Synthesis and characterization of APTMS/melamine cured hyperbranched polyester-epoxy hybrid coatings

An epoxy-terminated hyperbranched polyester (EPHBP) was prepared by the reaction of hyperbranched polyester (HBP) and epichlorohydrin (EPH). Herein, we have synthesized a new kind of highly epoxy ended branched polyester to enhance the chemical bonding at the interfaces and to reduce the melt viscosity. The structural investigation of the hyperbranched polyesters was carried by spectroscopic techniques such as nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) while molar masses were determined using gel permeation chromatography (GPC). The effect of the content of hexamethoxy methyl melamine (HMMA) and 3-amino propyltrimethoxysilane (APTMS) mixture on the thermal, mechanical and interfacial properties of EPHBP resins were also studied. The thermal, dynamic mechanical and mechanical properties of the heat cured coating films were also investigated. The combined analysis of the results indicate that the introduction of APTMS results in the enhancement of the thermal stability, glass-transition temperature (T_g), storage modulus, tensile strength and contact angle of the cured films. The improvement in properties depends on the APTMS content of the cured films. The cured films have also shown higher elongation at break due to the use of HMMA and presence of unmodified epoxide groups which indicates good flexibility and toughness of the coating films.     

Influence of Bi2O3/WO3 substitution on the optical,mechanical, chemical durability and gamma ray shielding properties of lithium-borate glasses

Six different lithium bismuth boro-tungstate glasses with chemical composition 20Li₂O-(20-x)Bi₂O₃-xWO₃-60B₂O₃ (x = 0, 1, 2, 3, 4 and 5 mol%) were produced by the quenching method. Then, the glasses were investigated by means of their optical, mechanical, chemical durability and gamma ray shielding properties. Measured values of density and ultrasonic velocities were used to determine the elastic properties of the glasses. The optical band gap determined using the absorbance spectrum fitting (ASF) model was found to decrease under Bi₂O₃/WO₃ substitution. The presence of BO₃, BO₄, BiO₆, and WO₄ structural groups in the glasses was confirmed by Fourier transform infrared spectroscopy (FTIR). The dissolution rate in the glass 20Li₂O–15Bi₂O₃–5WO₃–60B₂O₃ (LBWB5) was found to be 10 times lower than 20Li₂O-20Bi₂O₃– 60B₂O₃. Mass attenuation coefficients (MAC) values of the produced glasses were determined using the MCNPX Monte Carlo code and Phy-X/PSD program. The photon attenuation parameters such as half value layer (HVL), mean free path (MFP), effective atomic number (Z_eff), exposure buildup factor (EBF) and energy absorption buildup factor (EABF) were also studied. The obtained results showed that Bi₂O₃/WO₃ substitution has a direct impact on the photon attenuation abilities of produced glasses. More specifically, HVL values increased from 0.252 × 10^?2 cm for LBWB0 glass to 0.275 × 10^?2 cm for LBWB5 glass. However, different trends were observed for the photon buildup factors for the produced glasses. It can be concluded that the produced glasses have promising structural, optical, and photon attenuation properties to be used for gamma shielding applications.     

Isomer‐Pure Bis‐PCBM‐Assisted Crystal Engineering of Perovskite Solar Cells Showing Excellent Efficiency and Stability

A fullerene derivative (α‐bis‐PCBM) is purified from an as‐produced bis‐phenyl‐C₆₁‐butyric acid methyl ester (bis‐[60]PCBM) isomer mixture by preparative peak‐recycling, high‐performance liquid chromatography, and is employed as a templating agent for solution processing of metal halide perovskite films via an antisolvent method. The resulting α‐bis‐PCBM‐containing perovskite solar cells achieve better stability, efficiency, and reproducibility when compared with analogous cells containing PCBM. α‐bis‐PCBM fills the vacancies and grain boundaries of the perovskite film, enhancing the crystallization of perovskites and addressing the issue of slow electron extraction. In addition, α‐bis‐PCBM resists the ingression of moisture and passivates voids or pinholes generated in the hole‐transporting layer. As a result, a power conversion efficiency (PCE) of 20.8% is obtained, compared with 19.9% by PCBM, and is accompanied by excellent stability under heat and simulated sunlight. The PCE of unsealed devices dropped by less than 10% in ambient air (40% RH) after 44 d at 65 °C, and by 4% after 600 h under continuous full‐sun illumination and maximum power point tracking, respectively.     

