Partial vacuum, impact

Cavitation can destroy hydraulic structures. As the bubbles which have been formed at a partial vacuum at the inlet gradually progress along the impeller toward the outlet, the sudden increase in pressure causes an impact force. Continuous action of this force shortens the life of the impeller. 

Several instances of apparently stable solvated metal perchlorates being converted by partial desolvation into explosively unstable materials indicate that this may be a more common potential hazard than has been realised [1]. Neodymium perchlorate tetra-solvated with acetonitrile (obtained by vacuum evaporation of the solution at ambient temperature) had not been found to be thermally- or shock-sensitive, but when vacuum dried at 80°C to the di-solvate, it exploded violently on contact [2]. Erbium perchlorate tetrasolvated with acetonitrile had likewise appeared stable, but when vacuum dried at 150°C to a glassy solid which still contained some solvent, it too exploded when scraped with a spatula [3]. Mercury(II) perchlorate hexa-solvated with DMSO appears stable [4], but when dried to the tetrasolvate, it is impact- and friction-sensitive [5], The fact that the solvating species may also be water suggests that this is not a direct effect of a perchlorate oxidising an organic solvent. Thus,... 

The collapse of the Soviet Union brought another set of fundamental changes to the livelihoods of the indigenous people of Chukotka. Especially in the 1990s, when dramatic socio-economic change accompanied the transition period, the small-scale coastal communities of Chukotka were heavily impacted. The collapse of the Soviet infrastructure, which underscored and enabled the economic expansion in the North, rendered local economies obsolete. Industrial sea mammal hunt completely vanished, the reindeer herding industry suffered a total collapse, and supply chains to the rest of the country were severely interrupted. The difficulties and the economic vacuum produced by decollectivization and partial privatization of former state enterprises had increased the predicament of native people even more. 

The GTR vacuum chamber is partially cooled by a cryogenic shield on the interior of the vacuum chamber. The release of this cryogenic fluid into the vacuum chamber could have a thermal impact on the GTR and may introduce material contamination concerns. 

Figure 10.17a shows the impact of the degassing conditions on the SSA of anhydrous portland cement. When the degassing is conducted under vacuum and/or at temperatures higher than 40°C, a partial or total dehydration of gypsum occurs involving an increase in the SSA (see Figure 10.17b). Mantellato et al. (2015b) proposed degassing anhydrous cement samples at 40°C under N2 flow for 16 hours as an optimum degassing method, since cement composition is preserved. When using this protocol, reproducible results with a scatter of less than 5% can be obtained.

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