Thermal Breakdown Research Articles

MEMS Thermocouple Sensor Based on 4H-Silicon-Carbide-On-Insulator (4H-SiCOI)

With the high thermal conductivity and breakdown voltage, silicon carbide (SiC) has been treated as a promising material to work in harsh environment especially high temperature. However, due to its chemical inertness and wide band-gap, it is difficult to achieve the ion implantation, etching and good ohmic contact. In this study, silicon carbide on insulator (4H-SiCOI) is applied to fabricate MEMS thermocouple sensor, which can simultaneously compatible with bulk silicon CMOS process. The stress and temperature distribution of the sensor was simulated by COMSOL. After optimized the process parameters, the sensor based on 4H-SiCOI was successfully fabricated. Preliminary test results demonstrated the sensor shows good sensitivity about 1.44 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 10^{-{8}}\,\,{V}{m}^{{{2}}}/{W}$ </tex-math></inline-formula> and response time of 3.24ms, which also keeps good linearity and repeatability. This sensor can satisfy the needs of fast and high precision heat detection and our work may have a meaningful reference value for other same type SiC-based MEMS thermocouple sensor design and preparation.

Advanced Data-Driven Modeling Framework for Predicting Thermal Failures in Li-Ion Pouch Batteries

With the rapid development and widespread applications of lithium-ion batteries (LIBs), there is an ongoing need to extend and apply theoretical models that assist LIB’s safety aspects. It is particularly important for electric vehicles (EVs) due to numerous recent fire accidents. Thermal runaway (TRA) is one of the principal causes of LIB’s failures in EVs occurring due to thermal or mechanical breakdown, internal/external short-circuiting, or electrochemical abuse. During EV’s operation, it is impossible to directly monitor the TRA; however, the change in thermo-electrical characteristics (pattern) during TRA-like events could signal the presence of a failure, allowing for the prediction of LIB malfunction. Thus, in this work, we employ machine learning-based techniques informed by multi-physics models to predict and prevent the TRA in large pouch LIBs as presently used in various EVs.The multi-physics model is implemented in commercial software Comsol, with the P2D electrochemical model1 and a 3D thermal model. The degradation sub-model2 includes oxygen release in the positive electrode to simulate the overcharge phenomenon during EV’s charging. In addition, the oxygen released in the positive electrode may exothermically react with the electrolyte as well as create significant stress in the electrode, which may lead to the mechanical deformation of the electrode and a subsequent TRA. An LG Chem lithium-ion pouch cell consisting of Li(Ni0.6Mn0.2Co0.2)O2 – NMC622 – cathode and graphite anode are studied to address this severe TRA problem.As a result of the time-varying nature of the variables that affect TRA, we propose three potential machine learning algorithms. These are Support Vector Machine, Deep Neural Network, and Recurrent Neural Network, tailored and implemented for estimating the TRA likelihood, using thermal images acquired from the multi-physics modeling of LIB pouch cells. Hyperparameters optimization has been performed to identify a set of variables for the best performing ML method. The proposed combined multi-physics and machine learning modeling methodology provide interesting insight and predictive capabilities for TRA prediction.References J. Newman and W. Tiedemann, J. Electrochem. Soc., 140, 1–5 (1993).X. Feng, X. He, M. Ouyang, L. Wang, L. Lu, D. Ren and S. Santhanagopalan, J. Electrochem. Soc., 165, A3748–A3765 (2018).

Thermal Decomposition Behavior of Nickel-Water Nanofluids

Size affects breakdown behavior in most materials. There has been little focus on studying the thermal breakdown characteristics of typical heat transfer fluid mediums that contain dispersed nanoparticles. Researchers attempted to quantify the thermal degradation of irregularly shaped Nickel (Ni) nanofluids in this work. To determine Ni nanoparticle crystal size and morphology, X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used. It is ultrasonically dispersed into distilled water (DW) at varied Ni nanoparticle volume concentrations. Then the resulting Ni-DW nanofluids are created and their quasi-isothermal thermograms are determined using TG and DT (DTA). According to the results, DW's thermal breakdown resistance was increased by 28% when Ni nanoparticles were used in a homogenous dispersion.

