română ILEANA MOHANU, NICOLETA VLAD, GEORGE STANCIU, ROXANA FECHET
Abstract
Clinker is the basis component of Portland cement, which participate in forming of the strength structure of the binder matrix. Clinker storage in improper conditions may have as consequence modification of its characteristics and implicitly, of the cement preformaces. The work follows storage influence in uncover stockpiles of clinker and granulated furnace slag on their characteristics and on the performances of a cement type CEM II/A-S with 20% granulated furnace slag. In this way, at different periods, chemical and mineralogical investigations (X-ray diffraction, optical microscopy) are carried out. Also, hydraulic activity influence of the clinker and granulated furnace slag on physical-mechanical characteristics of the cement is presented.
Keywords
clinker, blast furnace slag, storage
MARIA GEORGESCU, GABRIELA NICULAE
Abstract
Waste derived from different industries co-processing represents a priority for cement industry in its efforts towards the sustainable development. In this respect, it becomes highly important identifying the impact of the alternative fuels use on the composition and structure of the clinker and on the cement properties.
The paper presents some investigations on some industrial clinkers produced by using a complex alternative fuel mix and a relatively high substitution rate of the traditional fuel with alternative fuels – 34 % - 60 %, in comparison with a reference clinker burnt using coal.
The investigations of the mineralogical composition by Rietveld method and of the structural and textural characteristics by electronic microscopy SEM, showed no significant difference in terms of main mineralogical compounds content and of the structure and textural appearance, between the clinker burnt with traditional fuels and the clinkers produced in the same installation, but using various types of alternative fuels and thermal substitution up to 60 %.
Keywords
waste-derived alternative fuels, clinker quality, Rietveld method, SEM
ION TEOREANU, NICOLETA DENEANU, MIRELA DULAMĂ
Abstract
There are a variety of matrix materials and commercially techniques available for conditioning organic radioactive wastes. This paper provides an overview of the application context and evolution of several important matrix materials and offers comments on the waste form requirements under disposal conditions. In this paper emphasis has been placed on the conditioning options available commercially and that have, to various degrees, been demonstrated to be viable. At the same time, it is recognized that other matrices are being researched as possible for future options. Included in these options are magnesium phosphates binding systems and mixed cement with Portland composite cement and Calcium
Keywords
composite cements, calcium aluminate cement, magnesium phosphate binding systems, organic radioactive wastes
DAN GEORGESCU, ADELINA APOSTU, GHIULGIAN MIRON
Abstract
The article presents the results of experimental researches conducted for the first time in Romania, in the Research and Testing Laboratory of Reinforced Concrete from Technical University of Civil Engineering Bucharest, Romania, in order to study the possibility to apply in Romania a new European evaluation criteria of concretes freeze-thaw resistance, concrete mixes with different cement types. Concrete freeze-thaw resistance was evaluated applying the standard methods on European level (CEN/TS 12390-9, CEN/TR 15177) depending on the calculation of the scaled material quantity and on determination of dynamic elastic modulus values of concrete samples tested on repeated standard freeze-thaw cycles. The mass reducing of the concrete samples and dynamic elastic modulus are compared with proposed limit values, depending on the situation in one of XF exposure class.
Keywords
durability, composite cement, concrete
CONSTANTIN BUDAN, DANIEL NICOLAE STOICA, ADRĂNEL MARIN COTESCU
Abstract
Reinforcement corrosion in principle is due by the slurry pH of concrete pores reduction and the presence of oxygen.
Time of occurrence of the phenomenon, as an effect on the strength characteristics, is in principle at least two years. If in the natural corrosion, the elements of monolithic concrete bear the blame is on the coverage with concrete for the reinforcement, at the precast concrete, corrosion may occur mainly due to chloride ions contained in concrete. Can be taken into account other possible causes, related to the concentration of static or dynamic external loads on the elements, the presence of lime in the concrete repair compositions or dispersion currents. Whatever the cause, the phenomena must be known and kept under control at least as concrete elements containing highly corroded reinforcement that are not apparent, can suffer significant degradation (up to collapse) in during exceptional applied loads. However, knowledge deployment of reinforcement corrosion processes contributes to improving the control of reinforced concrete, to prevent and reduce destruction.
Keywords
corrosion, reinforcement, concrete, influence factors, anticorrosive protection
ION NEAMŢU
Abstract
Compactness is a main feature of concrete tiles. Compactnessess increase influence positive mechanical resistance of tiles while reducing their permeability to water before and especially improves reaction time to gelivity processes.
