Thixotropic, slurry rheology

Solids concentrations can vary from a few percent to well over 50% in a typical stirred tank. Solids concentration, particle shape, and the viscosity of the suspending phase are the main factors affecting the rheology and settling characteristics of the slurry. Cubic- and spherical-shaped solids tend to form Newtonian slurries, while needle-, oblong-, and plate-shaped solids form thixotropic slurries. Such slurries exhibit yield stresses even at quite low solids concentrations. This can lead to the development of caverns, as shown in Section 9.4. Proper design can usually overcome these stagnation problems. 

Flow and self-leveling characteristics of these products are governed by the rheological behavior of the slurry-like materials. At the low water-cement ratios required to ensure proper suspension of the solids, most self-leveling compositions are characterized by a yield stress and thixotropic behavior [75], To obtain selfleveling properties, the yield stress has to be reduced and this is achieved by the... 

Chem. Descrip. Bentonite CAS 1302-78-9 EINECS/ELINCS 215-108-5 Uses Rheology control agent, thixotrope, thickener for aq. paints/coatings, PVC architectural coatings, texture coatings, stuccoes Features Rec. as co-thickener high swelling shear tolerant heat-stable Properties Off-wh. dens. 21.62 Ib/gal pH 9.0-10.5 (10% slurry) Bentone 27V [Elementis Spec. U.S.]... 

At high particle concentrations, slurries are often non-Newtonian. For non-Newtonian fluids, the relationship between the shear stress and shear rate, which describes the rheology of the slurry, is not linear and/or a certain minimum stress is required before flow begins. The power-law, Bingham plastic and Herschel-Bulkley models are various models used to describe the flow behaviour of slurries in which these other types of relationships between the shear stress and shear rate exist. Although less common, some slurries also display time-dependent flow behaviour. In these cases, the shear stress can decrease with time when the shear rate is maintained constant (thixotropic fluid) or can increase with time when the shear rate is maintained constant (rheopectic fluid). Milk is an example of a non-settling slurry which behaves as a thixotropic liquid. 

Cellulose pretreated in the presense of TMAC failed to exhibit enhanced activity toward sodium trichloroacetate in an isopropanol slurry. Products with essentially identical D.S. s were isolated from "catalysed and control experiments. However, solutions of catalysed CMC, (D.S.=0.7), appeared more fiber free than those prepared from controls with similar D.S.. The catalysed solutions (1%) exhibited slightly higher viscosities (500 cp vs 325 cp) and were less thixotropic than standard CMC. Efforts to ascertain if this difference in rheological behavior can be attributed to a more homogeneous distribution of substituents are in progress. 

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