Papers by Keyword: Synthesis Temperatures

Abstract: Ti-SBA-15 mesoporous materials were directly synthesized via a hydrothermal process and characterized by using nitrogen adsorption-desorption measurements, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, diffuse reflectance ultraviolet-visible spectroscopy, and infrared ray spectroscopy. The effect of synthesis temperatures on the structure and catalytic efficiency in epoxidation of cyclohexene was discussed in details. The results showed that the optimal temperature was 100 °C under the reaction conditions.

Abstract: Pyramid sharp pyrolysis flame is a new method for carbon nanotubes synthesis. Oxy-acetylene flame outside the frustum of pyramid sharp reactor provides the necessary high temperature circumstance for carbon nanotubes synthesis, while inside the interior mixture of CO, H2, He, and iron pentacarbonyl (Fe(CO)5) is heated. CO is used as the source of carbon, Fe(CO)5 as the source of catalyst precursor. Special structure of the frustum of pyramid sharp reactor makes the oxy-acetylene flame folded gradually above the reactor. And it meets the condition that the interior mixture which has reacted initially under high temperature and will flow out of reactor avoids exposing to air completely and burning abundantly. Immersing a sampling substrate into the incomplete burning flame can gain carbon nanotubes. By adjusting the distance between the oxy-acetylene flame jet and the synthesis area, achieved the purpose that just changing one factor of synthesis or pyrolysis temperature while the other one constant, then respectively studied the effects of them on experimental. The perfect synthesis temperature in experimental is about 595°C, while the pyrolysis temperature is about 1000°C.

Abstract: Pyramid shaped pyrolysis flame is a new method for carbon nanofibes (CNFs) synthesis. Oxy-acetylene flame outside the frustum of pyramid shaped reactor provides the necessary high temperature environment, while CO is used as the source of carbon, iron pentacarbonyl (Fe(CO)5) as the source of catalyst precursor in reactor. Inside, the mixture of CO, H2, and Fe(CO)5 will burn incompletely after initial reaction under high temperature. Inserting a sampling substrate into the incomplete burning flame can gain CNFs. Field emission scanning electron microscope (FE-SEM) was used to illustrate the results of experimental. By adjusting the distance between the oxy-acetylene flame jet and the synthesis zone, studied the effects of pyrolysis and synthesis temperature. The preferable pyrolysis temperature in experimental is about 693°C while the synthesis temperature is about 595°C, and preferable synthesis temperature is about 535°C while pyrolysis temperature is about 1000°C. It can be also concluded that when the synthesis temperature is high (595°C, comparing with 535°C), preferable pyrolysis temperature is low (693°C, comparing with 1000°C), vice versa. Effects of sampling substrate were also studied. Using 304 stainless steel wire as sampling substrate can not gain CNFs, while 201 stainless steel plate can gain straight and uniform, and silicon chip can gain curly ones.

Abstract: In this study, we report the synthesis of carbon nanotubes by ethanol catalytic chemical vapor deposition, which employs ferrocene as the catalyst precursors and ethanol as carbon source. We obtained massive deposits. The deposits were characterized by scanning electron microscopy, transmission electron microscopy, and visual laser Raman spectroscopy. We discussed the effects of synthesis temperature on the synthesis of carbon nanotubes by floating catalytic chemical vapor deposition. Our results indicated that the synthesis temperature could affect not only on the graphitization degree, but also on the aligned growth of carbon nanotubes and the diameter of carbon nanotubes.

Abstract: ZnO as a semiconductor is used in many applications such as gas sensor devices, laser and optoelectronic devices, photocatalysts, solar cells, and varistors. The applications and properties of ZnO nanoparticles highly depend on the size and morphology of these particles. In this research ZnO nanoparticles were prepared via chemical bath deposition at various temperatures in order to see the effects of synthesis temperature and also 2- methoxyethanol (2-ME) as a novel solvent on the morphology of obtained nanoparticles. For synthesizing of ZnO nanostructured materials, 2-ME has been highly used in sol-gel process but it is the first time that it is used in the chemical bath deposition process. For this purpose 1 M solutions of zinc acetate dehydrate in 2-ME were prepared and added to the solution of NaOH in the same solvent dropwisely. Monoethanolamine (MEA) was used as surfactant. The synthesis temperatures were 30°C, 60°C and 90°C. After filtering and drying, morphologies of obtained nanoparticles were characterized and compared.

Abstract: The cubic pyrochlore phase Bi1.5ZnNb1.5O7 nanopowder was successfully synthesized by the hydrothermal method (HTM) from the starting materials: Bi(NO3)3·5H2O, ZnO, Nb2O5 and the mineralizer: KOH. The XRD patterns prove that the cubic pyrochlore phase Bi1.5ZnNb1.5O7 nanopowder can be obtained by HTM, and TEM photographs show that the powders present the regularly granular shape, when the hydrothermal reactions were conducted at synthesis temperatures 140~220°C and reaction time for 6~48h. The crystalline sizes of the powders were calculated by the Scherrer equation to be about 43~49nm. The crystalline sizes decreased both with the increase in synthesis temperature and the prolonged reaction time until they reached to the minimum size about 43nm at 220°C for 24h.However, they tended to increase when the reaction time was above 24h.

Abstract: High crystalline Ti-substituted MCM-41’s in the range of Si/Ti ≥ 30 were synthesized. We have carried out the controlling of the pore size of highly crystalline Ti-substituted MCM-41 simply by varying the synthesis temperature in 100-165 oC range. Depending on the reaction temperature, highly crystalline Ti-substituted MCM-41 with different d100 values in the range of 34.6-55.8 Å while using the same gel mixture (1.0 SiO2 : 0.27 CTABr : 0.19 TMAOH : 0.017 Ti(OEt)4 : 40 H2O) were synthesized. The pore size distribution, the surface area and the wall thickness for Ti-substituted MCM-41 samples by N2 adsorption method were 29.2-35.8 Å, 1140- 959 m2/g and 10.7-28.7 Å, respectively. Ti atoms substituted in MCM-41 were atomically dispersed in the framework of MCM-41, which was investigated by IR and UV/Vis spectrophotometer. The d100 values of Ti-MCM-41 samples of Si/Ti=30 under same reaction have a range of 39.2-53.5 Å.