B. Sava | University Politehnica of Bucharest (original) (raw)

Papers by B. Sava

Journal of Optoelectronics and Advanced Materials, 2009

Semiconductor nanoparticles represent a very interesting research topic mainly for the optoelectr... more Semiconductor nanoparticles represent a very interesting research topic mainly for the optoelectronics applications. The semiconductor particles exhibit properties dependent on the crystallites size, such as the band gap width and the linear optical characteristics (transmission and fluorescence cut-off) besides the non-linear characteristics (refractive index, second and third harmonic generation, two photons absorption, etc). The paper presents the synthesis of CdS nanocrystals and their integration in polymeric matrix. The effect of some polymers with different electrical charges, like polyvinyl alcohol, polyvinyl pyrrolidone, or copolymers maleic anhidride/styrene, maleic anhidride/vynil acetate upon the physico-chemical properties of nanocrystals generated in the aqueous phase was studied. The synthesized nanocrystals were dispersed in polymeric matrix and then were applied on glass support to form films. The properties of the prepared nanoparticles and also the deposited films...

Applied Surface Science, 2008

ABSTRACT

From the constructive and functional point of view, a controlled aquaculture system can be assimi... more From the constructive and functional point of view, a controlled aquaculture system can be assimilated with a classical water treatment system, functionally customized to the requirements of technology for intensive fish in confined spaces. A physicochemical process cheap, fast, secure which has the potential to replace the widespread technique of biologically removal of nitrogen compounds is based on the separation of nitrogen compounds from the water using zeolite. By using clinoptilolite, a zeolite with high affinity for nitrogen compounds, it was maintained in normal range the ammonia, nitrite and nitrate in a fish pound. The water recirculated in the controlled system was mechanically filtered and passed through the zeolite column. Clinoptilolite zeolite is an aluminosilicate from the microporous family solids which act as molecular sieve. The experiments were performed in the Laboratory of Fisheries and Aquaculture, Faculty of Animal Science, University of Agronomic Science an...

In 2016, the global aquaculture was 46.82%of total fish production, which means 80 million tonnes... more In 2016, the global aquaculture was 46.82%of total fish production, which means 80 million tonnes of 170.9 million tonnes. Latest researches highlighted that using the natural zeolites in aquaculture in order to maximize the use of resources (water, food, species) and to ensure the lowest negative impact on the environmentwas the most viable solution. The studies on zeolites use, clinoptilolitein particular, were focused on their use as feed additives (up to 2.5% concentration) and also as water quality improvers; this is mainly due to their ability to remove ammonia, its compounds and heavy metals, to reduce water hardness and to consequently prevent diseases and decrease the losses on fish population. A practical and efficient use of natural zeolites in aquaculture will determine increased economic efficiency.

Journal of Optoelectronics and Advanced Materials, 2005

The sintering-sublimation technics was conceived for increasing the reliability of the photocondu... more The sintering-sublimation technics was conceived for increasing the reliability of the photoconductive devices, by decreasing the concentration of mobiles donors, which are utilised for photoconductive material sensibilisation. The technics combines three different technics: the vapor phase deposition; the vacuum vaporising; the ceramic sinterisation. This special technics gives stoichiometric layers. The technics avoids dissociation (the flash sublimation technic), sublimates the compounds from two different sources, on heated support, or sublimates the compound, with Cd excess. It was investigated, by mass spectrometry and optical absorption studies, the presence, in gaseous state, of the A I I B V I molecules. The condensation on the substrate of the vapors is difficult because the Cd, Zn and Hg elements have difficulties in the condensation process. The Frenkel model, of the condensation, can be successfully used for describing the process. This model uses the observations conce...

