Silica aerogels were prepared by sol-gel technique from industrial silicon derivatives (polyethoxydisiloxanes, E40), followed by silylation and drying under ambient pressure. The specific surface area, pore size dis...Silica aerogels were prepared by sol-gel technique from industrial silicon derivatives (polyethoxydisiloxanes, E40), followed by silylation and drying under ambient pressure. The specific surface area, pore size distribution and thermal conductivity of the silica aerogels were investigated and the results showed that the diameter of the silica particles is about 6 nm and the average pore size of the silica aerogels is 14.7 nm. The specific surface area of which is about 1000 m^2.g^-1 and the thermal conductivity is about 0.014 wm^-l.K^-1 at room temperature and pressure of 1.01×10^5 Pa. The Si-CH3 groups were also detected on the internal surface of the silica aerogels, which show hydrophobic. Silica aerogels derived by this technique is low cost and have wide applications.展开更多
Nanoporous silica films were prepared by sol-gel process with base, acid and base/acid two-step catalysis.Transmission electron microscope (TEM) and particle size analyzer were used to characterize the microstructur...Nanoporous silica films were prepared by sol-gel process with base, acid and base/acid two-step catalysis.Transmission electron microscope (TEM) and particle size analyzer were used to characterize the microstructure and the particle size distribution of the sols. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectroscopic ellipsometer were used to characterize the surface microstructure and the optical properties of the silica films. Stability of the sols during long-term storage was investigated. Moreover,the dispersion relation of the optical constants of the silica films, and the control of the microstructure and properties of the films by changing the catalysis conditions during sol-gel process were also discussed.展开更多
Mesoporous poly(styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis was achieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydrid...Mesoporous poly(styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis was achieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymer in the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template or pore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m(2)/g) and pore volumes (e.g. 0.6 cm(3)/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, pore volumes and pore diameters of the hybrid materials increase.展开更多
Dry stock of silica sol ceramic mould was prepared by using of colloidal moulding technique with an optimized vacuum drying process.Effect of roasting process on the shrinkage rate and compressive strength of zircon-s...Dry stock of silica sol ceramic mould was prepared by using of colloidal moulding technique with an optimized vacuum drying process.Effect of roasting process on the shrinkage rate and compressive strength of zircon-silica sol ceramic mould,and the relationship between the roasting temperature and microstructure of zircon-silica sol ceramic mould were studied.The optimum roasting temperature of zircon-silica sol ceramic mould gained by the experiments is 900℃ and the holding time is 2 h.The scanning electron microscope(SEM) observation showed the growth of refractory particles during the roasting process.The occurrence of sintering was observed in the zircon-silica sol ceramic mould when roasting temperature was above 1,000℃.展开更多
An effective and reproducible preparation of silica sol nanospheres via a modified sol-gel process has been described. Monodisperse and stable silica sol nanospheres with uniformsize were successfully obtained through...An effective and reproducible preparation of silica sol nanospheres via a modified sol-gel process has been described. Monodisperse and stable silica sol nanospheres with uniformsize were successfully obtained through the optimized synthesis in which the mixture of tetraethyl orthosilicate (TEOS) and ethanol was followed by the addition of water and ammonium hydroxide (NH3) separately, and the size of silica sol spheres was strictly controlled in the range of 25-119 nm with a narrow size distribution by fine adjustment of several reaction parameters. Results showed that in the presence of low concentration of TEOS, spheres size rose first and reached maximum when H2O concentration was up to 66 g/L. However, the diameter of silica sol spheres decreased above 66 g/L of H2O concentration. Furthermore, it was also found that the size and size distribution of silica sol nanospheres were affected by NH3 concentration. As NH3 concentration increased from 15 to 35 g/L, the diameter declined from 83 to 64 nm. Nevertheless, higher NH3 concentration would result in relatively broad size distribution, and gelation occurred when NH3 concentration reached 44 g/L. In addition, the effect of the different feed rates ofNH3 on the size growth of silica sol nanospheres was also discussed.展开更多
