To alleviate catalytic coking on the inner surface of radiant tube for ethylene production in petrochemical plants,SiO2/S coatings were deposited on HP40 alloy specimens using dimethyldisulfide （DMDS） and tetraethox...To alleviate catalytic coking on the inner surface of radiant tube for ethylene production in petrochemical plants,SiO2/S coatings were deposited on HP40 alloy specimens using dimethyldisulfide （DMDS） and tetraethoxysilane （TEOS） by atmospheric pressure chemical vapor deposition （APCVD）. A two-dimension mathematical model was made to predict the growth rate of SiO2/S coating and to study the effects of deposition parameters on the deposition rate. The results show that the predicted deposition rate is in good agreement with the experimental one. The deposition rate mainly depends on the concentrations of precursors in the total gas flow, concentrations of intermediates on the deposition surface, total gas flow rate and deposition temperature. The weight of SiO2/S coating linearly increases with the deposition time. When the gas flow rate is below 0.3 m/s, the rate-limiting step of SiO2/S coating deposition is the diffusions of intermediates.However, the surface reactions of intermediates will be the rate-limiting step after the gas flow rate is above 0.3 m/s. When the deposition temperature is below 780℃, the rate-limiting step of SiO2/S coating deposition mainly depends on the surface reactions of intermediates. When the deposition temperature is above 780℃,the rate-limiting step depends on the diffusions of intermediates. The deposition rate increases with increasing the concentrations of the intermediates. However, when the partial pressures of the intermediates reach 8 Pa,the deposition rate keeps constant.展开更多
SiO2 coated Ce2S3 red pigment was prepared in ethanol/H2O system via sol-gel method and TEOS were used as silica sources. X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy...SiO2 coated Ce2S3 red pigment was prepared in ethanol/H2O system via sol-gel method and TEOS were used as silica sources. X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDX）, UV-visible spectro-photometer and automatic colorimeter were used to investigate the properties of the samples. The results showed that the compact SiO2 film formed on the surface of Ce2S3 pigment at a cerium silicon molar ratio of 2. The thermal stability temperature of Ce2S3 pigment was improved to 450 oC after SiO2 coating. In addition, the color of Ce2S3 pigment was not affected significantly through coating colorless and transparent SiO2 and it could be used as safe red pigment in higher temperature fields.展开更多
文摘To alleviate catalytic coking on the inner surface of radiant tube for ethylene production in petrochemical plants,SiO2/S coatings were deposited on HP40 alloy specimens using dimethyldisulfide （DMDS） and tetraethoxysilane （TEOS） by atmospheric pressure chemical vapor deposition （APCVD）. A two-dimension mathematical model was made to predict the growth rate of SiO2/S coating and to study the effects of deposition parameters on the deposition rate. The results show that the predicted deposition rate is in good agreement with the experimental one. The deposition rate mainly depends on the concentrations of precursors in the total gas flow, concentrations of intermediates on the deposition surface, total gas flow rate and deposition temperature. The weight of SiO2/S coating linearly increases with the deposition time. When the gas flow rate is below 0.3 m/s, the rate-limiting step of SiO2/S coating deposition is the diffusions of intermediates.However, the surface reactions of intermediates will be the rate-limiting step after the gas flow rate is above 0.3 m/s. When the deposition temperature is below 780℃, the rate-limiting step of SiO2/S coating deposition mainly depends on the surface reactions of intermediates. When the deposition temperature is above 780℃,the rate-limiting step depends on the diffusions of intermediates. The deposition rate increases with increasing the concentrations of the intermediates. However, when the partial pressures of the intermediates reach 8 Pa,the deposition rate keeps constant.
基金Project supported by National Science and Technology Support Program(2011BAE30B03)Special Fund from Shaanxi Provincial Department of Education(12JK0467the Graduate Innovation Fund of Shaanxi Universityof Science and Technology for the financial support
文摘SiO2 coated Ce2S3 red pigment was prepared in ethanol/H2O system via sol-gel method and TEOS were used as silica sources. X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDX）, UV-visible spectro-photometer and automatic colorimeter were used to investigate the properties of the samples. The results showed that the compact SiO2 film formed on the surface of Ce2S3 pigment at a cerium silicon molar ratio of 2. The thermal stability temperature of Ce2S3 pigment was improved to 450 oC after SiO2 coating. In addition, the color of Ce2S3 pigment was not affected significantly through coating colorless and transparent SiO2 and it could be used as safe red pigment in higher temperature fields.
