A novel technique for the preparation of gels and powders of AI203-Si02 system by the sol-gel method (original) (raw)
Related papers
Structural investigation of gel-derived materials from the SiO2Al2O3 system
Journal of Molecular Structure, 2018
Aluminosilicate glasses from the binary SiO 2 eAl 2 O 3 system, AT1 (50% SiO 2-50% Al 2 O 3 , %mol) and AS1 (80% SiO 2-20% Al 2 O 3 , %mol), were obtained by the sol-gel process in the form of powders. Additionally, Al 2 O 3 and vitreous SiO 2 were synthesized by the same technique and used as reference materials. The essential information concerning samples structural properties was provided by the XRD diffraction and the FTIR and UV Raman methods. The XRD confirmed the amorphous character of the materials, except for the pure Al 2 O 3, where a small tendency for crystallization of the geAl 2 O 3 phase was noticed. The local environment of silicon and aluminum atoms was determined by the 29 Si and 27 Al MAS-NMR as well as 27 Al 3MQ-MAS-NMR spectroscopies. Moreover, for the materials containing Al 2 O 3, the average Al coordination parameter was calculated basing on the data provided by the 27 Al MAS-NMR. The 29 Si MAS-NMR spectra of the materials indicated various chemical environments around silicon amongst particular materials and presence of the Q 2 , Q 3 , and Q 4 structural units. Moreover, the data provided with the 27 Al MAS-NMR indicated the presence of aluminum in the AlO 4 , AlO 5, and AlO 6 coordination forms. Proportions of the particular units revealed favoring formation of the Al in the higher coordination (AlO 5 and AlO 6) over commonly the dominant AlO 4 units, which can be explained by the charge balance requirement in the system that is deprived of charge compensating alkali cations.
2007
Roumanian Academy, Institute of Physical Chemistry “Ilie .Murgulescu”, 202 Splaiul Independentei, 060021 Bucharest, Roumania, E-mail: mzaharescu@icf.ro 2 Department of Material Science and Engineering, Rutgers University, 607 Taylor Rd, Piscataway, NJ 08854, USA National NMR Laboratory, Institute of Organic Chemistry ”C.D. Nenitescu”, 202B Splaiul Independentei, 060021 Bucharest, Roumania Chemical Research Institute, 202 Splaiul Independentei, 060021Bucharest, Roumania
Comparative study of the sol–gel processes starting with different substituted Si-alkoxides
Journal of Non-crystalline Solids, 2003
In the present work a comparative study of the hydrolysis-polycondensation processes of different Si-substituted alkoxides, leading to hybrid materials with covalent -Si-C-bonds, was carried out. The following alkoxides were used: tetraethoxysilane (TEOS), methyltriethoxysilane (MTEOS) and vinyltriethoxysilane (VTEOS). Using gas chromatography coupled with mass spectrometry (CG-MS), nuclear magnetic resonance ( 29 Si-NMR) and infrared spectrometry (IR), information about the sol-gel process in the mentioned systems were obtained. The differences in the reactivity of the studied alkoxides are connected with the steric effect of the organic substituents. The reactivity of the alkoxides in the early stages of the hydrolysis-polycondensation process increased in the order TEOS < VTEOS < MTEOS.
Structural Investigations of Alkali Silicate Gels
Investigation of a series of synthetic alkali silicate gels and gels produced by the alkali silica reaction (ASR) in field concrete using 29 Si NMR spectroscopy, X-ray diffraction, and bulk chemical analysis shows that local structures of the synthetic and field gels are quite similar. The most abundant Si sites for the field and synthetic gels with similar compositions have Q 3 polymerization, and the number of non-bridging oxygens per Si is similar for these samples. These samples also yield a basal X-ray diffraction peak near 8-12 Å , suggesting that the structure is dominated by sheet-like units, consistent with the dominant Q 3 polymerization. Calculations based on the relative site abundances of the sites observed by 29 Si NMR and the bulk chemical compositions indicate that there is insufficient alkali to charge-balance all the non-bridging oxygens and that there is a significant concentration of Si-OH linkages. The results provide strong support for the basic structural concepts of the so-called kanemite model for ASR gel proposed by Wieker and coworkers, although the overall gel structure is likely to be more complex.
27 Al and 29 Si NMR study of sol-gel derived aluminosilicates and sodium alumino
J Mater Sci, 1988
Solid state 27AI and 29Si NMR was used to examine the structures of aluminosilicates and sodium aluminosilicates prepared by the sol-gel method from metal alkoxides. In contrast to the borosilicate system, where B-O-Si bonds are not formed until heat treatment above 1 50 ~ C, AI-O-Si formation appears complete upon gelation. Aluminium occupies tetrahedral [AIO4]-sites in the polymer network and octahedral [AI(H20)6] 3+ (or similar) sites in the intersticies for charge balance. When sodium is added as a counter ion the octahedral aluminium is converted to tetrahedral aluminium in the oxide network. In gels of high aluminium content prepared from (BuSO)2AI-O-Si(OEt)3, some aluminium in five coordinate environments is also observed. All gels remain amorphous on heating to 800 ~ C.
Synthesis of silicalite-1 from organo-silicic gels
Journal of colloid and interface science, 2008
Well crystallized silicalite-1 has been obtained from three sources of amorphous silica, namely, rice hull ashes, commercial Davisil, and a fume silica from Aldrich. The silicas were first dissolved in glycerol according to a recently described reaction. This reaction transforms rapidly and efficiently large surface area silicates into poly-alkoxide gels. It can be schematized as an etherification of an alcohol function of glycerol by the weakly acid surface silanol groups. The facile hydrolysis of the alkoxide permits the preparation of relatively pure and reactive silica, keeping the mesoporous character of the parent starting material. We insist on the mesoporous character of the solids obtained upon hydrolyzing the organo-silicic gel because we believe the gel plays a role of template in the secondary synthesis of mesoporous structures. The hydrolysis is carried out in presence of a structure directing agent, namely tetra-propylammonium hydroxide, TPAOH. After aging, the residue is dried and calcined. The first advantage of using the organo-silicic gel is probably related to the high degree of depolymerization of silica, witness by the C/Si ratio. The second one, more subtle to define, is to provide an intermediate silica with hydrophilic a hydrophobic regions, interfering differently with the surfactant. After calcination at 500 °C, well crystallized silicalite-1 is obtained. The texture of the starting silica influences the textural characteristics of the final silicalite-1.Left: silicalite-1 structure. Center: correlation between pore volume of silicalite-1 and pore volume of the starting silica. Right: large crystal of silicalite-1 obtained from rice hull ash (SLR).
Journal of Non-crystalline Solids, 2010
SiO 2 -Na 2 O-CaO based bioglass-ceramics was synthesized through sol-gel route using rice husk ash as silica source. The decomposition behavior of gel was evaluated. Sodium-calcium-silicate phases were crystallized above 700°C. Pellet made of glass-ceramics powder was sintered at 900°C. In vitro bioactivity and biodegradability of glass-ceramics were investigated by incubation in simulated body fluid and Tris buffer solution respectively. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to monitor the surface deposition on glass-ceramics during incubation. The material showed a good bioactivity with a formation of carbonated hydroxy apatite phase in 3 days of incubation. A quick degradation of the material was observed in Tris solution associated with an increase of pH due to the dissolution of Ca 2+ and Na + ionic species. All these results suggest the glass-ceramics, prepared utilizing rice husk ash, would be a low cost biomaterial for potential biomedical applications.