română KODURI RAMAM, K.CHANDRAMOULI
Abstract
A unique binary structured perovskite (Lead Lanthanum Zirconium Titante: PLZT) and tungsten bronze (Lead Barium Bismuth Niobate: PBBiN) piezoelectric material with Ordinary Portland Cement: OPC composites were fabricated by solid state reaction method. The composites were fabricated with ceramic to cement in the ratios of 25:75vol%, 50:50vol% and 75:25vol%, respectively. The X-ray diffraction patterns of these composites confirmed both perovskite and tungsten bronze phases. The scanning electron micrographs indicated homogeneity between ceramic and cement. These composites showed combined characteristics of perovskite and tungsten bronze ceramics with a high dielectric and piezoelectric properties. The dielectric constant (RT) and piezoelectric charge coefficient (d33) were found optimum at 75:25vol% composite which showed promising results that are potential for sensing and actuating in intelligent structures or structural health monitoring applications.
Keywords
A. Solid State Reaction; D. Composite Cement; b. Dielectric properties; b. Piezoelectric properties; Structural Health Monitoring
MIHAI BRATU, IOAN ROPOTĂ, OVIDIU VASILE, OVIDIU DUMITRESCU, MARCELA MUNTEAN
Abstract
The paper aims to introduce innovative systems to absorb and attenuate noise from industry or urban and extra-urban environment, efficient and sustainable, based on composite materials made by recycling solid wastes. The composite materials are obtained by including some materials considered wastes – pellets from plastic bottles, sawdust, ash from thermal plant and sterile municipal waste - in a polymer type organic matrix. Thus are obtained new organic materials which embed non-biodegradable waste, which can affect seriously the environment. The sound absorption capacity of these new composites varies depending on the proportion and nature of the waste used. The absorption coefficient which determines the phonic absorbing capacity of all new obtained materials is calculated for each sample. Samples are made of resin and reinforcement material in different proportions, which are tested to determine the absorption coefficient against frequency, using a device called KUNDT TUBE. Both for material preparation and sampling tests the in force standards are respected.
Keywords
Cuvinte cheie (engleza)
GEORGETA VOICU, CRISTINA DANIELA GHIŢULICĂ, ELENA DINU, ECATERINA ANDRONESCU
Abstract
In the sol-gel synthesis of dicalcium silicate (Ca2SiO4 – C2S) the calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and trietoxysilane ( C6H16O3Si - TEOS) were used as precursors. The C2S was obtained at 800-1100°C.
Thermal analysis methods (DTA/TG), X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX) were used to investigate the formation of dicalcium silicate.
The in-vitro behavior was also investigated by soaking of the dicalcium silicate powder in simulated body fluid (SBF) for 7 days. Our results indicated that dicalcium silicate formed in SBF hydrosilicates as principal mineralogical phases and bound a small proportion of the phosphor from liquid as phosphate phases.
Keywords
dicalcium silicate; sol-gel synthesis; in-vitro behavior
RALUCA STAN, CRISTINA OTT, GEORGETA VOICU, ADRIANA LUNGU, SORIN I. ROŞCA
Abstract
We report the synthesis of Cr-doped silica with different morphologies by sol-gel polymerization of tetraethoxysilicate in the presence of D-sorbitol derived organogelators (1,3:2,4-bis-O-benzylidene-D-sorbitol, DBS and its p-nitro and p-methoxy derivatives) and hexadecyltrimethylamonium bromide with S-(+)-1-phenylethylamine-tricarbonyl-chromium, acting both as chiral catalyst and source of chromium, for a 10 wt% Cr/SiO2 loading. Two different types of morphologies were observed: silica tubes with 300-500nm diameter and 10-15μm length for the nitro-substituted template and “necklace” type agglomerated silica granules for the other templates. EDX and XPS analyses revealed a uniform distribution of Cr ions on silica matrix consisting of 80% Cr3+ and 20% Cr6+.
Keywords
sol-gel, Cr-doped nanostructured silica, arene-tricarbonyl-chromium complexes, organogelator
Synthesis and characterization of calcia stabilized zirconia nano-powder, obtained by sol-gel method
RODICA ROGOJAN, ECATERIANA ANDRONESCU, IRINA ILIESCU, ROXANA TRUŞCĂ, BOGDAN ŞTEFAN VASILE
Abstract
The purpose of this study is to obtain nanometric zirconia powders, by sol-gel method, using precursors of different chemical nature - inorganic (ZrCl4) and organic (C12H28O4Zr). The obtained gels were dried at 100oC, and then heat treated to 1000oC for 2 hours. In order to identify obtained phases and their degree of crystallinity, powders were analyzed using X-ray diffraction. Analyses of scanning electron microscopy and transmission electron microscopy have been used to investigate the morphology and size of the obtained powders. Experimental analyzes show that, from different precursors (organic and inorganic), nanometric powders of partially stabilized zirconia with CaO are obtained.
Keywords
zirconia nanoparticles, sol-gel method, organic precursors, inorganic precursors
ŞTEFANIA STOLERIU, ECATERIAN ANDRONESCU, ALEXANDRA LUCIA CARABĂŢ, BOGDAN ŞTEFAN VASILE
Abstract
The paper’s aim was to prepare and characterize ceramic powders of fully stabilized zirconia (with 8 mol% yttria), and alumina, obtained through co-precipitation starting from the corresponding chlorides. Co-precipitation was taken using water or ethanol as a solvent and considering the pH influence (7.5, 10.5 and 12.5 obtained by using ammonia solution) upon precipitation was analyzed. The obtained powders were dried at 80 °C for 24 h and afterwards calcinated at 350°C for 2 hours.
The powders were evaluated through thermal analysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
The XRD results show that 8YSZ calcinated powders is a tetragonal ZrO2 and, concerning alumina powder, besides -Al2O3, -Al2O3. The TEM examination shows that the tetragonal ZrO2 has a spherical like morphology with a size ranging from 5 nm to 12 nm. Also, it was observed that the best condition for nanopowders obtaining was using as solvent water and a pH value of 12.5.
Keywords
zirconia, alumina, nanopowders, (co-)precipitation
RĂZVAN STATE, ADRIAN VOLCEANOV, ENIKÖ VOLCEANOV, ŞTEFANIA STOLERIU
Abstract
The structural ceramic materials are important because they are usually lightweight, harder than metals, resistant at higher temperatures and also present an impressive series of mechanical properties, including good mechanical strength in extreme conditions. The alumina based materials and composites are of great importance for ballistic protection. The aim of the present paper is focused on behavior of various alumina types after being sintered in different conditions.
The materials used in present study are α-Al2O3 powder (from 3 different sources) and additions of different rare-earth oxides (La2O3, Y2O3, Nd2O3) [1] in two proportions: 500 ppm and respectively 1000 ppm.
The Al2O3 dense ceramics were obtained by various sintering environments, using both traditional sintering ways at temperatures of 1500 ° C (electric furnace) and 1815° C (gas furnace) and a non-conventional technique (cold plasma sintering).
After sintering the samples were analyzed by X-Ray diffraction and scanning electron microscopy (SEM). Ceramic properties like contraction, absorption, porosity, and relative density were also determined.
The final conclusions highlight o series of interpretations and correlations of the sintering parameters with the properties of the sintered materials.
Keywords
ceramic composites, structural ceramics, cold plasma, alumina ceramics