In this work the effect of firing temperature and firing time on the phase composition, microstructure, biaxial flexural strength, and temperature coefficient of expansion (TCE) of low-temperature cofired ceramic (LTCC) material is presented. At temperatures around 700°C the Al2O3 starts to dissolve in a low viscosity glass phase and this takes place up to 800°C, when 10 wt% of Al2O3 ceramic filler is dissolved in the glass phase forming the alumina-enriched area. This area is suitable for the crystallization of anorthite, which nucleates on the Al2O3 particles. The crystallization starts at 875°C and the mass fraction of anorthite increases with increasing temperature until it reaches a plateau value of around 22 wt% at higher temperatures or longer firing times. The biaxial flexural strength of the LTCC increases with increasing firing temperature from 135 MPa (at 800°C) to around 300 MPa (at 900°C). The major effect on the biaxial flexural strength of LTCC is that of porosity. The effect of the amount of anorthite on the LTCC biaxial flexural strength is minor. The TCE of the LTCC decreases from 5.6 × 10−6 to 5.0 × 10−6 K−1 with increasing firing temperatures or times and it is correlated with the anorthite mass fraction, which crystallizes at the expense of a decreasing amount of glass phase in the LTCC.
COBISS.SI-ID: 25443367
A novel approach leading to indolo[3,2,1-jk]carbazoles with various functional groups by palladium-catalyzed transformation, where N-(2-bromoaryl)carbazoles are cyclized to give the target molecules via C–X/C–H cross-coupling are reported. Palladium facilitates the formation of an aromatic palladium bromide by oxidation addition, while the base provides the driving force for carbon–carbon bond formation of the expected indolo[3,2,1-jk]carbazoles in either polar or non-polar solvents. A mechanism for this palladium-catalyzed reaction has been proposed.
COBISS.SI-ID: 36145413
Three related mononuclear copper coordination compounds with vanillin (natural model compound for lignin) and water are connected by three different hydrogen bond patterns within their molecular structures. For them, three different types of magnetic interactions were experimentaly detected and further theoretically analyzed.
COBISS.SI-ID: 35802373
Carbon deposits are the most probable mode of deactivation for Solid Oxide Fuel Cell (SOFCs) using methane or higher hydrocarbons as fuel. The deposition of various carbon allotropes on the anode material was studied under dynamic and isothermal conditions. The results show methane dissociation on Ni-YSZ (nickel-yttrium stabilized zirconia) under the temperature-programmed mode in three general steps. Under isothermal conditions various carbon species formed depending on the temperature. The presence amorphous, filamentous, pyrolitic and graphitic carbon allotropes was determined by Quadrupole Mass Spectroscopy (QMS), X-ray crystallography, Field Emission Scanning Electron Microscopy (FE-SEM), Infrared Spectroscopy (IR). Carbon allotropes were subsequently oxidized in atmosphere with 20.0 vol% and 0.5 vol% of oxygen in argon and show markedly different reacivity towards oxidation.
COBISS.SI-ID: 36119301
A new method for the synthesis of Ce0.80Sm0.20O1.90 was presented. A drying of a solution of ethylene glycol and stoichiometric amounts of the acetates Ce(C2H3O2)3•xH2O and Sm(C2H3O2)3•xH2O resulted in a highly crystalline product of [Ce0.80Sm0.20(C2H3O2)3(C2H6O2)]n, a new chained polymeric coordination compound. With the calcination of this precursor at 900 °C and sintering at 1150 °C, pure Ce0.80Sm0.20O1.90, was obtained with the desired homogeneity and density. This paper reports elemental (CHN and ICP-MS) and single crystal X-ray structure analyses of the precursor [Ce0.80Sm0.20(C2H3O2)3(C2H6O2)]n. Its thermal decomposition to Ce0.80Sm0.20O1.90 has been studied via HT-XRD and TG–DTA analysis. The structure and composition of Ce0.80Sm0.20O1.90 was also confirmed by powder XRD (Rietveld refinement).
COBISS.SI-ID: 35887365