N. Nikolic

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.

Thermal, electron transport and far infrared properties of PbTe single crystals doped with Br

Understanding the properties of PbTe remains in focus as enhancement of thermoelectric efficiency of this material is studied extensively. In this work single crystals of PbTe, doped with less than 2 at % Br, were synthesized using the Bridgmann technique and their thermal, electron transport and far infrared properties were studied. Thermal diffusivity was determined using the photoacoustic method with a transmission detection configuration. Electron transport was determined by Seebeck coefficient measurements. IR reflectivity measurements showed that reflectivity in the region of plasma resonance was low. Measured reflectivity diagrams were numerically analyzed-enabling calculation of the carrier concentration and mobility-and compared with the values obtained by Hall measurements.

Evaluation of formulation and process parameters effects on drug release and mechanical properties of tramadol hydrocloride sustained release matrix tablets

This study investigates using of high molecular weight polyethylene oxide (PEO WSR Coagulant) for the preparation of sustained release matrix tablets containing high dose, highly water soluble drug, tramadol HCl. Proportion of PEO polymer, type of insoluble filler, proportion of tramadol HCl, amount of drug in tablet, tablet diameter and compression pressure were recognized as critical formulation and process parameters and their influence on drug release and tablet mechanical properties was evaluated. Percentages of tramadol HCl released after 30 and 240 minutes were selected for evaluation of drug release, while tensile strength was used as indicator of tablet mechanical properties. Only proportion of tramadol HCl exhibits statistically significant effect on percentages of tramadol HCl released after 30 and 240 minutes, with higher, wherein increasing of the tramadol HCl proportion increased its release rate among the evaluated variables in selected ranges. All of the investigated factors exhibit statistically significant effect on tablets tensile strength, with the largest influence of filler type. Tablets prepared with highly compressible filler (microcrystalline celullose) exhibit higher tensile strength and therefore better mechanical properties to those prepared with partially pregelatinised starch (Strach 1500). [Projekat Ministarstva nauke Republike Srbije, br. TR 34007]