Quartz, turbidity

Electrophoretic mobilities of the quartz particles in cobalt (II) perchlorate solutions were determined with a calibrated Zeta-Meter apparatus. Coagulation sedimentation behavior was followed using a stop-flow type apparatus. The dispersion is pumped in a closed loop from an equilibration vessel through an optical cell located in the sample compartment of a recording spectrophotometer. From the optical densitytime curve obtained from the time the pump is switched off, the turbidity index (in arbitrary units) is obtained as the slope of the curve at zero time. 

The variation with pH of the electrophoretic mobility of quartz in 10"4M cobalt (II) perchlorate and a comparison of the mobility of quartz in 10 4M KC1 is shown in Figure 5. Included in Figure 5 is the variation with pH of electrophoretic mobility of precipitated cobalt (II) hydroxide. It can be seen that the silica surface with adsorbed Co (II) acts as cobalt (II) hydroxide for pH values above 8.0. The turbidity vs. pH behavior at 10 4M Co(C104)2 is shown in Figure 6. The two curves represent the behavior for increasing and decreasing pH and within experimental error the curves superimpose. 

The various influences on the efficacy of UV disinfection are compiled in Fig. 9-1 (cf Malley Jr, 2000). Primarily, the efficacy of UV disinfection depends on the germicidal fluence Ho=EoXt which is the product of fluence rate Eq and the duration time t of the irradiation (often called UV dose , Chapter 2.1) (see Sommer et al., 1998). Other key factors include the hydraulics and hydrodynamics of the UV reactor (Kreft et al., 1986), its geometry (FIGAWA, 1998, Hoyer, 1996), the number and type of UV lamps required (Loge et al., 1996), their temperature profiles with respect to a maximum fluence rate Eq (in the case of LP Hg lamps, cf Fig. 4-8), the water quality and its variability such as UV absorbance/transmittance (Bolton et al., 2001, Sommer et al., 1997), the water matrix, e.g. nitrate concentration, its potential for quartz fouling by inorganic constituents particularly iron ions and hardness (cf Chapter 8-2), the turbidity, the particle content (total sus-... 

Measure the turbidity of each aliquot (amount of light scattered at 90°) in a lO-mmxlO-mm quartz cuvette at 37°C and under magnetic stirring. Before reading, leave each sample in the cuvette for at least 5 min to reach equilibrium. Determine the turbidity of the solution with a fluorometer by setting the excitation and emission wavelengths at 480 nm. 

In addition to varying the substrate (TMOS), we were also interested in the effects of temperature on particle formation kinetics and product morphology. The particle growth was studied using turbidity measurements as described below. It is noted that, in the absence of any peptide, only gelation, and no particle formation was observed, which was also reflected in the weak absorbance (Figure SI). A typical reaction mixture containing 40 pL of TMOS (0.067 M) pre-hydrolyzed in 1 mM HCl and 520 pL citrate - phosphate buffer at pH 7.55 was prepared in a stirred quartz cuvette. Immediately after addition of these reactants to the cuvette, 40 pL of the 20 mg/ml R5 (final concentration of... 

The oxides used in this study were a-Si02 (a-quartz), obtained commercially, and a-FeOOH (goethite), which was prepared in a manner similar to that of Forbes et al. (18). The silica was washed initially in Q.IN nitric acid. Both oxides were washed with double distilled water, dried at 100°C for 24 hr, powdered with a mortar and pestle, and passed through a 200 mesh (75 /xm) sieve. Powdered x-ray diffraction verified the existence of a-quartz and goethite. BET-Ng adsorption indicated specific surface areas of 1.7 m /g for silica and 85 m /g for goethite. Corresponding ZPC values, determined by electrophoresis and turbidity measurements, were 1.7 and 5.5. Dielectrics were taken to be 4.3 for silica and 14.2 for goethite (19). 

Figure 4. Temperature dependence of the PNIPAM colloid diameter and turbidity. The diameter was determined using a commercial quasielastic light scattering apparatus (Malvern Zetasizer 4). The turbidity was measured for a disordered dilute dispersion of these PNIPAM colloids by measuring light transmission through a 1.0 cm pathlength quartz cell with a UV-visible-near IR spectrophotometer. Solids content of the sample in the turbidity experiment was 0.071%, which corresponds to a particle concentration of 2.49 x 10 spheres/cc. Also shown is the temperature dependence of the turbidity of this random colloidal dispersion. The light scattering increases as the particle becomes more compact due to its increased refractive index mismatch from the aqueous medium (76) (Adapted from ref 16).

Procedure. The reaction is conducted in a quartz crucible. A small portion of the powdered sample is treated with about 5-10 times the quantity of zinc chloride and a drop of water. After evaporation, the crucible is covered and the contents heated for five minutes over a bare flame. The cooled mass is stirred with a drop or two of hot water, the suspension is transferred to a conical tube, and centrifuged. One drop of the clear liquid is treated with a drop of a 1 % aqueous solution of sodium tetraphenyl borate. If potassium is present, a white precipitate or turbidity appears. 

The experiments in the first series were conducted with methylated surfaces immersed in aqueous solutions of alkylbenzenesulfonates. The free energy of interaction between methylated glass and quartz spherical surfaces having radii of about 1 mm was studied as described in Section 1.2. Parallel to these studies, the colloid stability of 10 mn particles of methylated Aerosil (i.e., hydrophobized nanoparticles of quartz) suspensions was monitored via turbidity measurements. A characteristic sharp increase in turbidity was observed at the coagulation threshold. This behavior was reversible an increase in the surfactant concentration resulted in a decrease in turbidity, while dilution of the solutions caused the turbidity to increase. 

In the case of finer suspensions such as wheat starch or quartz powder, the particles of which have a diameter of 0.001 to 0.005 mm., the effect of electrolytes is more marked. The particles flock together to form larger aggregates, and these aggregates precipitate more rapidly than do the individual particles. The much investigated turbid solutions of clay exhibit this to a marked degree, as shown by the work of Schlosing f and Bodlander.f These solutions behave in a manner very similar to that of irreversible hydrosols such as colloidal metals, which are also very sensitive to the action of electrolytes. 

UV disinfection A water-treatment process used to eradicate harmful bacteria and viruses by exposing potentially contaminated water to ultraviolet radiation. At a certain level of intensity, ultraviolet light is fatal to all microorganisms that inhabit water. Mercury arc lamps are used to generate the ultraviolet radiation with low-pressure lamps being the most common and effective. The lamp is made of fused silica or quartz to allow transmission of the ultraviolet light. The efficiency of UV disinfection is diminished by turbidity and by the build-up of scale on the tubes. 

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