Heating coils utilize the concept of resistive heating to convert electrical energy into thermal energy. Uniform heating of the target area is the key performance indicator for heating coil design. Highly uniform distribution of temperature can be achieved by using a dense metal distribution in the area under consideration, however, this increases the cost of production significantly. A low-cost and efficient heating coil should have excellent temperature uniformity while having minimum metal consumption. In this work, space-filling fractal curves, such as Peano curve, Hilbert curve and Moore curve of various orders, have been studied as geometries for heating coils. In order to compare them in an effective way, the area of the geometries has been held constant at 30 mm × 30 mm and a constant power of 2 W has been maintained across all the geometries. Further, the thickness of the metal coils and their widths have been kept constant for all geometries. Finite Element Analysis (FEA) results show Hilbert and Moore curves of order-4, and Peano curve of order-3 outperform the typical double-spiral heater in terms of temperature uniformity and metal coil length.

In the present work, the photocatalytic activity of metal Fe-Zn nanoparticles was evaluated through the degradation of the synthetic AZO colorant allura red. A Phytosynthesis method developed here takes advantage for the first time of the plant extract of Hydrocotyle ranunculoides as the reducing agent. A fitted Folin-Ciocalteu assay showed about 40% of total polyphenolic compounds used in the nanoparticles generation. UV-Vis and TEM analysis allowed identification of the nanoparticles as oxides of Fe and Zn. Finally, during measurement of the photocatalytic activity a load of 0.5 g/L was applied on a 15 μM solution of allura red as standard model pollutant, while environmental oxygen was used as the initiating agent. Tests showed a 66% degradation of the azo-type dye obeying a degradation kinetics of the first order after short times.

From the present work, the wear behavior of aged Ni-based superalloy was analyzed under dry sliding conditions. Such alloy was melted in a vacuum induction furnace and cast into a ceramic mold. Then the alloy was solubilized at 1080°C for 4 hours and then aged at 760°C for 4, 8, 16, 24, 48, 72 and 150 hours. The alloy was characterized as-cast and also in the heat-treated conditions by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Mechanical characterization included just Vickers hardness and wear resistance under dry sliding conditions by a block on ring configuration according to the ASTM G77 standard. Wear tests were undertaken for 2000 m at a speed of 0.7 ms-1 at two different loads (25 and 78 N). The worn samples were analyzed by an optical profiler to determine the wear volume and by SEM to analyze the worn surface and the microstructure below the worn surface. The main findings indicate the formation of an oxide layer mainly formed by Cr and Ni during sliding. The thickness of such a layer is about 10 μm for short aging times and about 5 μm for longer aging times. For this load, the wear resistance was 50% higher for the shorter aging times than that for the longer aging times. This behavior is described in terms of the thickness of the protecting layer, and on the availability of chromium to form such a layer since it forms Cr23C6 at long aging times. On the other hand, for a load of 78 N the wear behavior is in agreement with hardness. Wear resistance increases with aging time due to the higher precipitation of prime gamma phase.

Bulk production by Chemical Vapor Deposition (CVD) of ultra-long Carbon Nanotubes (CNTs) with lengths greater than several centimeters is desirable for materials applications, but is not presently feasible. A principal reason for this limitation is cessation of CNT growth due to erosion of the nano-sized catalyst particles from which the CNTs nucleate and grow: at elevated CVD growth temperatures, atoms of catalytic metal detach and diffuse away from the particles, resulting in erosion and eventual deactivation of the particles. Recently, a novel idea was introduced to slow this diffusion and erosion by including heavy refractory metals with the catalyst metals in the nanoparticles. Here are presented recent and ongoing investigations into this method. The metal system investigated uses iron as catalyst and rhenium as diffusion inhibitor. Results show that inclusion of Re in the catalyst particles will substantially increase the catalysts particle lifetimes, and hence the growth time of the CNTs produced. These results are compared to previous results obtained using the iron/molybdenum system of catalyst/inhibitor.

Network formation by cross-linking is a common method to incorporate functions like elastic deformability, shape-memory capability or hydrogel formation into polymer materials for medical applications. Since these materials are often intended to degrade, their design would benefit from a quantitative prediction of the interdependence between network architecture and degradation behavior. Here, we introduce a quantitative description of the degradation behavior of polymer networks. A simplified model was developed under the assumption of having an ideal network, where all network strands are terminated by network nodes and each node is connected to the same number of strands. To describe the degradation of real networks, the model was modified by allowing for a varying connectivity of network nodes, which also included free chain-ends. The models were validated by comparison with Langmuir monolayer degradation data from 2D networks formed by cross-linking oligo(ε-caprolactone)diols with dialdehydes. We found that both the ideal network hypothesis and the real network model were in excellent agreement with the experimental data, with the ideal network hypothesis requiring longer network strands than the real network to result in the same degradation behavior. The models were further used to calculate the degradation curves of the corresponding, non cross-linked molecules. By comparison, it was found that the network formation increases the time required to reach 50% degradation of oligo(ε-caprolactone)diols by only 20%. This difference mainly arises from attaching free chain ends to network points.

