română ADRIANA RUSU, LUMINIȚA PREDOANĂ, SILVIU PREDA, JEANINA PANDELE CUSU, SIMONA PETRESCU, MARIA ZAHARESCU
Abstract
The Er3+ doped silica–titania or silica-titaniaalumina nanopowders were prepared by sol-gel method that represents one of the most flexible and convenient way to prepare oxide films and nanopowders. The selected molar compositions were un-doped and 0.5%Er2O3 doped 90%SiO2-10%TiO2 and 85%SiO2-10%TiO2-5%Al2O3 systems. Similar compositions were previously used for obtaining films for wave guides applications but the mechanism of the phase formation by thermal treatment of the corresponding gels was not previously approached. The gels obtained by gelation of the solutions were analyzed by thermogravimetric and thermodifferential analysis (DTA/TGA) in order to determine their thermal behavior and by IR spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) to evaluate their structure and morphology. Based on the results obtained, the gels were thermally treated at 500oC and 900oC. The thermally treated powders were characterized by SEM, FT-IR, X-ray diffraction (XRD) and photoluminescence (PL). The significant influence of the Er3+ on the phase formation was established in both studied systems.
Keywords
sol-gel method, erbium, nanopowders, phase formation
TULAY HURMA , SABIHA AKSAY
Abstract
Iron sulphide nanocrystalline (FeS NCs) may have significant potential for applications in many areas. Ultrasonic spray pyrolysis (USP) method is used to deposit mackinawite FeS NCs film on glass substrate at 335 oC in this study. The film was characterized by vibrational (FTIR and Raman) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis spectra. The observed diffraction peaks at 2θ angles 28.12° and 50.45° correspond to the lattice planes (103) and (112) respectively. The crystallite size was calculated to be around 10 nm by using the Scherrer equation with the peak corresponding to the (112) plane. Raman spectrum revealed four peaks placed in the region of 200-750 cm-1 due to mackinawite FeS phase. FTIR spectrum revealed two peaks at 649 cm−1 and 827 cm−1 that are attributed to stretching frequency of FeS. Optical band gap of the FeS film was determined to be 2.52 eV. Refractive index, extinction coefficient and optical conductivity of this film were determined using transmittance and reflectance spectra.
Keywords
FeS film; Mackinawite; XRD; Raman; FTIR; Optical properties
LIGIA TODAN , MARIANA VOICESCU, DANA C. CULIȚĂ, SIMONA PETRESCU, MARIA MAGANU, CRINU CIUCULESCU
Abstract
Sol-gel obtained silica and organo silica particles, doped with rhodamine B (Rh B), with potential applications as sensing platforms for fluorescent pH probes were obtained. The silica matrices were generated by sol-gel method from different SiO2 sources and using different routes: the aqueous one with colloidal silica as precursor and the alkoxide one starting with tetraethoxysilane (TEOS) as such and with different organic functionalities. The product was characterized from structural and compositional point of view (FTIR, UV-VIS, SEM, BET surface area and porosity). The leaching of the dye from the matrices was detected by GC-MS. The fluorescence properties and variation with pH were determined. Structural interconversions of the dye take place as a function of the matrices and pH which influence the maximum absorption and emission wavelength of RhB. The presence of organic substituents in TEOS generates a quenching of the RhB fluorescence.
Keywords
silica/organosilica particles, sol-gel, rhodamine B, fluorescent pH probes
T. K. MANDAL , S. P. K. MALHOTRA , R. K. SINGHA
Abstract
Photocatalytic degradation of methylene blue was studied using ZnO nanopowders prepared through a green synthesis process. An aqueous solution of methylene blue was investigated in an open vessel equipped with sun light using ZnO nanopowders, as catalyst, with a concentration of 7.815 × 10-6 M. ZnO nanomaterials, prepared through a green synthesis method, was characterized with XRD, FTIR, SEM, EDX and BET measurements. The photodegradation of methylene blue in terms of concentration change with respect to different time intervals was studied with the UV-vis spectroscopy. The mechanism for this photocatalytic degradation process has also been presumed.
