română VICTOR FRUTH, CRISTIAN ANDRONESCU, CRISTIAN HORNOIU, ECATERINA ŢENEA, ADRIANA RUSU, RAREŞ SCURTU
Abstract
Sr and Mg doped lanthanum gallate perovskites (La1−xSrxGa1−yMgyO3−δ) shortened as LSGM are promising electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs).
The evolution of secondary phases, such as LaSrGa3O7 has been identified to be a problem in the preparation of LSGM. Actually, no mater what technical preparation route was adopted (wet-based or solid state-based method) the presence of the secondary phases, accompanying the main phase LSMG was reported.
The results regarding an attempt to obtain pure Sr and Mg doped LaGaO3 ceramics using a specific annealing treatment was reported in this work. The obtained ceramics were characterized using different techniques. Thermal analyses (DTA/TG) on the stoichiometric raw mixture and dilatometric measurements on sintered bodies were performed. Morphological and structural aspects were investigated by means of X-ray diffractometry, FT-IR spectroscopy and scanning electron microscopy. The electrical behavior of the obtained ceramic was characterized by complex impedance spectroscopy.
Choosing an appropriate annealing program, almost pure Sr and Mg doped LaGaO3 can be obtained.
Keywords
solid electrolytes, Sr and Mg doped LaGaO3, solid state technique, electric properties
ELENA CRĂCIUN, ANGHEL IONCEA, IOANA JITARU, MARIUS GHIUREA, OVIDIU OPREA
Abstract
In this paper a water based organo-inorganic dispersion as coating material has been prepared in the system polymer emulsion – inorganic filler – additive. The structure, topography, morphology and thermal stability of the film coating have been determined by SEM and TG analysis. The properties of the dried film like hardness, scratch abrasion, blocking resistance, elasticity, flexibility, dielectrical rigidity and optical aspect have been determined and compared with those of the conventional acrylic coating.
Keywords
nanofillers, nanocomposite, silica sol, abrasion
ZENO GHIZDĂVEŢ
Abstract
Based on the results of a comprehensive analysis made in the first part of the article, here we are handling the issue of developing prediction models on a large industrial dataset. The outcome of the first part is to ascertain, through a careful analysis, which of the process parameters will be selected as regressors and whom will be predictors. In this second part of the article they will be used in several models and the results will be assessed by their efficiency. Though formally distinct, these two parts should be read together, as they are mutually linked together. In practice, continuous exchange of information should be considered between these two parts.
Keywords
time series, prediction, industrial processes
VICTOR LECA, ECATERINA ANDRONESCU
Abstract
The results of the influence of thermal and chemical treatments on the surface morphology of (110) NdGaO3 substrates are described in this paper. The treated surfaces were analyzed by Atomic Force Microscopy (AFM), in air, and by in-situ high pressure Reflection High Energy Electron Diffraction (RHEED). The thermal treatment of substrates resulted in a NdO1+x single terminated surface, while a surface with GaO2-x terminating layer and atomically flat terraces without etch pits could be obtained by chemical etching in a HF + NH4F + H2O solution, followed by an annealing step at high temperatures (900-1000oC) in air or in oxygen flow, for surface recrystalization.
Keywords
NdGaO3, surface morphology, AFM, RHEED, annealing, chemical treatment
OANA CADAR, MIRELA MICLEAN, CECILIA ROMAN, LUCIA GAGEA, LUDDOVIC FERENCZI
Abstract
Pigment dispersion properties are extremely important for paint, papermaking or plastic industries. To obtain multifunctional features like moisture resistance, antibacterial and self-cleaning properties, the dispersing ability of two alkali-modified styrene-maleic anhydride copolymers (StMa-X, X=Na, K) was studied. It was found that these copolymers showed excellent dispersion action on the M/ZnO (M = Ag, Au and Pt) nanopowders. Sedimentation tests were also performed to observe the compatibility between the M/ZnO nanopowders and copolymers. In addition, an agar plate method was used for the evaluation of antibacterial effect of these materials. Experiments were carried out using the following bacteria: Escherichia coli CCM 3954, Pseudomonas aeruginosa CCM 3955 and Staphylococcus aureus CCM 6188. The quantitative examination of bacterial activity was estimated by the antibacterial rate as calculated from the number of viable cells, which form colonies on the nutrient agar plates. The obtained results are discussed in order to justify their possible application in the field of coating materials with superior properties.
