Effect of Heat-Treatment on the Microstructure and Properties of SiO2-TiO2 Aerogels Synthesized via Supercritical Drying

2016 ◽  
Vol 848 ◽  
pp. 770-776 ◽  
Author(s):  
Yong Gang Jiang ◽  
Yan Qing Qin ◽  
Jun Zong Feng ◽  
Jian Feng ◽  
Lin Xu
Keyword(s):  
Heat Treatment ◽  
Specific Surface ◽  
Three Dimensional ◽  
Supercritical Drying ◽  
High Specific Surface Area ◽  
Sem Images ◽  
Average Pore ◽  
Microstructure And Properties ◽  
Surface Areas ◽  
Heat Treated

Monolithic SiO2-TiO2 aerogels were prepared via supercritical drying using tetraethoxysilane and tetrabutyltitanate as precursors and ethanol as solvent. Influence of the heat-treatment on the microstructure and properties of SiO2-TiO2 aerogels were investigated in detail. The results showed that the as-prepared SiO2-TiO2 aerogels had low densities, high specific surface areas, small average pore diameters, and three-dimensional nanoporous structures. The anatase TiO2 phase of SiO2-TiO2 aerogels could form during supercritical drying process, and the transition to rutile TiO2 phase occurred after experiencing 1200°C for 2 h. SiO2-TiO2 aerogels containing 30 wt% TiO2 (ST3) still presented relatively high specific surface area of 451 m2/g even they undergo the treatment of 1000°C for 2 h. And the SEM images indicated that the agglomerated particles derived from ST3 appeared gradually to some extent. The glassy luster of ST3 heat-treated at 1200°C for 2 h illuminates SiO2 started to vitrify. Besides, the thermal conductivity of ST3 at room temperature is up to 0.03257 W·m-1·K-1.

Synthesis of Ytterbium Sulfides by the Sulfurization and Heat Treatment

2015 ◽  
Vol 655 ◽  
pp. 224-229 ◽  
Author(s):  
Liang Li ◽  
Shinji Hirai ◽  
Hai Bin Yuan ◽  
Eiji Nakamura
Keyword(s):  
Heat Treatment ◽  
Specific Surface ◽  
Single Phase ◽  
Polymorphic Form ◽  
Particle Sizes ◽  
Orthorhombic Structure ◽  
Surface Areas ◽  
Plasma Sintering ◽  
Heat Treated ◽  
Spark Plasma

Single-phase ytterbium sulfides (Yb2S3 and YbS) were synthesized by sulfurization of Yb2O3 with CS2 gas and heat treatments. Four kinds of Yb2O3 powders with different particle sizes and specific surface areas were employed as starting materials. When specific surface area of Yb2O3 powder is about 50 m2/g, a new polymorphic form Yb2S3 with an orthorhombic structure could be obtained by the sulfurization at 600°C for 8 hr. Single-phase hexagonal Yb2S3 was also synthesized form former three kinds of Yb2O3 powders by sulfurization above 1000 °C for 8 hr. Subsequently, the synthesized Yb2S3 powders were heat-treated under different conditions. Upon heat treatment at 1000 °C for 3 hr in Ar/CS2 atmosphere, orthorhombic Yb2S3 phase underwent phase transition to hexagonal Yb2S3 phase. Moreover, XRD results showed that orthorhombic Yb3S4 was main phase after heat treatment at 1050°C for 8 hr under Ar atmosphere and Yb2S3 disappeared upon prolonged (12 hr) heat treatment. Single Yb3S4 phase could be obtained after treatment at 1000 °C for 3 hr, or at 1200 °C for 1 hr, under vacuum (~1.2×10-3 Pa). YbS was formed upon treatment at 1200 °C for 5 hr. Single-phase YbS with a homogeneity range of YbS1.11-1.15 could be synthesized by treatment at 1500 °C for 3 hr. PartialYb2S3 transformed to Yb3S4 at 1300 °C for 1 hr by spark plasma sintering.

scholarly journals Synthesis of Monolithic TiO2 Aerogels With Relatively Low Shrinkage and Improved Formability Assisted by CTAB

2021 ◽  
Vol 8 ◽  
Author(s):  
Tingting Niu ◽  
Bin Zhou ◽  
Zehui Zhang ◽  
Jianming Yang ◽  
Xiujie Ji ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Sol Gel ◽  
Supercritical Drying ◽  
High Specific Surface Area ◽  
Structure Property ◽  
Surface Areas ◽  
Polycondensation Process