Keywords
ZnO nanopowders, Green synthesis, XRD study, FTIR study, Photocatalytic degradation, UV-vis study
JIAN SUN, YU-HOU WU, PENG ZHOU, SONG-HUA LI, LI-XIU ZHANG, KE ZHANG
Abstract
Using diamond wheels to grindingengineering ceramics is the most common method. Due to the large grinding resistance there is often a surface damage such as cracks on the workpiece. The crack depthmodel of grinding surface on ceramics is established based on indentation fracture mechanics in this paper and the extendingprocess of the crack is simulated by Two-Dimensional discrete element simulation of UDEC. Through simulation results the extending mechanism of cracks in silicon nitride ceramics is discovered. Moreover, the planegrinding experiment of silicon nitride ceramics by diamond wheel is carried out and the extending of its cracks is observed on the surface. The theoreticalresults are validated by grinding experiment. Cracks appear on the surface of the ceramics under the action of singlediamondgrain,theleadcrack extends along the interior of the ceramic in the form of longitudinal cracks. In the lead crack propagation path, a small amount of oblique cracks will appear in other directions. The failure zone consists of tensile failure element and shear failure element. The shear failure is main failure form for the failure zone. When the grain stops, the crack ceases to expand into the interior of the ceramic, the crack failure elements in the zone are all shear failure elements.Because of the grinding and tensile failure of the grinding wheel, the crack extends along the arc and the wheel direction of rotation in the contact area between the wheel and the ceramic. When the penetration depth increases, the crack form is gradually transformed from the tensile failure element to the shear failure element. The number of broken parts in the cut is obviously more than that of the cutting part. Grinding damage of engineering ceramics could be forecasted and controlled by this simulation. So, grinding process could be optimized, and grinding efficiency and quality could be improved.
Keywords
diamond wheel, silicon nitride, surface damage, cracks, UDEC
AYDIN RUSEN
Abstract
High temperature crystal chemistry and thermal behavior of the boron minerals bear special attraction, owing to the increase in their application areas requiring elevated temperature. Colemanite 2CaO·3B2O3·5H2O) is one of the most commonly found and used compound among the boron minerals. In this study, therefore, thermal and mineralogical characterization of the colemanite was performed by X-ray Diffractometer (XRD) and Thermal Gravimetric Analysis (TG-DTA). Also, mineralogical changes in crystal structure were measured and recorded during heating from room temperature up to its melting temperature for each 50°C by using High Temperature XRD device. By this way, structural changes in the colemanite up to melting point were determined with increasing temperature for the first time. Results indicate that the thermal decomposition of colemanite has revealed a multi stage internal process; i) moisture removal, ii) dehydration- dehydroxylation, iii) amorphization of the crystal structure, iv) recrystallization of the amorphous solid (gradual reconstitutions).
Keywords
Colemanite, Thermal decomposition, HTXRD, TG-DTA
ZENO GHIZDĂVEȚ, DOREL RADU
Abstract
Six glasses belonging to the Na2O – Al2O3 – B2O3 oxide system with the molar composition (35-x)Na2O·xAl2O3·65B2O3 were synthesized. Refractive index, n, and density, d, were measured on these glasses; the experimental values were used to compute a series of optical properties: transmission, T, molar refractivity, Rm, mass refractivity, RM, and specific refractivity, r.
Correlations between optical properties and chemical composition, glass features at the first structural level (molar volume, Vm) and compactness, C, were drawn.
It was concluded that glass compactness (a feature describing the atomic level – sub-nanoscale) is an influential parameter on optical properties of the glasses, which manifest on a macroscopic scale.
