Papers by Keyword: Temperature Dependence

Abstract: The temperature dependence of the thermal conductivity of plasma‑sprayed ZrO₂-5 wt.% CaO, (ZrO₂-5 wt.% CaO)-10 wt.% Ni, and (ZrO₂-5 wt.% CaO)-30 wt.% Ni coatings was investigated. A combined experimental and numerical approach was employed, comprising specimen heating with a propane–oxygen torch with in situ temperature field measurements and numerical simulation using COMSOL Multiphysics®. Thermal conductivity was calculated via an iterative solution of the inverse heat conduction problem. It was found that thermal conductivity increases with increasing Ni content: for the ZrO₂/CaO ceramic coating, thermal conductivity in the temperature range 20–1100°C ranged from 0.76 to 1.22 W·m⁻¹·K⁻¹, whereas for the metal–ceramic coatings containing 10% and 30% Ni, the values were 1.11–1.87 W·m⁻¹·K⁻¹ and 1.71–4.18 W·m⁻¹·K⁻¹, respectively. These results provide valuable insights for the design and optimization of thermal barrier coatings.

Abstract: A unique hybrid structure of the 4H-SiC bonded substrate offers advantages not achievable with conventional 4H-SiC bulk substrates, such as a reduction in on-state resistance and the suppression of forward bias degradation in power devices. This study focuses on the contact resistance between the polycrystalline layer and the backside metal (Ni/Ti) of 4H-SiC bonded substrates, along with its temperature dependence. The results indicate that the bonded substrates exhibit low backside specific contact resistance (SCR) , even without annealing, and this resistance remains stable at elevated temperatures. Furthermore, power devices utilizing bonded substrates demonstrated reduced on-state resistance, as evaluated using Schottky barrier diodes (SBDs). Specifically, 4H-SiC bonded substrates without contact annealing lowered the forward voltage by 13.4% at room temperature (RT) compared to 4H-SiC bulk substrates with contact annealing. These findings suggest that 4H-SiC bonded substrates simplify the backside contact process compared to 4H-SiC bulk substrates, offering significant benefits in reducing on-state resistance in SiC power devices.

Abstract: The growing interest for the use of 4H-SiC in photonics is triggering the interest for more accurate characterizations of this semiconductor from the optical and opto-electronic point of view. In this work we report about new measurements run on an undoped 4H-SiC substrate, finalized at determining the precise dependence of its refractive index on temperature in the visible spectrum, and precisely at the wavelength of λ=632.8 nm, in a temperature range from room temperature (RT) to 400K. Measurements are performed by exploiting the properties of a Fabry-Perot cavity interrogated with a laser beam. It is known that the transmitted radiation intensity shows fringes that shift with temperature and the refractive index. By precisely monitoring the transmitted signal, the thermo-optic coefficient dn/dT can be determined with a resolution that approaches 10^-6 K^-1.

Abstract: The paper discusses computer modeling of the temperature dependences of the dielectric constant of polymer composite materials. Issues of the combined radio wave and thermal methods of diagnostics of nondestructive inspection of the polymer composite materials in the laboratory conditions are considered. The paper offers a method for combining the measurement and heating processes. This method can be implemented, the way is to do the heating and the measurement at the same frequency with using a high-power sounding wave. As a result, the radiant material heating is obtained, and we judge about the substance parameters and a presence of defects in the substance by a reflected wave in an indirect method. A descriptive characteristic of such a problem boils down to describing all the processes in the sample by the electrodynamic theory. The heating process can also be described by the electrodynamics equations, but the process will be described by the thermal equations in the nonstationary heating conditions in the most accurate way.

Abstract: For the first time, the time dependences of the temperature of aluminum, zinc and zinc-aluminum alloys alloyed with II A group elements under spontaneous cooling mode were obtained; an anomalous course and two characteristic times of the cooling process were found, and their mechanism was explained; the temperature dependence of the thermophysical properties of the investigated metals and alloys was established; the temperature dependence of the coefficients of convective heat transfer and radiation of Al, Zn and Zn55Al and Zn5Al alloys was experimentally determined; the influence of the concentration of II A group elements and temperature on the heat capacity and thermodynamic functions of Zn55Al and Zn5Al alloys was revealed.