Synthesis of Mixed Ligand 3D Cobalt MOF: Smart Responsiveness towards Photocatalytic Dye Degradation in Environmental Contaminants

A new metal organic framework {[Co3(BTC)2(Bimb)2.5]·2H2O}n(1) (Bimb = 1,4-bis[(1H-imidazol-1-yl)methyl]benzene and H3BTC = 1,3,5-Benzenetricarboxylic acid) has been synthesized and structurally characterized by elemental analysis, single-crystal X-ray diffraction (SC-XRD), vary temperature powder X-ray diffraction (VT-PXRD) and vary temperature Fourier transform infrared spectroscopy (VT-FTIR) have been used to establish the complex (1) and its physico-chemical analysis.. According to single crystal structure analysis, complex (1) features a three-dimensional network made up of trinuclear cobalt constructed by two-dimensional layer supported by BTC3− and Bimb ligands. Variable temperature luminescence relationship of as-prepared and excited form of complex (1) investigated luminescence emission in the region of 441-461 nm (2.81-2.69 eV) at room temperature with little difference in physical facade. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDAX), VT-PXRD and VT-FTIR studies revealed globular shaped Co3O4 nanoparticles with average sizes of about 20 nm as a result of thermal breakdown of (1). The photocatalytic experiments revealed that complex (1) displayed efficient photocatalytic capabilities to decompose the Fluorescein, Eriochrome Black T, Methyl Violet, Crystal Violet, Methyl Orange, Rhodamine B, Methylene Blue, Rhodamine 6G, Neutral Red and Congo Red under UV light irradiation. The photodegradation of FS, EBT, MV, CV, MO, RhB, MB, Rh6G, NR and CR exposed to be 91.7, 77.5, 68.7, 53.9, 50.9, 50.8, 47.4, 38.1, 19.5 and 15.8 %, respectively, after 135 minutes of irradiation with as-prepared MOF (1).

Impregnation assisted graphene oxide/polyimide nanofiber composites with improved thermal conductivity and breakdown strength

Impregnation assisted graphene oxide/polyimide nanofiber composites with improved thermal conductivity and breakdown strength

Study on the CCM breakdown voltage of proton exchange membrane fuel cells

Proton exchange membrane (PEM) short circuits are one of the failure forms of fuel cells. In this paper, the change in breakdown voltage (BV) after the preparation of PEMs into catalyst coated membranes (CCMs) is studied, and the impact of the catalyst layer (CL) and its composition on the BV of the CCM is analysed. The results show that the BV of the CCM is significantly lower than that of the uncoated PEM. The higher the platinum (Pt) loading of the coated CL is, the lower the BV. Further research finds that the BV of the single-side CL-coated CCM only decreases when the CL side is connected to the positive pole of the power supply, while it is comparable to that of the PEM when the CL side is connected to the negative pole. The experimental results demonstrate that the Pt and carbon particles in the CCM undergo electrochemical reactions during the breakdown process when the CL is connected to the positive pole, which eventually leads to thermal breakdown. Therefore, when the BV is chosen for detecting whether the CCM preparation process causes PEM damage, single-side CL-coated CCM should be adopted, and the CL should be connected to the negative pole of the power supply.

The stability of polyaromatic naphthalene sulfonates in hydrothermal solutions to 330 °C at equilibrium saturated vapour pressure

Naphthalene sulfonates and disulfonates have been widely used in the geothermal industry as tracer chemicals and knowledge of their rates of thermal breakdown is essential to ensure their successful use. In this study the stabilities of six polyaromatic sulfonates: 1-naphthalene sulfonate (1-NS); 2-naphthalene sulfonate (2-NS); 2,6-naphthalene disulfonate (2,6-NDS); 2,7-naphthalene disulfonate (2,7-NDS); 1,5- naphthalene disulfonate (1,5-NDS); and 1,6-naphtahlene disulfonate (1,6-NDS) in 0.050 mol kg−1 NaCl solution was investigated. The NDS/NS thermal stabilities were studied as a function of temperature and pH in oxygen-free solutions. Three sets of experiments were conducted using quartz glass ampoules. The first set of experiments studied the breakdown rates of both 1,5-NDS and 2-NS at a range of pH values at 200 and 300 °C. The second set studied 1,6-NDS thermal decay to determine the breakdown products at 200, 250, and 300 °C. The third set involved a mixture of 1,5-NDS, 1,6-NDS, 2,6-NDS, 2,7-NDS, and 2-NS in 0.050 mol kg−1 NaCl, with and without the presence of greywacke, at temperatures up to 300 °C. The results show that 1,5-NDS and 2-NS breakdown is temperature and pH-dependent. The breakdown of 1,6-NDS forms mainly 2-naphthalene sulfonate (2-NS), whereas above 300 °C, 1,6-NDS generated significant amounts of naphthalene (NAP). The results show that the stabilities of all tested NDS/NS compounds are temperature-dependent with their relative stabilities increasing in the order 1,5-NDS < 1,6-NDS < 2,6-NDS ≈ 2,7-NDS < 2-NS. In the presence of greywacke, fluid-rock interactions served to buffer pH thereby stabilizing the NDS over experiments where no rock was present. The finding presented in this study support need for reevaluation of historic NDS tracer tests, and consideration of reservoir temperature and pH when planning future tests.

