Surface area of quartz

The average size and surface area of quartz chips were 50 to 70 mesh and 0.29 g/m respectively. The effect of the quartz chips on the reaction were already discussed in a previous work. A flow rate of 10 mL/min of argon (1%) in helium was used as an internal standard to obtain the semi-quantitative data. 

A CA approach described zinc adsorption on aquifer sand material from Cape Cod by assuming that the aluminum and iron phases present in the quartz grain coatings have a surface area and site density similar to those of poorly crystalline materials (Davis et al., 1998). A similar approach provided only a semiquantitative prediction of uranium adsorption on an alluvial aquifer sediment from Naturita, Colorado, depending on the assumptions made about the relative amounts of surface area of quartz, ferrihydrite, and goethite (Davis et al., 2004). In both of these studies, the surface complexation model considered... 

Example 6.1. Geometric specific surface area of quartz grains... 

Table 5. The Effect of Surface Area of Quartz (cm /g) on the DTA Exothermal Area...

Estimate the specific surface area of the quartz powder used in Fig. X-1. Assume that a monolayer of C4H9OH is present at P/P = 0.2 and that the molecule is effectively spherical in shape. 

The experiment was carried out in a reaction cell shown in Fig. 3.3 with inner walls covered by a zinc oxide film having thickness 10 pm [20]. The surface area of the measuring film on the quartz plate was about 1/445 of the total film area on the wall of the vessel. The results of direct experimental measurements obtained when the adsorbent temperature was -196 C and temperature of pyrolysis filament (emitter of H-atoms) 1000°C and 1100°C, are shown on Fig. 3.4. One can see a satisfactory linear dependence between parameters A r (the change in film conductivity) and APh2 (reduction of hydrogen pressure due to adsorption of H-atoms), i.e. relations... 

To assign the amount of quartz in the system, we arbitrarily specify a specific surface area of 1 cm2 g-1. Then, we need only set the quartz mass to a value in grams equal to the desired surface area in cm2. Finally, we set for each run the amount of time At it takes the packet of water to flow along the fracture. 

Each mineral in the calculation dissolves and precipitates according to the kinetic rate law (Eqn. 26.1) used in the previous examples and the rate constants listed in Table 26.1. We take the same specific surface areas for quartz and cristobalite as we did in our calculations in Section 26.1, and assume a value of 20 000 cm2 g-1 for the amorphous silica, consistent with measurements of Leamnson el al. (1969). The procedure in react is... 

Minerals in the soil can dissolve or, if they become supersaturated, precipitate according to the kinetic rate law in the previous section (Eqn. 27.2). We take a rate constant of 4.2 x 10-18 mol cm-2 s-1 for quartz, as before, and of 30 x 10-18 mol cm-2 s-1 for potassium feldspar and 100 x 10-18 mol cm-2 s-1 for albite, from Blum and Stillings (1995). We assume a specific surface area of 1000 cm2 g-1, typical of sand-sized grains (Leamnson el al., 1969), for each of the minerals. 

A quartz-free nontronite sample (6) was expanded by reacting a slurry containing 0.0075 g clay/g water with an excess of ChlorhydrolA pillared product was obtained that after drying at -100 C had a d(OOl) spacing of 19.4A. Calcination in air at 400 C/10h reduced the d(OOl) value to 16.9A the calcined ACH-Nontronite had BET surface area of 310 m /g and contained 31.9% FegOj. All powder diffraction measurements were obtained with a Siemens D-500 diffractometer at a scan of r/min using monochromatic Cu-Ka radiation. 

Consider two closed air-sampling vessels made out of (a) teflon and (b) glass (assume like quartz) with an air volume Fa = 10 3m3 (1 L) and an inner surface area of ASUTf = 6 x 10" 2m2. In these vessels you capture air samples that you want to analyze for phenanthrene. Calculate the fraction of the total phenanthrene present in the air in the two vessels after adsorption equilibrium between the gas phase and the walls of the vessel has been established at 15°C (288 K) and 50% relative humidity. Assume that only adsorption at the surface of the walls is important. (Note that in the case of teflon, absorption could also be important.)... 

A comparative study of microsilicas from 18 sources showed considerable variation in composition and properties, one of those examined containing as little as 23% of SiOj and having a specific surface area of only 7.5 m g (A21). The same study showed that in most of the samples the diffuse XRD peak from the glass accounted for 98-99.5% of the total diffracted intensity and that it peaked at the value of 0.405 nm characteristic of vitreous silica. The commonest crystalline impurities detected were KCl, quartz, metallic iron and iron silicide, and pozzolanic reactivity was found to depend more on the chemical composition and nature of impurities than on the fineness or SiOj content. A surface layer of carbon, if present, greatly decreased reactivity. 

For the adsorption tests, a sample of silica (Merk) with a specific surface area of 388 m g measured by the BET method was used. The solid specimens used to measure the contact angles were microscope glass slides and pieces of quartz polished using a rotating plate covered with a polishing cloth impregnated with 10 pm diamond polishing particles. 

Stone et al. (S29) developed by a mathematical analysis the functional relationship between the rate of extraction of silica from pure quartz in sodium hydroxide solution and time, temperature, sodium hydroxide concentration, and particle size. With the use of response surface methodology, a comprehensive picture of this dissolution process was obtained from a few well-chosen experiments. The fractional extraction of silica can be expressed by a second-order equation. The effect of quartz particle size and temperature are predicted to be about equal and greater than the influence of sodium hydroxide concentration and reaction time. The reaction rate is controlled by the surface area of the quartz. An increase in sodium hydroxide concentration increases the activation energy for the reactions and is found to be independent of quartz size. 

---