Keywords
antibacterial properties, copolymer, dispersing ability, nanopowder
CEZAR COMĂNESCU, PETRU PALADE, DENISA FICAI, CORNELIA GURAN
Abstract
The present paper presents the synthesis and characterization of some new functionalized SBA-15 silica, by an improved synthesis route leading to well-organized mesoporous materials belonging to p6mm symmetry group. In a one-pot co-condensation synthesis we obtained and characterized SBA-APTMS and SBA-APTES samples. Variation of the initial APTMS/TEOS and APTES/TEOS molar ratios and different TEOS pre-hydrolysis time were investigated. N2 sorption, FT-IR, NIR and XRD method were employed in determining the mesostructure characteristics of the obtained materials (SBA-15, SBA-APTMS x%, SBA-APTES x%, with x= 2, 4 and 8 % molar percent ).
Keywords
SBA-15, pre-hydrolysis, functionalization, APTMS, APTES
GEORGETA VELCIU, ALINA MELINESCU, PETER STORCH, VIRGIL MARINESCU
Abstract
The purpose of this paper is to achieve a ceramic material based on cerium dioxide and copper as an attempt to optimize the properties of the anode used for intermediate temperature fuel cells SOFC-IT.
The synthesis of the material was accomplished by the precipitation method using the corresponding salts.The parameters of the precipitation route (solution pH as well as synthesis temperature) have been carefully contoled in order to obtain a homogenous material of cerium oxide particles uniformly coated with copper oxide nanoparticles. The obtained material was characterized by XR diffraction, scanning electron microscopy, measurements of specific surface area, density and
Keywords
anodes, solid electrolyte fuel-cell, precipitation method, copper oxide, ceria oxide
MILOŠ R. VASIĆ, ZAGORKA M. RADOJEVIĆ, MILICA V. ARSENOVIĆ, ŽELJKO B. GRBAVČIĆ
Abstract
The equation for drying kinetics is obtained, based on the analytical solution of the differential equation with a boundary condition in the form of the flux. This equation was initially developed by G. Efremov. In this paper a modification of the Efremov drying equation will be presented. Shrinkage correction will be included in that equation for the first time.
Two programs were designed to compute the effective diffusion coefficient. First program did not include shrinkage effect during drying into the computation algorithm while the second one has included it. Two models for predicting the drying behavior were obtained as the result of cited programs calculation. First model did not include shrinkage (model 1) and second one (model 2) has included it. The predicted values obtained from model 2 fit with experimental data. Results presented in this study showed that the values of effective diffusion coefficient determined by designed computer programs have similar values with values available in literature related to the same coefficient determined for different clays.
Keywords
effective diffusion coefficient, analytical solution, software
GEORGETA VOICU, CRISTINA DANIELA GHIŢULICĂ, ELENA DINU, ECATERINA ANDRONESCU
Abstract
In the sol-gel synthesis of dicalcium silicate (Ca2SiO4 – C2S) the calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and trietoxysilane ( C6H16O3Si - TEOS) were used as precursors. The C2S was obtained at 800-1100°C.
Thermal analysis methods (DTA/TG), X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) were used to investigate the formation of dicalcium silicate.
The in-vitro behavior was also investigated by soaking of the dicalcium silicate powder in simulated body fluid (SBF) for 7 days. Our results indicated that dicalcium silicate formed in SBF hydrosilicates as principal mineralogical phases and bound a small proportion of the phosphor from liquid as phosphate phases.
Keywords
dicalcium silicate; sol-gel synthesis; in-vitro behavior
RALUCA STAN, CRISTINA OTT, GEORGETA VOICU, ADRIANA LUNGU, SORIN I. ROŞCA
Abstract
We report the synthesis of Cr-doped silica with different morphologies by sol-gel polymerization of tetraethoxysilicate in the presence of D-sorbitol derived organogelators (1,3:2,4-bis-O-benzylidene-D-sorbitol, DBS and its p-nitro and p-methoxy derivatives) and hexadecyltrimethylamonium bromide with S-(+)-1-phenylethylamine-tricarbonyl-chromium, acting both as chiral catalyst and source of chromium, for a 10 wt% Cr/SiO2 loading. Two different types of morphologies were observed: silica tubes with 300-500nm diameter and 10-15μm length for the nitro-substituted template and “necklace” type agglomerated silica granules for the other templates. EDX and XPS analyses revealed a uniform distribution of Cr ions on silica matrix consisting of 80% Cr3+ and 20% Cr6+.
