Aging phenomena

The rate studies are complicated by an aging phenomenon the velocity falls if the Cr(III) solution has been left to stand. However, the effect is reproducible and aged solutions were invariably employed. The best fit with the results is obtained with the equation... 

Even if 5A zeolite is widely used in iso-paraffin separation from an n/iso paraffin mixture, the adsorbent is affected by a slow deactivation mainly due to coke formation inside the molecular sieve porosity. Its aging phenomenon decreases its sorption properties. According to previous studies, 5A zeolite deactivation results essentially from heavy carbonaceous compound formation in a-cages blocking the 5A zeolite microporosity [1-2]. 

On this superannuated New Age phenomenon, see Moffitt, Picturing Extraterrestials. 

The first study of the cationic polymerisation of styrene by triflic acid was undertaken before 1970 by Mathias and Plesch They fixind that very tow catalyst con-centratimis (10 — 10 M) were needed to induce a fairly rapid polymerisation in dichloromethane. These reactions were followed calorimetric y, conductimetrically and spectrophotometrically. The mqor obstacle precluding a stematic study was the poor reproducibility of the results. This problem was finally traced to the ng of the acid solutions contained in sealed phials. It was concluded that a slow reaction between the catalyst and the solvent was the cause of this aging phenomenon ... 

An example of this effect is illustrated in Figure 10, which shows a series of stress-strain curves as a fiinction of time for a material made with tri-ethoxysilane-end-capped PTMO(2000) (50 wt %) in conjunction with titanium isopropoxide (30 wt %) and TEOS (20 wt %). Over a period of many days, the material clearly stiffens in terms of modulus build-up hence, the time-dependent mechanical characteristics would have to be recognized for any application. However, such materials can be further cured thermally to achieve a more stable mechanical response with time. Therefore, if this aging phenomenon is noted, it can be dealt with accordingly. 

This reagent exhibits an unusual aging phenomenon. If it is used immediately after its preparation, then reduction of 1-phenylethanone provides the (7 j-alcohol with 68 % cc. However, if the reagent is refluxed briefly in diethyl ether and then allowed to stand for several hours, then reduction of 1-phenylethanone gives the (S)-alcohol with 66% ee (Table 3, reagents D and E). 

If the crystal growth process accompanying the aging phenomenon is diffusion-controlled, it can be shown (Nyvlt et al. 1985) that the size of particle in equilibrium with the solution can be obtained from the relation... 

The most common form of hair loss is genetically involved and is linked to androgens, thus the term androgenetic alopecia. Androgenetic alopecia or common baldness is a normal aging phenomenon and occurs in both sexes. To the extent that it is a cosmetic concern or problem, it occurs in about 40% of men and in about 10% of women. 

A final confirmation of the lengthy reaction time came from the customer who found that the same material that made bad product when fresh made excellent material after it had aged for 6 months. Since then this aging phenomenon has been observed in a few additional applications but for the most part is not a problem in most applications of the positive sols. 

In addition to long term influences due to creep and diffusion, at temperatures slightly below glass transition, an aging phenomenon occurs in a polymer which is evidenced by an increase in stiffness with elapsed time. This phenomenon, known as physical aging, can cause a polymer to become... 

The IFPYV of the interfacial films between water and resin model oils is zero. Hence, no structured film is formed on the interface between the water and the resin model oils. The interfacial viscosity is almost the same as that between water and blank oil, and much smaller than the values found for the interface between water and model oils containing asphaltenes. Neither the variation of resin concentration nor the nature of the oil phase have any effect on the interfacial viscosity. No aging phenomenon of the film between water and model oils containing 1% resins were ob-... 

Figure 7.17 Influence of porous aromatic frameworks (PAFs) on the CO2 permeability coefficient of different glassy polymers, polyftrimethylsilyl propyne) (PTMSP), PMP, and polymers of intrinsic microporosity (PIM)-l, with respect to the aging phenomenon.

The only study of the temperature dependence of the mechanical properties of terbium was compression tests by Sokolov et al. (1970) who reported the purity of their metal to be 98.88 percent, but no analysis of non-metallics was made. Although fig. 8.33 shows only one compression flow stress (20% strain) versus temperature curve, Sokolov et al. did furnish curves for two additional strain rates. These additional curves were parallel to the flow stress curve reproduced in fig. 8.33 and the peak in the flow stress shown at 500 K shifted to higher temperatures with higher strain rates in the manner characteristic of strain aging or some other thermally-activated process. The dip in the maximum compression strain tends to support a strain aging phenomenon. No obvious manifestation of the a(h.c.p.) to a (orthorhombic) phase change at about 220 K is evident in the mechanical properties. More data in the critical region are needed to determine whether the transformation produces an effect. 

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