Selecting a cryogenic cooling system for superconducting machines: General considerations for electric machine designers and engineers

In this paper, general considerations for selecting a cryogenic cooling system for superconducting machine in different applications were explained with respect to the design, operation, and condition monitoring constraints. These considerations are explained so that they help electric machine engineers and designers to get familiar with cryogenic aspects of selecting and using cryogenic cooling system of superconducting machines. In fact, the main questions are: what are the important factors that one should take into account when selecting a cooling system for a superconducting machine application? Also, which one of these factors could later affect the performance of the cooling system so that it can efficiently cope with the expected heat load withoutfacing a thermal breakdown? To adress these questions, common cooling system structures, different cryogenic fluids, the associated parameters with the value of heat loads, and safety margins were discussed to help the machine engineers to choose the most appropriate cryogenic cooling system that adjusts better with their superconducting machine and the specific considerations that they might have. Some considerations regarding the auxiliary devices such as heat exchangers and pumps, were explained as the next priority in selecting a cooling system. Special challenges and considerations imposed to the cooling systems of superconducting machines in aerospace applications such as electric- and hydrogen-powered aircraft, naval applications, and wind energy application were also discussed. Although all of these applications share similar concerns like weight, cost, and specific mass of cooling systems, each one of them have their specific concerns and constraints which come with higher priority.

Review on Research Progress of C6F12O as a Fire Extinguishing Agent

Clean gas fire suppressants with high efficiency are widely applied. This paper provides a systematic review of the research advances in the novel environmentally friendly suppressant, C6F12O. Considering the principle of screening fire suppressants, the physical and chemical properties of C6F12O are presented first. Specifically, research on the measurement of the thermodynamic parameters, toxicity, corrosion, environmental compatibility and dispersion characteristics are summarized, revealing that the poor dispersibility, corrosion of the hydrolysates (perfluoropropionic acid), corrosion and toxicity of thermal breakdown products such as HF and COF2 and environmentally unfriendly products such as perfluorocarbons should be paid more attention. Three main synthesis routes of C6F12O are also introduced in view of its promising prospects for application. Furthermore, the fire extinguishing efficiency of C6F12O has been fully investigated in both a laboratory burner scale and full-scale fire extinguishing experiment, the results of which show that the minimum extinguishing volume concentration of C6F12O is lower than HFCs, but the mass concentration is much higher. Although C6F12O has shown satisfactory fire extinguishing performance in various fire protection scenarios, fire enhancement phenomenon and the large production of HF have been observed during fire extinguishment. Finally, the fire extinguishing mechanism of C6F12O has been discussed. The flame suppression effect of C6F12O, combustion enhancement phenomenon and the influence of water in the reaction zone have been revealed. This review fully evaluates C6F12O, in hope that it will provide a reference for follow-up research and the development of a halon replacement.

EXCITATION OF OWN OSCILLATIONS IN SEMICONDUCTOR COMPONENTS OF RADIO PRODUCTS UNDER THE EXPOSURE OF THIRD-PARTY ELECTROMAGNETIC RADIATION

