Quartz iron contamination

AMETHYST. A purple- or violet-colored quartz having the same physical characteristics as quartz, Tile source of color is not definite but thought to be caused by ferric iron contamination. Oriental amethysts are purple corundum. 

The influence of milling intensity (Equation (17.6)) as well as additives (grinding environment) that is, liquids of various polarity (water, methanol, or toluene) on the contamination of quartz by iron during the course of milling in vibratory ball mill was investigated in detail [72]. Important result derived is that, neither the milling intensity nor milling time influences iron contamination... 

The synthesis of 2f/(fl)-TaS2 powder is carried out in fused quartz or Vycor ampules—typically 10 cm long and 1.7 cm in diameter, with a wall thickness of 1.0-2.0 mm (Fig. 2a). About 1.41 g (0.008 mol) of 0.020-in.-diameter tantalum wire (99.8% purity) is cut in the form of 3.8-cm lengths, washed in hot dilute HCl to remove iron contamination introduced in the cutting process, rinsed in distilled water, and dried. Sulfur powder, 0.500 g (0.016 mol, 99.9999% purity),t is then added, and the ampule is sealed under a vacuum of about 10" torr. The sealed ampule is placed into a cold laboratory tube furnace with the tantalum wire charge placed in the end of the ampule towards the center of the oven and elevated about 1 cm (see Fig. 2b). Thus, as the sample is heated, the sulfur melts and remains in the lower, cooler end of the ampule. A thermocouple is placed near this end to ensure that the temperature is at or below 450° (the pressure of sulfur vapor in equilibrium... 

Clays occur naturally either in a relatively pure condition or mixed with other materials and they are therefore classified into one of two large groups primary and secondary clays. Primary clays are quite pure, uncontaminated by other materials, and have a rather uniform composition. Secondary clays are mixtures of clay with other minerals such as quartz, talc, mica, iron oxides, and even organic matter (the latter derived from the decay of dead plants and animals) the particles of most of the contaminating materials are generally of similar size to those of the clay (Kingery et al. 1976). 

Secondary clay has been transported from the site of the parent rock. As a result, this clay has fine particles and might be contaminated with iron, quartz, mica, and carbonate compounds. Ball clays are secondary clays. They are higher in iron content, more fusible, finer in particle size, and more plastic than kaolin clays. 

Mounted Thermocouples.—The question of properly mounting and protecting a thermocouple is of great importance. The type of protection necessary depends upon the particular industrial process for which a couple is employed. In the laboratory if it be desired to measure the temperature of a perfectly clean platinum-wound porcelain furnace containing no material such as iron, etc. which could contaminate platinum, a rare-metal couple may be used without any protection whatever. For most laboratory experiments, however, a rare-metal couple requires protection. The usual rare-metal couple consists of wires 0.5 mm. or preferably 0.6 mm. in diameter and from 50 to 125 cm. in length. Wires as small as 0.1 mm. and even less are frequently used for special research work. One or both of the wires are insulated by threading them through small porcelain or quartz tubes. 

COCIF may be prepared by the passage of a gas stream of chlorine(I) fluoride and an excess of carbon monoxide at -18 C into an iron reaction vessel, with the exclusion of air and moisture. The gaseous reaction product is then condensed into a quartz vessel and the crude product distilled through, and from, antimony powder. The yield was found to vary between 85 and 90% (based upon CIF), and was greater if the reaction was performed more slowly the main contaminants were COF and COClj [1194]. Only a ten percent yield of COCIF was obtained by reaction of CIF 3 and CO (diluted with dinitrogen) at -180 C over activated charcoal [1196a],... 

Deposits of pure feldspar are not very common, being confined principally to Norway, Sweden, the U.S.S.R., and the U.S.A. Rocks containing feldspar in association with other minerals are, however, much more abundant. Examples of such rocks are the granites and pegmatites, which consist mainly of quartz, mica and feldspar cemented together. Unfortunately these rocks are often contaminated with iron-bearing minerals which are undesireable in the manufacture of pottery, since their inclusion discolours the ware. 

Tkacova, K., Stevulova, N., Lipka, J., and Sepelak, V., Contamination of quartz by iron in energy-intensive grinding in air and liquids of various polarity. Powder TechnoL, 83 (1), 163-171, 1995. 

In a conventional laboratory, Adeloju and Bond [42] observed considerable variations when periodically measuring voltammetrically standard solutions of cobalt, nickel, copper, zinc, selenium, and lead owing to the variability of airborne contamination. They stress that the adoption of a blank substraction approach is no more than a futile exercise because of the variability of the analytical blank levels with time. Boutron [43] assessed the effect of air purity on the analysis of a standard solution containing 10 ng/mL of iron. When samples were prepared in an ordinary laboratory environment, values of 20.6 ng/mL were observed Finally, Gretzinger et al. [44] filled carefully cleaned quartz beakers (cross-section, 16 cm volume 20 mL) with 10 mL of 1 M HCl, prepared by subboiling (or nonebullient) distillation [45], deposited them uncovered in an ordinary laboratory on different days, and measured the iron level in the HCl solution. The weather was found to play an important role as a rule, when it is raining the air is essentially more pure than when it is dry. On one dry day, the amount of iron in the 10 mL of 1 M HCl over a periode of 6 hr was up approximately 20 ng, on another up to more than 30 ng. 

The extraordinary occurrence of quar(z crystals 100 nm in size in the pell wall of the microorganism Chlorochytridion tuberculatum was described by Brandenberger and Frey-Wyssling (48). It is extremely unlikely that quartz crystals of such small size could have beeh present as a contaminant and it can only be concluded that the crystals were formed In situ. The question arises as to why the siliceous skeletons of decomposed diatoms do not redissolve in the seawater, which is greatly undersaturated. Jorgenson found that the skeletons of freshly killed diatoms dissolved in water (49), but as shown by Lewin (50) and discussed in Chapter 1, the rate of dissolution is very slow when traces of aluminum and iron are present. 

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