Abstract: As it stands, in terms of environmental impact and efficiency, photovoltaic (PV) energy has appeared to be a potential renewable power source that notably contends with the traditional power generation schemes. More so, a noteworthy factor that contrariwise influences the PV module efficiency is the PV module temperature. Therefore, the more the PV module temperature increases, the lesser the PV module efficiency. More importantly, the impact of undesired spectrum wavelengths on the PV module temperature is further reduced by passive optical filters, nonetheless, active optical filters which is more superior to the passive type, based on the PV module temperature and output power during the day, dynamically change the cut-off wavelength. Consequently, the efficiency as well as the lifecycle is both enhanced by controlling the active optical filter so as to attain optimal output power. Therefore, in this paper, a wavelength-based thermo-electrical model of a PV module was designed and simulated, the essence of this model is mainly to predict the impact of each module wavelength on both the temperature and the output power of the PV module. In view of this, since the output power is affluence by the module temperature, it is expedient to design a controller that locates the optimal cut-off spectral wavelength to lessen the module temperature whereas getting the most out of the output power over a period of time. In this vein, we designed a Model Predictive Controller whose objective is to maximize the output power by simply controlling the input power through filtering the spectrum wavelength for a photovoltaic (PV) system. The design and simulation of the plant model as well as the MPC controller were carried-out on MATLAB/Simulink environment.

Abstract: The dependence of the young modulus of metals and alloys on the high temperature must be taken into account in metallurgy in the hot rolling of steel sheet on sheet-rolling mills, hot flattening of steel sheet in the sheet straightening machines, press forming forgings from hot steel sheet, hot volume stamping of metal products, and so on. For example, on the mill 5000 by SMS Siemag, the sheet-rolling of steel strips from the hot slabs at the stand Quarto (the maximum force of 120 MN) occurs at a temperature from 750 °С to 1050 °С, but the pre-flattening of hot steel strip on the five-roller sheet-straightening machine by SMS Siemag occurs usually in the temperature range from 600 °С to 760 °С. In this paper, based on the analysis of experimental data about the dependence of the young modulus for various steel alloys, the analytical dependence of the young modulus on temperature is obtained.

Abstract: Temperature dependent microwave detected photoconductivity MDP and time-resolved photoluminescence TRPL were employed to investigate the carrier lifetime in CVD grown 4H-SiC epilayers of different thickness. The minority carrier lifetime may be found from both theMDP and defect PL decay at room temperature for all epilayers, whereas the near bandedge emission (NBE) decay is much faster for thin epilayers (<17 μm) due to the substrate proximity and only follows the minority carrier lifetime for thicker samples at lower excess carrier concentrations.

Abstract: Within the kinetic energy driven superconducting mechanism, we have studied the temperature dependence of commensurate magnetic resonance in cuprate superconductors. It is shown that the commensurate magnetic resonance peak at the antiferromagnetic wave vector point persists in the superconducting state until the temperature rises to the superconducting transition temperature $T_{\rm c}$. The intensity of the resonance peak decreases with increasing temperature which is just like the temperature dependence of the superconducting gap parameter. Our results are in qualitative agreement with the inelastic neutron scattering experimental data and reflect that the commensurate magnetic resonance is closely related to the creation of the charge carrier pairs and thus the superconducting mechanism of cuprate superconductors.

Abstract: This work reports an SiC-MOSFET which replaces a part of the channel resistance with an additional embedded resistance, called a source resistance (R_s). MOSFETs with R_s have higher resistance during short circuit compared with MOSFETs without R_s and suppress short-circuit currents. An improvement of the trade-off relationship between short-circuit capability and on-resistance was obtained with MOSFETs including embedded R_s.