It’s a universal engineering problem to seal micro-cracks of low-permeability argillaceous rock mass by grouting in the fields of civil engineering and mining.This paper achieved the grouting sealing of lowpermeabili...It’s a universal engineering problem to seal micro-cracks of low-permeability argillaceous rock mass by grouting in the fields of civil engineering and mining.This paper achieved the grouting sealing of lowpermeability artificial rocks with the permeability of 0.1–40 mD by adopting silica sol imbibition grouting.The variation characteristics of particle size,viscosity,and contact angle of silica sol during solidification and the pore size distribution of low-permeability artificial rocks were measured,and spontaneous imbibition tests of the artificial rocks were carried out.Finally,combined with the imbibition theory,percolation theory,and fracture medium grouting principle,the silica sol imbibition mechanism of lowpermeability rocks and soil was discussed.The results show that:(1)Silica sol can be injected into artificial rocks with the minimum permeability of 0.1 mD through spontaneous imbibition;(2)The particle size increase of silica sol leads to decreased wettability,affinity,and injectability in grouting materials;and(3)In the range of 0.1–40 mD,the grout absorption first increases and then decreases with increased permeability.The number of large pores and fractures in the rock mass is related to injectability,and the number of small and medium pores is related to the internal driving force of imbibition.This study provides a theoretical basis for silica sol grouting sealing of low-permeability argillaceous rocks and is,therefore,an important reference for application.展开更多
In this research work silica coating was produced on nickel substrates by a sol-gel process. In order to increase the rate of hydrolysis and to reduce the rate of polymerization several acid catalysts including nitric...In this research work silica coating was produced on nickel substrates by a sol-gel process. In order to increase the rate of hydrolysis and to reduce the rate of polymerization several acid catalysts including nitric acid-hydrochloric acid, acetic acid, hydrochloric acid and nitric acid were add to silica sol. Conversely, in order to control the rate of hydrolysis and to increase the rate of polymerization, basic catalyst of ammonia and ammonia hydroxyl were introduced in to the solution. Nickel specimens of known surface roughness were chemically cleaned and prepared by dipping in the sols. In order to produce a suitable silica coating the drying and firing cycles were optimized on these substrates. The structure and uniformity of the coatings produced were examined by scanning electron microscopy. Coatings composition was determined using glow discharge optical spectroscopy and EDAX microanalysis. Experimental result showed that hydrochloric acid, acetic acid, ammonia and acetic acid - ammonia are suitable catalytic agents for silica coating formation on nickel type substrate.展开更多
Nano silica-modified epoxy resins were synthesized by the sol-gel process, The materials have the morphological structure of nano particales dispersed in the epoxy matrix. The dispersed phase formed a physical network...Nano silica-modified epoxy resins were synthesized by the sol-gel process, The materials have the morphological structure of nano particales dispersed in the epoxy matrix. The dispersed phase formed a physical network in the resin and thus influenced the rheological behavior greatly. However, the nano silica did not show a significant influence on the mechanical properties of the cured resins.展开更多
Mesoporous carbon monolith was synthesized by the direct carbonization of compressed sucrose/silica composite, which was prepared by using sol-gel method. The structural and textural properties of the materials were i...Mesoporous carbon monolith was synthesized by the direct carbonization of compressed sucrose/silica composite, which was prepared by using sol-gel method. The structural and textural properties of the materials were investigated by XRD, DRIFT, N2-adsorption and SEM. The characterization study shows that the resultant carbon monolith possesses a relatively high surface area, large pore volume and well interconnected pore system. Addition of a certain amount of citric acid or aluminum nitrate into the sol-gel precursor of sucrose/silica composite could considerably change the structure parameters of the carbon monolith.展开更多
