M.V. Nikolić

Application of the Master Sintering Curve Theory to Non-Isothermal Sintering of BaTiO3 Ceramics

In this paper a practical approach to the analysis of sintering of BaTiO3 using the Master Sintering Curve concept has been presented. Non-isothermal sintering of high-purity non-doped BaTiO3 ceramics was monitored using a sensitive dilatometer at three different heating rates (10, 20 and 30 oC/min) up to 1380oC. Densification of BaTiO3 during sintering was analyzed using the Master Curve Sintering Theory. A MSC was defined characterizing the sintering behavior of barium-titanate regardless of the heating rate. Construction of the MSC enabled estimation of the process activation energy. Using defined MSC, densification behavior of BaTiO3 ceramics during sintering can be predicted for arbitrary temperature-time excursions and these predictions can be used in controlling and planning the sintering process of this material.

The dependence of the work function of rare earth metals on their electron structure

Abstract The work function primarily depends on the electron structure of the analysed material. Having in mind the importance of rare earth metals in advanced electronics, in this paper the dependence of the work function of rare earth metals on their electron structure has been analysed. It is shown that dependencies of work functions on the number of electrons of the most stable f 7 and f 14 configurations can be established for the series CeSm and GdTm.

Micro‐flow sensor for water using NTC thick film segmented thermistors

Purpose – The purpose of this paper is to apply negative thermal coefficient (NTC) thick film segmented thermistors (TFSTs) in a micro‐flow sensor for water.Design/methodology/approach – A TFST is printed using NTC paste based on nickel manganite. The resistance of this thermistor is measured in a climatic chamber and the resulting curves are calibrated. A micro‐flow sensor is designed using a self‐heated segmented thermistor. The sensing principle is based on heat loss depending on the water flow intensity through the capillary. Water flow calibration is performed. The sensor sensitivity, inertia, and stability are analyzed.Findings – The micro‐flow sensor exhibits good stability, suitable sensitivity, and inertia for integral measurements of water flow.Practical implications – Advantages of a micro‐flow sensor using a TFST include low energy consumption, simple measuring procedure, and passive electronics.Originality/value – This paper describes initial work on a micro‐flow sensor for water using TFSTs.

Investigation of Zinc-Stannate Synthesis Using Photoacoustic Spectroscopy

Mixtures of ZnO and SnO2 powders, with molar ratio of 2:1, were mechanically activated for 40, 80 and 160 minutes in a planetary ball mill. The resulting powders were compacted into pellets and non-isothermally sintered up to 1200˚C with a heating rate of 5˚C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusivity. Based on the results obtained a correlation between thermal diffusivity and experimental conditions as well the samples microstructure characteristics was discussed.

A Thermal Sensor for Water Using Self-Heated NTC Thick-Film Segmented Thermistors

A simple thermal (heat loss) sensor system was designed in a small plastic tube housing using a negative thermal coefficient (NTC) thick-film thermistor as a self-heating sensor. The voltage power supply [range constant voltage (RCV)-range constant voltage] uses the measured input water temperature to select the applied voltage in steps (up and down) in order to enable operation of the sensor at optimal sensitivity for different water temperatures. The input water temperature was measured using a “cold” NTC thick-film segmented thermistor. The measured calibration curves were modeled. Additional calculated curves were interpolated between the experimental curves in fine steps to cover each temperature of input water and can be used for determining the water volume flow rate or water velocity. The realized prototype flow meter inertia, stability, repeatability, and tolerance were measured and analyzed. The proposed intelligent RCV thermal flow meter system will include a smart power supply with range-constant-voltages (auto-range), a simple acquisition card and custom designed flow meter software.

