Silica limitations

NOTE Refer to Table 12.11 (BS 2486 1997 Table 3) for starting point recommendations for OH alkalinity and silica limit ratios. 

Silica limits are based on the avoidance of silicate scale deposition and the limitation of silica solubility in steam. 

Silica limits are based on the avoidance of silicate scale deposition and the limitation of silica solubility in steam. The BW silica levels in this table have been set to achieve a level of 0.002 mg/kg in the steam, the normal level specified for modem steam turbines. 

Carry-over of volatile silica is generally a problem only at pressures of 1000 psi (68 atm) or above, although it can be encountered at pressures as low as 600 psi (41 atm). For the protection of the turbine, it is important that silica carryover he prevented in this pressure range by adherence to the silica limits of Fig. 7. 

In normal phase HPLC, the cyano and amino columns, in conjunction with the diol bonded phase columns, are now often used in preference to unmodified silica or alumina. Whilst silica can demonstrate remarkable selectivity for the separation of closely related isomers (e.g. E/Z isomers are commonly separated on silica), some of the operational demands of silica limit its usefulness. The difficulty of manufacturing reproducible microcrystalline silica and the possible effect of trace amounts of water on... 

Polymer-silica Limited Mainly alkanes 1-20 Very good Yes... 

Sandgren, C.D., Hall, S.A. and Barlow, S.B. (1996) Siliceous scale production in chrysophyte and synurophyte algae. 1. Effects of silica-limited growth on cell silica content, scale morphology, and the construction of the scale layer of Synura petersenii. Journal of Phycology, 32, 675—692. 

Another GRIN system is the binary titania-silicate system of Konishi and coworkers [62,63]. Small 2 mm diameter lens of low A-n have been produced with good index profiles [62, 63]. The low solubility of titanium dioxide in silica limits the maximum refractive index gradient in this binary system. 

Based on information about biogenic silica revealed from three sediment cores from Jiaozhou Bay, the reasons for silica limitation in local phytoplankton growth were discussed. The main conclusions can be summarized as follows ... 

INEOS Silicas Limited, PO Box 26,4 Liverpool Rd., Warrington, Cheshire, WA5 1AB, UK (Tel 441925 416100 FAX 441925 416116 E-mail steven.steggerda crogb.sprintcom)... 

TABLE 2.19 Silica Limits for Three Treatment Schemes... 

Acids are not limited to liquid (or gaseous) systems. Solid acids also play a significant role. Acidic oxides such as silica, silica-alumina, etc. are used extensively as solid acid catalysts. New solid acid systems that are stronger than those used conventionally are frequently called solid superacids. 

The analysis of cigarette smoke for 16 different polyaromatic hydrocarbons is described in this experiment. Separations are carried out using a polymeric bonded silica column with a mobile phase of 50% v/v water, 40% v/v acetonitrile, and 10% v/v tetrahydrofuran. A notable feature of this experiment is the evaluation of two means of detection. The ability to improve sensitivity by selecting the optimum excitation and emission wavelengths when using a fluorescence detector is demonstrated. A comparison of fluorescence detection with absorbance detection shows that better detection limits are obtained when using fluorescence. 

A number of cement materials are used with brick. Standard are phenolic and furan resins, polyesters, sulfur, silicate, and epoxy-based materials. Carbon-filled polyesters and furanes are good against nonoxidizing acids, salts, and solvents. Silica-filled resins should not be used against hydrofluoric or fluosihcic acids. Sulfur-based cements are limited to 93°C (200°F), while resins can be used to about 180°C (350°F). The sodium silicate-based cements are good against acids to 400°C (750°F). 

Two techniques for sorption-spectroscopic determination of ascorbic acid have been proposed. The first one is the recovery by silica modified with tetradecyl ammonium nitrate of blue form of molibdophosphoric HPA in the presence of vitamin C. And the second one is the interaction between the ascorbic acid in solution and immobilized on silica ion associate of molibdophosphoric acid with lucigenine. The detection limits of vitamin C are 0.07 and 2.6 mg respectively. The techniques were successfully applied to the determination of ascorbic acid in fmit juices. 

In this work the results of reseai ch common sorbtion-X-Ray-fluorescence analysis of Pb(II), Cd(II), Zn(II) and Mo(VI) with preconcentration on complexing chemical silica gel modified with mercaptane groups and modified with 8-hydroxyquinoline were described. The conditions and limits of determination of the X-Ray-fluorescence method in the thin lawyers ai e discussion. 

Eor the selective pre-concentration of deactivated phenols a new silica-based material with the grafted 2,3,5-triphenyltetrazole was proposed. This method is based on the formation of molecular chai ge-transfer comlexes of 2,3,5-triphenyltetrazole (7t-acceptor) with picric acid (7t-donor) in the phase of the sorbent. Proposed SPE is suitable for HPEC analysis of nitrophenols after their desorption by acetonitrile. Test-system for visual monitoring of polynitrophenols under their maximum concentration limits was developed using the proposed adsorbent. 

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

The American Boiler Manufacturers Association (ABMA) has established limits for boiler water composition. The limits are set to help assure good quality steam (for example, limiting silica in the steam to 0.02-0.03 ppm). Blowdown is normally based on the most stringent of these limits shown in Table 1. 

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