Intelligent control of friction and adhesion has attracted much attention for use in soft robotics, human-sensor interfaces, and bionics. Here we introduce a shape memory photonic crystal (SMPC) polymer that can be programmed and recovered by solvent to realize switchable surface friction. Micro sliding test show that the friction coefficient on this SMPC in the programmed and recovered state can vary by three times. We also show that the mechanism behind this switchable friction coefficient is the surface roughness related adhesion.

We report a simple and feasible technique for the formation of well-distributed nickel nanodot arrays on both oxidized and unoxidized silicon substrate by a conventional annealing process. The shape and distribution of nickel nanodots were maintained by adjusting annealing temperature, time and the SiO2 buffer layer thickness in between nickel film and the silicon substrate. The diffusion of nickel into the silicon is significantly reduced when the nickel film on the oxidized silicon substrate is annealed at high temperature. From this conventional annealing technique, we achieve a maximum nickel nanodots density up to (7.94±1.92) nanodot counts/µm2 on the oxidized silicon substrate with a well-defined spherical shape by adjusting the thickness of nickel film as well as buffer SiO2 layer. In the next experiment, the surface charge distribution on the nickel nanodot arrays were characterized through the Kelvin probe force microscope (KPFM) on tapping mode. It is found that the nickel nanodots can store and release the electric charges under an applied bias voltage.

Carbon steel has gained wide applications as a structural material due to its combination of strength, ductility, and low cost; in fact, this material has been studied as one of the proposals for the manufacture of radioactive waste containers in countries such as Japan, France, and the United States. One of the biggest problems of carbon steel is its susceptibility to general corrosion, while copper and its alloys, despite not having high mechanical resistance, are materials with good corrosion resistance properties. This work evaluates the reliability of protective films developed from copper nanoparticles to improve the corrosion resistance of carbon steel plates. The nanoparticles were synthesized by a chemical reduction method using copper sulphate (CuSO4) as a precursor, sodium borohydride (NaBH4) as a reducing agent, and citric acid as an antioxidant. These nanoparticles were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), as well as by Dynamic Light Scattering (DLS) before and after being treated with citric acid. Finally, they were deposited on the carbon steel surface by Electrophoretic Deposition using a current of 0.5 mA/cm2. The protective capacity of the films developed from copper nanoparticles was evaluated by means of Electrochemical Impedance Spectroscopy and Linear Polarization Resistance techniques in 0.1 M HCl solution.

Samples of real irradiated (i-)graphite from bushings of RBMK reactor after several types of decontamination treatments were put in contact with aqueous solutions modelling underground water of Nizhnekansky massif (Russia) equilibrated with bentonite for periods up to 1.5 years. Leach rates of radionuclides and evolution of graphite surface morphology and oxidation state were monitored using nuclear spectroscopy, SEM and XPS. After the experiment, less than one third of surface carbons remains unoxidised. Extensive precipitation of secondary phases (alumosilicates, carbonates) was observed on some samples and is possibly correlated with surface oxidation extent. The leach rates of dose-forming 14C and 36Cl are comparable with the leach rates of radionuclides in glassy waste forms. According to the current study i-graphite could be regarded as a waste form, which is suitable for near-surface disposal.

To improve the corrosion resistance and to increase the hardness of copper substrate in marine environment, the Cu-Ni/Ni-P composite coatings were prepared on the copper substrate using the galvanostatic electrolytic deposition method. The deposition current densities were explored to find the optimized deposition conditions for forming the composite coatings. Corrosion resistance properties were analyzed using the polarization curves and electrochemical impedance spectroscopy (EIS). Considering the corrosion resistance and hardness, the −20 mA/cm2 was selected to deposit Cu-Ni coatings on copper substrate and the −30 mA/cm2 was selected to deposit Ni-P coating on the Cu-Ni layer. The Cu-Ni/Ni-P composite coatings not only exhibited superior corrosion resistance compared to single Cu-Ni coating in 3.5 wt.% NaCl solution, but also showed much better mechanical properties than single Cu-Ni coating.

