Defect and Diffusion Forum Vols. 334-335

Abstract: The precipitation of tungsten nitride upon internal nitriding of ferritic Fe-0.5 at.% W alloy was investigated at 610°C in a flowing NH₃/H₂ gas mixture. Different tungsten nitrides developed successively; the thermodynamically stable hexagonal δ-WN could not be detected. The state of deformation of the surface plays an important role for the development of tungsten nitride at the surface. The morphologies of the tungsten nitrides developed at the surface and those precipitated at some depth in the specimen are different. The nitride particles at the surface exhibit mostly an equiaxed morphology (with the size of the order 0.5 µm) and have a crystal structure which can be described as a superstructure derived from hexagonal δ-WN. These nitride particles show a strong preferred orientation with respect to the specimen frame of reference but have no relation with the crystal orientation of the surrounding ferrite matrix. In the bulk, nanosized and finely dispersed platelet-like precipitates grow preferentially along {100}_α-Fe. It is unclear whether these precipitates consist of binary iron nitride α´´-Fe₁₆N₂ or of a ternary Fe-W-N. Additionally to the finely dispersed particles, bigger nitrides at ferrite grain boundaries develop exhibiting platelet-type morphology and possessing a crystal structure which can be also described as a superstructure derived from hexagonal δ-WN. Upon prolonged nitriding assumed discontinuous precipitation of the initially precipitated finely dispersed nitrides starts from the ferrite-grain boundaries resulting in lamellas consisting of alternate ferrite and hexagonal nitride lamellas, whereas the nitride lamellas having a Pitsch-Schrader orientation relationship with the surrounding ferrite matrix. The nitrides precipitated upon nitriding in the bulk were found to be unstable during H₂ reduction at 470°C. Remarkably, upon such low temperature dissolution of the nitrides took place but only the nitrogen from the nitride particles could diffuse out of the nitride platelets and the specimen, leaving W-rich regions (W-clusters) at the location of the original precipitates.

Abstract: Doped ZnO:Al thin films were deposited on glass substrates by the solgel dip technique. Optical parameters such as the refractive index and the extinction coefficient tend to change with increasing annealing temperature.

Abstract: rradiation of ZnO:Al thin film by reactor neutrons with neutron/gamma ratio at 1.44x10⁴ (n.cm^-2.s^-1.mR^-1) leads to a decrease in resistivity in this material. The observed effects in electrical resistivity are attributed to irradiation-induced formation of defects in the ZnO:Al thin film structure.

Abstract: Titanium and its alloys are widely used as biomaterials due to their mechanical, chemical and biological properties. To enhance the biocompatibility of titanium alloys, various surface treatments have been proposed. In particular, the formation of titanium oxide nanotubes layers has been extensively examined. Among the various materials for implants, calcium phosphates and hydroxyapatite are widely used clinically. In this work, titanium nanotubes were fabricated on the surface of Ti-7.5Mo alloy by anodization. The samples were anodized for 20 V in an electrolyte containing glycerol in combination with ammonium fluoride (NH₄F, 0.25%), and the anodization time was 24 h. After being anodized, specimens were heat treated at 450 °C and 600°C for 1 h to crystallize the amorphous TiO₂ nanotubes and then treated with NaOH solution to make them bioactive, to induce growth of calcium phosphate in a simulated body fluid. Surface morphology and coating chemistry were obtained respectively using, field-emission scanning electron microscopy (FEG-SEM), AFM and X-ray diffraction (XRD). It was shown that the presence of titanium nanotubes induces the growth of a sodium titanate nanolayer. During the subsequent in-vitro immersion in a simulated body fluid, the sodium titanate nanolayer induced the nucleation and growth of nanodimensioned calcium phosphate. It was possible to observe the formation of TiO₂ nanotubes on the surface of Ti-7.5Mo. Calcium phosphate coating was greater in the samples with larger nanotube diameter. These findings represent a simple surface treatment for Ti-7.5Mo alloy that has high potential for biomedical applications.

Abstract: We model the flow of the contaminated water through the porous media sample. We model the inflow of water, flux of water in the sample, flux of the contaminant in the water in the sample, adsorption of the contaminant in the sample and the outflow of the contaminated water from the sample. During the process, there appears fully saturated zone, partially saturated zone and dry zone. We consider Darcys law for flux of the water in fully saturated zone and Richards equation for flux in the partially saturated zone. Flux of the contaminant is governed by Ficks law and the adsorption of contaminant is modeled using Freundlich isotherm. Problem is solved in 1D using numerical solution based on the MOL method. Since flow of the water is independent of the contaminant, we compute separately saturation in the whole time interval and then contamination of water and adsorption of contaminant in the sample.