On Parameters Affecting the Sensitivity of Ultrasonic Testing of Tubes: Experimental and Simulation

The response (amplitude) of the reference notch during ultrasonic testing of tubes is dependent on several parameters like (1) size, shape and location of notch in the material (2) operating parameters like pitch, incidence angle, focusing, beam profile etc (3) Electronic parameters like PRF, pulse width etc. A thorough analysis of several parameters is made in this paper which affects the calibration sensitivity and its repeatability. Calibration during ultrasonic testing of tubes is carried out by using reference notches made on the tubes. The size and shape of the reference notches are defined in the specification of the tube. Different specifications like ASTM, ASME, AMS, BS etc recommend the type of notch to be used for calibration. These are varying from one standard to another and there is no comparison available for the achieved sensitivity during calibration. This paper deals with a comparison of the recommended size and shape of the notches in different codes and specifications. The sensitivity of test is dependent on the calibration notch size and shape. In the present work a comparison is made on the sensitivity (in terms of gain level) for different size and shape of notches used during calibration of a tube. Usually, these notches are made on the ID and OD surface of the tubes which are generally equal in size. During calibration equalization of the amplitude of indication from the ID and OD is recommended. However no sound basis is available for the reason for unequal amplitude indication from ID and OD notch. In the present work, response from the notches at ID and OD is experimentally determined and compared with modeling of the response from the ID and OD notches. The repeatability of the calibration is demonstrated by carrying out a series of repeated measurements of the gain of the response from the notch. Different specifications recommend different tests for demonstrating the repeatability of the calibration. A comparison is made here for the repeatability requirements in different specifications. An analysis of the operating and electronic parameters responsible for variation in gain during a repeatability test is made.     

Erbium-Doped Fluoroborate Glasses for Near Infrared Broadband Amplifiers

Erbium (Er³⁺)-doped alkali lead tellurofluoroborate (RLTB) glasses were prepared and characterized systematically through optical absorption and emission measurements. The emission spectra in the range 450–900 and 1400–1800 nm were recorded by exciting the samples with 532 nm (Nd : YVO₄ crystal) and 514.5 nm (Ar⁺ laser), respectively. Applying Judd–Ofelt analysis, the intensity parameters have been determined using experimental oscillator strengths of absorption bands. From the Judd–Ofelt intensity parameters, some important fluorescence properties such as spontaneous transition probabilities, radiative lifetimes and luminescence branching ratios for the ⁴S_3/2→⁴I_15/2 (0.55 μm), ⁴S_3/2→⁴I_13/2 (0.85 μm), and ⁴I_13/2→⁴I_15/2 (1.54 μm) emission transitions of Er³⁺ ion in RLTB glasses have been calculated. The continuous pumping of the samples results in fast nonradiative decay through ²H_11/2→⁴F_9/2 (~3500 cm⁻¹) transition, which in turn causes the population of Er³⁺ ions from ²H_11/2 state to the higher ⁴F_3/2 state. The emission cross sections determined for the ⁴I_13/2→⁴I_15/2 (1.54 μm) transition using the McCumber theory are in good agreement with the values obtained from the Judd–Ofelt analysis. From evaluated radiative parameters, it is suggested that these RLTB glasses are more suitable candidates for 0.85 and 1.54 μm broadband optical amplifiers.     

Numerical computation of nonlinear oscillatory two‐immiscible magnetohydrodynamic flow in dual porous media system: FTCS and FEM study

The transient Hartmann magnetohydrodynamic flow of two immiscible fluids flowing through a horizontal channel containing two porous media with oscillating lateral wall mass flux is studied. A two‐dimensional spatial model is developed for two fluids, one of which is electrically conducting and the other is electrically insulating. Both the fluid regimes are driven by a common pressure gradient. A Darcy‐Forchheimer drag force model is used to simulate the porous media effects on the flow in both the fluid regimes. Special boundary conditions are imposed at the interface. The governing second‐order nonlinear partial differential dimensionless equations are obtained for each region using a set of transformations. The resulting transport equations are controlled by the Hartmann hydromagnetic parameter (Ha), viscosity ratio parameter (α), two Darcy numbers (Da ₁ and Da ₂), two Forchheimer numbers (Fs ₁ and Fs ₂), two Reynolds numbers (Re ₁ and Re ₂), frequency parameter ( εA) associated with the transpiration (lateral wall flux) velocity and a periodic frequency parameter ( ω*t*). Numerical forward time/central space finite‐difference solutions are obtained for a wide range of the governing parameters. Bench marking is performed with a Galerkin finite‐element method (MAGNETO‐FEM), and the results are found to be in excellent agreement. Applications of the model include magnetic cleanup operations in coastal/ocean seabed oil spills and electromagnetic purification of petroleum reservoir fluids.     

Implementation of Advanced Tunnel Field Effect Transistor (DP-TFET) for High Power Switching Applications

Silicon - As the technology advances to the nanoscale, advanced Tunnel Field-Effect Transistors are very prominent as a part of integrated circuits in the present trend. Advanced Tunnel FET devices...