Papers by Keyword: Irradiation

Abstract: Properties of composite materials irradiated by electrons have been studied. Effects of lavsan and montmorillonite nanocluster fillers on mechanical properties of polyimide-based polymer film materials have been studied. Catastrophic destruction models adequately describing stress-strain relationship curves for all test composites have been suggested.

Abstract: Fiber-reinforced plastics (FRP) are of great importance for the transport sector, the aerospace industry, for wind power plants, in the building sector and in the field of sports and leisure applications. Optimization of the adhesive bonding process for FRP structures, especially the surface preparation prior to bonding, will be of a central importance in forthcoming expansion of FRP use. In this connection the key problem depends on the FRP polymer matrix. In the case of duroplastic matrix the main problem is the presence of release agent on the surface of joining components. For the thermoplastic matrix such as polypropylene (PP), the main problems are the low surface energy and the inertness of its surface. Conventional pretreatment methods, such as manual grinding, shall be replaced by energetic radiation technics like VUV lamps (vacuum ultraviolet spectral range: 100 – 200 nm). This approach is a non-contact method, characterized by high treatment homogeneity and material-saving properties, combined with no further fibers to be released. The surface of the thermoplastics is activated by the incorporation of oxygen, release agent contamination on the thermoset is cleaned or modified [1 - 8]. The results of the VUV surface activation of PP and CFRP with regard to the incorporation of functional groups, increase of surface energy, matrix degradation and the adhesion increase of adhesive bonds are presented. In addition, studies on the release agent coating and the release agent modification by VUV radiation are presented. The work is completed by considerations concerning possibilities to accelerate the process (in particular, wavelength dependence, influence of an inert gas or the moisture content). Finally, an evaluation of the VUV pretreatment is carried out on the basis of two specific applications.

Abstract: Changes in the structure and the tungsten surface erosion by hydrogen plasma irradiation are studied in the article. It is shown that the change in the surface topography as a result of the development of the non-homogeneous surface etching is observed after surface irradiation. Metallographic analysis showed that the degree of relief is low in comparison with tungsten sample irradiated at T=700°C by tungsten samples irradiation at T=1000°C and 1500°C. However, these samples have small cracks, while the temperature increases the size and number of cracks also increases. It is determined, that the surface roughness varies depending on the irradiation temperature after hydrogen plasma exposure. The greatest increase in the roughness occurs in samples irradiated at T=1500°C, which is associated with the formation of small cracks in the surface layer. It is shown that a degree of surface erosion is increased with increase of the target temperature and the ion energy. Appreciable tungsten erosion due to irradiation of the plasma flow, plasma simulating stationary mode occurs only at relatively high temperatures of the target.

Abstract: The article studies the structure and properties, regularities of their change with the introduction of various fillers and under the influence of gamma – irradiation (γ-radiation). PCM structure study was performed using electron microscopy with scanning electron microscope BS -350 (TESLA) and with X-ray structural analysis method using X-ray diffractometer DRON-3. Shooting of wide-angle X-ray patters was performed in the range of Bragg angles reflection 2Q=5° - 96°. We selected the following properties to study: tensile strength, static tensile modulus. The findings allowed determining: firstly, we determined that based on electron microscopy the supramolecular structural organization depends on the type and percentage of filler in PTFE matrix. Changes take place from lamellar (pure PTFE) to a defective spherulitic (20% of coke) structure. Secondly, we completed X-ray structural analysis (we determined the degree of crystallinity, crystallite size, with parameters а = b in the hexagonal cell, interlayer distance of amorphous area) showed the nature of supramolecular structure changes according to the nature of the filler and subsequent radiation dose. Thirdly there was conducted connection between changes in mechanical strength (tensile strength, statical module of elasticity) and structural changes; the depth of these changes depends on the original supramolecular structure, type and percentage of the filler and the dose of the absorbed radiation energy. The studies will allow change purposefully the supramolecular structure of polymer composite materials to improve the performance properties.

