Contact period

Check the grounding contacts periodically for their positive around connections. 

Molten salts are characterized by the formation of discrete complex ions that are subjected to coordination phenomenon. Such complex ions have specific compositions that are related to the rearrangement of their electronic configuration and to the formation of partially covalent bonds. The life time of the coordinated ions is longer than the contact period of the individual ions [293]. 

Chlorine addition may be a prerequisite to sanitize the RO RW supply line and oxidize any organics (followed by dechlorination using sodium bisulfite after the MM filtration stage). Where chlorine is required, it is usual to provide a 20- to 25-minute contact period by means of a temporary storage tank. This is followed by a repressurization pump system. 

This hydroperoxide decomposes slowly, avoiding accumulation. However, if the conditions are ideal for peroxidation (heat, prolonged time exposure to air, solar light), the hydroperoxide converts into extremely dangerous peroxides. Phenolic antioxidants inhibit this peroxidation efficiently. If tetrahydrofuran is peroxidised, it is not possible to destroy peroxides with ferrous salts or sulphites since tetrahydrofuran dissolves in water. Alumina or active carbon (passing over an alumina column or activated carbon at 20-66 C with a contact period of two minutes) are used, or by stirring in the presence of cuprous chloride. 

In our studies, the WBDs accumulated an average of 13,757 pg chlorpyrifos (n = 13), which would represent an administered dose of about 200 pg/kg. If the dermal absorption rate of chlorpyrifos is 9.6%/24 hr in humans (Thongsinthusak, personal communication), then the ADD would be 200 pg/kg x 0.096 = 19 pg/kg. If clothing penetration is taken into account, the estimated (daily) ADD resulting from the intensive 20-min contact period was about 2 pg/kg. 

Moreau, J.-F. and Hancock, R. G. V. (1996). Chrono-cultural technique based on the instrumental neutron activation analysis of copper-based artifacts from the contact period of northeastern North America. In Archaeological Chemistry organic, inorganic and biochemical analysis, ed. Orna, M. V., ACS Symposium Series 625, Washington, DC, American Chemical Society, pp. 64-82. 

All samples were submitted to post-treatment with mineral acid. The purpose of the acid post-treatment was to eliminate the ZnO phase in the materials obtained from the thermally treated LDH and a similar procedure was also performed on the other samples for comparison purposes. Hence, 400 mg of each sample was added under stirring to 50 cm3 of a 1 mol dm 3 HCI (Merck) solution at 25 °C under stirring. After a contact period of 2 hours, the residual solid material was separated and washed, centrifuged, and dried at 120 °C for 12 hours. 

The shorter-term exposure experiments show that some portion of the organically-bound chlorine, such as trichlorethane or its decomposition products, remains absorbed on a 304 stainless steel surface, even after heating at 35-40°C in a high vacuum. Conversion to an ionic species begins after a short contact period and can be detected using XPS. Formation of the ionic chloride is likely the result of hydrolysis by water also absorbed on the surface, and is perhaps catalyzed by the surface metal oxides. Further atmospheric exposure up to a few months increases the relative amount of the ionic form of chlorine. The composition of the surface oxide layer was altered, with chromium oxide replacing iron oxide as the major species. There was further evidence that chlorine was present as iron chloride, perhaps up to 5% of the surface film. The conditions under which oxidation of such surfaces occurred are quite comparable to those which could occur on steel surfaces in industrial usage. 

Isothiazolone has also been used as a non-oxidizing biocide for RO applications. However, the residence time required is much longer than for DBNPA. For example, a dosage of 50 to 100 ppm requires a 4-hour contact period. Thus, isothiazolone is not recommended for shock feed or continuous feed, but is recommended for cleaning events. Isothiazolone is more effective than DBNPA in high-organic waters. 

R2 refers to the temperature during the contact period of the mbber product with the food or beverage. At a temperature lower than or equal to 130 °C, R2 has a value calculated according to the formula R2 = 0.05e° where e is the base of the natural or Napierian logarithms and T is the contact temperature, expressed in °C. For temperatures higher than 130 °C, R2 always has the value 1.00. 

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