română SORIN ION JINGA
Abstract
The paper deals with the analysis of LiF single crystals growth conditions in order to establish the main parameters that are involved in the crystal quality. Taking into account the experimental data, correlations between the growing conditions and the single crystals quality used as active media or Q-switches were made. The dependence of the crystals length, fixed as driving property function, on the growth process independent variables was achieved.
Keywords
lithium fluoride, optical materials, Q-switches, high purity, crystal growth
CRISTIAN MATEI, CRISTINA ILEANA COVALIU, BOGDAN ŞTEFAN VASILE, DANIELA BERGER
Abstract
Ceria nanoparticles were synthesized by two different wet soft chemistry routes, the thermal decomposition of a tartrate-based precursor and the reverse microemulsion method. The tartrate-based precursor was characterized by FTIR spectroscopy and thermal analysis, whereas the sample isolated from the microemulsion by X-ray diffraction. The precursors were calcined at 500°C, 3h in air and oxide nanopowders were investigated by X-ray diffraction, transmission electron microscopy and selected area electron diffraction. Ceria sample obtained by decomposition of tartrate-based precursor has nanoparticles in the range of 6 - 12 nm with a slight tendency of agglomeration and a specific surface area of 28 m2/g, whereas the sample synthesized by reverse microemulsion method has nanoparticles of 6 nm average size, with very narrow size distribution, and higher specific surface aria, 68 m2/g.
Keywords
ceria nanoparticles, reverse microemulsion, thermal decomposition method, tartrate-based precursor
CRISTIAN ANDRONESCU, VICTOR FRUTH, ENIKÖ VOLCEANOV, RAREŞ SCURTU, CORNEL MUNTEANU, MARIA ZAHARESCU
Abstract
Sr2+ and Mg2+ simultaneously doped lanthanum gallate (LSGM) powders, prepared by a modified Pechini route using polyvinyl alcohol (PVA) as polymeric alcohol, were densified using an activated microwave technique at 2.45 GHz, to develop a dense stable electrolyte for application in intermediate temperatures solid oxide fuel cells (IT-SOFC). Thermal behaviour of precursors was investigated by means of differential thermal analysis combined with thermogravimetric analysis (DTA/TGA). The powders and sintered samples were characterized using scanning electron microscopy and energy dispersive analysis (SEM-EDAX), X-ray diffraction (XRD) and infrared spectroscopy (FT-IR). The thermal expansion coefficient (TEC) and ionic conductivity of the sintered samples were also evaluated. Fine, homogeneous and high density pellets of almost pure LSGM phase were obtained after sintering at 14000C for a short period time in an activated microwave field. Using activated microwave field, due to the volumetric in situ heating, the sintering process is highly specific and instantaneous, leading to a faster kinetics compared to the conventional process (electric oven). With an optimized sintering schedule, a fine grained and dense microstructure of the samples were obtained.
Keywords
solid electrolytes, LSGM, microwave technique, IT-SOFC
DOREL RADU, CORINA MITU
Abstract
The formation and the properties of the oxide compounds are determined by intrinsic factors (depending on the reactants) and extrinsic ones (the reaction conditions). The formation reactions are defined by a series of thermodynamic functions. In this paper we highlight the correlation between the Gibbs free energy of formation, the reaction energy and the basicity of the reacting oxides, respectively, evaluated through the basicity percentage, pB, in % in the CaO - SiO2 system.
At the same time, for a series of properties (interaction with water, hydration degree, mechanical resistance to compression, shrinkage) of some mineralogical constituents of the Portland cement clinker it is highlighted their interdependence with basicity.
Keywords
basicity percentage, standard free energy of reaction, properties of oxide compounds, properties of clinkers.