Ceramics International, 2018

Articole în reviste din RM-4. Publicaţii la conferinţe din RM-18. Publicaţii peste hotare-1. 2018... more Articole în reviste din RM-4. Publicaţii la conferinţe din RM-18. Publicaţii peste hotare-1. 2018-3 Bismuth and lead oxides codoped boron phosphate glasses for Faraday rotators

Journal of Non-Crystalline Solids, 2017

Bi 3+ , Pb 2+ and Bi 3+-Pb 2+-containing aluminophosphate glasses were obtained by unconventional... more Bi 3+ , Pb 2+ and Bi 3+-Pb 2+-containing aluminophosphate glasses were obtained by unconventional wet method, the molar formula of the glasses being: i) 58LiPO 3 , 29Al(PO 3) 3 , 10Ba(PO 3) 2 , 3Bi 2 O 3 ; ii) 58LiPO 3 , 29Al(PO 3) 3 , 10Ba(PO 3) 2 , 3PbO and iii) 6LiPO 3 , 3Al(PO 3) 3 , 1Ba(PO 3) 2 , 10Bi(PO 3) 3 , 80Pb(PO 3) 2. The glass samples were investigated to determine the density, the thermal expansion coefficients and the chemical stability. The magnetic measurements for Bi and Pb-single doped glasses revealed a diamagnetic behavior and those of Bi-Pb-containing glass disclosed a diamagnetic behavior superposed a small paramagnetic contribution, observed in low magnetic fields that can be attributed to the impurities presented in the matrix. The Verdet constant for the analyzed glasses appeared to have positive values proving a diamagnetic behavior of the investigated material.

A transparent Eu 3+-doped lithium aluminophosphate glass was prepared by melt-quenching technique... more A transparent Eu 3+-doped lithium aluminophosphate glass was prepared by melt-quenching technique. The thermal behavior of the glass was investigated by differential thermal analysis (DTA), the structure was studied by X-ray diffraction (XRD) and the morphology was observed by optical polarization microscopy and scanning electron microscopy (SEM). The activation energy of glass transition and the activation energy of crystallization and Avrami exponent have been evaluated under non-isothermal conditions from the data obtained by DTA at different heating rates. DTA curves exhibited an endothermic peak associated with the glass transition and two exothermic peaks. The mean value calculated for the activation energy of glass transition was 545 kJ mol −1. The activation energy of crystallization was~400 kJ mol −1 for the first exothermic peak and~170 kJ mol −1 for the second peak. The Avrami exponent was~1 for both peaks indicating surface crystallization. XRD results showed that the main crystalline phase, aluminum metaphosphate, Al(PO 3) 3 , and aluminum phosphate, AlPO 4 , were formed together with lithium barium phosphate, Li 3 Ba(PO 3) 7 , during the first exothermic peak and together with barium pyrophosphate, Ba 2 P 2 O 7 , during the second peak. Morphological study of heat-treated glass samples revealed microstructural features that confirmed a surface crystallization process.

Materials Science and Engineering: B, 2013

Abstract The present work investigates alumino-phosphate glasses from Li 2 O–BaO–Al 2 O 3 –La 2 O... more Abstract The present work investigates alumino-phosphate glasses from Li 2 O–BaO–Al 2 O 3 –La 2 O 3 –P 2 O 5 system containing Sm 3+ and Eu 3+ ions, prepared by two different ways: a wet raw materials mixing route followed by evaporation and melt-quenching, and by remelting of shards. The linear thermal expansion coefficient measured by dilatometry is identical for both rare-earth-doped phosphate glasses. Comparatively to undoped phosphate glass the linear thermal expansion coefficient increases with 2 × 10 −7 K −1 when dopants are added. The characteristic temperatures very slowly decrease but can be considered constant with atomic weight, atomic number and f electrons number of the doping ions in the case of T g (vitreous transition temperature) and T sr (high annealing temperature) but slowly increase in the case of T ir (low annealing temperature–strain point) and very slowly increase, being practically constant in the case of T D (dilatometric softening temperature). Comparatively to undoped phosphate glass the characteristic temperatures of Sm and Eu-doped glasses present lower values. The higher values of electrical conductance for both doped glasses, comparatively to usual soda-lime-silicate glass, indicate a slightly reduced stability against water. The viscosity measurements, showed a quasi-linear variation with temperature the mean square deviation ( R 2 ) being ranged between 0.872% and 0.996%. The viscosity of doped glasses comparatively to the undoped one is lower at the same temperature. Thermogravimetric analysis did not show notable mass change for any of doped samples. DSC curves for both rare-earth-doped phosphate glasses, as bulk and powdered samples, showed T g values in the range 435–450 °C. Bulk samples exhibited a very weak exothermic peak at about 685 °C, while powdered samples showed two weak exothermic peaks at about 555 °C and 685 °C due to devitrification of the glasses. Using designed melting and annealing programs, the doped glasses were improved regarding bubbles and cords content and strain elimination.

