Silica-carbon composite

First preliminary variants of DDM were applied in the full-profile X-ray diffraction structure analysis of a series of new silica mesoporous materials and ordered nanopipe mesostructured carbons. DDM allowed stable back-ground-independent full-profile refinement of the structure parameters of these advanced nanomaterials, a result that was unattainable by any other method. To date, DDM has been applied to many various mesoporous and mesostructured substances. The structural parameters of a series of face-centred cubic (Fm3m), body-centred cubic Im3m), and two-dimensional hexagonal (pGmm) mesoporous silicates were determined by DDM from synchrotron XRD. A comprehensive structural analysis of mesoporous silicates SBA-16 (cage-type cubic Irriim), their carbon replicas, and silica/carbon composites was performed by applying DDM. The structure of MCM-48 mesoporous silicate materials was analysed in detail by DDM from different laboratory and synchrotron XRD data. The pore wall thickness of both as-made and... 

Firstly, a mesoporous silica S , like SBA-15 is impregnated with an organic carbon source [5]. Carbonization of this precursor results in a silica/carbon composite, from which the mesoporous carbon C is obtained by dissolution of the silica. The pores of this carbon are impregnated with a gel for the synthesis of a zeolite which is subsequently submitted to a hydrothermal synthesis yielding a zeolite/carbon composite. Combustion of the carbon and the template molecules should result in mesoporous zeolite Z . 

The SAXRD patterns of samples S41, the silica/carbon composite, C41 and Z41(X) are demonstrated in Fig. 2. The pattern of S41 shows three distinct peaks, which can be attributed to the 100, 110 and 200 reflections of a pseudohexagonal unit cell with an unit cell parameter oq equal to 4.02 nm. After carbonization of the impregnated sucrose in the mesopores, the silica/carbon composites shows one peak with decreased intensity which can be attributed to the 100 reflection of a pseudohexagonal system with ag = 3.54 nm. The pattern of C41, obtained after dissolution of the silica, shows only a shoulder around 2.38 29, corresponding to a plane distance of 3.71 nm. For samples Z41(X) obtained after calcination of the respective zeolite/carbon composites, no reflections can be observed below 7 20 and only peaks attributable to the microporous ZSM-5 structure are evident around 8 and 9 20. The formation of... 

The reduced intensity of the SAXRD pattern of the silica/carbon composite is probably due to a similar scattering power between the silica framework and the pore filling carbon [15]. On the other hand, the observed decrease of the unit cell parameter of the silica/carbon composite might be caused by condensation of the SiOH groups in the pore walls during carbonization at 800 °C. Therefore, the hexagonal mesoporous structure is probably preserved in the composite and only collapses after dissolution of the silica framework. 

FIGURE 2.35 (a) Nitrogen adsorption isotherms and (b) BJH-PSDs of silica-carbon composite, mesoporous carbon, and mesoporous silica. (From Su, F. and Zhao, X.S. Unpublished work, 2006c.)... 

Tan, X.C.,Tian, Y.X., Cai, P.X. andZou, X.Y. (2005) Glucose biosensor based on glucose oxidase immobilized in sol—gel chitosan/silica hybrid composite film on Prussian blue modified glass carbon electrode. Analytical and Bioanalytical Chemistry, 381, 500-507. 

The chemical composition of the cooling water makeup supply used in the plant determines the choice of the cycles of concentration. Some of the important constituents that must be controlled in the tower are calcium, magnesium, silica, carbonate, bicarbonate and sulfate ions. Alkalinity levels are regulated by the addition of acid or alkali to achieve the desired pH. When adding H2S04 (sulfuric acid) for pH control, it should be assured that calcium sulfate solubility limits are not exceeded (see Chapter 8). 

Synthetically, the question of which product is formed from a given carbonyl compound, the pinacol or the alcohol, is obviously of great interest. We have already noted the critical importance of the proton-donating ability of the medium in this respect. Attention has turned to the effect of other variables on the pinacol/alcohol ratio. Formaldehyde can be reduced cleanly to ethylene glycol at an electrode composed of a special type of carbon, in a process of potential commercial significance50. Nonaka and coworkers have found that reduction of aldehydes proceeds more selectively to aldehydes at nickel-Teflon-silica gel composite electrodes51. Nonaka and coworkers have also shown that for aromatic... 

The listed chemical formulae are ideal and most of these minerals contain trace and minor elements which undoubtedly affect the CL. Several of these minerals have polymorphic or compositional varieties which also may, or do, show CL (e.g. the silica polymorphs quartz, cristobalite, tridymite phosphate compositional varieties apatite, whitlockite, farringtonite, buchwaldite carbonate compositional varieties calcite, dolomite, magnesite). Glass and maskelynite (shock modified feldspar), although not strictly minerals, are relatively common. Below are described the CL observations for the most common phases including enstatite, feldspar and forsterite and they are related to their use for interpreting the mineralogy of meteorites. The observations for the other minerals are sporadic and many details have yet to be studied. 

The aim of this work was to study the effect of solutions of polystyrene as a precursor on the fabrication, by carbonization, of carbon nanostructures in fine silica based composites-matrices. 

Instead of the system silica/silicate also other systems such as titania/titanate, zirconia/zirconate can be used as a reference system [xiv]. The response time of freshly fabricated thick-film sensors based on thin-film /3-alumina is very short (about 15 ms at 650 °C). After several weeks of operating this time increases 10 times (150 ms) [xv]. Solid electrolyte C02 sensors using Ni/carbonate composite as measuring electrode are suited for measuring of C02 in equilibrated water gases [xiv]. Using semiconducting oxides and carbonates like ITO (indium tin oxide) Nasicon-based C02 sensors are able to measure at room temperature [xvi]. 

Special methods of incorporation carbon fiber was added at the end of mixing to limit breakage " silane addition stage was varied to improve properties of silica-filled composite ... 

The early sulfur cements were used to join clay sewer pipe, clay tile, cast iron pipe, paving brick, acid reaction vessels, and for similar applications. The composition of the materials varied but were mostly sulfur containing 1-10% of an organic polysulfide. Silica, carbon black, and wood rosin also were used frequently. However, the compositions varied considerably, and one promising material contained 60% air blown asphalt and 40% sulfur (49). 

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