Abstract: We performed deep level transient spectroscopy (DLTS), in capacitance, constant-capacitance and current mode, on 5 MeV proton irradiated 4H-SiC p⁺-i-n diodes. The study has revealed the presence of several majority and minority traps, ranging in the 0.4-1.6 eV below the conduction band edge and in the 0.4-1.5 eV above the valence band edge. We present a comparison of the results obtained with the three modes and discuss the nature of the detected traps, in the light of previous results found in the literature. At last, the impact of the irradiation on the minority carrier lifetime is evaluated by electrical measurements.

Abstract: In this paper investigation of degradation 4H SiC Schottky diodes parameters after irradiation by electrons with an energy of 0.9 MeV was doine. It was determined the carrier removal rate (Vd), which amounted to 0.07 - 0.09 cm^-1. It is shown that the investigated Schottky diodes retained rectifying current-voltage characteristics of up to doses ~ 10¹⁷ cm^-2. It is concluded that the radiation resistance of SiC Schottky diodes is much greater than the radiation resistance of Si p-i-n diodes with the same breakdown voltages

Abstract: The presented article deals with the research of micro-mechanical properties in the surface layer of modified linear polyethylene (LLDPE). These micro-mechanical properties were measured by the Depth Sensing Indentation - DSI method on samples which were non-irradiated and irradiated by different doses of the β - radiation (0, 66, 132 and 198 kGy ). Individual radiation doses caused structural and micro-mechanical changes which have a significant effect on the final properties of the LLDPE tested. The highest values of micro-mechanical properties were reached at radiation dose of 132 kGy, when the micro-hardness values increased by about 29%. These results indicate advantage crosslinking of the improved mechanical properties.

Abstract: Shape memory composite (SMC) structures are of great interest for the aerospace applications. In previous works, the authors have studied SMC lab-scale deploying prototypes manufactured by using two carbon fiber composite layers with a shape memory polymer interlayer. The prototypes were produced in an initial configuration and subsequently it was changed in the memorizing step. The initial configuration was then recovered by heating. Memorization and recovery phases were performed by means of conventional heating (by hot air gun or heater plate). In this work, for the first time the authors evaluate the SMC heating by means of radiating lamps. A square plate was purposely produced and recovered after different memory steps. Time, temperature and recovery are measured during and after the tests. The radiating lamp power and type, and the distance of the SMC from the lamp are fundamental parameters for the heating phase. As result of the irradiation tests, the initial configuration can be successfully recovered without failures. This study is especially aimed to future space applications in which the deployment (recovery) phase will be initiated only by exposure to solar radiation.

Abstract: A theoretical approach is developed to describe creation of space-periodical modulation of microstructure by means irradiation and influence of this modulation on properties of the irradiated material. It has considered nonlinear dynamics of development of radiation-induced defects. The structure of defects drives microstructure and changes material properties. It is found that nanoscale space-periodical distribution is results of interaction of radiation-induced defects both with each other and with elements of microstructure. It is shown that homogenous defect distribution become instable and bifurcation happen with respect to development of space-periodical distribution. Thus change of microstructure and material properties become space-periodical. Period of inhomogeneity and bifurcation values of parameters have been obtained.

Abstract: In this study, the composites for wood substitution made of benzoxazine filled with rubber wood-flour were fabricated. The wood flour contents was varied from 0 to 30 wt%. The effects of gamma radiation on the thermal and mechanical properties of wood-flour filled polybenzoxazine were determined. The different radiation dose (i.e. 0, 10, 20, and 30 kGy) was applied to the fabricated samples. The differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA) were used to evaluate glass transition temperature (T_g) and degradation temperature (T_d), respectively. While the flexural strength was determined using Universal Testing Machine (UTM). It could be noted that the increase of radiation dose provided the decrease of T_d. Moreover, the values of T_g, flexural strength, and water absorption reveals the similar trend with the maximum point at 20 kGy of radiation dose.