Ceramics International, 2014

A kinetic analysis under non-isothermal conditions has been performed on europium-doped phosphate... more A kinetic analysis under non-isothermal conditions has been performed on europium-doped phosphate glasses with molar composition 20.42 Li 2 O-10.25 Al 2 O 3-58.49 P 2 O 5-7.23 BaO-1.44 La 2 O 3-2.16 Eu 2 O 3 and particle size o 30 mm, 4 50 mm. Differential scanning calorimetry measurements at four heating rates, from room temperature up to 900 1C using synthetic air have revealed that no significant mass change occurs during the heat treatment, as normally expected for glass samples. The step changes in heat flow signals are associated with the presence of three important effects: the first one, that occurs as a slope corresponds to the glass transition effect (T g) is followed by two exothermic peaks, first of them more pronounced, associated with the first crystallization process (T p1), while, the second one, lower in intensity corresponds to the second crystallization (T p2) process. As expected, all peaks (T g , T p1 and T p2) increase with the increasing of the heating rate. Both the activation energy of crystallization process and the crystallization mechanism were comparatively analyzed by two free-model estimations and using the formal theory of transformations for heterogeneous nucleation.

Journal of Non-Crystalline Solids, 2013

ABSTRACT The work deals with optical and structural properties of aluminophosphate glasses from L... more ABSTRACT The work deals with optical and structural properties of aluminophosphate glasses from Li2O–BaO–Al2O3–La2O3–P2O5 system containing Sm3 + and Eu3 + ions. X-ray fluorescence (XRF) has been used to establish the elemental composition of these materials. The influence of Sm3 + and Eu3 + ions on the optical properties of these glasses has been investigated in relation with their structural characteristics. The optical behavior of these materials has been studied by ultra-violet–visible (UV–Vis) spectroscopy, revealing absorption maxima specific to the doping ions. Structural information via vibration modes was provided by Fourier Transform Infrared (FTIR) absorption spectra evidenced as POP symmetrical and asymmetrical stretching vibration modes, POP bend, PO2− symmetrical and asymmetrical stretching vibration modes, PO stretching vibration mode and POH water absorbance. Raman spectra acquired by 514.5 nm laser excitation disclosed peaks specific to metaphosphate network. Information about the elemental compositional homogeneity of Sm3 + and Eu3 +-containing glasses as well as about the defects of the doped-glasses is revealed by scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). Fluorescence spectroscopy measurements put in evidence important fluorescence peaks found at 596 nm and 643 nm for Sm3 + ions in phosphate matrix and 611 nm and 700 nm in the case of Eu3 +-doped glass.

This study aimed to investigate the effect of preparation conditions on different hydroxyapatite ... more 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 Pb 2+ 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 sh...