Monolithic TiO2 aerogels without severe shrink were obtained by the sol-gel method with the addition of the surfactant cetyltrimethylammonium bromide (CTAB) to control the hydrolysis and polycondensation process and acetonitrile solvent as the solvent to improve the crystallinity. After CO2 supercritical drying, the shrinkage ratio of monolithic TiO2 aerogels modified by CTAB decreased by up to ∼26.9%, compared with the pure TiO2 aerogel. Their apparent densities were all lower than 300 g/cm3. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR) and BET Specific Surface Area Analysis were used to analyze the as-synthesized samples. The results revealed that all the samples were anatase-TiO2 phase with nanoporous network structures. The specific surface areas reached 250.2 m2/g confirmed by the BET (Brunaur–Emmett–Teller method) analysis. However, TiO2 aerogels without the addition of CTAB showed evident agglomeration and collapse of the network in comparison with CTAB-added samples. To further study the structure-property relationship, the photocatalysis performance of as-synthesized and 300°C-calcined aerogels was carried out contrastively. Interestingly, the influences of the CTAB adding amount of as-synthesized and calcined TiO2 aerogels are negative and positive, respectively, which is probably due to the synergistic effect of CTAB hindrance and grain refinement. Potentially, This kind of TiO2 aerogels assisted by CATB with low density, small shrinkage, improved formability, high specific surface area and fine crystalline grain may be applied in various applications, such as electrochemistry, photocatalysis, etc.

Nitrogen Doping to Metatitanic Acid by NH3 Heat Treatment for Achieving Visible-Light-Responsive Photocatalytic Activity

2013 ◽  
Vol 761 ◽  
pp. 35-39
Author(s):  
Se Keun Park ◽  
Jun Ho Eun ◽  
Hyun Ho Shin
Keyword(s):  
Heat Treatment ◽  
Photocatalytic Activity ◽  
Visible Light ◽  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Nitrogen Doping ◽  
High Specific Surface Area ◽  
Metatitanic Acid ◽  
Heat Treated

Nitrogen doping can be achieved by heating TiO2-based photocatalyst powders under dopant-generating atmospheres such as NH3. In the present work, metatitanic acid (MTA) powder was used as a raw material to obtain nitrogen-doped titania using heat treatment in NH3flow. MTA is an industrially available intermediate product in sulfate process for TiO2production, which is mesoporous material with high specific surface area. The MTA powder was heat-treated in flowing NH3at 400–550°C. For comparison, commercial P25 TiO2powder was heat-treated under the same conditions. The results show that nitrogen dopant can be successfully incorporated into the MTA by heating in NH3 atmosphere. This obviously results in the enhanced visible-light photocatalytic activity, especially in MTA sample heated at 400°C. Due to the fascinating properties of MTA powder such as high specific surface area, the N-doping effect on MTA powder is much higher than the P25 TiO2powder.

Effect of Cooling Rate on Microstructure and Properties of Heat-Treated Fe3Al Intermetallics

2011 ◽  
Vol 189-193 ◽  
pp. 3891-3894
Author(s):  
Ya Min Li ◽  
Hong Jun Liu ◽  
Yuan Hao
Keyword(s):  
Heat Treatment ◽  
Cooling Rate ◽  
Lattice Distortion ◽  
Annealing Furnace ◽  
Microstructure And Properties ◽  
Homogenizing Annealing ◽  
Heat Treated ◽  
Mixed Fracture ◽  
Sand Mould ◽  
The Impact

The casting Fe3Al intermetallics were solidified in sodium silicate sand mould and permanent mould respectively to get different cooling rates. After heat treatment (1000°С/15 h homogenizing annealing + furnace cooling followed by 600°С/1 h tempering + oil quenching), the microstructure and properties of Fe3Al intermetallics were investigated. The results show that the heat-treated Fe3Al intermetallics at higher cooling rate has finer grained microstructure than lower cooling rate, and the lattice distortion increases due to the higher solid solubility of the elements Cr and B at higher cooling rate. The tensile strength and hardness of the Fe3Al intermetallics at higher cooling rate are slightly higher also. However, the impact power of intermetallics at higher cooling rate is 67.5% higher than that at lower cooling rate, and the impact fracture mode is also transformed from intercrystalline fracture at lower cooling rate to intercrystallin+transcrystalline mixed fracture at higher cooling rate.

scholarly journals Synthesis, Characterization and Photocatalytic Activity of Nanocrystalline First Transition-Metal (Ti, Mn, Co, Ni and Zn) Oxisde Nanofibers by Electrospinning

2018 ◽  
Vol 9 (1) ◽  
pp. 8 ◽  
Author(s):  
Yu Chen ◽  
Weipeng Lu ◽  
Yanchuan Guo ◽  
Yi Zhu ◽  
Haojun Lu ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Transition Metal ◽  
Metal Oxide ◽  
Specific Surface ◽  
Three Dimensional ◽  
Photogenerated Electron ◽  
Practical Applications ◽  
Surface Areas ◽  
Tio2 Nanofiber ◽  
Transmission Electron

