Silica gel

About: Silica gel is a research topic. Over the lifetime, 22313 publications have been published within this topic receiving 325516 citations. The topic is also known as: Amorphous silica & Precipitated amorphous silica.

Two Luminescent Molecular Hybrids Composed of Bridged Eu(III)-β-Diketone Chelates Covalently Trapped in Silica and Titanate Gels

Abstract: In the context, a kind of β-diketone, dibenzoylmethane (DBM) was first grafted with the coupling reagent 3-(triethoxysilyl)-propyl isocyanate (TESPIC), and the as-derived monomers were introduced into inorganic network through powerful covalent bonds. Subsequently, two novel chemically bonded hybrid materials, Eu(III)-modified dibenzoylmethane with silica and titanate hosts, were prepared and characterized by IR, phosphorescence, fluorescence spectroscopy, time-resolved photoluminescence spectroscopy, and scanning electron microscopy (SEM). The above spectroscopic data indicate that the modified DBM could sensitize Eu(III) ions to exhibit attracting red luminescence in the two respective hosts. It is noted that the covalently bonded silicate hybrid material presents a stronger red/orange intensity ratio, longer lifetimes, and higher quantum efficiency than a covalently bonded titanate one and europium complex of DBM, suggesting that the silica network is more suitable for the emissions of covalently bonde...

Conversion of melt-derived microfibrous borate (13-93B3) and silicate (45S5) bioactive glass in a simulated body fluid

Abstract: Microfibrous bioactive glasses are showing a considerable capacity to heal soft tissue wounds, but little information is available on the mechanism of healing. In the present study, the conversion of microfibrous borate bioactive glass (diameter = 0.2–5 μm) with the composition designated 13-93B3 (5.5 Na2O, 11.1 K2O, 4.6 MgO, 18.5 CaO, 3.7 P2O5, 56.6 B2O3 wt%) was evaluated in vitro as a function of immersion time in a simulated body fluid (SBF) at 37 °C using structural and chemical techniques. Silicate 45S5glass microfibers (45 SiO2, 24.5 Na2O, 24.5 CaO, 6 P2O5 wt%) were also studied for comparison. Microfibrous 13-93B3 glass degraded almost completely and converted to a calcium phosphate material within 7–14 days in SBF, whereas >85 % of the silica remained in the 45S5 microfibers, forming a silica gel phase. An amorphous calcium phosphate (ACP) product that formed on the 13-93B3 microfibers crystallized at a slower rate to hydroxyapatite (HA) when compared to the ACP that formed on the 45S5 fibers. For immersion times >3 days, the 13-93B3 fibers released a higher concentration of Ca into the SBF than the 45S5 fibers. The fast and more complete degradation, slow crystallization of the ACP product, and higher concentration of dissolved Ca in SBF could contribute to the capacity of the microfibrous borate 13-93B3 glass to heal soft tissue wounds.

Organic/inorganic polymer hybrids

Abstract: The present article describes a group of new materials by the combination between organic polymer and silica gel, one of typical inorganic substances. Characteristics of these materials exist in the dimension of blending of the two components, i.e., blending at the molecular level dispersion. The new materials are transparent glassy ones, which are well expressed by a word of “Hybrid”. The hybrids are readily prepared by the sol-gel reaction of Si(OEt)4, the precursor of silica gel, in the presence of an organic polymer which consists of a repeating unit containing -N(R)-C(=O)- group (R=hydrogen or alkyl), i.e., N-alkyl or N,N-dialkyl substituted carboxyl amide, urea and urethane groups. Hydrogen-bond between the above group of organic polymer component and silanol group which is a key intermediate of the sol-gel reaction plays an important role to form a homogeneous transparent material. The formation of hydrogen bond has been established by FT-IR spectrum, i.e., the shift of vC=O absorption. Calcination of the transparent hybrid produces another interesting material of highly porous silica gel. At a higher temperature, e.g. 600°C, the organic polymer is decomposed but the framework of silica gel remains unchanged. Thus, the space which organic polymer occupies becomes a pore. The new porous silica gel is characterized by a high surface area of inner surface (∼ 810 m2/g) and a pore size of diameter around 20 A.

Silica gel formation during fault slip: Evidence from the rock record

Abstract: Dynamic reduction of fault strength is a key process during earthquake rupture. Many mechanisms for causing coseismic weakening have been proposed based on theory and laboratory experiments, including silica gel lubrication. However, few have been observed in nature. Here we report on the fi rst documented occurrence of a natural silica gel coating a fault surface. The Corona Heights fault slickenside in San Francisco, California, is covered by a shiny layer of translucent silica. Microstructures in this layer show fl ow banding, armored clasts, and extreme comminution compared to adjacent cataclasites. The layer is composed of ~100 nm to 1 µm grains of quartz, hydrous crystalline silica, and amorphous silica, with 10‐100 nm inclusions of Fe oxides and ellipsoidal silica colloids. Kinematic indicators and mixing with adjacent cataclasites suggest the shiny layer was fl uid during fault slip. The layer therefore represents a relict silica gel that formed during fault motion, and which could have resulted in frictional instability. These observations confi rm that the silica gels formed in rock friction experiments do occur in natural faults and therefore that silica gel formation can act as a dynamic weakening mechanism in faults at shallow crustal conditions.