Materials Science Forum Vol. 970

Abstract: The role of spin states in the process of charge carrier transport in copper phthalocyanine (CuPc) nanowires has been established. According to the data obtained, CuPc nanowires are in the η-phase. The current-voltage characteristics (IVC) of a photosensitive cell based on CuPc nanowires in a magnetic field are investigated. As a result of experiments, it was found that applying an external magnetic field, the spins of two positively charged polarons are oriented in one direction. The channel of formation of the bipolaron is blocked. As a result, a decrease in the short-circuit current of the photosensitive cell is observed by more than 61%.

Abstract: The mathematical modeling of wildland fires impact on buildings have been carried out to study the effects of fires at different conditions of buildings ignition. The forest is modeling as a porous reactive medium. The formulation of this problem was developed using standard nonstationary three-dimensional Reynolds equations for flow in a multiphase reactive medium. These equations are solved numerically using finite volume method. The influence of meteorological conditions, properties of the forest and its state on the possibility of ignition of buildings located near forests is studied.

Abstract: There are two distinctive regions can be identified (low (LC) and high currents (HC)) of a watt-ampere (W-I) characteristic of initial LEDs based upon GaP with 590 nm wavelength. The established patterns differ in the exponent. At the same time, the LC region corresponds to an increase in the efficiency of conversion of operating current into light radiation, and the HC region is a slow decline with an increase in the operating current. As a result of irradiation with gamma-quanta in the passive power mode, the change in the shape of W-I characteristic is established, which can be characterized by an increase in the threshold current separating the LC and HC regions with an increase in the irradiation dose. The change in the emissive power of the LEDs and the shift of the threshold current occurs in two stages: in the first stage, the emissive power decreases due to radiation-stimulated rearrangement of the initial defect structure. At the same time, with an increase in the radiation dose, a partial recovery of the emissive power is observed against the background of its overall decrease. At the end of the first stage, the dependence of the damage coefficient on the operating current density in measurements of the W-I characteristics is manifested explicitly. The second stage of reducing the emissive power due to the introduction of radiation defects. In this case, the damage coefficient does not depend on the working current density, and the observed differences are due to the fact that by the end of the first stage its contribution to the overall reduction in emissive power is inversely proportional to the working current density. The established patterns can be used at the stage of designing the LEDs to substantiate the choice of the optimal value of the operating current density and to predict the resistance to irradiation with gamma rays.

Abstract: Opal matrix is a regular 3D-packing of spherical particles of amorphous SiO₂, forming an ordered system of voids. Opal matrixes with spherical particles of SiO₂ diameter d ≈ 260 nm (Δd ≈ 2 %) were synthesized. The frequency dependences of the conductivity, real and imaginary components of the dielectric and magnetic conductivity of nanocomposites containing crystallites 16–65 nm in size of magnetic materials ‒ double phosphates (LiNiPO₄, LiCoPO₄) and vanadates (GdVO₄ and DyVO₄) were measured. The dielectric losses of nanocomposites remain low (at a level of ~ 0.06) in the frequency range 10⁷–10¹⁰ Hz for nanocomposites with DyVO₄ and LiCoPO₄. The dielectric loss increases both in the direction of low frequencies (< 10⁶ Hz) and in the direction of THz frequencies.

Abstract: The paper deals with the fluxgate transducer intended for navigation and attitude control systems for moving vehicles. The finite element modeling of the half-sine and sawtooth pulse loads of various durations is performed for the proposed fluxgate configuration with regard to the properties of materials used.

Abstract: Gas tungsten arc welding (GTAW) is a widely used method of joining aluminium and its alloys. Despite the fact that a lot of research has been done in this area for several decades, there are many unresolved issues on the welding process control. Optimization of square wave alternating current profiles is one of them. This paper presents the results of studies on control of spatial position of an arc by an improved heat input algorithm taking into account the necessary relationship between direct current of straight and reverse polarity. It is shown that an increase in direct current reverse polarity to over 10 A contributes to expansion of a cathode spots space and, consequently, a greater deviation of the arc from the axis of a tungsten electrode. The spatial position of the arc is almost coaxial to the tungsten electrode when direct current reverse polarity is short-term reduced to 5 A at the final stage. These results are correct for a wide range of the square wave alternating current profiles.

Abstract: The article discusses the technological process for MEMS sensors manufacturing, which provides the minimum allowable technological defects to achieve MEMS technical characteristics. The paper deals with experiments on the definition of technological operations and the choice of their parameters. The factors influencing the size of technological defects are revealed. There is a technology to manufacture MEMS considered as "silicon on glass." There were successful experiments with the use of mask thickness of 540 nm and 450 nm. The slope of the faces does not exceed 1o, the maximum height of the surface roughness profile was 75 nm.

Abstract: The paper addresses the issues of subjective and instrumental quality assessment of flaw detection materials by Sherwin, Bycotest, Spotcheck, Chemetall and R-test penetrant materials using non-metallic test panels and software code.

Abstract: This work presents the analysis of damage assessment for dangerous industrial objects of acoustic emission method. Samples of low carbon and low alloy steels were researched. The aim of this work is to experimentally determine damage assessment for the state of developed and unacceptable sources of acoustic emission. Cracks of various lengths have been obtained by low-cycle loading. According to research, it is necessary to use several criteria simultaneously to increase the reliability of inspection of each growing crack.

Abstract: This paper presents the results of optimization of parameters for resistance spot welding of parts made of E110 zirconium alloy with a thickness of 0.25 + 0.25 mm. Its purpose was to determine the influence of welding current profiles on nugget metal structure and mechanical properties of welds. The highest tensile strength comparable with base metal (380...440 MPa) was observed when the ratio of integral heat input to current pulse duration was about two. Formation of martensitic structure and coarsening of nugget metal was observed with larger ratios. A proper fusion zone was not formed with lower ratios. Annealing of welded joints at a pressure of ~ 10^–4 Pa and a temperature of 580 °C for one hour was necessary to reduce residual stresses and transformation of metastable martensitic phase to a more stable state. This reduced microhardness of nugget metal by 30...35% and increased tensile strength of welds. It was also possible to increase tensile strength and reduce dispersion of its values by increasing duration of current down slope after formation of a nugget. An increase in duration from 1 to 14 ms caused rise in tensile strength by ~ 18% and dispersion of its values by ~ 3%.