In this work, five nanocrystalline first transition-metal (Ti, Mn, Co, Ni and Zn) oxide nanofibers were prepared by electrospinning and controlled calcination. The morphology, crystal structure, pore size distribution and specific surface area were systematically studied by scanning electron microscope (SEM), transmission electron microscope (TEM), surface and pore analysis, and thermo gravimetric analyzer (TGA). The results reveal that the obtained nanofibers have a continuously twisted three-dimensional scaffold structure and are composed of neat nanocrystals with a necklace-like arrangement. All the samples possess high specific surface areas, which follow the order of NiO nanofiber (393.645 m2/g) > TiO2 nanofiber (121.445 m2/g) > ZnO nanofiber (57.219 m2/g) > Co3O4 nanofiber (52.717 m2/g) > Mn2O3 nanofiber (18.600 m2/g). Moreover, the photocatalytic degradation of methylene blue (MB) in aqueous solution was investigated in detail by employing the five kinds of metal oxide nanofibers as photocatalysts under ultraviolet (UV) irradiation separately. The results show that ZnO, TiO2 and NiO nanofibers exhibit excellent photocatalytic efficiency and high cycling ability to MB, which may be ascribed to unique porous structures and the highly efficient separation of photogenerated electron-hole pairs. In brief, this paper aims to provide a feasible approach to achieve five first transition-metal oxide nanofibers with excellent performance, which is important for practical applications.

scholarly journals Catalytic Decomposition of H2O2 over Pure and Li2O-Doped Co3O4 Solids

1998 ◽  
Vol 16 (9) ◽  
pp. 733-746 ◽  
Author(s):  
Gamil A. El-Shobaky ◽  
Nagi R.E. Radwan ◽  
Farouk M. Radwan
Keyword(s):  
Heat Treatment ◽  
Specific Surface ◽  
Catalytic Decomposition ◽  
Nitrogen Adsorption ◽  
Progressive Increase ◽  
Lithium Oxide ◽  
Lithium Nitrate ◽  
Surface Areas ◽  
Catalytically Active ◽  
Cobaltic Oxide

Pure and doped Co3O4 samples were prepared by the thermal decomposition at 500–900°C of pure and lithium nitrate-treated basic cobalt carbonate. The amounts of dopant added were varied in the range 0.75–6 mol% Li2O. The effects of this treatment on the surface and catalytic properties of cobaltic oxide solid were investigated using nitrogen adsorption at −196°C and studies of the decomposition of H2O2 at 30–50°C. The results obtained revealed that Li2O doping of Co3O4 followed by heat treatment at 500°C and 600°C resulted in a progressive increase in the value of the specific surface area, SBET, to an extent proportional to the amount of dopant present. However, the increase was more pronounced in the case of solid samples calcined at 500°C. This increase in the specific surface areas has been attributed to the fixation of a portion of the dopant ions on the uppermost surface layers of the solid leading to outward growth of the surface lattice. The observed increase in SBET due to Li2O doping at 500°C might also result from a narrowing of the pores in the treated solid as a result of the doping process. Lithium oxide doping of cobaltic oxide followed by heat treatment at 700–900°C resulted in a significant decrease in the SBET, Vp and r̄ values. Pure and doped solids precalcined at 500°C and 600°C exhibited extremely high catalytic activities which were not much affected by doping with Li2O. On the other hand, doping followed by calcination at 700–900°C brought about a considerable and progressive increase in the catalytic activity of the treated solids. This treatment did not modify the activation energy of the catalysed reaction, i.e. doping of Co3O4 solid followed by heating at 700°C and 900°C did not alter the mechanism of the catalytic reaction but increased the concentration of catalytically active constituents taking part in the catalytic process without altering their energetic nature.

Effect of the drying on morphology and texture of aerogels and zirconia cryogels

MRS Advances ◽  
2019 ◽  
Vol 4 (64) ◽  
pp. 3513-3521
Author(s):  
Tzipatly A. Esquivel-Castro ◽  
Antonia Martínez-Luévanos ◽  
Luis Alfonso García-Cerda ◽  
Juan C. Contreras-Esquivel ◽  
Pascual Bartolo Pérez ◽  
...  
Keyword(s):  
Drug Delivery ◽  
Cetyltrimethylammonium Bromide ◽  
Sol Gel ◽  
Three Dimensional ◽  
Supercritical Drying ◽  
Sem Images ◽  
Texture Properties ◽  
Dimensional Network ◽  
Zirconia Aerogel