The subject matter is the processes of analysis and mechanisms of interaction of EMP-induced currents and voltages with the processes characterizing the functional purpose of radio products, is usually carried out within the framework of the theory of distributed circuits. The presented approach makes it possible to evaluate the performance criteria in general (for example, to evaluate the critical energy characterizing a thermal breakdown), however, issues related to the determination of various types of electromagnetic interactions that occur directly in the components of a product under the influence of EMR remain open. The aim is the possibility of setting up theoretical and experimental studies based on the proposed calculation model for excitation of natural vibrations of a semiconductor structure (exponential growth of amplitude). The parameters of a third-party pulsed electromagnetic field, induced currents and characteristics of semiconductor devices have been established within which the regime of amplification of natural vibrations of a semiconductor structure is observed. The objectives are: mechanisms of interaction of induced currents with surface vibrations of semiconductor components of a radio product under the influence of pulsed electromagnetic radiation. The methods used are: methods of the theory of small perturbations in determining the spectrum of natural oscillations of the system - currents induced by electromagnetic radiation and natural oscillations of the components of the radio product. The following results are obtained: The mechanisms for the appearance of reversible failures of semiconductor components of radio products under the influence of third-party pulsed electromagnetic fields are determined. It has been established that the presence of a current induced by external radiation leads to the establishment of a mode of amplification of natural oscillations of semiconductor components of a radio product (reversible failures). Conclusion. Quantitative estimates of amplification (generation) modes of oscillations of semiconductor devices, distorting their performance depending on the parameters of external electromagnetic influence, allows developing mechanisms for electromagnetic compatibility of microwave radio products. A comparative analysis of the calculated data obtained in the work can be used in the manufacture of radio devices operating in the millimeter and submillimeter range (amplifiers, generators and frequency converters).

Detection, Characterization and Modeling of Localized Defects and Thermal Breakdown in Photovoltaic Panels from Thermal Images and IV Curves

In this work, a defective commercial module with a rounded IV characteristic is analyzed in detail to identify the sources of its malfunction. The analysis of the module includes thermography images taken under diverse conditions, the IV response of the module obtained without any shadow, and shadowing one cell at a time, as recommended by the IEC 61215 Standard. Additionally, a direct measurement of the IV characteristic and resistance of single cells in the panel has been conducted to verify the isolation between the p and n areas. In parallel, theoretical cell and module behaviors are presented. In this frame, simulations show how cell mismatch can be the explanation to the rounded IV output of the solar panel under study. From the thermal images of the module, several localized hot spots related to failing cells have been revealed. During the present study, thermal breakdown is seen before avalanche breakdown in one of the cells, evidencing a hot spot. Not many papers have dealt with this problem, whereas we believe it is important to analyze the relationship between thermal breakdown and hot spotting in order to prevent it in the future, since hot spots are the main defects related to degradation of modern modules.

Predicting isotopologue abundances in the products of organic catagenesis with a kinetic Monte-Carlo model

Thermal cracking of complex organic matter can occur under many geological settings. However, the role of thermal cracking vs. other chemistries (e.g., metallic catalysis or Fischer-Tropsch-type reactions) in petroleum formation remains controversial. Realistic modeling of isotope effects in chemical reaction networks involving thermal cracking might shed light on this problem, especially given the recent progress on measurements of intramolecular stable isotope distributions in organic compounds. Previously published models of thermal cracking in petroleum formation are incapable of predicting the intramolecular isotope patterns of products because they do not incorporate realistic precursors, elementary reactions and patterns of inheritance. In this study, we develop a kinetic Monte-Carlo (kMC) model to address this problem. We simulate thermal breakdown of different types of organic matter that is represented by molecular models. At the onset of each simulation, we initialize the model parent organic molecules with isotopic substitutions, and then subject them to free radical chain reactions in a many-step process. Every simulation captures a possible route of thermal degradation and tallies the numbers of each unique isotopologue of all product molecules at the end. Although this model produces data that contain information for all molecules and isotopic forms, in this study we focus on the proportions of many of the isotopologues of all of the C1-C7n-alkanes. We use two chemistry schemes that differ in complexity. The basic scheme (scheme A) includes only homolytic cleavage and capping of metastable radicals by hydrogen atoms. The more sophisticated scheme (scheme B) includes most reactions of importance in the free radical chain mechanism of thermal cracking. We find significant differences between the schemes A and B in predicted molecular and isotopic compositions of products. Scheme B is more consistent with natural data than scheme A, suggesting that full radical mechanisms should be considered in models of thermal cracking in natural hydrocarbon formation. Our model is further validated by reproducing results from hydrous pyrolysis experiments. For simulating natural petroleum formation, we found that the kMC model is acceptable at low maturity, but cannot match compositions and time estimates of mature gas formation, suggesting the influence of alternative mechanisms in late-stage, high-thermal-maturity catagenesis. Using our model, we provide mechanistic explanations for some of the existing observations, such as the evolution of intramolecular and intermolecular carbon isotope compositions with thermal maturity. Our study also makes predictions of intramolecular isotope compositions for higher-order alkanes (C4+) that have been little studied to date but present attractive targets for future measurements.

