Silica content determination

Because of this Roberts [7] took a different approach and determined the strength of slurries made at the same viscosity with binders containing different levels of colloidal silica. The binders were pre-diluted to the desired level and refractories added to make slurries. The strength of each was measured, plotted, and the optimum binder silica content determined from the plot. In all cases, the slurries were weak at low binder silica levels, went through a maximum and then became weaker when binder having higher silica contents were used. 

Bulk Samples Bulk samples must be submitted for all silica analyses. They have two purposes (1) For laboratory use only, to confirm the presence of quartz or cristobalite in respirable samples, or to assess the presence of other substances that may interfer in the analysis of respirable samples. (2) To determine the approximate percentage of quartz (or cristobalite) in the bulk sample. A bulk sample submitted "for laboratory use only" must be representative of the airborne free silica content of the work environment sampled otherwise it will be of no value. The order of preference for an evaluation is ... 

This input to design refers to the long-term stability of the raw material sources for the plant. It is only of importance where the raw materials can or do contain impurities which can have profound effects on the corrosivity of the process. Just as the design should cater not only for the norm of operation but for the extremes, so it is pertinent to question the assumptions made about raw material purity. Crude oil (where HjS, mercaptan sulphur and napthenic acid contents determine the corrosivity of the distillation process) and phosphate rock (chloride, silica and fluoride determine the corrosivity of phosphoric acid) are very pertinent examples. Thus, crude-oil units intended to process low-sulphur crudes , and therefore designed on a basis of carbon-steel equipment, experience serious corrosion problems when only higher sulphur crudes are economically available and must be processed. 

Procedure. The method to be described is especially suitable for ceramic materials such as fireclay, firebrick, or silica brick. The finely ground sample should be dried at 110 °C. The weight of sample to be employed depends largely upon the silica content of the material, since not more than 35 40 mg of silica should be present in the aliquot employed for the determination. For samples... 

It is seen that at high concentrations (a) becomes unity and the surface is completely covered with the more strongly adsorbed solvent. The adsorption isotherm of chloroform on silica gel, determined by Scott and Kucera (5) is shown in figure 1. It is seen that the monolayer of chloroform collects on the surface continuously until the chloroform content of the mobile phase is about 50%. At this concentration the monolayer appears complete. Thus, between 0 and 50% chloroform in the n-heptane, the interactions between the solute and the chloroform in the mobile phase are continuously increasing. 

The study of obsidian by NAA has proved to be particularly fruitful because of the relatively limited number of sources and the extent to which it was traded (Beardsley et al. 1996, Cook 1995, Darling and Hayashida 1995, Kuzmin et al. 2002, Leach 1996). Studies have also extended to include other volcanic materials such as pumice (Bichler et al. 1997, Peltz et al. 1999). NAA has also been used for the analysis of flint as OES is insensitive and not reproducible due to the effect of the high silica content, and AAS requires significant sample preparation (Aspinall and Feather 1972). The wide range of appropriate materials extends to organic materials such as human bone (Farnum et al. 1995), and its exceptional sensitivity to trace elements has led to its wide use in geochemistry (for example in determining trace [ppb] contaminants in waters) and more recently in forensic chemistry. 

A determination of the surface hydroxyl groups was made by Noll et al. (183). The total water content was determined by heating to 1100°. The content ofmolecular water was titrated by the Karl Fischer method. Silanol groups react with this reagent only very slowly. Good agreement was observed with silanol contents determined independently by other methods. With silica gel, 5.2 silanol groups were found per 100 A. ... 

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. 

Brown and coworkers (17) determined the silica content of gin dusts from Mississippi. The ratio of silica content to silicon was much higher than the corresponding ratio for cotton textile mills. 

The determination of silica in samples from two of the oil mills was made by Brown, et al. (17). The silica content was much higher in the cleaning area than in any other. 

This has been confirmed in the present study for chlorites from six rocks from the Belt series in northern Montana (Harrison and Jobin, 1963) and three samples from the outer zones in the Alpine chain. From these analyses, it is apparent that metamorphic chlorites which have crystallized with muscovite have low silica contents and a rather limited alumina content (27 3% A1 ions). The relatively large variation in chlorite Fe-Mg ratio from rock to rock suggests that bulk rock composition is more important in determining the chlorite composition than is the case of chlorites from clay mineral facies. 

Bentonite has expected silica content of 0.5 weight percent (F is 0.005). Silica density (A .) is 2.4 gm per cu cm, and bentonite (Ag) is 2.6. The calculation requires knowledge of mineral properties described by the factor ifsbd ). Value of the factor can be established from fundamental data (Gy) or be derived from previous experience. In this example, data from testing a shipment of bentonite of 10 mesh top-size screen analysis determined value of the mineral factor to be 0.28. This value is scaled by the cube of diameter to Vs-in screen size of the example shipment. The mineral factor is scaled from 0.28 to 52 by multiplying 0.28 with the ratio of cubed 9.4 mm (H-in screen top-size of the shipment to be tested) and cubed 1.65 mm (equivalent to 10 mesh). 

In one analytical method for air filters, the air filters are ashed, silica content is volatilized with hydrogen fluoride, uranium is extracted with triisooctylamine, purified by anion exchange chromatography and coprecipitated with lanthanum as fluoride. The precipitated uranium is collected by filtration, dried, and a-spectroscopy is performed (EPA 1984b). The activities of and are determined based on... 

Silica. The silica content of natural waters is usually 10 to x 10 ) M. Its presence is considered imdesirable for some industrial purposes because of the formation of silica and silicate scales. The heteropoly-blue method is used for the measurement of silica. The sample reacts with ammonium molybdate at pH 1.2, and oxalic acid is added to reduce any molybdophosphoric acid produced. The yellow molyb do silicic acid is then reduced with l-amino-2-naphthol-4-sulfonic acid and sodium sulfite to heteropoly blue. Color, turbidity, sulfide, and large amounts of iron are possible interferences. A digestion step involving NaHCO can be used to convert any molybdate-unreactive silica to the reactive form. Silica can also be determined by atomic... 

Alkali loss has been observed in compositions of low silica content in several alkali-silica systems with other oxides. Goldsmith [16] found a loss of Na20 by volatilization from melts in the NaAlSi04-CaO A1203 system, particularly in those melts rich in the latter component. He noted that the loss of Na20 influenced the amount and even the presence of nonsodic or soda-poor phases such as CaO 2A1203 and beta alumina. Schairer and Bowen [4] determined that in multi-component silicate systems, alkali losses are not controlled by alkali content alone. Rather the presence of other oxides has been observed to affect the alkali losses. For example, silica and alumina tend to stabilize compositions and prevent or minimize alkali losses, whereas CaO or MgO tends to increase the losses. 

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. 

Silica content may be determined by either the precise, tedious gravimetric silica procedure (2 or the more rapid but less precise fluosilicate method (3), The gravimetric method involves precipitation of the silica with acid, collecting the precipitate, ashing, volatilizing the silica with hydrofluoric acid and determining the weight loss after volatilization. 

Figure 7. Colloidal silica contents of silicic acid sols determined by extrapolating the linear portion of silicomolybdate reaction curve to zero time. Sol made from concentrated (5 M Si02) sodium silicate. Conditions pH 1.7 and 16.6 mM Si02 aged 5 min (A) and 10 d (B).

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