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1.
Giannakas AE Vaimakis TC Ladavos AK Trikalitis PN Pomonis PJ 《Journal of colloid and interface science》2003,259(2):244-253
Two binary oxides, a spinel, ZnAl2O4, and a typical perovskite, LaMnO3, have been prepared via CTAB-1-butanol-n-octane-nitrate salt microemulsion in the reverse and bicontinuous states. The exact point of the reverse and bicontinuous states of the microemulsion used in the synthesis was determined by conductivity experiments. The materials obtained after heating at 800 degrees C were characterized by XRD analysis for their crystal structure, N2 porosimetry for their surface area and porosity, and SEM and TEM photography for their texture. The ZnAl2O4 spinel obtained via the reverse microemulsion appears in SEM in a more fragmented form and with a higher specific surface area (143.7 m(2)g(-1)), compared to the corresponding solid prepared via the bicontinuous microemulsion, which appears more robust with lower surface area (126.7 m(2)g(-1)). Nevertheless both materials reveal in TEM a sponge-like structure. The perovskite materials LaMnO3 prepared via the reverse microemulsion showed in SEM a peculiar doughnut-like texture, each doughnut-like secondary particle having a diameter of 2 microm. The corresponding sample developed via the bicontinuous microemulsion showed in SEM uniform secondary particles of size approximately 0.2 microm. Both perovskite samples LaMnO3 appear well crystallized with relative low surface areas, 23.7 m(2)g(-1) for the reverse sample and 10.9 m(2)g(-1) for the bicontinuous one. The TEM photographs reveal that both of them, of reversed and bicontinuous origin, are made up of primary nanoparticles in the size range 40-100 nm. In SEM those materials showed a different secondary structure. 相似文献
2.
T. Giannakopoulou G. Pilatos N. Todorova N. Boukos T. Vaimakis I. Karatasios C. Trapalis 《Materials Today Chemistry》2021
The present article demonstrates a simple, eco-friendly route for the fabrication of carbon nanotubes (CNTs) with different morphologies, including the fascinating bamboo-like structures without complex catalyst/support preparation procedures. A thermal chemical vapor deposition (CVD) technique that utilized natural pozzolan supports and a solid carbon source, that is, a mixture of camphor and ferrocene in a weight ratio of 20:1, was carried out at different temperatures where the ferrocene played also the role of catalyst. The pozzolan chemical composition and mineral identification were determined by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The morphology of the fabricated CNTs was studied via scanning and transmission electron microscopies (SEM and TEM). It was revealed that both conventional tubular and bamboo-like nanotubes grow at 750 °C while the bamboo-like morphology prevails at 850 °C. The better nanostructure uniformity at higher deposition temperature was accompanied by an improved nanotube graphitization degree that was verified by Raman spectroscopy. Yet, the reduction of the CNTs production yield was recorded by thermogravimetric analysis (TGA). The experimental data are interpreted and discussed as an interplay between the CNTs processing temperature, morphology and growth mechanism. Thus, the growth of either tubular or bamboo-like nanostructures is suggested to be ruled by the competitive surface and bulk diffusions of carbon onto and into the catalyst surface. The growth depends on the size of catalyst nanoparticles sintered at different temperatures. The favorable role of the pozzolan supporting materials in the formation of bamboo-like tubes is emphasized. 相似文献
3.
Preparation of hydroxyapatite via microemulsion route 总被引:7,自引:0,他引:7
Koumoulidis GC Katsoulidis AP Ladavos AK Pomonis PJ Trapalis CC Sdoukos AT Vaimakis TC 《Journal of colloid and interface science》2003,259(2):254-260
Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degrees C, the A-type carbonate hydroxyapatite was crystallized at 635 degrees C in particles of similar size (40--120 nm) with no internal porosity. At a higher temperature (900 degrees C) a sintering process took place, resulting in network of a larger particles, consisting of HAp and beta-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degrees C with an activation energy of 62.7--72.2 kcalmol(-1). 相似文献
4.
Anastasios I. Mitsionis Tiverios C. Vaimakis 《Journal of Thermal Analysis and Calorimetry》2010,99(3):785-789
The precipitation of calcium phosphate was studied using a heat flow twin calorimeter (C80, Setaram, France). The process
was carried out using two identical membrane vessels. In the lower parts of both vessels 2 mL of a supersaturated solution
(solution A) containing Ca(H2PO4)·2H2O (0.054 M) and CaCl2·H2O (0.125 M) with a molar ratio Ca/P = 1.67 were added. Then 0.05 mL of an ammonium solution (25% w/w) (solution B) and 0.05 mL
of distilled water were transferred in the upper parts of sample and reference vessels, respectively. After temperature had
been maintained at 303, 313, 323 and 333 K the membranes of both sample and reference vessels were broken simultaneously.
