Hand-mixing process

Hand-Mixing Process. In the research and development of urethane foams, the hand-mixing technique (or bench-mixing technique) is widely used in the research and development of various foams, not only for flexible foams, but also for rigid foams, rather than the use of miniature foaming machines. Well-trained technicians can prepare excellent foams with good reproducibility by means of the hand-mixing process. 

Although the right-hand sides of Eqs. (8.27) and (8.28) are the same, the former applies to the mixture (subscript mix), while the latter applies to the mixing process (subscript m). The fact that these are identical emphasizes that in Eq. (8.27) we have calculated only that part of the total entropy of the mixture which arises from the mixing process itself. This is called the configurational entropy and is our only concern in mixing problems. The possibility that this mixing may involve other entropy effects—such as an entropy of solvation-is postponed until Sec. 8.12. 

Spray molding is the modification of the hand-lay process where the resin and glass fiber are deposited simultaneously on the molding tool. The fibers are mixed with the resin at the spray head before being deposited on the mold surface. Subsequent consolidation of the laminate is achieved by rolling in a similar manner to the hand-lay process. This method is suitable for large components. Here the capital cost is higher and the process is very operator sensitive. 

One extremely important point to realize is that different propellant types may have different rate-controlling processes. For example, the true double-base propellants are mixed on a molecular scale, since both fuel and oxidizing species occur on the same molecule. The mixing of ingredients and their decomposition products has already occurred and can therefore be neglected in any analysis. On the other hand, composite and composite modified-double-base propellants are not mixed to this degree, and hence mixing processes may be important in the analysis of their combustion behavior. 

The reaction of seawater with country rocks is also a possible but unlikely explanation. Tertiary volcanic sediments in the vicinity of Kuroko deposits are altered and tend to have lost both Ca and Sr (Farrell and Holland, 1983). The ratio of Sr loss to Ca loss is roughly equal to the Sr/Ca ratio in seawater. If seawater was the altering medium, its Sr/Ca ratio was probably not strongly affected by the alteration process. The 87sr/86si- ratio would be intermediate between an initial value of 0.7088 and ca. 0.740 — the Sr/ Sr ratio of unaltered Tertiary volcanics of the Hokuroku basin. It is unlikely, therefore, that this type of alteration can account for the Sr content and for the isotopic composition of Sr in the anhydrites at the upper end of the trend line in Fig. 1.49. On the other hand, mixing of seawater with solutions which have a Sr/Ca ratio much smaller than that of seawater could have led to the deposition of Kuroko anhydrites. 

The effect of variability in fluoride release between hand-mixed and cap-sulated systems was studied by Verbeeck et al. [266] who found that the mean value and variance of fluoride release were greater for the capsulated system than for the hand-mixed system. A two-process mechanism, consisting of a short-term elution (with a half life of nine hours) followed by diffusion controlled long-term release, for the release of F was suggested based on an empirical correlation of the data. The differences in the amounts of F released are attributed to the different mixing processes. 

On the other hand, there are very few regions of the surface ocean that maintain high dissolved siheate concentrations (Figure 4(d)). As a result, in regions of strong siheate gradients, the link between silicate utilization and silicon isotopic composition may be compromised by mixing processes in surface waters. 

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