The effect of milling energy input and molar ratio on the dehydrogenation and thermal conductivity of the (LiNH2 + nMgH2) (n = 0.5, 0.7, 0.9, 1.0, 1.5 and 2.0) nanocomposites

Hydride nanocomposites in the (LiNH₂ + nMgH₂) system have been synthesized by ball milling with varying input of milling energy injected into powder particles, Q_TR (kJ/g). The grain (crystallite) size of LiNH₂ and MgH₂ decreases rapidly with increasing Q_TR up to approximately 150–200 kJ/g and subsequently more or less saturates at the value of 10–20 nm. For the injected energy Q_TR ≈ 250–350 kJ/g the specific surface area (SSA) increases from the initial 2.4 m²/g for powder mixtures before milling to 30–37 m²/g for nanocomposites after milling. After injecting Q_TR ≈ 550 kJ/g there is a further increase of SSA to 52 m²/g which is over 20-fold increase of SSA from its initial value. That clearly indicates that a profound reduction of particle size has occurred. The hydride phases formed during ball milling with relatively low Q_TR are identified as a-Mg(NH₂)₂ (amorphous magnesium imide) and LiH. The ball milled (LiNH₂ + nMgH₂) nanocomposite system with n = 0.5–0.9 can effectively desorb about 4–5 wt.% H₂ with a reasonable rate at the temperature range close to 200 °C. Within a low temperature range up to ∼250 °C, regardless of the molar ratio n and the injected energy Q_TR the thermal desorption of the (LiNH₂ + nMgH₂) nanocomposites occurs without any release of ammonia, NH₃. For all molar ratios, n, the hydride nanocomposites are fully reversible at 175 °C under a relatively mild pressure of 50 bar H₂. The quantity of H₂ desorbed decreases with increasing molar ratio n, due to increasing fraction of inactive, retained MgH₂. However, at 125 °C the dehydrogenation rate is very sluggish and the quantity of released H₂ is minimal. At the temperature range lower than ∼250 °C dehydrogenation of ball milled nanocomposites occurs through formation of the Li₂Mg(NH)₂ hydride phase. The value of the measured dehydrogenation enthalpy change of 46.7 kJ/molH₂ is relatively low and apparently, it is not responsible for sluggish dehydrogenation at 125 °C. The measurements of thermal conductivity for non-milled powders and ball milled nanocomposites show a dramatic reduction of thermal conductivity after ball milling. It seems that this could be a principal factor responsible for such a low dehydrogenation rate at low temperatures.     

Application of graphite screen printed electrode modified with dysprosium tungstate nanoparticles in voltammetric determination of epinephrine in the presence of acetylcholine

The current work focuses on the development of a sensitive and selective electrochemical device based on a graphite screen printed electrode modified with Dy_2(WO_4)_3 nanoparticles(DWO/SPE) for the analysis of epinephrine in samples also containing acetylcholine. The study proves that the sensor has excellent electron-mediating behavior in the oxidation of epinephrine in a 0.1 mol/L phosphate buffer solution(PBS)(pH 7.0). The application of the DWO/SPE in differential pulse voltammetry(DPV) is found to lead to distinct response for the oxidation of epinephrine and acetylcholine, with the potentials of the epinephrine and acetylcholine peaks(△E_p) to be 550 mV apart. The detection limits of the method for epinephrine and acetylcholine are 0.5 and 0.7 μmol/L(S/N = 3) and the responses are found to be linear in the concentration ranges of 1.0-900.0 μmol/L and 1.0-1200.0 μmol/L in a PBS buffer(pH = 7.0)respectively. The modified electrode was used for the detection of epinephrine and acetylcholine in real samples and found to produce satisfactory results. These results can be a proof that Dy_2(WO_4)_3 nanoparticles can find promising applications in electrochemical sensors to be used for the analysis of(bio)chemical species.     

Investigating the structural effect of electrospun nano-fibrous polymeric films on water vapor transmission

Electrospun polymers have many applications in the industry.However, the structure of these polymers has been less widely considered by researchers.In this work, the structural effect of electrospun and casted films of polyacrylonitrile(PAN) and polyvinylidene fluoride(PVDF) polymers on water vapor transmission were investigated.Sorption of water vapor was measured at 35, 60 and 80 ℃ and different relative humidities.The diffusion coefficients were calculated based on mass changes of the polymer sample.The water vapor transmission rate(WVTR) was also measured at 35 ℃ and 90% relative humidity.The results indicated that electrospun nano-fibrous polymers(ESNPs) absorb much higher water vapor compared to non-porous casted polymers.The interaction of water molecules with mentioned polymers was investigated based on Flory-Huggins theory.The Flory-Huggins interaction parameter of electrospun films was less than casted films, suggesting much better interaction of water molecules with electrospun films.It was also found that electrospun films have anomalous kinetic behavior and do not obey the Fickian diffusion model.Finally, it was revealed that ESNPs show less resistance to water vapor transmission and they are good candidates for the applications of water vapor separation using membranes.     

