Dispersing apparatus

The detectable limits for a dispersion apparatus are a few g-g/g, and vary according to the environment around from a few pg/g for heavy elements in light matrices to a few mg/g for light elements. 

S latter er at. (1981) made a similar approach when evaluating a new spray dispersal apparatus. Physical measurements were made of the spray distribution, which was applied at four rales, with exposure of the insects for 1 hours. 

Fiocco and coworkers demonstrated the use of two dispersant apparatuses to test demulsifiers, the WRASET , which uses the wrist-action tester or EXDET test, and the ROFLET , which uses the rolling flask or Warren Springs test [J6S], To demonstrate the test, an emulsion with Kuwait crude oil was used with the Exxon products, Breaxit OEB-9, 7877, 8150, and 8160, and the surfactant dioctyl sulfosuccinate. Effectiveness was measured by visually observing the amount of water/oil separation. A Sture blend crude was used to evaluate the same demulsifiers plus Ameroid 372101, Breaxit 4018, 711, 7125, 7128, and 7652, as well as Shell LA 1834, Alcopol 60, and a demoussifier . Ameroid was found to be the best product, followed closely by Breaxit 4018, 7111, 4018, and then LA 1834. 

The focus in this chapter is on small scale preparation with a mortar and a pestle, a rotor stator mixer or an ointment miU. For preparation on a larger scale pharmacies in several countries use the mixing-dispersing apparatus Stephan mixer. This mixer exists in various models and is suitable for the preparation of almost aU cutaneous preparations (see Sect. 28.6.1). 

The Stephan mixer is a combined mixing and dispersing apparatus. The brand name Stephan is used because of its specific construction and qualities. The apparatus can be used for the preparation of ointments, creams, emulsions, suspensions, gels, pastes, solutions, powder mixtures and granulates. The apparatus was originally developed for food processing. 

The blender is a mixing and dispersing apparatus. At the bottom of the mixing beaker a mixing cross is situated consisting of four knives two of them lying horizmitally or are placed slantwise to the bottom a second pair are placed slantwise upwards, see Fig. 28.11. 

The mass should be mixed continuously during molding. A rotor-stator dispersing apparatus is not suitable for this purpose as it whips air into the mass and its mixing is insufficient. 

The power density Py is the characteristic quantity of turbulent flow. It determines the size of the smallest eddies and the intensity of microturbulence. In addition, it is a measure of the shear intensity in laminar flows or the intensity of cavitation in ultrasonic fields (see above). The power input P in the dispersion zone can be derived from the pressure drop (e.g. in pipes and nozzles) or can be measured caloricafly (e.g. for rotor-stator systems and ultrasonication Pohl 2005 Kuntzsch 2004). Additionally, P can be roughly approximated by the electric power consumption of the dispersion machine (e.g. for ultrasonication Mandzy et al. 2005 Sauter et al. 2008), even though the real values may be lower by a factor of 2 to 5. A further source of uncertainty is the volume of the dispersion zone (Vdisp). since the stress intensities are not uniformly distributed in dispersion apparatuses. In particular, this applies to agitated vessels, where the highest dissipation rates are obtained in the vicinity of the stirring instmment (Henzler and Biedermann 1996),... 

Spectrometers are used to produce the spectrum or to isolate narrow spectral ranges, without further deconvolution. In dispersive apparatus, the spectrum is produced with a prism or diffraction grating. In nondispersive apparatus, spectral regions are isolated from the radiation beam by reflection, interference, or absorption in interferometers or filter monochromators. The latter are of use only in flame emission spectrometry. 

Todd, P. Sounding Rocket Experiments in Biotechnology Using Materials Dispersion Apparatus. Final Report, Contract No. H8057B, Marshall Space Flight Center, Huntsville, AL, 1989. 

Rotating disc/inherent liquid spray compared with six-blade turbine, six-blade vaned disc, two-blade paddle, spinning cone, and fluid impact dispersion apparatus (to = 150-250 s-i)... 

The assembly of the dispersing apparatus is illustrated in Fig. 1 with details of the component parts as follows ... 

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