română 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
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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
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
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
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
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
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
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
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
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
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
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