Shear-sensitive slurry

PPDS works on the principle of metering pumps and employs diaphragm, bellows, centrifugal, or vacuum-pressure-dispense pumps. These systems may be used for slurries including shear-sensitive slurries and cause minimal recirculation during slurry usage and replenishment. 

This study shows the significant benefits of an MLP pump in handling shear-sensitive CMP slurries in single-pass applications and under normal turnovers ( 100) expected in a typical fab operation. Since, the MLC pump generated far fewer >lpm particles in shear-sensitive slurries, the filter lifetime for MLC pump-based slurry delivery systems should be longer than the other AOD or bellows pump-based systems, especially when relatively open (> 1 pm nominal rating) filters are used in the global loop and point-of-use (POU) locations. 

Rotary screw pumps (Progressing cavity pump moyno pump) for shear sensitive slurries particle diameter < 5 cm., temperature < 80 °C fluid viscosity, usually above 10 Pa.s head 0.2 to 300 m < 125 L/s self priming minimum foaming pulsation-free flow. Tends to be a constant volume device. 

Regardless of the needs dictated by these factors, the piping system itself will fall into a few general variations as shown in Fig. 4. Dead-head style piping systems are unusual and can only be used with a very well-suspended slurry. This type of system can minimize the loss of volatile components, such as ammonia from a slurry like Rodel Klebosol, since there is no circulation through a daytank or any other head space that would permit ammonia evaporation. It can also be attractive to minimize slurry turnovers to a shear- or gelling-sensitive slurry. Cabot SS-25 is well-suspended, but if... 

Historically, bulk delivery systems have used manual diaphragm valves located at the return end of the global piping system, another carryover from high-purity chemical systems. However, the shear sensitivity of many slurries has fostered the creation of other baek-pressure approaches, including... 

VPDS is designed on the principle of volumetric blending. These systems cause minimal handling shear on slurry and hence are ideal for shear-sensitive silica slurries. However, special care should be exercised in handling slurries with volatile or decomposing components, which may be affected by repeated vacuum application. 

Ram extrusion is generally used for specialty processing. Ram extruders are sometimes used to process polymer slurries such as PTFE or UHMWPE. These polymers will degrade if fiiey are heated to their melt temperature, so they are sometimes mixed with a liquid and processed via ram extrusion. Ram extrusion is also used on polymers that are sensitive to shear. Often the absence of shear is an advantage when processing thermoset materials and composites. 

---