română NICOLAE ŢĂRANU, DRAGOŞ BANU, GABRIEL OPRIŞAN, MIHAI BUDESCU, LILIANA BEJAN
Abstract
Fibre reinforced polymer (FRP) composites have been successfully implemented to strengthening of reinforced concrete (RC) slabs improving their structural response to various loading schemes. The most utilized techniques are based on prefabricated FRP composite strips bonded to the tension side with adhesives or by bonding quasi-unidirectional fabrics made of carbon or glass fibres impregnated with polymeric resins.
An extensive research program has been carried out at The Faculty of Civil Engineering and Building Services Iaşi, by testing a number of thin reinforced concrete (RC) slabs strengthened with CFRP strips in different solutions, to characterize the structural response, identify the failure modes and evaluate the structural efficiency of this composite strengthening solution. The structural response has been evaluated through testing a number RC slabs under bending from transverse loading. The difference in structural behaviour of unstrengthened and strengthened slabs has been revealed on both loading bearing capacity and stiffness. The validity of experimental results has been checked by numerical modelling using ABAQUS software package.
Keywords
thin RC slabs, strengthening, composite strips, bonding, failure modes, numerical modelling
BAOMIN WANG, HONGMEI AI, KAI SONG, YU HAN, TINGTING ZHANG
Abstract
The previous studies show that the concretes containing scrap rubber powder with particle size of 180µm, 150µm and 120µm exhibit a excellent freezing resistance durability. The influence of rubber powder content, particle size and water-cement ratio on resistance to chloride ion penetration of concrete were studied. The experimental results illustrate that the resistance to chloride ion penetration of rubber concrete improved along with the increasing of rubber powder content, decreased with powder particle size and decreased with the water-cement ratio. Compared with the reference concrete, the permeability grade of concrete with rubber powder content of over 20kg/m3 and powder particle size of less than 150µm will change from “low” grade to “medium” grade.
Keywords
scrap rubber powder, concrete, chloride ion penetration, durability
L. PALL, J – L. BOBET, E. ANDRONESCU
Abstract
We have studied the influence of the substitution of Al for Ni in the ternary systems RENi5-xBx (RE=Gd, Y). The compounds synthesized in the pseudo-ternary systems RENi4-xAlBx (RE=Gd, Y) were studied in terms of their crystal structure, chemical composition and hydrogen sorption properties. Most of the compounds obtained in these systems crystallize with the CeCo4B-type structure RENi3AlB, with Al atoms replacing Ni. The partial replacement of Ni by Al observed leads to a decrease of lattice parameters compared to ternary RENi4B compounds. The new pseudo-binary phase GdB3 was also observed in this study for the first time. Finally, it is reported that the compounds do not show any affinity towards hydrogen, with no absorption observed.
Keywords
intermetallics, borides, ternary compounds
ŞTEFANIA STOLERIU, ALEXANDRU CONSTANTINESCU, ECATERINA ANDRONESCU
Abstract
ZrO2 – Al2O3 composites were developed using the co-precipitation method starting from the corresponding chlorides (zirconia was fully stabilized by using 8% Y2O3 weight ratio).
relative density (over 99%) there were used oxide additives such as ZnO, CuO, MnO2 and TiO2 (2% weight ratio).
The sintering process of the compacted green bodies (obtained by uniaxial pressing) was carried out at temperatures between 1400° and 1600°C, with a maintaining time at highest temperature of 3 hours at the maximum temperature. For the heat treatment at 1500°C the soaking time was varied from 3 to 6 hours.
The microstructure and phase composition of the dense sintered ceramic composites were determined through the scanning electron microscopy (SEM) and X-ray diffraction (XRD). The compressive strength and Young’s modulus of sintered composites were measured, too. The results have indicated that the nature of the additive oxide and the sintering temperature are the key factors in controlling the mechanical behavior of studied ceramics composites.
Keywords
dense ceramic composite, high relative density, sintering additive
ŞTEFANIA STOLERIU, ALEXANDRU CONSTANTINESCU, ADRIAN VOLCEANOV
Abstract
The most common objective of the statistical analysis is to explain the influence of random variations and events. Perhaps the most important objective is to manage simultaneous and combined effects of several influencing factors, when those factors can not be easily controlled in the experimental frame.
Multivariate Analysis – MVA is based on the principle of multidimensional statistics, which involves observation and analysis of several statistical variables at a time. This analysis is used to study several dimensions simultaneously, taking into account the effects of all variables on the characteristics of interest [1-4].
By introducing ceramic properties of some dense composite ceramics, zirconia – alumina type, with oxide additives for densification as independent variables, it was obtained a quality model. The model proved that it is necessary a more rigorous control of these properties in order to improve the compressive strength [5-6].
The developed statistical models are consistent with existing assertions in this area - they are viable, but also offers new insights - of interest from the point of view of optimizing the composition and properties of specific ceramics.
Keywords
statistics, ZTA properties, prediction, dopants
CHRISTU ŢÂRDEI, MARIANA SPĂTARU, FLORENTINA M. ALBU, ŞTEFANIA STOLERIU, ANGHEL IONCEA
Abstract
The paper presents the preparation and characterization of alginate-tricalcium phosphate porous microspheres, in terms of size, morphology, water sorption and structure. Microspheres were prepared by the ionotropic gelation technique using CaCl2 as cross-linking agent. The effect of the amount of alginate, addition of porogen material, tricalcium phosphate and sintering temperature on density, porosity and microstructure of microporous ceramic granules, and the influence of tricalcium phosphate / alginate solution report on rheological characteristics of ceramic suspensions were investigated. Archimedes method was used for investigating physical properties. Depending on their characteristics, microporous granules may find application in dental, oral/maxillofacial and other orthopaedic surgical procedures.
Keywords
alginate, immiscibility, ionotropic gelation, tri-calcium phosphate, rheology, beads
DURMUŞ ALPASLAN KAYA, ZINA VULUGA, CRISTIAN ANDI NICOLAE, CONSTANTIN RADOVICI, MĂDĂLINA GEORGIANA ALBU
Abstract
The aim of this study was to prepare zeolites modified with oregano essential oil and to establish their morphological and thermal properties as well as the release ability of essential oil from zeolites. The chemical composition of oregano oil was determined by GS-MS. The crystalline structure and chemical composition of two natural zeolites were performed by X-ray diffraction (XRD) and X-ray fluorescence (EDXRF). Both natural zeolites presented similar structure with clinoptilolite type. The thermal characteristics of oregano oil, zeolites and their combination were carried out by thermogravimetric analyses (TGA). The oregano oil was loaded in zeolite in order to improve its stability. It gradually evaporated so that the percentage of oil removed after 2h from zeolites was two times lower than itself evaporation. This property allows to the natural combination between zeolite and essential oil to be used as basic material in medical, pharmaceutical, cosmetic and food industry.
