română OVIDIU DUMITRESCU, DOREL RADU
Abstract
In order to better understand oxide glass systems, one approach is based on the composition-structure-properties triad.
In the present article, a series of glasses, belonging to the system Na2O-Al2O3-B2O3 has been analyzed. For this analyze, data determined by authors, presented in a previous work, have been used.
Using the experimental determinations of the percentage basicity of glasses, pB, resulting from spectroscopic measurements and also the calculated values, the fractions BO3, BO4, AlO4 and AlO6 have been determined.
Using the experimental data of the measured properties, mathematical functions have been assessed for these, depending on the oxide composition. The values obtained approximate with high confidence the experimental data, thus validating the proposed approach.
Keywords
Na2O-Al2O3-B2O3 glass, basicity, BO3, BO4, AlO4 and AlO6, density, refraction index, thermal expansion coefficient, vitreous transition temperature
ALIN GIONEA , ECATERINA ANDRONESCU, CORALIA BLEOTU, GEORGETA VOICU
Abstract
The aim of this study is to investigate the influence of different thermal histories and yttrium oxide molar ratio on zirconia dental ceramics properties. Zirconia powders used in this study were stabilized with 2 mol%, 2.5 mol% and 3 mol% yttrium oxide. Final dense ceramics were obtained through hot isostatic pressing at temperature of 1300°C, plateau of 1 and 2 hours, under 150 MPa, in argon atmosphere. Phase composition and microstructure were determined through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Density of specimens was investigated through gas displacement method on a helium pycnometer. Compressive strength and Young’s modulus tests were also performed in order to evaluate the effect of HIP treatment. Finally, the ceramics were tested for biocompatibility, showing good results.
Keywords
ceramics, density, compressive strength, biocompatibility, dental
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Year
2016
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Issue
46 (1)
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Pages
17-24
CRISTINA-ELISABETA PELIN (BAN), ECATERINA ANDRONESCU, GEORGE PELIN, ADRIANA ŞTEFAN, ROXANA TRUŞCĂ
Abstract
In aeronautics applications, there is an increasing interest to replace the use of thermoset matrix in fiber reinforced composites with thermoplastic matrix. This paper presents the obtaining of hybrid carbon fabric reinforced laminated composites based on montmorillonite nanofilled polyamide matrix, using an innovative and cost efficient method involving polymer solvent dissolution, montmorillonite dispersion in different weight contents (1, 2, 4%) relative to the polymer, fabric impregnation with the obtained solution and high temperature pressing. The new laminated nanocomposites were characterized by FTIR spectroscopy to establish nanofiller/polymer chemical interaction, and they were tested in terms of mechanical and thermo-mechanical properties, the fracture cross section being analyzed by SEM and optical microscopy. The hybrid nanocomposites exhibited high mechanical performance, comparable to extensively used carbon fiber reinforced epoxy composites, 4% montmorillonite content generating significant enhancements of both strength and stiffness, as well as heat deflection temperature, results due to both the mechanically improved matrix due to uniformly dispersed montmorillonite, as well a strong fiber/matrix interface due to solvent impregnation processing.
Keywords
carbon fiber fabric, montmorillonite, laminated composites, tensile strength, young’s modulus
A. HADRI, B. FARES, A. AMARI, M. TAIBI , A. MZERD
Abstract
Transparent conducting Al-In codoped ZnO thin films were successfully synthesized onto glass substrates by spray pyrolysis technique. The influence of doping and codoping on the structural, optical and electrical properties was investigated. X-ray diffraction results showed that the samples have the hexagonal Würtzite structure with a preferred orientation toward the c-axis. No peaks belonging to In and Al or their oxides was observed in the limit of XRD technique detection. EDS analysis confirmed the presence of In and Al elements in ZnO thin films. The atomic percentage of In and Al elements was nearly equal to their nominal stoichiometry. The surface morphology of the codoped films showed well-defined hexagonal grains. Examination through transmission electron microscopy depicted that these films consists of an agglomeration of small grains with hexagonal shape. A high transmittance above 75% and electrical resistivity around 3×10-2 Ω.cm were reached after annealing.
Keywords
Spray pyrolysis, Hall Effect, ZnO, aluminum-indium codoped ZnO.
