Quartz impurities

Hardness. The hardness (qv), or related property abrasiveness, is an important filler property. Hardness is determined by comparison to materials of known hardness on the Mohs scale. On this nonlinear scale, diamond is rated 10, quartz 7, calcite 3, and talc 1. The abrasiveness of a filler is also dependent on psd and the presence of impurities, eg, ka olin clay (Mohs hardness of 3) can be quite abrasive because of the presence of quartz impurities. 

The present paper discusses two boiler tests, where sodium-rich plywood was combusted in quartz-free bed material GR GRANULE. The unused bed was frilly amorphous. After initial increase of the crystallinity of the bed material the content of amorphous material started again to grow as the tests proceeded. The content of amorphous material was generally higher in the test I than in the test II and the SEM-EDS studies showed the presence of small agglomerates in the bed of test I. All agglomerates were found to be formed around quartz impurities that were probably left in the boiler as a residue from a previous silica sand bed. 

The unused bed is quite homogenous, as seen in Fig. 4 for test I. As the test proceeds, two main trends in the compositional distributions are apparent. The distribution spreads out towards the Al+Si/ Na+P+S+K-edge on one hand, and to the Mg+Ca+Ti+Fe-comer on the other. The first trend is cormected to the formation of sodium-rich adhesive material in small agglomerates fomied around quartz impurities... 

When kaolin was leached with 1.0 M sodium carbonate at 200 C for 1 hr., most of the kaolinite was converted to the sodalite-type natrodavyne (NS) while the quartz and illite impurities were not affected noticeably (Table IV). Increasing the leaching temperature to 250 C resulted in the converion of the kaolinite to a mixture of mixed-type natrodavyne (NCS) and analcime (A) and complete dissolution of the quartz impurity. The illite impurity was not affected. Leaching at 300 C and above resulted in the conversion of the... 

Treatment of Illite (Containing Quartz Impurities) with Caustic and Microwave Irradiation, Followed by Water or 10% HCl Wash... 

Natural mordenite from Hickuoi, New Zealand. The sample contains less than 5% quartz impurities. Natural mordenite from Lovelock, Pershing Co., Nevada, USA. The sample contains about 20-30% ferrierite and 10-15% feldspar. 

The reports were that water condensed from the vapor phase into 10-100-/im quartz or pyrex capillaries had physical properties distinctly different from those of bulk liquid water. Confirmations came from a variety of laboratories around the world (see the August 1971 issue of Journal of Colloid Interface Science), and it was proposed that a new phase of water had been found many called this water polywater rather than the original Deijaguin term, anomalous water. There were confirming theoretical calculations (see Refs. 121, 122) Eventually, however, it was determined that the micro-amoimts of water that could be isolated from small capillaries was always contaminated by salts and other impurities leached from the walls. The nonexistence of anomalous or poly water as a new, pure phase of water was acknowledged in 1974 by Deijaguin and co-workers [123]. There is a mass of fascinating anecdotal history omitted here for lack of space but told very well by Frank [124]. 

Quartz. When colorless, quart2 [14808-60-7] is also known as rock crystal. When irradiated, it becomes smoky from a color center associated with a ubiquitous Al impurity at about the 0.01% level. The name citrine [14832-92-9] is used when quart2 is colored by Fe, and irradiation of this can produce the purple-colored amethyst [14832-91-8] under certain circumstances (2). Although not signiftcandy lower priced than the natural materials, synthetic citrine and amethyst ate used in jewelry because of the abiUty to provide matched sets of stones from large, up to 7-kg, hydrothermaHy grown crystals. 

Rehable deterrnination of the solubihty of sihca in water has been comphcated by the effects of impurities and of surface layers that may affect attainment of equihbrium. The solubihty behavior of sihca has been discussed (9,27). Reported values for the solubihty of quartz, as Si02, at room temperature are in the range 6—11 ppm. Typical values for massive amorphous sihca at room temperature are around 70 ppm for other amorphous sihcas, 100—130 ppm. Solubihty increases with temperature, approaching a maximum at about 200°C. Solubihty appears to be at a minimum at about pH 7 and increases markedly above pH 9 (9). 