Keywords
zeolite, essential oil, thermal analyses
ELENA DINU, MIHAELA BÎRSAN, CRISTINA GHIŢULICĂ, GEORGETA VOICU, ECATERINA ANDRONESCU
Abstract
Calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and triethyl phosphate (C6H15O4P) were used as raw materials in order to prepare at room temperature by the sol-gel method a phospahate-based nanopowder, as precursor for hydroxyapatite (HAp).
The thermal behavior of the precursors was investigated by thermal analysis methods (DTA/TG).The precursor powder was uniaxially pressed as cylindrical specimens, which were thermally treated at temperatures range between 850 and 1300°C for 2 hours. The as-prepared ceramics were investigated from phase composition, chemical and morphological point of view by X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM).
Besides, the HAp-based ceramics were characterized from the point of view of the mechanical behavior by determining the compressive mechanical proprieties.
Keywords
sol-gel method, thermal analysis, X-ray methods, SEM, TEM
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Year
2013
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Issue
43 (1)
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Pages
55-60
ELENA DINU, CRISTINA GHIŢULICĂ, GEORGETA VOICU, MIHAELA BÎRSAN, ECATERINA ANDRONESCU
Abstract
In order to obtain phosphate biomaterials, non-conventional wet-chemical methods are generally used. Therefore in this work the spray-pyrolysis method was chosen. For this purpose, calcium nitrate tetrahydrate (Ca (NO3)2·4H2O) and triethyl phosphate (C6H15O4P) were used as raw materials. By optimizing the spray-pyrolysis synthesis parameters, hydroxyapatite (HAp) nanopowders were prepared at different pyrolysis temperatures ranged between 600 and 1000°C.
The thermal behavior of the precursors was investigated by thermal analysis methods (TG- DTG). The HAp nanopowders were characterized from phase composition, chemical and morphological point of view by X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM).
Due to these techniques, information regarding the effect of the synthesis temperature on the main characteristics of the HAp powders were provided.
Keywords
spray-pirolysis, thermal analysis, X-ray methods, SEM, TEM
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Year
2013
-
Issue
43 (1)
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Pages
61-67
LUCICA BOROICA, DOREL RADU, RAREŞ MEDIANU, ILEANA CRISTINA VASILIU, IOANA SÂNZIANA BOROICA
Abstract
By controlled crystallization of glass samples from BaO - B2O3 - TiO2 system glass ceramics can be obtained, based on borates and barium titanate (β – BaB2O4 and BaTiO3), with potential uses in electronics and electrical engineering. In this paper are presented the obtaining and some properties of glasses from the ternary system BaO - B2O3 - TiO2, containing B2O3 between 20 and 50 molar%. For the obtained samples were determined density, thermal expansion coefficient, micro hardness, viscosity and hydrolytic stability. Determinations were also made by differential thermal analysis (DTA). The variation of the determined properties according to the oxide glass composition was explained.
Keywords
borate glasses, DTA, dilatometry, chemical properties
ÁNGEL PALOMO, OLGA MALTSEVA, INÉS GARCÍA-LODEIRO, ANA FERNÁNDEZ-JIMÉNEZ
Abstract
The binders known as blended or hybrid alkaline cements are obtained by alkali-activating cementitious blends in the Na2O-CaO-SiO2-Al2O3-H2O system. The present paper discusses the results of alkali activating blends prepared were: binder BSLAG = 20 % OPC clinker + 80 % BFS; and binder BFA = 20 % OPC clinker + 80 % FA. The 2-day mechanical strength was over 15 MPa. The main reaction products were gels whose composition varied depending on the initial Ca content. In alkali-activated BSLAG cement they consisted of a mix of C S H/C A S H and in activated BFA cement of a mix of C A S H /(N,C) A S H.
Keywords
hybrid cement, alkaline activation, C-A-S-H gel N-A-S-H gel, geopolymer
MARIA GHEORGHE, LIDIA RADU, DANIELA NĂSTAC, NASTASIA SACA
Abstract
A major environmental risk factor, associated with the use of construction materials, is their potential emission of pollutants and their migration in the aqueous medium (groundwater, surface water and precipitation).
The paper aim is to evaluate the environmental properties of concrete with cement manufactured by using of the alternative fuel.
Concrete matrix ability of heavy metals immobilization was assessed experimentally by appropriate leaching tests. Dynamic surface leaching test on monolithic concrete samples simulates release of contaminants from concrete products during service life. The potential leaching characteristics of the concrete after demolition were estimated by the extraction test, with assessment of the leaching availability (or the maximum leaching fraction). Also, there carried out the extractions at different values of pH for establishment the pH influence on heavy metals leaching.
The emission values of heavy metals from monolithic concrete samples after 64 days were compared with the regulated, as according to Dutch Building Materials Decree (DMBD). The release values of the heavy metals from concrete were well below of the DMBD regulated criteria, referring to categoria I of construction materials.
The extraction test results showed that pH plays a crucial role on the heavy metals leachability. The cationic contaminants (Mn, Ni, Co, and Cu) were leached at pH values < 7. The cations solubility is much lower than that of the oxyanionic in the alkaline aqueous medium of concrete pore with pH ≥ 12.5. The higher alkalinity of leachate provided from alkaline character of cement matrix was favorable to leach of Cr (VI), As (V), Sb (V) and V (V) as oxyanions.
The experimental results obtained can be a contribution referring to assessing the environmentally friendly character of the concrete due cementitious matrix ability to heavy metals immobilization.
Keywords
concrete, cement, alternative fuels, leaching test, heavy metals
SILVANA BORCĂNESCU, IOAN LAZĂU, RADU IOAN LAZĂU, CORNELIA PĂCURARIU
Abstract
Thermoresistant pigments interaction with molten glazes often restricts the use of some pigments in obtaining the desired glaze nuances.
Major difficulties arise when the nuance of the glaze colored with the dispersed pigment in the vitreous matrix is different from the ionic color generated by the pigment dissolution. As a common situation, CaSnSiO5 pink malayaite pigments with chromium as chromophore often undergo a color change from pink to green after structure deterioration by the molten glaze and inclusion of the chrompohore in the glass matrix, as Cr3+.
The obtained results show that in the case of tableware faience glazes, annealed at temperatures between 1150÷1190°C, the glaze aggressiveness can be controlled within certain limits by taking action on the chemical composition, and adding wollastonite, quartz or ZnO during the milling process.