Keywords
glass, optical properties, structural compactness, correlations
A.MELINESCU, M. EFTIMIE, A. NICOARĂ, R. TRUȘCĂ, M. PREDA
Abstract
Geopolymer technology can be used to obtain precursors for the synthesis of ceramic materials, being a much simpler alternative to conventional processes. In this paper we experimented the synthesis of nepheline-based material from calcined kaolin and NaOH solutions with 8M and 12M, respectively. To increase the SiO2 concentration, the Govora fly ash was used. Chemical reactions that take place at low temperature and high temperature heat treatment are studied. It was found that by reaction at 800°C the sodium ortho-silicate was formed and at 800°C this compound was consumed for nepheline formation and, in the same time, Na2O·SiO2 appeared. When introducing fly ash, the main crystalline phases are α-quartz, nepheline and the anorthite, the latter compound coming from the ash. Sodium metasilicate is no longer found in fly ash samples because it has reacted with the vitreous phase of ash leading to the formation of nepheline.
Keywords
nepheline, geopolymer technology, XRD, SEM
LIGIA TODAN, DANIELA C. CULIȚĂ, DOREL CRIŞAN, NICOLAE DRĂGAN, JEANINA PANDELE-CUŞU, FLORICA PAPA
Abstract
Mono- and bicomponent coordination compounds of Mg-Zr with tartaric acid were synthesized in an aqueous solution, at two different Mg/Zr molar ratios. Part of the obtained amorphous precursors were thermally treated at 6500C, the other part was calcined at 10000C, forming thus MgO-ZrO2 powders. The structure and properties of the precursors and of the oxide powders were determined by thermal analysis, FTIR, XRD, BET method for surface area and pore volume, CO2 adsorption. The influence of the thermal treatment temperature on the powders characteristics was considered. The coordination modes of the tartaric carboxilic groups in Mg, respectively or/and Zr-containing precursors is dissimilar and the dehydration and crystallization processes in the binary powders differ too. High-temperature ZrO2 polymorphs stabilized at low temperature by including the Mg2+ in the lattice, decrease in content with the raise of temperature, partialy turning into monoclinic zirconia.The specific surface area and porosity as well as the CO2 adsorption properties of the samples treated at 6500C are significantly higher than the ones of the powders calcined at 10000C. The CO2 adsoption efficiency of the binary oxides is lower than the one of MgO but higher when compared to ZrO2, one of the samples showing the best performance, although the Mg/Zr molar ratio in the binary calcined oxides is about the same. The oxide powders were stable at recycling.
Keywords
MgO-ZrO2 oxide powders, tartaric acid complexes, solution-gel, thermal analysis, CO2 adsorption
COSMIN VANCEA, ROMUL MARIUS JURCA, MARIUS GHEJU, GIANNIN MOȘOARCĂ
Abstract
The present paper investigates another alternative to immobilize the exhausted reactive mixtures resulted from the removal of Cr(VI) with Fe0 in continuous-flow system (column experiments), in glass based stoneware matrix. This study completes our previous investigations focused on vitreous matrix designed to retain the exhausted reactive mixtures [1]. In order to increase the ecological impact of the proposed solution, two types of recycled waste glasses were used: window panes and cathode ray tubes (CRT). The exhausted reactive mixtures and the two waste glasses were mixed together with the Bojidar kaolin and then pressed into cylinders having the diameter and height around 35 mm. The heat treatment was optimized considering the economically advantageous conditions at 1000°C for 90 minutes. The apparent porosity, used as compactness index for the obtained samples, range from 2.20% to 5.05% depending on the glass waste type and the amount of sand contained in the exhausted reactive mixture. The main crystalline phases confirmed by RX diffraction are wollastonite, tridymite, diopside, cristobalite and hematite. The chemical stability of the studied glass based stoneware, measured using the samples’ dissolution rate after 28 days in mediums having different pH range from 0.127 to 0.778 g/h depending on the samples’ porosity and type of chemical aggression. The chromium and iron ions leachability were determined and American Extraction Procedure Toxicity Test respectively. The amounts of both investigated ions removed from the structure by the chemical attack are very low, between 0-0.238% of the total chromium and between 0-0.258% of the total iron brought by the exhausted reactive mixtures. The obtained results confirm the viability of the suggested solution for immobilizing chromium contained in the exhausted reactive mixtures together with common waste glasses and kaolin as glass based stoneware having high chemical stability with multiple economic advantages.