GEORGETA VELCIU, ALINA MELINESCU, VIRGIL MARINESCU, VICTOR FRUTH, RAREŞ SCURTU, MARIA PREDA
Abstract
Four compositions in the range of 85-90 % CeO2, the other being SrO, CaO or 2O3 combined two or three were studied. The mixtures have been homogenized by a wet route for 10 hours. After drying the obtained powders were subjected to thermal analysis which showed that in the process of grinding chemical changes occur. The apparent and relative densities were measured on the samples sintered at temperatures of 1350 and 14000C resulting that the relative densities of the samples are between 79 and 92%. X-ray diffraction revealed that the main mineralogical compound of the samples, thermally treated in the range of 1300-14000C, is a solid solution with a structure of fluorite type specific to CeO2. For some samples were also identified CaY4O7 and SrCeO3, compounds resulting by solid-phase reactions and two solid solutions of the type SrCe0,85Y0,15O2,95 and (Ce,Y)2O3.The microstructure of the studied samples was investigated by electron microscopy and the results showed that the samples exhibit rounded and needle-shaped grains of different sizes. Electrical measurements have shown that three of samples have a corresponding behavior to solid electrolytes usable for IT-SOFC cells.
Keywords
solid electrolytes, LSGM, microwave technique, IT-SOFC
LAVINIA POPESCU, FLORIAN ZAMAN, ENIKÖ VOLCEANOV, MARIANA ENE, MIHAELA ULMANU, ILDIKO ANGHER
Abstract
The development of an analysis methodology with embedded identification of significant issues regarding the use of steelmaking slags from secondary metallurgy in agriculture for acidic soils improvement leads to "elimination” of "waste" term assigned for Ladle Furnace (LF) slag and determines its conversion into useful by-product and environmentally friendly. This paper analyzes comparatively three Romanian sources of LF slag:
1) a steel manufacturer for power industry equipments fabrication (Source 1) ,
2) an alloyed steel manufacturer for the obtaining of rolling stocks (Source 2),
3) a steel manufacturer as long semi-finished forms (Source 3).
Each of these sources (companies) have specific characteristics of the steel manufacturing and LF slags storage which have been investigated in the paper in an attempt to exploit them as secondary resources to obtain materials for acidic soils amelioration.
Keywords
environmental management, recycling, ladle furnace, white slag, acid soil amelioration, lime
ABDELAALI RAHMOUNI, ABDERRAHIM BOULANOUAR, MOHAMED BOUKALOUCH, ABDERRAHIM SAMAOUALI, YVES GERAUD, JAMAL SEBBANI
Abstract
Physical properties of rocks are measured and analyzed, and their relationships are discussed in this paper. Permeability and mercury porosimetry methods, porosity, and pore size distribution are determined. Furthermore, bulk and particle densities of rocks are determined. The morphology of the porous medium has been approached by mercury porosimetry which gives an appearance to the pore distribution of the material. The permeability of a variety of natural materials is characterized using a relatively new laboratory apparatus. Permeability and porosity are in close relation, and it could be assumed that its relationship is linear, i.e., with increasing porosity, permeability increases as well. This relationship is influenced by other rock properties, such as the amount of open and closed pores within the rock sample, size, and distribution of pores. From this point of view, it is necessary to study these physical properties of natural materials as well, because this enables an overall analysis of rocks and their possible use for construction.
Keywords
rocks, permeability, porosity, mercury porosimetry, bulk density, TinyPerm II
Y.EL RHAFFARI, M. HRAITA, A. SAMAOUALI, M. BOUKALOUCH, Y. GERAUD
Abstract
This paper presents a study on the thermal and petrophysical characteristics of porous calcarenites, sampled from a quarry located near the historical monument of Chellah (Rabat).
We measured the thermal conductivity using box method and Thermal Conductivity Scanner (TCS). The sample’s thermal conductivity map generated by exploiting the values produced by (TCS), gives a clear view of the thermal heterogeneity of the studied rock.
The measurement of mercury intrusion porosimetry shows two porous networks (macropores and micropores); the value of porosity is between 16,52% and 34,9%. We have also found that porosity is one of the main parameters that control the transfer of heat in the calcarenites of Rabat.
Keywords
calcarenites, thermal conductivity, mercury intrusion porosimetry, box method, TCS method
MIHAELA NORIŞOR, EDUARD MINCIUC, ROXANA PĂTRAŞCU, GEORGE DARIE, DIANA TUTICĂ
Abstract
The aim of the paper consists in optimising the integration of CO2 post-combustion capture technology using chemical absorption within the fluidised circulating coal combustion (FCCC) with direct application in glass and cement industries. The authors have performed some comparison of the effects of using primary amines (MEA) and tertiary amines (TEA) in order to reduce energy consumption of regeneration process, and, at the same time, keeping the efficiency of CO2 capture over 85 %. The paper presents results of an experimental study using laboratory equipment for fluidised circulating coal combustion, and also simulation results of CO2 post-combustion capture using specialised software HYSYS 3.2.