Keywords
faience glazes, UV-VIS spectroscopy, malayaite, pigment-glaze interaction
GEORGETA VELCIU, CRISTIAN ŞEITAN, ALINA DUMITRU, VIRGIL MARINESCU, MARIA PREDA, ALINA MELINESCU
Abstract
Solid electrolyte fuel cells (SOFC), the cleanest sources of electricity generation, are formed of three main components: solid electrolyte, cathode and anode. The cathode and anode (electrodes) are activation support of electrochemical reactions and transporting charge carriers, electrons and partly or totally ions. With electrolyte forms a triple interface "gas - electronic solid - solid ionic" that changes abruptly the conduction mechanism from electronic (TPB - Triple Phase Boundary) to ionic. The study of processes taking place in the TPB in a solid electrolyte fuel cell is important for optimization of electrochemical reactions. This paper presents the structural and microstructural characteristics of interfaces cathode / electrolyte / anode in a fuel cell with solid electrolyte with following ceramic components: solid electrolyte on CeO2 based with addition of calcium oxide and yttrium oxide, cathode of perovskite type based on lanthanum manganite doped (LSM) with strontium and anode a cermet from cerium oxide doped with gadolinium (Ni-CeGd). Mineralogical composition of components used for the fuel cell was performed by X-ray diffraction. Its microstructure was determined by electron microscopy, and the distribution of chemical elements at interfaces cathode / electrolyte and anode / electrolyte was examined by EDX. Cathode and anode surface condition was examined by AFM. The results show a good adhesion of the layers used as electrodes on solid electrolyte support.
Keywords
SOFC, cathode, electrolyte, anode, microstructure
DAN GEORGESCU, RADU GAVRILESCU
Abstract
The article presents novelty aspects for the modern approaches proposed in reviewing the European standard EN 206 „Concrete - Specification, performance, production and conformity” regarding concrete’s equivalent performance concept and the theoretic basis for the experimental determination of “k” coefficient in case of using additions in concretes in order to obtain performances equivalent to those of concretes without additions. In the article are presented theoretical application methods and/or experimental applications of such methods performed by the authors. The methods, suggested in the European standard, will be the basis for Romanian regulations’ review regarding the production of concrete.
Keywords
concrete, mechanical strengths, durability, equivalent performance
IONELA PETRE, MARCELA MUNTEAN, ADRIANA MOANŢĂ
Abstract
The paper presents investigations with regard to the influence of the surfactant additive HEA2 (triethanolamine acetate) on the specific power consumption at grinding, the particle size distribution and the mechanical properties of unitary cements and with addition of blast furnace slag with advanced fineness. The additive was dosed in three different ratios (0.03%, 0.05% and 0.1%), reported at the weight of cement subject to grinding. Grinding fineness of the cements, expressed through Blaine specific surface, was of 8000 cm2/g. It was found that even if grinding the blast furnace slag and the blast furnace slag cement were carried out without any surfactant, the power consumption was lower than when grinding the ordinary Portland cement. The effect of the surfactant on the specific power consumption at grinding is greater for the ordinary Portland cement than for the blast furnace slag cementIn terms of the surfactant effect on the particle size distribution, HEA2 was found to lead to a particle size distribution gliding towards finer fractions, namely, to a higher ratio of the fractions smaller than 3 and 16 microns, respectively, as compared to the reference cement (without additive).
Using of the additive HEA2 at grinding of the cements with addition of blast furnace slag lead to increasing of mechanical strengths at compression, at all hardening terms, in comparison with etalon cements.
Keywords
grindability, surfactants, advanced fineness cement, slag cement
GEORGE ŢĂRANU, IRINA LUNGU, NICOLAE ŢĂRANU, MIHAI BUDESCU
Abstract
Composite materials made of glass fibre reinforced mineral matrices are nowadays utilized in both new construction elements and in strengthening solutions of deteriorated civil engineering structures. The use of such materials requires a good knowledge of their strength and stiffness properties for the corresponding design works.
An extensive experimental program has been carried out at the Faculty of Civil Engineering and Building Services of the “Gheorghe Asachi” Technical University of Iasi to reveal the usage possibilities of mineral matrix composites, relating to regular construction elements and to specialized modules in emergency conditions. The research program has included theoretical and experimental studies regarding the utilization of ecological reinforced matrix, obtained by partial substitution of the ordinary Portland cement by a hydraulic binder manufactured from industrial wastes. The mechanical strengths and the elastic moduli from composites with various mixes and fibre volume fractions experimentally established confirm the suitability of these materials to structural members subjected mainly to axial loading.
Keywords
mineral matrix composites, glass fibre mesh, mechanical strength, elastic modulus, structural response
DANIELA FIAT, MIRELA LAZĂR, GHEORGHE HUBCA
Abstract
This paper highlights the influence of polymer additives on the durability of experimental dry-mix colored plasters compositions, that include them, after the exposure to urban-industrial environment (natural aging) and to UV radiation (accelerated aging).
Keywords
premixed dry mortar, polymer additive, redispersible powders, cellulose ethers
ALEXANDRU MIHAI GRUMEZESCU, ECATERINA ANDRONESCU, ANTON FICAI, GEORGETA VOICU, OCTAVIAN COCOŞ, MARIANA CARMEN CHIFIRIUC
Abstract
The aim of this paper was to obtain a hybrid biostructure, combining the Eugenia caryophyllata essential oil and a silica network and to demonstrate by in vitro studies its potential chemotherapeutic value to improve the efficacy of different classes of antibiotics currently used against Gram-positive and Gram-negative bacterial strains. The obtained hybrid structure significantly improved the activity of topic antibiotics, such as bacitracin and neomycin sulfate, by significantly decreasing their minimal inhibitory concentration. This antibiotics potentiating activity, together with no measurable in vitro cytotoxicity, make this hybrid structure potentially relevant for biomedicine applications, especially in the antimicrobial therapy.
Keywords
hybrid material, silica, drug delivery, biocompatibility, antimicrobial therapy
LU SHUANG, WANG ZHENG, DONGQING ZHANG
Abstract
The electrical conductivity of the cement based materials mainly depends on the properties of its pore solution, and its freeze-thaw cycling damage properties are related to the pore size and distribution definitely. This paper has studied on the relationship between the electrical resistivity variation and the freeze-thaw cycling damage behavior of the autoclaved fly ash brick. Test results show that, the hysteresis effect of the electrical conductivity of the autoclaved fly ash brick has been changed significantly, whereas its frost-resistance ability decrease in quantity with increasing amount of fly ash added. Bricks with more cement added give high frost-resistance ability, such that the remarkable descent stage of them change from -10~0 0C to -20~0 0C. The addition of air entraining agent has little or undesirable effect on the frost-resistance ability of the autoclaved fly ash bricks.
Keywords
Fly ash brick, electrical conductivity, frost-resistance, electrical resistance
ŞTEFANIA STOLERIU, ENIKÖ VOLCEANOV, ADRIAN VOLCEANOV
Abstract
The aim of present work was to obtain ceramic composites based on silicon carbide and vitreous silicon dioxide, under unconventional thermal treatment and sintering conditions.
Due to the low densification ability of silicon carbide, sintering additives were used to enhance the process. Thus, to the studied ceramic composites it was added in fixed proportion (10% wt.) a third component as sintering aid, namely: alumina, mullite and cubic zirconia.