Kinetic modelling for pyrolytic degradation of olive tree pruning residues with predictions under various heating configurations

Herein, the aim was to develop an in-depth understanding of the kinetic behaviour of olive tree pruning residue (OTPR), an abundant agricultural waste, during pyrolysis. Thermal analysis at 1, 2, 4, 6 and 10 °C.min−1 was performed using TGA-thermogravimetric analysis, with the results subsequently used to determine the OTPR's kinetic thermal breakdown behaviour. Furthermore, advanced kinetics and technology solutions (AKTS) thermo-kinetic tool was applied to investigate the kinetic behaviour of OTPR and to generate kinetic predictions for various heating configurations. Friedman's method was the main approach used to evaluate the kinetic parameters. For comparison, other established kinetic modelling techniques, such as ASTM-E698 and Flynn-Wall-Ozawa (FWO) methods, were applied. The ASTM-E698 approach yielded an apparent activation energy (Ea) of 172.09 kJ.mol−1, whereas the FWO method yielded an Ea range from 38 to 172 kJ.mol−1. Finally, the differential iso-conversional approach yielded Ea values ranging between 85 and 191 kJ.mol−1. Kinetic predictions were then developed for isothermal, non-isothermal, and stepwise configurations using the kinetic parameters obtained via Friedman’s model. The forecasts shed light on optimising production throughput in a variety of reactor configurations.

Numerical Study on Electromagnetic Coupled Heat Transfer and Ultrasonic Propagation in GIS Busbar Chamber

In the present paper, the electromagnetic coupled heat transfer and ultrasonic propagation in a 252 kV three-phase GIS busbar chamber were numerically studied by using the finite element method. The electromagnetic loss and distributions of SF6 gas velocity, temperature, and breakdown margin in the GIS busbar chamber were carefully analyzed, and the influences of SF6 gas velocity and temperature variations on ultrasonic propagation performances in the GIS chamber were discussed in detail. It is found that the SF6 gas breakdown margin in the GIS busbar chamber is mainly affected by the electric field intensity. When I = 3300 A and U = 1050 kV, the minimum SF6 gas breakdown margin in the GIS busbar chamber is 7.98 kV/mm, which is located at top of busbar conductor A, where the thermal breakdown risk is relatively high. Furthermore, it is noted that, when natural convection in GIS busbar chamber is weak, the influences of SF6 gas velocity and temperature variations on sound propagation would be insignificant. For this case, when acoustic propagation simulation is performed, the SF6 gas would be assumed to be stationary and its temperature would be set to the average gas temperature of natural convection in the GIS chamber, which would be beneficial to reduce the computational time and maintain the simulation accuracy as well.

Comprehensive characterization of efficiency limiting defects in the swirl-shaped region of Czochralski silicon

For Czochralski silicon (Cz-Si) solar cells, swirl-shaped regions in silicon wafers could lead to efficiency degradation, usually accompanied by hot spots and thermal breakdown. In this paper, comprehensive characterization methods including electroluminescence (EL), photo-induced current (LBIC), quantum efficiency (QE), cell efficiency, carrier lifetime, scanning electron microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and deep level transient spectroscopy (DLTS) were used to investigate the formation and properties of the Swirl defects. It is found that there exists a strong correlation between the as-grown swirl defects and the degradation in cell performance. The Swirl defects cause an energy level of E v + 0.33 eV in silicon bandgap, with the capture cross section of 2.3 × 10 −15 cm 2 , which is consistent with the feature of silicon/oxide interface states. The swirl defects can further be evolved into stacking faults after annealing at 1050 °C for 16 h, and cause an additional energy level of E v + 0.42 eV with the capture cross section is 1.0 × 10 −14 cm 2 . These results suggest that oxygen precipitates are the vital component or precursor for the formation of swirl-shaped regions in Cz silicon wafers. • A comprehensive study of the nature of Swirl defects in the photovoltaic Czochralski silicon is obtained. • The direct evidence that Swirl defects are related to oxygen precipitates is provided by deep level transient spectroscopy (DLTS) measurements. • The influence of Swirl defects on solar cell performances and material properties is characterized.

