Silica thermal analysis

Thermal analysis techniques reveal that water is bound in opal in more than one manner. Most of the water is physically held in inclusions or microscopic pores within the opal, that is, in spaces between the microspheres. Water held in this manner can escape through complex systems of microscopic fissures or cracks, induced by temperatures even below 100°C. Some water is held within the opal via chemical bonding ( adsorption ) to the surfaces of the silica microspheres and is retained to temperatures approaching 1000°CJ7J Furthermore, since the microspheres themselves are composed of much smaller silica particles, water is additionally coated on the surfaces of these minute particles. The porous nature of opal and its thermal sensitivity require special care, for dehydration may result in cracking that greatly diminishes the value of this gemstone. 

The parent siliceous materials of the SBA-15 and MLV types were synthesised after typical procedures [2], The carbon replicas were prepared via polymerisation, catalysed by ferric chloride, of pyrrole introduced into the mesopores of matrices [3]. The products were characterised by the nitrogen adsorption, TEM, and thermal analysis (DTG, DTA). The nitrogen content in carbons was determined using elemental analysis, XPS, and EDX, while the Si and Fe contents, with XPS. The replicas of SBA-15 and MLV-0.75 are denoted as CMK-3Nx and OCM-.Nx, respectively, were x refers to the number of g of FeCl3 per 1 g of silica used for preparations. 

Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) curves of the Ag/Si02 sample prepared by the two-step method are shown in Fig. 6.10. The TGA curve exhibits two evident weight loses, which are in the range of ca. 100 to 250°C and 250 to 550°C, corresponding to the loss of solvent, water, ethanol and THF, and the decomposition of organic silica, respectively. Four evident endothermic peaks can be observed from DTA curve, which centered at ca. 200°C, 350°C, 425°C and 480°C, respectively. 

On comparing reducibility and the results of differential thermal analysis, it can be seen that the order of difficulty with which the preparations are reduced is the same as the order of difficulty with which they are decomposed. One might therefore expect the decomposition of hydrosilicate into nickel oxide, silica, and water to determine the velocity of the reduction... 

We believe that these phenomena can be explained byassuminga skin of silica on the metal surface. The fact that such a skin develops is readily acceptable for the hydrosilicates, since actually the prereduction state shows this skin in the form of Si206 layers on top of the octahedral layers containing the Ni++ ions. That, however, even co-precipitation catalysts such as 5421 in which no hydrosilicate formation could be observed by thermal analysis show inaccessibility comes somewhat as a surprise (Fco/Fr = 0.8 46% Ni removable). 

This final degradative step in the thermal analysis can, of course, be replaced by some other analytical technique. Of course, water and possibly other volatile additives may have been lost. A novel approach which has been suggested involves trapping temperature fractions (e.g., 100-300 300-400 etc.) from the heated effluent of a TGS-1 (or possibly of a modified DSC-2), on a substrate such as a charcoal or silica gel filter, removal by heat or solvent and running gas chromatography on the degradation products. 

An examination of the magnetic susceptibility, thermal analysis characteristics, and X-ray powder patterns of samples of V02+ c( — 0.02 x < 0.03) prepared by heating V205-V203 mixtures in silica tubes has shown that the homogeneity range for V02 is very narrow.393"... 

Blumberg, A. A. Differential Thermal Analysis and Heterogenous Kinetics The Reaction of Vitreous Silica with Hydrofluoric Acid. J. Phys. Chem. 63, 1129 (1959). 

Shalliker, R.A. Douglas, G.K. Rintoul, L. Russell, S.C. The analysis of zirconia-silica composites using differential thermal analysis, Fourier transform-Raman spectroscopy and X-ray scattering/scanning electron microscopy. Powder Technol. 1998, 98, 109-112. 

The thermal extraction (calcination) of cetyltrimethyl ammonium bromide, which is one of the surfactant templates, from a pure silica mesophase to form MCM41 has been studied using SCTA (Sample Controlled Thermal Analysis) by the Marseilles Group. 

All the displacive inversions of silica exhibit well discernible enthalpic effects on DTA (differential thermal analysis) curves. Pure quartz produces a minor but... 

Polydimethylsiloxane and Zr oxo species have been reacted to give hybrid materials which were characterized by solid-state NMR.149 TEOS/PEG (polyethylene glycol) materials are biphasic systems. The materials were studied by 13C NMR, EPR, and thermal analysis.150 Other systems studied include titania/polyvinylacetate,151 titania/PEG,152 silica/polyacrylates,153 polyimide/ silica,154"156 linseed oil alkyds/titania,157 and PVC/titania and vanadia/sulfonated polyaniline... 

In addition, SCTA offers a unique possibility for preparative scale thermal analysis whilst maintaining high levels of sensitivity and resolution. Such an SCTA system has recently been developed.The focus of the system is a microbalance and a high-temperature water-cooled furnace, located above the balance and allowing operation to 1000°C. The sample is contained in a silica or platinum crucible and sits on top of a rise rod connected directly to the balance pan. Samples in excess of 1 g can be investigated, but routinely, samples of 500 mg are usually involved. Grinding of powdered samples to mesh size 150-250 pm is advantageous. The sample temperature is monitored by a thermocouple located centrally within the furnace tube. Radiation shields attached to the thermocouple... 

Sintered deposits form at the furnace exit at lower gas temperatures and in zones subject to rapid changes in direction. The deposit is composed of spheroidal particles, <40p, bound together by a molten substance. In those cases where substantial quantities of coarse pyrites are liberated from the pulverized coal, the spheroids are nearly pure FeaOa, as shown in Figure 11. The matrix contained silica, alumina, iron, and potassium, and has an initial deformation temperature of 1832°C, as determined by differential thermal analysis. The heavier pure iron spheroids deposit as a result of inertial impact. The mineral source of the molten phase is most likely illite. 

The silica content of the samples was determined with a Rigaku 3271E X-ray spectrometer. BET surface areas were measured on a Micromeritics ASAP 2010 Analyzer. X-ray powder diffraction patterns were recorded on a Rigaku D/MAX-2000 with Cu Ka radiation (The common Sn02 samples were analysed with a BD-86 X-ray Diffractometer). DTA-TG measurements were carried out on a Thermal Analysis SDT 2960 with a heating rate of 10 C/min. 

The sol-gel titania-silica mixed oxide contained 20 wt% titania. The catalyst was synthesized imder acidic conditions [5]. The acidic hydrolysant was added to an isopropanohc solution of tetraisopropoxytitanitam(IV) modified by acetylacetone (molar ratio alkoxide acetylacetone =1 1) and tetramethoxysilicon(IV). The water alkoxide acid molar ratio was 5 1 0.09. The resulting gel was dried by semicontinuous extraction with supercritical COg at 40 °C and 240 bar, and stored in a closed vessel under Ar. After calcination in flowing air at 600 °C, the BET smface area was 648 m g and the specific pore volume 2.9 cm g". Details on the synthesis and characterization of the sol-gel titania-sihca by means of FTIR, Raman and UV-vis spectroscopies, Ng-physisorption, XRD, XPS, TEM and thermal analysis have been reported previously [5, 6, 14, 15]. 

In another example of this technique, D. E. Cranton,36 at Imperial Oil, as part of a study on base stock oxidation stability, separated a midcontinent 150N solvent refined oil by thermal analysis and the ten fractions obtained were then further separated into saturates and aromatics by silica gel chromatography. Mass spectral analyses (Tables 3.11 and 3.12) show the results of the separation obtained in... 

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