Keywords
silicon carbide, unconventional sintering, composite, sintering aids
MIHAI EFTIMIE, ALEXANDRA POPESCU, VASILICA DIMA
Abstract
This paper presents experimental results made to obtain a composite material with glass matrix disperse reinforced with silicon carbide powder.
The glass matrix waste (E-type glass fibres) was grounded, with a specific surface area between 3500 - 4200 cm2/g, and the reinforcing material was the powder of SiC (F120 and F600) in a ratio of 10%, 20%, and 30%.
We determined the following physical and mechanical properties: density, porosity, thermal expansion. In order to characterize in terms of composition and microstructural we performed X-ray diffraction analysis and scanning electron microscopy measurements which showed the influence of the SiC powder particle size on the properties of the composite.
Keywords
Composite, glass matrix, SiC
ANA FERNÁNDEZ-JIMÉNEZ, ELENA FLORES, OLGA MALTSEVA, INÉS GARCÍA-LODEIRO, ÁNGEL PALOMO
Abstract
This part of the research explored the reaction of hybrid alkaline cements when they are exposed to acid (0.1-N HCl), sulphates and seawater. The hybrid cement used in the experiments comprised essentially metallurgical slag generated by the Fe and Zn industries. A standard Portland cement was used as the reference system. The findings showed that performance of these hybrid cements was similar to the results observed for the control. In a subsequent industrial trial, the concrete made with this experimental binder was successfully used in the manufacture of precast blocks and pavers.
Keywords
hybrid cement, alkali activation, geopolymer concrete, durability, blocks
ZENO GHIZDĂVEŢ, ROMAN GRĂDINARU, ADRIAN MUSTAŢĂ
Abstract
This paper presents a mathematical model for the heat transfer in the clinkering area of the rotary kiln. This problem can be solved in several ways. One simplistic approach would be to know the flame temperature in order to compute, among other secondary parameters, the temperature profile of the material. Another – much more practical – option is to know (to set) the temperature profile of the material over the length of the clinkering area of the rotary kiln, that further could be used to calculate the gas and kiln wall/shell temperature.
In this study it was consolidated this last alternative which requires the heating curve of the material (it is known/given the distribution of the material temperature in the rotary kiln, as necessary to obtain clinker quality). We then moved forward by implementing a broader approach, i.e. by assuming different amounts of fuel allocation over the length on the clinkering area; this distribution could be correlated with flame shape. Several coating width values were also included in simulation as an input parameter, thus contributing to broadening the options and to increase the realism level.
The model used a series of assumptions, limitations and simplifications. They are due to the complex nature of processes taking place in this area and are compulsory because the clinkering area could be considered independent and having a fixed length only under ideal conditions! In real life, complex interactions of material and energy with other parts of the clinkering plant can be easily identified.
Keywords
modeling, heat transfer, rotary kiln, clinker, flame simulation
IOAN LAZĂU, COSMIN VANCEA, GIANNIN MOŞOARCĂ
Abstract
An alternative recycling method for glass wastes (window panes, container glass and tableware) and fly ash as new glass matrix for lead waste immobilization was proposed in the following paper. The fly ash was previously used as adsorption support for the soluble lead waste from residual waters. The fly ash with 6% Pb2+ together with the glass wastes and borax were used as raw materials for the investigated glasses; three sets of glass samples were synthesized corresponding to weight ratios waste glass:borax:fly ash of 1:1:1, 1:0.75:1.25 and 1:0.5:1.5 respectively. The raw materials were melt for 90 minutes at 1200°C, resulting homogenous glasses. The hydrolytically and chemical stability, and lead leechability were determined according to the American Extraction Procedure Toxicity Test, ISO 719/1985 and DIN 12116/2001 respectively. The hydrolytically stability of all the studied glasses was between 11.16-17.95 g/g R2O soluble, qualifying them in the HGB1 stability class. The chemical stability of all glasses, characterized by the dissolution rate was 0-0.09 g/cm2h, depending on the glass composition. The lead leechability was 0-0.07 % of the total lead in glasses, depending on the glass composition and pH of the aggressive medium. The obtained results confirm the viability of the proposed solution for lead waste immobilization with multiple economic advantages.
Keywords
fly ash, glass wastes, container glass, tableware, chemical properties, immobilization
VASILE SHARAGOV, DUCA GHEORGHE
Abstract
The results of experiments on improving the chemical stability of various types of annealed commercial glassware (i.e., after their manufacture) as well as of those stored and used are analyzed and integrated. The main points of the technique developed are as follows. A fixed quantity of the reagent is introduced into the glassware at room temperature, followed by heat treatment, during which the glass surface is leached out. For the investigation, a variety of hollow glassware was used: containers (bottles, flasks, jars, etc.) from decolorized, green and brown glasses, laboratory and assorted glassware, ampoules made from medical glass, illuminating glassware made from transparent colorless and milk glasses etc. The glass surface was leached with sulfur dioxide, hydrogen chloride and fluoride, difluorodichloromethane, difluoro-chloromethane, and mixtures of gases. The reagents were fed into the glassware mainly in the gaseous state and in the form of solutions and solid substances. Thermochemical treatment of annealed hollow glassware by reagents gases was found to improve the water and acid resistance of glass by one-two orders of magnitude, mechanical strength – by 30 % thermostability and microhardness increased by 10 %.
Keywords
hollow glassware, surface layer, gas reagent, dealkalization, water resistance
ALINA MELINESCU, CHRISTU ŢÂRDEI, CLAUDIA MARIA SIMIONESCU, VIRGIL MARINESCU, ANGELICA MICLEA
Abstract
Natural or synthetic hydroxyapatite [Ca10(PO4)6(OH)2] has a high exchange capacity for divalent heavy metal ions and is used to treat wastewater containing such ions. The reaction mechanism of hydroxyapatite with lead salts is carried out by dissolution followed by precipitation pyromorphite. As-synthesized HAp granules were analyzed by X-ray diffraction and FTIR spectroscopy. For the study of retention of lead ions were added Ca-hydroxyapatite granules in a solution of lead nitrate. By treatment with a solution of lead nitrate in all cases the chemical reaction leading to the formation pyromorphite, which is a positive result, as it is a compound of the less soluble lead.
Keywords
hydroxyapatite, XRD, FTIR, pyromorphite
IONELA PETRE, ADRIANA MOANŢĂ, ROXANA TRUŞCĂ, MARCELA MUNTEAN
Abstract
In present conditions of extension and perfection of the types of materials used at injection works, determined by diversifying of cases of which solving is indicated the injection, using of the cements with advanced fineness present numerous advantages and opportunities of technical, ecological and economic order.