GEORGE STANCIU , NICU DOINEL SCĂRIŞOREANU, VALENTIN ION, MARIUS DUMITRU, ECATERINA ANDRONESCU, MARIA DINESCU
Abstract
Calcium doped strontium barium niobate Sr0.5Ba0.5Nb2O6 (SBN:50) is a tungsten bronze ferroelectric material with a tetragonal unit cell. SrxCayBa1-x-yNb2O6 (SCBN) compositions with (x = 0.5; y = 0.14 and 0.28) were obtained by solid-state reaction method. The phase structure, microstructure and dielectric properties of obtained SCBN ceramics were systematically investigated. XRD results showed that SCBN phase with tungsten bronze structure could be obtained in all ceramic samples. Higher Ca content (y = 0.28) lead to occurrence of a secondary phase of CaNb2O6. SEM micrographs show the formation of crystallites with sharp boundaries with an average grain size of about 4 ÷ 12 μm for all SCBN compositions. Compared with pure SBN:50 composition, Ca doping results in a reduction of the dielectric constant value, but the dielectric losses are found to be smaller for this compositions.
Keywords
SBN, SCBN, TTB structure, Dielectric properties
CHRISTU ŢÂRDEI, CLAUDIA MARIA SIMONESCU, CRISTIAN ONOSE, BOGDAN ALEXANRU SAVA, LUCICA BOROICA, BEATRICE-GABRIELA SBÂRCEA
Abstract
This study aimed to investigate the effect of preparation conditions on different hydroxyapatite nanopowders (n-HAP), obtained on the laboratory scale, by the solution–precipitation and sol-gel methods, and to correlate the main characteristics like crystallinity and specific surface area with the ion Pb2+ immobilization capacity. It is tested the increasing performance of nano-HAP so obtained, to remove heavy metals from aqueous solutions through dispersant addition (0.1…1.5%) and isomorphic substitution (Six-HAP, x=0.5; 1). Batch experiments were carried out using different synthetic nano-hydroxyapatites; powders were comparatively tested for lead removal process from aqueous solutions, under different conditions, i.e. initial metal ion concentration, and pH of the solutions. Results showed that all HAP powders obtained by precipitation contain hydroxyapatite as the only crystalline phase instead, the sol-gel HAP powders contains minor quantities of β-TCP. Experimental results shown that, the amount of metal ions (Pb2+) removed correlates to the nature of the adsorbents (morphology and specific surface area), and to the concentration of the synthetic solution in metallic ions.
Keywords
nano crystalline hydroxyapatite, heavy metals, lead removal, adsorption
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Year
2016
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Issue
46 (3)
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Pages
289-297
COSMIN VANCEA, GIANNIN MOȘOARCĂ, ADINA NEGREA, ADINA LAȚIA, ROMUL MARIUS JURCA
Abstract
The present paper proposes an alternative recycling method for two common glass wastes: window panes and funnel CRT glass, together with Bojidar kaolin as new glass matrix for chromium waste immobilization. The kaolin was previously used as adsorption support for the soluble Cr6+ waste from residual waters. Tree different weight ratios glass waste:kaolin (60:40, 70:30 and 80:20) were used for the glass-ceramic synthesis. The raw materials as powders (granulometric fraction under 0.1 mm) were mixed together and then pressed into cylinders having the diameter and height around 35 mm. The heat treatment was conducted at three different temperatures 900, 1000 and 1100°C respectively for 60 minutes. The compactness of the obtained glass-ceramic samples was characterized using their apparent porosity and apparent density. The obtained values range from 0 to 22.93% for the apparent porosity and from 1.93 to 2.25 g/cm3 for the apparent density respectively, depending on the glass waste type and heat treatment temperature. The microporous structure was illustrated using SEM. The phase composition of the studied samples was established by RX diffraction, cristobalite, diopside, tridymite and wollastonite being the main crystalline phases. The compressive strength of the obtained glass-ceramic products was measured and correlated with the heat treatment temperature. The highest values range from 136 to 175 N/mm2, corresponding to the samples obtained at 1000°C. The hydrolytically stability and chromium leachability were determined according to the ISO 719/1985 and American Extraction Procedure Toxicity Test respectively. All the studied samples completely immobilized the chromium ions in the glass-ceramic matrix so that no chromium extraction was recorded for the acid and neutral mediums. The glass ceramic matrix have a low sensibility to the alkaline medium, the total chromium extracted being less than 0.014% after 28 days. The obtained results suggest that the immobilization of the chromium wastes adsorbed on kaolin in glass ceramic matrix is a viable solution having multiple economic advantages.