To obtain greater compactness of tiles is used:
a) an aggregate (sand) with optimal characteristics;
b) the addition of ultra fine powders, hydraulic active, able to better fill the capillary and crazing pores of cement stone (fly ash);
c) the use of added superplasticising, whose complex action lead to increased growth workability concrete and concrete compactnessess.
The results clearly show that the use of sand or cement mixtures are substituted with ash from thermo present consisting advantages in better mechanical resistance, more uniform texture, better reaction to gelivity, lower cost price, and not least solveing environmental problems by using the waste ash resulting from coal combustion.
Keywords
porosity, gelivity, compactnessess, permeability, additives
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
ROXANA PĂTRAŞCU, GEORGE DARIE, ADRIAN VOLCEANOV, BOGDAN ALEXANDRU SAVA, MIHAI ELIŞA, ADINA STĂNCULEA
Abstract
The present article is an integrated approach of energetic efficiency in the field of glass manufacturing industry as well as the reduction of its environment impact. In the same time, this article is targeting an improvement of energetic and economic efficiency, a reduction of the environment impact (CO2, NOX, SO2 and dust emissions) and new equipment implementation in the field of glass manufacturing industry in Romania. This article takes also in consideration the consequences of the glass waste recycling.
As a result of the present model, complex appraisal methodologies of energetic efficiency, environmental impact and economic efficiency as well as new clean technologies will be available for the Romanian glass manufacturing domain.
In this way, Romanian glass industry will be able to reach European efficiency and environment standards. Emissions reduction, especially CO2, will create appropriate conditions to implement the main Kyoto Agreement measures.
New methodologies techniques and technologies (solutions, equipments, etc) and also the new developed evaluation models might have a replication potential for other industrial branches.
Keywords
glass technology, environment, efficiency, equipment
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
DOREL RADU, ANDREEA DAVID, ZENO GHIZDĂVEŢ
Abstract
The more emphasized tendency to use alternative fuels along with the traditional ones in clinkering plants raises a series of problems regarding technological, thermo-technical, economical and environmental issues. Whereas technological and economical aspects are mostly established, from the thermo-technical point of view, not all changes that occur in a clinkering plant when one fuel is replaced by another one have been studied yet.
In present article, the second from a series of four, it is emphasized the way that certain thermo-technical parameters influence the flow and chemical composition of the hot gases exhausted into the atmosphere. The thermo-technical parameters that were taken into account were: absolute productivity, theoretical temperature, dissociation degree of some components of the hot gases and coefficient of air in excess used for the combustion.
Keywords
kilns, hot gases, dissociation, productivity, emissions
NICOLAE ANGELESCU, MARCELA MUNTEAN, CRISTINA IONIŢĂ
Abstract
The aluminous cement is the compound, which by its hydration-hydrolysis, is involved in the hardening process of the refractory concretes, under normal condition, like the consequence of hydraulic binding. A high value of aluminous cement dosage in concrete is followed by the decrease of the maximum use temperature and the depreciation of the mechanical and structural characteristics for this refractory material. The refractory concretes are widely manufactured mainly by using a common values of aluminous cement dosage (~20%). Also, there is the trend to decrease the cement dosage, at to very low limits, even up to its remove in order to improve the quality and use properties for these products. This is possible with by substitution of the aluminous cement with admixtures which are capable to develop other binding forms, next to hydraulic one. The aim of the present paper is to present the utilization possibilities of the aluminous and siliceous powders like substituents of the aluminous cement which are able to develop other binding forms, different from the hydraulic one.
Keywords
Refractory concrete, coagulation, hydraulic binding, complex binding system, admixtures, reaction activator
MARIN AMĂREANU
Abstract
The paper presents a study focused on behavior in cement concrete of the macromolecular compounds and of macromolecular compounds associated with various mineral addition materials, and their influence on hydration-hydrolysis processes, emphasizing the mechanisms related to setting and hardening of these complex binding systems. The studies are concerning the complex hardening processes of complex binding systems: Portland cement - epoxy resin - water, Portland cement - epoxy resin + hardening agent - water, Portland cement - polyvinyl acetate – water. To these binding systems, different additions (of ultrafine particles): silica fume (SF), diatomite (D), and fly ash (FA) were added.
Keywords
Polymer concrete, mechanical properties, epoxy resin, vinyl polyacetate, mineral addition materials
LIANA TEREC, TUDOR BUGNARIU, MIRCEA PĂSTRAV
Abstract
An important theoretic research program was conducted in INCERC Cluj, in order to study the strengthening technique of the low or moderate damaged reinforced concrete frame structures, one of the existing construction types susceptible to damage.
The principal objectives of the analytical studies were to analyze the behavior under seismic loads of infill walls connected to the reinforced concrete frame with bonded anchors and to evaluate the influence of several parameters, like the thickness of infill walls, the thickness of the jackets, respectively the longitudinal reinforcement ratio in the jacket of the columns.
