Quartz particle production

Fig. 6 Schematic drawing of ZSM5 catalyst bed deactivation. View of the fused silica reaction tube at about 40 % of catalyst life time. Black zone (I) of deactivated catalyst particles covered with coke ("methanol coke"). Small dark reaction zone (II) in which methanol conversion to 100 % occurs. Blue/grey zone (III) of active catalyst on which a small amount of "olefin coke" produced by the olefinic hydrocarbon product mixture has been deposited on the crystallite surfaces. The quartz particles before and behind the catalyst bed (zones 0) remain essentially white.

Fig. 5. A 90° polished cross section of a production white titania enamel, with the microstructure showing the interface between steel and direct-on enamel as observed by reflected light micrography at 3500 x magnification using Nomarski Interface Contrast (oil immersion). A is a steel substrate B, complex interface phases including an iron—nickel alloy C, iron titanate crystals D, glassy matrix E, anatase, Ti02, crystals and F, quartz particle.

Early commercial units utilized 10- to 20-mesh quartz but, because of the low surface area and consequent low activity of the catalyst, the quartz size was reduced to 28 to 35 mesh. The quartz is activated by pumping the reactor full of 75% phosphoric acid, allowing the excess acid to drain out, and then charging hot hydrocarbon to the unit. Even with the smaller quartz particles the catalyst activity is much lower than that of the Solid Phosphoric Acid catalyst. This lower activity has resulted in lower olefin conversion in this type of unit. Increased conversion has been obtained by separating the olefins from the product with very efficient fractionators and returning them to the reactor. However, this factor requires relatively large units with high utility consumption. 

Fig. 1.23 Temperature-programmed separation of chlorides of fission products [90], Conditions quartz column, length 75 cm, 8 mm i.d., packed with 0.25 mm quartz particles coated with NaCl heating rate 24.5 K min carrier gas nitrogen, 1cm3 min reagent CCI4, 100 mmHg.

Large quartz particles originally present in coal are only surface vitrified and do not spheridize in the flame. The coalescence by sintering and fusion of the small alumino-silicate particles dispersed in the fuel substance occurs when the host coal particles bum in the flame. The products are sintered ash skeletons, cenospheres and plerosphers up to 250 pm in diameter. 

The set-up for catalytic tests contained a parallel arrangement of 6 U-form quartz reactors (0mt = 6 mm), kept at a constant temperature by means of a fluidized bed of sand. The catalyst (rricat = 0.3 g, dp = 250 - 355pm) was packed between two layers of quartz particles of the same size. The reactors were operated at ambient pressure and the reaetion mixture was sequentially passed over the catalysts. The analysis of the products is achieved by on-line gas chromatography. A more detailed description of the set-up can be found in [5]. 

When quartz tubes are cut open with an emery wheel (1 mm. thick), it is not always possible to prevent quartz splinters from getting into the product. If the material is not a mass with a solid, glossy surface affording easy visual separation, the embedded quartz particles should always be removed by shaking with bromoform followed by centrifugation. 

A typical product layer on a quartz particle after being reacted with calcium carbonate under dry CO2 conditions at 842°C can be seen in Fig. S(a), The sample consisted of 57-// quartz particles in a matrix of Ge I CaCOa. The weight loss data indicated a 46% reaction. Assuming Ca2Si04 as the reaction product, layer thickness measurements indicated a 58% reaction. The product layer for these conditions was observed to be well defined. The amount of reaction calculated from weight loss data agreed well with values calculated from product layer thicknesses on the basis of 20 different measurements. This agreement was found for all three calcium carbonate matrix materials and confirmed the HF acid test in that reaction was restricted to the quartz particle surfaces. 

When similar samples were reacted at 756°C in CO2 atmospheres containing water vapor the micrographs [see Fig. 8(6)] showed no clearly defined product layer on the quartz particles. Hdwever, the weight loss of the sample of Fig. 8(6) indicated 45% reaction to Ca2Si04. Under optical observation the quartz particles in these samples were found to exhibit a blue-black color. The color intensity and weight loss were far greater for samples employing a vaterite matrix than for samples with the Baker or GE II calcite matrices. 

The electron microprobe results for samples reacted in dry and wet CO2 are shown in Figs. 9 and 10, respectively. The samples were comprised of 57-// quartz particles in a matrix of GE I CaCOa (2-3// vaterite) and are representative of samples shown in Fig. 8(//) and (6). The silicon and calcium traces shown in these figures represent concentration profiles for the respective elements for a beam traverse across the quartz particle, the product layer, and into the calcium carbonate bulk material. 

The reaction product layer can be distinguished easily in both the calcium and silicon Kcl patterns (Fig. 11) of the quartz particle reacted in dry CO2. No calcium can be detected in the unreacted portion of the quartz particle. However, for the quartz particle reacted in wet CO2 (Fig. 12) the area rich in silicon appears significantly larger than the area of calcium exclusion, strongly indicating the presence of calcium within the quartz particle. In addition, no distinct product layer can be observed in this particle even though significant reaction has occurred. 

The microprobe results on the GE I CaCOj matrix samples reacted in dry and wet CO2 clearly suggested a different reaction occurring under the two different conditions. For the dry CO2 atmospheres a distinct product layer of essentially constant chemical composition was observed. When the same type of sample was reacted in the presence of water vapor no product layer was observed, but a finite amount of calcium was found within the quartz particles. This observation was checked by making 10-sec counts... 

Nitric oxide may induce deleterious effects when airway epithelial or immunological cells are exposed to mineral particles (asbestos, quartz). These particles also stimulate cells to produce NO in large quantities, but pulmonary cells are unable to destroy these particles, and a non-physiologically excess production of NO results, perhaps causing tissue damage due to a reaction of NO with cellular macromolecules. 

---