Structural strengthening of the nano porous silica films has been reported. The films were prepared with a base/acid two-step catalyzed TEOS-based sol-gel processing and dip-coating, and then baked in the mixed gas of...Structural strengthening of the nano porous silica films has been reported. The films were prepared with a base/acid two-step catalyzed TEOS-based sol-gel processing and dip-coating, and then baked in the mixed gas of ammonia and water vapor. The silica films were characterized with TEM, AFM, FTIR, spectrophotometer, ellipsometer, and abrasion test, respectively. The experimental results have shown that the films have a nanostructure with a low refractive index and can form an excellent scratch-resistant broadband anti-reflectance. The two-step catalysis noticeably strengthens the films, and the mixed gas treatment further improves mechanical strength of the silica network. Finally the strengthening mechanism has been discussed.展开更多
The effect of drying techniques on the microstructure,morphology and pore structure of porous silica gels was studied in the paper.The gels were prepared by using sol-gel process and different drying routes:freeze-dry...The effect of drying techniques on the microstructure,morphology and pore structure of porous silica gels was studied in the paper.The gels were prepared by using sol-gel process and different drying routes:freeze-drying (FD),low pressure drying (LPD),high temperature drying (HTD) and chemical modification & ambient drying (CMD) techniques.Observation under pore distribution and structural properties showed that CMD technique leads to homogenous mesoporous silica material with specific surface area of 745 m2/g,and the average pore size around 20 nm,while LPD and HTD result in loosely packed particles with non-isotropic aggregation pattern.The specific surface areas of LPD and HTD samples are 419 and 513 m2/g respectively,and the pore size distribution of the samples are observed distributing widely in range of 10-100 nm.Freeze drying method is a new but prospective way to prepare mesoporous silica.The specific area of FD sample is around 500 m2/g.By the comparison for the properties of the gels,this paper wants to induce a further interest in finding a proper method to synthesize the porous silica gels for low price use.展开更多
基金This work was supported by tile National Natural Science Foundation of China(Grant No.20133040,59802007,69978017)Chinese National Foundation of High Technology(2002AA842052)+2 种基金Shanghai Committee of Science and Technology(055211010,0352nm022,0352nm056)Shanghai Key Subject Programme,Shanghai Phospher Program(05QMH1413)Trans-Century Training Programme Foundation for the Talents by the State Education Commission.
文摘Silica aerogels were prepared by sol-gel technique from industrial silicon derivatives (polyethoxydisiloxanes, E40), followed by silylation and drying under ambient pressure. The specific surface area, pore size distribution and thermal conductivity of the silica aerogels were investigated and the results showed that the diameter of the silica particles is about 6 nm and the average pore size of the silica aerogels is 14.7 nm. The specific surface area of which is about 1000 m^2.g^-1 and the thermal conductivity is about 0.014 wm^-l.K^-1 at room temperature and pressure of 1.01×10^5 Pa. The Si-CH3 groups were also detected on the internal surface of the silica aerogels, which show hydrophobic. Silica aerogels derived by this technique is low cost and have wide applications.
基金the National Natural Science Foundation of China(Grant No.20133040)the Chinese National Foundation of High Technology(2002AA842052)+1 种基金the Shanghai Nanotechnology Promotion Center(0352nm022,0352nm056)the Shanghai International Cooperation Program and Trans-Century Training Programme Foundation for the Talents by the State Education Commission.
文摘Nanoporous silica films were prepared by sol-gel process with base, acid and base/acid two-step catalysis.Transmission electron microscope (TEM) and particle size analyzer were used to characterize the microstructure and the particle size distribution of the sols. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectroscopic ellipsometer were used to characterize the surface microstructure and the optical properties of the silica films. Stability of the sols during long-term storage was investigated. Moreover,the dispersion relation of the optical constants of the silica films, and the control of the microstructure and properties of the films by changing the catalysis conditions during sol-gel process were also discussed.
