Ljiljana Zivkovic

Fractal Geometry and Properties of Doped BaTiO3 Ceramics

Taking into account that the complex grain structure is difficult to describe by using traditional analytical methods, in this study, in order to establish ceramic grain shapes of sintered BaTiO3, new approach on correlation between microstructure and properties of doped BaTiO3 ceramics based on fractal geometry has been developed. BaTiO3 ceramics doped with various dopants (MnCO3, Er2O3, Yb2O3) were prepared using conventional solid state procedure, and were sintered at 1350oC for four hours. The microstructure of sintered specimens was investigated by SEM-5300. Using method of fractal modeling a reconstruction of microstructure configurations, like grains shapes, or intergranular contacts has been successfully done. Furthermore, the area of grains surface was calculated using fractal correction that expresses the irregularity of grains surface through fractal dimension. The presented results, indicate that fractal method for ceramics structure analysis provides a new approach for describing, predicting and modeling the grain shape and relations between the BaTiO3-ceramic structure and dielectrical properties.

Grain growth during sintering of BaTiO3 with LiF

Abstract The sintering behavior of BaTiO3 with LiF showed that it was possible to sinter barium titanate at temperatures below 1000°C. Different combinations of the sintering powders were prepared by adding 1 to 5 w% LiF and sintering at the temperature of 950°C for 20 hours. The grain growth of LiF fluxed BaTiO3 was studied, and electron microscopy was used to investigate and characterize the microstructure of the samples. The dielectric constant and dielectric losses were determined. It was shown that the composition of the liquid phase formed during this process had a prominent influence on the grain growth and on the formation of BaTiO3 with better dielectric properties.

Testing of Level of Vibration and Parameters of Bearings in Industrial Fan

Climate chambers are a complex system of electromechanical components used for conditioning of air for providing comfort and projected parameters of temperature, humidity, velocity and air cleanliness in the area. In this paper is presented examination of the fan unit company Flaktwoods GJLB-5-071, 17.95 kW, n=1450 rpm, with a multi-functional device Vibrotest 60, the Danish manufacturer Bruel & Kjaer, for diagnostic of parameters of vibration and condition of bearing. The measured parameters are related to: - levels of vibrations (including measurement points on the motor and on the fan) in the directions of coordinate axes, according to ISO 10816-1. - parameters of condition of bearing through the index of bearing condition BCU (Bearing Conditions Unit) and BCS (Bearing Spectrum Conditions) - analysis of the characteristic frequency of vibration in the spectrum, presented by FFT (Fast Fourier Transformation).

Structure and Properties of Barium Bismuth Titanate Prepared by Mechanochemical Synthesis

Bi 4 Ti 4 O 15 [BBT], a member of Aurivillius bismuth-based layer-structure perovskites, was prepared from stoichiometric amounts of BaTiO 3 [BT] and Bi 4 Ti 3 O 12 [BIT] obtained via mechanochemical synthesis. Mechanochemical synthesis was performed in air atmosphere in a planetary ball mill. BBT ceramics were sintered at 1100°C for 4 h without pre-calcination step within heating rate 10°C/min. The formation of phase and crystal structure of BT, BIT and BBT were approved using X-ray analysis. The morphology of obtained powders and microstructure were exhamined using scanning electron microscopy. The electrical properties of sintered samples were carried out.

Application of the Prediction Model "SCHALL 03" for Railway Noise Calculation in Serbia

Application of the prediction models for railway noise indicators calculation, which was already developed by other countries, represents a major challenge in Serbia. Prediction model Schall 03 was developed in line with technical and technological characteristics of the rolling stock and infrastructure of German Railways. Prior to its application at the national level, due to different technical-technological characteristics of railway stock and railway infrastructure it is necessary to perform its validation and, depending on the needs, the calibration in accordance with local conditions. This will assure accuracy and precision of the calculations of noise indicators, as well as confidence in the results obtained by prediction model Schall 03. This paper presents the analysis of the possibilities to apply German prediction model Schall 03 on the Serbian railway network, more precisely railway section from Belgrade to Romanian border. Calculated values of noise indicators were compared with the results of measurements of noise indicators within measuring interval, which correspond to the referent time intervals for different day periods.

Demographic changes and processes in Negotin municipality settlement network

The analysis of demographic factors of the studied area points to the different demographic development models. Uneven economic and regional development of industry caused the regional demographic polarization of the population of Negotin municipality. In relatively short period, the transition has caused spontaneous urbanization and deagrarization. All that influenced the faster tempo of social and demographic processes, especially the migrations towards Negotin, which led to the developmental unevenness and regional polarization to the zone of population concentration (town and the suburban areas). Contrary to the town center, there are depopulation rural areas, with outstanding economic undevelopment.