Abstract: Numerical modelling of unsaturated-saturated flow under centrifugation with moving arms is studied. A numerically efficient approximation is presented for mathematical model based on Richard's nonlinear and degenerate equation expressed in terms of effective saturation using Van Genuchten-Mualem ansatz with soil parameters in unsaturated zone. The method is suitable for determination of soil parameters via the solution of inverse problem in an iterative way. Using centrifuge offers significant time savings and provides us with many data for the parameter estimation. The present implementation of our method requires only very cheap measurements of global characteristics.

Abstract: The problem concerns the structure and properties heterogeneity of cast products, on the example of the Al-Si (A356) alloy. The trends of usage of this knowledge by constructors of that kind of products are described in this paper. It is well known that soundness of cast products is a postulate formulated by designers and users of machines and devices, where castings are among important parts. It is often forgotten though, that perfect soundness (density) of the cast material in ready for use parts simply does not exist. The gas and shrinkage porosities, present in semi-finished casting products, obtained from a liquid state of an alloy is the result of phenomena occurring during multiphase metallic system crystallization. Still, general introduction of the tolerance of damage rule requires knowledge about casting technology, inspection of the state of discontinuity of casting structure. The use of coupled experimental researches (including NDT non-destructive testing and local mechanical properties of castings) and simulation tests (Procast, ANSYS) have shown how the properties gradient influences on the safety factor distribution in the casting subjected by chosen load.

Abstract: The present study focuses on fluid flow and particle transport in symmetric T-shaped structures formed by tubes with circular and square cross-section. The performances of optimized structures (i.e., structures designed based on constructal allometric laws for minimum flow resistance) and not optimized structures were studied. Flow resistance and particle penetration efficiency were studied both for laminar and turbulent flow regimes, and for micrometer and submicrometer particles. Optimized structures have been proven to perform better for fluid flow but they have a similar performance for particle transport.

Abstract: Ammonia production is a high energy and capital intensive industry as it requires high temperature (400500°C) and high pressure (150300 bar) for its daily operations. By introducing nanocatalyst with the new concept of micro-reactor with applied magnetic field induction, the catalytic activity can be induced and the output can be enhanced. Magneto-dynamics will be introduced in the ammonia production process in order to replace the concept of thermodynamics in the Haber Bosch process. The nanocatalysts (Y₃Fe₅O₁₂, Fe₂O₃, MnO, Mn_0.8Zn_0.2Fe₂O₄) have been reduced by using the temperature reduction method (TPR). The Y₃Fe₅O₁₂ (YIG) catalyst with magnetic induction produced242.56µmol/h.g-cat output of ammonia which is 2% much higher than ammonia synthesis without magnetic induction (237.52 µmol/g.h).The ammonia output based on the magnetic induction method at a temperature of 0°C is 242.56µmole/h.g-cat which is 0.90% higher than the synthesis at 25°C temperature (240.4 µmol/g.h). The ammonia output at 0.2Tesla is 249.04 µmole/h.g-cat which is higher 2.6% than the output at 0.1Tesla which is 242.56µmol/g.h. It is proven that the higher the applied magnetic field is, the more effective the catalytic activity will be as a better alignment of the electron spin of the catalyst occurs and enhances the adsorption and desorption process. Y₃Fe₅O₁₂ (YIG) shows the best catalytic reaction followed by Fe₂O₃ (hematite) and MnO (manganese oxide). By this new route, synthesis of ammonia at low temperature is realized and offers ammonia producers an economic advantage compared to the classical routes.

Abstract: The crystallization of soluble salts is a major mechanism of degradation of some building materials, including stone. This mechanism of deterioration is based on the pressure exerted by the formation of salt structures in porous materials, with increased volume and is dependent on the type of salts involved and the size and arrangement of pores. When the pressure exceeds the internal strength of the material, and particularly when the salt formations undergo cycles of crystallization and dissolution in response to fluctuating levels of humidity, the deterioration of materials typically becomes apparent. It is therefore essential to understand the phenomenon of crystallization and dissolution of salts, i.e., to know the conditions of crystallization of each salt, depending on relative humidity and air temperature. For this purpose we developed an experimental work, using four samples of stone (one limestone and three granites), which consists, initially, to study the variation of the water absorption coefficient with and without soluble salts.