Adherent Particles

In most cases, the impregnation process is followed by an electrochemical formation where the plaques are assembled into large temporary cells filled with 20—30% sodium hydroxide solution, subjected to 1—3 charge—discharge cycles, and subsequentiy washed and dried. This eliminates nitrates and poorly adherent particles. It also increases the effective surface area of the active materials. 

In a gas stream cariying dust or fume, some degree of particle flocculation will exist, so that both discrete particles and clusters of adhering particles will be present. The discrete particles composing the clusters may be only loosely attached to each other, as by van der Waals forces [Lapple, Chem. Eng., 75(11), 149 (1968)]. Flocculation tends to increase with increases in particle concentration and may strongly influence collector performance. 

The pressure drop through the filter is a function of two separate effects. The clean filter has some initial pressure drop. This is a function of filter material, depth of the filter, the superficial gas velocity, which is the gas velocity perpendicular to the filter face, and the viscosity of the gas. Added to the clean filter resistance is the resistance that occurs when the adhering particles form a cake on the filter surface. This cake increases in thickness as approximately a linear function of time, and the pressure difference necessary to cause the same gas flow also becomes a linear function with time. Usually, the pressure available at the filter is limited so that as the cake builds up the flow decreases. Filter cleaning can be based, therefore, on (1) increased pressure drop across the filter, (2) decreased volume of gas flow, or (3) time elapsed since the last cleaning. 

To make a screen analysis, the individual screens (see Figure 3.4) are cleaned and tapped free of any adhering particles. The screens are nested together vertically with the coarsest mesh at the top and the finest mesh at the bottom. A bottom pan and a top cover complete the set. A known amount of material is then placed on the top screen, the cover is replaced, and the stack is rotated, shaken, and bumped at intervals. Although this process could be done by hand, it is usually done mechanically to avoid operator... 

Current best estimates for natural plagioclase weathering rates are one to three orders of magnitude lower than laboratory rates. Surface characteristics which may play a role in determining rates and mechanisms of feldspar dissolution (including non-stoichiometric dissolution and parabolic kinetics) in the laboratory include adhered particles, strained surfaces, defect and dislocation outcrops, and surface layers. The narrow range of rates from experiments with and without pretreatments indicates that these surface characteristics alone cannot account for the disparity between artificial and natural rates. 

Having considered the factors that govern the extent or rate of flocculation in an aerosol, it is also important to consider the effects of flocculation on the properties of an aerosol. Consider a large sphere of diameter Dpl, with its surface covered with small particles of diameter Dpi. If the adhering particles are no more than one layer thick, it can be shown as a good first approximation that... 

Even when the reduction is thoroughly effected, it is most difficult to detach the incrustation of metal sufficiently complete for accurate determination. To facilitate this the neck of the retort is coated interiorly with plumbugo to diminish the adhesion of the distilled zinc to the body of the apparatus. When all tho metal is reduced and driven over, the ossnyer is often necessitated to break off the neck of the retort to enable him to collcot the metal, and not unfrcquently to dissolve the adhering particles with nitric acid, and evaporate and calcine tho residue, adding the four-fifths of its weight to that of the metal already estimated. 

Sample Preparation. The basalt was crushed and sieved, and the -120 + 230 mesh fraction was used. The grains were ultrasoni-cally washed in deionized water to remove very fine adhering particles. If these particles are not removed, they will preferentially dissolve under hydrothermal conditions, resulting in abnormally high rates of mineral-fluid reactions (10). Examination of samples of the basalt on a scanning electron microscope assured that all fines had been removed. Nitrogen B.E.T. specific surface area of the washed basalt was 2.7 m2/g. 

The critical KNO3 concentration for the detachment process was 3 X 10 M for the a-Fe203(l) sample and 1 X lO Af for the samples of a-Fe203(ll) and Ti02. Those obtained by SdFFF particle diameters after the detachment of the adherent particles [0.148 jU-m for a-Fe203(I), 0.245 /im for a-Fe203(II),... 

In PBSdFFF, the concentration step consists of feeding the column with the diluted samples at such experimental conditions, so as to decrease the repulsive component and increase the attractive component of the total potential energy of the particles under study. Because the stability of a colloid varies (increases or decreases) with a number of parameters (surface potential, Hamaker constant and ionic strength of the suspending medium), the proper adjustment of one or more of these parameters can lead not only to the adhesion of the dilute colloidal samples, which leads to their concentration, but also to the total release of the adherent particles during the elution step. 

Rubber policeman A small length of rubber tubing that has been crimped on one end used to dislodge adherent particles of precipitate from beaker walls. 

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