Radioluminescence and photoluminescence of hafnia-based Eu-doped phosphors

Crystal structures of hafnia are discussed and it is shown that addition of about 7 at.% of Lu to the HfO₂ host lattice enforces the mixed composition to crystallize in cubic structure even at room temperature. Without Lu HfO₂ crystallizes in monoclinic structure. Luminescence and luminescence excitation spectra of Hf_0.93Lu_0.07O_1.965 are presented and discussed for powders prepared at different temperatures (600–1000 °C) and with different content of Eu. It is shown that decay of the 595.4 nm luminescence is longer (2.5 ms) than the 610 nm (1.6 ms). Radioluminescence efficiency of the cubic Hf_0.93Lu_0.07O_1.965 is low and does not exceed 10% of the commercial Gd₂O₂S:Eu.     

Electromotive force measurements in liquid Ag-In-Pd lead-free alloys

Emf technique was employed to determine indium activities in the liquid Ag-In-Pd alloys using galvanic cells with yttria-stabilised-zirconia as solid electrolyte according to the scheme： kanthal/rhenium, Ag-In-Pd, In2O3 ｜ YSZ ｜ Ni, NiO, Pt. Composition and temperature measurement ranges were limited, because of very steep liquidus surface; 35 compositions for Xpd up to 0.3 were investigated and at temperatures from near-liquidus up to 1700 K. High temperature experiments required special moly furnace to be constructed with unique automatic gas supply system for fumace winding protective atmosphere. Emf readings were taken and recorded by automatic data acquisition system. Linear dependence of emf on temperature was observed for all compositions investigated, and results were approximated by straight line equa- tions. Then In activities were calculated using well-known relations and taking into account correction for thermoelectric power between kanthal and platinum. Results are to be used along with other existing data to perform assessment of the ternary system under accord.     

Grinding of coal in the presence of vapours of organic compounds

The effect exerted by the sorption of vapour of several chemical compounds on the crushing of bituminous coal was investigated. Air-dry samples of a low-rank coal (82.7 wt%C) a coking coal (87.0 wt%C) and a high-rank coal (91.7 wt%C) were saturated with methanol, ammonia and benzene vapour for 100 h, crushed in a ball-mill, and subjected to sieve analysis. Sorption of methanol causes a marked increase of the crushability of all coals tested. Coal crushability increasing with increase of rank. The results have been interpreted according to the polymeric model of coal structure.     

Einfluß des Erweichungsprozesses auf die Geschwindigkeit der Reduktion von Sinter mit Wasserstoff

Im vorliegenden Beitrag wurde der Einfluß des Erweichungsprozesses auf die Reduktionsgeschwindigkeit von Sinter untersucht. Dabei wurde die Reduktionsgeschwindigkeit von Hochofensinter in einem Temperaturbereich um den Erweichungspunkt bestimmt. Es wurde ein rapider, mit dem Erweichungseffekt wie auch mit dem Porositätsschwund verknüpfter Geschwindigkeitsrückgang festgestellt. Diese Erscheinung findet in einem Temperaturbereich statt, der den Temperaturen des Erweichungsbeginns beim untersuchten Sintermaterial im vorreduzierten Zustand entspricht. Somit ist der Erweichungsvorgang als grundlegende Ursache für die festgestellte Abnahme der Reduktionsgeschwindigkeit zu betrachten. Mikroskopische Direktbeobachtungen der Reduktion von Sinter im Erweichungszustand zeigten Erscheinungen, die zu einem Porositätsschwund führen. Messungen des Porenvolumens und der spezifischen Porenoberfläche an Sinter – vor wie nach abgeschlossener Erweichung und Reduktion – bestätigten die Porositätsabnahme. Diese erschwert den Reduktionsgaszufluß zu den Eisenoxiden und verlangsamt so die Reduktionsgeschwindigkeit.     

The phase stability of solid LiAlO2 used for the electrolyte matrix of molten carbonate fuel cells

LiAlO₂ is used as a solid matrix for molten carbonate fuel cell (MCFC) electrolyte tiles. These devices operate within the temperature range of 870–970 K. The -crystallographic form of this compound is commonly used for fabrication of these matrix tiles. The thermodynamic stability of this phase within the above temperature range is not clear and it is reasonable to consider the transformation to take place in solid LiAlO₂ in presence of molten alkali carbonates. In order to establish the crystallographic form of the compound that forms as a product of reaction between the liquid Li₂CO₃ and solid Al₂O₃, the kinetics of LiAlO₂ formation has been investigated. Values of conversion factor as a function of the reaction time have been determined both for a stoichiometric reaction mixture and for mixtures with an excess of the liquid 0.53 Li₂CO₃ + 0.47 Na₂CO₃ eutectic. The simultaneous determination of the reaction conversion factor and the relative intensity of the characteristic x-ray peak for the – LiAlO₂ form in the reaction mixture have shown that, within 843–973 K, in experiments of ca 100–10 hours, respectively, only this phasev of LiAlO₂ is formed. These results may explain the presence of some – LiAlO₂ amount in the MCFC electrolyte tiles after long run tests of these devices.     

LTCC Microfluidic System

A simple and inexpensive low-temperature cofired ceramic (LTCC) microfluidic device with integrated optical fibers is designed, manufactured, and tested with positive results. Fluidic channels, mixer, detector, optical fiber, light source, light detector, heater, and temperature sensor are integrated in one LTCC module. The optical system in the LTCC microsystem permits measurements of light transmittance and fluorescence. The design, technology, and results of the module's evaluation are presented.     

Through-hole membranes of nanoporous alumina formed by anodizing in oxalic acid and their applications in fabrication of nanowire arrays

The nanopore arrays were fabricated by two-step self-organized anodization of aluminum carried out in 0.3 M oxalic acid at the temperature of 20 °C. This relatively high temperature shortens significantly the anodizing time and allows to fabricate quickly thick through-hole membranes without the additional operating cost of a cooling circuit. The structural features of anodic porous alumina such as pore diameter, interpore distance, porosity, pore density and pore circularity were investigated at various durations of pore opening/widening process carried out in 5% H₃PO₄. An excellent agreement of AAO structural features measured in FE-SEM images of the studied samples with results from software calculations was observed. The pore shape can be monitored qualitatively by fast Fourier transforms (FFTs) and quantitatively by calculation the percentage of pore circularity. Additionally, the regularity of the hexagonal arrangement of nanopores in through-hole AAO membranes was compared for various opening/widening time ranging from 40 to 100 min. It was shown that three-dimensional (3D) representations of FE-SEM images and their surface-height distribution diagrams provide interesting information about the surface roughness evolution during the pore opening/widening process. A template-assisted fabrication of Ag and Sn nanowire arrays by electrochemical deposition into the pores of the prepared AAO templates was also successfully demonstrated.