The paper presents the results obtained as consequence of researches made in laboratory regarding obtaining of some mix cements with advanced grinding fineness. It were performed and characterized from physical-mechanical point of view with unique addition of 15% granulated blast furnace slag, fly ash respectively. Grinding fineness of cements, expressed as Blaine specific surface was of 8000 cm2/g. With obtained cements were performed fluids of injection with ratios water/cement varying between 0.4 and 0.8 and different proportions of superplasticizer SP430. Fluids of injection were
Keywords
Cement with advanced fineness, Granulated blast furnace slag, Fly ash, Fluids of injection, Rheology
MARIA STEFANIDOU
Abstract
Repair mortars based on lime known as “traditional” mortars have been applied the last decades in monuments and historic buildings as the best solution in terms of compatibility. However, problems of durability have been arising due to their weak structure and easy fracture pattern. In order to improve their durability, the new developed tools of nanotechnology are tested in order to strengthen the structure of repair mortars and restrict the durability problems. In the present work, nano-SiO2 of approximately 14nm in diameter is added in lime- natural pozzolana binders, which are the most common used binders of the “traditional” mortars, in different percentages in order to study the micro and nano structure of the produced pastes using Scanning and Transmission Electron Microscopy. Additionally, their mechanical and physical properties are tested from 3 up to the age of 28 days. From the study derives that nano-modified lime-pozzolana binders have a dense structure with reduced large pores and increased strength. Additionally, the catalytic role of nano-particles to crystal formation is confirmed.
Keywords
nano-SiO2; lime-pozzolana pastes; strength; SEM; TEM
DANIEL COVATARIU, IRINA LUNGU, NICOLAE ŢĂRANU, MIHAI BUDESCU, IONUŢ OVIDIU TOMA
Abstract
Low strength mortars have been widely utilized to masonry buildings representing historical heritage. These mortars use as binder lime, clay or mixes of those materials. The masonry failure very often occurs within the joints filled with weak mortars. Structural rehabilitation of masonry framing systems using weak mortars is mainly focused on the enhancing load bearing characteristics of their joints using durable materials, fibrous composites or mortar with various additives.
A research program has been carried out at the Faculty of Civil Engineering and Building Services of Iasi aiming to evaluate a number of strengthening solutions for the masonry joints, using reinforcing chords made of steel, carbon and glass fibres. In addition, strengthening measures have been taken by re-joining the masonry units with mortars including rubber powder and polypropylene fibres.
Mechanical tests have been performed to evaluate the structural response of the masonry components and of the masonry samples with strengthened joints. The experimental results have revealed significant increase in strength and stiffness depending on the used materials and solutions.
Keywords
structural rehabilitation, weak mortars, joints strengthening, structural response, fibre chords, improved mortars
IVANA JOVANOVIĆ, SANJA BUGARINOVIĆ, DANIELA UROŠEVIĆ, LJUBIŠA OBRADOVIĆ, SRĐANA MAGDALINOVIĆ
Abstract
This paper presents an overview of laboratory testing carried out to determine the influence of fly ash, as a component in cement mixture, on physical-mechanical properties of cement. Fly ash, used in this testing, was treated by different physical methods – grinding, very fine grinding and classification. The addition of fly ash varied from 10 to 50% by weight in the mixtures with cement. In the first instance, the results were evaluated by the most important criteria, the compressive strength of mortar containing prepared mixtures. In addition to that, the flexural strength of mortar, soundness of cement pastes, initial and final setting time, as well as the amount of water, required to produce the standard consistency of cement paste, were also investigated. The reported values have completly satisfied the appropriate standard.
Keywords
Portland cement, fly ash, grinding, classification
ANJA TERZIĆ, ZAGORKA RADOJEVIĆ, LILJANA MILIČIĆ, LJUBICA PAVLOVIĆ, JOVICA STOJANOVIĆ
Abstract
High-temperature concrete binders in which fly ash, as environmentally harmful secondary raw material, is combined with masonry and refractory cement is a new option for reapplication of this coal combustion by-product. In this study, the design of the bonding agents was based on the fly ash from lignite coal combustion process and two types of cement: Portland cement and aluminate cement. Fly ash was applied without any further mechanical or thermal treatment. Mechanical properties of the binders were investigated and subsequently correlated with changes which occurred in the phase composition and microstructure of the agents. Scanning electron microscopy was used in investigation of microstructural changes caused by temperature. X-ray diffraction method was used in monitoring of the mineral phase changes also induced by increasing temperature. The investigations conducted on the bonding agents highlighted presence of good refractory properties and temperature-resistance, and also showed high values of compressive strength. The investigated bonding agents, thus, can be applied in refractory concretes, but also in various types of thermo-insulations.
Keywords
Portland cement, refractory cement, fly ash, microstructure, compressive strength
M.MOHAMMADIAN, A.K.HAGHI
Abstract
Plastic waste management is one of the major environmental concerns in the world. Plastics can be separated into two types. The first type is thermoplastic, which can be melted for recycling in the plastic industry, such as polyethyleneterephthalate (PET). The second type is thermosetting plastic. This plastic cannot be melted by heating (such as melamine). At present, these plastic wastes are disposed by either burning or burying. Therefore, both the ways contributing to the environmental problems. This paper describes the use of thermosetting plastic waste as aggregate within lightweight concrete for building application and possibilities for re-use of thermosetting plastic waste in the concrete are described in detail.
Keywords
Recycled thermosetting plastic, composite, concrete
AURELIA CRISTINA NECHIFOR, LUCIAN DĂNUŢ GHINDEANU, CRISTINA ORBECI, OCTAVIAN DORCA, EUGENIA EFTIMIE TOTU
Abstract
In this paper it is presented the synthesis and characterization of magnetite nanoparticles coated with polyethylene glycol (PEG) and functionalized with cyanuryl chloride. The synthesis of magnetic core through modified Massart method, starts from high stability materials and it uses polyethylenglycols with variable molecular weight (300, 600, 1000, 2000, 4000 and 10,000 D). The obtained nanoparticles were structurally and morphologically analyzed by help of SEM, TEM, FT-IR spectroscopy and EDAX. The chemical responsiveness of the obtained nanoparticles was evaluated by help of FTIR spectrometry, titration and electrochemical evaluation.
Keywords
magnetic nanoparticles, PEG, cyanuril chloride
BURCU ERTUG
Abstract
Porous barium titanate ceramics were produced by solid state synthesis. Stoichiometric amounts of high-purity powders containing 0.18 wt.% of La2O3 were mixed by ball-milling. The resultant mixtures were dried, sieved and were cold pressed into green samples then sintered at 1200-15000C for 6h. in air to form the perovskite phase. The porosity of the sintered bars were measured by Archimedes method. The obtained ceramics were characterized by SEM. The average grain size values and microstructural features were determined for four different compositions. The electrical conductivity values were measured under humid environment and transformed into humidity sensitivity values. Effects of porosity and working temperatures on porous barium titanate ceramics were investigated and results were evaluated in terms of microstructure.