基金Project supported by the National Natural Science Foundation of China (No. 29874002) and the Outstanding Young Scientist Award from National Natural Science Foundation of China (No. 29825504)
文摘Mesoporous poly(styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis was achieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymer in the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template or pore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m(2)/g) and pore volumes (e.g. 0.6 cm(3)/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, pore volumes and pore diameters of the hybrid materials increase.
基金supported by the Research Fund of the Key Disciplinary of Materials Processing Engineering,Xihua University
文摘Dry stock of silica sol ceramic mould was prepared by using of colloidal moulding technique with an optimized vacuum drying process.Effect of roasting process on the shrinkage rate and compressive strength of zircon-silica sol ceramic mould,and the relationship between the roasting temperature and microstructure of zircon-silica sol ceramic mould were studied.The optimum roasting temperature of zircon-silica sol ceramic mould gained by the experiments is 900℃ and the holding time is 2 h.The scanning electron microscope(SEM) observation showed the growth of refractory particles during the roasting process.The occurrence of sintering was observed in the zircon-silica sol ceramic mould when roasting temperature was above 1,000℃.
基金Funded by the Guangdong Well-Silicasol Company Limited,China
文摘An effective and reproducible preparation of silica sol nanospheres via a modified sol-gel process has been described. Monodisperse and stable silica sol nanospheres with uniformsize were successfully obtained through the optimized synthesis in which the mixture of tetraethyl orthosilicate (TEOS) and ethanol was followed by the addition of water and ammonium hydroxide (NH3) separately, and the size of silica sol spheres was strictly controlled in the range of 25-119 nm with a narrow size distribution by fine adjustment of several reaction parameters. Results showed that in the presence of low concentration of TEOS, spheres size rose first and reached maximum when H2O concentration was up to 66 g/L. However, the diameter of silica sol spheres decreased above 66 g/L of H2O concentration. Furthermore, it was also found that the size and size distribution of silica sol nanospheres were affected by NH3 concentration. As NH3 concentration increased from 15 to 35 g/L, the diameter declined from 83 to 64 nm. Nevertheless, higher NH3 concentration would result in relatively broad size distribution, and gelation occurred when NH3 concentration reached 44 g/L. In addition, the effect of the different feed rates ofNH3 on the size growth of silica sol nanospheres was also discussed.
基金This work was supported by National Natural Science Foundation of China(Nos.52034007,52074263,52108365 and 52104104)the Post-graduate Research and Practice Innovation Program of Jiangsu Province(No.KYCX21_2340).
文摘It’s a universal engineering problem to seal micro-cracks of low-permeability argillaceous rock mass by grouting in the fields of civil engineering and mining.This paper achieved the grouting sealing of lowpermeability artificial rocks with the permeability of 0.1–40 mD by adopting silica sol imbibition grouting.The variation characteristics of particle size,viscosity,and contact angle of silica sol during solidification and the pore size distribution of low-permeability artificial rocks were measured,and spontaneous imbibition tests of the artificial rocks were carried out.Finally,combined with the imbibition theory,percolation theory,and fracture medium grouting principle,the silica sol imbibition mechanism of lowpermeability rocks and soil was discussed.The results show that:(1)Silica sol can be injected into artificial rocks with the minimum permeability of 0.1 mD through spontaneous imbibition;(2)The particle size increase of silica sol leads to decreased wettability,affinity,and injectability in grouting materials;and(3)In the range of 0.1–40 mD,the grout absorption first increases and then decreases with increased permeability.The number of large pores and fractures in the rock mass is related to injectability,and the number of small and medium pores is related to the internal driving force of imbibition.This study provides a theoretical basis for silica sol grouting sealing of low-permeability argillaceous rocks and is,therefore,an important reference for application.