Keywords
sol-gel, Cr-doped nanostructured silica, arene-tricarbonyl-chromium complexes, organogelator
Synthesis and characterization of calcia stabilized zirconia nano-powder, obtained by sol-gel method
RODICA ROGOJAN, ECATERIANA ANDRONESCU, IRINA ILIESCU, ROXANA TRUŞCĂ, BOGDAN ŞTEFAN VASILE
Abstract
The purpose of this study is to obtain nanometric zirconia powders, by sol-gel method, using precursors of different chemical nature - inorganic (ZrCl4) and organic (C12H28O4Zr). The obtained gels were dried at 100oC, and then heat treated to 1000oC for 2 hours. In order to identify obtained phases and their degree of crystallinity, powders were analyzed using X-ray diffraction. Analyses of scanning electron microscopy and transmission electron microscopy have been used to investigate the morphology and size of the obtained powders. Experimental analyzes show that, from different precursors (organic and inorganic), nanometric powders of partially stabilized zirconia with CaO are obtained.
Keywords
zirconia nanoparticles, sol-gel method, organic precursors, inorganic precursors
ELENA DINU, CRISTINA DANIELA GHIŢULICĂ, GEORGETA VOICU, ECATERINA ANDRONESCU
Abstract
The decreasing in particle size, from micro to nanometer dimensions, allows the development of new materials, with improved properties. The pyrolysis method is a modern, unconventional synthesis method of various powders which leads to the preparation of very small (few nanometers) particles. This method is based on the spray-pyrolysis technique - pyrolysis of an aerosol obtained by ultrasonic spray.
The present paper describes the evolution of the powders microstructure and composition with different processing parameters. Using different precursors, phosphate powders - hydroxyapatite (HAp) and β-tricalcium phosphate (βTCP) - were synthesized In order to obtain homogeneous and fine powders of calcium phosphates the following experimental parameters were modified: the concentration of the solution of precursors, the flow of carrying gas, the frequency of piezoelectric ceramics ultrasonic vibration and the temperature of the pyrolysis furnace.
The obtained powders were investigated using Thermogravimetric Analysis (or TGA) and Differential Thermal Analysis (or DTA) measurements, X-ray diffraction and scanning electron microscopy. The average crystallite size of powders was also estimated from diffraction data. The results are emphasizing that by the pyrosol method can be obtained powders with various compositions, consisting of spherical particles, with size within the nanometer range, which may have many medical applications.
Keywords
hydroxyapatite, β-tricalcium phosphate, spray-pyrolysis technique
ŞTEFANIA STOLERIU, ECATERIAN ANDRONESCU, ALEXANDRA LUCIA CARABĂŢ, BOGDAN ŞTEFAN VASILE
Abstract
The paper’s aim was to prepare and characterize ceramic powders of fully stabilized zirconia (with 8 mol% yttria), and alumina, obtained through co-precipitation starting from the corresponding chlorides. Co-precipitation was taken using water or ethanol as a solvent and considering the pH influence (7.5, 10.5 and 12.5 obtained by using ammonia solution) upon precipitation was analyzed. The obtained powders were dried at 80 °C for 24 h and afterwards calcinated at 350°C for 2 hours.
The powders were evaluated through thermal analysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
The XRD results show that 8YSZ calcinated powders is a tetragonal ZrO2 and, concerning alumina powder, besides -Al2O3, -Al2O3. The TEM examination shows that the tetragonal ZrO2 has a spherical like morphology with a size ranging from 5 nm to 12 nm. Also, it was observed that the best condition for nanopowders obtaining was using as solvent water and a pH value of 12.5.
Keywords
zirconia, alumina, nanopowders, (co-)precipitation
ALINA MELINESCU, GEORGETA VELCIU, VIRGIL MARINESCU, MARIA PREDA
Abstract
The IT-SOFC cells are consisting of three main components: solid electrolyte, cathode and anode. A solid electrolyte was synthesized based on solid solutions of CeO2 with strontium oxide, which was sintered at 1400°C. The solid electrolyte obtained has the relative density of 71% of theoretical density. The composition, La0,45Sr0,55MnO3 was used to obtain a cathode. The anode was prepared using a CeO2-CuO cermets. The heat treatment was performed at 1050°C for the cathode and at 970°C for the anode. By X-ray diffraction, was determined that the solid electrolyte consists of a solid solution with specific structure of cerium oxide and small amounts of SrCeO3 and the cathode is a solid solution of type La1-xSrxMnO3. The two electrodes were deposited by spraying on the solid electrolyte and the thickness of layers was 65-85 µm. By scanning electron microscopy there was found a good adhesion of the electrodes at solid electrolyte. No cracks were observed that may indicate mechanical incompatibility between the solid electrolyte and electrodes.
Keywords
solid electrolyte, XRD, SEM