Keywords
Cuvinte cheie (engleza)
ALIONA ILJINA, KESTUTIS BALTAKYS, MARIUS BALTAKYS,RAIMUNDAS SIAUCIUNAS
Abstract
In this work the possibility of neutralizing or removing compounds containing fluoride ions from waste silica gel was investigated. The elution of F– ions from waste silica gel to the liquid medium was performed under static and hydrothermal conditions. It was determined that waste silica gel consists of silicon dioxide (77.77%) and other compounds containing 8.64% F– and 4.03% Al3+ ions, which are stable during the drying process (500C; 48 h). It was determined that under static elution conditions it is possible to remove only 6–7 wt. % F– ions into a liquid medium from waste silica gel. It was found that CaO additive has a positive influence on the decomposition of AlF3·3H2O and the formation of CaF2. It was found that silica gel is a prospective raw material for synthesis of Z-phase because the kinetics of compound formation is faster than in pure mixtures. A principal technological scheme has been designed for waste silica gel neutralization and utilization by using Ca(OH)2 under static or hydrothermal conditions.
Keywords
silica gel, waste, fluoride, aluminum fluoride trihydrate, neutralization
DANIELA COVACIU ROMONŢI, GEORGETA VOICU, DANIELA IONIŢĂ, IOANA DEMETRESCU
Abstract
CoCrMo alloys are extensively used in tissue engineering in both dental and orthopaedic applications and are highly recommended due to the good ratio quality /price comparing with other metallic biomaterials. The present approach is related to electrodeposition of fluoridated phosphate masses with good ratio calcium to phosphorus close to the one existing in bone.
SEM and EDX analysis confirm that the electrochemical method for deposition of fluoridated apatite on CoCrMo is efficient and the results were quantified using electrochemical and mechanical measurements.
Keywords
CoCrMo alloys, electrochemical deposition, SEM, EDX, artificial saliva, physiological serum
HERI SUTANTO, ILS NURHASANAH, H. HADIYANTO
Abstract
The objective of this research was to study the change of Mn mole fraction to the structure and magnetic properties of GaN:Mn thin film by sol-gel method. A thin film ferromagnetic semiconductor of GaN:Mn has been deposited on Si(111) substrate by using Chemical Solution Deposition method (CSD) and spin coating technique. Atomic composition, crystal structure, morphology and magnetic properties of the GaN:Mn thin film were characterized using Energy dispersive of X-ray (EDX), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Scanning Probe Microscopy (SPM) and Vibrating Sample Magnetometer (VSM). The results showed that the GaN:Mn thin film still contains carbon atom impurity and non-stochiometri. The GaN:Mn thin film has polycrystalline form in which the 2θ angle of GaN peaks have been shifted (~ 0.22o) for that with Mn composition of 5.24% at 32.62° angle. SEM and SPM investigation show the surface of GaN:Mn thin film with 6% Mn distributed by homogeneous grains and the level of surface roughness was 15.3 to 29.90 nm. However, the other magnetic phases (Ga5.2Mn) and oxide phases of Mn, Si and Ga were also detected in the GaN:Mn thin films. Sample with 7.43% Mn exhibits optimum composition results in appearance of ferromagnetic properties. The remanent magnetic (Mr) and saturation magnetic (Ms) of sample were achieved at 5.04 emu/cm3 and 91.5 emu/cm3, respectively.
Keywords
GaN:Mn; Chemical Solution Deposition; spin coating; Si(111) substrate; magnetic properties; ferromagnetic
CRISTIAN OLIVIU BURADA, COSMIN MIHAI MIRIŢOIU, DUMITRU BOLCU, MARIUS MARINEL STĂNESCU
Abstract
In this paper, we have built some new composite sandwich platbands with different core (made of polypropylene honeycomb and polystyrene) and different reinforcement (glass-fiber, carbon-fiber and steel wire mesh). Starting from the dynamic response of these sandwich beams with damping, that are in free vibration, we have established a way to determine the damping factor. We have experimentally determined the damping factor per unit mass for the beams and the stiffness.
Keywords
composite, damping factor, glass-fiber, carbon-fiber, steel wire mesh