ABSTRACTDue to their excellent properties, aerogel has attracted the attention of the scientific community to use it in the biomedical area as a drug delivery system. This work reports on the synthesis and characterization of ZrO2 aerogels and cryogels obtained by the sol-gel method. The influence of different cetyltrimethylammonium bromide (CTAB) and the type of drying on structural, morphological and texture properties of ZrO2 aerogels and cryogels was investigated. SEM images reveal that a porous interconnected three-dimensional network was formed into aerogels due to supercritical drying. Zirconia aerogel sample has a specific surface area (SBET) larger than zirconia cryogels. Therefore, our results indicate that zirconia aerogel is an adequate material for applications in drug delivery systems.

Vacuum Heat Treatment of MgO -Densified Pressureless Sintered Silicon Nitride Ceramics

2007 ◽  
Vol 554 ◽  
pp. 107-112 ◽  
Author(s):  
V. Demir ◽  
Derek P. Thompson
Keyword(s):  
Heat Treatment ◽  
Silicon Nitride ◽  
Pressureless Sintering ◽  
Vacuum Heat Treatment ◽  
Sem Images ◽  
Edx Analysis ◽  
Heat Treated ◽  
Nitride Ceramics ◽  
Different Temperatures ◽  
Sintered Silicon

Silicon nitride samples were pressureless sintered with up to 5 w/o MgO to give densities in the range 98-99% of theoretical. After pressureless sintering, selected samples were placed in a vacuum heat treatment furnace surrounded by a carbon bed in a carbon crucible at a pressure of less than 4x10-4 mbar, and vacuum heat treated at different temperatures and times to remove grainboundary glass. The results showed that this was substantially achieved at 1575oC for 3h and that increasing the time to 5 hours gave still further improvement. SEM images, EDX analysis and oxidation tests provided additional evidence for the removal of Mg from the samples.

Alumina aerogel catalysts prepared by two supercritical drying methods used in methane combustion

1995 ◽  
Vol 10 (6) ◽  
pp. 1424-1428 ◽  
Author(s):  
Yasuyuki Mizushima ◽  
Makoto Hori
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Methane Combustion ◽  
Supercritical Drying ◽  
High Specific Surface Area ◽  
The Other ◽  
Drying Methods ◽  
Alumina Aerogel ◽  
Lower Temperature

Palladium-supported alumina aerogels were prepared by two different supercritical drying methods. In one method, an alumina wet gel was dried under supercritical conditions of ethanol in an autoclave. In the other, the aerogel was supercritically dried by extracting ethanol using carbon dioxide in an extractor. The Pd-supported alumina aerogel prepared in the autoclave exhibited a high specific surface area of 112.8 m2/g after firing at 1200 °C for 5 h, while the other had a specific surface area of only 5.2 m2/g due to α-alumina transformation. Their catalytic properties for methane combustion were measured. The Pd-supported alumina aerogel prepared in the autoclave combusts methane perfectly at 50–60 °C lower temperature than the other. Palladium particles on the alumina aerogel prepared in the autoclave contained palladium oxide, while those prepared in the CO2 extractor contained only palladium metal.

Indium-Sensitized UV Photocatalysts Made from Alkali Titanate Microfibers

2009 ◽  
Vol 620-622 ◽  
pp. 651-654
Author(s):  
Leticia M. Torres-Martínez ◽  
Cecilia Sánchez-Trinidad ◽  
Vicente Rodríguez-González ◽  
Ricardo Gómez
Keyword(s):  
Heat Treatment ◽  
Annealing Time ◽  
Uv Light ◽  
Sol Gel ◽  
Dichlorophenoxyacetic Acid ◽  
Sem Images ◽  
Uv Light Irradiation ◽  
Heat Treated ◽  
Munk Function ◽  
Sol Gel Process

Indium-alkali microfibers doped ceramic were prepared by the sol-gel process. The gels preparation samples, were heat treated at 700°C for different length of time. The products were characterized by means of XRD, SEM-EDS and UV–Vis-DRS. The XRD showed the formation of the Na2Ti6O13 phase whose crystallinity depends on the annealing time. The band gap calculated from the UV–Vis Kubelka-Munk function shows very similar values (3.53-3.55 eV). The SEM images of the indium-alkali titanates show microfiber clumps morphologies of about 5 µm, and the EDS spectra show that In2O3 is on the Na2Ti6O13 surface. The results of the evaluation of the In-Na2Ti6O13 semiconductors in the 2, 4-dichlorophenoxyacetic acid (2, 4-D) photodecomposition under UV light irradiation, show that the photoactivity depends on the time of heat treatment of the samples.

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