within the next decades, but allows the use of hydrogen for the pursuit of stringent climate policy in the second half of the century.     

Electrochemical boriding and characterization of AISI D2 tool steel

D2 is an air-hardening tool steel and due to its high chromium content provides very good protection against wear and oxidation, especially at elevated temperatures. Boriding of D2 steel can further enhance its surface mechanical and tribological properties. Unfortunately, it has been very difficult to achieve a very dense and uniformly thick boride layers on D2 steel using traditional boriding processes. In an attempt to overcome such a deficiency, we explored the suitability and potential usefulness of electrochemical boriding for achieving thick and hard boride layers on this tool steel in a molten borax electrolyte at 850, 900, 950 and 1000 °C for durations ranging from 15 min to 1 h. The microstructural characterization and phase analysis of the resultant boride layers were performed using optical, scanning electron microscopy and X-ray diffraction methods. Our studies have confirmed that a single phase Fe₂B layer or a composite layer consisting of FeB + Fe₂B is feasible on the surface of D2 steel depending on the length of boriding time. The boride layers formed after shorter durations (i.e., 15 min) mainly consisted of Fe₂B phase and was about 30 μm thick. The thickness of the layer formed in 60 min was about 60 μm and composed mainly of FeB and Fe₂B. The cross sectional micro-hardness values of the boride layers varied between 14 and 22 GPa, depending on the phase composition.     

The growth of single Fe2B phase on low carbon steel via phase homogenization in electrochemical boriding (PHEB)

In this study, we introduce a new electrochemical boriding method that results in the formation of a single-phase Fe₂B layer on low carbon steel substrates. Although FeB phase is much harder and more common than Fe₂B in all types of boriding operations, it has very poor fracture toughness; hence, it can fracture or delaminate easily from the surface under high normal or tangential loading. We call the new method “phase homogenization in electrochemical boriding” (PHEB), in which carbon steel samples undergo electrochemical boriding for about 15 min at 950 °C in a molten electrolyte consisting of 90% borax and 10% sodium carbonate, then after the electrical power to the electrodes is stopped, the samples are left in the bath for an additional 45 min without any polarization. The typical current density during the electrochemical boriding is about 200 mA/cm². The total original thickness of the resultant boride layer after 15 min boriding was about 60 μm (consisting of 20 μm FeB layer and 40 μm Fe₂B layer); however, during the additional phase homogenization period of 45 min, the thickness of the boride layer increased to 75 μm and consisted of only Fe₂B phase, as confirmed by glancing-angle x-ray diffraction and scanning electron microscopy in backscattering mode. The microscopic characterization of the boride layers revealed a dense, homogeneous, thick boride layer with microhardness of about 16 GPa. The fracture behavior and adhesion of the boride layer were evaluated by the Daimler-Benz Rockwell C test and found to be excellent, i.e., consistent with an HF1 rating.     

Gold nanoparticle modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrole-1-l) benzenamine for potential use as a biosensing material

Gold nanoparticle (AuNP) modified conducting polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzenamine (SNS-NH₂) was used as the biosensing platform for glucose analysis. Electrochemical measurements were carried out by following the consumed oxygen due to the enzymatic reaction of glucose oxidase (GOx) at −0.7 V vs Ag/AgCl. Optimisation of pH, enzyme loading, stability experiments were carried out. Effect of NP was investigated by monitoring the signal responses at different AuNP sizes and amounts. A linear relation of y = 1.597x + 0.264 (R² = 0.993) was found for glucose concentrations between 0.002 and 5.0 mM. The analytical characteristics of the system were also evaluated for glucose determination in flow injection analysis (FIA) mode. Finally, the system was checked for glucose detection on real samples.     

Influence of laser parameters in surface texturing of polyphenylene sulfide composites

Creating dimples at the ideal geometries to enhance the tribological properties of the polyphenylene sulfide (PPS) composite surface is the principal purpose of this study. In this manner, the effects of focus position (FP), pulse number (PN), and energy used for the making dimple geometry were investigated. In the ablation process, Nd:YAG laser with 1064 nm wavelength was used. Optimum laser process parameters were intended to obtain the largest ratio of dimple depth to width, circular dimples with a minimum ratio of molten zone diameter to spot size. The most effective parameters for obtaining dimple of desired properties are pulse energy (PE) with 60.64%, pulse duration (PD) with 55.61%, and FP with 55.94% for aspect ratio, circularity, and ratio of the diameter of the dimple to the spot size, respectively. In order to achieve a high aspect ratio or good circularity or minimum molten zone-to-spot size ratio, Taguchi optimization predicted the laser parameters. In the confirmation experiment with the proposed parameters, the highest aspect ratio was obtained as 2.05, the best circularity was obtained as 1.05, and minimum molten zone-to-spot size ratio was obtained as 1.073. Using the Taguchi method, accurate results were found with less experimentation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47976.     

