Process Degradation

Concrete, like other materials commonly submitted to weathering, such as natural rocks or man-made construction materials, shows degradation as a function of service life the degradation strongly depends both on the cement type and environmental conditions. As a general 

For industrial Portland cements, tetracalcium aluminum monosulfate hydrate (C ASH ), which is a major component of fully hydrated hardened cement, reacts with gypsum to form secondary ettringite (C ASjHj ). This reaction also causes expansion of 57 vol.% of the solid components  

In the presence of portlandite (CH), the tetracalcium aluminum monosulfate hydrate (C ASHjj) is converted to ettringite when the hydrated cement paste comes into contact with free sulfuric acid from the wet oxidation of sulfides  

Note that all these reactions involve a large volume increase and hence the formation of 

Alkali-silica reaction. The second destructive problem is attributed to a reaction of the silica-rich aggregates (e.g., cherts, obsidian, opal, quartzite), and alkalis present in the cement paste. In theory, any aggregate containing silica has the potential to participate in the alkali-silica reaction. 

It is important to understand the accelerating factors in RH cycling test. In-cell RH cycling tests are typically carried out by alternating an inert feed gas (N2) of controlled dew points. The water content of the membrane can be monitored by high-frequency cell resistance measurements. The result of the RH cycling test of a Nation based MEA cycled from 0 to 100% RH at 80°C is shown in Fig. 13. It can be seen that with the chosen cycling period ( 30 min) 

High resolution SEM images of the freeze-fractured cross section of the RH-cycled samples were obtained. Many craze-like defects were observed on the cross section of samples that had been cycled from 80 to 120% RH, as shown in Fig. 16. In comparison, 

Based on our observation, a membrane degradation and failure mechanism under the RH cycling, a pure mechanical effect is theorized as the following sequence electrode-microcracking- - crazing initiation at the electrode/electrolyte interface - crack growth under stress cycling- -fast fracture/instability. 

Experiments indicate that the critical strain-to-failure is also affected by the average molecular weight and by material processing history. McGrath40 reported strain-to-break of a non-crystalline ionomer (a poly(arylene-ether) random copolymer, biphenyl sulfone in H form, or bi-phenyl sulfone in H form (BPSH)) is proportional to the length of the chain. We found in our laboratory that the casting procedure also affects the strain-to-break of the solution-cast ionomer film. As shown in Fig. 19, a Nation film cast at near room 

Control After Fenton Test Control After Fenton Test 

The order in which hydrocarbons are oxidized depends on numerous factors. However, in general small carbon molecules up to C20 are consumed before larger 

FIGURE 4.7 Conversion of n-butane to ketone and acid via microbiological oxidation. 

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The amount of oxygen used in the degradation process is called the biochemical oxygen demand (BOD). A standard test has been devised to measure BOD in which the oxygen utilized by microorganisms in contact with the wastewater over a 5-day period at 20°C is measured. 

Chemical degradation (141), whether thermally or photo-iaduced, primarily results from depolymerization, oxidations, and hydrolysis. These reactions are especially harmful ia objects made from materials that coataia ceUulose, such as wood, cottoa, and paper. The chemistry of these degradation processes is quite complex, and an important role can be played by the reaction products, such as the acidic oxidation products which can catalyze hydrolysis. 

A second degradation process is oxidation, often photo-induced especially by exposure to light not filtered for uv. The radicals resulting from this reaction promote depolymerization of the cellulose, as well as yellowing and fa ding of paper and media. Aging causes paper to become more crystalline and fragile, and this can be exacerbated particularly if the paper is subjected to poor conditions. 

Eig. 3. Eirst degradation process used to produce progesterone. 

It is generally accepted that transamidation is not a concerted reaction, but occurs through the attack of a free end on the amide group via aminolysis (eg, eq. 4) or acidolysis (eg, eq. 3) (65). Besides those ends always present, new ends are formed by degradation processes, especially hydrolysis (eq. 5), through which the amide groups are in dynamic equiUbrium with the acid and amine ends. 

Processing Raw Materials. Along with the aforementioned chemical methods of processing steroid raw materials, microbial transformations have been and are used in a number of commercial degradation processes. The microbial degradation of the C17 side chain of the two most common sterols, cholesterol (2) and P-sitosterol (41), is a principal commercial method for the preparation of starting materials in Japan and the... 

