Virgin silica

The surface of the virgin silica gel is covered with water. Heating to 110°C forms a monolayer of silanol groups on the surface (8 pmo of silanol groups per m2). Heating to over 600 °C produces a surface siloxane structure, and this is rehydrated to the silanol form under humid conditions, as shown in Figure 3.1. 

The large "hardened" a-chromia crystallites formed on catalysts containing 5 wt% Cr and calcined at 900 °C were easily reoxidized and migrated to a fresh virgin silica surface when the two were co-calcined at 900 °C. 

FIGURE 26 HLMI of polymers made with two Cr/silica catalysts, one made from virgin silica and the other made from a silica that had been thermally cycled two times by calcination at 900 °C followed by wetting in liquid water. 

Titania applied as a surface coating also promotes sintering. In one experiment, silica (500 m2 g, 1.6 mL g ) was titanated to contain 1.7 Ti atoms ran-2. When activated at 900 °C, the catalyst lost 60% of its surface area and 68% of its pore volume. For comparison, the virgin silica lost only 6% of its surface area and 4% of its pore volume. 

This solid product was incorporated into SBR/butadiene rubber (BR) blends at various levels, and the mechanical and dynamic properties were compared with those of conventional silica/carbon black (2 1 ratio) filled SBR/BR compounds. The results showed that the physical properties, and the dynamic ones (such as heat build-up and tan 8), of the two types of compound were comparable. Their work showed that the recovered silica had a similar particle size to virgin silica, and its ability to disperse evenly within the rubber matrix was also similar. 

Symbol designation Bt (virgin bitumen) S/A (silica-alumina catalyst) MS (molecular sieve catalyst) SB (semibatch Cat A mode) B (batch mode) f (powdered catalyst) T (thermal coking). 

Similar well fitting simulation curves for the experimental stress-strain data as those shown in Fig. 46b can also be obtained for higher filler concentrations and silica instead of carbon black. In most cases, the log-normal distribution Eq. (55) gives a better prediction for the first stretching cycle of the virgin samples than the distribution function Eq. (37). Nevertheless, adaptations of stress-strain curves of the pre-strained samples are excellent for both types of cluster size distributions, similar to Fig. 45c and Fig. 46b. The obtained material parameters of four variously filled S-SBR composites used for testing the model are summarized in Table 4, whereby both cluster... 

Comparative laboratory evaluations of silica-alumina, silica-magnesia, and activated-clay catalysts have been confirmed by performance characteristics in pilot-plant and commercial operations (5,51,100,131,236,274). The important differences are illustrated in Table XII, which shows data obtained in a pilot plant when cracking a mixture of virgin and coke-still gas oils derived from West Texas crude. The blend contained about 10% of material boiling just below the end point of gasoline. 

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