HIGH-ACCURACY QUASISTATIC NUMERICAL MODEL FOR BODIES OF REVOLUTION TAILORED FOR RF MEASUREMENTS OF DIELECTRIC PARAMETERS

We have developed rotationally symmetrical coaxial chambers for measurements of dielectric parameters of disk-shaped samples, in the frequency range from 1 MHz to several hundred MHz. The reflection coefficient of the chamber is measured and the dielectric parameters are hence extracted utilizing a high-accuracy quasistatic numerical model of the chamber and the sample. We present this model, which is based on the method-of-moments solution of a set of integral equations for composite metallic and dielectric bodies. The equations are tailored to bodies of revolution. The model is efficient and accurate so that the major contribution of the measurement uncertainty comes from the measurement hardware

Mechanical Activation and Cation Site Disorder in Mgal2o4

The synthesis and crystallographic site occupancy were investigated for MgAl2O4 with and without mechanical activation of the precursor powders. Heating to 1200 °C or higher resulted in the formation of a single spinel phase regardless of whether the powders were mechanically activated or not. Neutron diffraction analysis was used to determine cation site occupancy and revealed that mechanical activation resulted in a lower degree of cation site inversion compared to the nonactivated materials, which indicated that the powders were closer to thermodynamic equilibrium. This is the first study to characterize the effects of mechanical activation on crystallographic site occupancy in magnesium aluminate spinel using neutron diffraction

Characterization of MgAl₂O₄ Sintered Ceramics

Single phase MgAl2O4 was made from a one-to-one molar ratio of MgO and Al2O3 powders mixed using ball-milling. Mixtures of MgO and Al2O3 were subsequently treated in planetary ball mill for 30, 60, 90 and 120 minutes in air. The aim of this study was to examine phase composition, microstructure, and densification behavior of sintered specimens. After sintering in dilatometer at 1500 °C, the powder was converted to single phase MgAl2O4. The results show that mechanical activation improved the densification behavior of MgAl2O4 sintered specimens, and it reduced the onset temperature for sintering by approx. 100°C. Based on dilatometer data, powders were subsequently densified at 1450°C by hot pressing. Almost all specimens exhibited full density, while sample activated for 30 minutes showed the fastest densification rate

III Advanced Ceramics and Applications Conference

This is the Proceedings of III Advanced Ceramics and Applications conference, held in Belgrade, Serbia in 2014. It contains 25 papers on various subjects regarding preparation, characterization and application of advanced ceramic materials

A quality of life assessment and the correlation between generic and disease-specific questionnaires scores in outpatients with chronic liver disease-pilot study

Introduction. Chronic liver diseases (CLD) are an important cause of morbidity and mortality in general population. The aim of this study was to analyze potential differences between patients with CLD and healthy control group, and to estimate the severity of CLD by using simple questionnaires: general health questionnaire (GHQ-12) and chronic liver disease questionnaire (CLDQ). Methods. A cross-sectional pilot study was performed in Zemun Clinical Hospital during years 2014 and 2015. Sixty participants were divided into 4 groups (15 per group): chronic alcoholic hepatitis, other chronic hepatitis, liver cirrhosis, and healthy control group. Entire study population chose one of four offered answers of structured questionnaires GHQ-12 and CLDQ, based on which mean model of end-stage liver disease (MELD) and Child-Turcotte-Pugh (CTP) scores were calculated. Results. Mean GHQ12 and CLDQ scores were 10.5 and 5.21 ± 1.11 respectively. Regarding certain CLDQ domain scores, a significant difference between alcoholic and non-alcoholic hepatitis groups in the worry domain was observed. Mean MELD score was 7.42 ± 2.89 and did not differ between chronic hepatitis groups, while mean CTP score was 5.73 ± 0.88. A statistically significant correlation was observed between GHQ12 and CLDQ scores (ρ = -0.404, p < 0.01), but not between subjective and objective scores. Conclusions. Mean GHQ12 and CLDQ scores pointed out to general psychological no-distress condition of the studied participants, as well as scarcely expressed CLD-specific complaints. Mean MELD and CTP scores indicated stable chronic liver diseases, with low three-month mortality rates in the cases of chronic hepatitis, as well as determination to Child A group in the case of liver cirrhosis

Characterization of FeCoV alloy processed by PIM/MIM route

© 2016 Authors. In this study the characterization of FeCo-2V alloys toroidal samples produced by PIM/MIM technology was presented. The feedstock for metal injection molding (MIM) was prepared by mixing starting FeCoV powder with a low viscosity binder. Green samples were subjected to solvent debinding and subsequent thermal debinding followed by sintering. Sintering was performed during 3.5 hours from 1370 °C to 1460 °C in hydrogen atmosphere in order to attain the appropriate mechanical and magnetic properties. Microstructure, hardness HV10 and magnetic hysteresis B(H) were investigated as a function of sintering temperature. Optimum combination of functional properties was observed after sintering at temperature of 1370 °C. In addition, magnetic properties were analyzed as frequency dependent and successfully simulated in operating frequency range from 5 Hz to 60 Hz

Electrical properties of magnesium titanate ceramics post-sintered by hot isostatic pressing

Post-sintering of magnesium titanate ceramics by hot isostatic pressing (HIP) in an oxygen-free atmosphere significantly alters various electrical properties of the product. In particular, the sintered material becomes a semiconductor. The aims of this paper are: to extend our investigations of the electrical properties of this material by expanding the frequency range of measurements, to design interpolation formulas for the frequency dependence of the complex relative permittivity, and to propose HIP-sintered magnesium titanate as a material for thermistors that have a negative-temperature-coefficient resistance (NTCR), as well as for varistors

Three-Axis' Heat Loss Anemometer Comprising Thick-Film Segmented Thermistors

© 2001-2012 IEEE. NTC thick-film segmented thermistors were used as anemometer sensing devices. They were screen printed of thick-film thermistor paste based on modified NiMn2O4 fine powder, organic vehicle, and glass frit. Their electrical properties, such as resistance vs. temperature R(T) and thermistor exponential factor B were obtained using measurements in the climatic test chamber. A uniaxial anemometer was formed using a thick-film segmented thermistor, which was placed in the hole drilled in rectangular piece of thermally insulating material. The uniaxial anemometer was used for the optimization of operating point of segmented thermistors as self-heating/wind sensing devices. The dc supply voltage was correlated with the air temperature sub-ranges (RCV). The power save mode such as 30s self-heating/5 min pause was used to measure the thermistor response on stable wind blow. The three-axis' anemometer was formed using five sensor devices placed in five holes drilled in the cubical piece of thermally insulating material: three thermistor sensors measure wind speed on the x, y, z - axes, the fourth sensor Pt 1000 measures the air temperature T, while the fifth sensor (capacitive type) measures humidity H. The obtained sensitivity and inaccuracy were compared with respective ones of other anemometers

Influence of MgO addition on the synthesis and electrical properties of sintered zinc-titanate ceramics

Starting mixtures of ZnO, TiO(2) and MgO (0, 1.25 and 2.5 wt.% MgO) powders were mechanically activated for 15 min in a planetary ball mill. The powders obtained were sintered non-isothermally to temperatures between 800 and 1100 degrees C and then held at those temperatures for 120 min. Analysis of the influence of MgO addition on the synthesis of zinc-titanate ceramics showed that its addition increased slightly the temperature at which the reaction process started, accelerated the reaction and resulted in higher sample densities. These results were correlated with the results of structural characterization using X-ray powder diffraction method and SEM analysis. Also, the results of electric resistivity, capacitance and loss tangent of the sintered samples were obtained. (C) 2008 Elsevier B.V. All rights reserved