Investigation of Heat Flux Propagation in Heat-Conducting Oxide Substrates with Different Heat Conductivity by the Linear Heat Source Method

Introduction. For controlled thermal management of power electronics devices, an important task is to increase the efficiency of heat removal from active components. Aim. To introduce a new approach to placing a linear contact-type heat source on the surface of thin samples in order to study the features of propagation of heat fluxes in oxide substrates from materials with different thermal conductivities. Methods and materials. The paper presents the results of studies of the propagation of heat fluxes in oxide substrates with different thermal conductivity (glassceramic and aluminum oxide ceramic - polycor). To generate the heat flux, a linear heat source was used, for which an electrically conductive carbon fiber was applied. Results. Thermograms and temperature distribution profiles were obtained at different periods of heating time on the surface of the substrate with a heating element and on its reverse side. It was shown that the placement of the linear heat source, implemented using an electrically conductive carbon filament, on the surface of the studied samples and time monitoring of thermograms from two opposite surfaces of the samples allowed to obtain data for evaluating the thermal properties of oxide substrates. The distribution of the heat flux in a homogeneous material near the generation point had the form of a cone of a heat pipe with a base on the surface with a heat source. The thermal cone for an aluminum oxide ceramic substrate had a larger angle of inclination than that in the case of glassceramic. Conclusion. The results obtained allowed to propose a method for reduction of thermal resistance of a heatconducting substrate by creating conditions for increasing the area of heat-conducting section.

Aluminum Oxide Ceramic Coatings on 316l Austenitic Steel Obtained by Plasma Electrolysis Oxidation Using a Pulsed Unipolar Power Supply

AISI 316 steel has good corrosion behavior and high-temperature stability, but often prolonged exposure to temperatures close to 700 °C in aggressive environments (e.g., in boilers and furnaces, in nuclear installations) can cause problems that lead to accelerated corrosion degradation of steel components. A known solution is to prepare alumina ceramic coatings on the surface of stainless steel. The aim of this study is to obtain aluminum oxide ceramic coatings on 316L austenitic steel, by Plasma Electrolysis Oxidation (PEO), using a pulsed unipolar power supply. The structures obtained by PEO under various experimental conditions were characterized by XPS, SEM, XRD, and EDS analyses. The feasibility was proved of employing PEO in NaAlO2 aqueous solution using a pulsed unipolar power supply for ceramic–like aluminum oxide films preparation, with thicknesses in the range of 20–50 μm, and a high content of Al2O3 on the surface of austenitic stainless steels.

Integrated Microwave Noise Suppressor Fabricated on Magnetic/Dielectric Composite Ceramic Substrate

We fabricated coplanar waveguide noise suppressors on anodic aluminum oxide ceramic substrates filled with 20 nm Co ferromagnetic nanowires, and measured the microwave properties of the integrated noise suppressors from 10 MHz to 40 GHz. The working frequency of the device is 16–20 GHz and the transmission coefficient S21 of the device is about −5 dB. We analyzed the characteristic impedance matching for the magnetic nanowire-based noise suppressors and provided the theoretical equations to calculate the ferromagnetic resonance frequency of the magnetic nanowires for various cases.