Applications slurries

Polishing Objects Purpose of Application Slurry Types... 

As a result of the strongly varying selectivity requirements, the consumables manufacturers have developed sets of proprietary additives, which allow the designing of slurries for very specihc applications. Slurries for poly-Si CMP with a high selectivity of 100 1 to Si02 or SiN are likewise available hke slurries for Si02 CMP with a high selectivity to Si or poly-Si. These tunable slurries are available with silica or with cetia abrasive particles. 

Practically all slurry pumps are single stage. Multistage pumps are limited to mine dewatering applications. Slurry pumps are rubber lined whenever they are designed to handle particles finer than 6 mm or Because rubber is susceptible to thermal degradation when the tip speed of the impeller exceeds 28 m/s or 5500 ft/mrn, ruhher-Uned pumps are typically reserved for a maximum head of 30 m (98.5 ft) per stage. 

A single slurry application should not exceed 50000 litres/ha. At least a three-week interval should be allowed between applications. Slurry should not be applied during the closed period . When applying slurry through irrigation lines, the precipitation should not exceed 5 mm/hour. Rain guns should be avoided. 

Ivlimng applications IvIining industry IvIining Law o f 18 7 2 IvIining slurries Ivlimpress... 

Separation Efficiency. Similarly to other unit operations in chemical engineering, filtration is never complete. Some soflds may leave in the hquid stream, and some Hquid will be entrained with the separated soHds. As emphasis on the separation efficiency of soHds or Hquid varies with application, the two are usually measured separately. Separation of solids is measured by total or fractional recovery, ie, how much of the incoming solids is coUected by the filter. Separation of Hquid usually is measured in how much of it has been left in the filtration cake for a surface filter, ie, moisture content, or in the concentrated slurry for a filter-thickener, ie, solids concentration. 

Lime stabilization originated in Texas after World War II, and now it is used throughout the world. Lime is most commonly applied at a 4 wt % application or ca 11 kg/m (20 Ib/yd ) for 15 cm of compacted depth. It can be applied dry as hydrated time or granular quicklime or as a wet slurry. Distribution of the latter form is dusfless. Copious amounts (as much as 5—10%) of water are always needed in excess of the optimum moisture content of the soil. Then, a requisite for success is intimate mixing with a rotary mixer, followed by compaction to a minimum of 95% Proctor density. 

Viscous fluids Sterilized surface required Polished surface required Future expansion required Space restrictions Barrier coolant services Slurry applications... 

Tyj)e of dryer Applicable with dry-product recirculation True and colloidal solutions emulsions. Examples inorganic salt solutions, extracts, milk, blood, waste liquors, rubber latex, etc. Pumpable suspensions. Examples pigment slurries, soap and detergents, calcium carbonate, bentonite, clay sbp, lead concentrates, etc. does not dust. Recirculation of product may prevent sticking Examples filter-press cakes, sedimentation sludges, centrifuged sobds, starch, etc. 

Viscosity markedly changes the picture and, usually, increasing viscosity lowers the mass-transfer coefficient. For the common application of waste treating and for some of the pubhshed data on biological slurries, data for kiO (shown in Fig. 18-28) is obtained in the literature. For a completely new gas or liquid of a liquid shiny system. Fig. 18-26 must be obtained by an actual experiment. 

Slurries of free-filtering sohds that are difficult to suspend are sometimes filtered on a top-feed drum filter or filter-diyer. An example application is in the production of table salt. An alternative for slurries of extremely coarse, dense solids is the internal drum filter. In the chemical-process industiy both top-feed and internal drums (which are described briefly by Emmett in Schweitzer, op. cit., p. 4-41) have largely been displaced by the horizontal vacuum filter (q.v). 

For PM applications, wet scrubbers generate waste in the form of a slurry or wet sludge. This creates the need for both wastewater treatment and solid waste disposal. Initially, the slurry is treated to separate the solid waste from the water. The treated water can then be reused or discharged. Once the water is removed, the remaining waste will be in the form of a solid or sludge. 

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