Petru Pascuta

Structural properties of molybdenum-lead-borate glasses.

Glasses and glass ceramics in the system xMoO₃·(100 - x)[3B₂O₃·PbO] with 0 ≤ x ≤ 30 mol% have been prepared from melt quenching method and characterized by means of X-ray diffraction, FTIR, UV-VIS and EPR spectroscopy. We have examined and analyzed the effects of systematic molybdenum ions intercalation on lead-borate glasses and glass ceramics with interesting results. The observations present in these mechanisms show the lead ions bonded ionic have a strong affinity towards [BO₃] units containing non-bridging oxygens and [MoO₄]²⁻ molybdate units. The pronounced affinity towards molybdate anions yields the formation of the PbMoO₄ crystalline phase. Then, the excess of oxygen can be supported into the glass network by the formation of [MoO₆] and [Mo₂O₇] structural units. Pb²(+) ions with 6s² configuration show strong absorption in the ultraviolet due to parity allowed s²-sp transition and yield an absorption band centered at about 310 nm. The changes in the features of the absorption bands centered at about 310 nm can be explained as a consequence of the appearance of additional absorption shoulder due to photoinduced color centers in the glass such as the formation of borate-molybdate and lead-molybdate paramagnetic defect centers in the glasses. The concentration of molybdenum ions influences the shape and width of the EPR signals located at g ∼ 1.86, 1.91 and 5.19. The microenvironment of molybdenum ions in glasses is expected to have mainly sixfold coordination. However, there is a possibility of reduction of a part of molybdenum ions from the Mo⁶(+) to the Mo⁵(+) and Mo⁴(+) to the Mo³(+) states.

Preparation and structural characterization of some Fe2O3-B2O3-ZnO glasses and glass ceramics

X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy have been employed to investigate the (Fe2O3)x?(B2O3)(60-x)?(ZnO)40 samples, with 0 ? x ? 20 mol%. The samples have been prepared by melting at 1100 ?C for 10 minutes followed by rapid cooling at room temperature. The structure of samples was analyzed by means of XRD. XRD pattern show that the sample without iron ions and the samples contained 3 and 5 mol% were glasses. For samples contain 10, 15 and 20 mol% Fe2O3 it obtains glass ceramics. These glass ceramics contains a unique crystalline phase, zinc ferrite (ZnFe2O4), embedded in an amorphous matrix. FTIR spectroscopy data suggest that for the glass samples the iron ions play the network modifier role. These data show that the glass network consists of BO3 and BO4 structural units. For glass ceramics samples FTIR spectra show characteristic bands of ZnFe2O4.

FTIR spectroscopic study of some lead germanate glasses

The structures of two lead germante glasses – yGeO2(100-y)PbO and xNd2O3(100-x)[GeO2PbO] – are investigated by the Fourier transform infrared (FTIR) spectroscopy. The structural role of germanium, lead and neodymium ions is discussed. The presence of GeO4, GeO6 and PbO4 structural units was evidenced in the studied glass networks. In the case of the xNd2O3(100-x)[GeO2PbO] glasses it was shown that the ratio of the mentioned structural units depends on the Nd2O3 content of the samples. Therefore Nd2O3 play the network modifier role in studied glasses.

Stability of Phases in Ball-Milled Zinc Ferrite/Iron Composite Produced by Spark Plasma Sintering

Three milling modes have been used for the synthesis of zinc ferrite/iron composite/nanocomposite powders. A partial or total reaction between zinc ferrite and iron (followed by the formation of zinc oxide and iron oxide) appears in the composite compact during Spark Plasma Sintering (SPS), for sintering temperature range of 400 to 550°C. Low sintering temperature led to a good preservation of zinc ferrite and iron when a composite powder obtained in low energetic milling mode was used. The milled powders and sintered compacts were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy, and energy dispersive X-ray spectrometry (EDX). The milling mode and sintering parameters influence on the stability of phases of composite/nanocomposites powder and compacts were investigated and discussed.

