排序方式: 共有30条查询结果,搜索用时 187 毫秒
1.
Nasser Y. Mostafa Abdallah A. Shaltout Lachezar Radev Hassan M. Hassan 《Central European Journal of Chemistry》2013,11(2):140-150
The present work investigates surface biocompatibility of silicon-substituted calcium phosphate ceramics. Different silicon-substituted calcium phosphate ceramic bodies were prepared from co-precipitated powders by sintering at 1300°C. The in vitro bioactivity of the ceramics was assessed in simulated body fluid (SBF) at 37°C for periods up to 4 weeks. The changes in the surface morphology and composition were determined by scanning electron microscopy (SEM) coupled with electron probe microanalysis and energy dispersive spectrometer (EDX). Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to observe the change in ionic concentration of SBF after removal of the samples. The bioactivity of the ceramics increased with an increasing silicate ion substitution in a systematic way. The surface of ceramics with 2.23% silicon substitution was partially covered with apatite layer after one week, while ceramics with 8.1% silicon substitution were completely covered with apatite in the first week. The porous microstructure of high-concentration Si-substituted ceramics helps the dissolution of surface ions and the leaching process. This allows SBF to reach supersaturation in a short time and accelerate the deposition of apatite layer. 相似文献
2.
Nadezhda Rangelova Lachezar Radev Sanchi Nenkova Isabel M. Miranda Salvado Maria H. Vas Fernandes Michael Herzog 《Central European Journal of Chemistry》2011,9(1):112-118
Methylcellulose (MC) / SiO2 organic / inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized
by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO2. AFM depicts surface roughness which depends on the silica precursor and MC content.
相似文献
3.
The physicochemical and catalytic properties of cobalt- and silicon-substituted AlPO-5 molecular sieves were studied by means of temperature-programmed reduction, temperature-programmed desorption of ammonia and the reaction of toluene disproportionation. 相似文献
4.
S. G. Dinev Ch. I. Radev K. V. Stamenov K. A. Stankov 《Optical and Quantum Electronics》1980,12(3):231-235
The X-ray emission of a laser plasma from metal targets in a 26 kV cm–1 electric field is investigated experimentally. A substructure of the X-ray pulse, corresponding to the laser pulse train period is found. The spectrum of the radiation in the range 2–25 keV is measured. 相似文献
5.
The temporal characteristics of the X-ray emission from a laser irradiated Ai target in a 20 kV/cm electric field are measured with electronic detectors. Spatial and spectral distributions of the X-ray radiation are evaluated using a pinhole camera and filter technique. 相似文献
6.
Lachezar Radev Vladimir Hristov Irena Michailova Bisserka Samuneva 《Central European Journal of Chemistry》2009,7(3):322-327
Ceramics, with basic composition based on the CaO-SiO2-P2O5-MgO system with different Ca+ Mg/P+Si molar ratio (R), were prepared via polystep sol-gel technique. The structure of the
obtained ceramic materials has been studied by XRD, FTIR spectroscopy, and SEM. X-ray diffraction showed the presence of akermanite
and HA for the sample with R = 1.68 and Mg substituted β-TCP and silicocarnotite for the sample with R = 2.16, after thermal
treatment at 1200°C/2 h. The obtained results are in good agreement with FTIR. In vitro test for bioactivity in static condition
proved that the carbonate containing hydroxyapatite (CO3HA) can be formed on the surface of the synthesized samples. CO3HA consisted of both A- and B-type CO32− ions. SEM micrographs depicted different forms of HA particles, precipitated on the surface after soaking in 1.5 simulated
body fluid (SBF).
相似文献
7.
Lachezar Radev Maria Helena V. Fernandes Isabel Miranda Salvado Daniela Kovacheva 《Central European Journal of Chemistry》2009,7(4):721-730
In this work we present our experimental results on synthesis, structure evolution and in vitro bioactivity assessment of new gelatin/silicocarnotite hybrid materials. The hybrids were obtained by diluting gelatin (G)
and silicocarnotite (S) ceramic powder with G:S ratios of 75:25 and 25:75 wt.% in hot (40°C) water. The hybrids were characterized
using XRD, FTIR, SEM/EDS and XPS. FTIR depicts that the “red shift” of amide I and COO− could be attributed to the fact that the gelatin prefers to chelate Ca2+ from S. The growth of calcium phosphates on the surface of the hybrids synthesized and then immersed in 1.5 SBF for 3 days
was studied by using of FTIR, XRD and SEM/EDS. According to FTIR results, after an immersion of 3 days, A and B-type CO3HA can be observed on the surface. XRD results indicate the presence of hydroxyapatite with well defined crystallinity. SEM/EDS
of the precipitated layers show the presence of CO3HA and amorphous calcium phosphate on the surface of samples with different G/S content when immersed in 1.5 SBF. XPS of the
G/S hybrid with 25:75 wt.% proved the presence of Ca-deficient hydroxyapatite after an in vitro test for 3 days. 相似文献
8.
P. Kovacheva D. Todorovsky D. Radev N. Minkova 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(3):481-490
The effect of the mechanoactivation on UO3 and U3O8 in agate or stainless steel vessels in air or in toluene is studied. UO2(OH)2 is the main product of UO3·H2O activation in steel vessel in air. The presence of toluene leads to strong amorphization and dispersity increase and, probably,
to the formation of U2O5. The activation of U3O8 leads to its reduction to U3O7 which relative content in the reaction mixture depends on the mechanoactivation conditions. 相似文献
9.
Fabrice Onofri Anne Lenoble Stefan Radev Paul-Henri Guering 《Experiments in fluids》2007,42(4):601-610
We report unsteady experimental results on the stability of fibre diameter in a continuous glass forming process, using two
unique laser systems: a high resolution diffractometer and a backward phase Doppler interferometer. For draw ratios close
to those used in the industry, the glass fibre diameter exhibits small fluctuations, which cannot be considered to be a result
of draw resonance. It is shown that the amplitude of fibre diameter fluctuations decreases with increasing draw ratio, while
the corresponding frequency increases with the temperature of the molten glass. Although the origin of these fluctuations
is still not well understood, it appears that their frequency depends on the characteristics of the molten glass jet. 相似文献
10.
Lachezar Radev Darina Zheleva Irena Michailova 《Central European Journal of Chemistry》2013,11(9):1439-1446
In the present work Polyurethane (PU)/Bioglass (BG) composite materials were synthesized with different content of BG (10 and 20 mol.%) as filler. The 85S Bioglass was synthesized via polystep sol-gel method. The chemical composition of BG is 85SiO2-10CaO-5P2O5 (wt.%). The synthesis of PU was carried out by a two-step polyaddition reaction. The 85S BG was added in situ during the polymerization reaction. In vitro bioactivity of the prepared composites was examined in the presence of 1.5 SBF for 7 days in static conditions. The structure of synthesized PU/BG composites before and after in vitro test was determined by XRD, FTIR and SEM. XRD of the samples before in vitro test proved that the phase of γCa2P2O7 in the PU/20BG is visible. FTIR revealed the presence of urethane bond between OH-(from BG) and NCO groups (from PU). Based on FTIR results after in vitro test in 1.5 SBF solutions, A/B-carbonate containing hydroxyapatite (CO3HA) was formed. XRD proved that HA was formed on the surface of the samples, but Ca2P2O7 does not undergo any changes in the 1.5 SBF solution. SEM depicted the nano-HA agglomerated in spherical particles after immersion in 1.5 SBF for 7 days. 相似文献