جستجوی مقالات مرتبط با کلیدواژه "chemical vapor deposition" در نشریات گروه "مواد و متالورژی"

Photocatalytic water splitting technology is one of the new methods that has a high potential for hydrogen production. In this research, chemical vapor deposition method was used for the synthesis of hematite on FTO substrate as a photoelectrochemical cell photoanode. To determine the structure of the synthesized iron oxide and study the morphology of the synthesized structures, X-ray diffraction spectroscopy, scanning electron microscopy and X-ray energy diffraction spectroscopy were used, which well confirmed the synthesis of hematite on FTO substrate. In the hematite synthesis step, it was found that the prewash steps, the presence of TEOS and its amount in the uniformity and thickness of the layer and the type of precursor used in the structure and morphology of the synthesized hematite have a significant effect. Using ferrocene, pyramidal structures of hematite with optimal thickness in the amount of 2 ml TEOS were obtained and for pentacarbonyl iron, cauliflower structures were obtained in the optimal ratio of pentacarbonyl iron (1 ml) / TEOS (0.5 ml) 2: 1. The results of photoanode efficiency of synthesized hematite on FTO substrate showed that the thickness and morphology of hematite have a special role in the photon flux and the maximum photon flux was obtained 1.42 mA/cm2 for the synthesized hematite cauliflower structure.

Reinforcing of materials using carbon nanotubes are new approach for development of new and or advanced composites. In the meantime, the use of carbon nanotubes to reinforce cementitious materials, especialy reconstructing cement, is considered. The synthesis process of nanotubes on cement is the main problem in making the composite. In the paper, synthesis and characterization of cement-CNT composite produced by CVD process was investigated. The CVD process at 800°C using acetylene gas as a carbon source, argon as carrier gas and hematite iron oxide as a catalyst was performed. Wet impregnation method for preparing the catalyst bed of cement and iron oxide particles were used. FESEM, EDX, TEM and Raman spectroscopy were used to characterization CNTs/Cement composite and the size, morphology and quality of CNTs respectively. The growth yield of carbon nanotubes was determined by TGA. The results showed that the chemical vapor deposition method allows the deposition of carbon nanotubes with proper distribution of diameters and quality. It was also observed that most of the synthesized carbon nanotubes have open ends that represent the end growth of the carbon nanotubes. Finally the result of mechanical tests indicated that CNTs addition to the cement paste dramatically the increased compressive strength by bridging between cracks and filling pores.

Molybdenum disulfide (MoS2) is one of the most widely used solid lubricants applied in different ways on the surfaces under friction. In this work, AISI 316 austenitic stainless steel was coated with MoS2, using chemical vapor deposition (CVD) at four different temperatures (400, 500, 600 and 700°C). Coatings properties were investigated using SEM, EDX, XRD and FTIR, Hardness Tester and Roughness tester. The results showed that with simultaneous evaporation of sulfur and molybdenum trioxide (MoO3) in the CVD chamber, a uniform coating layer containing MoS2 and MoO2 phases is formed. Increase in the substrate temperature resulted in the rise in the proportion of MoS2 to MoO2 phases as well as the thickness of coating. The thickness, grain size and the hardness of the coating were 17-29 µm, 50-120 nm and 260- 480 HV respectively.

A method for bulk growth of mono- to few-layer graphene on Nickel substrate by chemical vapor deposition of methane at atmospheric pressure is described. Optical microscopy، scanning and transmission electron microscopy and XRD measurements reveal the high quality of the obtained graphene. After the growth of graphene، the nickel particles can be effectively removed by a modest treatment without degradation of the quality of producing high yield and high purity graphenes with no carbon impurities such as carbon nanotubes.

In this paper, tin dioxide (SnO2) nanowires with different diameter have been fabricated for gas sensor applications by a chemical vapour deposition (CVD) technique. Alumina (Al2O3), quartz, and gold Au-coated silicon (Si) (100) were used as substrates. X-ray diffraction (XRD), photoluminescence spectroscopy (PL), and a scanning electron microscope were employed to characterize the synthesized products. Nanostructured gas sensor devices were fabricated using SnO2 nanowires as the active layer and gold (Au) for the electrode contacts. Gas sensing performance of synthesized SnO2 nanostructures are studied for two most widely used gases suchas liquefied petroleum gas (LPG) and ethanol (C2H5OH) vapor. The responses of SnO2 nanowires were checked at different temperatures ranging from 50 to 300 °C, so as to optimize sensing efficiency. Sensing performances were discussed for parameters such as response time, recovery time, and operating temperature. Fabricated sensor is shown a high sensitivity to low concentrations of LPG at elevated temperatures. Prepared sensor was revealed fast response and recovery time at working temperature of 200 °C for ethanol vapor detection.