The precipitation process also repeated with the same conditions for periods of 15, 60 and 120 min in a bath. The first two
calorimetric curves (303, 313 K) show a single exothermic step during the process as a sharp peak in the initial stage. On
the contrary at the experimental temperature of 323 K except of the sharp peak in the initial stage, a steadily exothermic
tendency appears after 100 min time. In higher temperature (333 K) the sharp peak appears in the initial stage followed by
a broad exothermic step between 75 and 320 min time. The XRD analyses show that the solids in the initial experimental stages
are mainly consisted of dicalcium phosphate dihydrate (DCPD) for the lower temperature and a biphasic or triphasic system
consisted of hydroxyapatite (HA), dicalcium phosphate anhydrous (DCPA) and octacalcium phosphate (OCP) for the rest temperatures.
The XRD analyses show also that during the solution aging the initial products are transformed into the more stable thermal
forms of HA and octacalcium phosphate (OCP). 相似文献
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7.
A. Athanasiou A. Mitsionis G. Skouras N. Todorova C. Trapalis T. Vaimakis 《Journal of Thermal Analysis and Calorimetry》2014,116(1):15-25
Mesoporous anatase TiO2 materials with specific surface areas between 70 and 110 m2 g?1 were prepared via sol–gel technique using surfactants oleic acid and Triton-X (TX), in the presence or absence of diethanolamine, in methanol. Surfactants like TX or oleic acid (OA), as well as a gelating and chelate agent like diethanolamine (DEA) are commonly used in TiO2 formation from a titanium isopropoxide solution. Thermogravimetric methods were applied in order to evaluate the effect of the addition of such molecules in a precursor suspension before TiO2 materials preparation. The in situ investigation of such systems showed that numerous interactions occur between large molecules such as TX and OA that attributed on both steric effects and hydrogen bond formation. Materials prepared through modified sol–gel technique seem to be stabilized through DEA addition in the precursor suspension. 相似文献
8.
Chilas GI Stylianou M Kubicki M Vaimakis T Kögerler P Keramidas AD Kabanos TA 《Inorganic chemistry》2008,47(11):4451-4453
Partial oxidation of an aqueous solution of CoIICl(2).6H2O with (NH4)6[Mo7VIO24].4H2O in the presence of (NH4)2SO3.H2O and LiCl, at pH approximately 5.3, leads to isolation of the octanuclear cluster (NH4)11(Li subset[Co4IICo4III(SO3)16(NH3)8].10H2O), 1. The structure of the anion of 1 consists of a central [Co4II], almost ideal square planar unit, and a pair of symmetry-related CoIII dimers above and below the Co4II plane grafting onto the tetramer by 16 bridging sulfite groups. The [Co8(SO3)16(NH3)8]12- cluster encapsulates a lithium cation which lies at the center of the Co4II square. 相似文献
9.
G. C. Koumoulidis C. C. Trapalis T. C. Vaimakis 《Journal of Thermal Analysis and Calorimetry》2006,84(1):165-174
Hydroxyapatite
powders, which consisted of lath-like single-crystalline particles, were calcined
at two different temperatures. Green and calcined powders were used for sintering
HAp ceramic samples under uniaxial pressing. Powders and sintered samples
were studied using various analytical techniques in order to determine how
calcination affects the particle properties and the sintering behavior of
HAp powders. It was found that calcination decreases the particles length
and changes the particles morphology from lath-like to spherical shape. The
relative density increases with increasing calcination temperature and aging
time. It was found that long aging time favor the formation of thermally stable
HAp particles, whereas a shorter one results in the formation of β-calcium
phosphate during thermal treatment. Sintering of compacted powders begins
at temperatures greater than 900°C, with a trend to increase the onset
temperature as the calcination temperature is increased. 相似文献
10.
T. C. Vaimakis E. D. Economou C. C. Trapalis 《Journal of Thermal Analysis and Calorimetry》2008,92(3):783-789
In this report, we present a thermodynamic and kinetic study of the selective dissolution of calcite from low-grade phosphate
ores (Epirus area, Greece) by dilute acetic acid at isothermal conditions. A twin calorimeter with two identical membrane
vessels, for the acid dissolution process, and for the reference was used. The curves of rate vs. time of the phosphorite
dissolution for various temperatures show that the maximum (.q
max) was increased, whereas the time (t
peak) to achieve the corresponding .q
max values was decreased, as the experimental temperature was increased. The dissolution enthalpy was increased from 13.1 to
16.7 kJ mol−1, as the experimental temperature was increased from 10.0 to 28.0°C. The chemical analysis of the supernatant solutions shows
that the main process was the calcite dissolution. The reaction model with general form, ln(1/(1-X))=kt
m, was found to fitted the experimental data regardless of the experimental temperature. These results were assigned in the
presence of two different kinds of particles in the phosphorite. The activation energy of the dissolution process was found
69.7 kJ mol−1. The SEM micrographs of acid dissolution samples showed two different textures after acid dissolution. 相似文献