Influence of processing variables on the pore structure of silica gels obtained with tetraethylorthosilicate

Silva, Rubia F.; Vasconcelos, Wander L.

doi:10.1590/s1516-14391999000300014

Cited by 27 publications

(14 citation statements)

References 2 publications

(2 reference statements)

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“…10 to be 84 and 73 kJ/mol for monodisperse 3M particles and polydisperse NexSil5 particles, respectively. These apparent activation energies for bridging of aggregates are comparable to the values reported by Silva and Vasconcelos (1999); Wang and Zhang (2009) and Amiri et al (2011). The decrease in gelation time at high temperature was attributed to larger Brownian motion of the particles resulting in faster collisions (Metin et al 2011).…”

Section: Rheological Measurementssupporting

confidence: 84%

Phase behavior and rheological characterization of silica nanoparticle gel

2012

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Preferential injection into high permeability thief zones or fractures can result in early breakthrough at production wells and large unswept areas of high oil saturation, which impact the economic life of a well. A variety of conformance control techniques, including polymer and silica gel treatments, have been designed to block flow through the swept zones. Over a certain range of salinities, silica nanoparticle suspensions form a gel in bulk phase behavior tests. These gels have potential for in situ flow diversion, but in situ flow tests are required to determine their applicability. To determine the appropriate scope of the in situ tests, it is necessary to obtain an accurate description of nanoparticle phase behavior and gel rheology. In this paper, the equilibrium phase behavior of silica nanoparticle solutions in the presence of sodium chloride (NaCl) is presented with four phase regions classified as a function of salinity and nanoparticle concentration. Once the gelation window was clearly defined, rheology experiments of silica nanoparticle gels were also carried out. Gelation time decreases exponentially as a function of silica concentration, salinity, and temperature. Following a power law behavior, the storage modulus, G 0 , increases with particle concentration. Steady shear measurements show that silica nanoparticle gels exhibit nonNewtonian, shear thinning behavior. This comprehensive study of the silica nanoparticle gels has provided a clear path forward for in situ tests to determine the gel's applicability for conformance control operations.

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Section: Rheological Measurementssupporting

confidence: 84%

Phase behavior and rheological characterization of silica nanoparticle gel

2012

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“…The decrease in gelling time as gelling agent concentration was increased is in agreement with work by Silva and Vasconcelos 27 on the gelation of sol-gel-derived silica with the use of HF catalysis. However, they found that the mean diameter of mesopores increased from 7 to 21 nm as HF concentration increased from 0.02 to 0.12 M, but the surface area decreased and the permeability increased.…”

Section: Gelling Agentsupporting

confidence: 90%

Factors affecting the structure and properties of bioactive foam scaffolds for tissue engineering

2003

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Resorbable 3D macroporous bioactive scaffolds have been produced for tissueengineering applications by foaming sol-gel-derived bioactive glasses of the 58S (60 mol% SiO 2 , 36 mol% CaO, 4 mol% P 2 O 5 ) composition with the aid of a surfactant. Bioactive glasses are known to have the ability to regenerate bone, and to release ionic biological stimuli that promote bone-cell proliferation by gene activation. The foams exhibit a hierarchical structure, with interconnected macropores (10 -500 m), which provide the potential for tissue ingrowth and mesopores (2-50 nm), which enhance bioactivity and release of ionic products. Many factors in the sol-gel and foaming processes can be used to control these pore sizes and distributions. This work concentrates on the effect of the processing temperature, gelling agent concentration, and the amount of water used for the foam generation on the structure, pore morphology, and the properties of the foam scaffold. The simplest and most reproducible method for controlling the modal pore diameter was by the amount of water added during the foaming process. The in vitro dissolution and bioactivity of the bioactive foams were compared to that of unfoamed monoliths and powders (< 20 m in diameter) of the same composition.

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“…Glasses obtained by this method have been recommended for several applications such as bioactive materials; encapsulation of proteins, enzymes and biomolecules for controlled drug delivery; and, incorporation of nuclear waste. A new generation of ceramic materials with great structural properties has emerged with the sol-gel processing due to the possibility of manipulation and control of the nanoestructures 7,8 .…”

Section: Introductionmentioning

confidence: 99%

Analysis of bioactive glasses obtained by sol-gel processing for radioactive implants

2003

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This paper presents the chemical and physical characterizations of SiO 2 and SiO 2 -CaO bioactive glasses incorporated with samarium atoms, produced by sol-gel synthesis. The objective is to provide biocompatible and biodegradable radioactive seeds as an alternative to be used in Brachytherapy for the treatment of prostate cancer. The glasses were produced and analyzed by X-ray fluorescence spectroscopy (XRF), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), He picnometry and nitrogen adsorption analysis. A theoretical evaluation of the specific activity of the samples upon neutron activation is proposed. The XRF and EDS results demonstrate the incorporation of samarium atoms in the glass matrix. The experimental data coupled with the theoretical studies in neutron activation suggest that it is possible to obtain radioactive seeds with activities equivalent to 125 I seeds used in brachytherapy prostatic.

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Influence of processing variables on the pore structure of silica gels obtained with tetraethylorthosilicate

Cited by 27 publications

References 2 publications

Phase behavior and rheological characterization of silica nanoparticle gel

Phase behavior and rheological characterization of silica nanoparticle gel

Factors affecting the structure and properties of bioactive foam scaffolds for tissue engineering

Analysis of bioactive glasses obtained by sol-gel processing for radioactive implants

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