Defect and Diffusion Forum Vols. 237-240

Abstract: In this work it will be presented the results of calculation of energy activation Q of selected industrial steels (e.g. grade 55 - carbon steel, LH15 – bearing steel, H10S2M, 4H14N14W2M and 50H21G9N4 valve steels) according to Polish Norm by two methods. In the first method the calculations of Q are based on the dependence of value of parabolic growth rate constants kp in function of reciprocal temperature. The second method is based on the calculated parameters, which allow to determine the value of Q for examined steels by using value of Q for pure iron, taken from literature data, and the particular values of mass concentrations of elements in oxidised steels. The growth kinetics of layers were almost according to parabolic law. The values of parabolic rate constant kp were calculated on the basis of measurements of thickness of oxide layers. To the experiment the cylindrical specimens were used. The isothermal process of oxidation was conducted in chamber furnace at 1100, 1060, 1020, 980 and 940°C in the air. Time of oxidation various from 3 till 1303.5 hrs. The comparison of obtained results of activation energy Q for mentioned methods of each individual examined steels gives a good agreement.

Abstract: Calculational and experimental approach was developed for life time analysis of MCrAlY coatings for industrial gas turbine blades. This approach based on the model that describes the main diffusion and oxidation processes within the coating-base metal system as well as the experimental data for specimens after different short time exposures at different temperatures. In comparison with existing models the proposed model describes interdiffusion zone between coating and base alloy. The models adequacy to physical processes is provided by model parameters identification with short-time experiment data for coating – base alloy systems. The measured Al concentration profiles were used as input values for the model parameters estimation and a calculational prediction of the long term diffusion and oxidation behaviour of the coating was performed. The model, calculational and experimental approach as well as MCrAlY life time estimation results for 10000 h at 950°C are presented. These results were obtained with short time experimental data for Al concentration profiles across the coating thickness measured after 300 and 1000 h. The predicted and measured b-phase content at coating during oxidation for coating thickness 200 micron at 900, 950 and 1000 °C are presented too. The b-phase content disappear at coating was assumed as a corrosion life time criterium.

Abstract: The metallization of organic thin films is a crucial point in the development of organic electronic devices. There is no method established yet to detect trace amounts of metal atoms in the organic thin films after metal deposition. Radiotracer measurements are probably the most sensitive tool to study diffusion and to quantify even very small amounts of material penetrating into the bulk. So far, this has been shown for metals and polymers, but not for thin ordered molecular organic films. Here, the first application of this technique on a well-characterized organic thin film system, diindenoperylene using thermally evaporated Ag containing 110mAg radiotracers is shown. The results show that Ag is mainly adsorbed on the surface, but indicate that already at moderate substrate temperatures small concentrations of Ag can penetrate into the organic thin films and agglomerate at the interface during metallization.

Abstract: Boron diffusion in Si and strained SiGe with and without C was studied. Using gassource molecular beam epitaxy (MBE), B containing epitaxial layers of: (i) Si, (ii) Si containing 0.1% C, (iii) SiGe with 11% Ge and (iv) SiGe with 11% Ge and with a 0.1% C, were grown on substrates. These samples were then rapid thermal annealed (RTA) at 940, 1000 and 1050°C in an O2 ambient. Self-interstitial-, vacancy- and non-injection conditions were achieved by annealing bare, Si3N4- and Si3N4+SiO2-coated surfaces, respectively. Concentration profiles of B, Ge and C were obtained using Secondary-Ion Mass Spectrometry (SIMS). Diffusion coefficients of B in each type of matrix were extracted by computer simulation. We find that B diffusivity is reduced by both Ge and C. The suppression due to C is much larger. In all materials, a substantial enhancement of B diffusion was observed due to self-interstitial injection compared to non-injection conditions. These results indicate that B diffusion in all four types of layers is mediated primarily by interstitialcy type defects.

Abstract: Lithium diffusion properties of Li1-2yCo1+yVO4 (y = 0, 0.05, 0.1) with inverse spinel structure as cathode materials for a Li-ion battery were investigated in view of lithium vacancies. >From galvanostatic intermittent titration technique (GITT) analysis, it is evaluated that diffusion coefficients of lithium ion DLi in Li1-xCoVO4 were decreasing from about 10-10 cm2 s-1 (x = 0.05) to 10-12 cm2 s-1 (x = 0.4), and also decreasing for Li1-2y-xCo1+yVO4 in spite of production for lithium vacancies that is related to pre-exponential factor D0. EXAFS analysis revealed that the Debye-Waller factors which corresponded to the local distortion of each V-O and Co-O bonds were increasing by production of cation vacancies, indicating that the large local distortion of the lattice around vanadium and cobalt ions occurred. The result suggested that lithium diffusion path in these materials was disturbed by the local distortion and caused increasing the activation energy DG‡.

Abstract: Diffusion in nanocrystalline materials is becoming an increasingly important topic. The analysis of diffusion profiles obtained in nanocrystalline materials with enhanced grain boundary diffusion, however, is not straightforward since assumptions made in the deviation of the conventional models are often not fulfilled. In this contribution numerical diffusion studies are performed in order to investigate effects caused by the high density of interfaces in nanocrystalline material. A continuum model based on the 2D 2-nd Fick’s law was solved by means of the finite element method. This allows us to analyze diffusion profiles for different geometrical situations such as a single boundary, square grains with the grain size of 80 nm and 25 nm and geometries comprising differently oriented boundaries of the average length of 30 nm . The analysis was carried out for different diffusion lengths corresponding to Harrison type A and type B kinetic regimes. For the isolated boundary a very good agreement was achieved in comparison with the classical Whipple’s solution. For nanocrystalline material, however, considerable errors can occur when analyzing the averaged diffusion profiles in the conventional Harrison type A and B kinetics.

Abstract: We present ultra-shallow diffusion profiles performed by short-time diffusion of boron from the gas phase using controlled surface injection of self-interstitials and vacancies into the ntype Si(100) wafers. The diffusion profiles of this kind are found to consist of both longitudinal and lateral silicon quantum wells of the p-type that are self-assembled between the layers of microdefects, which are produced by previous oxidation. These layers appear to be passivated during short-time diffusion of boron thereby forming neutral d - barriers. The fractal type selfassembly of microdefects is found to be created by varying the thickness of the oxide overlayer, which represents the system of microcavities embedded in the quantum well plane.