Defect and Diffusion Forum Vols. 312-315

Abstract: The paper presents test results and characterizes the structural stability of powders, which form a mixture of aluminium oxide (Al2O3) and gadolinium, based on rare earth zirconates. This mixture is provided to create thermal barrier coatings (TBCs) by spraying. The purpose of the tests was to determine the influence of temperature on reactions, occurring between those powders within a temperature range from 25°C to 1500°C, while such conditions were to simulate the conditions, which occur during creation of TBCs and they give an answer to the question concerning mutual reactivity of the powders. The requirements for new materials, provided to spray the TBCs, indicate the necessity to prepare the materials, which do not show tendency towards reactions with the Al2O3, formed during oxidation of Ni (Co) CrAlY, while this reaction is of type bond coat. The tests included differential scanning calorimetric (DSC) analysis and differential thermal analysis (DTA) of powder mixtures. Diffraction analysis was also performed before and after the tests have been finished. The DSC analysis results, obtained at a range of high temperature, did not show any thermal effects, which indicate a low level of mutual reactivity of the powders. However, the DTA analysis suggests presence of such effects at temperature close to 1300°C, and it indicates the necessity to verify exactly the obtained results. Results of the XRD measurement showed that after annealing process already at 1100°C the perovskite oxide of GdAlO3 was present.

Abstract: A TiN nanocoating was deposited on carbon fibres before their consolidation with AZ91E magnesium alloy, provided as a matrix of the composite. The main interest was the interface microstructure. Structural investigations were performed with a FE-SEM Hitachi 3200S scanning electron microscope and a Tecnai G2 FEG high resolution electron microscope equipped with energy dispersive X-ray spectrometer (EDS) and high angle annular dark field (HAADF) detectors. The observations of the fibre-matrix interface revealed the presence of a multilayered zone around the fibres. It consisted of a regular oxide layer with a thickness of approx. 100 nm around the fibre, followed by a titanium-rich layer and a region of longitudinal sharp shaped crystals directed toward the magnesium alloy matrix. This type of interface microstructure suggests that deposition of TiN as a technological nanolayer ensures the proper wettability of fibres by the metal matrix, but does not prevent diffusion processes. It was revealed that both, i.e. diffusion of elements contained in the matrix through the TiN nanolayer and diffusion of oxygen and carbon toward the surface took place.

Abstract: The study describes aluminium-silicon protective coatings produced by the slurry cementation process on a substrate of creep-resistant Ni-Cr cast steel. The mechanism of the coating growth on a substrate was examined and the effect of annealing time and temperature on total thickness of the coatings and on the thickness of the individual zones was analyzed. The coating structure is composed of two zones. In the external zone, elements like Al, Ni and Fe are concentrated, forming intermetallic phases of an Al(Ni,Fe) type, while the internal zone contains an (Fe,Cr,Si) solution. The internal zone formed in a sub-surface layer of the substrate has hardness values intermediate between the hardness of the substrate and that of the external layer.

Abstract: Gas turbines are increasingly deployed throughout the world to provide electrical and mechanical power in consumer and industrial sectors. A health management system can incorporate prognostic algorithms to effectively interpret and determine the healthy working span of a gas turbine. The research project’s objective is to develop real-time monitoring and prediction algorithms for simple cycle natural gas turbines to forecast short and long term system behavior.

Abstract: One dimensional (1D) nanostructure materials such as nanowires, nanofibers, and nanorods with porous structures have potential for use in various applications. Electrospinning is one of the versatile techniques with the ability of producing cost-effective, large production, highly porous nanofibers and membrane with large surface to volume ratios. Poly ether sulfone (PES) is a kind of special engineering plastic with good processing characteristics. In this paper, synthesis of PES membrane was investigated by two main methods, i.e. phase inversion and electrospiing. For electrospining, the main effective parameters such as concentration of polymer and solvent, for finding the optimized condition of electrospun PES membrane was studied. The produced membranes were characterized by SEM for morphology and BET observation of surface area, permeability, flux, and mechanical propertise for different applications.