Keywords
Barium titanate, sintering, graphite, electrical conductivity, humidity sensitivity
ALINA MARIA HOLBAN, ALEXANDRU MIHAI GRUMEZESCU, ANTON FICAI, CARMEN MARIANA CHIFIRIUC, VERONICA LAZĂR, RADU RĂDULESCU
Abstract
During recent years there is an increased interest in magnetite nanoparticles for their wide use in biomedical applications, as prevention of microbial colonization and targeted drug delivery systems. They could stabilize the volatile active components of the essential oils improving their antimicrobial activity. Here we report a newly prepared nano-bio-active coated surface for improved antimicrobial activity of classical wound dressings. Our results demonstrate that the reported nano-modified wound care textiles exhibit a great anti-fungal biofilm activity. These properties recommend the recently fabricated nano-bio-active coatings for the design of new antimicrobial medical surfaces.
Keywords
hydroxyapatite, XRD, FTIR, pyromorphite
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Year
2013
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Issue
43 (3)
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Pages
300-305
GEORGIANA-LAURA PARASCHIV, ŞTEFANIA STOLERIU
Abstract
Nanocrystalline TiO2 semiconductor represents the ideal photocatalyst due to its high photocatalytic reactivity, chemical stability, non-toxicity, low price, availability, and redox efficiency. However, only the optoelectronic properties of anatase structure make it adequate for its useage as a photocatalytic material able to oxidize many organic and inorganic molecules in the presence of near-UV radiation.
In order to obtain anatase TiO2-polymorph nanoparticles, four methods were studied, all using titanium (IV) butoxide as precursor alkoxide. Method A was the simple precipitation method, and method B involved a sol-gel route. The methods C and D were derived from sol-gel technique: C - involves obtaining an yellow gel; and D – where water was not added for hydrolysis.
The obtained powders were calcinated and characterized using specific methods: X-ray diffraction, high resolution transmission electron microscopy-HRTEM, differential thermal analysis and FT-IR spectroscopy.
Keywords
anatase, nanoparticles, synthesis methods, titanium (IV) butoxide
AYKUT CANAKCI, TEMEL VAROL
Abstract
This paper was focused on the structural evolution and characterization of Al-15vol.% Al2O3 composite. Composite powders were characterized by X-ray diffraction and scanning electron microscopy, respectively. The relationship among the stages of mechanical alloying, relative density and microstructure of both pressed and sintered materials were also investigated. It was observed that mechanical alloying process reached the steady state after 5h of milling time and relatively equiaxed powders were synthesized within this time frame. The results showed that as the milling time increased, more homogeneous dispersion of Al2O3 particles was obtained in the Al alloy matrix.
Keywords
composites; mechanical alloying; sintering; porosity; hard materials
THANIDA CHAROENSUK, CHITNARONG SIRISATHITKUL, UPSORN BOONYANG
Abstract
Sol-gel derived porous bioactive glasses were prepared by using the dual-templating method. Block copolymers used as one template component produced mesopores and the polymethyl methacrylate (PMMA) colloidal crystals as the other template component yielded three-dimensionally ordered macroporous bioactive glasses (3DOM-BG). The dual-templating 3DOM-BG with two different compositions exhibited greater weight loss in thermogravimetric analysis (TGA) and larger heat release in the major exothermic peak in differential thermal analysis (DTA) than the single-templating counterparts. It can be concluded that 3DOM-BG have higher crystalline phase and moisture absorption in their scaffolds.
Keywords
Porous bioactive glass, sol-gel, crystallization, thermal properties
MYKOLA ZAICHENKO, SERHII LAKHTARYNA
Abstract
In order to optimize the grain size composition of Portland cement with the addition of silica fume and to activate the hardening process of composite cement the method for surface modification in high-voltage electric field is proposed. The electrical agglomeration setup to produce modified composite cement has been designed. An observation of a cross-section of a cement particle by scanning electron microscopy and an analysis of the element distribution on the surface of modified composite cement particles are shown. According to the test results, cement pastes based on the modified composite cement possess the 28-day compressive strength of up to 89.3MPa, a 37% increase over the reference.
Keywords
Portland-composite cements, silica fume, spherical cement, agglomeration
ZENO GHIZDĂVEŢ, ROMAN GRĂDINARU
Abstract
In this paper, heat balance calculations were performed on a clinkering plant based on the dry process, no calciner. Parameter values were iteratively averaged over different time periods. The purpose of this work is to determine the influence of the averaging time interval on the precision and accuracy of the calculations and to extract some useful information about the process itself.
Five parameters that were selected by a simple statistical correlation analysis were considered. For each parameter two series of data of the same length (256 hours) of uninterrupted processing were used. Ordinary variations for the process parameters’ evolution and for the particular plant were recorded.
Fractal dimension calculations were made on each parameter, for both hourly and averaged sequences of data and for the two series (this has been done for confirmation). Results clearly show that each parameter can be identified by a particular fractal dimension. This simple technique can be used, for instance, to detect abnormal trends that can escape visual analysis.
Keywords
clinkering plant, heat balance, fractal dimension
BOGDAN ALEXANDRU SAVA, LUCICA BOROICA, MIHAI ELIŞA
Abstract
Glasses from lithium-aluminum-phosphate system doped with rare-earth oxides were studied. The following molar oxide composition was proposed: 17.88 Li2O 8.93 Al2O3 6.31 BaO 1.27 La2O3 63.72 P2O5 1.89 RE2O3, RE= Tb, Eu.
The glass was melt in an electrical furnace equipped with superkanthal heating resistance, in alumina crucibles, at 1250oC, for minimum 2 hours. In order to improve the optical properties of the final glass a special device was used, consisting in a mechanical device equipped with alumina stirrer for mixing the melt. The rotation speed was varied between 100 and 500 rot/min. The glass was casted in graphite mould and then annealed in an electrical furnace with kanthal heating wire. The glass samples were annealed at the high annealing temperature for minimum 4 hours in order to obtain improved properties.
The light transmission, structure and homogeneity of the obtained glass were characterized by ultraviolet-visible (UV-Vis) spectrophotometry and scanning electron microscopy–energy dispersive X-ray (SEM-EDX) analysis, respectively. Transmission in the visible range was found to be above 90% and the chemical homogeneity was satisfactory.
The optical quality of the glass was enhanced by stirring the melt so that the cords and threads were much more reduced in the glass. The number and dimension of bubbles were minimized by the selection of an appropriate melting-refining thermal program, based on a proper selection of the temperature, duration, type and speed of stirring.
Keywords
phosphate glasses, rare-earth oxides, thermal treatment, EDAX, electronic microscopy, optical spectroscopy
RADU COJOCARU, RADU ANDREI, MARIUS MUSCALU, NICOLAE ŢĂRANU, MIHAI BUDESCU, IRINA LUNGU
Abstract
The crushed cement concrete obtained as a result of rehabilitation of road and airport pavements is actually inefficiently used in road and airport construction. To integrate this recycled aggregate in the new pavement structure it was necessary to know its mechanical performance and to consider it in the structural design process.
