Defect and Diffusion Forum Vols. 334-335

Abstract: Moisture is one of the most deteriorating factors of buildings. The deteriorating effect of moisture occurs mainly during the drying phase, and appropriate parameters of the drying kinetics are required for the building materials. Environmental factors, such as air temperature and air humidity affect drying. An experimental campaign was performed to investigate the drying performance of External Thermal Insulation Systems (ETICS). Drying kinetics was examined at three air temperatures, four solar orientations and two different air humidities. A first-order kinetics model was obtained, in which the drying time constant was a function of the drying conditions, and the equilibrium material moisture content was described by several different models, such as linear type, power type, exponential type, Arrhenius type and Logarithmic type. The parameters of the proposed model were found to be affected strongly by the material and the drying air conditions.

Abstract: ZnO:Al/p-Si heterojunctions were fabricated by sol-gel dip coating technique onto p-type Si wafer substrates. Capacitance-Voltage (C-V) characteristics of ZnO:Al/p-Si heterojunctions were determined after the ZnO:Al thin film coated Si wafers were annealed at 700 and 800°C, respectively. C-V results indicate an abrupt interface.

Abstract: Structure phase transitions in nonstoichiometry oxides with perovskite structure were considered. The microscopic description of cooperative Jahn-Teller transition was suggested and the effects caused by mechanical activation of oxide systems (their conversion into nanostructural state, acceleration of oxidation-renewal reactions and immiscibility) were analized. The correspondence of the theoretical results to the data of experiment on phase states of mechanically activated oxide NdMnO₃ is shown.

Abstract: A compact finite differences method is used to calculate two-dimensional viscous flows through complex geometries. The immersed boundaries are set through body forces that allow for the imposition of boundary conditions that coincide with the computational grid. Two different flow configurations are simulated. First, the flow through a row of cylinders with square cross-sections is calculated and used as a validation study. The computed average drag coefficient and Strouhal number are compared to data available in the literature, showing a good agreement between the results. The second flow configuration analyzed is the flow through a porous matrix composed of equal size staggered square cylinders. Flow visualization results are shown and various flow regimes identified. Different inlet boundary conditions are compared. The drag coefficient is larger when a uniform inlet velocity is prescribed and the variability between cylinders is lower.

Abstract: Sewage sludge from wastewater treatment is being more and more produced in many countries. For sewage sludge disposal, drying operation is usually required and greatly energy-consuming. Paddle dryers, one kind of indirect dryers, are widely used in removing moisture of sewage sludge recently, but the design, to some extent, still depends on empirical and limited data. In this paper, we presented preliminary experimental results of sewage sludge drying based on a 3 m² paddle dryer prototype. The effects of thermal oil inlet temperature on outlet moisture content and mass flowrate of initial sludge are recorded and analyzed. A simple monotonic relation between mass flowrate of initial sludge and thermal oil inlet temperature does not exist. Besides, we performed the drying experiment of adding low-value biomass (rice husk) into wet sewage sludge. The results show that the drying performance is improved significantly.

Abstract: Electrochemical behaviour of mechanoactivated β-MnO₂ powders has been studied by the method of cyclic voltammetry with a carbon-paste electroactive electrode. Mechanical activation was carried out by dry grinding in an AGO-2 planetary ball mill. It was found that the grinding process results in a mechanochemical effect in the surface layer of the oxide particles: Mn (IV) cations are reduced to Mn (III). Voltammetry test detects that mechanical activation of β-MnO₂ leads to a new state, which is characteristic for the γ-modification of manganese dioxide (β-MnO₂ γ-MnO₂).

Abstract: The technique of defining the minimum coke consumption in blast furnace smelting allows for the calculation of the reserve of coke economy on the basis of thermodynamic principles. In this reserve the constitutive role belongs to the reducibility of the iron ore materials (the agglomerate and pellets). In the present paper, the questions of the reduction kinetics of the iron ore materials and diffusion processes at reduction of iron from its oxides are considered. It is shown that the reducibility of the iron ore materials is the basic reserve of economy the scarce and expensive coke in the blast furnace smelting.

Abstract: Zirconium carbide (ZrC) has extended application in many ceramic and metal matrix composites especially used for ultra high temperature conditions. The synthesis of zirconium carbide powder is costly and difficult because of its high refractoriness and chemically inert properties. In this research, the synthesis of zirconium carbide nanopowder at low temperature via carbothermal reduction route was investigated according to thermodynamic data. The starting materials were zirconium acetate and sucrose as zirconium and carbon sources, respectively. After preparation of different carbon/zirconium ratio containing precursors, the dried precursors were heat treated at 1400°C and vacuum atmosphere. Also the ZrC formation was followed by thermal analysis of the produced precursors. The phase evolutions and microstructural studies were carried out using X-ray diffraction and scanning electron microscopy. The results showed that it is possible to synthesis zirconium carbide nanopowder with round shape and crystallite sizes smaller than 20 nm at low temperatures. Also according to thermodynamic calculations, it was concluded that by applying vacuum condition, the zirconium carbide formation can occur at less than 1000°C which is very effective on the size reducing of produced ZrC nanopowders.

Abstract: Because of their size and versatile chemistry, nanomaterials represent today powerful tools for (bio) sensing applications. Various types of nanomaterials have proven to be practical, not only for the determination of clinically relevant parameters, but also for diagnostics, drug delivery and treatment of diseases (e.g. cancer). In this short review, types of nanomaterials used in medical applications are briefly described along with some of their applications where the nanomaterials optical properties can be exploited. The question of the toxicity of nanomaterials and the issue of future trends are also raised.