Keywords
construction (D, d), composites (B), concrete (D, a), reinforcement (D, a), modeling (B)
KSENIJA JANKOVIC, DRAGAN BOJOVIC, DRAGAN NICOLIC
Abstract
By using crushed brick as aggregate, the structure of concrete can be effectively modeled and materials with very different physical-mechanical characteristics can be obtained. Determination of the influence of polymer admixture on some modified concrete properties is shown in this paper. Experimental work included several types of concrete made with different cement content (250 or 350 kg/m3), and same consistency (slump about 5 cm). Few types of concrete made with 4% admixture of polymer (dry material) by weight of cement. Recycled brick or combination of river sand and recycled brick were used as aggregates. Results of determination of concrete compressive and bending strength, modulus of elasticity, coefficient of thermal conductivity, resistance to freezing-thawing, water permeability, shrinkage and creep, and stress - strain diagram were observed.
Keywords
lightweight concrete, recycled bricks, polymer, mechanical-rheological properties
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
ECATERINA ANDRONESCU, CARMEN STELUŢA CIOBANU, LIVIA PALL, MARIETA COSTACHE, DANIELA PREDOI
Abstract
Bioceramic composites were obtained by combining two biocompatible components (by example- in our studies - hydroxyapatite and iron oxide nanoparticles). The preparation method determines the particle size and shape, the size distribution, the surface chemistry of the iron oxide particles and consequently their magnetic properties.
The samples were analysed by X-ray diffraction and IR spectroscopy. Their thermal behaviour was studied by thermogravimetric and thermodifferential analysis. These characterization techniques confirmed the presence of hydroxyapatite on the magnetite surface. Osteoblast cell cultures were used to determine cell proliferation, viability and cytotoxicity on interaction with the samples. The cultures displayed good in vitro behaviour.
Keywords
Nanoparticles, Iron oxide, Hydroxyapatite, Biocomposites, Cell viability, Cell culture
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
MARIA GEORGESCU, NASTASIA SACA, GEORGETA VOICU
Abstract
The behaviour of the blended cements containing limestone filler exposed to corosive environment is important for the durability of the concretes made with such of binders. The paper brings information regarding the behaviour of some blended cements containing Portland cement with 10-40% limestone filler additions in contact with a 5% MgCl2 solution.
The interaction processes between the binding matrices and MgCl2 solution were assessed by XRD analysis and scanning electron microscopy (SEM). New types of hydrates are formed as a result of these processes.
The interaction processes take place gradually from the surface of the samples to their inside, and determines compositional and structural differences between the two zones.
The changes determined by the chemical processes in the composition of the mortar samples in contact with MgCl2 solution have negative consequences on their mechanical strengths, more important after longer periods of time. The behaviour of the blended cement containing 10% limestone filler exposed to MgCl2 solution is similarly to those of Portland cement.
Keywords
limestone filler cements, chemical stability, electronic microscopy analysis, mechanical strength
ALINA BĂDĂNOIU, GEORGETA VOICU
Abstract
The paper presents data regarding the freeze-thaw resistance of mortar specimens based on binary and ternary blended cements with limestone filler, slag or volcanic tuff additions in the presence/absence of de-icing salt (NaCl). Mortar’s degradation process was assessed visually and by compressive strength tests. The nature and microstructure of the hydrates present in mortar specimens subjected to freezing-thawing cycles were assessed by SEM microscopy. Mortars based on binary blended cements with slag or fly ash had a better frost resistance, in presence of de-icing salt, as compared with the mortar specimens with limestone filler content. The use of ternary blended cements (with limestone filler and slag or volcanic tuff) combined with a complex admixture (fluidizer and air-entrained) for mortars preparation, improves freeze-thaw resistance, as compared with mortars based on blended cement with limestone filler and, in some cases, on normal Portland cement.
Keywords
freeze-thaw resistance, portland cement, slag, volcanic tuff, limestone filler
ADRIANA MOANŢĂ, CARMEN CIONOIU, VICTOR FARAON, GEORGETA BĂLEANU, VASILICA DIMA
Abstract
The article presents the results of laboratory investigations regarding the performing of some reducing agents of Cr6+ for cement, which allow the manufacture of some ecological binders of high quality, according both for conditions imposed by the legislation in force and for elimination of inconveniences brought by ferrous sulphate used as a reducing agent of Cr6+.
Testing of reducing agents, for their characterization, was performed on unitary cements type CEM I and cements with additions type CEM II / A – S.