Keywords
glass based stoneware, waste glasses, glass recycling, chromium wastes
A.M. KHWAILEH, A.A. AL-SHORMAN, W. A. AL SEKHANEH, J.C. ROSE
Abstract
Hydroxyapatite in tooth enamel uptakes several elements while in burial environment (diagenesis), which alters the chemical composition and consequently the life history reconstruction. Fourier Transform Infrared Spectroscopy (FTIR) is used in this study to evaluate the diagenesis of hydroxyapatite by measuring the peaks of phosphate and francolite vibrations. The study comprises 28 teeth from the sites of Ya’amun (MBA) and Yasieleh (B) in northern Jordan, dated to the Middle Bronze Age (MBA) and the Byzantine (B) period respectively. The FTIR results showed that all of samples contained calcite and fluorine, and thus, point to soil-tooth exchange after decomposition. The average values of Crystallinity Index in the tombs of Ya’amun (MBA) and Yasieleh(B) signify minimal if any diagenesis, significance level of the test is α = 0.05. The analysis of variance on the francolite absorbance values shows that the mean value of francolite absorbance among the two sites is different and consequently varied tomb use chronologies, which was shorter at Yasieleh(B). The results conclude that the short deposition time at the site of Yasieleh (B) is a clear indication of massive deaths caused probably by an epidemic disease.
Keywords
Hydroxyapatite, diagenesis, FTIR, Middle Bronze Age, Byzantine period, Crystallinity Index
CRISTINA BUSUIOC, IZABELA CONSTANTINOIU, MONICA ENCULESCU, MIHAELA BEREGOI, SORIN - ION JINGA
Abstract
Ceramic thin films belonging to SiO2–P2O5–CaO–MgO–ZnO–CaF2 system were obtained by combining the sol-gel approach with the spin coating technique. Titanium plates were employed as substrates. The deposited coatings were characterized in terms of composition, structure and morphology with the help of the following methods: X-ray diffraction, Fourier - transform infrared spectroscopy and scanning electron microscopy coupled with energy - dispersive X-ray spectroscopy. In order to assess the bioactivity of a potential metallic implant covered with such layers, the samples were immersed in simulated body fluid for 14 days and their surface was investigated. The results showed that the thin films calcined at a lower temperature have a better biological response due to the vitroceramic nature.
Keywords
Ceramics; Thin films; Sol-gel; Spin coating; Medical implants
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Year
2018
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Issue
48 (4)
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Pages
401-406
DANIELA VRÎNCEANU, BOGDAN BĂNICĂ, CĂTĂLIN FLORIN CÎRSTOIU, RALUCA PAPACOCEA, TOMA PAPACOCEA
Abstract
The orbital floor has several anatomical features which are essential during reconstruction. The task of reconstructing the orbital floor wall is difficult and usually exist an important discrepancy between the shape of the implant to be inserted and the anatomical three dimensional shape of the orbital wall. We present the case of a 25 years old woman, with a left orbital fracture after domestic assault; for the reconstruction of the defect from left orbital floor, we used a Matrix Orbital plate, with minima adjustments to the length of the plate, not to the predesigned contour. The follow up extended 6 months after the titanium implant with excellent biocompatibility. The Matrix Midface Preformed orbital plate has the advantage of insertion without contouring, except bending and trimming of the fixation holes, thus is more independent on experience of the surgeon.