In these respect, two types of cement concrete, namely plain cement concrete and roller compacted concrete, having in their composition different percentages of recycled aggregates have been used in the experimental program. Also disperse reinforcement with recycled steel fibres has been considered, in order to improve the pavement behaviour during exploitation.
This paper presents the results of an experimental program in which it has been found that the requirements of the present design standards concerning the strength characteristics of these new materials are fulfilled but with rigidity characteristics different than those found in the existing design diagrams.
Therefore implementation of these cement concretes made with recycled materials for airport pavements can be achieved only with the condition to adapt the actual structural design methods, such as to cover the extended range calculation parameters.
The paper deals with the laboratory research of these new materials and based on these results proposes to take into account a larger range of elasticity modulus values, in order to use them in the process of structural design of airport rigid pavements.
Keywords
plain cement concrete, recycled materials, mechanical performances, rigid airport pavements structures, structural design
SANJEEV KUMAR VERMA, SUDHIR SINGH BHADAURIA, SALEEM AKHTAR
Abstract
Chloride ingress in concrete structures has been defined and modeled using Fick’s law of diffusion by many researchers, and most of the researchers considered diffusion coefficient and surface chloride content as constants. Now, it has been recognized that diffusion coefficient (D) and surface chloride content (Cs) varies with the increase in age of the structure. This paper presents a methodology for evaluating the values of D and Cs for concrete structures of different age groups, and also investigated the variation of these parameters with respect to age of structure by using results of a field survey.
Keywords
Concrete, Chloride diffusion coefficient, Modeling transport
SLOBODAN RANKOVIĆ, RADOMIR FOLIĆ, MARINA MIJALKOVIĆ
Abstract
The paper presents the results of experimental and numerical investigations of the reinforced concrete (RC) beams strengthened with the near surface mounted (NSM) carbon and glass FRP bars. Three concrete beams were tested for bending during which the deformations of beams, pattern of cracks and the strains in steel, FRP and concrete were recorded until failure under monotonically increased loading. Additional glass (Ø10mm) and carbon (Ø8mm) FRP bars improved the bearing capacity over the control RC beams by increasing it by 73% and 89%, respectively. A nonlinear analysis model based on FEM is proposed to analyse the behaviour of the strengthened beams. The model was developed using ANSIS software package and the recommended constitutive models therein for concrete, steel and FRP reinforcement. The numerical results obtained using the developed model correlated very well with the experimental results and demonstrated not only significantly increased loading capacity and stiffness, but also considerable ductility of the strengthened beams.
Keywords
FRP reinforcement, NSM method, flexural strengthening, RC beams, testing, non-linear FEM analysis
IOSIF BUCHMAN, TAMAS DENCSAK
Abstract
Special industrial concrete (SIC) had the following composition: cement, silica fume, water, superplasticizer, aggregates, and steel fibers. Studies and researches have been carried out at the Civil, Industrial and Agricultural Buildings Department of “POLITEHNICA” University of Timisoara, for the introduction of this concrete in Romania. This work presents some of the technical and economic aspects of the studies and researches concerning the special industrial concrete.
Keywords
special industrial concrete, silica fume, superplasticizer, steel fibers, production cost
SORIN ION JINGA, GEORGETA VOICU, IONELA VASILE, ALINA IOANA BĂDĂNOIU
Abstract
Synthesis of vitreous material which was the basis for the obtaining the glass-ceramic type masses was performed by sol-gel method at normal temperature; its composition corresponds to the system CaO-SiO2-P2O5-CaF2-MgO. Tetraethyl orthosilicate (C6H~16O3Si - TEOS), calcium nitrate tetra hydrate (Ca(NO3)2·4H2O), triethyl phosphate (C6H15O4P - TEP), magnesium acetate ((CH3-COO)2Mg) and calcium fluoride (CaF2) were used as raw materials. The glass-ceramic masses were obtained by the thermal treatment at 700°C of dry gel resulted in sol-gel synthesis, followed by calcination at different temperatures- 700°C, 800°C and 1000°C. The obtained glass-ceramic materials were characterized by thermal analysis (DTA-TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The glass-ceramics were also characterized from the point of view of bioactivity by an in-vitro test, which consists in soaking the samples in simulated body fluid (SBF) for a period of 14 days at a temperature of 37°C; the resulted materials were characterized from the point of view of their mineralogical composition (by XRD) and morphology (by SEM). At the surface of the specimens was observed the formation of a brittle layer containing mainly fluoroapatite with a spherical morphology i.e. agglomerations of spherical shaped crystals and rods, as well as the presence of fluoroapatite with "raspberry" type morphology.
Keywords
sol-gel method, glass-ceramic, apatite phases, fluoroapatite, in-vitro test
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Year
2013
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Issue
43 (4)
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Pages
396-401
ANA MARIA HOLBAN, ALEXANDRU MIHAI GRUMEZESCU, ECATERINA ANDRONESCU, VALENTINA GRUMEZESCU, CARMEN MARIANA CHIFIRIUC, RADU RĂDULESCU
Abstract
With the continuous increasing rate of antibiotic resistance, novel therapeutic approaches aiming to reduce resistance and bacterial tolerance to antibiotics are currently developing. Nanotechnology seems an efficient approach in dealing with resistant infections. One of the most challenging idea is to produce materials and surfaces exhibiting high antimicrobial effects but also a good biocompatibility with human cells. In this paper, we report a newly fabricated biocompatible, resorbable bioactive wound dressing based on polyvinyl alcohol and usnic acid functionalized magnetite nanoparticles (Fe3O4@UA). This material revealed a good anti-staphylococcal activity, mainly due to the bio-active natural usnic acid (UA) compound entrapped into Fe3O4@UA. This wound dressing produces an efficient and prolonged release of the bio-active compound. Furthermore, its absorbent structure recommends this material as a good candidate for treating infected wounds.
Keywords
magnetite nanostructure, usnic acid, antimicrobial activity, functionalized nanoparticles
OVIDIU OPREA, CRISTINA DANIELA GHIŢULICĂ, GEORGETA VOICU, BOGDAN ŞTEFAN VASILE, ANGELICA OPREA
Abstract
Nanocatalysts of TiO2 doped with 0.5% Fe (III) were prepared by the sol-gel method at 75°C. Titanium (IV) tetrabutoxide (Ti(OC4H9)4), anhydrous iron (III) chloride (FeCl3), acetic acid and acetyl acetone were used as starting materials. The synthesized materials were characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM, HRTEM, SAED) and specific surface area by Brunauer, Emmett and Teller method (BET). The photocatalytic activity, measured by UV-Vis adsorption spectroscopy, was evaluated by the photocatalytic degradation of methylene blue (MB) in water under UV irradiation. From XRD and SAED analyses, the results indicate that anatase was obtained at temperature up to 800°C; above this temperature the rutile was obtained, with low photocatalytic properties. The TEM, HRTM and BET analyses showed the presence of nano size and mesoporous particles with high surface area.
