Aging hydro-thermal

Hematitic iron ores of hydrothermal-sedimentary origin and Palaeozoic in age, are those of the Lahn-Dill-type in West and Central Europe (Harder, 1964). Hydro-thermal solutions associated with submarine volcanic activities have transported Fe (as FeCl3) into a marine environment, where after hydrolysis, hematite was formed (via ferrihydrite) at the margin of the basin, whereas siderite (after reduction) was formed in its centre. These ores are - in contrast to true sedimentary ores - low in Al,Ti and trace elements, which betrays their volcanic origin. 

This paper reports on the aging behavior of an RT-cured and of a hot-cured epoxy network under thermal and hydro-thermal loading in the bulk and in layers on stainless steel. During a period of 100 days, the chemical and stractur-al changes have been observed by IR spectroscopy and differential scanning calorimetry (DSC). 

Hydro-thermal aging (HTA) is performed in the glassy state by immersion in distilled water at the same temperatures as for thermal aging. % values of 40 °C and 60 °C correspond to 38 mg O2 and 23 mg O2 per liter H2O, respectively. 

Fig. 30.10 IR-ATR intensity of the normalized aging band at 1660 cm for EPl-PC40 in the bulk during thermal and hydro-thermal aging at 40°C up to 85 days.

Fig. 30.12 DSC measurement of EP1-PC40 in the bulk during hydro-thermal aging...

Hydro-thermal aging of EP1-PC40 bulk samples produces only one new IR band, at 1660 cm. It is assumed that this band belongs to the same product 1 (with oxime functionality) discussed for thermal aging. For long aging times, the concentration of product 1 is similar for TA and HTA (see Fig. 30.10). Since no band develops at 1730 cm or anywhere else in the spectra, it is concluded that the presence of water suppresses the oxidation of secondary amines in the bulk samples. 

Fig. 30.14 M DSC Tg of EP1-PC40 on SSI and SS2 during hydro-thermal aging up to 100 days.

Fig. 30.21 Tg(second run) of EP2 in the bulk and in the layers on stainless steel on hydro-thermal aging at 60°C up to 100 days.

In the contact zone with air, the network degrades by the oxidation of primary and secondary amines. In the presence of water, only primary amines are oxidized. Consequently, the amines are consumed by the ongoing cure and by oxidation. These mechanisms complete the picture of the degradation mechanisms discussed in the hterature for low aging temperatures. Hydro-thermal aging at the presence of both types of stainless steel increases the oxidative modification in EPl. 

Water induces a similar phase separation at least in the bulk. It breaks the imino ether-like crosslinks specific for the DDA-cured epoxy systems in the bulk as well as in the layers on the two types of stainless steel. The proposed mechanism describes the aging behavior of DDA-cured epoxy systems well, since it explains all the observed effects of chemical modification, irreversible plasticization, and irreversible water uptake. Additionally, it is understood why there is no complete disintegration of the network the hydrolysis cleaves only the imino ether-like crosslinks but not the amine-like or the ether-like crosslinks that are also formed during curing. Hence, after hydro-thermal aging the macromolecu-lar mobility in EP2 is similar in the layers and in the bulk because the content of amine-like and ether-like crosslinks is similar. 

The ages of the Cenozoic volcanic rocks of the McMurdo Volcanic Group were determined by Armstrong (1978), Fleck et al. (1972), Forbes et al. (1974), Wright-Grassham (1987), and others by the whole-rock K-Ar method. Under ideal circumstances, these dates indicate the crystallization ages of late Cenozoic volcanic rocks that cooled rapidly after they were erupted on land, provided they were not hydro-thermally altered and provided that all " Ar was out-gassed from the lava at the time eruption. 

In addition, Schmieg et al. analyzed a vehicle-aged SCR catalyst and found that, at the end of its useful life (1,35,000 miles vehicle operation), the hydro-thermal exposure of the SCR catalyst was equivalent to the laboratory hydro-thermal aging at 800 °C for 16 h. This is below the borderline, which predicts that the catalyst can still maintain its high SCR activity even if it is hydrothermally aged at 800 °C for 70 h. Clearly, the development of small-pore zeolite supported Cu SCR catalysts has overcome the hydrothermal stability requirement needed for real world applications. 

FCC catalysts are deactivated via several mechanisms," which all result in a loss in activity and a change in yield selectivity Catalyst will age, meaning change chemical and physical structure due to the (hydro) thermal conditions during the 10,000 to 50,000 reaction and regeneration cycles it will endure. The catalysts can also be poisoned, whereby the active sites are covered by coke and/or polars (nitrogen) that neutralize the catalytic activity or by metals (vanadium, nickel, sodium) which can destroy or alter the activity. 

The method consists of the addition of a solution of the metal cations to a basic alkaline metal solution (usually NaOH or KOH). The crystallinity of the particles formed is rather low and they need to be submitted to hydro-thermal or other ageing treatment to increase it [100]. 

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