Abstract: An important recent discovery in the membrane science is the polymeric nanofiber membrane. Membranes have many applications in protein purification, wastewater treatment and fuel cells. One of the versatile technique with the ability of producing cost-effective, highly porous non-woven membranes with large surface area is electrospining. In this study the effect of TiO2 nanoparticles in membrane performance has been investigated. A PES/TiO2 nanofibers membrane has higher flux and permeability than a pristine PES membrane. Also the measurments show that the surface area of the membrane will increase by addition of TiO2 nanoparticles. Moreover, the contact angle was investigated.

Abstract: The charge transport is one of the most important factors for the efficiency in nanostructured devices. The detailed nature of transport processes in these systems is still not completely resolved. Starting from the Drude model, we have proposed an analytical method for describing classically the most important quantities concerning transport phenomena, i.e. the velocity correlation functions, the mean square deviation of position and the diffusion coefficient. To fully account for quantum effects arising in systems of reduced dimensions, in this work we present the quantum mechanical version of this model, comprehending the oscillator strength weights, and apply the model to single-walled carbon nanotube films, extracting the oscillator weights from reflectivity data reported in the literature. We are able to give a complete and precise description of time correlations avoiding time-consuming numerical or simulation procedures. This method demonstrates high generality and offers perspectives even in the study of ions, like mass transfer, and solutions, so as in nano bio systems. This quantum mechanical extension allows significant applications for the nanodiffusion in nanostructured, porous and cellular materials, as for biological, medical and nanopiezotronic devices.

Abstract: The Diffusion coefficient of sulfur in a ternary slag with composition of 51.5% CaO- 9.6% SiO2- 38.9% Al2O3 was measured at 1723 K by chemical diffusion from the variation of concentration of sulfur in silver metal. A MATLAB program was developed to find the concentration variation of sulfur in silver metal using various critical parameters like the diffusion coefficient of sulfur in slag available in literature, sulfur partition ratio, sulfide capacity of the slag and the its density. The PS2 and PO2 pressures were calculated from the Gibbs energy of the equilibrium reaction between CaO in the slag and solid CaS and confirming the same by using ThermoCalc. The density of the slag at 1723 K was obtained from earlier experiments. Initially the order of magnitude for the diffusion coefficient was taken from the works of Saito and Kawai but later was modified so that the concentration changes of Sulfur obtained from the program agreed with the experimental results. The diffusion coefficient of sulfur in 51.5% CaO- 9.6% SiO2- 38.9% Al2O3 slag at 1723 K was estimated as 4.14x10-6 cm2/sec.

Abstract: We address an experimental investigation of evaporation waves. They are obtained when a liquid contained in a vertical glass tube is suddenly depressurized from a high initial pressure down to the atmospheric one. After the release of pressure, the state of the liquid, which is at ambient pressure and the initial temperature, is well known to be metastable when the corresponding stable state is vapour. For moderately large evaporation rates (moderately large initial to ambient pressure ratios), the vapour-liquid interface ultimately evolves into an evaporation wave in which a highly corrugated front propagates downwards into the liquid with a well defined mean velocity. This mean velocity turns out to be a function of the ratio between the initial and the ambient pressures. In addition, attention to some new phenomena not previously reported is brought.

Abstract: The primary aim of this study is to simulate numerically the heat and mass transfer characteristics in the annular adsorber that is the most important component of the solar cooling machine, and to evaluate the solar and thermal coefficients of performance as an optimisation criterion of the system, for different adsorbent/adsorbate pairs. The porous medium constituted of the adsorbent/adsorbate is contained in the annular space and it is heated by solar energy. A general model equation is used for modeling the transient heat and mass transfer. The adsorption phenomenon is described by using different models of solid-adsorbate equilibrium. Effects of the key parameters on the adsorbed quantity, the generating temperature, the performance coefficients and thus on the system performances are investigated.