română VICTOR LECA, ECATERINA ANDRONESCU
Abstract
BaTiO3 thin films with a tetragonal symmetry were grown on (001) SrTiO3 single crystal substrates by pulsed laser ablation (PLD). The evolution of the growth front was monitored in-situ and in real time by means of high-pressure reflection high-energy electron diffraction (RHEED), while atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to analyze the surface morphology. The films microstructure, substrate-film interface properties, and the type and level of epitaxial strain were determined by X-ray diffraction (XRD) studies. RHEED data showed that under optimum deposition conditions the films grow following a Stransky-Krastanov mechanism. The films morphology and microstructure is strongly dependent on the deposition and post-deposition vacuum annealing parameters, as well as on the substrate-film interface properties.
Keywords
BaTiO3, pulsed laser ablation, reflection high-energy electron diffraction, X-ray diffraction
ZENO GHIZDĂVEŢ
Abstract
Various analysis and prediction techniques were corroborated in the paper to extract knowledge from a bi-dimensional industrial dataset. It was intended to consider the least human intervention possible in all, the selection of the system predictors and dependant variables and of the data records that hold valuable information on the process. In that purpose, no prior experience was used and only results that could not be subjectively interpreted were elected (however, extracted correlations between parameters could be confirmed on an experiential base). As the paper addresses [a large amount of] practical issues, the theoretical part was omitted, though sometimes referred. This is also the case for the way several software packages mentioned at the end of the paper were used on this particular real-life analysis and prediction task. Techniques were manually iterated within a heuristic approach. In this paper we deal with the analysis of the database and the selection of the pertinent process parameters to be used in the second part of the article.
Keywords
knowledge discovery, multivariate analysis, industrial processes
MARCEL BENEA, MARIA GOREA, NICOLAE HAR
Abstract
In a previous work [1], 17 Roman ceramic fragments (bricks and tiles) from Sarmizegetusa were analysed for emphasizing some physical characteristics and thermal treatment parameters. The present study intends to answer a very frequent archaeological question: which are the raw materials used for manufacturing the Roman ceramic tegular materials? In this respect, six samples of clays from different locations in the vicinity of the former capital of the Roman Province Dacia were analysed. The interpretation of the X-ray diffraction patterns of the bulk clay samples and of the fine clay fraction (< 2 m) evidences a relatively simple mineralogical composition: kaolinite, smectite/vermiculite, quartz, Ca-Na feldspars (albite–anorthite), K-feldspars (microcline), illite, micas, chlorites, calcite and hematite. Scanning electron microscopy allowed illustrating the well-shaped kaolinite plates. The mineralogical and chemical composition, as well as the mechanical properties allowed separating three different clay types: (1) plastic clay, (2) sandy clay and (3) carbonate-rich clay. The main characteristics recommend the plastic clay as the proper raw material for ceramics. To verify, the mineralogical composition (by using XRD and optical microscopy), and the technical characteristics of the plastic, kaolinitic clay, after thermal treatment at 800°, 850°, 900° and 950° C, were analysed. The brown-reddish colour after firing, the water adsorption (12.82–13.89 %), density (1.95–2.00 g/cm3) and apparent porosity (25.61–27.16 %) are very similar to the previous studied Roman bricks and tiles. This means that the same clay source could have been used for obtaining any type of ceramics, following specific shaping and firing patterns.
Keywords
clays, mineralogical and physical analyses, Roman ceramics, Sarmizegetusa
ALINA MELINESCU, CRISTINA RIZEA-ORBECI, MARIA PREDA
Abstract
Double exchange reactions occur between CA-HAp and lead ions, the latter replacing Ca2+ ions in the network. The reaction is specific since Ca-HAp in a strong basic environment is stable and Pb-HAp in acid. This study summarized calcium hydroxyapatite by microwave heating, after which it was introduced in solutions of Pb(NO3)2 with different concentrations between 0.01 and 0.1 mol. It was found that, depending on working conditions, can result in either solid solution (Ca,Pb)(PO4)3(OH)0.67, hydrated phosphate lead or mixing two types of hydroxyapatite, Ca-HAp, respectively Pb-HAp. They defined the conditions under which hydroxyapatite calcium passes into hydroxyapatite lead.
Keywords
immobilization, Ca-HAp, Pb-Hap, XRD, SEM, chemosorbtion
OANA CADAR, CECILIA ROMAN, LUCIA GAGEA, SERGIU CADAR, MIRELA MICLEAN
Abstract
In this paper, we report a simple and economic procedure capable of producing large amount of metal/ZnO [M/ZnO, M = Au (1), Fe (2) and Pt (3)] nanopowders, namely coprecipitation. The obtained zinc oxide nanopowders contain the doping component in an amount of 0.1 wt.% and were characterized using specific techniques: X-ray diffraction analysis, scanning electron microscopy, specific surface and X-ray fluorescence. XRD characterization of obtained nanopowders confirmed the exclusive formation of the host ZnO with the wurtzite hexagonal structure and no signature of dopant as separate phase. Obvious differences were not observed in the XRD patterns of samples. Subsequently, it was possible to confirm that new phase(s) were not formed by including Au3+/Fe3+/Pt2+ in ZnO lattice. SEM analyses show highly crystalline nanopowders and particle size less than 100 nm. Also, the antibacterial properties of the specimens against Escherichia coli and Streptococcus faecalis were examined. The obtained results will be discussed in order to justify the suitability for commercial use.
