Silica determination

Values of pore volume of samples of porous silica, determined by ethanol titration (v (EtOH)) and by mercury porosimetry (v (Hg, i) and v (Hg, ii)) ... 

Table 38.1. Ninhydrin assays for surface amines using grafted silicas. Determined from grafting synthesis and elemental analysis. "Typical standard deviations were...

Brown, Berni and Mitcham (17) report ash, aluminum, silicon and silica contents of four samples taken from an electrostatic precipitator in a model card room. The silica determinations were made using X-ray diffraction and IR spectroscopy. The results are shown in Table XIII. Based on these data, only a small fraction of the silicon can be attributed to silica. 

Metal Content of Old and TEOS Type Silicas Determined by ICP/AES after Dissolution of Silica... 

For the modification of silica with aminosilanes, the liquid phase procedure is usually applied. Only few studies have described the vapour phase APTS modification.6,7 The modification proceeds in three steps, (i) A thermal pretreatment of the silica determines the degree of hydration and hydroxylation of the surface, (ii) In the loading step, the pretreated substrate is stirred with the silane in the appropriate solvent, (iii) Curing of the coating is accomplished in a thermal treatment. On industrial scale ethanol/water is used as a solvent, on lab-scale an organic solvent is used. The reasons for this discrepancy is the increased control on the reaction processes, possible in an organic solvent. This will be clarified by the discussion of the modification mechanism in aqueous solvent and the effect of water in the different modification steps. 

Kf is a function of properties of the liquid enclosed in the pores (constant). The tf term is tentatively proposed to be identical to the thickness of a surface layer of nonfteezing water, which effectively reduces the actual pore radius frrom rp to rp - tf. The pore size distribution of amoiphous silica determined independently by NMR and nitrogen adsorption agreed well. However, the application of this method to microporous materials (rp < 10 A) may be limited. By establishing a correlation between the freezing point depression AT and the pore size rp of mesoporous mat ials, a new method for the determination of pore size distributions was created (81). 

The chemical compositions of the ancient Egyptian Blue samples (reported in the following section) were determined by atomic absorption spectrophotometry using the hydrofluoric acid digestion method together with the lithium metaborate fusion method for the silica determination (9). Some 20-30 mg of powder drilled from the objects was used for these analyses. Additionally, the arsenic concentrations were determined by x-ray fluorescence spectrometry. The precision of the analytical data was 1-2% for the major elements (>10% concentration) and deteriorated to 5-20% for the trace elements (<0.1% concentrations). However, due to the inhomogeneity of the material, variations in elemental concentrations (i.e., major, minor, and trace) of 10-15% can be expected within a single object. 

Cardenas, J.T., Surface charge of silica determined using X-ray photoelectron spec-ti oscopy. Colloids. Surf. A, 252, 213, 2005. 

Fig. 5.6-2 Schematic illustration of the orientation of imidazolium cations at the surface of silica determined by sum-frequency vibrational spectroscopy [45],...

In the Polish standard PN-87/B-01 1000 the classification, names and determination of particular types of aggregates are given. In the PN-EN 932-3 standard the simplified method of aggregate petrographic constitution verification is recommended, and eventually the chemical composition analyzing. In the PN-G-11010 Polish standard the methods of some hazardous components determination in water leachates are given. Finally, in the PN-EN 1744 standard a group of methods of harmful components (chlorides, fluorides, sulphates), as well as the reactive silica determination is recommended. 

Fig. 5.7 Crack propagation values 7/ of S-SBR vulcanizates with different contents of silica, determined at different sizes of crack opening /r.

For classes (a)-(c) and for SiC, the main analysis solution is prepared via a low flux/sample ratio fusion or, in the case of alumina, a sinter at 1200°C. The flux used is a mixture of fusion mixture (NaKCOs) and boric acid a lower flux/sample ratio is used for aluminous materials, and a larger flux/ sample ratio is used for zircons. The melt is dissolved and the silica is dehydrated in a mixture of hydrochloric and sulfuric acids with the assistance of polyethylene oxide. The main silica is then determined gravimetrically. Other constituents, including residual silica, are determined on the filtrate combined with the residue remaining after the gravimetric silica determination. 

Petrographical studies on thin sections and X-ray diffraction were made and the results obtained were compared with the behavior of these aggregates in structures in service and with standard test methods (accelerated mortar bar method, ASTM 1260 and dissolved silica determined according to chemical... 

In both cases the mineralogical form of the silica, determined by chemical analysis, plays a significant part. Large amounts of free quartz will cause heavy mechanical wear by abrasive action and will, in contrast with the clay minerals, become reactive only at high temperatures. 

Silica Determination in Water Extract of Black Liquor and Pulp... 

Silica Determination in Radioactive Defense Waste Salt Solutions... 

Silica Determination in Boiler and Feed Water Samples... 

Silica Determination in Samples Containing Large Quantities of Phosphate... 

Silica Determination in Water Samples Containing SnCh, SnCh, and CeHgOe in HClOi... 

Silica Determination in Water Samples Using BuOH or BuOH-CsHs Mixture... 

Concentration Range The linearity of the proposed SIA method for silica determination was studied imder optimum conditions described above. The correlation coefficient was 0.9999. The method is linear between 0.5 and 50 ppm. The detection limit was 0.5 ppm. The equation for absorbance measurement was A = 0.220 + 0.009x. 

Xia, X.P., Beland, R., Miersch, S. et al.. Development and validation method for silica determination by spectrophotometry in some herbs and pharmaceutical formulations. Analytical Letters... 

Andersson, L.H., Determination of silica. VII. Some experiments with the gravimetric silica determinations, Arkiv foer Kemi (1962), 19(17), 223-233. 

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