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.

Glass sealed thin-film electroluminescent display panel free of moisture and the fabrication method thereof

Abstract: A thin-film electroluminescent display panel is sealed by a pair of glass substrates for protection from the environment. A protective liquid is introduced between a counter glass substrate and a substrate for supporting the electroluminescent display unit. The protective liquid comprises silicone oil or grease which assures the thin-film electroluminescent film of preservation in the electroluminescent display panel. The counter glass substrate is bonded to the support substrate through an adhesive of, for example, photo-curing resin. A capillary tube is provided within the glass substrate for injecting the liquid under vacuum conditions. The liquid has the capability of spreading into pin holes generated on dielectric layers, and is resistant to high voltage, high humidity and high temperature and is inert to layers constituting the thin-film electroluminescent display panel and has a small vapour pressure and a small coefficient of thermal expansion. A moisture absorptive member is introduced into the protective liquid. The member can be an Al film coated by silica gel or silica gel particles themselves. The silica gel particles, if necessary, may be confined within a tube or dispersed within the spacer. Alternatively, they are dispersed within the protective liquid. The Al film is adhered to one of the substrates. The member serves to absorb moisture contained within the protective liquid. The protective liquid can be colored by a dye material to provide a background for the EL device.

Silica gel dissolution in aqueous alkali metal hydroxides studied by 29SiNMR

Abstract: The rate of silica gel dissolution in aqueous alkaline media was investigated using 29Si nuclear magnetic resonance spectroscopy. A profound difference of alkali metal hydroxides on the dissolution rate of amorphous silica gel was observed. The dissolution rate increases in order LiOH ≈ CsaOH) < (RbOH ≈ NaOH) < KOH, as was confirmed by the β = silicomolybdate complexation method. Silica gel dissolution involved formation of monomeric silicic acid, Q0. The monomeric anions oligomerise into dimer species, which in turn form cyclic and lineartrimer species. The structure of highly polymerised silicate species depends on the alkali metal cation, i.e. low pH silicate solutions have structurally different silicate species as a function of alkali metal hydroxide, as is shown by 29Si-NMR spectroscopy. Potassium cations gave rise to more polymerised silica species compared with other alkali metal cations studied. On the contrary, when lithium hydroxide and silica gel are mixed in a molar SiO2/Li2O = 1:1, a microcrystalline phase is formed which consists of lithium silicate crystals. Crystallisation of the lithium silicate proceeds via monomeric silica being in solution.

The role of N,N-dimethylformamide, a DCCA, in the formation of silica gel monoliths by sol-gel method

Abstract: In order to find the role of N,N-dimethylformamide (DMF), a newly found DCCA (drying control chemical additive), in producing silica gel monoliths by the sol-gel method, microstructures of the silica gel monolith prepared from tetramethoxysilane (TMOS) solutions containing DMF and formamide, respectively, have been examined. Dry gels prepared from the solutions containing DMF and formamide had larger pores, which was interpreted to be one of the effects of the DCCA in suppressing occurrence of cracks and fractures in the process of drying wet gels. When drying gel discs prepared from solutions containing DMF were exposed to the vapors and, subsequently liquids of DMF, formamide, methanol and water whose surface tensions are different from each other, cracks were generated for formamide and water having high-surface tensions and no cracks were produced for DMF and methanol. This was interpreted to indicate that the low surface tension of DMF may be one of the effects in protecting the drying gel from crack generation. It was assumed that DMF vaporizes at last during the drying process and weakens the capillary force exerting on the silica network structure.

Colloidal gold and silica in mesothermal vein systems

Abstract: Some of the textural features of mesothermal gold-quartz veins may be best explained by the initial precipitation of amorphous silica gel (colloid), which subsequently crystallizes to quartz. This can occur in brittle-ductile shear zones where a significant fluid-pressure drop occurs during stick-slip failure. Such a process rapidly supersaturates the hydrothermal fluid with respect to amorphous silica, which precipitates instead of quartz, owing to favorable kinetics. Depressurization also commonly leads to fluid unmixing and destabilization of soluble gold complexes. However, the presence of colloidal silica can stabilize gold colloid, allowing further transport of particulate gold in suspension in the hydrothermal fluid. Silica gel would be highly unstable under mesothermal conditions and would undergo rapid syneresis and crystallization to form quartz; solid impurities would tend to be expelled toward grain boundaries. This model can account for the primary anhedral aggregate textures typical of mesothermal quartz veins, the concentration of gold along grain boundaries and the formation of discrete gold nuggets, and the rare occurrence of low-order silica polymorphs and relict spheroidal structures. The transport of gold in colloidal form may be one reason for the frequently consistent bulk grade distribution in gold-quartz vein systems over many hundreds of metres (in some cases kilometres) of depth. In addition, the formation of charged colloidal particles may help to explain the attraction of gold grains to specific mineral surfaces.