Structural and physical characteristics of xGd2O3(100-x)[Bi2O3 B2O3] glasses

A study on the xGd2O3(100-x)[Bi2O3 B2O3] glass system where 0 < x ≤ 30 mol% was carried by using X-ray diffraction, FTIR spectroscopy and density measurements. The relationships between composition and properties were demonstrated. The results indicate that Gd2O3 play a network modifier role and stabilizes the structure of the vitreous matrix.

Structural, Spectroscopic, and Magnetic Characterization of Cobalt(III) Oxide–Disodium Tetraborate Glasses

ABSTRACT Co2O3–Na2B4O7 glasses were prepared by melt-quenching and characterized by X-ray diffraction, density measurements, infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy, and magnetic measurements. Results show that addition and successive increase of cobalt oxide determines important properties of the glasses. An increase in cobalt oxide concentration converted BO4 structural units into BO3 units and led to intensification of magnetic interactions between cobalt ions. The presence of cobalt(III) in glasses was confirmed by optical spectroscopy and magnetic data.

Structural and Morphological Evaluation of 25% vol. Ni/Al2O3 Nanocomposite Powders Produced by Mechanical Milling

The evolution of the Al2O3/Ni (25% vol. Ni) composite powders, during the milling and the stability of the composite phases were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX). SEM images show a high level of homogenization of the Ni and Al2O3 phases for milling times larger than 120 minutes. The X-ray study indicates no reaction between the two phases. The crystallite grain size decreases with the milling time for both phases.

Influence of Milling Time on the Homogeneity of the Al2O3/Ni Composite Powders Obtained by Mechanical Milling

Al2O3/Ni nanocomposite powder was obtained by high-energy mechanical milling starting from a mixture of Al2O3 and Ni commercially powders. The Al2O3+15%vol. Ni mixture was homogenized for 15 minutes in the Turbula-type blender and then was milled in a planetary ball mill (Fritsch, Pulverisette 4) under argon atmosphere up to 120 min. Several milling times were used: 10, 30, 60, 90 and 120 minutes respectively. The evolution of the powders during milling and the stability of the composite phases were investigated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX). The SEM and OM images show a high level of homogenization of the Ni and Al2O3 phases for milling times larger than 90 minutes. The X-ray studies indicate no mixing between the two phases. The crystallite grain size is decreasing with the milling time.

The local structure of gadolinium-borate-tellurate vitroceramics investigated by FTIR and EPR spectroscopy

The present study provides interesting information concerning devitrification behavior of xGd2O3(100-x)[6TeO24B2O3] vitreous system with 0 ≤ x ≤ 30 mol%. The structural changes have been analyzed with increasing rare earth concentration. Two halos characteristic of the amorphous compounds can be observed in XRD diffraction pattern for sample with x ≥ 20 mol% Gd2O3. These changes can be explained only if we admit that the adding of gadolinium oxide now participate in the network as [GdOn] structural units yielding a change from the continuous borate-tellurate network to the continuous gadolinium-borate-tellurate network with interconnected through Gd-O-B and Gd-O-Te bridges. The EPR spectra of the studied glass ceramics reveal an increase of the content of Gd+3 ions in network former and modifier positions. Therefore, Gd+3 ions will coordinate more with non-bridging oxygens leading the decreased of the number of individual Gd+3 ions.

STRUCTURAL AND MAGNETIC BEHAVIOR OF STRONTIUM-BORATE GLASSES DOPED WITH IRON IONS

Glasses of the xFe2O3 · (100 - x)[2B2O3 · SrO] system (0 ≤ x ≤ 40 mol%) were prepared and studied by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. EPR investigations indicated the compositional domains favorable to the presence of isolated iron ions or to those magnetically clustered. The magnetic susceptibility data evidenced the presence of both Fe3+ and Fe2+ ions, with their relative content depending on the Fe2O3 concentration. Dipolar and superexchange interactions involving iron ions were revealed depending on the iron content of the sample.