Sol–Gel/Chitosan/Gold Nanoparticle-Modified Electrode in Mediated Bacterial Biosensor

A mediated whole cell biosensor was designed and characterized using glucose as the substrate. Gluconobacter oxydans cells were immobilized on the graphite electrode via sol–gel (tetraethyl orthosilicate)/chitosan hybrid composite modified with gold nanoparticles (TEOS/CHIT/AuNPs/G. oxydans). A soluble mediator, potassium hexacyanoferrate (III), was used for the amperometric detection of the respiratory activity of the intact bacterial cells. After optimization of preparation conditions of the TEOS/CHIT/AuNPs/G. oxydans biosensor, characterization studies have been carried out. The linear range for glucose was found to be 0.5–2.0 mM with a response time of 80 s. Moreover, repeatability and electrode-to-electrode reproducibility of the system were investigated and relative standard deviations were calculated as 1.7% and 2.2% for 1.0 mM glucose (n = 5). Finally, the proposed system was applied to ethanol and glucose detection in real samples and the results were compared with a reference method.     

Effect of W incorporation on the product distribution in steam reforming of bio-oil derived acetic acid over Ni based Zr-SBA-15 catalyst

Zirconia incorporated SBA-15 type mesoporous material was synthesized following a one-pot hydrothermal route, characterized and used as the catalyst support in the synthesis of Ni and bi-metallic Ni–W based catalysts. Performances of these catalysts were tested in steam reforming of AcOH. Catalytic activity tests proved that the performances of SBA-15 and Zr-SBA-15 supported Ni based catalysts were highly stable and they also showed very high activity in steam reforming of acetic acid, giving complete conversion at temperatures over 700 °C. Product distributions were shown to be strongly influenced by the composition of the catalyst. In the case of 5Ni@Zr-SBA-15, syngas produced at 750 °C contained about 54% H₂, 22% CO, 20% CO₂ and 4% CH₄. These results indicated that decarboxylation reaction of AcOH to CH₄ and CO₂ was minimized over this catalyst. Results were considered to be highly promising for the production of hydrogen rich syngas. It was most interesting to observe that modification of this catalyst by the addition of tungsten caused significant changes in the product distribution. For instance, syngas produced over 5Ni-50W@Zr-SBA-15 at the same reaction conditions, contained equimolar quantities of H₂ and CO (about 47.5% each) with very small amounts of CO₂ and CH₄ (about 3% and 2%, respectively). Production of a syngas with such a composition was considered to be highly attractive from the point of view of a resource gas for dimethyl ether and Fischer-Tropsch synthesis.     

A genetic algorithm approach to determine stratum boundaries and sample sizes of each stratum in stratified sampling

Stratified sampling is a methodology in which a heterogeneous population is partitioned into homogeneous subgroups called strata. The focus is on solving the combined problem of sample allocation and stratum boundary determination with the genetic algorithm (GA). Assuming that the number of strata and the total sample size are arbitrarily predetermined, stratum boundaries are determined using an objective function of minimum variance of the estimator; with sample size allocated through equal, proportional, Neyman, and GA allocation methods. Some numerical examples are given and the performance of GA is compared with the geometric and the cumulative root frequency methods.     

Computed tomography with linear shift-invariant optical systems

Optical systems capable of three-dimensional transmission imaging are considered; these systems employ a conventional tomographic setup with an added linear shift-invariant optical system between the sample and the detector. A theoretical analysis is presented of image formation and sample reconstruction in such systems, examples of which include diffraction tomography and phase-contrast tomography with the use of analyzer crystals. An example is introduced in which the image is obtained by scanning the beam along the line orthogonal to the optic axis and to the axis of rotation with a one-dimensional slit or grating parallel to the rotation axis. We show that under certain conditions the proposed system may allow quantitative local (region-of-interest) tomography.