Lucrarea studiază o serie de materiale vitroase din sistemul ternar ZnO-TiO 2-SiO 2 obţinute pe c... more Lucrarea studiază o serie de materiale vitroase din sistemul ternar ZnO-TiO 2-SiO 2 obţinute pe cale sol-gel, din precursori organici şi anorganici. Probele obţinute au fost analizate prin tehnici FTIR şi Raman, conducând la informaţii structurale la nivel molecular. Maximele de absorbţie în IR în transformată Fourier sunt identificate şi interpretate potrivit cu datele din literatură. Spectrele Raman, cu excitare laser Ga-As la lungimea de undă de 785 nm, pun în evidenţă modurile de vibraţie caracteristice pentru cei trei componenţi oxidici. The paper studies a series of vitreous materials from the ternary ZnO-TiO2-SiO2 system obtained by sol-gel route from organic and inorganic precursors. The obtained samples have been analysed by FTIR and Raman techniques, leading to structural information at molecular level. The FTIR absorption maxima have been identified and interpreted according to literature data. The Raman spectra using Ga-As laser, at 785 nm, put in evidence the characteri...

UPB Scientific Bulletin, Series B: Chemistry and Materials Science

The paper studies a series of vitreous materials from the ternary ZnO-TiO2-SiO2 system obtained b... more The paper studies a series of vitreous materials from the ternary ZnO-TiO2-SiO2 system obtained by sol-gel route from organic and inorganic precursors. The obtained samples have been analysed by FTIR and Raman techniques, leading to structural information at molecular level. The FTIR absorption maxima have been identified and interpreted according to literature data. The Raman spectra using Ga-As laser, at 785 nm, put in evidence the characteristic vibration modes for the three oxidic components.

ABSTRACT The ceramic composites from the quaternary Al2O 3-SiO2-MgO-ZrO2 system, with the major c... more ABSTRACT The ceramic composites from the quaternary Al2O 3-SiO2-MgO-ZrO2 system, with the major compounds: mullyte, cordyerite, zircone silicate and silica have important applications for the dental technics, because of their interesting thermo-mechanical properties. There can be obtained materials of high purity, good homogeneity, fine precision and also very good thermo-mechanical properties (the thermal expansion coefficient a from 20 to 920 °C between 2.5 and 4 × 10-6 K-1), extremely good chemical stability, without rise related to toxic inclusions in dental materials. Several thermal treatement programs are proposed for the obtaining of the samples from ceramic composite materials of four different compositions and there is determined the influences of thermal history on the properties of the studied samples. The chemical composition influence on the thermo-mechanical properties is also studied, especially for the systems with different proportions of cordyerite.The samples are investigated through the determinations of the physical and chemical properties comprising: density, porosity, water absorbtion, mechanical strenght, thermal expansion coefficient, thermal schock resistance, chemical resistance, X-ray diffraction, Raman and FTIR Spectroscopy, Scanning Electronic Microscopy-SEM.

Springer Proceedings in Energy, 2020

The integral transform technique, merging the Anisimov-Nolte Two Temperature Model with the Catta... more The integral transform technique, merging the Anisimov-Nolte Two Temperature Model with the Cattaneo—Vernotte equation, is used in the present paper. Using the integral transform technique, relatively simple expressions for the electrons and phonon temperatures can be obtained, which can provide great help for the experimentalists especially for laser flash experiment on graphene. The obtained expressions are easy to handle in the software package MATHEMATICA 9.0.

Applied Surface Science, 2018

optical properties of Ce 3+ and Tb 3+doped silico-phosphate sol-gel thin films,

Revista Româna De Materiale, 2010

Journal of Physics D: Applied Physics, 2016

Aluminophosphate glasses from the Li2O-BaO-Al2O3-P2O5 system with the addition of nonmagnetic and... more Aluminophosphate glasses from the Li2O-BaO-Al2O3-P2O5 system with the addition of nonmagnetic and paramagnetic rare earth ions, were prepared using a wet nonconventional method to process the raw materials, followed by a melting–quenching procedure. The glasses obtained were characterized with respect to their magnetic and magneto-optical properties using superconducting quantum interference device magnetometry and spectroscopic ellipsometry. The assumption of a linear dependence of the Verdet constant on the magnetic susceptibility, with a proportionality constant dependent on the type of vitreous matrix and doping ion, is critically discussed. The diamagnetic and paramagnetic contributions to the Faraday rotation were separately analyzed and specific designs for optimal active and passive elements are proposed.