Effect of electron injected air on the gasification performance of biomass

The mathematical modeling and the experimental study employing the pilot-scale up-draft fixed bed gasifier were carried out to investigate the effect of the electron injected air on the performance of biomass gasification. The goal of the mathematical modeling was to illustrate the temperature and chemical composition fields. Moreover, the stream function provided by the electron injected air to the flame, and to consider its effect on the development of the flame reaction zone. The results obtained showed that the electron injection generated the electric field, which enhanced the flame's stability greatly. The influence of the flame reaction zone generated by the field-induced ionic wind on the thermal breakdown of biomass was explored, as well as the improvement mechanism of gasification properties by the electric field.

Synthesis of ZrO2 Based Nanofluids for Cooling and Insulation of Transformers

Nanofluids have recently emerged as an important new technology for heat transfer in various engineering applications. In this work, zirconia (ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanoparticles were synthesized using a microwave-assisted sol-gel method for the preparation of nanofluids through a two-step synthesis process. The electrical, thermal, and rheological properties of the nanofluids produced were studied as a function of the ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration (g/L). These fluids showed potential as an alternative to the traditionally available ester-based transformer oil. The effect of the ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticle additions on the nanofluid was evaluated by the measurements of thermal conductivity, breakdown voltage (BDV), and viscosity. The results show an improvement in cooling, insulation, and BDV due to ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , which is explained in terms of a nanoparticle-assisted charge capture mechanism. The optimal performance of the nanofluid was obtained for a concentration of 0.2 g/L of ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles in the transformer oil.

0D + 1D = 1D Zn-orotate-Bimb polyrotaxane coordination polymer: Synthesis, structure, thermogravimetric and variable temperature luminescence analysis

A new polyrotaxane coordination polymer {[Zn(Or)(Bimb)(H2O)]2·6H2O}n(1) has been synthesized using Zn(II) ion with 1,4-bis[(1H-imidazol-1-yl)methyl]benzene) (Bimb) and potassium orotate (OrK) ligands at ambient temperature. Single-crystal X-ray diffraction, elemental analysis, variable temperature Powder X-ray diffraction (VT-PXRD), variable temperature FTIR (VT-FTIR) and TG/DT/TDG were used to characterize the complex. Complex (1) contains 0D binuclear Zn(1)–based molecular “loop”, 1D Zn(2)–based molecular “string” yielding to 0D + 1D = 1D polyrotaxane coordination polymers. Supramolecular network in complex (1) is stabilized by classical strong NH∙∙∙O and OH∙∙∙O hydrogen bonds resulting in the formation of 2D inter-layer polyrotaxane coordination polymers and 3D supramolecular network via these non-covalent interactions. The solid-state variable temperature-luminescence studies of as synthesized and heated forms of (1) emit strong luminescence in the range of 363–439 nm (2.82–3.41 eV) with slight contrast in physical façade. The thermal breakdown of (1) yielded spherical shaped ZnO nanoparticles with diameters of ̴ 32 nm, as confirmed by FESEM, EDAX.

Diamond/GaN HEMTs: Where from and Where to?

Gallium nitride is a wide bandgap semiconductor material with high electric field strength and electron mobility that translate in a tremendous potential for radio-frequency communications and renewable energy generation, amongst other areas. However, due to the particular architecture of GaN high electron mobility transistors, the relatively low thermal conductivity of the material induces the appearance of localized hotspots that degrade the devices performance and compromise their long term reliability. On the search of effective thermal management solutions, the integration of GaN and synthetic diamond with high thermal conductivity and electric breakdown strength shows a tremendous potential. A significant effort has been made in the past few years by both academic and industrial players in the search of a technological process that allows the integration of both materials and the fabrication of high performance and high reliability hybrid devices. Different approaches have been proposed, such as the development of diamond/GaN wafers for further device fabrication or the capping of passivated GaN devices with diamond films. This paper describes in detail the potential and technical challenges of each approach and presents and discusses their advantages and disadvantages.

Shading Effect on Flow Rate of Solar DC Water Pump

Partial shading (PS) has a negative impact not only on the shaded Photo Voltaic PV modules/arrays but also on the power generated by the partially shaded photovoltaic (PSPV) system. It decreases the output power of the (PV) system and adds to hot fleck issues, which may result in the thermal breakdown of shaded PV modules. Solar water pumping is based on a (PV) system that converts solar energy into electrical energy to power a DC motor. This paper includes a practical investigation on the DC pump performance, as well as the influence of (1/4, 1/2, 3/4, and completely) shading on the performance of the DC pump motor. The current study shows that by Using maximum power point tracking (MPPT) control, the motor voltage will be stabilized and not affected by the increase in the shading area.