Keywords
glass wastes, glass recycling, chromium wastes, glass ceramic
Coating magnetite nanoparticles with mesostructured silica shell of different pore size and geometry
RAUL-AUGUSTIN MITRAN, DOINA GEORGESCU, NICOLAE STĂNICĂ, CRISTIAN MATEI, DANIELA BERGER
Abstract
Composite nanomaterials combining magnetic properties and porosity have various applications as catalysts, in targeted drug delivery, depollution, energy storage etc. However, the synthesis of magnetite nanoparticles coated with SBA-16-type mesoporous silica is very challenging due to the acidic medium required, which leads to the dissolution of iron oxides. Here, we report a simple synthesis of Fe3O4@SBA-16 composite with high content of magnetic nanoparticles in a weak acidic medium. The influence of reagents addition order was also studied. The resulting materials have been investigated by small- and wide-angle X-ray diffraction, infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, nitrogen sorption analysis and magnetic measurements. The properties of Fe3O4@SBA-16 samples are discussed and compared with a Fe3O4@SBA-41 material, obtained in basic medium. All magnetic composites present high porosity and superparamagnetic behavior.
Keywords
superparamagnetic, mesoporous silica, SBA-16, Fe3O4@SBA-16, magnetite, MCM-41
V. KARAYANNIS, K. NTAMPEGLIOTIS, S. LAMPRAKOPOULOS, D. KASITEROPOULOU, G. PAPAPOLYMEROU, X. SPILIOTIS
Abstract
In the current research, clay-based bricks with beneficial utilization of industrial “scrap-soil” as admixture were developed and characterized, in order to contribute to circular economy, environmental protection and conservation of natural resources. “Scrap-soil” is an industrial soil containing residues of steel scrap and/or steel making by-products as a result of their temporary storage in open steel industry soil spaces. Brick-shaped specimens were formed by extrusion of clay/”scrap-soil” mixtures in various proportions up to 9 %wt. industrial soil, and then fired at different peak temperatures (850-1100oC). Shrinkage and weight loss upon sintering as well as bulk density, porosity, mechanical strength and thermal conductivity of sintered ceramic microstructures were determined and studied as a function of the admixture percentage and firing temperature. The experimental results confirm that incorporation of “scrap-soil” into standard red ceramic bodies is feasible, as their shape, density, mechanical performance and thermal conductivity remain practically unaffected with increasing the admixture percentage. Moreover, the sintering temperature can be optimized either to obtain specific characteristics of the brick bodies or to attain energy savings.
Keywords
“scrap-soil”, steel industry, clay bricks, extrusion, sintering, characterization
DOREL RADU, OVIDIU DUMITRESCU , IRINA PINCOVSCHI
Abstract
Vitreous oxide systems can be described at several structural levels. Thus, the first considered is the atomic level, where typical structural entities are oxygen ions and various cations in fixed proportions. In this case, the determined properties of the glass are the molar volume, the molar volume of oxygen ion and compactness.
In our research work all these properties were calculated based on the experimental data obtained by analyzing glasses with (35–x) Na2O·xAl2O3·65B2O3 molar formula, where x = 0; 5; 10; 12.5; 15; 17.5. Practically, there were established mathematical relations for quantities such as structural compactness - chemical composition, structural compactness – structural characteristics of the studied glasses, respectively.
Keywords
Na2O–Al2O3–B2O3 glass, molar volume, molar volume of oxygen ion, compactness, density, correlation
MIHAI EFTIMIE, EDUARD MARINESCU, ALINA MELINESCU, ANDREEA MONCEA
Abstract
In recent years, electronic equipments containing cathode ray tubes (CRTs) have ceased to be produced in developed countries and were replaced by modern equipment, more economical and lighter. The glass waste resulting from the cathode ray tube is a valuable raw material which can be used to obtain other materials such as glass-ceramics, with different applications.
Present paper aims to study the crystallization of CRT glass with low barium oxide content with 15% by weight added nucleating agent (TiO2, ZrO2 and ZnO). For the obtained samples X-ray diffraction analysis were carried to determine the crystalline phases and scanning electron microscopy to examine the microstructure and the resulting phases from heat treatment. Thus, the influence of nucleating agent and heat-treatment temperature on the properties of the glass ceramic were revealed.
The material has applicability in constructions, e.g. decorative or insulation tiles. Its advantages result from the high percentage of waste reused, with positive impact on the environment, and from the low temperature needed for manufacturing [1-3].
Keywords
cathode ray tubes, glass-ceramics, low barium oxide content