Quartz reaction with

In an alkali silica cement, we see a new setting/hard-ening reaction with quartz becoming a factor. 

Bromine(III) fluoride is an extremely reactive, straw-colored liquid at room temperature. It reacts rapidly with glass and most siliceous materials. The reaction with quartz is noticeable at 30°. It will set fire to materials like wood and paper. It reacts violently with water and with many organic substances. A small quantity frozen at —80°, when dropped into liquid toluene at the same temperature, reacts with great violence. 

Any lead(II) sulphate formed in this process is converted to lead(II) silicate by reaction with the quartz. The oxide produced is then mixed with limestone and coke and heated in a blast furnace. The following reactions occur ... 

The second analytical method uses a combustion system (O Neil et al. 1994) in place of reaction with BrF,. This method was used for the crocodiles because they were represented by very thin caps of enamel. The enamel was powdered and sieved (20 mg), pretreated in NaOCl to oxidize organic material and then precipitated as silver phosphate. Approximately 10-20 mg of silver phosphate were mixed with powdered graphite in quartz tubes, evacuated and sealed. Combustion at 1,200°C was followed by rapid cooling in water which prevents isotopic fractionation between the CO2 produced and the residual solid in the tube. Analyses of separate aliquots from the same sample typically showed precisions of 0.1%o to 0.4%o with 2 to 4 repetitive analyses even though yields are on the order of 25%. 

The catalytic test of propane ODH reaction was performed in the 350-600°C range in a quartz fixed bed flow reactor with on line GC analysis. The free volume of the reactor after the catalyst bed was filled with quartz particles to minimize the homogeneous reactions. All the testing set was placed in a thermostat with heated lines to the gas chromatographs at about 100°C to prevent water condensation. The feed gas composition was C3H8/02/N2 = 20/10/70 vol.% at total gas flow 50 cm3 min-1. Catalyst fractions of 0.2-0.315 mm particle size and of 80 mg weight were loaded into the reactor. Before the reaction, the catalyst samples in the reactor were kept under airflow at 600°C for lh. 

A spiral coil of Teflon, or a spiral groove on a stainless steel surface covered with quartz, is used as a flow cell in the CL detector. These cells are placed in front of a photomultiplier tube (PMT), which detects photons emitted by the CL reaction. The cell volumes are generally in the range of 60-120 J.L. 

Heptamide has been prepared by heating heptanoic add with ammonia in a sealed tube 2 at 230°, by treating heptanoic anhydride with ammonia,3 by passing ammonia through heptanoic acid4 at 125-190°, by the rearrangement of heptaldehyde oxime in the presence of Raney nickel in a quartz tube at 150° for 5 minutes,6 by the Will-gerodt reaction with 2-, 3-, or 4-heptanone or heptanal,6-7 and by the action of ammonia on heptanoyl chloride.8... 

Since we have no direct information about the chemistry of the Fountain fluid, we assume that its composition reflects reaction with minerals in the evaporite strata that lie beneath the Lyons. We take this fluid to be a three molal NaCl solution that has equilibrated with dolomite, anhydrite, magnesite (MgCC>3), and quartz. The choice of NaCl concentration reflects the upper correlation limit of the B-dot (modified Debye-Hiickel) equations (see Chapter 8). To set pH, we assume a CO2 fugacity of 50, which we will show leads to a reasonable interpretation of the isotopic composition of the dolomite cement. 

Fig. 26.1. Reaction of quartz with water at 25 °C, showing approach to equilibrium (dashed lines) with time. Top diagram shows variation in SiC>2(aq) concentration and bottom plot shows change in quartz saturation. In calculation A, the fluid is initially undersaturated with respect to quartz in B it is supersaturated.

To see how a second kinetic reaction might affect the fluid s silica concentration, we add 250 grams of cristobalite to the system. The mass ratio of quartz to cristobalite, then, is twenty to one. Taking the fluid to be in equilibrium with quartz initially, the procedure in REACT is... 

Fig. 26.2. Kinetic reaction of quartz and cristobalite with water at 25 °C. In calculation A the fluid is originally in equilibrium with quartz, in B with cristobalite. The top diagram shows how the SiChlaq) concentration varies with time, and the bottom plot shows the change in quartz saturation. The reaction paths approach a steady state in which the fluid...

Fig. 26.7. Variation in silica concentration (top) and saturation indices (log Q/K) of the silica polymorphs (bottom) over the course of the reaction path shown in Figure 26.6. The dashed lines in the top diagram show Si02(aq) concentrations in equilibrium with quartz, cristobalite, and amorphous silica.

Figure 26.7. Only after the mineral has almost disappeared does the silica concentration begin to decrease. Since the surface area and rate constant for cristobalite are considerably greater than those of quartz, the fluid remains near equilibrium with cristobalite until it in turn nearly disappears. Finally, after several hundred thousand years of reaction, the fluid approaches saturation with quartz and hence thermodynamic equilibrium.

In a final application of kinetic reaction modeling, we consider how sodium feldspar (albite, NaAlSisOs) might dissolve into a subsurface fluid at 70 °C. We consider a Na-Ca-Cl fluid initially in equilibrium with kaolinite [Al2Si20s (OF )/ ], quartz, muscovite [KAl3Si30io(OH)2, a proxy for illite], and calcite (CaC03), and in contact with a small amount of albite. Feldspar cannot be in equilibrium with quartz and kaolinite, since the minerals will react to form a mica or a mica-like... 

To illustrate the effects of to and 2 on reaction rates, we consider the reaction of quartz with dilute water, from Chapter 16. As before, we begin in react... 

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