Ground quartz

Equation (2.28), being statistical in nature, requires a large number of particles to be measured, especially if the spread of particle size is wide. The possibility of error from this source is stressed by Arnell and Henneberry who found that in a particular sample of finely ground quartz, two particles in a total of 335 had a diameter about twenty times the most probable diameter, and that if these were overlooked the calculated value of A would be nearly doubled. 

CO conversion data relative to (N1 SI ) and (ThNl Fe, series were taken from ref. ( ) and (,9), respectively. Catalytic measurements were obtained for oxygen treated N1 Th Intermetallics. Prior to each run, a sample mixture (50 mg cata ys + 50 mg ground quartz) was reduced In H. at 275 C for 16 hours. CO hydrogenation was carried out at 275 C using H /C0 ratio 9. More experimental details are given elsewhere (10). 

It is known [65, 66] that oxygen is observed at the surface of freshly ground quartz in several forms which are characteristic of various conditions of formation, thermal stability, concentration, etc. Jointly with other physical and chemical methods application of semiconductor sen-... 

Fig. 6.17. The intensity of emission of singlet oxygen as a function of temperature in freshly ground quartz 1 — grinding in helium atmosphere, chemisorption of O2 at 20 C 2 - same as above + treatment at 280"C 3 sample obtained as stage 2 followed by oxidation at 20 C.

For SiC>2, we have only considered sources for silica suspensions which were non-porous, such as Ludox (39), pyrogenic silica (40), heat-treated BDH silica (22), or ground quartz (41). The data from these sources at 0.1M concentration has been collected in Figure 7. The data of the various researchers is quite consistent, in spite of the differences in origin of the suspensions, and the different electrolytes used. The slope of the points above pH 7 shows that the adsorption capacitance for cations is very large for both sodium and potassium ions, around 200 pF/cm2. Such a capacitance corresponds to a distance of 0.25.X, when using the dielectric constant of immobilized water molecules. The equilibrium constant for adsorption is low, however, since both KNa+ and Kk+ lie between 0.1 and 0.01 dms/mol. A possible interpretation of these results is as follows there is little specific attraction between SiC>2 and alkali cations,... 

Crystalline Silica. Quartz sand is of course the principal raw material for the production of glass (qv). Cristobalite and 3-quartz are used in glass ceramics (qv), ie, ceramics produced by the controlled crystallization of glass. Silica is a main constituent of ceramics (qv). For example, refractory silica brick containing small amounts of A O is used as roof brick for open-hearth furnaces at temperatures >1600° C (see Refractories). Silica sand or flour (ground quartz) is the raw material for soluble silicates, such as sodium silicate, which is consistently ranked as one of the top 50 U.S. industrial chemicals (98) (see Silicon compounds, synthetic inorganic silicates). 

Stoneware, composed of plastia clay from the Palatinate, ground quartz from Oberwald or Bern-cast e, calcareous tufa from Stork. The glaze contains lead, and the waie has ft yellow tint. 

Porcelain Stoneware, containing plastic clay from the Palatinate and from Vallendar, with ground quartz and hono ashes. The glazo free from lead and composed of borax, alkali, and felspar. 

Ground quartz, passing through a 2 mm. sieve but not through a 1-5 mm. sieve, may be used. 

The mineral quartz is crystallized silicon dioxide. Sea sand consists mostly of rounded grains of broken quartz. If finely ground quartz or sand is fused for a long time with sodium carbonate, the weaker, but non-volatile, acid anhydride displaces the carbon dioxide, and sodium silicate is obtained. This is a glass-like substance, which, however, can slowly be dissolved by water heated under pressure. The solution so obtained is evaporated to a sirup-like consistency and is sold on the market under... 

Richardson and Waddams (31) found the same behavior for silica. Ground quartz particles agitated with water release some monosilicic acid molecules which form a true solution and, in addition, some very small quartz crystals which form a dispersion in water until a hydrated equilibrium surface is established. Analogous to the ferric oxide, heating the quartz to a temperature above 600° C. regenerates the anomalous solubility behavior. 

At the high temperatures encountered in deep wells, pozzolanic admixtures are essential to prevent strength retrogression, as in high-pressure steam curing (Section 11.7). Silica flour (finely ground quartz) and silica sand are the most commonly used. There are few data on the effects of prolonged... 

We have used our proposed method to study the rates of dissolution and precipitation of silica on both freshly ground quartz (Figure 4y) and quartz which had been treated once with HF and NaOH (24) (Figure 4m, 1-HF) and then treated again (Figure 4m,... 

HF). The freshly ground quartz gave an apparent solubility value which was essentially identical to acid-cleaned biogenic silica and silica gel ( 1, 19),... 

Minerals were used in the range of 30 to 60 percent by weight. The most useful minerals were ground quartz (SIO2), Wollastonlte (CaSiOs) and calcined clay. Although the silica is very abrasive and could not be tolerated in an injection molding or extrusion resin, the slurries in the low viscosity caprolactam were pumped and cast without excessive abrasion. Calcined clay is much less abrasive than silica and is preferred if the mineral reinforced polymer Is to be post-processed by injection molding. 

This is the case for water adsorbed on the silica (ground quartz). The corresponding experimental heats of immersion curve were reported by Partyka et al. [76,77] and are redrawn here by us in Fig. 7(A). Also in this figure the heat of immersion of kaolinite in water is shown for comparison, redrawn from the work of Fripiat et al. [95]. Figure 7(B) shows the comparison of the isosteric heats of adsorption Qst calculated from these immersion curves according to Eq. (35). Note that also in the case of water adsorption on kaolinite, Qst does not reach the value of the heat of liquefaction, equal to 40.7 kj mol . ... 

Quartz, specified to contain 99.8% Si02, supplied by Sifraco (France). Ground quartz crystals were sieved and sedimented. This product was first leached repeatedly in boiling 2N HCl and thoroughly washed with deionized water until the filtrate showed no trace of chloride ion [53]. 

With particles containing rough edges, the situation is more complex, as demonstrated by Johansson and Pugh [32], using finely ground quartz particles of different size fractions, the surfaces of which had been hydrophobised by methylation. The results of these studies and others confirmed the importance of the size, shape and hydrophobicity of the particles on foam stability. 

The basis for a paste is a concentrated dispersion of solids in a limited amount of liquid. To make a beautiful porcelain vase like the one in the photo, ground quartz and feldspar are mixed with a white clay called kaolin... 

Polymers are often used in conjunction with other materials as composites. The most familiar types are the fiber-filled composites such as fiberglass and the carbon-, boron-, or Kevlar-filled advanced composites. Granular-filled composites such as those using clay as extenders in some plastics or ground quartz added to dental plastics to increase their wear resistance also represent an important class of materials. In these cases the presence of a second phase as well as the interface between polymer and filler increases the complexity of the failure analysis. 

Spectra of gases are taken using enclosed cells, with an evacuated cell as a reference. Spectra of solids may be taken in the form of pellets. Potassium bromide pellets similar to those used in infra red spectroscopy have been found suitable. Pellet holders for measurements on solids are commercially available. In order to avoid complications due to nonparslM sides of solid samples, a rough-ground quartz diffuser is placed In front of the photo-cell. 

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