Keywords
titanium, implants, orbital floor, fracture, reconstruction
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Year
2018
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Issue
48 (4)
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Pages
407-411
ENIKÖ VOLCEANOV, CRISTINA GEORGIANA POPA, ADRIAN VOLCEANOV, SORIN CIUCĂ
Abstract
Alumina and zirconia-based ceramics present reduced wear rates and excellent long-term biocompatibility, which can increase the longevity of the implants. In this study, the effects of simultaneous admixture of CaO and MgO on the crystalline phases, crystallite sizes and sintering properties of coprecipitated Al2O3-ZrO2 powder are investigated using complex thermal analysis (TG, DTA, DTG), X-ray diffractometry (XRD), scanning electron microscopy (SEM) coupled with EDS.
Correlations among composition - microstructure and properties of the coprecipitated Al2O3-ZrO2 powder after sintering at 1050 °C, 1350 °C, and 1500 °C with 2 hours soaking time at each temperature were performed. The results showed that development of tetragonal and cubic phase of zirconia stabilized with Ca2+ and Mg2+ was effective at 1350°C and 1500 °C respectively. In dental applications, dental materials are soaked in saliva, which contains a large number of ions which in turn may accelerate the corrosion of materials. In such context, the chemical stability in modified Fusayama-Meyer type artificial saliva of sintered alumina – zirconia ceramics was also investigated. The ceramic samples sintered at 1500 °C show a better chemical stability, as the pH variation is lower when using a starting immersion solution with pH = 7.4. However, the variation of pH after immersion in artificial saliva is obvious after 216-288 hours due to the ionic transport between ceramic and the solution, even after sintering at 1500 °C
Keywords
Zirconia Thoughned Alumina, bioceramic, chemical stability, artificial saliva
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Year
2018
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Issue
48 (4)
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Pages
412-421
DALILA MOUDIR, NOUR EL HAYET KAMEL, ABD EL BAKI BENMOUNAH, SOUMIA IKHADDALENE, YASMINA MOUHEB, FAIROUZ AOUCHICHE
Abstract
An aluminosilicate nuclear glass storage was synthesized by a double melting method and characterized using both X-ray diffraction and scanning electron microscopy (SEM) techniques. Physical parameters like density and molar volume were measured. Fourier Transform Infrared Spectroscopy (FTIR) confirms the glass chemical composition. Differential thermal analysis (DTA) was used to determine the glass-transition temperature (Tg). Samples microstructure was also characterized by Vickers microhardness, young’s modulus and electrical resistivity.
Keywords
nuclear glass, storage, SEM, DTA, FTIR
M.VASIĆ, Z. RADOJEVIĆ
Abstract
The description of the moisture transfer in porous media during drying was the subject of many scientific studies. The unique drying theory was developed five years ago and has recently won a general recognition in the scientific community. This paper is providing the update of the recently reported method for setting up the optimal drying parameters inside the heavy clay dryer. The main goal of this paper was to find a way how to reduce the number of experiments without affecting the quality of the previously proposed calculation method. The critical drying rate, as well as the drying behavior can be easily registered inside the laboratory recirculation dryer for any heavy clay product. These data provides a clear perception of how far the real drying curve, used in industrial dryer, is away from the shortest possible one. The algorithm of the updated procedure was based on the Box-Wilkinson’s orthogonal multi - factorial experimental design. The updated model outputs were represented as the governing equations which were used to predict the time intervals between any two chosen characteristic points, specified in the unique drying theory, as a function of the drying air parameters. These equations were valid for any value of the drying air parameters taken from the previously established limiting boundary range. The updated procedure was compared with the original one for two predefined drying air parameters sets. Regardless to the fact that in the first case the results were not experimentally obtained they were similar to those which were in the second case experimentally identified. This was additional confirmation that the same quality degree has been maintained in both procedures, despite the fact that the total number of experiments was lower in the upgraded procedure than in the original one.
Keywords
dryer optimization, drying porous media, effective diffusion coefficient, clay tile, software