Combined FTIR and SEM-EDS study of Bi2O3 doped ZnO-SnO2 ceramics

The effects of Bi2O3 addition on the phase composition, microstructure and optical properties of ZnO–SnO2 ceramics were investigated. Starting powders of ZnO and SnO2 were mixed in the molar ratio 2:1. After adding Bi2O3 (1.0 mol.%) this mixture was mechanically activated for 10 min in a planetary ball mill, uniaxially pressed and sintered at 1300°C for 2 h. Far‐infrared reflection spectra were measured (100–1000 cm–1). To investigate the occurred differences in FTIR spectra, the Bi2O3‐doped sample was examined more carefully with a Perkin–Elmer FTIR spectrometer (Perkin Elmer, Waltham, MA, USA) connected with a Perkin–Elmer FTIR microscope and itemized points of interest were also studied with SEM‐EDS.

Analysis of electronic properties of pseudobrookite thick films with possible application for NO gas sensing

Two pseudobrookite (PSB) containing pastes were composed of a mixture of starting nanopowders of hematite (a-Fe2O3) and anatase (TiO2) in the molar ratios 1:1 (referred to as PSB-1) and 1:1.5 (referred to as PSB-1.5), respectively, organic vehicle and glass frit. The pastes were screen printed on alumina (Al2O3) substrates and sintered in a hybrid conveyor furnace at 850 °C/10 min in air. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis showed that the resulting thick film samples were composed of pseudobrookite (Fe2TiO5) and also excess rutile (TiO2) in the case of PSB-1.5 samples with a small grained and relatively homogenous microstructure. An electric resistivity with negative temperature coefficient (NTC) was observed. An interdigitated electrode geometry was designed and different electrode spacing (0.2 and 0.25 mm) was analyzed. The electrode structure was printed of PdAg paste. The resistivity of pseudobrookite was measured and analyzed in view of possible applications as a sensor of environmental gases with sufficiently high sensitivity at operating temperatures lower than conventional gas sensor systems.

Optimization and Application of NTC Thick Film Segmented Thermistors

NTC thermistor paste for printing thermal sensors on alumina was formed of very fine Ni0.5Cu0.2Zn1.0Mn1.3O4 thermistor powder obtained by a combined mechanical activation/thermal treatment process, organic vehicle and glass frit. Sheet resistivity was measured using an R-test matrix and it was much lower than the value determined for pure nickel manganite thermistors. The thermistor exponential coefficient was calculated from the R[ diagram measured in the temperature range-30 to +120°C in a climatic chamber. Thick film segmented thermistors with reduced dimensions (optimized construction) were printed sequentially layer by layer, dried and fired at 850°C/10 min in air. Electrodes were printed of PdAg conductive and solderable paste. The samples obtained were characterized by electrical and thermal measurements. The obtained NTC segmented thermistors with reduced dimensions were applied in a thermal sensor for water flow in the water mains. It contained a cold thermistor for measuring input water temperature and a self-heating thermistor for measuring the dependence of water current on water flow rate at a set input voltage power. Initial measurements show that the thermal sensor system requires a low input voltage power making it much easier and safer for operation.

Analysis of isothermal sintering of zinc-titanate doped with MgO

The aim of this work was analysis of isothermal sintering of zinc titanate ceramics doped with MgO obtained by mechanical activation. Mixtures of ZnO, TiO2 and MgO (0, 1.25 and 2.5%) were mechanically activated 15 minutes in a planetary ball mill. The powders obtained were pressed under different pressures and the results were fitted with a phenomenological compacting equation. Isothermal sintering was performed in air for 120 minutes at four different temperatures. Structural characterization of ZnO-TiO2-MgO system after milling was performed at room temperature using XRPD measurements. DTA measurements showed different activation energies for pure and doped ZnO-TiO2 systems. Thus addition of MgO stabilizes the crystal structure of zinc titanate.

Photoacoustic and Optical Properties of Zinc-Stannate Thin Films

Thin films of single-phase zinc-stannate (Zn2SnO4) were grown by rf magnetron sputtering onto glass substrates. Transmission in the visible range was measured allowing determination of the energy gap and thickness of analyzed thin film samples using interference fringes. The photoacoustic phase and amplitude spectra of all samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled calculation of thermal diffusivity, the coefficient of minority carrier diffusion, their mobility and lifetime.