The Influence of KrF Excimer Laser Annealing on Magnetic and Structural Properties of FePt/PtIr Thin Films

A series of 60-nm FePt thin films were deposited by RF magnetron sputtering system on Si/SiO₂ substrate. Platinum–iridium alloy was deposited as a buffer film between the FePt thin film and Si/SiO₂ substrate. These films were annealed by KrF excimer laser annealing with 248 nm of wavelength. The number of laser pulses which were applied on the film was varied from 3 to 20. The A₁ to L₁₀ phase transformation of FePt was confirmed by X-ray diffraction. Three pulses of laser were not sufficient for A₁ to L₁₀ phase transformation. A maximum order parameter of 0.91 was obtained after applying 18 pulses of laser. The roughness of films changed in different pulses, and the films were in the best condition after applying 18 pulses; the roughness was 3.51 nm and its morphology that was observed from AFM was 129 nm. The maximum coercivity was 0.61 MA/m. The coercivity increased with the application of different pulses of laser. Increasing coercivity to the maximum value of 0.61 MA/m related to grain growth. Coercivity of samples in 3, 6, 9, 12, 18, and 20 pulses was 0.24, 0.402, 0.488, 0.522, 0.64, and 0.6 MA/m respectively. Determining the grain growth under condition of annealing was done by field emission scanning electron microscopy (FESEM). Growth of all specimens was calculated with imager software. Grain size in as deposited and 3, 6, 9, 12, and 18 pulses of laser was 15, 20, 29, 44, 47, and 59 respectively.     

Perchlorate-selective membrane sensors based on two nickel-hexaazamacrocycle complexes

The perchlorate salts of nickel(II) complexes of 1,3,5,8,10,13-hexaazacyclotetradecane (1) and 1,8-tert-butyl-1,3,5,8,10,13-hexaazacyclotetradecane (2) were used in construction of PVC based membrane electrodes. These sensors show very good selectivity for ClO₄⁻ ions over a wide variety of anions. These electrodes exhibit Nernstian behavior with the slopes of 59.5 and 59.3 mV per decade for (1) and (2), respectively. The working concentration ranges of the sensors are 1.0 × 10⁻¹–9.0 × 10⁻⁷ M (1) and 1.0 × 10⁻¹–5.0 × 10⁻⁷ M (2) with the detection limits of 6.0 × 10⁻⁷ and 2.0 × 10⁻⁷ M, respectively. The response time of the both sensors is very fast, and can be used for 2 (I) and 12 (II) weeks in a pH range of 3.0–11.0. These electrodes were applied to the determination of perchlorate ions in wastewater and cattle urine samples.     

Mealiness Detection in Agricultural Crops: Destructive and Nondestructive Tests: A Review

Mealiness is known as an important internal quality attribute of fruits/vegetables, which has significant influence on consumer purchasing decisions. Mealiness has been a topic of research interest over the past several decades. A number of destructive and nondestructive techniques are introduced for mealiness detection. Nondestructive methods are more interesting because they are rapid, noninvasive, and suitable for real‐time purposes. In this review, the concept of mealiness is presented for potato, apple, and peach, followed by an in‐depth discussion about applications of destructive and nondestructive techniques developed for mealiness detection. The results suggest the potential of electromagnetic‐based techniques for nondestructive mealiness evaluation. Further investigations are in progress to find more appropriate nondestructive techniques as well as cost and performance.     

Investigation on the Effect of Mold Constraints and Cooling Rate on Residual Stress During the Sand-Casting Process of 1086 Steel by Employing a Thermomechanical Model

In this study, the effects of mold constraints and cooling rate on residual stress were analyzed during the shaped casting process. For this purpose, an H-shaped sample was designed in which the contraction of its middle portion is highly restricted by the mold during the cooling process. The effects of an increasing cooling rate combined with mold constraints were analyzed by reducing the thickness of the middle portion in the second sample. A three-dimensional coupled temperature-displacement analysis was performed in finite-element code ABAQUS to simulate residual stress distribution, and then numerical results were verified by the hole-drilling strain-gauge method. It was concluded that the mold constraints have a greater effect on the values of residual stress than the cooling rate (thin section) in steel sand casting. Increasing the cooling rate would increase the amount of residual stress, only in the presence of mold constraints. It is also suggested that employing the elastic-plastic stress model for the sand mold will satisfy the experimental results and avoid exaggerated values of residual stress in simulation.     

Joint coordinate method for analysis and design of multibody systems: Part 2. System topology

In Part 1 of this paper, the method of joint coordinate formulation for multibody dynamics was reviewed. The application of this method to forward and inverse dynamics, static equilibrium, and design sensitivity analyses was studied. In Part 2 of the paper, systematic procedures for constructing the necessary matrices for the joint coordinate formulation are discussed in detail. These matrices are; the primary and the secondary path matrices describing the topology of the system, the velocity transformation matrix, and the generalized inertia matrix. The procedures for constructing these matrices and other necessary elements for the joint coordinate formulation can easily be implemented in a computer program for analysis and design process.