Keywords
sol-gel method, anatase, rutile, Fe-doping, photocatalytic properties
MUNIR TAŞDEMIR, SEZGIN ERSOY
Abstract
Thermoplastic resin-mineral filler composites have been widely used in molded products due to effective cost reduction. Generally, the addition of mineral fillers will have an embrittling effect on polymers although the rigidity of the polymers can be increased. Much effort has been devoted to improving the properties of polymers by the addition of inorganic fillers, such as SiO2, ZnO, CaCO3 and Mg(OH)2.
In this study, mechanical properties of the high density polyethylene (HDPE) composites filled with silicon dioxide (SiO2), zinc oxide (ZnO) magnesium hydroxide [Mg(OH)2] and calcium carbonate (CaCO3) were investigated. The structure and properties of the composites are characterized using a scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS). Furthermore, HDPE composites were subjected to examinations to obtain their tensile strengths, yield strengths, elasticity modulus, % elongation, Izod impact strength, hardness and melt flow index (MFI).
Keywords
silicon dioxide, zinc oxide, magnesium hydroxide, calcium carbonate
IOAN LAZĂU, CRISTIAN CORCOVEANU, CORNELIA PĂCURARIU, RADU IOAN LAZĂU
Abstract
NiAl2O4 spinel was obtained by combustion synthesis method, using nickel and aluminum nitrate and a fuel mixture consisting of urea-dosed in relation to aluminum nitrate and maleic anhydride-dosed in relation to nickel nitrate. The compatibility of each metal nitrate and the respective fuel was established based on the thermal analyses, considering the decomposition temperature range of each reagent. Following the combustion reaction initiated at 500°C results the designed phase NiAl2O4 . By further annealing at 900°C there is only a slight increase of the crystallite size, from 15.8 nm to 16.7 nm. Using the fuels in 10% excess of the stoichiometric amount required, after the combustion results a mixture of NiAl2O4, NiO and metallic Ni; after further annealling of this mixture at 1000°C, NiAl2O4 is formed as single phase. NiAl2O4 specific blue color development, in which the chromophore cations Ni2+ are present tetrahedralyl and octahedrally coordinated, requires the annealing at 900°C of the resulted powders after combustion.
Keywords
combustion synthesis, X-ray diffraction, thermal analysis, nickel spinel.
CRISTINA BUSUIOC, SORIN ION JINGA
Abstract
The ceramics of Nb5+, Zr4+ or Eu3+ doped BaZn1/3Ta2/3O3 complex perovskite oxide were obtained by the conventional solid-state reaction method, being sintered in air, at temperatures between 1400 and 1600°C, for 2 h. X-ray diffraction, scanning electron microscopy and dielectric measurements were used for the compositional, structural, morphological and dielectric characterization. All BaZn1/3Ta2/3O3 ceramics present single-phase compositions after removing the surface layer in which zinc volatilization occurred. Furthermore, the 1:2 ordering of zinc and tantalum cations on the octahedral positions of the perovskite structure was observed for all sintering temperatures. The microstructure of BaZn1/3Ta2/3O3 ceramics is strongly influenced by the dopant type, in terms of grains size and shape. The dielectric constant varies between 16.9 and 31.5. BaZn1/3Ta2/3O3 resonator doped with 1.00 % Nb2O5 and sintered at 1600 °C, 2 h, exhibits the highest value for the quality factor, Q×f ~ 157 THz at 10 GHz.
Keywords
dielectric, perovskite, microwave resonator
ŞTEFANIA STOLERIU, ANAMARIA PUIA, SORIN ION JINGA, ECATERINA ANDRONESCU
Abstract
The paper’s aim is to present the preparation and characterization of ceramic sensors in SnO2 – ZrO2 binary system, using nanopowders obtained through co-precipitation from the corresponding chlorides.
All nanopowders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD results show specific diffraction lines of tin oxide solid solutions and tetragonal zirconia solid solutions. The TEM examination shows particle size being below 10 nm with tendency of agglomeration in large agglomerates.
For ceramic sensors obtaining, the nanopowders were shaped and thermally treated in air for sintering, at temperatures between 900° and 1300°C, for 2 hours.
In order to determine the sensitivity of ceramic sensors, the electrical resistanced was measured in air, in methane saturated atmosphere and in methanol vapor saturated atmosphere, as well. The obtained sensors are more sensitive to methanol than to methane, the compositions with a higher amount of tin oxide showing higher sensitivity values to both methanol and methane.
Keywords
ceramic sensors, tin oxide, sensitivity, nanopowders
JENICA PACEAGIU, GHERGHINA CIORTAN
Abstract
Information about the evaluation of the behavior of Portland cement to chemical attack exerted by organic acid medium is still limited and there is no standardized method for evaluation of its chemical stability. Most studies assess the durability of cement without addition (type CEM I) or containing various proportions of granulated blast furnace slag (type CEM II /A-S, CEM III/B) in contact with organic media such as acetic or lactic acid, and most refer to the behavior of cement pastes and mortars.
This paper presents data on the acid corrosion resistance of common cements type CEM II/A-V, CEM II/B-M(S-V) and CEM V/A(S-V) (according to EN 197-1) compared with that of cement without additions (type CEM I). The evolution of the mechanical strengths and weight changes of the mortar specimens, immersed into 5% solution of lactic acid, acetic acid or lactic acid + acetic acid for periods of time up to 180 days, combined with evolution of the pH and concentration of species presented in solution have shown that the acid corrosion resistance of cements containing granulated blast furnace slag and fly ash is higher than that of fly ash cement and sole Portland cement.
Keywords
composite cements, chemical stability, organic acids, mechanical strength
VASILE SHARAGOV, SVETLANA RAIFURA, OLGA AZARENKO, GALINA LYSENKO, VITALIE BOTEZATU
Abstract
The article presents the results of the investigation which studied the influence of impulse magnetic fields on structural changes in industrial colorless glasses with the help of section etching. Regimes of treatment include: temperature – between 300 and 6000C, vector’s magnitude of the magnetic induction - up to 0.15 T, duration – between 1 and 600 s. Analysis of structural changes in glasses is made with the help of section etching of solution HF. During one etching a layer of 0.05-10 μm is dissolved. Concentrations of Na+, K+, Ca2+ is determined in extracts after etching. Compactness of flat glass structure changes after thermomagnetic treatment. A 5-15 % decrease of dissolution rate of glass surface layers shows it. It is complicated to interprete the results obtained because of the stratified structure of glass. The tickness of the separate layers makes small parts of μm. Analysis of changes in the compactness of glass structure is made depending on the type of magnetic field and its parameters, temperature and duration of treatment magnetic.
Keywords
industrial colorless glass, impulse magnetic field, section etching, surface layer, structure, microhardness