Slurry properties

In addition to the four compounds discussed above, the final Portland cement may contain gypsum, alkali sulfates, magnesia, free lime and other components. These do not significantly affect the properties of the set cement, but they can influence rates of hydration, resistance to chemical attack and slurry properties. 

DlatomaceOUS Earth. Diatomaceous earth has a lower specific gravity than bentonite. Like bentonite this additive also requires additional water to be added to the slurry. This additive will affect the slurry properties similar to the addition of bentonite. However, it will not increase the viscosity as bentonite will do. Diatomaceous earth concentrations as high as 40% by weight of cement have been used. This additive is more expensive than bentonite. 

To avoid a modification of the slurry properties (e.g., rheology, density, thickening time)... 

A pipeline is installed to transport a red mud slurry from an open tank in an alumina plant to a disposal pond. The line is 5 in. sch 80 commercial steel, 12,000 ft long, and is designed to transport the slurry at a rate of 300 gpm. The slurry properties can be described by the Bingham plastic model, with a yield stress of 15 dyn/cm2, a limiting viscosity of 20 cP, and an SG of 1.3. You may neglect any fittings in this pipeline. 

A water slurry containing coal particles (SG = 1.35) is pumped into the bottom of a large tank (10 ft diameter, 6 ft high), at a rate of 500 gal/hr, and overflows the top. What is the largest coal particle that will be carried out in the overflow If the flow rate is increased to 5000 gal/hr, what size particles would you expect in the overflow The slurry properties can be taken to be the same as for water. 

Heat transfer in slurry reactors follows the same behavior as that described for, gas-liquid systems as long as liquid properties are appropriately substituted by the slurry properties. 

Detecting and characterizing subtle differences in slurry properties due to the above effects are an ongoing challenge. 

Another practical difficulty in characterizing the correlation between slurry properties and defect level is that the absolute number of these oversized particles is very less in relation to the overall number of particles in the slurry. As shown in Fig. 13.29, the number of large particles that is capable of causing defects is in the range of 2.0 x 10 to 9.0 x 10. A typical slurry with mean size of 130 nm has an average of 1.1x10 oversize particles >0.5 pm and 2.3 X 10 total abrasive particles. 

Monitoring and control of CMP slurry properties is essential for effective and uniform CMP processes. Bench-top blend sensitivity analysis helps in identification of the most sensitive blend monitoring and control parameter. Two- and three-component blends of CMP slurries can be created and monitored based on the measurements of density, wt% solids, refractive index, pH, and oxidizer level. Typical silica oxide slurry blend ratio is controlled using density as a control parameter, whereas tungsten and copper CMP slurries usually need an autotitrator for periodic monitoring of the oxidizer level. 

Singh RK, Roberts BR. Behavior of CMP slurry properties in continuous blending and distribution systems. Proceedings of the 17th International VMIC 2000. p 545-547. 

Of the four applications for coal slurries given here, coal slurry fuels have the most stringent requirements. Hence, the following discussion of slurry properties is with reference to coal slurry fuels. 

Solid-liquid mixing involves the suspension, distribution, and the drawing down of solids by agitation. In addition to vessel geometiy, impeller variables include type, diameter, number, speed, and location. Process results include the desired level (quality) of suspension, such as just off-the-bottom, complete uniformity, or any intermediate condition. The slurry properties, density difference (solid/liquid), viscosity, and solids concentration all determine how difficult the task may be. As alternatives to stirred vessels, jets (see Section 9.10) can be used for light-duty suspension. Literature references deal mainly with settling solids as opposed to floating solids. We will try to address both conditions. 

Besides the feed (slurry) properties and feed rate, the following variables in dryer design and operation affect the characteristics of the dried product. 

In Table 11.1, some of the slurry properties are listed, whith influence plant selection [Tiller Crun, 1977]. Figure 11.1 presorts a broad classification of suitable filtos against tire partide size distribution parameters. Of course, sudi dassifications caimot be viewed as being rigorous in all circumstances, but tire data indicate that pressure filters will be found most commonly in those processes containing dow-sOtling, dow-fihering suspensions. 

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