Ozone can be used to completely oxidize low concentrations of organics in aqueous streams or partially degrade compounds that are refractory or difficult to treat by other methods. Compounds that can be treated with ozone include alkanes, alcohols, ketones, aldehydes, phenols, benzene and its derivatives, and cyanide. Ozone readHy oxidizes cyanide to cyanate, however, further oxidation of the cyanate by ozone proceeds rather slowly and may require other oxidation treatment like alkaline chlorination to complete the degradation process. 

Under acidic conditions the degradation process becomes more complex. The substituent on the 6-position has an important effect on the rate of degradation. Thus, acid stability has been found to increase as follows 6-APA > ampicillin, cyclacillin>... 

GRASSIE, n., Chemistry of High Polymer Degradation Processes, Butterworths, London (1956)... 

There is a great deal of uncertainty as to the mechanism of PVC degradation but certain facts have emerged. Firstly dehydrochlorination occurs at an early stage in the degradation process. There is some infrared evidence that as hydrogen chloride is removed polyene structures are formed (Figure 12.18). 

The basic product in these reactions varies with the nature of the initial substance and the character of the degradation process, as the following selected instances show —... 

Later Goto and Shishido prepared di-3-ethoxy-5 6-dimethoxy-A -ethylnoraporphine ethiodide, m.p. 186-7°, and this, by the Hofmann degradation process, gave the ethiodide of the de-At-ethyl base, m.p. 194°, from which the dimethoxyethoxyvinylphenanthrene, m.p. 108°, was obtained, identical with that from natural Z-tuduranine. The latter is therefore 3-hydroxy-5 6-dimethoxy-A -H0)aporphine. A later paper (1941) also relating to tuduranine is not yet accessible. 

Unlike most alkaloids of the group, glaueine was assigned a formula without the use of the Hofmann degradation process, but since then this process has been applied to glaueine or its derivatives by a number of workers, especially in connection with the investigation of boldine (p. 325) and of laurotetanine (p. 320). 

Phaeanthine, C3JH42O0N2. (Item 8 list, p. 350.) This alkaloid was isolated by Santos.It has m.p. 210°, [a]u°° — 278° (CHCI3), yields a hydriodide, m.p. 268°, picrate, m.p. 263°, aurichloride, m.p. 170-1°, and a platinichloride, m.p. 280° (dec.), and contains four methoxyl and two methylimino groups. By the Hofmann degradation process it yields an optically inactive methine base A, m.p. 173°, which is oxidised by potassium permanganate in acetone to 2-methoxy-5 4 -dicarboxydiphenyl ether (p. 348). A comparison of the properties of phseanthine and tetrandrine by Kondo and Keimatsu indicates that these two alkaloids are optical antipodes, so that phseanthine will be represented by either (XXXIX) or (XL) as given on p. 348, 1 and of these two formula (R = Me) one must represent oxyacanthine methyl ether and the other berbamine methyl ether (centres of asymmetry d- and 1-) tetrandrine (centres of asymmetry both d-) and phseanthine (centres of asymmetry both 1-). 

A recent communication described the cleavage of 17a-hydroperoxy-20-keto steroids with base to give 17-ketoandrostanes in good yield. Since such hydroperoxides are now accessible from 20-ketopregnanes in one step vide infra), this constitutes a convenient two-step degradation process. In practice, the intermediate hydroperoxide need not be isolated. Other enolizable... 

The authors describe a clear enhancement of the catalyst activity by the addition of the ionic liquid even if the reaction medium consisted mainly of CH2CI2. In the presence of the ionic liquid, 86 % conversion of 2,2-dimethylchromene was observed after 2 h. Without the ionic liquid the same conversion was obtained only after 6 h. In both cases the enantiomeric excess was as high as 96 %. Moreover, the ionic catalyst solution could be reused several times after product extraction, although the conversion dropped from 83 % to 53 % after five recycles this was explained, according to the authors, by a slow degradation process of the Mn complex. 

PBR increases the stability of the degradation process itself by absorbing the evolved HCl and preventing it from catalyzing further degradation. 

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