基金supported by electroceramics research center in Malek Ashtar university of Technology(Shahin-Shahr)and Isfahan university of Technology
文摘In this research work silica coating was produced on nickel substrates by a sol-gel process. In order to increase the rate of hydrolysis and to reduce the rate of polymerization several acid catalysts including nitric acid-hydrochloric acid, acetic acid, hydrochloric acid and nitric acid were add to silica sol. Conversely, in order to control the rate of hydrolysis and to increase the rate of polymerization, basic catalyst of ammonia and ammonia hydroxyl were introduced in to the solution. Nickel specimens of known surface roughness were chemically cleaned and prepared by dipping in the sols. In order to produce a suitable silica coating the drying and firing cycles were optimized on these substrates. The structure and uniformity of the coatings produced were examined by scanning electron microscopy. Coatings composition was determined using glow discharge optical spectroscopy and EDAX microanalysis. Experimental result showed that hydrochloric acid, acetic acid, ammonia and acetic acid - ammonia are suitable catalytic agents for silica coating formation on nickel type substrate.
基金This work was supported by the Ford-China Research and Development Fund (No.9415311).
文摘Nano silica-modified epoxy resins were synthesized by the sol-gel process, The materials have the morphological structure of nano particales dispersed in the epoxy matrix. The dispersed phase formed a physical network in the resin and thus influenced the rheological behavior greatly. However, the nano silica did not show a significant influence on the mechanical properties of the cured resins.
基金Supported by the National Natural Science Foundation of China(Nos.20403006 and 20773050)the State Basic Research Project of China(No.2005CB221405)
文摘Mesoporous carbon monolith was synthesized by the direct carbonization of compressed sucrose/silica composite, which was prepared by using sol-gel method. The structural and textural properties of the materials were investigated by XRD, DRIFT, N2-adsorption and SEM. The characterization study shows that the resultant carbon monolith possesses a relatively high surface area, large pore volume and well interconnected pore system. Addition of a certain amount of citric acid or aluminum nitrate into the sol-gel precursor of sucrose/silica composite could considerably change the structure parameters of the carbon monolith.
基金the National Natural Science Foundation of China(No:69978017,20133040)Shanghai Key Subject Programme,Chinese Foundation of High Technology(2002AA842052)Shanghai Natural Science Foundation(02ZE14101)as well as Shanghai Nanotechnology Promotion Center(0159um039).
文摘Structural strengthening of the nano porous silica films has been reported. The films were prepared with a base/acid two-step catalyzed TEOS-based sol-gel processing and dip-coating, and then baked in the mixed gas of ammonia and water vapor. The silica films were characterized with TEM, AFM, FTIR, spectrophotometer, ellipsometer, and abrasion test, respectively. The experimental results have shown that the films have a nanostructure with a low refractive index and can form an excellent scratch-resistant broadband anti-reflectance. The two-step catalysis noticeably strengthens the films, and the mixed gas treatment further improves mechanical strength of the silica network. Finally the strengthening mechanism has been discussed.
基金Sponsored by the National Mega-Project of Scientific & Technical Supporting Programs,Ministry of Science &Technology of China (Grant No.2006BAJ04A04)the Science Foundation of Liaoning Province,China (Grant No. 2008S190)
文摘The effect of drying techniques on the microstructure,morphology and pore structure of porous silica gels was studied in the paper.The gels were prepared by using sol-gel process and different drying routes:freeze-drying (FD),low pressure drying (LPD),high temperature drying (HTD) and chemical modification & ambient drying (CMD) techniques.Observation under pore distribution and structural properties showed that CMD technique leads to homogenous mesoporous silica material with specific surface area of 745 m2/g,and the average pore size around 20 nm,while LPD and HTD result in loosely packed particles with non-isotropic aggregation pattern.The specific surface areas of LPD and HTD samples are 419 and 513 m2/g respectively,and the pore size distribution of the samples are observed distributing widely in range of 10-100 nm.Freeze drying method is a new but prospective way to prepare mesoporous silica.The specific area of FD sample is around 500 m2/g.By the comparison for the properties of the gels,this paper wants to induce a further interest in finding a proper method to synthesize the porous silica gels for low price use.