In situ X-ray diffraction is one of the most useful tools for studying a variety of processes, among which crystallization of nanoparticles where phase purity and size control are desired. Growth kinetics of a single phase can be completely resolved by proper analysis of the diffraction peaks as a function of time. The peak width provides a parameter for monitoring the time evolution of the particle size distribution (PSD), while the peak area (integrated intensity) is directly related to the whole diffracting volume of crystallized material in the sample. However, to precisely describe the growth kinetics in terms of nucleation and coarsening, the correlation between PSD parameters and diffraction peak widths has to be established in each particular study. Corrections in integrated intensity values for physical phenomena such as variation in atomic thermal vibrations and dynamical diffraction effects have also to be considered in certain cases. In this work, a general correlation between PSD median value and diffraction peak width is deduced, and a systematic procedure to resolve time-dependent lognormal PSDs from in situ XRD experiments is described in details. A procedure to correct the integrated intensities for dynamical diffraction effects is proposed. As a practical demonstration, this analytical procedure has been applied to the single-phase crystallization process of bismuth ferrite nanoparticles.

Gold nanoparticles (AuNPs) have been classified as one of the most attractive nanotechnologies, thanks to their potential or already implemented applications; therefore, biological methods for their synthesis have been widely investigated. This study explores the synthesis of AuNPs using the extract of Anemopsis californica, and determinates the effect of the solvent used (water, methanol, and isopropanol) to obtain the AuNPs. Biogenic nanoparticles were analysed through UV-Vis spectroscopy and transmission electron microscopy (TEM, HRTEM, and SAED). Significant differences in polydispersity and morphology of AuNPs among the different methods used were found; the aqueous extract and the extract based on methanol formed nanotriangles and polyhedral nanoparticles; the shape of the nanoparticles is predominantly polyhedral when isopropanol is used as the solvent. The as obtained nanoparticles were placed on glass slides to perform Surface-Enhanced Raman Scattering (SERS) experiments, an amplification of the methylene blue Raman signal was observed when triangular nanoparticles cover the biogenic SERS substrate.

Methane dehydroaromatization (MDHA) is a direct activation approach to covert methane to value-added chemicals in a single step. This requires no intermediate step, making it a commercially economic approach. Mo supported on HZSM-5/MCM-22 is a well-studied catalyst for this reaction, where Mo sites are responsible for activating methane to C2Hy dimers, which can oligomerize on HZSM-5 Bronsted acid sites to produce aromatics. Challenges for these bifunctional catalysts involve rapid coking and low product yield. In this study, a novel catalytic approach is introduced using group VIB metals (Cr, Mo, W) supported on sulfated zirconia (SZ) solid acid. It is believed that the Bronsted acidity of SZ should help to convert the dimers generated from metal sites to ethylene and aromatics like benzene.

Here, fresh Mo, W and Cr were doped into SZ and characterized using pyridine DRIFTS, ammonia TPD, BET and SEM-EDS.. Catalytic activity for MDHA was ranked as Mo>W>Cr. Mo/SZ showed greater selectivity towards ethylene and benzene, followed by W/SZ, which was selective primarily towards ethylene. Cr/SZ showed the least activity under similar reaction conditions, producing only a small amount of ethylene. Higher catalytic activity for Mo/SZ was possibly due to reduced Mo oxide sites, found from XANES analysis, as well as higher acidity, observed from TPD. Deactivation was mainly due to coking, observed from subsequent TPO analysis. Further investigation is necessary to enhance the activity of this novel catalytic approach before considering for potential industrial applications.

Many physicochemical processes depend on the diffusion of small molecules through solid materials. While crystallinity in polymers is advantageous with respect to structure performance, diffusion in such materials is difficult to predict. Here, we investigate the impact of crystal morphology and organization on the diffusion of small molecules using a lattice Monte Carlo approach. Interestingly, diffusion determined with this model does not depend on the internal morphology of the semi-crystalline regions. The obtained insight is highly valuable for developing predictive models for all processes in semi-crystalline polymers involving mass transport, like polymer degradation or drug release, and provide design criteria for the time-dependent functional behavior of multifunctional polymer systems.

Photodetectors operating in the ultraviolet (UV) play a pivotal role in applications such as ozone monitoring and biosensing. One key factor to successfully implementing such photodetectors is that they must be solar-blind to avoid detecting ambient visible and infrared light. Unfortunately, UV photodetectors based on silicon and other typical semiconductors are not natively solar-blind, since their band gap energies are in the visible range. Hexagonal boron nitride (h-BN) is an example of a wide band gap semiconductor which shows promise for use as the absorbing medium in a UV photodetector device, since its band gap is wide enough to make it inherently insensitive to light in the visible range and above. Here we report on the fabrication and characterization of a graphene-h-BN-heterostructure photodetector which utilizes a vertical geometry, in principle allowing for highly scalable production. We find that our device shows a finite photoresponse to illumination by a 254 nm light source, but not to a 365 nm source, thus suggesting that our device is solar-blind.