Silica fluxes

Major element (alkali, alkali earth, silica) flux... 

The rain rate of BSi is dependent on (1) the rate of its production by marine organisms, (2) shell dissolution rates, and (3) the time required for a shell to reach the seafloor. High rates of production by siliceous plankton ensure a large supply of opal to the water column. The fraction reaching the seafloor is largest when transit times are shortest. Thus, shells that sink fastest will be preferentially preserved and a greater fraction of the particulate silica flux reaches sediments that lie in shallow waters. 

Gehlen M, Malschaert H, van Raaphorst WR (1995) Spatial and temporal variability of benthic silica fluxes in the southeastern North Sea. Cont Shelf Res 15(13) 1675-1696... 

The feed mixture of the copper flash furnace consists of different copper concentrates, copper containing precipitates and residues, silica flux, slag concentrate and flue dust. The chemical compositions vary considerably from concentrate to concentrate and the mineralogy of residues and slag concentrate differ strongly from those of the concentrates. In order ensure stable oxidation reactions and stable temperatures in the flash smelting furnace it is important to prepare the feed mixture so that the concentration fluctuations of the main components are small. 

Originally, lump sulfide ores were fed to the blast furnace, but this tended to produce large quantities of matte, requiring appropriate levels of iron flux to form the matte. Silica fluxing was also important to displace lead from sulfates and to form a slag. Limits on the input of sulfur due to excessive matte formation were generally around 15 per cent in the feed material. Speiss (an iron-arsenic-antimony intermetallic) was often also present as a separate phase. 

Accident Classification Explosives and Breaking Agents Type of Mine Silica Flux - Surface Location New Mexico... 

A soft, gritty amorphous silica composed of minute siliceous skeletons of small aquatic plants. Used in filtration and decoloration of liquids, insulation, filler in dynamite, wax, textiles, plastics, paint, and rubber. Calcined and flux-calcined diatomaceous earth contains appreciable amounts of cristobalite, and dust levels should be the same as for cristobalite. 

Cells used for high-temperature measurements in furnaces often consist of silica sample tubes, supported by thin vanadium sleeves. The key to the analysis is whether it is possible to have a container that scatters in a sufficiently predictable way, so that its background contribution can be subtracted. With the current neutron flux available from both pulsed and reactor sources, sample volumes of... 

In formulating holloware enamels the degree of acid resistance required is less than for chemical plant, e.g. reaction vessels, and consequently the RO2 (Si02 and Ti02) is lower thus permitting increased quantities of fluxes to be incorporated which confer improved workability . Furthermore, they can be fired at lower temperatures and have superior chip resistance. Conversely, chemical plant enamels are higher in silica and dissolved titania and require harder firing. An example of such an enamel is shown in Table 16.1. 

As an acidic oxide, SiOj is resistant to attack by other acidic oxides, but has a tendency towards fluxing by basic oxides. An indication of the likelihood of reaction can be obtained by reference to the appropriate binary phase equilibrium diagram. The lowest temperature for liquid formation in silica-oxide binary systems is shown below ... 

Substances which are insoluble or only partially soluble in acids are brought into solution by fusion with the appropriate reagent. The most commonly used fusion reagents, or fluxes as they are called, are anhydrous sodium carbonate, either alone or, less frequently, mixed with potassium nitrate or sodium peroxide potassium pyrosulphate, or sodium pyrosulphate sodium peroxide sodium hydroxide or potassium hydroxide. Anhydrous lithium metaborate has found favour as a flux, especially for materials containing silica 12 when the resulting fused mass is dissolved in dilute acids, no separation of silica takes place as it does when a sodium carbonate melt is similarly treated. Other advantages claimed for lithium metaborate are the following. 

Typically, for any given pressure, industrial packaged boilers operate at higher heat-flux rates than field-erected boilers, This requires that the package boiler FW quality should be substantially better (i.e., lower overall TDS and lower levels of silica and sodium). Appropriate MU water pretreatment may, for example, necessitate the use of twin bed and mixed bed demineralization ion exchange, or RO and mixed bed (in addition to mechanical deaeration and other processes). 

If BW silica levels increase above 180 to 200 ppm, it may not, in fact, be possible to totally control silica deposition by water chemistry means alone. Also, as boiler pressures, temperatures, and heat-flux densities increases, so does the need for external silica removal equipment. 

Although the risk of scale deposition and fouling in the boiler section is related to several factors such as the FW volume demands, boiler pressure, and heat flux density at various boiler surfaces, it is equally a function of the level of FW contaminants such as residual hardness, sulfates, silica, and iron. Thus, as a generality, the higher the quality of FW (reduced levels of contaminants), the lower the risk of deposition on boiler surfaces. 

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