The transformations are aided by or may requke the presence of impurities or added mineralizers such as alkaH metal oxides. Indeed, it has been suggested that tridymite cannot be formed at all in the absence of impurities, and some texts assert that pure Si02 occurs in only two forms quartz and cristobaHte... 

China clay or kmlin, which is predominantly kaolinite, is particularly valuable because it is essentially free from iron impurities (and therefore colourless). World production in 1991 was 24.7M1 (USA 39%, UK 13%, Colombia, Korea and USSR 7% each). In the USA over half of this vast tonnage is used for paper filling or paper coating and only 130000 tonnes was used for china, crockery, and earthenware, which is now usually made from ball clay, a particularly fine-grained, highly plastic material which is predominantly kaolinite together with clay-mica and quartz. Some 800000 tonnes of ball clay is used annually in the USA for white ware, table ware, wall and floor tiles, sanitary ware, and electrical porcelain. 

FIGURE 14.33 Three common forms of silica (Si02) (a) quartz (b) quartzite and (c) cristobalite. The black parts of the sample of cristobalite are obsidian, a volcanic rock that contains silica. Sand consists primarily of small pieces of impure quartz. 

Silica, Si02, is a hard, rigid network solid that is insoluble in water. It occurs naturally as quartz and as sand, which consists of small fragments of quartz, usually colored golden brown by iron oxide impurities. Some precious and semiprecious stones are impure silica (Fig. 14.36). Flint is silica colored black by carbon impurities. 

Single-phase tantalum diboride of composition TaB, <,o-TaB, 5 is deposited using reaction (e) on a quartz substrate when the B/Ta ratio in the source gas is higher than 1.5, and T > 1000°C. At lower T and B/Ta ratios, deposition of metallic Ta is predominant. On substrates containing Ni or Pd impurities, woolly crystals up to 100 m in length can be grown in 30 min at 1050°C. As in the case of NbBj, a tip-VLS mechanism of growth is presumed . 

TXRF is frequently used for contamination control and ultrasensitive chemical analysis, in particular in relation to materials used in semiconductor manufacturing [278,279], and metallic impurities on resin surfaces, as in PFA sheets [279,280], TXRF has been used by Simmross et al. [281] for the quantitative determination of cadmium in the four IRMM polyethylene reference materials (VDA-001 to 004). Microsamples (20-100 ig) from each reference material were transferred by hot pressing at 130 °C as 3 xm thin films straight on to quartz glass discs commonly used for TXRF analysis. The results obtained were quite satisfactory (Table 8.50). Other reports of the forensic application to plastic materials by TXRF have appeared [282], including a study of PE films by elemental analysis [283],... 

A colorless gel formed which was isolated by vacuum evaporation of the volatiles. The resulting colorless glassy solid was pyrolyzed in vacuo at 900°C for 24 hours in a quartz tube and the evolved volatiles identified as NH3 and NH4CI. The remaining solid was briefly (2 hours) heated in air at 1200°C in order to remove minor carbon impurities and to improve crystallinity. This solid was then treated at room temperature with 40% aqueous HF to remove boric acid and silica formed in small quantities. The solid obtained at 900°C was identified as boron nitride however, the majority of the material was amorphous. After treatment at 1200°C, white crystalline boron-nitride was obtained in about 55% yield. 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

Chert Cristobalite A mir rocryslalline form of silica. An impure form of flint used in abrasives. A crystalline form of free silica, extremely hard and inert chemically very resistant to heal. Quartz in refractory bricks and amorphous silica in rlialomaceous earth are altered to cristobalite when exposed to high temperatures (calcined). Cristobalite is extensively used in precision casting by the hot wax process, dental laboratory work, and certain speciality ceramics. 

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