Synthesis of Nanocrystalline Titania via Microwave-Assisted Homogeneous Hydrolysis Under Hydrothermal Conditions

The synthesis of partially substituted silicon hydroxyapatite (Si-HAp) nanopowders was systematically investigated via the microwave-assisted hydrothermal process. The experiments were conducted at 150 °C for 1 h using TMAS (C4H13NO5Si2) as a Si4+ precursor. To improve the Si4+ uptake in the hexagonal structure, the Si precursor was supplied above the stoichiometric molar ratio (0.2 M). The concentration of the TMAS aqueous solutions used varied between 0.3 and 1.8 M, corresponding to saturation levels of 1.5–9.0-fold. Rietveld refinement analyses indicated that Si incorporation occurred in the HAp lattice by replacing phosphate groups (PO43−) with the silicate (SiO4−) group. FT-IR and XPS analyses also confirmed the gradual uptake of SiO4− units in the HAp, as the saturation of Si4+ reached 1.8 M. TEM observations confirmed that Si-HAp agglomerates had a high crystallinity and are constituted by tiny rod-shaped particles with single-crystal habit. Furthermore, a reduction in the particle growth process took place by increasing the Si4+ excess content up to 1.8 M, and the excess of Si4+ triggered the fine rod-shaped particles self-assembly to form agglomerates. The agglomerate size that occurred with intermediate (0.99 mol%) and large (12.16 mol%) Si contents varied between 233.1 and 315.1 nm, respectively. The excess of Si in the hydrothermal medium might trigger the formation of the Si-HAp agglomerates prepared under fast kinetic reaction conditions assisted by the microwave heating. Consequently, the use of microwave heating-assisted hydrothermal conditions has delivered high processing efficiency to crystallize Si-HAp with a broad content of Si4+.

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SYNTHESIS AND PROCESSING OF InVO4 CERAMICS

International Journal of Modern Physics B ◽

10.1142/s021797921006440x ◽

2010 ◽

Vol 24 (06n07) ◽

pp. 770-779 ◽

Cited By ~ 4

Author(s):

EVA BARTONICKOVA ◽

JAROSLAV CIHLAR

Keyword(s):

High Temperature ◽

Solid State ◽

Solid State Reaction ◽

Reaction Times ◽

Rechargeable Batteries ◽

Microwave Assisted Synthesis ◽

Hydrothermal Conditions ◽

Powder Morphology ◽

Preparation Methods ◽

Microwave Assisted

Indium vanadates for severe applications as photocatalysts, anodes for Li rechargeable batteries or electrochromic devices were prepared via conventional and non-conventional preparation methods. The conventional high temperature solid state reaction was performed at 800°C for 25 hours and the non-conventional microwave-assisted synthesis was performed at 220°C for different reaction times under hydrothermal conditions. The as-prepared powders were characterized in terms of phase composition by X-Ray diffraction analysis (XRD) and infrared spectroscopy (IR) and of powder morphology by scanning electron microscopy (SEM) and BET method. Nanosized indium vanadate powders were successfully synthesized by non-conventional microwave-assisted hydrothermal method. The dense ceramic bodies suitable for electrical conductivity measurements with 96% t.d. were obtained by sintering of powders prepared by high-temperature solid state reaction at 1100°C for 4 h with admission of oleic acid as a binder additive.

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Phase Composition of Nanocrystalline Titania Synthesized under Hydrothermal Conditions from Different Titanyl Compounds

Inorganic Materials ◽

10.1023/b:inma.0000037927.87964.6d ◽

2004 ◽

Vol 40 (8) ◽

pp. 822-828 ◽

Cited By ~ 10

Author(s):

Yu. V. Kolen'ko ◽

A. A. Burukhin ◽

B. R. Churagulov ◽

N. N. Oleinikov

Keyword(s):

Phase Composition ◽

Hydrothermal Conditions ◽

Nanocrystalline Titania

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Morphological aspects of Bismuth ferrite powders prepared by microwave-assisted hydrothermal method

Proceedings International ◽

10.33263/proceedings11.00520053 ◽

2019 ◽

Vol 1 (1) ◽

pp. 52-53

Keyword(s):

Reaction Mechanism ◽

Hydrothermal Method ◽

Bismuth Ferrite ◽

Magnetic Behavior ◽

Secondary Phase ◽

Secondary Phases ◽

Hydrothermal Conditions ◽

Microwave Assisted ◽

Microwave Hydrothermal ◽

Morphological Aspects

BiFeO3 particles were synthetized by a fast, reproducible and environmental friendly microwave-assisted hydrothermal method. The aim of the study was the investigation of increased pressure and mineralizer concentration on the reaction mechanism, morphology of particles and aggregates as well as magnetic behavior. Powders were studied when using KOH mineralizer concentration from 4 to 12 M at room temperature and under microwave-hydrothermal conditions at 40 bar and 150 or 200°C. The reaction mechanism depends on the temperature of the microwave-hydrothermal treatment and the concentration of KOH mineralizer. The precursor powder obtained after coprecipitation step consists of Bi2O3, Fe2O3 and Bi25FeO40 in different ratios. After the treatment at 40 bar and 150°C for 1h the reaction between precursors is not complete, therefore resulting secondary phases of Bi25FeO40 and Fe2O3. BiFeO3 particles were successfully synthesized at 40 bar under microwave-hydrothermal conditions at a temperature of 200°C and a concentration of KOH of at least 8M. At 6M, the composition consisted of 98.5% BiFeO3 and 1.5% Bi2O3 as evidenced by Rietveld refinement. The competition between dissolution and precipitation of Bi3+ and Fe3+ in KOH solutions of different concentrations was investigated by Raman spectroscopy and EDS analysis. Thus, at 200°C there was evidenced a Bi2O3 secondary phase for 6 M KOH concentration and poor control of Bi/Fe ratio in BiFeO3 at KOH concentrations of 10 and 12 M. Particle and aggregates morphology depicted by FE-SEM investigations showed a tendency to form irregular shaped particles at KOH concentration of 6 M, for which the reaction is not complete. When increasing the concentration, BiFeO3 particles exhibit regular shapes from cubic at 8 M to cvasi-spherical at 14 M. M-H curves characteristics illustrate that Bi/Fe ratio and preferential orientation of crystal growth influence the magnetic behavior of BiFeO3 crystalline powders.

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