Search results for "MINERALOGY"
showing 10 items of 1516 documents
Enhanced manganese content in Mn-MCM-41 mesoporous silicas
2005
The use of triethanolamine containing complexes of Si and Mn as hydrolytic precursors allows the synthesis of doped mesoporous silicas in which the Mn content can be modulated up to reach a minimum value of the Si/Mn molar ratio of 3. This limit value corresponds to a Mn relative content significantly higher than those reported to date for similar materials (Si/Mn = 6). According to XRD, TEM and porosity data, the mesoporous nature typical of the MCM-41 silicas is retained even for the samples having the highest Mn content.
Crystallization and upconversion luminescence of distorted fluorite nanocrystals in Ba2+ containing oxyfluoride glass ceramics
2016
Abstract In this study novel Er 3+ -doped transparent glass ceramics were prepared from melt-quenched glasses with general composition of Na 2 O-NaF-BaF 2 -YF 3 -Al 2 O 3 -SiO 2 . The phase composition of the annealed glass ceramics strongly depends on the BaF 2 content in glass matrix. Crystallization of β-NaYF 4 , cubic fluorite type, tetragonal nanocrystals and rhombohedral Ba 4 Y 3 F 17 was observed. An introduction of BaF 2 in the glass matrix suppresses the crystallization of β-NaYF 4 , promotes the formation of Ba 2+ containing fluoride phases and reduces the cross-relaxation between Er 3+ ions in fluoride crystals. Small rate of the nonradiative processes and low local symmetry of r…
SINTERING OF LEAD-FREE (K0.5Na0.5)NbO3 BASED SOLID SOLUTION
2009
ABSTRACT In this study lead-free solid solution (K0.5Na0.5)NbO3 was prepared, structure, dielectric parameters of ceramics were investigated. The doping of sintering aids did not affect the crystallographic structure of the ceramics significantly; all ceramic samples had a single-phase perovskite structure. Added elements CdO, ZnO, MnO2, V2O5 effectively decreased the sintering temperature of KNN by 50°–80°C. All sintering aids influenced sinterability, microstructure and dielectric properties of ceramics. Dielectric constant for doped samples increased from 6000 up to 8000; Pr = 15 μC/cm2, Ec = 9 kV/cm, d33 = 110 pC/N, kp = 0.38 and Qm = 190 for MnO2 doped samples.
Electron-microscopy studies of pure and doped electrooptic PLZT ceramics
1992
Abstract Data on chemical composition and spatial fluctuations thereof as well as fracture mode behaviour of pure and doped PLZT ceramics have been obtained.
Effects of Pressure, Thermal Treatment, and O2 Loading in MCM41, MSU-H, and MSU-F Mesoporous Silica Systems Probed by Raman Spectroscopy
2015
We present a Raman study of the effects induced by pressure, thermal treatments, and O2 loading in MCM41, MSU-H, and MSU-F representative mesoporous silica. We compared the starting powders with the mechanically pressed tablets produced applying pressures of ∼0.2 and ∼0.45 GPa. The spectra of the three untreated tablets evidence that the main value of the Si-O-Si angle decreases and that in the MCM41 and the MSU-H Si-O-Si hydrolysis occurs, whereas such a process is absent or much less efficient in the MSU-F. Despite their different networks, the three powders tend to crystallize in cristobalite when treatments are at 1000 °C. The MCM41 and MSU-H tablets exhibit behavior similar to their st…
Contributions regarding chemical composition variation in ultrasonic field overlaying welding
2016
Paper presents a new reconditioning method based on ultrasonic field and analyses the modificated structure composition in three zone: filler material, thermal influenced zone, and base material. Also, chemical composition variation as a result of ultrasonic wave influence is studied besides the ultrasonic wave influence on dilution process.
Hydrothermal growth of ZnO nanostructures in supercritical domain: Effect of the metal salt concentration (Zn(NO3)2) in alkali medium (KOH)
2015
Abstract The metal salt concentration effect on the size and morphology of ZnO NPs was highlighted through its synthesis thanks to a continuous one-step method at 401 ± 15 °C and 306 ± 8 bar. Experiments were performed from Zn(NO3)2 and KOH as reactants in concentration ranges of 10–480 mM and 40–1920 mM, respectively. A constant [KOH]/[Zn(NO3)2] ratio of 4 was fixed in order to maintain a constant pH value between 12.5 and 13.0. The as-prepared NPs were characterized by X-ray diffraction and (high-resolution) transmission electron microscopy. Based on Louer's method, ZnO crystal exhibiting a hexagonal structure was considered as cylinder with a diameter D and a height H. The D/H parameter …
Mechanical activation conditions of the Fe2O3 and V2O3 mixture powders in order to obtain a nanometric vanadium spinel ferrite
1999
Abstract Co-milling of iron and vanadium oxides allows to obtain an intimate oxides mixture at a nanoscale, similar to a coprecipitate elaborated by soft chemistry. Reduction of such a mixture in the same temperature and oxygen partial pressure conditions (500°C and 10−25 Pa) as the soft chemistry products leads to a nanometric vanadium ferrite with the only spinel phase. The characterization of the powders is achieved by X-ray diffraction (XRD), scanning electron microscopy, infrared (IR) spectrometry, thermogravimetry and calorimetry. Homogeneity of grain size and chemical composition is reached if the initial oxides have similar grain size.
Hysteresis in nitrogen sorption and mercury porosimetry on mesoporous model adsorbents made of aggregated monodisperse silica spheres
1989
Abstract An elucidation of the hysteresis phenomena in nitrogen sorption (NS) and mercury porosimetry (MP) on porous aggregates of non-porous silica spheres of particle diameter 90–1000 nm is presented. First, it is demonstrated that highly ordered and dense aggregates of a porosity of 26–30% are formed by gravity settling and centrifugation. A hexagonal and cubic close-packed structure within the layers and a vertical stacking between the layers were observed. Minor deteriorations were seen between the ordered domains. Second, the pore size distribution (PSD) curves calculated from the adsorption branch of the nitrogen isotherms by means of the Cohan equation and from the desorption branch…
Biocalcite, a multifunctional inorganic polymer: Building block for calcareous sponge spicules and bioseed for the synthesis of calcium phosphate-bas…
2014
Calcium carbonate is the material that builds up the spicules of the calcareous sponges. Recent results revealed that the calcium carbonate/biocalcite-based spicular skeleton of these animals is formed through an enzymatic mechanism, such as the skeleton of the siliceous sponges, evolutionarily the oldest animals that consist of biosilica. The enzyme that mediates the calcium carbonate deposition has been identified as a carbonic anhydrase (CA) and has been cloned from the calcareous sponge species Sycon raphanus. Calcium carbonate deposits are also found in vertebrate bones besides the main constituent, calcium phosphate/hydroxyapatite (HA). Evidence has been presented that during the init…