The obtained results allowed establishing of an optimal prescription of reducing agent, both from composition and its dosage point of view and of efficiency for reducing in time of Cr6+ from cement.
Keywords
reducing agent, hexavalent chromium, cement, ferrous sulphate, zeolite
JENICA PACEAGIU, ELENA RĂDULESCU, ANA MARIA DRAGOMIR, RAMONA HOTNOG
Abstract
This paper presents results of laboratory investigations on the technological behavior of the raw mix containing slag steel (a non-carbonated waste) as a partial substitute of clay, compared with typical raw mix (containing limestone, clay and pyrite cinder). It followed the influence on the grindability and burnability of the two raw mixtures and the characteristics of obtained clinkers. Also, were estimated theoretical heat consumption and CO2 emissions generated by the formation of the two clinkers. Finally, it assessed the influence of steel slag on physical and mechanical properties (water demand, setting time, soundness, compressive strength) of cement obtained by grinding clinker with gypsum up to o fineness of approx. 3500 cm2/g as compared with reference cement. The presence of steel slag introduced in the raw meal promoted better raw mix burnability. Being a non-carbonated source of lime (it contains calcium oxide bonded as silicates and alumino-silicates forms), it allows a reduction of both thermal requirement and emission of CO2 at clinker manufacture.
Keywords
steel slag, sintering, clinker, microstructure, cement properties
ROXANA FECHET, MARIUS ZLĂGNEAN, ADRIANA MOANŢĂ, ILEANA MOHANU
Abstract
The paper presents aspects concerning the obtaining of clinckers and Portland by using minerals from tailings ponds from Romania. Processing of solid minerals sterile and obtaining of subproducts which are economically usable has major importance, both from economical and ecological point of view, through environment protection.
The laboratory researches had followed elaboration of ecological technologies of processing the waste as mineral sterile, in order to obtain recovered products. Mainly, elaborated technological flows contain a first stage of hydro-gravitational concentration followed by a magnetic and electric separation of obtained concentrates. Thus, obtained sterile may be also used as raw material in order to obtain building materials. the use of the wastes as mineral sterile from settling ponds as a corrective addition to the raw mix in cement manufacturing have led to obtaining of clinkers with ordinary modular composition. From structural - mineralogical point of view, the quality of the obtained clinkers is good, being typical alite Portland clinkers. Cements of type CEM I, obtained through grinding of the clinkers with gypsum, at a fineness of about 3500cm2/g have presented physical mechanical characteristics in accordance with quality requirements imposed by SR-EN 197-1:2002 norm.
Keywords
mineral steriles, tailing ponds, ecological technologies, cement Portland
NICOLAE ŢĂRANU, CĂTĂLIN BANU, GABRIEL OPRIŞAN, MIHAI BUDESCU, VLAD MUNTEANU, OANA IONIŢĂ
Abstract
Glass fibre reinforced polymer (GFRP) composites are currently being used as reinforcing bars in concrete and hybrid structures. An appropriate characterization of GFRP bars for concrete reinforcement is required by the structural designers prior to their use in structural applications. An extensive experimental program has been carried-out and the test results obtained from tensile tests on samples made of glass fibres and vinyl ester resins are presented and analysed in the paper.
The experimental tests have been accompanied by a numerical modelling performed to characterize the stress field in the bar ends and along the test portion of the specimens.
Three sets of 10 bars with diameters 8, 12 and 16 mm have been tested in tension, determining the ultimate tensile strength, the elastic longitudinal modulus and the ultimate tensile strain.
The experimental results are in line with similar work carried out by other research teams. It has been found out that the experimental procedure and the accompanying numerical modelling provide an adequate characterization of the GFRP bars giving the main properties needed for design.
Keywords
glass fibre, end anchorages, tensile modulus, tensile strength, numerical modelling
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
MARIA FICAI, ECATERINA ANDRONESCU, GEORGETA VOICU, DENISA FICAI, MĂDĂLINA GEORGIANA ALBU, ANTON FICAI
Abstract
In this work our attention was focused on the characterization of a corbicula species shell and the synthesis and characterization of collagen/mollusc shell composite materials. The mollusc shell and the composite material were characterized by XRD, SEM, FTIR and DTA-TG. It can be concluded that mollusc shell contain more than 98% of CaCO3 and less than 2% organic phase. The composite material was obtained by mixing fine milled mollusc shell and collagen in 4:1 weight ratio. The recorded SEM images of the obtained composite material exhibit a very good homogeneity; the collagen nanofibrils acting as glue between carbonate particles.
Keywords
mollusc shell, calcium carbonate, collagen, composite, bone graft
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Year
2010
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Issue
40 (4)
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Pages
359-364
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.