Keywords
metal doping, zinc oxide, coprecipitation, characterization, antibacterial properties
DOREL RADU, VASILICA DIMA, MIHAI EFTIMIE
Abstract
The paper deals with an important technological aspect regarding vitreous materials: to determine the optimal composition for glass fibres with low biopersistence and with high chemical stability in service.
To reach this goal, in the first part of the study, according with requirements of a systemic approach, a technologic characterisation of these fibre types is made. Also the properties of interest (chemical stability, dissolution rate of the fibres) are selected based on fixed points of viscosity, both in terms of production technology and the glasses behaviour in different fields of use.
Keywords
Glass fibers, optimal design, low biopersistence
DOREL RADU, VASILICA DIMA, MIHAI EFTIMIE
Abstract
Present paper deals with a mathematical programming model applied to the optimal design of oxide composition for glass fibres with low biopersistence.
The developed general model is applied on two case studies.
In the first case it is designed a composition for E glass type (boro-silicate glass). The result of modelling indicates a relatively low value of the carcinogenic index, KI, and therefore a high biopersistence.
In the second case study, the optimal model is applied to some glass fibres having chemical compositions in the frame of MgO-CaO-SrO-Al2O3-SiO2 oxide system.
The results of our modelling show that in this oxide system glass fibre with low biopersistence can be obtained and the values of the carcinogenic index around 39, are comparable with literature data.
Keywords
glass fibers, optimal design, low biopersistence
MARIA SPĂTARU, OVIDIU DUMITRESCU
Abstract
Zircon and alumina are two raw materials used for the production of ceramic materials with good thermal-chemical properties. As shaping technology in the ceramic industry it is use, among other technologies, the casting of aqueous suspensions in plaster mouldings, for small series and complicated thin section forms or simple thick section forms.
The aim of our paper is to present the preparation conditions for some aqueous suspensions of non-plastic materials and some of their characteristics.
There were prepared some alumina-zircon concentrated aqueous suspensions in order to study the influence of water and additives amount and the homogenisation-grinding time on the suspension properties, as well. The water amount necessary for obtaining the suspensions depends on the grinding time and on the additives amount. There were used different values of water amount for homogenized suspensions between 3 and 9 hours. The amount of additives varied between 0.30% ÷ 0.38%. The obtained pH values with a pH-meter Consort P901, varied between 7.23 ÷ 9.52. It was not added hydroxide for pH adjustment. The volume weight, average dimension of the particles, the grain-size distribution and viscosity were determined.
After preparation and analysis of casting samples the correlation of the aqueous suspensions optimum parameters with the preparation conditions are emphasized.
Keywords
aqueous suspensions, alumina, zircon, casting behaviour
MARIA MIHALACHE, TIBERIU MELEG, MARGARIT PAVELESCU
Abstract
Analysis of postulated loss-of-cooling accidents (LOCA) in CANDU 6 reactors has to consider oxidised state and Zr-2.5%wtNb alloy microstructure. During thermal transients, in oxidized alloy, microstructure changes in oxide layer and material base have been observed by optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Samples isothermally oxidized at 7000C, with variable thickness oxide layers, were subjected to the various temperature transients up to 10000C, at different controlled heating/cooling rates. The effects of oxide and alloy microstructural changes are correlated with the characteristics of thermal transients.
Keywords
oxide, electronic microscopy, thermal treatment, pressure tube, CANDU
VICTOR LECA, DRAGOŞ NEAGU, ELENA ŞTEFAN, ECATERINA ANDRONESCU
Abstract
High quality, single phase c-axis oriented YBa2Cu3O7-δ thin films with superconducting properties were grown by laser ablation on (001) SrTiO3 substrates. The surface morphology of the films has been investigated by means of high-pressure reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and scanning electron microscopy (SEM), while the structural properties were studied by X-ray diffraction (XRD). Deposition under optimum conditions produces films with relatively smooth surface, with a roughness of about 10-15 nm, as confirmed by AFM and SEM data. The growth follows a Stransky-Krastanov mechanism governed by the substrate-film interface properties due to presence of epitaxial strain. The films show good superconducting properties with Tc values of 85-91 K. Results on the fabrication and electrical transport properties of ramp-type Josephson junctions with YBa2Cu3O7-δ electrodes and PrBa2Cu3O7-δ barrier are presented.
Keywords
YBa2Cu3O7-δ, pulsed laser ablation, morphology, X-ray diffraction, ramp-type Josephson junctions.